SEA05LTR

SEA05L Advanced constant voltage and constant current controller with very efficient LED pilot-lamp driver Preliminary data Features ■ Constant voltage and constant current control ■ Very efficient LED pilot-lamp driver ■ Wide operating VCC range (3.5 V - 36 V) ■ Low quiescent consumption: 250 µA ■ Voltage reference: 2.5 V ■ Voltage control loop accuracy ± 0.5% ■ Current sense threshold: 50 mV ■ Current control loop accuracy ± 4% ■ Low external component count ■ Open-drain output stage ■ SOT23-6L package SOT23-6L (plastic package) Figure 1. Block diagram 1.23 V V CC 6 2.5 V 50m V + - 5 Out 3 V ctrl + - 4 LD Applications ■ AC-DC adapter with LED pilot-lamp ■ Battery chargers with LED pilot-lamp ■ SMPS with LED pilot-lamp 1 Isen se The voltage reference, along with one op-amp, is the core of the voltage control loop. The current sensing circuit and the other op-amp make up the current control loop. Description The device is a highly integrated solution for SMPS applications, with an LED pilot-lamp requiring a dual control loop to perform CV (constant voltage) and CC (constant current) regulation. The IC allows very efficient LED pilot-lamp driving which helps to reduce the standby consumption of the SMPS. It integrates a voltage reference, two op-amps (with OR-ed open-drain outputs), a lowside current sensing circuit and an LED pilot-lamp driver pin implemented with an open-drain mosfet driven by square waveform with 12.5% duty cycle at 1 kHz that allows reducing LED consumption. The external components needed to complete the two control loops are: - a resistor divider that senses the output of the power supply and fixes the voltage regulation setpoint at the specified value - a sense resistor that feeds the current sensing circuit with a voltage proportional to the DC output current; this resistor determines the current regulation setpoint and must be adequately rated in terms of power dissipation - the frequency compensation components (R-C networks) for both loops. The device is ideal for space-critical applications. Table 1. February 2011 2 GND OSC Device summary Order code Package Packing SEA05LTR SOT23-6L Tape & reel Doc ID 18462 Rev 1 This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice. 1/12 www.st.com 1 Contents SEA05L Contents 1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 Voltage and current control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3 LD pin function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2/12 Doc ID 18462 Rev 1 SEA05L 1 Operation Operation Table 2. Absolute maximum ratings Symbol Pin VCC 6 Vout Value Unit DC supply voltage –0.3 to 38 V 5 Open-drain voltage –0.3 to VCC V Iout 5 Max. sink current 20 mA VLD 4 Open-drain voltage –0.3 to VCC V ILD 4 Max. sink current 15 mA Isense 1 Analog input Vctrl Parameter 3 –0.3 to VCC –0.3 to VCC < Analog input 12(1) V V 1. Vctrl cannot exceed VCC and cannot exceed 12 V. Table 3. Thermal data Symbol Rth j-amb Parameter Value Unit 250 °C/W Thermal resistance, junction-to-ambient Tjop Junction temperature operating range –40 to 150 Tstg Storage temperature –55 to 150 Figure 2. °C Pin configuration Isense 1 6 V cc GND 2 5 O ut V ctrl 3 4 LD AM04985v1 Table 4. Pin functions Pin number Name 1 Isense Inverting input of the current loop op-amp. The pin is typically used for the current control loop, connecting it to the positive end of the current sense resistor through a decoupling resistor. GND Ground. Return of the bias current of the device. 0 V reference for all voltages. The pin has to be tied as close as possible to the ground output terminal of the converter to minimize load current effect on the voltage regulation setpoint. 2 Function Doc ID 18462 Rev 1 3/12 Operation SEA05L Table 4. 4/12 Pin functions (continued) Pin number Name Function 3 Vctrl Inverting input of the voltage loop op-amp. The pin is typically used for the voltage control loop and is connected to the midpoint of a resistor divider that senses the output voltage. 4 LD Open-drain output able to sink 5 mA (peak), driven by the internal oscillator at 1 kHz square waveform with 12.5% duty cycle. The internal mosfet starts to switch when VCC is above the turn-on threshold (typ. 3 V) and it is off (LD high impedance) when VCC is below the UVLO of the IC. The pin can be connected to an external LED pilot-lamp with a resistor in series in order to limit the LED current 5 OUT Common open-drain output of the two internal op-amps. The pin, only able to sink current, is typically connected to the branch of the optocoupler's photodiode to transmit the error signal to the primary side. 6 VCC Supply voltage of the device. A small bypass capacitor (0.1 µF typ.) to GND, located as close to the IC pins as possible, might be useful to get a clean supply voltage. Doc ID 18462 Rev 1 SEA05L Operation Table 5. Electrical characteristics (–25 C° < Tj < 125 °C, VCC = 20 V; unless otherwise specified) Symbol Parameter Test condition Min. Typ. Max. Unit 36 V 500 µA Device supply VCC Voltage operating range ICC Quiescent current (Ictrl = Vsense = 0, OUT = open) 3.5 250 Voltage control loop op-amp Gmv Transconductance (sink current only)(1) Vctrl Voltage reference default value Ibias Inverting input bias current (2) Tj = 25 °C 1 3.5 2.488 2.5 S 2.512 V 25 nA 1.5 7 S 48 50 Current control loop Gmi Transconductance (sink current only) (3) Vcsth Current sense threshold at I(Iout) = 1 Ibias Non-inverting input source current mA(4) 52 mV 6 µA Output stage VOUTlow Low output level at 2 mA sink current 200 400 mV LED driver ILD LED driver sink current capability (peak) 10 fLD LED driver current modulation frequency 0.6 VLDlow Low output level at 5 mA sink current (internal mosfet on) ILD_LKG LED driver leakage current (internal mosfet off) mA 1 1.4 kHz 450 900 mV 0.5 µA 1. If the voltage on Vctrl (the negative input of the amplifier) is higher than the positive amplifier input, and it is increased by 1mV, the sinking current at the output OUT will be increased by 3.5 mA. 2. The internal voltage reference is set at 2.5 V. The voltage control loop precision takes into account the cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the transconductance operational amplifier. The internal voltage reference is fixed by bandgap, and trimmed to 0.48 % accuracy at room temperature. 3. When the inverting input at Isense is greater than 50 mV, and the voltage is increased by 1 mV, the sinking current at the output Out will be increased by 7 mA. 4. The internal current sense threshold is triggered when the voltage on pin Isense is 50 mV. The current control loop precision takes into account the cumulative effects of the internal voltage reference deviation as well as the input offset voltage of the transconductance operational amplifier. Doc ID 18462 Rev 1 5/12 Application information SEA05L 2 Application information Figure 3. Typical application schematic 0.1μ F LED 1.23 V V cc 6 2.5 V 5 + - 50m V R1 Out 3 Vo V ctrl + - R2 4 LD 2 1 GND Isen se OSC R sen se Io VO = 2.1 R1 + R 2 * 2.5 V R2 IO max = 0.05 V Rsense AM04986v1 Voltage and current control Voltage control The voltage loop is controlled via a transconductance operational amplifier, the voltage divider R1, R2, and the optocoupler which is directly connected to the output. It is possible to choose the values of R1 and R2 resistors using Equation 1 and Equation 2: Equation 1 VO = Vctrl ∗ ( R1 + R2 ) R2 Equation 2 R1 = R2 ∗ (VO + Vctrl ) Vctrl where VO is the desired output voltage. As an example, with R1 = 100 kΩ and R2 = 15 kΩ VO = 19.17 V. 6/12 Doc ID 18462 Rev 1 SEA05L Application information Current control The current loop is controlled via a transconductance operational amplifier, the sense resistor Rsense, and the optocoupler. The control equation verifies: Equation 3 Rsense ∗ I O max = Vcsth Equation 4 Rsense = Vcsth I O max where IOmax is the desired limited current, and Vcsth is the threshold voltage for the current control loop. As an example, with Iomax = 1 A, Vcsth = 50 mV, then Rsense = 50 mΩ. Note that the Rsense resistor should be chosen, taking into account the maximum dissipation (Plim) through it during full load operation. Equation 5 Plim = Vcsth ∗ I O max As an example, with IOmax = 1 A and Vcsth = 50 mV, Plim = 50 mW. Therefore, for most adaptor and battery charger applications, a low-power resistor is suitable for the current sensing function. Vcsth threshold is achieved internally by a voltage divider tied to an internal precise voltage reference. Its midpoint is tied to the positive input of the current control operational amplifier, and its endpoint is connected to GND. The resistors of this voltage divider are matched to provide the best precision possible. The current sinking outputs of the two transconductance operational amplifiers are common (to the output of the IC). This makes an OR function which ensures that whenever the current or the voltage reaches excessively high values, the optocoupler is activated. The relationship between the controlled current and the controlled output voltage can be described with a square characteristic as shown in the following V/I output-power graph (with power supply of the device independent from the output voltage). Doc ID 18462 Rev 1 7/12 Application information Figure 4. SEA05L Output voltage versus output current V out C urrent regulation V oltage regulation (V cc of the device independent from output voltage) Iout AM04987v1 2.2 Compensation The voltage control transconductance operational amplifier can be fully compensated. Both its output and negative input are directly accessible for external compensation components. 2.3 LD pin function The device provides a unique feature that allows highly efficient driving of an LED pilot-lamp. The main benefit of this new feature is to allow reducing the standby power consumption of the SMPS with the LED pilot-lamp. The LD pin is an open-drain output able to sink 5 mA (peak), driven by the internal oscillator at 1 kHz (typ.) square waveform with 12.5% duty cycle (see Figure 6). The internal mosfet starts to switch when VCC is above the turn-on threshold (typ 3 V) and it is off (LD high impedance) when VCC is below the UVLO of the IC. Connecting the LED pilot-lamp, with a resistor in series in order to limit the LED current, to pin LD (as shown in Figure 5) reduces the power consumption of the LED while keeping the same driving peak current. The LED driving current modulation frequency of 1 kHz (typ.) eliminates the visual perception of flickering. 8/12 Doc ID 18462 Rev 1 SEA05L Application information Figure 5. Connection of LED to pin LD V cc LED 1.23 V IL E D V cc 6 2.5 V 5 + - 50m V Out R LED 3 V ctrl + - 4 LD 2 1 GND Isen se OSC AM04988v1 Figure 6. LED current waveform with a typical frequency of 1 kHZ I T=1ms (f=1kHz) ton=125 µs (T/8) ILED t AM04989v1 Doc ID 18462 Rev 1 9/12 Package mechanical data 3 SEA05L Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark. Table 6. SOT23-6L (2.90 mm x 2.80 mm) package mechanical data mm inches Sym Min Typ A Min Typ 1.45 A1 0.00 A2 0.90 b c Max 0.057 0.15 0.000 1.30 0.035 0.30 0.50 0.012 0.020 0.08 0.22 0.003 0.009 1.15 0.006 0.045 D 2.90 0.114 E 2.80 0.110 E1 1.60 0.063 e 0.95 0.037 e1 1.90 0.075 0.051 L 0.30 0.45 0.60 0.012 0.018 0.024 è 0° 4° 8° 0° 4° 8° N Note: Max 6 6 Dimensions per JEDEC MO178AB Figure 7. SOT23-6L (2.90 mm x 2.80 mm) package mechanical drawing 7049717_G 10/12 Doc ID 18462 Rev 1 SEA05L 4 Revision history Revision history Table 7. Document revision history Date Revision 23-Feb-2011 1 Changes Initial release. Doc ID 18462 Rev 1 11/12 SEA05L Please Read Carefully: Information in this document is provided solely in connection with ST products. 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