LTC3245
Wide VIN Range,
Low Noise, 250mA Buck-Boost
Charge Pump
Description
Features
2.7V to 38V VIN Range
IQ = 18µA Operating; 4μA in Shutdown
12V to 5V Efficiency = 81%
Multimode Operation (2:1, 1:1, 1:2) with Automatic
Mode Switching
n Low Noise, Constant Frequency Operation
n Pin Selectable Burst Mode ® Operation
n V
OUT: Fixed 3.3V, 5V or Adjustable (2.5V to 5V)
n I
OUT Up to 250mA
n Overtemperature and Short-Circuit Protection
n Operating Junction Temperature: 150°C Maximum
n Thermally Enhanced 12-Pin MSOP and Low Profile
12-Pin (3mm × 4mm) DFN Packages
The LTC®3245 is a switched capacitor buck-boost DC/DC
converter that produces a regulated output (3.3V, 5V or
adjustable) from a 2.7V to 38V input. The device uses
switched capacitor fractional conversion to maintain
regulation over a wide range of input voltage. Internal
circuitry automatically selects the conversion ratio to
optimize efficiency as input voltage and load conditions
vary. No inductors are required.
Applications
Low operating current (20μA with no load, 4μA in shutdown) and low external parts count (three small ceramic
capacitors) make the LTC3245 ideally suited for low power,
space constrained automotive/industrial applications. The
device is short-circuit and overtemperature protected, and
is available in thermally enhanced 12-pin MSOP and low
profile 3mm × 4mm 12-pin DFN packages.
n
n
n
n
Automotive ECU/CAN Transceiver Supplies
Industrial Housekeeping Supplies
n Low Power 12V to 5V Conversion
n
n
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
The unique constant frequency architecture provides a
lower noise output than conventional charge pump regulators. To optimize efficiency at the expense of slightly
higher output ripple, the device has pin selectable Burst
Mode operation.
Typical Application
Efficient Regulated 5V Output
5VOUT Efficiency vs Output Current
90
1µF
400
VIN = 12V
80
350
EFFICIENCY
C–
LTC3245
VIN
VIN = 2.7V TO 38V
1µF
SEL2
BURST
SEL1
VOUT
OUTS/ADJ
PGOOD
GND
500k
VOUT = 5V
IOUT UP TO 250mA
10µF
300
60
250
50
200
40
150
PLOSS
30
PLOSS (mW)
C+
EFFICIENCY (%)
70
100
20
50
3245 TA01a
10
0.1
1
10
IOUT (mA)
100
0
1000
3245 TA01b
3245fa
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1
LTC3245
Absolute Maximum Ratings
(Note 1)
VIN, SEL1, SEL2, BURST............................. –0.3V to 38V
VOUT, OUTS/ADJ, PGOOD............................. –0.3V to 6V
IPGOOD.......................................................................2mA
VOUT Short-Circuit Duration.............................. Indefinite
Operating Junction Temperature Range (Notes 2, 3)
(E-/I-Grade)......................................... –40°C to 125°C
(H-Grade)............................................ –40°C to 150°C
(MP-Grade)......................................... –55°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
(MSE Only) ........................................................... 300°C
Pin Configuration
TOP VIEW
VIN
TOP VIEW
12 GND
1
–
VIN
2
11 C
VIN
3
10 VOUT
BURST
4
SEL1
SEL2
13
GND
VIN
VIN
VIN
BURST
SEL1
SEL2
9
C+
5
8
PGOOD
6
7
OUTS/ADJ
1
2
3
4
5
6
13
GND
12
11
10
9
8
7
GND
C–
VOUT
C+
PGOOD
OUTS/ADJ
MSE PACKAGE
12-LEAD PLASTIC MSOP
DE PACKAGE
12-LEAD (3mm × 4mm) PLASTIC DFN
TJMAX = 150°C, θJA = 40°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB GND
TJMAX = 150°C, θJA = 43°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB GND
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3245EDE#PBF
LTC3245EDE#TRPBF
3245
12-Lead (3mm × 4mm) Plastic DFN
–40°C to 125°C
LTC3245IDE#PBF
LTC3245IDE#TRPBF
3245
12-Lead (3mm × 4mm) Plastic DFN
–40°C to 125°C
LTC3245EMSE#PBF
LTC3245EMSE#TRPBF
3245
12-Lead Plastic MSOP
–40°C to 125°C
LTC3245IMSE#PBF
LTC3245IMSE#TRPBF
3245
12-Lead Plastic MSOP
–40°C to 125°C
LTC3245HMSE#PBF
LTC3245HMSE#TRPBF
3245
12-Lead Plastic MSOP
–40°C to 150°C
LTC3245MPMSE#PBF
LTC3245MPMSE#TRPBF
3245
12-Lead Plastic MSOP
–55°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
Electrical
Characteristics
The
l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C, (Note 2). VIN = 12V, VOUT = 5V, CFLY = 1µF unless otherwise
noted.
SYMBOL
PARAMETER
VIN
Operating Input Voltage Range
VUVLO
VIN Undervoltage Lockout Threshold
CONDITIONS
MIN
l
VIN Rising
VIN Falling
l
TYP
2.7
2.4
2.2
MAX
UNITS
38
V
2.7
V
V
3245fa
2
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LTC3245
Electrical
Characteristics
The
l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C, (Note 2). VIN = 12V, VOUT = 5V, CFLY = 1µF unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
IVIN
VIN Quiescent Current
SEL1 = SEL2 = 0V
VOUT Enabled, BURST = 0V
VOUT Enabled, BURST = VIN
Shutdown, VOUT = 0V
CP Enabled, Output in Regulation
CP Enabled, Output in Regulation
VOUT5_BM
Fixed 5V Burst Mode Output Regulation
(OUTS/ADJ Connected to VOUT,
BURST = 0V, SEL2 = VIN, SEL1 = 0V)
(Note 5)
5V ≤ VIN < 38V, IOUT ≤ 250mA
4V ≤ VIN < 5V, IOUT ≤ 150mA
3.3V ≤ VIN < 4V, IOUT ≤ 75mA
3V ≤ VIN < 3.3V, IOUT ≤ 45mA
l
l
l
l
VOUT5_LN
Fixed 5V Low Noise Output Regulation
(OUTS/ADJ Connected to VOUT,
BURST = VIN, SEL2 = VIN, SEL1 = 0V)
(Note 5)
5V ≤ VIN < 38V, IOUT ≤ 200mA
4V ≤ VIN < 5V, IOUT ≤ 120mA
3.3V ≤ VIN < 4V, IOUT ≤ 60mA
3V ≤ VIN < 3.3V, IOUT ≤ 35mA
VOUT33_BM
Fixed 3.3V Burst Mode Output Regulation
(OUTS/ADJ Connected to VOUT,
BURST = 0V, SEL2 = VIN, SEL1 = VIN)
(Note 5)
VOUT33_LN
4
18
20
8
35
40
µA
µA
µA
4.8
4.8
4.8
4.8
5.2
5.2
5.2
5.2
V
V
V
V
l
l
l
l
4.8
4.8
4.8
4.8
5.2
5.2
5.2
5.2
V
V
V
V
5V ≤ VIN < 38V, IOUT ≤ 250mA
4V ≤ VIN < 5V, IOUT ≤ 175mA
3.3V ≤ VIN < 4V, IOUT ≤ 110mA
2.7V ≤ VIN < 3.3V, IOUT ≤ 60mA
l
l
l
l
3.17
3.17
3.17
3.17
3.43
3.43
3.43
3.43
V
V
V
V
Fixed 3.3V Low Noise Output Regulation
(OUTS/ADJ Connected to VOUT,
BURST = VIN, SEL2 = VIN, SEL1 = VIN)
(Note 5)
5V ≤ VIN < 38V, IOUT ≤ 220mA
4V ≤ VIN < 5V, IOUT ≤ 140mA
3.3V ≤ VIN < 4V, IOUT ≤ 90mA
2.7V ≤ VIN < 3.3V, IOUT ≤ 50mA
l
l
l
l
3.17
3.17
3.17
3.17
3.43
3.43
3.43
3.43
V
V
V
V
VADJ
OUTS/ADJ Reference Voltage (Note 4)
SEL2 = 0V, SEL1 = VIN, IOUT = 0mA
l
1.176
1.224
V
1.200
RCL
Load Regulation (Referred to ADJ)
SEL2 = 0V, SEL1 = VIN
0.2
VPG_RISE
PGOOD Rising Threshold
VOUT% of Final Regulation Voltage
95
UNITS
mV/mA
98
%
VPG_FALL
PGOOD Falling Threshold
VOUT% of Final Regulation Voltage
VPG_LOW
PGOOD Output Low Voltage
IPGOOD = 0.2mA
IPG_HIGH
PGOOD Output High Leakage
VPGOOD = 5V
VLOW
BURST, SEL1, SEL2 Input Voltage
l
VHIGH
BURST, SEL1, SEL2 input Voltage
l
ILOW
BURST, SEL1, SEL2 Input Current
VPIN = 0V
–1
IHIGH
BURST, SEL1, SEL2 Input Current
VPIN = 38V
0.5
ISHORT_CKT
IVOUT Short-Circuit Current
VOUT = GND
900
mA
ROUT
Charge Pump Output Impedance
2:1 Step-Down Mode
1:1 Step-Down Mode
1:2 Step-Up Mode (VIN = 3.3V)
3
3.5
14
Ω
Ω
Ω
fOSC
Oscillator Frequency
88
l
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime. This IC has overtemperature protection that is
intended to protect the device during momentary overload conditions.
Junction temperatures will exceed 150°C when overtemperature is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 2: The LTC3245E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3245I is guaranteed over the
–40°C to 125°C operating junction temperature range. The LTC3245H is
guaranteed over the –40°C to 150°C operating junction temperature range
and the LTC3245MP is tested and guaranteed over the full –55°C to 150°C
operating junction temperature range. High junction temperatures degrade
operating lifetimes; operating lifetime is derated for junction temperatures
91
%
0.1
0.4
V
–1
0
1
µA
0.4
0.9
l
V
1.2
2
V
0
1
µA
1
3
450
500
µA
kHz
greater than 150°C. Note that the maximum ambient temperature consistent
with these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal resistance and
other environmental factors.
Note 3: The junction temperature (TJ, in °C) is calculated from the ambient
temperature (TA, in °C) and power dissipation (PD, in Watts) according to
the formula:
TJ = TA + (PD • θJA) where θJA (in °C/W) is the package thermal
impedance.
Note 4: VOUT programming range is from 2.5V to 5V. See the
Programming the Output Voltage section for more detail.
Note 5: The maximum operating junction temperature of 150°C must be
followed. Certain combinations of input voltage and output current will
cause the junction temperature to exceed 150°C and must be avoided. See
Thermal Management section for information on calculating maximum
operating conditions.
3245fa
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3
LTC3245
Typical Performance Characteristics
Input Operating Current
vs Input Voltage
Input Shutdown Current
vs Input Voltage
500
475
40
16
35
14
30
12
ISD (µA)
VOUT = 5V
20
VOUT = 3.3V
15
10
6
4
5
2
0
0
5
10
15
20 25
VIN (V)
125°C
8
10
30
35
0
40
450
150°C
25°C
–55°C
0
5
10
15
20 25
VIN (V)
30
5.15
5.15
5.10
5.10
4.80
IOUT = 150mA
IOUT = 0mA
5.00
IOUT = 150mA
IOUT = 250mA
4.90
IOUT = 250mA
4.80
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3.50
3.45
3.45
3.40
3.40
VOUT (V)
VOUT (V)
3.35
3.20
IOUT = 150mA
3.10
3.30
3245 G07
LOW NOISE
60
50
40
30
0
0.1
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
1
10
IOUT (mA)
100
1000
3245 G06
3.3V Fixed Output Efficiency
vs Output Current
100
90
3.10
VIN = 9V
80
IOUT = 0mA
IOUT = 150mA
IOUT = 250mA
70
Burst Mode OPERATION
60
LOW NOISE
50
40
30
20
3.15
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
Burst Mode OPERATION
10
3.25
3.20
3.15
VIN = 12V
70
3.3V Fixed Output Voltage
vs Input Voltage (Low Noise
Operation)
3.50
IOUT = 250mA
150
3245 G05
3.3V Fixed Output Voltage
vs Input Voltage (Burst Mode
Operation)
3.25
120
20
4.85
3.30
0
30
60
90
TEMPERATURE (°C)
5V Fixed Efficiency
vs Output Current
80
4.95
IOUT = 0mA
–30
3245 G03
90
3245 G04
3.35
300
–60
40
100
5.05
VOUT (V)
VOUT (V)
IOUT = 0mA
5.00
4.85
35
3245 G02
5.20
4.90
375
5V Fixed Output Voltage
vs Input Voltage (Low Noise
Operation)
5.20
4.95
400
325
3245 G01
5V Fixed Output Voltage
vs Input Voltage (Burst Mode
Operation)
5.05
425
350
EFFICIENCY (%)
ICC (µA)
20
18
fOSC (kHz)
BURST = 0V
Oscillator Frequency
vs Temperature
EFFICIENCY (%)
50
45
25
TA = 25°C, unless otherwise noted.
10
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
0
0.1
1
10
IOUT (mA)
100
1000
3245 G09
3245 G08
3245fa
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LTC3245
Typical Performance Characteristics
TA = 25°C, unless otherwise noted.
3.3V Fixed Output Voltage
vs Falling Input Voltage
(Burst Mode Operation)
5V Fixed Output Voltage
vs Falling Input Voltage
(Burst Mode Operation)
ADJ Regulation Voltage
vs Temperature
5.100
3.400
1.220
5.075
3.375
1.215
IOUT = 1mA
5.050
3.350
5.025
1.205
4.975
IOUT = 250mA
4.950
3.300
3.275
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3.200
800
35
25
10
Burst Mode OPERATION
25
20
15
0
30
60
90
TEMPERATURE (°C)
120
60
90
0
30
TEMPERATURE (°C)
–30
120
3245 G13
0
150
Operating Mode Transition
Voltage vs Input Voltage
12
IOUT = 150mA
11
BUCK
10
9
9
4
RISING
3
FALLING
RISING
7
6
RISING
5
4
BOOST
3
1
0
2.5
3245 G16
3
FALLING
3
2
3.5
4
VOUT (V)
4.5
5
3245 G17
BUCK
LDO
RISING
4
BOOST
FALLING
1
0
2.5
5
7 8 9 10 11 12 13 14
VIN (V)
FALLING
5
2
4.5
6
RISING
6
1
0
2.5
3.5
4
VOUT (V)
5
7
2
3
4
8
LDO
FALLING
VIN (V)
VIN (V)
5
8
LDO
FALLING
6
3
12
IOUT = 250mA
11
BUCK
10
RISING
2
Operating Mode Transition
Voltage vs Input Voltage
9
8
3.3V Burst Mode
OPERATION
3245 G15
10
7
3.3V LOW NOISE
300
3245 G14
Operating Mode Transition
Voltage vs Input Voltage
IOUT = 1mA
400
100
0
–60
150
500
200
Burst Mode OPERATION
5
–30
150
600
LOW NOISE
10
5
0
–60
120
5V LOW NOISE
5V Burst Mode
700 OPERATION
VIN = 2.7V
IOUT (mA)
ROUT (Ω)
15
VIN = 3.3V
30
VIN = 3.3V
LOW NOISE
0
30
60
90
TEMPERATURE (°C)
Output Current vs Input Voltage
(VOUT 5% Below Regulation)
40
VIN = 2.7V
20
–30
3245 G12
3.3V Output Impedance
vs Temperature (Boost Mode)
30
ROUT (Ω)
1.180
–60
3245 G11
5V Output Impedance
vs Temperature (Boost Mode)
VIN (V)
1.185
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3245 G10
12
11
1.190
–55°C
25°C
125°C
3.225
1.200
1.195
IOUT = 250mA
3.250
–55°C
25°C
125°C
4.925
ADJ (V)
VOUT (V)
VOUT (V)
3.325
5.000
4.900
1.210
IOUT = 1mA
3
3.5
4
VOUT (V)
BOOST
4.5
5
3245 G18
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5
LTC3245
Typical Performance Characteristics
3.3V Output Transient Response
5V Output Transient Response
Burst Mode
OPERATION
AC 50mV/DIV
Burst Mode
OPERATION
AC 50mV/DIV
LOW NOISE
AC 50mV/DIV
LOW NOISE
AC 50mV/DIV
200mA
IOUT 5mA
3245 G19
VIN = 12V
VOUT = 5V
TA = 25°C, unless otherwise noted.
150mA
IOUT 5mA
3245 G20
VIN = 12V
VOUT = 3.3V
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LTC3245
Pin Functions
VIN (Pins 1, 2, 3): Power Input Pins. Input voltage for both
charge pump and IC control circuitry. The VIN pin operates from 2.7V to 38V. All VIN pins should be connected
together at pins.
BURST (Pin 4): Burst Mode Logic Input. A logic high on
the BURST pin operates the charge pump in low noise
constant frequency. A logic low will operates the charge
pump in Burst Mode operation for higher efficiency at
low output currents. The BURST pin has a 1μA (typical)
pull-down current to ground and can tolerate 38V inputs
allowing it to be pin-strapped to VIN.
SEL1 (Pin 5): Logic Input Pin. See Table 1 for SEL1/SEL2
operating logic. The SEL1 pin has a 1μA (typical) pull-down
current to ground and can tolerate 38V inputs allowing it
to be pin-strapped to VIN.
SEL2 (Pin 6): Logic Input Pin. See Table 1 for SEL1/SEL2
operating logic. The SEL2 pin has a 1μA (typical) pull-down
current to ground and can tolerate 38V inputs allowing it
to be pin-strapped to VIN.
Table 1: VOUT Operating Modes
SEL2
SEL1
MODE
LOW
LOW
Shutdown
LOW
HIGH
Adjustable VOUT
HIGH
LOW
Fixed 5V
HIGH
HIGH
Fixed 3.3V
OUTS/ADJ (Pin 7): VOUT Sense / Adjust Input Pin. This pin
acts as VOUT sense (OUTS) for 5V or 3.3V fixed outputs
and adjust (ADJ) for adjustable output through external
feedback. The ADJ pin servos to 1.2V when the device is
enabled in adjustable mode. (OUTS / ADJ are selected by
SEL1 and SEL2 pins; See Table 1)
PGOOD (Pin 8): Power Good Open Drain Logic Output.
The PGOOD pin goes high impedance when VOUT is about
6% of its final operating voltage. PGOOD is intended to
be pulled up to VOUT or other low voltage supply with an
external resistor.
C+ (Pin 9): Flying Capacitor Positive Connection.
VOUT (Pin 10): Charge Pump Output Voltage. If VIN drops
below its UVLO threshold, the connection from VIN becomes high impedance with no reverse leakage from
VOUT to VIN. VOUT regulation only takes place above the
UVLO threshold. VOUT can be programmed to regulate
from 2.5V to 5V.
C – (Pin 11): Flying Capacitor Negative Connection.
GND (Pin 12, Exposed Pad Pin 13): Ground. The exposed
package pad is ground and must be soldered to the PC
board ground plane for proper functionality and for rated
thermal performance.
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7
LTC3245
Simplified Block Diagram
C+
C–
CHARGE PUMP
VIN
VOUT
EN
BURST
BURST
DETECTED
OVERTEMPERATURE
OUTS/ADJ
ADJ
3.3V
MUX
–
+
PGOOD
1.2V
–
1.14V
5V
SD
+
SEL1
SEL2
GND
3245 BD
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LTC3245
Applications Information
General Operation
The LTC3245 uses switched capacitor based DC/DC
conversion to provide the efficiency advantages associated with inductor based circuits as well as the cost and
simplicity advantages of a linear regulator. The LTC3245’s
unique constant frequency architecture provides a low
noise regulated output as well as lower input noise than
conventional switch capacitor charge pump regulators. The
LTC3245 uses an internal switch network and fractional
conversion ratios to achieve high efficiency and regulation over widely varying VIN and output load conditions.
Internal control circuitry selects the appropriate conversion ratio based on VIN and load conditions. The device
has three possible conversion modes: 2:1 step-down
mode, 1:1 step-down mode and 1:2 step-up mode. Only
one external flying capacitor is needed to operate in all
three modes. 2:1 mode is chosen when VIN is greater than
two times the desired VOUT. 1:1 mode is chosen when
VIN falls between two times VOUT and VOUT. 1:2 mode is
chosen when VIN falls below the desired VOUT. An internal
load current sense circuit controls the switch point of the
conversion ratio as needed to maintain output regulation
over all load conditions.
Regulation is achieved by sensing the output voltage and
regulating the amount of charge transferred per cycle. This
method of regulation provides much lower input and output
ripple than that of conventional switched capacitor charge
pumps. The constant frequency charge transfer also makes
additional output or input filtering much less demanding
than conventional switched capacitor charge pumps.
The LTC3245 has a Burst Mode operation pin that allows
the user to trade output ripple for better efficiency/lower
quiescent current. The device has two SEL pins that select
the output regulation (fixed 5V, fixed 3.3V or adjustable)
as well as shutdown. The device includes soft-start function to limit in-rush current at startup. The device is also
short-circuit and overtemperature protected.
VOUT Regulation and Mode Selection
As shown in the Simplified Block Diagram, the device uses
a control loop to adjust the strength of the charge pump to
match the current required at the output. The error signal
of this loop is stored directly on the output charge storage
capacitor. As the load on VOUT increases, VOUT will drop
slightly increasing the amount of charge transferred until
the output current matches the output load. This method
of regulation applies regardless of the conversion ratio.
The optimal conversion ratio is chosen based on VIN,
VOUT and output load conditions. Two internal comparators are used to select the default conversion ratio. Each
comparator has an adjustable offset built in that increases
(decreases) in proportion to the increasing (decreasing)
output load current. In this manner, the conversion ratio
switch point is optimized to provide peak efficiency over
all supply and load conditions while maintaining regulation.
Each comparator also has built-in hysteresis to reduce the
tendency of oscillating between modes when a transition
point is reached.
Low Noise vs Burst Mode Operation
Burst Mode operation is selected by driving the BURST
pin low. In Burst Mode operation the LTC3245 delivers a
minimum amount of charge each cycle forcing VOUT above
regulation at light output loads. When the LTC3245 detects
that VOUT is above regulation the device stops charge
transfer and goes into a low current sleep state. During
this sleep state, the output load is supplied by the output
capacitor. The device will remain in the sleep state until the
output drops enough to require another burst of charge.
Burst Mode operation allows the LTC3245 to achieve high
efficiency even at light loads. If the output load exceeds
the minimum charge transferred per cycle, then the device
will operate continuously to maintain regulation.
Unlike traditional charge pumps who’s burst current is
dependant on many factors (i.e., supply, switch strength,
capacitor selection, etc.), the LTC3245 burst current is
regulated which helps to keep burst output ripple voltage
relatively constant and is typically 50mV for COUT = 10μF.
Driving the BURST pin high puts the LTC3245 in low noise
operation. In low noise operation the minimum amount
of charge delivered each cycle and sleep hysteresis
are reduced compared to Burst Mode operation. This
results in lower burst output ripple (typically 20mV for
COUT = 10µF) and will transition to constant frequency
operation at lighter loads.
3245fa
For more information www.linear.com/LTC3245
9
LTC3245
Applications Information
Short-Circuit/Thermal Protection
The LTC3245 has built-in short-circuit current limiting as
well as overtemperature protection. During short-circuit
conditions the device will automatically limit the output
current.
The LTC3245 has thermal protection that will shut
down the device if the junction temperature exceeds the
overtemperature threshold (typically 175°C). Thermal
shutdown is included to protect the IC in cases of excessively high ambient temperatures, or in cases of excessive
power dissipation inside the IC. The charge transfer will
reactivate once the junction temperature drops back to
approximately 165°C.
When the thermal protection is active, the junction temperature is beyond the specified operating range. Thermal
protection is intended for momentary overload conditions
outside normal operation. Continuous operation above the
specified maximum operating junction temperature may
impair device reliability.
Driving both SEL1 and SEL2 low shuts down the device
causing VOUT to go high impedance.
LTC3245
VOUT
VOUT
FIXED 3.3V OR
FIXED 5V
OUTS
COUT
GND
3245 F01
Figure 1: Fixed Output Operation
Adjustable output programming is accomplished by connecting ADJ (OUTS/ADJ pin) to a resistor divider between
VOUT and GND as shown in Figure 2. Adjustable operation
is enabled by driving SEL1 high and SEL2 low. Driving
both SEL1 and SEL2 low shuts down the device causing
VOUT to go high impedance.
LTC3245
VOUT
VOUT
RA
Soft-Start Operation
ADJ
To prevent excessive current flow at VIN during start-up,
the LTC3245 has built-in soft-start circuitry. Soft-start is
achieved by increasing the amount of current available to
the output charge storage capacitor linearly over a period
of approximately 500μs. Soft-start is enabled whenever
the device is brought out of shutdown, and is disabled
shortly after regulation is achieved.
Programming the Output Voltage (OUTS/ADJ Pin)
The LTC3245 output voltage programming is very flexible
offering a fixed 3.3V output, fixed 5V output as well as
adjustable output that is programmed through an external
resistor divider. The desired output regulation method is
selected through the SET pins.
For a fixed output simply short OUTS (OUTS/ADJ pin) to
VOUT as shown in Figure 1. Fixed 3.3V operation is enabled
by driving both SEL1 and SEL2 pins high, while fixed 5V
operating is selected by driving SEL2 high with SEL1 low.
RB
(
R
1.2V 1+ A
RB
)
COUT
GND
3245 F02
Figure 2: Adjustable Output Operation
Using adjustable operation the output (VOUT ) can be
programmed to regulate from 2.5V to 5V. The limited
programming range provides the required VOUT operating
voltage without overstressing the VOUT pin.
The desired adjustable output voltage is programmed by
solving the following equation for R A and RB:
R A VOUT
=
–1
R
1.2V
B
Select a value for RB in the range of 1k to 1M and solve
for RA. Note that the resistor divider current adds to the
total no load operating current. Thus a larger value for RB
will result in lower operating current.
3245fa
10
For more information www.linear.com/LTC3245
LTC3245
Applications Information
2:1 Step-Down Charge Pump Operation
1:2 Step-Up Charge Pump Operation
When the input supply is greater than about two times
the output voltage, the LTC3245 will operate in 2:1 stepdown mode. Charge transfer happens in two phases. On
the first phase the flying capacitor (CFLY ) is connected
between VIN and VOUT. On this phase CFLY is charged up
and current is delivered to VOUT. On the second phase the
flying capacitor (CFLY ) is connected between VOUT and
GND. The charge stored on CFLY during the first phase
is transferred to VOUT on the second phase. When in 2:1
step-down mode the input current will be approximately
half of the total output current. The efficiency (η) and chip
power dissipation (PD) in 2:1 are approximately:
When the input supply is less than the output voltage the
LTC3245 will operate in 1:2 step-up mode. Charge transfer happens in two phases. On the first phase the flying
capacitor (CFLY ) is connected between VIN and GND. On
this phase CFLY is charged up. On the second phase the
flying capacitor (CFLY ) is connected between VIN and VOUT
and the charge stored on CFLY during the first phase is
transferred to VOUT. When in 1:2 step-up mode the input
current will be approximately twice the total output current. Thus efficiency (η) and chip power dissipation (PD)
in 1:2 are approximately:
η≅
POUT VOUT • I OUT 2VOUT
=
=
PIN V • 1 I
VIN
IN
2 OUT
V
PD = IN – VOUT I OUT
2
η≅
1:1 Step-Down Charge Pump Operation
When the input supply is less than about two times the
output voltage but more than the programmed output
voltage, the LTC3245 will operate in 1:1 step-down mode.
This method of regulation is very similar to a linear regulator. Charge is delivered directly from VIN to VOUT through
most of the oscillator period. The charge transfer is briefly
interrupted at the end of the period. The interruption in
charge transfer improves stability and transient response.
When in 1:1 step-down mode the input current will be
approximately equal to the total output current. Thus
efficiency (η) and chip power dissipation (PD) in 1:1 are
approximately:
η≅
POUT VOUT • I OUT VOUT
=
=
PIN
VIN • I OUT VIN
PD = ( VIN– VOUT ) I OUT
POUT VOUT • I OUT VOUT
=
=
PIN VIN • 2 I OUT 2VIN
PD = ( 2VIN– VOUT ) I OUT
Due to the limited drive in 1:2 step-up mode the device
always operates in Burst Mode operation when operating
at this conversion ratio. This is done to delay the onset of
dropout at the expense of more output ripple.
PGOOD Output Operation
The LTC3245 includes an open-drain power good (PGOOD)
output pin. If the chip is in shutdown or under UVLO conditions (VIN < 2.2V typical), PGOOD is low impedance to
ground. PGOOD becomes high impedance when VOUT rises
to 95% (typical) of its regulation voltage. PGOOD stays
high impedance until VOUT is shut down or drops below
the PGOOD threshold (91% typical) due to an overload
condition. A pull-up resistor can be inserted between
PGOOD and a low voltage positive logic supply (such as
VOUT ) to signal a valid power good condition. The use of
a large pull-up resistor on PGOOD and a capacitor placed
between PGOOD and GND can be used to delay the PGOOD
signal if desired.
VOUT Ripple and Capacitor Selection
The type and value of capacitors used with the LTC3245
determine several important parameters such as regulator control loop stability, output ripple and charge pump
3245fa
For more information www.linear.com/LTC3245
11
LTC3245
Applications Information
strength. The value of COUT directly controls the amount
of output ripple for a given load current when operating
in constant frequency mode. Increasing the size of COUT
will reduce the output ripple.
To reduce output noise and ripple, it is suggested that a
low ESR (equivalent series resistance < 0.1Ω) ceramic
capacitor (10μF or greater) be used for COUT. Tantalum
and aluminum capacitors can be used in parallel with a
ceramic capacitor to increase the total capacitance but
are not recommended to be used alone because of their
high ESR.
Both the style and value of COUT can significantly affect the
stability of the LTC3245. As shown in the Block Diagram,
the device uses a control loop to adjust the strength of the
charge pump to match the current required at the output.
The error signal of this loop is stored directly on the output
charge storage capacitor. The charge storage capacitor also
serves to form the dominant pole for the control loop. To
prevent ringing or instability it is important for the output
capacitor to maintain at least 4μF of capacitance over all
conditions (see Ceramic Capacitor Selection Guidelines).
Likewise excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3245. The closed
loop output resistance of the device is designed to be 0.3Ω
for a 5V output and 0.2Ω for a 3.3V output. For a 250mA
load current change, the output voltage will change by
about 1.5%V. If the output capacitor has more ESR than
the closed loop impedance, the closed loop frequency
response will cease to roll off in a simple 1-pole fashion
and poor load transient response or instability could result.
Ceramic capacitors typically have exceptional ESR performance, and combined with a tight board layout, should
yield excellent stability and load transient performance.
VIN Capacitor Selection
The constant frequency architecture used by the LTC3245
makes input noise filtering much less demanding than with
conventional regulated charge pumps. Depending on the
mode of operation the input current of the LTC3245 can
vary from IOUT to 0mA on a cycle-by-cycle basis. Low ESR
will reduce the voltage steps caused by changing input
current, while the absolute capacitor value will determine
the level of ripple. The total amount and type of capacitance
necessary for input bypassing is very dependant on the
applied source impedance as well as existing bypassing
already on the VIN node. For optimal input noise and ripple
reduction, it is recommended that a low ESR ceramic
capacitor be used for CIN bypassing. An electrolytic or
tantalum capacitor may be used in parallel with the ceramic capacitor on CIN to increase the total capacitance,
but due to the higher ESR it is not recommended that an
electrolytic or tantalum capacitor be used alone for input
bypassing. The LTC3245 will operate with capacitors less
than 1μF but depending on the source impedance input
noise can feed through to the output causing degraded
performance. For best performance 1μF or greater total
capacitance is suggested for CIN.
Flying Capacitor Selection
Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitors since
the voltage can reverse upon start-up of the LTC3245.
Ceramic capacitors should always be used for the flying
capacitors. The flying capacitors control the strength of
the charge pump. In order to achieve the rated output
current, it is necessary for the flying capacitor to have
at least 0.4μF of capacitance over operating temperature
with a bias voltage equal to the programmed VOUT (see
Ceramic Capacitor Selection Guidelines). If only 100mA
or less of output current is required for the application,
the flying capacitor minimum can be reduced to 0.15μF.
The voltage rating of the ceramic capacitor should be
VOUT + 1V or greater.
Ceramic Capacitor Selection Guidelines
Capacitors of different materials lose their capacitance
with higher temperature and voltage at different rates.
For example, a ceramic capacitor made of X5R or X7R
material will retain most of its capacitance from –40°C
to 85°C, whereas a Z5U or Y5V style capacitor will lose
considerable capacitance over that range (60% to 80%
loss typical). Z5U and Y5V capacitors may also have a
very strong voltage coefficient, causing them to lose an
additional 60% or more of their capacitance when the rated
voltage is applied. Therefore, when comparing different
capacitors, it is often more appropriate to compare the
amount of achievable capacitance for a given case size
3245fa
12
For more information www.linear.com/LTC3245
LTC3245
Applications Information
rather than discussing the specified capacitance value. For
example, over rated voltage and temperature conditions,
a 4.7μF, 10V, Y5V ceramic capacitor in an 0805 case may
not provide any more capacitance than a 1μF, 10V, X5R
or X7R available in the same 0805 case. In fact, over bias
and temperature range, the 1μF, 10V, X5R or X7R will
provide more capacitance than the 4.7μF, 10V, Y5V. The
capacitor manufacturer’s data sheet should be consulted
to determine what value of capacitor is needed to ensure
minimum capacitance values are met over operating
temperature and bias voltage. Below is a list of ceramic
capacitor manufacturers and how to contact them:
MANUFACTURER
WEBSITE
AVX
www.avxcorp.com
Kemet
www.kemet.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
TDK
www.tdk.com
Because of the wide input operating range it is possible to
exceed the specified operating junction temperature and
even reach thermal shutdown. Figure 3 shows the available output current vs temperature to ensure the 150°C
operating junction temperature is not exceed for input
voltages less than 20V.
Figure 3 assumes worst-case operating conditions. Under
some operating conditions the part can supply more current
than shown without exceeding the 150°C operating junction temperature. When operating outside the constraints
of Figure 3 it is the responsibility of the user to calculate
worst-case operating conditions (temperature and power)
to make sure the LTC3245’s specified operating junction
temperature is not exceeded for extended periods of time.
The 2:1 Step-Down, 1:1 Step-Down, and 1:2 Step-Up
Charge Pump Operation sections provide equations for
calculating power dissipation (PD) in each mode.
300
Layout Considerations
When using the LTC3245 with an external resistor divider
it is important to minimize any stray capacitance to the
ADJ (OUTS/ADJ pin) node. Stray capacitance from ADJ
to C+ or C– can degrade performance significantly and
should be minimized and/or shielded if necessary.
250
200
IOUT (mA)
Due to the high switching frequency and transient currents produced by the LTC3245, careful board layout is
necessary for optimal performance. A true ground plane
and short connections to all capacitors will optimize
performance, reduce noise and ensure proper regulation
over all conditions.
VIN < 20V
150
100
50
0
70
80
90
100 110 120 130
TEMPERATURE (°C)
140
150
3245 F03
Figure 3. Available Output Current vs Temperature
Thermal Management
The on chip power dissipation in the LTC3245 will cause the
junction to ambient temperature to rise at rate of 40°C/W
or more. To reduce the maximum junction temperature, a
good thermal connection to the PC board is recommended.
Connecting the die paddle (Pin 13) with multiple vias to a
large ground plane under the device can reduce the thermal
resistance of the package and PC board considerably. Poor
board layout and failure to connect the die paddle (Pin 13)
to a large ground plane can result in thermal junction to
ambient impedance well in excess of 40°C/W.
For example, if it is determined that the maximum power
dissipation (PD) is 1.2W under normal operation, then the
junction to ambient temperature rise will be:
Junction to ambient = 1.2W • 40°C/W = 48°C
Thus, the ambient temperature under this condition cannot
exceed 102°C if the junction temperature is to remain below
150°C and if the ambient temperature exceeds about 127°C
the device will cycle in and out of the thermal shutdown.
3245fa
For more information www.linear.com/LTC3245
13
LTC3245
Typical Applications
Regulated 5V Low Noise Output
1µF
C+
C–
LTC3245
VIN
+
12V
LEAD ACID
BATTERY
1µF
VOUT
BURST
OUTS/ADJ
SEL2
PGOOD
SEL1
GND
100k
VOUT = 5V
IVOUT UP TO 250mA
10µF
3245 TA02
High Efficiency 3.3V Microcontroller Supply from 9V Alkaline
(with Power-On Reset Delay)
1µF
C+
C–
LTC3245
VIN
+
9V
ALKALINE
BATTERY
1µF
VOUT
SEL1
OUTS/ADJ
SEL2
PGOOD
VOUT = 3.3V
510k
MICROCONTROLLER
VDD
10µF
POR
1µF
BURST
GND
GND
3245 TA03
Wide Input Range Low Noise 3.6V Supply
1µF
C+
C–
LTC3245
VIN
VIN = 2.7V TO 38V
1µF
VOUT
BURST
VOUT = 3.6V
499k
SEL1
OUTS/ADJ
SEL2
PGOOD
10µF
249k
GND
3245 TA04
3245fa
14
For more information www.linear.com/LTC3245
LTC3245
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MSE Package
12-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1666 Rev G)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
5.10
(.201)
MIN
2.845 ±0.102
(.112 ±.004)
0.889 ±0.127
(.035 ±.005)
6
1
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102 3.20 – 3.45
(.065 ±.004) (.126 – .136)
12
0.65
0.42 ±0.038
(.0256)
(.0165 ±.0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.35
REF
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
7
NO MEASUREMENT PURPOSE
0.406 ±0.076
(.016 ±.003)
REF
12 11 10 9 8 7
DETAIL “A”
0° – 6° TYP
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
1 2 3 4 5 6
0.650
(.0256)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
0.86
(.034)
REF
0.1016 ±0.0508
(.004 ±.002)
MSOP (MSE12) 0213 REV G
3245fa
For more information www.linear.com/LTC3245
15
LTC3245
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DE/UE Package
12-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1695 Rev D)
0.70 ±0.05
3.60 ±0.05
2.20 ±0.05
3.30 ±0.05
1.70 ± 0.05
PACKAGE OUTLINE
0.25 ± 0.05
0.50 BSC
2.50 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
7
R = 0.115
TYP
0.40 ± 0.10
12
R = 0.05
TYP
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ± 0.10
0.75 ±0.05
6
0.25 ± 0.05
1
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
(UE12/DE12) DFN 0806 REV D
0.50 BSC
2.50 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE A VARIATION OF VERSION
(WGED) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3245fa
16
For more information www.linear.com/LTC3245
LTC3245
Revision History
REV
DATE
DESCRIPTION
A
7/13
Added MP-grade in MSOP package to Order Information table
PAGE NUMBER
2
Modified Note 2 to add MP-grade
3
3245fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of its information
circuits as described
herein will not infringe on existing patent rights.
For more
www.linear.com/LTC3245
17
LTC3245
Typical Application
Wide VIN 5V Supply with Battery Backup
1µF
C+
12V TO 24V
C–
LTC3245
VIN
+
+
+
1µF
4 × AA
SEL2
BURST
VOUT
OUTS/ADJ
PGOOD
VOUT = 5V
IVOUT UP TO 250mA
10µF
SEL1
+
GND
3245 TA05
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LTC1751-3.3/
LTC1751-5
100mA, 800kHz Regulated Doubler
VIN: 2V to 5V, VOUT(MAX) = 3.3V/5V, IQ = 20μA, ISD < 2μA, MS8 Package
LTC1983-3/
LTC1983-5
100mA, 900kHz Regulated Inverter
VIN: 3.3V to 5.5V, VOUT(MAX) = –3V/–5V, IQ = 25μA, ISD < 2μA, ThinSOT™ Package
LTC3200-5
100mA, 2MHz Low Noise, Doubler/
White LED Driver
VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 3.5mA, ISD < 1μA, ThinSOT Package
LTC3202
125mA, 1.5MHz Low Noise, Fractional
White LED Driver
VIN: 2.7V to 4.5V, VOUT(MAX) = 5.5V, IQ = 2.5mA, ISD < 1μA, DFN, MS Packages
LTC3204-3.3/
LTC3204B-3.3/
LTC3204-5/
LTC3204B-5
Low Noise, Regulated Charge Pumps
in (2mm × 2mm) DFN Package
VIN: 1.8V to 4.5V (LTC3204B-3.3), 2.7V to 5.5V (LTC3204B-5), IQ = 48μA, B Version without
Burst Mode Operation, 6-Lead (2mm × 2mm) DFN Package
LTC3440
600mA (IOUT) 2MHz Synchronous
Buck-Boost DC/DC Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25μA, ISD ≤ 1μA, 10-Lead MS
Package
LTC3441
High Current Micropower 1MHz
Synchronous Buck-Boost DC/DC
Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25μA, ISD ≤ 1μA, DFN Package
LTC3443
High Current Micropower 600kHz
Synchronous Buck-Boost DC/DC
Converter
96% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN) = 2.4V, IQ = 28μA, ISD < 1μA, DFN Package
LTC3240-3.3/
LTC3240-2.5
3.3V/2.5V Step-Up/Step-Down Charge
Pump DC/DC Converter
VIN: 1.8V to 5.5V, VOUT(MAX) = 3.3V / 2.5V, IQ = 65μA, ISD < 1μA, (2mm × 2mm) DFN Package
LTC3260
Low Noise Dual Supply Inverting
Charge Pump
VIN Range: 4.5V to 32V, IQ = 100µA, 100mA Charge Pump, 50mA Positive LDO, 50mA
Negative LDO
LTC3261
High Voltage Low IQ Inverting Charge
Pump
VIN Range: 4.5V to 32V, IQ = 60µA, 100mA Charge Pump
3245fa
18 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC3245
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC3245
LT 0713 REV A • PRINTED IN USA
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