1
LTC1502-3.3
Single Cell to 3.3V
Regulated Charge Pump
DC/DC Converter
■
Input Voltage Range: 0.9V to 1.8V
■
0.9V Guaranteed Start-Up Voltage
■
Regulated Output Voltage: 3.3V ±4%
■
Output Current: 10mA (V
IN
≥ 1V)
■
No Inductors
■
Shutdown Disconnects Load from V
IN
■
Low Operating Current: 40µA
■
Low Shutdown Current: 5µA
■
Short-Circuit and Overtemperature Protected
■
Application Circuit Fits in <0.125in
2
PCB Area
■
Available in 8-Pin MSOP and SO Packages
The LTC
®
1502-3.3 is a quadrupler charge pump DC/DC
converter that produces a regulated 3.3V output from a
single alkaline cell input. It requires only five small external
capacitors—no inductors are required. Low supply cur-
rent (40µA typical, 5µA in shutdown) and minimal external
components make the LTC1502-3.3 ideal for space and
power conscious single-cell applications. The total printed
circuit board area of the circuit shown below is less than
0.125in
2
.
Forcing the C1
–
/SHDN pin low through an external resis-
tive pull-down puts the part into shutdown mode. During
shutdown, the internal oscillator is stopped and the load is
disconnected from V
IN
. An internal pull-up current on the
C1
–
/SHDN pin forces the part back into normal operation
once the pull-down resistance is removed.
The LTC1502-3.3 is short-circuit protected and survives
an indefinite V
OUT
short to ground. The LTC1502-3.3 is
available in 8-pin MSOP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Output Voltage vs Input Voltage
1
2
3
1502-3.3 TA01
4
8
7
1µF6
5
V
IN
GND
1µF
V
IN
SINGLE CELL
NiCd or
ALKALINE
10µF
10µF10µF
V
OUT
= 3.3V
I
OUT
= 10mA
LTC1502-3.3
C2
C1
+
C1
–
/SHDN
V
OUT
C3
+
C3
–
Single Cell to 3.3V DC/DC Converter
■
Pagers
■
Battery Backup Supplies
■
Portable Electronic Equipment
■
Handheld Medical Instruments
■
Glucose Meters
INPUT VOLTAGE (V)
0.8
OUTPUT VOLTAGE (V)
3.3
3.4
3.5
1.6
1502-3.3 TA02
3.2
3.1
3.0 1.0 1.2 1.4 1.8
T
A
= 25°C
I
OUT
= 10mA
I
OUT
= 15mA
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
PCB LAYOUT FITS IN <0.125IN
2
2
LTC1502-3.3
ABSOLUTE MAXIMUM RATINGS
W
WW
U
Operating Temperature Range
Commercial ............................................ 0°C to 70°C
Extended Commercial (Note 4).......... –40°C to 85°C
Industrial ........................................... –40°C to 85°C
Lead Temperature (Soldering, 10 sec)................. 300°C
V
IN
to GND.................................................. –0.3V to 2V
V
OUT
to GND ............................................... –0.3V to 5V
All Other Pins to GND ................................. –0.3V to 5V
V
OUT
Short-Circuit Duration............................ Indefinite
Storage Temperature Range ................ –65°C to 150°C
(Note 1)
PACKAGE/ORDER INFORMATION
W
UU
ORDER PART
NUMBER ORDER PART
NUMBER
LTC1502CS8-3.3
LTC1502IS8-3.3
S8 PART MARKING
Consult factory for Military grade parts.
T
JMAX
= 125°C, θ
JA
= 150°C/ W
LTC1502CMS8-3.3
MS8 PART MARKING
LTEC
T
JMAX
= 125°C, θ
JA
= 250°C/ W
1
2
3
4
C2
C1
+
C1
–
/SHDN
GND
8
7
6
5
V
OUT
C3
+
C3
–
V
IN
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
1
2
3
4
8
7
6
5
TOP VIEW
V
OUT
C3
+
C3
–
V
IN
C2
C1
+
C1
–
/SHDN
GND
S8 PACKAGE
8-LEAD PLASTIC SO
150233
502I33
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Operating Voltage ●0.9 1.8 V
Minimum V
IN
Start-Up Voltage T
A
= 0°C to 70°C (Note 2) ●0.75 0.9 V
T
A
= –40°C to 85°C (Note 2) ●1.1 V
V
OUT
Voltage I
OUT
≤ 3.5mA, 0.9V ≤ V
IN
≤ 1.8V ●3.17 3.3 3.43 V
I
OUT
≤ 10mA, 1V ≤ V
IN
≤ 1.8V ●3.17 3.3 3.43 V
V
IN
Operating Current I
OUT
= 0mA ●40 90 µA
V
IN
Shutdown Current C1
–
/SHDN = 0V ●515 µA
Output Ripple I
OUT
= 10mA, V
IN
= 1.25V 50 mV
P-P
Efficiency V
IN
= 1V, I
OUT
= 10mA 77 %
Switching Frequency Oscillator Free-Running 500 kHz
C1
–
/SHDN Shutdown Input Threshold C1
–
/SHDN in Hi-Z Sampling State ●0.20 0.55 0.85 V
C1
–
/SHDN Shutdown Input Current C1
–
/SHDN = 0V (Note 3) ●–0.5 –2.5 –8 µA
V
OUT
Turn-On Time V
IN
= 1V, I
OUT
= 0mA 5 ms
V
OUT
Short-Circuit Current V
IN
= 1.5V, V
OUT
Forced to 0V 20 mA
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 0.9V to 1.8V, C1 = C3 = 1µF, CIN = C2 = COUT = 10µF unless otherwise specified.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: Start-up testing is done with a 100kΩ equivalent load on V
OUT
.
Note 3: Currents flowing into the device are positive polarity. Currents
flowing out of the device are negative polarity.
Note 4: Commercial grade specifications are guaranteed over the 0°C to
70°C operating temperature range. In addition, commercial grade
specifications are assured over the –40°C to 85°C operating temperature
range by design, characterization and correlation with statistical process
controls. Industrial grade specifications are guaranteed and tested over the
–40°C to 85°C operating temperature range.
3
LTC1502-3.3
TYPICAL PERFOR A CE CHARACTERISTICS
UW
INPUT VOLTAGE (V)
0.8
INPUT CURRENT (µA)
40
60
1.6
1502-3.3 G01
20
01.0 1.2 1.4 1.8
80
T
A
= 25°C
T
A
= 0°CT
A
= –40°C
I
OUT
= 0mA
T
A
= 70°C
T
A
= 85°C
No Load Input Current
vs Input Voltage
OUTPUT CURRENT (mA)
0.01
OUTPUT VOLTAGE (V)
3.30
3.35
T
A
= 25°C
V
IN
= 1V
100
1502-3.3 G03
3.25
3.20 0.1 110
3.40
V
IN
= 1.5V V
IN
= 1.8V
Output Voltage vs Output Current
Shutdown Input Current
vs Input Voltage
INPUT VOLTAGE (V)
0.8
INPUT CURRENT (µA)
8
12
1.6
1502-3.3 G02
4
01.0 1.2 1.4 1.8
16
T
A
= 70°C
T
A
= 85°C
T
A
= 25°C
T
A
= – 40°CT
A
= 0°C
C1
–
/SHDN = 0V
Maximum Start-Up Load Current
vs Input Voltage
INPUT VOLTAGE (V)
0.8
LOAD CURRENT (mA)
8
12
1.6
1502-3.3 G04
4
01.0 1.2 1.4 1.8
16 T
A
= 25°C
Load Transient Response
200µs/DIV
I
OUT
0mA to 10mA
5mA/DIV
V
OUT
AC COUPLED
50mV/DIV
Efficiency vs Output Current
OUTPUT CURRENT (mA)
0.01
EFFICIENCY (%)
40
60
100
1502-3.3 G05
20
00.1 110
100
80
TA = 25°C
VOUT = 3.3V
VIN = 1V
VIN = 1.25V
VIN = 1.5V
VIN = 1.8V
1502-3.3 G06
Oscillator Frequency
vs Input Voltage Shutdown Waveforms
(See Figure 1)
Calculated Battery Life,
Battery = 2400mA • Hr AA Cell
INPUT VOLTAGE (V)
0.8
OSCILLATOR FREQUENCY (kHz)
500
600
1.6
1502-3.3 G07
400
300 1.0 1.2 1.4 1.8
700
T
A
= 70°C
T
A
= – 40°C
T
A
= 25°C
T
A
= 85°C
T
A
= 0°C
AVERAGE LOAD CURRENT (mA)
0.001
10
BATTERY LIFE (HOURS)
1k
100k
0.1 1 100.01 100
1502-3.3 G08
100
10k
100µs/DIV
V
OUT
2V/DIV
OFF
1502-3.3 G09
ON
V
IN
= 1.25V
R
LOAD
= 10k
T
A
= 25°C
V
CTRL
V
IN
= 1.25V
T
A
= 25°C
4
LTC1502-3.3
GND (Pin 4): Ground. Connect to a ground plane for best
performance.
V
IN
(Pin 5): Input Supply Voltage. Bypass V
IN
with a ≥10µF
low ESR capacitor to ground.
C3
–
(Pin 6): Charge Pump 2 (CP2) Flying Capacitor
Negative Terminal.
C3
+
(Pin 7): Charge Pump 2 Flying Capacitor Positive
Terminal.
V
OUT
(Pin 8): 3.3V Regulated Output Voltage. V
OUT
is
disconnected from V
IN
during shutdown. Bypass V
OUT
with a ≥10µF low ESR capacitor to ground.
PIN FUNCTIONS
UUU
C2 (Pin 1): Charge Pump 1 (CP1) Output. This pin also
serves as the input supply for charge pump 2 (CP2). To
ensure proper start-up, the C2 pin must not be externally
loaded. Bypass the C2 pin with a ≥10µF low ESR capacitor
to ground.
C1
+
(Pin 2): Charge Pump 1 Flying Capacitor Positive
Terminal.
C1
–
/SHDN (Pin 3): Charge Pump 1 Flying Capacitor Nega-
tive Terminal and Shutdown Input. Pulling this pin to
ground through a ≈100Ω resistor will put the part into
shutdown mode. With a high resistance pull-down FET,
the series resistor may be eliminated. The external pull-
down device must be high impedance for normal opera-
tion (see Applications Information). Peak voltage present
on this pin is approximately equal to V
IN
.
BLOCK DIAGRAM
W
–
+
–
+
–
+
TIMING
CONTROL
BIAS
CONTROL 1.2V
REF
CP2
C3C1
CP1
SHDN OSCEN
INTERNAL
VCC
CLK1/CLK2
U3
U4
U2
C2
VOUT
HIZ2
HIZ1 1M
1.2M
2.1M
COUT
C2
COMP2COMP3
COMP1
400k
0.55V
+
2.5µA
C1–/SHDN
SHUTDOWN
C1+C3–C3+
VIN
32 C2
1 6 7
VOUT
8
VIN
5
GND
1502-3.3 BD
4
CIN
5
LTC1502-3.3
TEST CIRCUIT
APPLICATIONS INFORMATION
WUUU
Regulator Operation
The LTC1502-3.3 uses a quadrupler charge pump DC/DC
converter to produce a boosted output voltage. The
quadrupler charge pump consists of two voltage doubler
charge pumps (CP1 and CP2 on the Block Diagram)
cascaded in series. CP1 doubles the input voltage V
IN
and
the CP1 output voltage is stored on external capacitor C2.
The C2 pin also serves as the input for doubler CP2 whose
output is stored on the output capacitor C
OUT
. Each
doubler is controlled by a two-phase clock which is
generated in the Timing Control circuit. On phase one of
the clock, the flying capacitors C1 and C3 are charged to
their respective input voltages. On phase two each charged
flying capacitor is stacked on top of the input voltage and
discharged through an internal switch onto its respective
output. This sequence of charging and discharging the
CP1 and CP2 flying capacitors continues at the free
running oscillator frequency (500kHz typ) until the output
is in regulation.
Regulation is achieved by comparing the divided down
output voltage to a fixed voltage reference. The charge
pump clocks are disabled when the output voltage is
above the desired regulation point set by COMP1. When
the output has dropped below the lower trip point of
COMP1, the charge pump clocks are turned back on until
V
OUT
is boosted back into regulation.
Enhanced Start-Up
Enhanced start-up capability is provided by the COMP2
circuitry. COMP2 compares the divided down C2 voltage
to the input voltage V
IN
. The COMP2 output disables the
output charge pump CP2 whenever the divided C2 voltage
is lower than V
IN
. The CP2 output is thereby forced into a
high impedance state until the voltage on C2 has been
raised above V
IN
(the C2 pin should not be loaded for
proper start-up). This allows a higher internal gate drive
voltage to be generated (from the C2 pin) before the output
(V
OUT
) is connected to a load. Hysteresis in COMP2 forces
CP2 to be turned ON and OFF while C
OUT
is charging up to
prevent a lockup condition if C2 droops too low during
start-up. By the time the output nears the regulation point,
the C2 voltage is well above the lower trip point of COMP2
and CP2 will remain enabled. This method of disabling the
output charge pump while an internal boosted gate drive
supply is developed allows the part to start up at low
voltages with a larger output current load than would
otherwise be possible.
Shutdown
Shutdown is implemented using an external pull-down
device on the C1
–
/SHDN pin. The recommended external
pull-down device is an open-drain FET with resistive cur-
rent limiting (see Figure 1). The pull-down device must sink
up to 300µA and pull down below 0.2V to ensure proper
shutdown operation, however, the actual series resistance
is not critical. The pull-down device must also go into a Hi-
Z state for the LTC1502-3.3 to become active.
The timing control circuitry forces the CP1 switches into
a high impedance state every 16 clock cycles. The Hi-Z
duration is equal to one clock cycle. At the end of the
Hi-Z time interval, the voltage on the C1
–
/SHDN pin is
sampled. If the C1
–
/SHDN pin has been pulled to a logic
low state, the part will go into shutdown mode. When the
pull-down device is disabled, an internal pull-up current
1
2
3
1502-3.3 TC
4
8
7
1µF
100Ω
6
5
V
IN
GND
100pF
SWITCH
CLOSED FOR
SHUTDOWN
1µF
10µF
10µF10µFI
OUT
V
IN
LTC1502-3.3
C2
C1
+
C1
–
/SHDN
V
OUT
C3
+
C3
–
6
LTC1502-3.3
APPLICATIONS INFORMATION
WUUU
1
2
3
1502-3.3 F01
4
V
CTRL
ON OFF
8
7
100Ω
6
5
V
IN
GND
10µF
LTC1502-3.3
C2
C1
+
C1
–
/SHDN
V
OUT
C3
+
C3
–
Figure 1. Pull-Down Circuitry for Shutdown
will force a logic high on the C1
–
/SHDN pin and put the part
back into active mode. If no external pull-down is present
during the Hi-Z interval, the internal pull-up current will
maintain a logic high on the C1
–
/SHDN pin thereby keep-
ing the part in active mode.
The shutdown feature can be used to prevent charge pump
switching during noise sensitive intervals. Since the charge
pump oscillator is disabled during shutdown, output switch-
ing noise can be eliminated while the external pull-down is
active. The LTC1502-3.3 takes between 20µs and 50µs to
switch from shutdown to active mode once the pull-down
device has been turned off (assuming a 100pF external
capacitance to GND on the C1
–
/SHDN pin). A 100k pull-up
resistor from V
IN
to C1
–
/SHDN will speed up this transition
by a factor of five at the expense of 10µA or so of additional
shutdown current. To maintain regulation, a sufficiently
large output capacitor must be used to prevent excessive
V
OUT
droop while the charge pump is in shutdown. Also,
there must be adequate time for the charge pump to
recharge the output capacitor while the part is active. In
other words, the average load current must be low enough
for the LTC1502-3.3 to maintain a 3.3V output while the
part is active.
Capacitor Selection
For best performance, it is recommended that low ESR
capacitors be used for C
IN
, C2 and C
OUT
to reduce noise
and ripple. The C
IN
, C2 and C
OUT
capacitors should be
either ceramic or tantalum and should be 10µF or greater.
If the input source impedance is very low (<0.5Ω), C
IN
may not be needed. Ceramic capacitors are recommended
for the flying capacitors C1 and C3 with values of 0.47µF
to 2.2µF. Smaller values may be used in low output current
applications (e.g., I
OUT
< 1mA).
Output Ripple
Normal LTC1502-3.3 operation produces voltage ripple
on the V
OUT
pin. Output voltage ripple is required for
regulation. Low frequency ripple exists due to the hyster-
esis in the sense comparator and propagation
delays in the charge pump enable/disable circuits. High
frequency ripple is also present mainly from the ESR
(equivalent series resistance) in the output capacitor. Typi-
cal output ripple (V
IN
= 1.25V) under maximum load is
50mV peak-to-peak with a low ESR 10µF output capacitor.
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to C
OUT
per charging cycle.
Large output current load and/or a small output capacitor
(<10µF) results in higher ripple due to higher output
voltage dV/dt. High ESR capacitors (ESR > 0.5Ω) on the
output pin cause high frequency voltage spikes on V
OUT
with every clock cycle.
There are several ways to reduce the output voltage ripple.
A larger C
OUT
capacitor (22µF or greater) will reduce both
the low and high frequency ripple due to the lower C
OUT
charging and discharging dV/dt and the lower ESR typi-
cally found with higher value (larger case size) capacitors.
A low ESR ceramic output capacitor will minimize the high
frequency ripple, but will not reduce the low frequency
ripple unless a high capacitance value is chosen. A reason-
able compromise is to use a 10µF to 22µF tantalum
capacitor in parallel with a 1µF to 3.3µF ceramic capacitor
on V
OUT
to reduce both the low and high frequency ripple.
An RC filter may also be used to reduce high frequency
voltage spikes (see Figure 2).
LTC1502-3.3 10µF
TANTALUM
V
OUT
V
OUT
V
OUT
1µF
CERAMIC
2Ω
8
8
10µF10µF
V
OUT
1502-3.3 F02
+
+ +
LTC1502-3.3
Figure 2. Output Ripple Reduction Techniques
7
LTC1502-3.3
APPLICATIONS INFORMATION
WUUU
Short-Circuit Protection
When the output is shorted to ground, the LTC1502-3.3
will continuously charge the C2 capacitor up to approxi-
mately 1.4 times V
IN
, and then discharge C2 into the
shorted output. Since the discharging of C2 into V
OUT
will
bring the C2 voltage below the COMP2 start-up compara-
tor trip voltage, the output charge pump will be forced
Hi-Z while C2 charges up again. Hence, the internal charge
pump gate drive voltage is limited to (1.4)(V
IN(MAX)
) on the
C2 pin, and no continuous current is supplied to V
OUT
. The
resulting output short-circuit current is limited to under
20mA (typ) thereby allowing the LTC1502-3.3 to endure
an indefinite output short circuit without damage. When
the short is removed, the part will start up, and operate
normally.
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters) unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
MSOP (MS8) 1098
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.021 ± 0.006
(0.53 ± 0.015)
0° – 6° TYP
SEATING
PLANE
0.007
(0.18)
0.040 ± 0.006
(1.02 ± 0.15)
0.012
(0.30)
REF
0.006 ± 0.004
(0.15 ± 0.102)
0.034 ± 0.004
(0.86 ± 0.102)
0.0256
(0.65)
BSC 12
34
0.193 ± 0.006
(4.90 ± 0.15)
8765
0.118 ± 0.004*
(3.00 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
0.016 – 0.050
(0.406 – 1.270)
0.010 – 0.020
(0.254 – 0.508)× 45°
0°– 8° TYP
0.008 – 0.010
(0.203 – 0.254)
SO8 1298
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
1234
0.150 – 0.157**
(3.810 – 3.988)
8765
0.189 – 0.197*
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
8
LTC1502-3.3
15023f LT/TP 0899 4K • PRINTED IN USA
LINEAR T ECHNOLOGY CORPORATION 1999
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
TYPICAL APPLICATIONS
U
PART NUMBER DESCRIPTION COMMENTS
LT1307/LT1307B 750mA Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from 1 Cell, MSOP Package
LT1308A/LT1308B 2A Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 300mA from 1 Cell, SO-8 Package
LTC1517-3.3 Micropower Regulated 3.3V Charge Pump DC/DC Converter I
OUT
= 15mA (V
IN
≥ 2.5V)
LTC1558/LTC1559 Backup Battery Controller with Programmable Output Uses Single NiCd Cell, 100mW Output (Min)
LT1610 Single Cell Micropower 1.7MHz PWM DC/DC Converter 30µA I
Q
, MSOP Package
LT1611 1.4MHz Inverting Switching Regulator 5V to –5V at 150mA, Low Output Noise, SOT-23 package
LT1613 1.4MHz Boost Switching Regulator 5V at 200mA from 3.3V Input, SOT-23 Package
LT1615 Micropower Boost Switching Regulator 30µA I
Q
, V
OUT
Up to 34V, SOT-23 Package
LTC1682 Low Noise Doubler Charge Pump 60µV
RMS
Noise, I
OUT
Up to 50mA, MSOP
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1
2
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4
SHDN
µCONTROLLER
8
7
1µF
100Ω
6
5
V
IN
GND
1µF
SINGLE CELL
NiCd OR
ALKALINE
10µF
10µF10µF
V
OUT
= 3.3V
I
OUT
= 10mA
LTC1502-3.3
C2
C1
+
C1
–
/SHDN
V
OUT
C3
+
C3
–
1
7
6
1502-3.3 TA04
5
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31
2
LT1521-3.3
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8Q1
2N7002
V
IN
GND
1µF
100Ω
10µF
150k
1µF
10µF
3.9V V
TRIP
*
1 CELL
NiCd
1.1M
10µF
V
OUT
= 3.3V
I
OUT
= 300mA
(I
OUT
= 10mA
IN BACKUP MODE)
LOGIC LOW =
BACKUP MODE
LTC1502-3.3
3
4
5
6
21
LTC1540
C2
C1
+
C1
–
/SHDN
V
OUT
C3
+
C3
–
TRICKLE
CHARGE
MAIN
SUPPLY
5V
470k
*REFERRED TO MAIN SUPPLY
+
–
