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Final Electrical Specifications
LTC1502-3.3 Single Cell to 3.3V Regulated Charge Pump DC/DC Converter
January 1999
FEATURES
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DESCRIPTION
The LTC(R)1502-3.3 is a quadrupler charge pump DC/DC converter that produces a regulated 3.3V output from a single alkaline cell input. The part requires only five small external capacitors--no inductors are required. Low supply current (40A typical, 5A 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. 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. The part 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.
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: ICC = 40A Low Shutdown Current: ICC = 5A Short-Circuit and Overtemperature Protected Application Circuit Fits in < 0.125in2 PCB Area Available in 8-Pin MSOP and SO Packages
APPLICATIONS
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Pagers Cordless Phones Battery Backup Supplies Portable Electronic Equipment Handheld Medical Instruments Glucose Meters
TYPICAL APPLICATION
Single Cell to 3.3V DC/DC Converter
3.5
1 10F 2
C2
VOUT
8 10F 1F
OUTPUT VOLTAGE (V)
100
C1+ 1F LTC1502-3.3 6 3 C1-/SHDN C3 - 4 5 VIN GND
7 C3 +
VOUT = 3.3V IOUT = 10mA
3.4 IOUT = 1mA 3.3 IOUT = 10mA IOUT = 15mA
10F SHDN
SINGLE CELL NiCd OR ALKALINE
3.2
3.1
CONTROLLER
1502-3.3 TA01
3.0 0.8
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.
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Output Voltage vs Input Voltage
1.0
1.4 1.6 1.2 INPUT VOLTAGE (V)
1.8
1502-3.3 TA02
1
LTC1502-3.3
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 Operating Temperature Range .................... 0C to 70C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW C2 C1+ C1 -/SHDN GND 1 2 3 4 8 7 6 5 VOUT C3 + C3 - VIN
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
TJMAX = 125C, JA = 250C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN = 0.9V to 1.8V, C1 = C3 = 1F, CIN = C2 = COUT = 10F, TA = 25C unless otherwise specified.
PARAMETER VIN Operating Voltage Minimum VIN Start-Up Voltage VOUT Voltage VIN Operating Current VIN Shutdown Current Output Ripple Efficiency Switching Frequency C1-/SHDN Shutdown Input Threshold C1-/SHDN Shutdown Input Current VOUT Turn-On Time VOUT Short-Circuit Current TA = 0C to 70C (Note 2) IOUT 3.5mA, 0.9V VIN 1.8V IOUT 10mA, 1V VIN 1.8V IOUT = 0mA C1-/SHDN = 0V IOUT = 10mA, VIN = 1.25V VIN = 1V, IOUT = 10mA Oscillator Free-Running C1-/SHDN in Hi-Z Sampling State C1-/SHDN = 0V (Note 3) VIN = 1V, IOUT = 0mA VIN = 1.5V, VOUT Forced to 0V
q q
CONDITIONS
q q q q q q
The q denotes the specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired.
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TOP VIEW 8 7 6 5 VOUT C3 + C3 - VIN
ORDER PART NUMBER LTC1502CS8-3.3
S8 PART MARKING 150233
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 150C/ W
MIN 0.9
TYP 0.75
MAX 1.8 0.9 3.43 3.43 90 15
UNITS V V V V A A mVP-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 A ms mA
Note 2: Start-up testing is done with a 100k equivalent load on VOUT. Note 3: Currents flowing into the device are positive polarity. Currents flowing out of the device are negative polarity.
LTC1502-3.3 TYPICAL PERFOR A CE CHARACTERISTICS
No Load Input Current vs Input Voltage
80 IOUT = 0mA
16
INPUT CURRENT (A)
INPUT CURRENT (A)
TA = 70C TA = 25C 40 TA = 0C 20
OUTPUT VOLTAGE (V)
60
0 0.8
1.0
1.4 1.6 1.2 INPUT VOLTAGE (V)
Maximum Start-Up Load Current vs Input Voltage
16 TA = 25C
100
LOAD CURRENT (mA)
12
EFFICIENCY (%)
8
4
20
0 0.8
1.0
1.4 1.6 1.2 INPUT VOLTAGE (V)
UW
1502-3.3 G01
1502-3.3 G04
Shutdown Input Current vs Input Voltage
C1-/SHDN = 0V
3.40
Output Voltage vs Output Current
TA = 25C
12
3.35 VIN = 1.5V 3.30 VIN = 1V
8 TA = 25C TA = 70C 4 TA = 0C
3.25
1.8
0 0.8
1.0
1.4 1.6 1.2 INPUT VOLTAGE (V)
1.8
3.20 0.01
1 10 0.1 OUTPUT CURRENT (mA)
100
1502-3.3 G03
1502-3.3 G02
Efficiency vs Output Current
TA = 25C VOUT = 3.3V VIN = 1V VIN = 1.25V 60 VIN = 1.5V
Load Transient Response VIN = 1.25V
IOUT 0mA to 10mA 5mA/DIV
80
40
VOUT AC COUPLED 50mV/DIV
200s/DIV
0 0.01
1502-3.3 G06
1.8
1 0.1 10 OUTPUT CURRENT (mA)
100
1502-3.3 G05
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 10F low ESR capacitor to ground. (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 100 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. C1+ GND (Pin 4): Ground. Connect to a ground plane for best performance. VIN (Pin 5): Input Supply Voltage. Bypass VIN with a 10F 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 10F low ESR capacitor to ground.
BLOCK DIAGRAM
SHUTDOWN C1-/SHDN C1+ C2 C3- C3+
VIN 5 CIN 2.5A CP1 400k VIN CP2 8 VOUT COUT
COMP3 U2
0.55V HIZ1 CLK1/CLK2 1M
SHDN
TIMING CONTROL
OSCEN
U3
C2 VOUT
BIAS CONTROL
INTERNAL VCC
COMP1
4
-
+
+
+
-
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-
+
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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 10F 2 C2 VOUT 8 10F 1F IOUT 7 C1+ C3 + 1F LTC1502-3.3 6 3 C1-/SHDN C3 - 4 5 VIN GND
100 SWITCH CLOSED FOR SHUTDOWN
10F 100pF
VIN
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 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 300A 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
APPLICATIONS INFORMATION
1 2 C2 VOUT 8
100 SHDN
C1+ LTC1502-3.3 6 3 C1-/SHDN C3 - 4 5 VIN GND 10F
7 C3 +
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 20s and 50s 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 10A 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 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 10F or greater. If the input source impedance is very low (< 0.5), CIN may not be needed. Ceramic capacitors are recommended for the flying capacitors C1 and C3 with values of 0.47F to 2.2F. Smaller values may be used in low output current applications (e.g., IOUT < 1mA).
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Output Ripple Normal LTC1502-3.3 operation produces voltage ripple on the VOUT pin. Output voltage ripple is required for the parts to regulate. 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 10F 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 (<10F) results in higher ripple due to higher output voltage dV/dt. High ESR capacitors (ESR > 0.5) 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 (22F 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 10F to 22F tantalum capacitor in parallel with a 1F to 3.3F 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).
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VOUT LTC1502-3.3
+
VOUT 10F TANTALUM 1F CERAMIC
VOUT LTC1502-3.3
8
2
+
10F
+
10F
VOUT
1502-3.3 F02
Figure 2. Output Ripple Reduction Techniques
LTC1502-3.3
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 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.
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
0.040 0.006 (1.02 0.15) 0.007 (0.18) 0.021 0.006 (0.53 0.015) 0 - 6 TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP
* 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
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 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 0.053 - 0.069 (1.346 - 1.752) 0.004 - 0.010 (0.101 - 0.254) 8 7 6 5
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
*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
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MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 0.004* (3.00 0.102) 0.034 0.004 (0.86 0.102) 8 76 5
0.006 0.004 (0.15 0.102)
0.192 0.004 (4.88 0.10)
0.118 0.004** (3.00 0.102)
MSOP (MS8) 1197
1
23
4
0.050 (1.270) TYP
SO8 0996
1
2
3
4
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LTC1502-3.3
TYPICAL APPLICATIONS
Minimum Component Count Single Cell 3.3V Regulated Supply
1 10F 1F 2 C2 VOUT 8 10F 1F VIN SINGLE CELL NiCd or ALKALINE
1502-3.3 TA03
Single Cell Battery Backup Supply with Autoswitchover and No Reverse Current
MAIN SUPPLY 5V BAT54 3 1F 2 1 10F 7 8 10F 1F 1
TRICKLE CHARGE
1.1M 3.9V VTRIP 470k 3 4 5 6
RELATED PARTS
PART NUMBER
LT1307/LT1307B LT1308 LTC1517-3.3 LTC1558/LTC1559 LT1610
DESCRIPTION
Single Cell Micropower 600kHz PWM DC/DC Converter Single Cell Micropower 600kHz PWM DC/DC Converter Micropower Regulated 3.3V Charge Pump DC/DC Converter Backup Battery Controller with Programmable Output Single Cell Micropower 1.7MHz PWM DC/DC Converter
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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C1+ LTC1502-3.3 6 3 C1-/SHDN C3 - 4 5 VIN GND
7 C3 +
VOUT = 3.3V IOUT = 10mA
10F
LT1521-3.3
VOUT = 3.3V IOUT = 300mA (IOUT = 10mA IN BACKUP MODE)
150k
C2
VOUT
1 CELL NiCd
2 C1+ C3 + 1F LTC1502-3.3 3 6 C3 - C1-/SHDN 5 4 VIN GND
100
10F 7 LTC1540 + - 8 Q1 2N7002 LOGIC LOW = BACKUP MODE
1502-3.3 TA04
2
1
COMMENTS
3.3V at 75mA from 1 Cell, MSOP Package 3.3V at 300mA with Low Output Ripple IOUT = 15mA (VIN 2.5V) Uses Single NiCd Cell, 100mW Output (Min) 30A IQ, MSOP Package
15023i LT/TP 0199 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1999

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