LTC1502-3.3 - Single Cell to 3.3V Regulated Charge Pump DC/DC Converter

LTC1502-3.3
Single Cell to 3.3V
Regulated Charge Pump
DC/DC Converter
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FEATURES
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DESCRIPTIO
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 current (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
0.125in2.
Input Voltage Range: 0.9V to 1.8V
0.9V Guaranteed Start-Up Voltage
Regulated Output Voltage: 3.3V ±4%
Output Current: 10mA (VIN ≥ 1V)
No Inductors
Shutdown Disconnects Load from VIN
Low Operating Current: 40µA
Low Shutdown Current: 5µA
Short-Circuit and Overtemperature Protected
Application Circuit Fits in < 0.125in2 PCB Area
Available in 8-Pin MSOP and SO Packages
Forcing the C1 –/SHDN pin low through an external resistive pull-down puts the part into shutdown mode. During
shutdown, the internal oscillator is stopped and the load is
disconnected from VIN. An internal pull-up current on the
C1 –/SHDN pin forces the part back into normal operation
once the pull-down resistance is removed.
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APPLICATIO S
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Pagers
Battery Backup Supplies
Portable Electronic Equipment
Handheld Medical Instruments
Glucose Meters
The LTC1502-3.3 is short-circuit protected and survives
an indefinite VOUT 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.
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TYPICAL APPLICATIO
Single Cell to 3.3V DC/DC Converter
Output Voltage vs Input Voltage
3.5
10µF
C2
VOUT
8
2
1µF
7
C1+
C3 +
LTC1502-3.3
6
3
C1–/SHDN C3 –
4
5
GND
VIN
10µF
3.4
1µF
10µF
TA = 25°C
VOUT = 3.3V
IOUT = 10mA
VIN
SINGLE CELL
NiCd or
ALKALINE
1502-3.3 TA01
OUTPUT VOLTAGE (V)
1
3.3
IOUT = 10mA
IOUT = 15mA
3.2
3.1
PCB LAYOUT FITS IN < 0.125IN2
3.0
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
1.8
1502-3.3 TA02
1
LTC1502-3.3
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ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN to GND .................................................. – 0.3V to 2V
VOUT to GND ............................................... – 0.3V to 5V
All Other Pins to GND ................................. – 0.3V to 5V
VOUT 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
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PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
C2
C1+
–
C1 /SHDN
GND
1
2
3
4
8
7
6
5
VOUT
C3 +
C3 –
VIN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 250°C/ W
ORDER PART
NUMBER
TOP VIEW
C2 1
8
VOUT
C1+ 2
7
C3 +
C1–/SHDN 3
6
C3 –
GND 4
5
VIN
LTC1502CMS8-3.3
MS8 PART MARKING
LTC1502CS8-3.3
LTC1502IS8-3.3
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
LTEC
150233
502I33
TJMAX = 125°C, θJA = 150°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
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.
PARAMETER
CONDITIONS
MIN
VIN Operating Voltage
●
TYP
MAX
UNITS
1.8
V
0.75
0.9
1.1
V
V
3.3
3.3
3.43
3.43
V
V
0.9
Minimum VIN Start-Up Voltage
TA = 0°C to 70°C (Note 2)
TA = –40°C to 85°C (Note 2)
●
●
VOUT Voltage
IOUT ≤ 3.5mA, 0.9V ≤ VIN ≤ 1.8V
IOUT ≤ 10mA, 1V ≤ VIN ≤ 1.8V
●
●
VIN Operating Current
IOUT = 0mA
●
40
90
µA
VIN Shutdown Current
C1–/SHDN = 0V
●
5
15
µA
Output Ripple
IOUT = 10mA, VIN = 1.25V
Efficiency
VIN = 1V, IOUT = 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
C1–/SHDN Shutdown Input Current
C1–/SHDN = 0V (Note 3)
●
– 0.5
– 2.5
–8
VOUT Turn-On Time
VIN = 1V, IOUT = 0mA
5
ms
VOUT Short-Circuit Current
VIN = 1.5V, VOUT Forced to 0V
20
mA
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 VOUT.
Note 3: Currents flowing into the device are positive polarity. Currents
flowing out of the device are negative polarity.
2
3.17
3.17
50
mVP-P
V
µA
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
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TYPICAL PERFOR A CE CHARACTERISTICS
No Load Input Current
vs Input Voltage
Shutdown Input Current
vs Input Voltage
16
60
TA = 70°C
INPUT CURRENT (µA)
INPUT CURRENT (µA)
IOUT = 0mA
TA = 85°C
TA = 25°C
40
TA = 0°C
TA = – 40°C
20
3.40
C1–/SHDN = 0V
12
8
TA = 85°C
TA = 70°C
4
TA = – 40°C
0
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
Output Voltage vs Output Current
OUTPUT VOLTAGE (V)
80
0
0.8
1.8
1.0
VIN = 1.5V
3.30
VIN = 1V
3.25
1.4
1.6
1.2
INPUT VOLTAGE (V)
1.8
3.20
0.01
1
10
0.1
OUTPUT CURRENT (mA)
100
TA = 25°C
Load Transient Response
TA = 25°C
VOUT = 3.3V
IOUT
0mA to 10mA
5mA/DIV
VIN = 1V
80
EFFICIENCY (%)
12
4
VIN = 1.25V
60
VIN = 1.5V
VOUT
AC COUPLED
50mV/DIV
VIN = 1.8V
40
20
VIN = 1.25V
TA = 25°C
0
0.8
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
0
0.01
1.8
Oscillator Frequency
vs Input Voltage
1502-3.3 G06
100
Calculated Battery Life,
Battery = 2400mA • Hr AA Cell
Shutdown Waveforms
(See Figure 1)
100k
700
TA = 85°C
600
BATTERY LIFE (HOURS)
OSCILLATOR FREQUENCY (kHz)
1
0.1
10
OUTPUT CURRENT (mA)
200µs/DIV
1502-3.3 G05
1502-3.3 G04
TA = 70°C
TA = 25°C
500
TA = 0°C
400
300
0.8
100
1502-3.3 G03
Efficiency vs Output Current
8
VIN = 1.8V
1502-3.3 G02
Maximum Start-Up Load Current
vs Input Voltage
LOAD CURRENT (mA)
3.35
TA = 25°C
TA = 0°C
1502-3.3 G01
16
TA = 25°C
TA = – 40°C
1.0
1.4
1.6
1.2
INPUT VOLTAGE (V)
1.8
1502-3.3 G07
10k
VOUT
2V/DIV
1k
OFF
VCTRL
ON
100
10
0.001
VIN = 1.25V
RLOAD = 10k
TA = 25°C
0.01
0.1
1
10
AVERAGE LOAD CURRENT (mA)
100µs/DIV
1502-3.3 G09
100
1502-3.3 G08
3
LTC1502-3.3
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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 Negative 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 pulldown device must be high impedance for normal operation (see Applications Information). Peak voltage present
on this pin is approximately equal to VIN.
GND (Pin 4): Ground. Connect to a ground plane for best
performance.
VIN (Pin 5): Input Supply Voltage. Bypass VIN 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.
VOUT (Pin 8): 3.3V Regulated Output Voltage. VOUT is
disconnected from VIN during shutdown. Bypass VOUT
with a ≥10µF low ESR capacitor to ground.
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BLOCK DIAGRAM
C1
C3
C2
SHUTDOWN
C1–/SHDN
3
2
C1+
C3–
C2
1
6
7
C3+
VIN
CP1
5
CP2
2.5µA
CIN
8
–
VIN
–
HIZ2
+
+
COMP3
+
0.55V
2.1M
COMP2
1M
HIZ1
U2
CLK1/CLK2
U4
VOUT
BIAS
CONTROL
OSCEN
U3
INTERNAL
VCC
1.2M
COMP1
+
C2
TIMING
CONTROL
–
SHDN
1.2V
REF
4
GND
1502-3.3 BD
4
VOUT
COUT
400k
LTC1502-3.3
TEST CIRCUIT
1
10µF
C2
VOUT
8
2
7
C3 +
C1+
1µF
LTC1502-3.3
3
6
C1–/SHDN C3 –
4
5
GND
VIN
100Ω
10µF
10µF
SWITCH
CLOSED FOR
SHUTDOWN
IOUT
1µF
VIN
100pF
1502-3.3 TC
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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 VIN 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 COUT. 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
VOUT 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 VIN. The COMP2 output disables the
output charge pump CP2 whenever the divided C2 voltage
is lower than VIN. The CP2 output is thereby forced into a
high impedance state until the voltage on C2 has been
raised above VIN (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
(VOUT) is connected to a load. Hysteresis in COMP2 forces
CP2 to be turned ON and OFF while COUT 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 current 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 HiZ 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
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LTC1502-3.3
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APPLICATIONS INFORMATION
1
2
100Ω
C2
VOUT
Output Ripple
8
7
C3 +
C1+
LTC1502-3.3
3
6
C1–/SHDN C3 –
4
5
GND
VIN
10µF
ON OFF VCTRL
1502-3.3 F01
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 keeping 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 switching 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 VIN 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
VOUT 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
Normal LTC1502-3.3 operation produces voltage ripple
on the VOUT pin. Output voltage ripple is required for
regulation. Low frequency ripple exists due to the hysteresis 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. Typical output ripple (VIN = 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 COUT 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 VOUT
with every clock cycle.
There are several ways to reduce the output voltage ripple.
A larger COUT capacitor (22µF or greater) will reduce both
the low and high frequency ripple due to the lower COUT
charging and discharging dV/dt and the lower ESR typically 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 reasonable compromise is to use a 10µF to 22µF tantalum
capacitor in parallel with a 1µF to 3.3µF ceramic capacitor
on VOUT 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).
VOUT
8
+
LTC1502-3.3
For best performance, it is recommended that low ESR
capacitors be used for CIN, C2 and COUT to reduce noise
and ripple. The CIN, C2 and COUT capacitors should be
either ceramic or tantalum and should be 10µF or greater.
If the input source impedance is very low (< 0.5Ω), CIN
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., IOUT < 1mA).
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VOUT
LTC1502-3.3
VOUT
1µF
CERAMIC
10µF
TANTALUM
2Ω
8
+
VOUT
+
10µF
10µF
1502-3.3 F02
Figure 2. Output Ripple Reduction Techniques
LTC1502-3.3
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APPLICATIONS INFORMATION
Short-Circuit Protection
When the output is shorted to ground, the LTC1502-3.3
will continuously charge the C2 capacitor up to approximately 1.4 times VIN, and then discharge C2 into the
shorted output. Since the discharging of C2 into VOUT will
bring the C2 voltage below the COMP2 start-up comparator trip voltage, the output charge pump will be forced
Hi-Z while C2 charges up again. Hence, the internal charge
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PACKAGE DESCRIPTION
pump gate drive voltage is limited to (1.4)(VIN(MAX)) on the
C2 pin, and no continuous current is supplied to VOUT. 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.
Dimensions in inches (millimeters) unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
0.118 ± 0.004*
(3.00 ± 0.102)
0.034 ± 0.004
(0.86 ± 0.102)
8
7 6
5
0° – 6° TYP
SEATING
PLANE 0.012
(0.30)
0.0256
REF
(0.65)
BSC
0.021 ± 0.006
(0.53 ± 0.015)
0.118 ± 0.004**
(3.00 ± 0.102)
0.193 ± 0.006
(4.90 ± 0.15)
0.006 ± 0.004
(0.15 ± 0.102)
MSOP (MS8) 1098
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* 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
2 3
4
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.014 – 0.019
(0.355 – 0.483)
TYP
*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
7
6
5
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
SO8 1298
1
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 circuits as described herein will not infringe on existing patent rights.
2
3
4
7
LTC1502-3.3
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TYPICAL APPLICATIONS
Single Cell to 3.3V DC/DC Converter with Shutdown
1
10µF
C2
2
8
VOUT
+
7
C3 +
10µF
C1
LTC1502-3.3
3
6
C1–/SHDN C3 –
4
5
GND
VIN
1µF
100Ω
VOUT = 3.3V
IOUT = 10mA
1µF
10µF
SINGLE CELL
NiCd OR
ALKALINE
SHDN
µCONTROLLER
1502-3.3 TA03
Single Cell Battery Backup Supply with Autoswitchover and No Reverse Current
MAIN
SUPPLY
5V
3
1
LT1521-3.3
VOUT = 3.3V
IOUT = 300mA
(IOUT = 10mA
IN BACKUP MODE)
1µF
2
TRICKLE
CHARGE
1
150k
10µF
VOUT
8
7
1µF
1 CELL
NiCd
C2
2
C1+
C3 +
LTC1502-3.3
6
3
C3 – C1–/SHDN
5
4
GND
VIN
10µF
1µF
100Ω
10µF
7
1.1M
3.9V VTRIP*
LTC1540
3
4
470k
+
8
–
Q1
2N7002
5
LOGIC LOW =
BACKUP MODE
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*REFERRED TO MAIN SUPPLY
1502-3.3 TA04
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Linear Technology Corporation
15023f LT/TP 0899 4K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1999