LTC1502-3.3
Single Cell to 3.3V
Regulated Charge Pump
DC/DC Converter
FEATURES
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DESCRIPTIO
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.
APPLICATIO S
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Pagers
Battery Backup Supplies
Portable Electronic Equipment
Handheld Medical Instruments
Glucose Meters
TYPICAL APPLICATIO
1
10µF
2
8
Single Cell to 3.3V DC/DC Converter
3.5
C2
V
OUT
7
C1
+
C3
+
1µF
LTC1502-3.3
6
3
C1
–
/SHDN C3
–
4
5
GND
V
IN
10µF
1µF
V
IN
SINGLE CELL
NiCd or
ALKALINE
1502-3.3 TA01
V
OUT
= 3.3V
I
OUT
= 10mA
3.4
OUTPUT VOLTAGE (V)
3.3
I
OUT
= 10mA
I
OUT
= 15mA
10µF
3.2
3.1
PCB LAYOUT FITS IN < 0.125IN
2
3.0
0.8
U
Output Voltage vs Input Voltage
T
A
= 25°C
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
1.8
1502-3.3 TA02
U
U
1
LTC1502-3.3
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
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
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
PACKAGE/ORDER INFORMATION
TOP VIEW
C2
C1
+
C1
–
/SHDN
GND
1
2
3
4
8
7
6
5
V
OUT
C3
+
C3
–
V
IN
ORDER PART
NUMBER
LTC1502CMS8-3.3
MS8 PART MARKING
LTEC
C2 1
C1
+
2
C1
–
/SHDN 3
GND 4
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 250°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 0.9V to 1.8V, C1 = C3 = 1µF, C
IN
= C2 = C
OUT
= 10µF unless otherwise specified.
PARAMETER
V
IN
Operating Voltage
Minimum V
IN
Start-Up Voltage
V
OUT
Voltage
V
IN
Operating Current
V
IN
Shutdown Current
Output Ripple
Efficiency
Switching Frequency
C1
–
/SHDN Shutdown Input Threshold
C1
–
/SHDN Shutdown Input Current
V
OUT
Turn-On Time
V
OUT
Short-Circuit Current
T
A
= 0°C to 70°C (Note 2)
T
A
= –40°C to 85°C (Note 2)
I
OUT
≤
3.5mA, 0.9V
≤
V
IN
≤
1.8V
I
OUT
≤
10mA, 1V
≤
V
IN
≤
1.8V
I
OUT
= 0mA
C1
–
/SHDN = 0V
I
OUT
= 10mA, V
IN
= 1.25V
V
IN
= 1V, I
OUT
= 10mA
Oscillator Free-Running
C1
–
/SHDN in Hi-Z Sampling State
C1
–
/SHDN = 0V (Note 3)
V
IN
= 1V, I
OUT
= 0mA
V
IN
= 1.5V, V
OUT
Forced to 0V
q
q
CONDITIONS
q
q
q
q
q
q
q
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.
2
U
U
W
W W
U
W
TOP VIEW
8
7
6
5
V
OUT
C3
+
C3
–
V
IN
ORDER PART
NUMBER
LTC1502CS8-3.3
LTC1502IS8-3.3
S8 PART MARKING
150233
502I33
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
MIN
0.9
TYP
0.75
MAX
1.8
0.9
1.1
3.43
3.43
90
15
UNITS
V
V
V
V
V
µA
µA
mV
P-P
%
kHz
3.17
3.17
3.3
3.3
40
5
50
77
500
0.20
– 0.5
0.55
– 2.5
5
20
0.85
–8
V
µA
ms
mA
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.
LTC1502-3.3
TYPICAL PERFOR A CE CHARACTERISTICS
No Load Input Current
vs Input Voltage
80
I
OUT
= 0mA
T
A
= 85°C
T
A
= 25°C
40
T
A
= 0°C
20
T
A
= – 40°C
OUTPUT VOLTAGE (V)
INPUT CURRENT (µA)
INPUT CURRENT (µA)
60
T
A
= 70°C
0
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
Maximum Start-Up Load Current
vs Input Voltage
16
T
A
= 25°C
100
LOAD CURRENT (mA)
12
EFFICIENCY (%)
V
IN
= 1.25V
60
V
IN
= 1.5V
V
IN
= 1.8V
40
8
4
0
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
Oscillator Frequency
vs Input Voltage
700
OSCILLATOR FREQUENCY (kHz)
BATTERY LIFE (HOURS)
600
T
A
= 85°C
T
A
= 70°C
T
A
= 25°C
T
A
= 0°C
500
400
T
A
= – 40°C
300
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
U W
1502-3.3 G01
Shutdown Input Current
vs Input Voltage
16
C1
–
/SHDN = 0V
3.40
Output Voltage vs Output Current
T
A
= 25°C
12
3.35
V
IN
= 1.5V
3.30
V
IN
= 1V
V
IN
= 1.8V
8
T
A
= 70°C
4
T
A
= 85°C
3.25
T
A
= – 40°C
1.8
T
A
= 25°C
T
A
= 0°C
1.8
3.20
0.01
1
10
0.1
OUTPUT CURRENT (mA)
100
1502-3.3 G03
0
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
1502-3.3 G02
Efficiency vs Output Current
T
A
= 25°C
V
OUT
= 3.3V
V
IN
= 1V
I
OUT
0mA to 10mA
5mA/DIV
Load Transient Response
80
V
OUT
AC COUPLED
50mV/DIV
20
V
IN
= 1.25V
T
A
= 25°C
200µs/DIV
1502-3.3 G06
1.8
0
0.01
1
0.1
10
OUTPUT CURRENT (mA)
100
1502-3.3 G05
1502-3.3 G04
Calculated Battery Life,
Battery = 2400mA • Hr AA Cell
100k
Shutdown Waveforms
(See Figure 1)
10k
V
OUT
2V/DIV
1k
OFF
V
CTRL
100
ON
V
IN
= 1.25V
R
LOAD
= 10k
T
A
= 25°C
0.01
0.1
1
10
AVERAGE LOAD CURRENT (mA)
100
100µs/DIV
1502-3.3 G09
1.8
10
0.001
1502-3.3 G07
1502-3.3 G08
3
LTC1502-3.3
PIN FUNCTIONS
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
.
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.
BLOCK DIAGRAM
SHUTDOWN
C1
–
/SHDN
C1
+
C2
C3
–
C3
+
V
IN
5
C
IN
2.5µA
CP1
400k
V
IN
CP2
8
V
OUT
C
OUT
COMP3
U2
0.55V
HIZ1
CLK1/CLK2
1M
SHDN
TIMING
CONTROL
OSCEN
U3
C2
V
OUT
BIAS
CONTROL
INTERNAL
V
CC
COMP1
4
–
+
+
+
–
W
–
+
U
U
U
C1
C2
C3
3
2
1
6
7
HIZ2
2.1M
COMP2
U4
1.2M
1.2V
REF
4
GND
1502-3.3 BD
LTC1502-3.3
TEST CIRCUIT
1
10µF
2
C2
V
OUT
8
10µF
1µF
I
OUT
7
C3
+
C1
+
1µF
LTC1502-3.3
3
6
C1
–
/SHDN C3
–
4
5
GND
V
IN
100Ω
SWITCH
CLOSED FOR
SHUTDOWN
10µF
100pF
V
IN
1502-3.3 TC
APPLICATIONS INFORMATION
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
U
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U
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