LM3535TME-2ALS

LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic Backlight Control Compatibility August 12, 2010 LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic Backlight Control Compatibility General Description The LM3535 is a highly integrated LED driver capable of driving 8 LEDs in parallel for large display applications. Independent LED control allows for a subset of the 6 main display LEDs to be selected for partial illumination applications. In addition to the main bank of 6, the LM3535 is capable of driving an additional 2 independently controlled LEDs to support Indicator applications. The LED driver current sinks are split into three independently controlled groups. The primary group can be configured to drive up to six LEDs for use in the main phone display. Groups B and C are provided for driving secondary displays, keypads and indicator LEDs. All of the LED current sources can be independently turned on and off providing flexibility to address different application requirements. The LM3535 provides multi-zone Ambient Light Sensing (1 or 2 ALS inputs depending on option) allowing autonomous backlight intensity control in the event of changing ambient light conditions. A PWM input is also provided to give the user a means to adjust the backlight intensity dynamically based upon the content of the display. The LM3535 provides excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2 or in Pass-Mode. The proper gain for maintaining current regulation is chosen, based on LED forward voltage, so that efficiency is maximized over the input voltage range. The LM3535 is available in National’s tiny 20-bump, 0.4mm pitch, thin micro SMD package. Features ■ Drives up to 8 LEDs with up to 25mA of Diode Current ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Each External PWM input for Dynamic Backlight Control Multi-Zone Ambient Light Sensing (ALS) Dual-ALS Sensor Inputs (LM3535-2ALS only) ALS Interrupt Reporting Independent On/Off Control for all Current Sinks 128 Exponential Dimming Steps with 600:1 Dimming Ratio for Group A (Up to 6 LEDs) 8 Linear Dimming States for Groups B (Up to 3 LEDs) and D1C (1 LED) Programmable Auto-Dimming Function Up to 90% Efficiency 0.55% Accurate Current Matching Internal Soft-Start Limits Inrush Current True Shutdown Isolation for LEDs Wide Input Voltage Range (2.7V to 5.5V) Active High Hardware Enable Total Solution Size < 16mm2 Low Profile 20 Bump micro SMD Package (1.650mm × 2.055mm × 0.6mm) Applications ■ Smart-Phone LED Backlighting ■ Large Format LCD Backlighting ■ General LED Lighting Typical Application Circuit 30082441 Minimum Layout 30082468 © 2010 National Semiconductor Corporation 300824 www.national.com LM3535 Connection Diagram 20 Bump micro SMD Package NS Package Number TMD20AAA 30082469 Pin Descriptions Bump #s TMD20AAA A3 A2 A1, C1, B1, B2 D3, E3,E4, D4 C4, B4 B3 Pin Names VIN VOUT C1+, C1-, C2+, C2D1A-D4A D53, D62 D1B / INT Pin Descriptions Input voltage. Input range: 2.7V to 5.5V. Charge Pump Output Voltage Flying Capacitor Connections LED Drivers - GroupA LED Drivers - Configurable Current Sinks. Can be assigned to GroupA or GroupB LED Driver/ ALS Interrupt - GroupB Current Sink or ALS Interrupt Pin. In ALS Interrupt mode, a pull-up resistor is required. A '0’ means a change has occurred, while a ‘1’ means no ALS adjustment has been made. LED Driver / ALS Input - Indicator LED current sink or Ambient Light Sensor Input External PWM Input - Allows the current sinks to be turned on and off at a frequency and duty cycle externally controlled. Minimum On-Time Pulse Width = 15µsec. Hardware Enable Pin. High = Normal Operation, Low = RESET Serial Data Input/Output Pin Serial Clock Pin Ground for LM3535 or Ambient Light Sensor B for LM3535-2ALS C3 D2 E1 C2 E2 A4 D1C / ALS PWM HWEN SDIO SCL GND (LM3535) ALSB (LM3535-2ALS) GND D1 Ground Ordering Information Order Information LM3535TME LM3535TMX LM3535TME-2ALS LM3535TMX-2ALS TMD20AAA Package Supplied As 250 Units, Tape & Reel 3000 Units, Tape & Reel 250 Units, Tape & Reel 3000 Units, Tape & Reel www.national.com 2 LM3535 Absolute Maximum Ratings (Note 1, Note 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN pin voltage SCL, SDIO, HWEN, PWM pin voltages IDxx Pin Voltages -0.3V to 6.0V -0.3V to (VIN+0.3V) w/ 6.0V max -0.3V to (VVOUT+0.3V) w/ 6.0V max Internally Limited 150°C -65°C to +150° C (Note 4) Operating Rating (Note 1, Note 2) Input Voltage Range LED Voltage Range Junction Temperature (TJ) Range Ambient Temperature (TA) Range (Note 6) 2.7V to 5.5V 2.0V to 4.0V -30°C to +110°C -30°C to +85°C Thermal Properties Junction-to-Ambient Thermal Resistance (θJA), TMD20 Package (Note 7) 40°C/W Continuous Power Dissipation (Note 3) Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature (Soldering) ESD Rating(Note 5) Human Body Model 2.0kV (Note 2, Note 8) Electrical Characteristics Limits in standard typeface are for TA = 25°C, and limits in boldface type apply over the full operating temperature range (-30°C to +85°C). Unless otherwise specified: VIN = 3.6V; VHWEN = VIN; VPWM = 0V;VDxA = VDxB = VDxC = 0.4V; GroupA = GroupB = GroupC = Fullscale Current; ENxA, ENxB, ENxC Bits = “1”; 53A, 62A Bits = "0"; C1 = C2 = CIN= COUT= 1.0µF. (Note 9) Symbol Parameter Condition 2.7V ≤ VIN ≤ 5.5V EN1A to EN4A = '1', 53A = 62A = '0'', EN53 = EN62 = ENxB = ENxC = '0' 4 LEDs in GroupA 2.7V ≤ VIN ≤ 5.5V EN1A to EN4A = EN53 = EN62 = '1', 53A = 62A = '1'', ENxB = ENxC = '0' 6 LEDs in GroupA Min 23.6 (-5.6%) Typ Max 26.3 (+5.2%) Units mA (%) 25 Output Current Regulation GroupA 23.2 (-7.2%) 25 26.3 (+5.2%) mA (%) IDxx Output Current Regulation GroupB Output Current Regulation IDC 2.7V ≤ VIN ≤ 5.5V EN1B = EN53 = EN62 = '1', 53A = 62A = '0', 23.3 (-6.8%) ENxA = ENC = '0' 3 LEDs in GroupB 2.7V ≤ VIN ≤ 5.5V ENC = '1', ENxA = ENxB = '0' 23.8 (-4.8%) 25 26.0 (+4.0%) 26.8 (+7.2%) mA (%) mA (%) 25 25 DxA Output Current Regulation GroupA, GroupB, and GroupC Enabled 3.2V ≤ VIN ≤ 5.5V VLED = 3.6V 25 DxB 25 DxC GroupA (4 LEDs) 0.25 0.55 0.25 130 2.40 2.78 2.41 mA IDxxMATCH LED Current Matching(Note 10) VDxx 1x to 3/2x Gain Transition Threshold Current sink Headroom Voltage Requirement (Note 11) Open-Loop Charge Pump Output Resistance 2.7V ≤ VIN ≤ 5.5V GroupA (6 LEDs) GroupB (3 LEDs) % VDxTH VHR VDxA and/or VDxB Falling IDxx = 95% ×IDxx (nom.) (IDxx (nom) = 25mA) Gain = 3/2 Gain = 1 3 mV 100 2.4 0.5 mV ROUT Ω www.national.com LM3535 Symbol IQ ISB ISD fSW tSTART VALS Parameter Quiescent Supply Current Standby Supply Current Shutdown Supply Current Switching Frequency Start-up Time ALS Reference Voltage Accuracy RALSA = 9.08kΩ Condition Gain = 3/2, No Load Gain = 1, No Load 2.7V ≤ VIN ≤ 5.5V HWEN = VIN, All ENx bits = "0" 2.7V ≤ VIN ≤ 5.5V HWEN = 0V, All ENx bits = "0" Min Typ 2.86 1.09 1.7 1.7 Max 4.38 2.31 4.0 4.0 1.56 1.05 (+5%) +5 +5 +5 +5 0.45 VIN 0.45 VIN 400 Units mA µA µA MHz µs V 1.10 VOUT = 90% steady state 0.95 (-5%) -5 -5 -5 -5 Reset Normal Operation Diodes Off Diodes On 0 1.2 0 1.2 RALSA = 5.46kΩ RALSB = 9.13kΩ RALSB = 5.52kΩ 1.33 250 1 RALS ALS Resistor Accuracy % VHWEN VPWM VOL-INT VIL VIH VOL t1 t2 t3 t4 t5 HWEN Voltage Thresholds PWM Voltage Thresholds Interrupt Output Logic Low '0' Input Logic Low '0' Input Logic High '1' SDIO Output Logic Low '0' SCL (Clock Period) Data In Setup Time to SCL High Data Out stable After SCL Low SDIO Low Setup Time to SCL Low (Start) SDIO High Hold Time After SCL High (Stop) 2.7V ≤ VIN ≤ 5.5V 2.7V ≤ VIN ≤ 5.5V ILOAD = 3mA 2.7V ≤ VIN ≤ 5.5V 2.7V ≤ VIN ≤ 5.5V ILOAD = 3mA (Note 13) V V mV V V mV µs ns ns ns ns I2C Compatible Interface Voltage Specifications (SCL, SDIO) 0 1.225 0.45 VIN 400 2.5 100 0 100 100 I2C Compatible Interface Timing Specifications (SCL, SDIO)(Note 12) 30082413 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pins. www.national.com 4 LM3535 Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ = 125°C (typ.). Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112). Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. (MIL-STD-883 3015.7) Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX). Note 7: Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. For more information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112). Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 9: CIN, CVOUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics Note 10: For the two groups of current sinks on a part (GroupA and GroupB), the following are determined: the maximum sink current in the group (MAX), the minimum sink current in the group (MIN), and the average sink current of the group (AVG). For each group, two matching numbers are calculated: (MAX-AVG)/ AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the Group. The matching figure for a given part is considered to be the highest matching figure of the two Groups. The typical specification provided is the most likely norm of the matching figure for all parts. Note 11: For each Dxx pin, headroom voltage is the voltage across the internal current sink connected to that pin. For Group A, B, and C current sinks, VHRx = VOUT -VLED. If headroom voltage requirement is not met, LED current regulation will be compromised. Note 12: SCL and SDIO should be glitch-free in order for proper brightness control to be realized. Note 13: SCL is tested with a 50% duty-cycle clock. Block Diagram 30082467 5 www.national.com LM3535 Typical Performance Characteristics Unless otherwise specified: TA = 25°C; VIN = 3.6V; VHWEN = VIN; CIN= 1µF, COUT = 1µF, C1=C2= 1µF. ILED vs Input Voltage 6 LEDs ILED vs Input Voltage 30082420 30082419 ILED vs Brightness Code Linear Scale ILED vs Brightness Code Log Scale 30082423 30082422 www.national.com 6 LM3535 Input Current vs Input Voltage 4 LEDs LED Drive Efficiency vs Input Voltage 4 LEDs 30082464 30082463 Input Current vs Input Voltage 6 LEDs LED Drive Efficiency vs Input Voltage 6 LEDs 30082460 30082424 Input Current vs Input Voltage 8 LEDs LED Drive Efficiency vs Input Voltage 8 LEDs 30082461 30082462 7 www.national.com LM3535 LED Drive Efficiency vs Input Voltage Tri-Temp 6 LEDs ILED Matching vs Input voltage 6 LEDs 30082426 30082421 Switching Frequency vs Input Voltage Tri-Temp Shutdown Current vs Input Voltage VIO = 0V 30082431 30082427 Shutdown Current vs Input Voltage VIO = 2.5V Quiescent Current vs Input Voltage 1× Gain 30082428 30082429 www.national.com 8 LM3535 Quiescent Current vs Input Voltage 3/2× Gain ALS Boundary Voltage vs. Boundary Code Falling ALS Voltage 30082430 30082470 ALS Boundary Voltage vs. Boundary Code Falling ALS Voltage (Zoom) Diode Current vs PWM Duty Cycle 30082453 30082471 Ambient Light Sensor Response Diode Current Ramp-Up tSTEP = 6ms 30082454 30082458 9 www.national.com LM3535 Diode Current Ramp-Down tSTEP = 6ms 30082459 www.national.com 10 LM3535 Circuit Description OVERVIEW The LM3535 is a white LED driver system based upon an adaptive 3/2× - 1× CMOS charge pump capable of supplying up to 200mA of total output current. With three separately controlled Groups of constant current sinks, the LM3535 is an ideal solution for platforms requiring a single white LED driver IC for main display, sub display, and indicator lighting. The tightly matched current sinks ensure uniform brightness from the LEDs across the entire small-format display. Each LED is configured in a common anode configuration, with the peak drive current set to 25mA. An I2C compatible interface is used to enable the device and vary the brightness within the individual current sink Groups. For GroupA , 128 exponentially-spaced analog brightness control levels are available. GroupB and GroupC have 8 linearly-spaced analog brightness levels. Additionally, the LM3535 provides 1 or 2 inputs (LM3535 has 1 and LM3535-2ALS has 2) for an Ambient Light Sensor to adaptively adjust the diode current based on ambient conditions, and a PWM pin to allow the diode current to be pulse width modulated to work with a display driver utilizing dynamic or content adjusted backlight control (DBC or CABC). CIRCUIT COMPONENTS Charge Pump The input to the 3/2× - 1× charge pump is connected to the VIN pin, and the regulated output of the charge pump is connected to the VOUT pin. The recommended input voltage range of the LM3535 is 2.7V to 5.5V. The device’s regulated charge pump has both open loop and closed loop modes of operation. When the device is in open loop, the voltage at VOUT is equal to the gain times the voltage at the input. When the device is in closed loop, the voltage at VOUT is regulated to 4.3V (typ.). The charge pump gain transitions are actively selected to maintain regulation based on LED forward voltage and load requirements. Diode Current Sinks Matched currents are ensured with the use of tightly matched internal devices and internal mismatch cancellation circuitry. There are eight regulated current sinks configurable into 3 different lighting regions. Ambient Light Sensing (ALS) and Interrupt The LM3535 provides an Ambient Light Sensing input (2 inputs on LM3535-2ALS version) for use with ambient backlight control. By connecting the anode of a photo diode / sensor to the sensor input pins, and configuring the appropriate ALS resistors, the LM3535 or -2ALS version, can be configured to adjust the diode current to five unique settings, corresponding to four adjustable light region trip points. Additionally, when the LM3535 determines that an ambient condition has changed, the interrupt pin, when connected to a pull-up resistor will toggle to a '0' alerting the controller. See the I2C interface section for more details regarding the register configurations. Dynamic Backlight Control Input (PWM Pin) A PWM (Pulse Width Modulation) pin is provided on the LM3535 to allow a display driver utilizing dynamic backlight control (DBC), to adjust the LED brightness based on the content. The PWM input can be turned on or off (Acknowledge or Ignore) and the polarity can be flipped (active high or active low) through the I2C interface. The current sinks of the 11 LM3535 require approximately 15µs. to reach steady-state target current. This turn-on time sets the minimum usable PWM pulse width for DBC/CABC. LED Forward Voltage Monitoring The LM3535 has the ability to switch gains (1x or 3/2x) based on the forward voltage of the LED load. This ability to switch gains maximizes efficiency for a given load. Forward voltage monitoring occurs on all diode pins. At higher input voltages, the LM3535 will operate in pass mode, allowing the VOUT voltage to track the input voltage. As the input voltage drops, the voltage on the Dxx pins will also drop (VDXX = VVOUT – VLEDx). Once any of the active Dxx pins reaches a voltage approximately equal to 130mV, the charge pump will switch to the gain of 3/2. This switch-over ensures that the current through the LEDs never becomes pinched off due to a lack of headroom across the current sinks. Once a gain transition occurs, the LM3535 will remain in the gain of 3/2 until an I2C write to the part occurs. At that time, the LM3535 will re-evaluate the LED conditions and select the appropriate gain. Only active Dxx pins will be monitored. Configurable Gain Transition Delay To optimize efficiency, the LM3535 has a user selectable gain transition delay that allows the part to ignore short duration input voltage drops. By default, the LM3535 will not change gains if the input voltage dip is shorter than 3 to 6 milliseconds. There are four selectable gain transition delay ranges (4 for LM3535-2ALS and 3 for LM3535) available on the LM3535. All delay ranges are set within the VF Monitor Delay Register . Please refer to the INTERNAL REGISTERS section of this datasheet for more information regarding the delay ranges. Hardware Enable (HWEN) The LM3535 has a hardware enable/reset pin (HWEN) that allows the device to be disabled by an external controller without requiring an I2C write command. Under normal operation, the HWEN pin should be held high (logic '1') to prevent an unwanted reset. When the HWEN is driven low (logic '0'), all internal control registers reset to the default states and the part becomes disabled. Please see the Electrical Characteristics section of the datasheet for required voltage thresholds. I2C Compatible Interface DATA VALIDITY The data on SDIO line must be stable during the HIGH period of the clock signal (SCL). In other words, state of the data line can only be changed when SCL is LOW. 30082425 FIGURE 1. Data Validity Diagram A pull-up resistor between the controller's VIO line and SDIO must be greater than [ (VIO-VOL) / 3mA] to meet the VOL requirement on SDIO. Using a larger pull-up resistor results in lower switching current with slower edges, while using a www.national.com LM3535 smaller pull-up results in higher switching currents with faster edges. START AND STOP CONDITIONS START and STOP conditions classify the beginning and the end of the I2C session. A START condition is defined as SDIO signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as the SDIO transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition. During data transmission, the I2C master can generate repeated START conditions. First START and repeated START conditions are equivalent, function-wise. TRANSFERRING DATA Every byte put on the SDIO line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated by the master. The master releases the SDIO line (HIGH) during the acknowledge clock pulse. The LM3535 pulls down the SDIO line during the 9th clock pulse, signifying an acknowledge. The LM3535 generates an acknowledge after each byte is received. There is no acknowledge created after data is read from the LM3535. After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an eighth bit which is a data direction bit (R/W). The LM3535 7-bit address is 38h. For the eighth bit, a “0” indicates a WRITE and a “1” indicates a READ. The second byte selects the register to which the data will be written. The third byte contains data to write to the selected register. 30082411 FIGURE 2. Start and Stop Conditions 30082412 FIGURE 3. Write Cycle w = write (SDIO = "0") r = read (SDIO = "1") ack = acknowledge (SDIO pulled down by either master or slave) id = chip address, 38h for LM3535 www.national.com 12 LM3535 I2C COMPATIBLE CHIP ADDRESS The 7-bit chip address for LM3535 is 111000, or 0x38. INTERNAL REGISTERS OF LM3535 Register Diode Enable Register Configuration Register Options Register ALS Zone Readback ALS Control Register Internal Hex Address 0x10 0x20 0x30 0x40 0x50 1 ALS Version 2 ALS Version ALS Resistor Register ALS Select Register ALS Zone Boundary #0 ALS Zone Boundary #1 ALS Zone Boundary #2 ALS Zone Boundary #3 0x51 0x52 LM3535-2ALS Only 0x60 0x61 0x62 0x63 Power On Value 0000 0000 (0x00) 0000 0000 (0x00) 0000 0000 (0x00) 1111 0000 (0xF0) 0000 0011 (0x03) 0000 0000 (0x00) 0000 0000 (0x00) 1111 0001 (0xF1) 30082404 FIGURE 4. Diode Enable Register Description Internal Hex Address: 0x10 Each ENx Bit controls the state of the corresponding current sink. Writing a '1' to these bits enables the current sinks. Writing a '0' disables the current sinks. In order for current to begin flowing through the BankA current sinks, the brightness codes stored in either the BankA Brightness register or the ALS Brightness registers (with ALS enabled) must be non-zero. The BankA current sinks can be disabled in two different manors. Writing '0' to the ENx bits when the current sinks are active will disable the current sinks without going through the ramp down sequence. Additionally, setting the BankA brightness code to '0' when the current sinks are active (ENx = '1') does force the diode current to ramp down. All ramping behavior is tied to the BankA Brightness or ALS Brightness Register settings. Any change in these values will cause the LM3535 brightness state machine to ramp the diode current. Writing a '1 to ENC, EN1B, EN62 and EN53 (when EN62 and EN53 are assigned to BankB) by default will enable the corresponding current sinks and drive the LEDs to the current value stored in the BankB and BankC brightness registers. Writing a '0' to these bits immediately disables the current sinks. The ENC and EN1B bits are ignored if the D1C/ALS pin is configured as an ALS input and if the D1B/INT is configured as an interrupt flag. 0011 0011 (0x33) 0110 0110 (0x66) 1001 1001 (0x99) 1100 1100 (0xCC) 1001 1001 (0x99) 1011 0110 (0xB6) 1100 1100 (0xCC) 1110 0110 (0xE6) 1111 1111 (0xFF) 1000 0000 (0x80) ALS Brightness 0x70 Zone #1 ALS Brightness 0x71 Zone #2 ALS Brightness 0x72 Zone #3 ALS Brightness 0x73 Zone #4 ALS Brightness 0x74 Zone #5 Group A 0xA0 Brightness Control Register Group B 0xB0 Brightness Control Register Group C 0xC0 Brightness Control Register 30082405 FIGURE 5. Configuration Register Description Internal Hex Address:0x20 • • • • PWM-EN: PWM Input Enable. Writing a '1' = Enable, and a '0' = Ignore (default). PWM-P: PWM Input Polarity. Writing a '0' = Active High (default) and a '1' = Active Low. 53A: Assign D53 diode to BankA. Writing a '0' assigns D53 to BankB (default) and a '1' assigns D53 to BankA. 62A: Assign D62 diode to BankA. Writing a '0' assigns D62 to BankB (default) and a '1' assigns D62 to BankA. ALS-ENA: Enable ALS on BankA. Writing a '1' enables ALS control of diode current and a '0' (default) forces the BankA current to the value stored in the BankA brightness register. The ALS-EN bit must be set to a '1' for the ALS block to control the BankA brightness. ALS-ENB: Enable ALS on BankB. Writing a '1' enables ALS control of diode current and a '0' (default) forces the BankB current to the value stored in the BankB brightness register. The ALS-EN bit must be set to a '1' for the ALS block to control the BankB brightness. The ALS function for BankB is different than bankA in that the ALS will only enable and disable the BankB diodes depending on the ALS zone chosen by the user. BankA utilizes the 5 1100 0000 (0xC0) • 1111 1000 (0xF8) • 13 www.national.com LM3535 • • different zone brightness registers (Addresses 0x70 to 0x74). ALS-EN: Enables ALS monitoring. Writing a '1' enables the ALS monitoring circuitry and a '0' disables it. This feature can be enabled without having the current sinks or charge pump active. The ALS value is updated in register 0x40 (ALS Zone Register) ALSF: ALS Interrupt Enable. Writing a '1' sets the D1B/INT pin to the ALS interrupt pin and writing a '0' (default) sets the pin to a BankB current sink. 30082410 30082414 FIGURE 7. Brightness Control Register Description Internal Hex Address: 0xA0 (GroupA), 0xB0 (GroupB), 0xC0 (GroupC) 30082406 FIGURE 6. Options Register Internal Hex Address: 0x30 • RD0-RD2: Diode Current Ramp Down Step Time. : ‘000’ = 6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ = 6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms • RU0-RU2: Diode Current Ramp Up Step Time. : ‘000’ = 6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ = 6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms • GT0-GT1: Gain Transition Filter. The value stored in this register determines the filter time used to make a gain transition in the event of an input line step. Filter Times = ‘00’ = 3-6ms, ‘01’ = 0.8-1.5ms, ‘10’ = 20µs, On LM3535-2ALS, '11' = 1µs, On LM3535, ‘11’ = DO NOT USE The Ramp-Up and Ramp-Down times follow the following equations: TRAMP = (NStart - NTarget) × Ramp-Step Time Note: DxA6-DxA0: Sets Brightness for DxA pins (GroupA). 1111111=Fullscale. Code '0' in this register disables the BankA current sinks. DxB2-DxB0: Sets Brightness for DxB pins (GroupB). 111=Fullscale ALSZT2-ALSZT0: Sets the Brightness Zone boundary used to enable and disable BankB diodes based upon ambient lighting conditions. DxC2-DxC0: Sets Brightness for D1C pin. 111 = Fullscale The BankA Current can be approximated by the following equation where N = BRC = the decimal value stored in either the BankA Brightness Register or the five different ALS Zone Brightness Registers: 30082418 30082409 www.national.com 14 LM3535 TABLE 1. ILED vs. Brightness Register Data BankA or ALS Brightness Data 0000000 0000001 0000010 0000011 0000100 0000101 0000110 0000111 0001000 0001001 0001010 0001011 0001100 0001101 0001110 0001111 0010000 0010001 0010010 0010011 0010100 0010101 0010110 0010111 0011000 0011001 0011010 0011011 0011100 0011101 0011110 0011111 % of ILED_MAX BankA or ALS % of ILED_MAX BankA or ALS % of ILED_MAX BankA or ALS % of ILED_MAX Brightness Brightness Data Brightness Data Data 0100000 0100001 0100010 0100011 0100100 0100101 0100110 0100111 0101000 0101001 0101010 0101011 0101100 0101101 0101110 0101111 0110000 0110001 0110010 0110011 0110100 0110101 0110110 0111011 0110111 0111000 0111001 0111010 0111011 0111100 0111101 0111111 0.803% 0.845% 0.889% 0.935% 0.984% 1.035% 1.089% 1.146% 1.205% 1.268% 1.334% 1.404% 1.477% 1.554% 1.635% 1.720% 1.809% 1.904% 2.003% 2.107% 2.217% 2.332% 2.454% 2.582% 2.716% 2.858% 3.007% 3.163% 3.328% 3.502% 3.684% 3.876% 1000000 1000001 1000010 1000011 1000100 1000101 1000110 1000111 1001000 1001001 1001010 1001011 1001100 1001101 1001110 1001111 1010000 1010001 1010010 1010011 1010100 1010101 1010110 1010111 1011000 1011001 1011010 1011011 1011100 1011101 1011110 1011111 4.078% 4.290% 4.514% 4.749% 4.996% 5.257% 5.531% 5.819% 6.122% 6.441% 6.776% 7.129% 7.501% 7.892% 8.303% 8.735% 9.191% 9.669% 10.173% 10.703% 11.261% 11.847% 12.465% 13.114% 13.797% 14.516% 15.272% 16.068% 16.905% 17.786% 18.713% 19.687% 1100000 1100001 1100010 1100011 1100100 1100101 1100110 1100111 1101000 1101001 1101010 1101011 1101100 1101101 1101110 1101111 1110000 1110001 1110010 1110011 1110100 1110101 1110110 1110111 1111000 1111001 1111010 1111011 1111100 1111101 1111110 1111111 20.713% 21.792% 22.928% 24.122% 25.379% 26.701% 28.092% 29.556% 31.096% 32.716% 34.420% 36.213% 38.100% 40.085% 42.173% 44.371% 46.682% 49.114% 51.673% 54.365% 57.198% 60.178% 63.313% 66.611% 70.082% 73.733% 77.574% 81.616% 85.868% 90.341% 95.048% 100.000% 0.000% 0.166% 0.175% 0.184% 0.194% 0.204% 0.214% 0.226% 0.237% 0.250% 0.263% 0.276% 0.291% 0.306% 0.322% 0.339% 0.356% 0.375% 0.394% 0.415% 0.436% 0.459% 0.483% 0.508% 0.535% 0.563% 0.592% 0.623% 0.655% 0.689% 0.725% 0.763% GroupB and GroupC Brightness Levels = 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 25mA • Internal Hex Address: 0x40 ZONE0-ZONE2: ALS Zone information: '000’ = Zone0, ‘001’ = Zone1, ‘010’ = Zone2, ‘011’ = Zone3, ‘100’ = Zone4. Other combinations not used FLAG: ALS Transition Flag. '1' = Transition has occurred. '0' = No Transition. The FLAG bit is cleared once the 0x40 register has been read. • 30082407 FIGURE 8. ALS Zone Register Description 15 www.national.com LM3535 30082417 30082465 FIGURE 9. ALS Control / Silicon Revision Register Description Internal Hex Address: 0x50 • • Rev0-Rev1 : Stores the Silicon Revision value. LM3535 = '11', LM3535-2ALS = '00' AVE2-AVE0: Sets Averaging Time for ALS sampling. Need two to three Averaging periods to make transition decision.‘000’ = 25ms, ‘001’ = 50ms, ‘010’ = 100ms, ‘011’ = 200ms, ‘100’ = 400ms, ‘101’ = 800ms, ‘110’ = 1.6s, ‘111’ = 3.2s • • ALS Select Register (2-ALS Version Only) Internal Hex Address: 0x52 FIGURE 11. CP-EN: Forces the LM3535 to operate in the gain of 1.5x exclusively when the Dx current sinks are enabled. PASS-EN: Forces the LM3535 to operate in the 1x PassMode exclusively when the Dx current sinks are enabled. CP-EN 0 0 1 1 • PASS-EN 0 1 0 1 RESULT Normal Operation Pass-Mode Only 1.5x Gain Only 1.5x Gain Only 30082466 ALS Resistor Control Register Description Internal Hex Address: 0x51 FIGURE 10. • • • R3A-R0A are valid on both the LM3535 and LM3535-2ALS. R3B-R0B are only valid on LM3535-2ALS. R0-R3: Sets the internal ALS resistor value Internal ALS Resistor Table R3x R2x R1x R0x ALSA Resistor Value (Ω) 13.6k 9.08k 5.47k 2.32k 1.99k 1.86k 1.65k 1.18k 1.10k 1.06k 986 804 764 745 711 ALSB Resistor Value (Ω) • 13.65k 9.13k 5.52k 2.37k 2.05k 1.92k 1.70k 1.24k 1.15k 1.11k 1.04 858 818 799 765 • • • • SEL1-SEL0: ALS Selection Bits. SEL1 and SEL0 determine how the ALS sensor information is processed. '00' = Min. of ALSA and ALSB used, '01' = ALSA used and ALSB ignored (DEFAULT), '10' = ALSB Used and ALSA ignored, '11' = Max. of ALSA and ALSB used. 30082415 FIGURE 12. Zone Boundary Register Descriptions ZB7-ZB0: Sets Zone Boundary Lines with a Falling ALS voltage. 0xFF w/ ALS Falling = 992.3mV (typ.). VTRIP-LOW (typ) = [Boundary Code × 3.874mV] + 4.45mV For boundary codes 2 to 255. Code 0 and Code1 are mapped to equal the Code2 value. Each zone line has approx. 5.5mV of hysteresis between the falling and rising ALS trip points.. Zone Boundary 0 is the line between ALS Zone 0 and Zone 1. Default Code = 0x33 or approx. 200mV Zone Boundary 1 is the line between ALS Zone 1 and Zone 2. Default Code = 0x66 or approx. 400mV Zone Boundary 2 is the line between ALS Zone 2 and Zone 3. Default Code = 0x99 or approx. 600mV Zone Boundary 3 is the line between ALS Zone 3 and Zone 4. Default Code = 0xCC or approx. 800mV 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 High Impedance www.national.com 16 LM3535 • • • 30082416 • FIGURE 13. Zone Brightness Region Register Description • B7-B0: Sets the ALS Zone Brightness Code. B7 always = '1' (unused). Use the formula found in the BankA • Brightness Register Description (Figure 7) to set the desired target brightness. Default values can be overwritten Zone0 Brightness Address = 0x70. Default = 0x99 (25) or 0.084mA Zone1 Brightness Address = 0x71. Default = 0xB6 (54) or 0.164mA Zone2 Brightness Address = 0x72. Default = 0xCC (76) or 1.45mA Zone3 Brightness Address = 0x73. Default = 0xE6 (102) or 6.17mA Zone4 Brightness Address = 0x74. Default = 0xFF (127) or 25mA 17 www.national.com LM3535 Application Information AMBIENT LIGHT SENSING Ambient Light Sensor Block The LM3535 incorporates an Ambient Light Sensing interface (ALS) which translates an analog output ambient light sensor to a user specified brightness level. The ambient light sensing circuit has 4 programmable boundaries (ZB0 – ZB3) which define 5 ambient brightness zones. Each ambient brightness zone corresponds to a programmable brightness threshold (Z0T – Z4T). Furthermore, the ambient light sensing inputs (ALSA and ALSB(LM3535-2ALS)) features 15 internal software selectable voltage setting resistors. This allows the LM3535 the capability of interfacing with a wide selection of ambient light sensors. Additionally, the ALS inputs can be configured as high impedance, thus providing for a true shutdown during low power modes. The ALS resistors are selectable through the ALS Resistor Select Register (see Internal ALS Resistor Table). Figure 14 shows a functional block diagram of the ambient light sensor input. 30082442 FIGURE 14. Ambient Light Sensor Functional Block Diagram ALS Operation The ambient light sensor input has a 0 to 1V operational input voltage range. The Typical Application Circuit shows the LM3535 with an ambient light sensor (AVAGO, APDS-9005) and the internal ALS Resistor Select Register set to 0x40 (2.32kΩ). This circuit converts 0 to 1000 LUX light into approximately a 0 to 850mV linear output voltage. The voltage at the active ambient light sensor input is compared against the 8 bit values programmed into the Zone Boundary Registers (ZB0-ZB3). When the ambient light sensor output crosses one of the ZB0 – ZB3 programmed thresholds the internal ALS circuitry will smoothly transition the LED current to the new 7 bit brightness level as programmed into the appropriate Zone Target Register (Z0T – Z4T, See Figure 13). With bits [6:4] of the Configuration Register set to 1 (Bit6 = ALS Block Enable, Bit5 = BankB ALS Enable, Bit4 = BankA ALS Enable), the LM3535 is configured for Ambient Light Current Control. In this mode the ambient light sensing input (ALS) monitors the output of analog output ambient light sensing photo diode and adjusts the LED current depending on the ambient light. The ambient light sensing circuit has 4 configurable Ambient Light Boundaries (ZB0 – ZB3) programmed through the four (8-bit) Zone Boundary Registers. These zone boundaries define 5 ambient brightness zones. On start-up the 4 Zone Boundary Registers are pre-loaded with 0x33 (51d), 0x66 (102d), 0x99 (153d), and 0xCC (204d). The ALS input has a 1V active input voltage range which makes the default Zone Boundaries approx. set at: Zone Boundary 0 = 200mV Zone Boundary 1 = 400mV Zone Boundary 2 = 600mV Zone Boundary 3 = 800mV These Zone Boundary Registers are all 8-bit (readable and writable) registers. By Default, the first zone (Z0) is defined between 0 and 200mV, Z1’s default is defined between 200mV and 400mV, Z2 is defined between 400mV and 600mV, Z3 is defined between 600mV and 800mV, and Z4 is defined between 800mV and 1V. The default settings for the 5 Zone Target Registers are 0x19, 0x33, 0x4C, 0x66, and 0x7F. This corresponds to LED brightness settings of 84µA, 164µA, 1.45mA, 6.17mA and 25mA of current respectively. See Figure 15. www.national.com 18 LM3535 30082443 ALS Zone to LED Brightness Mapping FIGURE 15. ALS Configuration Example As an example, assume that the APDS-9005 is used as the ambient light sensing photo diode with its output connected to the ALSA input. The ALS Resistor Select Register (Address 0x51) is loaded with 0x40 which configures the ALS input for a 2.32kΩ internal pull-down resistor (see Internal ALS Resistor Table). This gives the output of the APDS-9005 a typical voltage swing of 0 to 875mV with a 0 to 1k LUX change in ambient light (0.875mV/Lux). Next, the Configuration Register (Address 0x20) is programmed with 0xDC, the ALS Control Register (Address 0x50) programmed to 0x40 and the Control Register is programmed to 0x3F . This configures the LM3535’s ambient light sensing interface for: • Ambient Light Current Control for BankA Enabled • ALS circuitry Enabled • Assigns D53 and D62 to bankA • Sets the ALS Averaging Time to 400ms Next, the Control Register (Address 0x10) is programmed with 0x3F which enables the 6 LEDs via the I2C compatible interface. Now assume that the APDS-9005 ambient light sensor detects a 100 LUX ambient light at its input. This forces the ambient light sensors output (and the ALS1 input) to 87.5mV corresponding to Zone 0. Since Zone 0 points to the brightness code programmed in Zone Target Register 0 (loaded with code 0x19), the LED current becomes: This Example still applies to the LM3535-2ALS version using two ambient light sensors. The ALS selector block makes the front end decision as to which sensor to use. ALS Averaging Time The ALS Averaging Time is the time over which the Averager block collects samples from the A/D converter and then averages them to pass to the discriminator block (see ). Ambient light sensor samples are averaged and then further processed by the discriminator block to provide rejection of noise and transient signals. The Averager is configurable with 8 different averaging times to provide varying amounts of noise and transient rejection (see Figure 9). The discriminator block algorithm has a maximum latency of two averaging cycles, therefore the averaging time selection determines the amount of delay that will exist between a steady state change in the ambient light conditions and the associated change of the backlight illumination. For example, the A/D converter samples the ALS inputs at 16kHz. If the averaging time is set to 800ms, the Averager will send the updated zone information to the discriminator every 800ms. This zone information contains the average of approximately 12800 samples (800ms × 16kHz). Due to the latency of 2 averaging cycles, when there is a steady state change in the ambient light, the LED current will begin to transition to the appropriate target value after approximately 1600ms have elapsed. The sign and magnitude of these Averager outputs are used to determine whether the LM3535 should change brightness zones. The Averager block follows the following rules to make a zone transition: • The Averager always begins with a Zone0 reading stored at start-up. If the main display LEDs are active before the ALS block is enabled, it is recommended that the ALS-EN bit be enabled at least 3 averaging cycles times before the ALS-ENA bit is enabled. • The Averager will always round down to the lower zone in the case of a non-integer zone average (1.2 rounds to 1 and 1.75 also rounds to 1). Figure 16 shows an example of how the Averager will make the zone decisions for different Ambient conditions. Next assume that the ambient light changes to 500 LUX (corresponding to an ALS1 voltage of 437.5mV). This moves the ambient light into Zone 2 which corresponds to Zone Target Register 2 (loaded with code 0x4C) the LED current then becomes: 19 www.national.com LM3535 Using the diagram for the ALS block (Figure 14), Figure 18 shows the flow of information starting with the A/D, transitioning to the Averager, followed by the Discriminator. Each state filters the previous output to help prevent unwanted zone to zone transitions. 30082450 FIGURE 16. Averager Calculation • The two most current averaging samples are used to make zone change decisions. • To make a zone change, data from three averaging cycles are needed. (Starting Value, First Transition, Second Transition or Rest) • To Increase the brightness zone, a positive Averager zone output must be followed by a second positive Averager output or a repeated Averager zone. ('+' to '+' or '+' to 'Rest') • To decrease the brightness zone, a negative Averager zone output must be followed by a second negative Averager output or a repeated Averager zone. ('-' to '-' or '-' to 'Rest') • In the case of two increases or decreases in the Averager output, the LM3535 will transition to zone equal to the last Averager output. Figure 17 provides a graphical representation of the Averager's behavior. 30082448 FIGURE 18. Ambient Light Input to Backlight Mapping When using the ALS averaging functionality, it is important to remember that the averaging cycle is free running and is not synchronized with changing ambient lighting conditions. Due to the nature of the Averager round down, an increase in brightness can take between 2 and 3 averaging cycles to change zones while a decrease in brightness can take between 1 and 2 averaging cycles to change. See Figure 9 for a list of possible Averager periods. Figure 19 shows an example of how the perceived brightness change time can vary. 30082451 FIGURE 19. Perceived Brightness Change Time Ambient Light Current Control + PWM The Ambient Light Current Control can also be a function of the PWM input duty cycle. Assume the LM3535 is configured as described in the previous example, but this time the Enable 20 30082449 FIGURE 17. Brightness Zone Change Examples www.national.com LM3535 PWM bit set to ‘1’ (Configuration Register bit [0]). Figure 20 shows how the different blocks (PWM and ALS) influence the LED current. 30082446 FIGURE 20. Current Control Block Diagram ALS + PWM Example In this example, the APDS-9005 sensor detects that the ambient light has changed to 1 kLux. The voltage at the ALS input is now around 875mV and the ambient light falls within Zone 5. This causes the LED brightness to be a function of Zone Target Register 5 (loaded with 0x7F). Now assume the PWM input is also driven with a 50% duty cycle pulsed waveform. The LED current now becomes: assigns D53 and D62 to the GroupB lighting region. With this added flexibility, the LM3535 is capable of supporting applications requiring 4, 5, or 6 LEDs for main display lighting, while still providing additional current sinks that can be used for a wide variety of lighting functions. MAXIMUM OUTPUT CURRENT, MAXIMUM LED VOLTAGE, MINIMUM INPUT VOLTAGE The LM3535 can drive 8 LEDs at 25mA each (GroupA , GroupB, GroupC) from an input voltage as low as 3.2V, so long as the LEDs have a forward voltage of 3.6V or less (room temperature). The statement above is a simple example of the LED drive capability of the LM3535. The statement contains the key application parameters that are required to validate an LEDdrive design using the LM3535: LED current (ILEDx), number of active LEDs (Nx), LED forward voltage (VLED), and minimum input voltage (VIN-MIN). The equation below can be used to estimate the maximum output current capability of the LM3535: ILED_MAX = [(1.5 x VIN) - VLED - (IADDITIONAL × ROUT)] / [(Nx x ROUT) + kHRx] (eq. 1) ILED_MAX = [(1.5 x VIN ) - VLED - (IADDITIONAL × 2.4Ω)] / [(Nx x 2.4Ω) + kHRx] IADDITIONAL is the additional current that could be delivered to the other LED Groups. LED CONFIGURATIONS The LM3535 has a total of 8 current sinks capable of sinking 200mA of total diode current. These 8 current sinks are configured to operate in three independently controlled lighting regions. GroupA has four dedicated current sinks, while GroupB and GroupC each have one. To add greater lighting flexibility, the LM3535 has two additional drivers (D53 and D62) that can be assigned to either GroupA or GroupB through a setting in the general purpose register. At start-up, the default condition is four LEDs in GroupA, three LEDs in GroupB and a single LED in GroupC (NOTE: GroupC only consists of a single current sink (D1C) under any configuration). Bits 53A and 62A in the general purpose register control where current sinks D53 and D62 are assigned. By writing a '1' to the 53A or 62A bits, D53 and D62 become assigned to the GroupA lighting region. Writing a '0' to these bits 21 www.national.com LM3535 ROUT – Output resistance. This parameter models the internal losses of the charge pump that result in voltage droop at the pump output VOUT. Since the magnitude of the voltage droop is proportional to the total output current of the charge pump, the loss parameter is modeled as a resistance. The output resistance of the LM3535 is typically 2.4Ω (VIN = 3.6V, TA = 25°C). In equation form: VVOUT = (1.5 × VIN) – [(NA× ILEDA + NB × ILEDB + NC × ILEDC) × ROUT] (eq. 2) kHR – Headroom constant. This parameter models the minimum voltage required to be present across the current sinks for them to regulate properly. This minimum voltage is proportional to the programmed LED current, so the constant has units of mV/mA. The typical kHR of the LM3535 is 4mV/mA. In equation form: (VVOUT – VLEDx) > kHRx × ILEDx (eq. 3) Typical Headroom Constant Values kHRA = kHRB = kHRC = 4 mV/mA The "ILED-MAX" equation (eq. 1) is obtained from combining the ROUT equation (eq. 2) with the kHRx equation (eq. 3) and solving for ILEDx. Maximum LED current is highly dependent on minimum input voltage and LED forward voltage. Output current capability can be increased by raising the minimum input voltage of the application, or by selecting an LED with a lower forward voltage. Excessive power dissipation may also limit output current capability of an application. Total Output Current Capability The maximum output current that can be drawn from the LM3535 is 200mA. DRIVER TYPE DxA DxB D1C MAXIMUM Dxx CURRENT 25mA per DxA Pin 25mA per DxB Pin 25mA PLEDTOTAL = (VLEDA × NA × ILEDA) + (VLEDB × NB × ILEDB) + (VLEDC × ILEDC) PIN = VIN × IIN PIN = VIN × (GAIN × ILEDTOTAL + IQ) E = (PLEDTOTAL ÷ PIN) The LED voltage is the main contributor to the charge-pump gain selection process. Use of low forward-voltage LEDs (3.0V- to 3.5V) will allow the LM3535 to stay in the gain of 1× for a higher percentage of the lithium-ion battery voltage range when compared to the use of higher forward voltage LEDs (3.5V to 4.0V). See the LED Forward Voltage Monitoring section of this datasheet for a more detailed description of the gain selection and transition process. For an advanced analysis, it is recommended that power consumed by the circuit (VIN x IIN) for a given load be evaluated rather than power efficiency. POWER DISSIPATION The power dissipation (PDISS) and junction temperature (TJ) can be approximated with the equations below. PIN is the power generated by the 3/2× - 1× charge pump, PLED is the power consumed by the LEDs, TA is the ambient temperature, and θJA is the junction-to-ambient thermal resistance for the micro SMD 20-bump package. V IN is the input voltage to the LM3535, VLED is the nominal LED forward voltage, N is the number of LEDs and ILED is the programmed LED current. PDISS = PIN - PLEDA - PLEDB - PLEDC PDISS= (GAIN × VIN × IGroupA + GroupB + GroupC ) - (VLEDA × NA × ILEDA) - (VLEDB × NB × ILEDB) - (VLEDC × ILEDC) TJ = TA + (PDISS x θJA) The junction temperature rating takes precedence over the ambient temperature rating. The LM3535 may be operated outside the ambient temperature rating, so long as the junction temperature of the device does not exceed the maximum operating rating of 110°C. The maximum ambient temperature rating must be derated in applications where high power dissipation and/or poor thermal resistance causes the junction temperature to exceed 110°C. THERMAL PROTECTION Internal thermal protection circuitry disables the LM3535 when the junction temperature exceeds 150°C (typ.). This feature protects the device from being damaged by high die temperatures that might otherwise result from excessive power dissipation. The device will recover and operate normally when the junction temperature falls below 125°C (typ.). It is important that the board layout provide good thermal conduction to keep the junction temperature within the specified operating ratings. CAPACITOR SELECTION The LM3535 requires 4 external capacitors for proper operation (C1 = C2 = CIN = COUT = 1µF). Surface-mount multi-layer ceramic capacitors are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance (ESR