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LTC1522 Micropower, Regulated 5V Charge Pump DC/DC Converter
FEATURES
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DESCRIPTION
The LTC(R)1522 is a micropower charge pump DC/DC converter that produces a regulated 5V output from a 2.7V to 5V input supply. Extremely low supply current (6A typical with no load, < 1A in shutdown) and low external parts count (one 0.22F flying capacitor and two 10F capacitors at VIN and VOUT) make the LTC1522 ideally suited for small, light load battery-powered applications. Typical efficiency (VIN = 3V) exceeds 75% with load currents between 50A and 20mA. Modulating the SHDN pin keeps the typical efficiency above 75% with load currents all the way down to 10A. The LTC1522 has thermal shutdown and can survive a continuous short from VOUT to GND. In shutdown the load is disconnected from VIN. The part is available in 8-pin MSOP and SO packages. The LTC1522 is pin compatible with the LTC1516 in applications where VIN 2.7V and IOUT 20mA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Ultralow Power: Typical Operating ICC = 6A Short-Circuit/Thermal Protected Regulated 5V 4% Output Voltage 2.7V to 5V Input Range No Inductors Very Low ICC in Shutdown: < 1A Output Current: 10mA (VIN 2.7V) 20mA (VIN 3V) Shutdown Disconnects Load from VIN Internal Oscillator: 700kHz Compact Application Circuit (< 0.1 in2) 8-Pin MSOP and SO Packages
APPLICATIONS
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SIM Interface Supplies for GSM Cellular Telephones Li-Ion Battery Backup Supplies Local 3V to 5V Conversion Smart Card Readers PCMCIA Local 5V Supplies
TYPICAL APPLICATION
Regulated 5V Output from a 2.7V to 5V Input
VIN 2.7V TO 5V 1
Efficiency vs Output Current
90 VIN = 3V
+
10F 2 3
NC VIN VOUT C+ 0.22F
NC SHDN LTC1522 GND C-
8 7 6 5
ON/OFF
80
EFFICIENCY (%)
+
10F 4
70 SHDN = 0V
60
VOUT = 5V 4% IOUT = 0mA TO 10mA, VIN 2.7V IOUT = 0mA TO 20mA, VIN 3V
1522 TA01
50 0.01
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LOW IQ MODE (SEE FIGURE 2)
0.1 1 10 OUTPUT CURRENT (mA)
100
1522 TA02
1
LTC1522
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN to GND .................................................. - 0.3V to 6V VOUT to GND ............................................... - 0.3V to 6V SHDN to GND ............................................. - 0.3V to 6V VOUT Short-Circuit Duration ............................ Indefinite
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW NC 1 VIN 2 VOUT 3 C+ 4 8 7 6 5 NC SHDN GND C-
LTC1522CMS8 MS8 PART MARKING LTCG
MS8 PACKAGE 8-LEAD PLASTIC MSOP
TJMAX = 125C, JA = 160C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN = 2.7V to 5V, CFLY = 0.22F, CIN = COUT = 10F, TMIN to TMAX unless otherwise specified. (Note 2)
SYMBOL PARAMETER VIN Input Voltage VOUT Output Voltage ICC Operating Supply Current Shutdown Supply Current Output Ripple Efficiency Switching Frequency SHDN Input Threshold SHDN Input Current VOUT Turn-On Time CONDITIONS
q
fOSC VIH VIL IIH IIL tON
2.7V VIN 5V, IOUT 10mA 3V VIN 5V, IOUT 20mA 2.7V VIN 5V, IOUT = 0mA, SHDN = 0V 2.7V VIN 3.6V, IOUT = 0mA, SHDN = VIN 3.6V < VIN 5V, IOUT = 0mA, SHDN = VIN VIN = 3V, IOUT = 10mA VIN = 3V, IOUT = 10mA Oscillator Free Running
VSHDN = VIN VSHDN = 0V VIN = 3V, IOUT = 0mA
The q denotes specifications which apply over the specified temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired.
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Commercial Temperature Range ................ 0C to 70C Extended Commercial Operating Temperature Range (Note 2) ............. - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
TOP VIEW NC 1 VIN 2 VOUT 3 C+ 4 8 NC 7 SHDN 6 GND 5 C-
ORDER PART NUMBER LTC1522CS8 S8 PART MARKING 1522
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 150C/ W
q q q q q
MIN 2.7 4.8 4.8
TYP 5.0 5.0 6 0.005 70 82 700
MAX 5 5.2 5.2 15 1 2.5
q q q q
(0.7)(VIN) 0.4 -1 -1 1 1 1
UNITS V V V A A A mVP-P % kHz V V A A ms
Note 2: C grade device specifications are guaranteed over the 0C to 70C temperature range. In addition, C grade device specifications are assured over the - 40C to 85C temperature range by design or correlation, but are not production tested.
LTC1522 TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Input Voltage
5.15 IOUT = 10mA COUT = 10F 5.10
OUTPUT VOLTAGE (V)
VRIPPLE P-P (mV)
EFFICIENCY (%)
5.05 TA = 70C 5.00 TA = 25C 4.95 TA = 0C
4.90 2.5
3.0
4.0 4.5 3.5 INPUT VOLTAGE (V)
No Load Input Current vs Input Voltage
9 IOUT = 0mA 8
INPUT CURRENT (A)
7
TA = 70C
TA = 25C
OUTPUT VOLTAGE (V)
6
TA = 0C
5
4 2.5
3.0
4.0 4.5 3.5 INPUT VOLTAGE (V)
PIN FUNCTIONS
NC (Pin 1): No Connect. VIN (Pin 2): Input Supply Voltage. Bypass VIN with a 3.3F low ESR capacitor. VOUT (Pin 3): 5V Output Voltage (VOUT = 0V in Shutdown). Bypass VOUT with a 3.3F low ESR capacitor. C + (Pin 4): Flying Capacitor, Positive Terminal. C - (Pin 5): Flying Capacitor, Negative Terminal. GND (Pin 6): Ground. SHDN (Pin 7): Active High CMOS Logic-Level Shutdown Input. Drive SHDN low to enable the DC/DC converter. Do not float. NC (Pin 8): No Connect.
UW
1522 G01
1522 G04
Efficiency vs Input Voltage
90 IOUT = 10mA TA = 25C 80 200 250
Output Ripple vs Input Voltage
IOUT = 10mA CFLY = 0.1F TA = 25C COUT = 3.3F 150 COUT = 6.8F 100 COUT = 10F 50 COUT = 22F
70
60
50
5.0
40 2.5
3.0
4.0 4.5 3.5 INPUT VOLTAGE (V)
5.0
1522 G02
0 2.5
3.0
4.0 4.5 3.5 INPUT VOLTAGE (V)
5.0
1522 G03
Typical Output Voltage vs Output Current
5.2 TA = 25C CFLY = 0.1F COUT = 6.8F
Load Transient Response
5.1
IOUT 0mA TO 10mA 10mA/DIV
5.0 VIN = 2.7V 4.9
VOUT AC COUPLED 50mV/DIV
VIN = 3V VIN = 3.3V
VIN = 3V COUT = 10F
500s/DIV
1522 G06
5.0
4.8
0
40 60 20 OUTPUT CURRENT (mA)
80
1522 G05
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3
LTC1522
BLOCK DIAGRAM
VIN CIN 10F
+
S2A
+
C CFLY 0.22F
C-
CHARGE PUMP SHOWN IN DISCHARGE CYCLE
APPLICATIONS INFORMATION
Operation The LTC1522 uses a switched capacitor charge pump to boost VIN to a regulated 5V 4% output voltage. Regulation is achieved by sensing the output voltage through an internal resistor divider and enabling the charge pump when the output voltage droops below the lower trip point of COMP1. When the charge pump is enabled, a 2-phase, nonoverlapping clock controls the charge pump switches. Clock 1 closes the S1 switches which enables the flying capacitor to charge up to the VIN voltage. Clock 2 closes the S2 switches that stack CFLY in series with VIN and connect the top plate of CFLY to the output capacitor at VOUT. This sequence of charging and discharging continues at a free-running frequency of 700kHz (typ) until the output has risen to the upper trip point of COMP1 and the charge pump is disabled. When the charge pump is disabled, the LTC1522 draws only 4A (typ) from VIN which provides high efficiency at low load conditions. In shutdown mode, all circuitry is turned off and the part draws only leakage current from the VIN supply. VOUT is also disconnected from VIN. The SHDN pin is a CMOS input with a threshold of approximately VIN/2; however, the SHDN pin can be driven by logic levels that exceed the VIN voltage. The part enters shutdown mode when a logic high is applied to the SHDN pin. The SHDN pin should not be floated; it must be driven with a logic high or low. Short-Circuit/Thermal Protection During short-circuit conditions, the LTC1522 will draw between 100mA and 200mA from VIN causing a rise in the junction temperature. On-chip thermal shutdown circuitry disables the charge pump once the junction temperature exceeds 160C, and reenables the charge pump once the junction temperature falls back to 145C. The LTC1522 will cycle in and out of thermal shutdown indefinitely without latchup or damage until the VOUT short is removed. Capacitor Selection For best performance, it is recommended that low ESR (< 0.5) capacitors be used for both CIN and COUT to reduce noise and ripple. The CIN and COUT capacitors should be either ceramic or tantalum and should be 3.3F or greater (aluminum capacitors are not recommended because of their high ESR). If the input source impedance is very low, CIN may not be needed. Increasing the size of COUT to 10F or greater will reduce output voltage ripple.
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SHDN S1A 1A S2B CLOCK 1 S1B CLOCK 2 CONTROL LOGIC COMP1
+
VOUT COUT 10F
+ -
VREF
CHARGE PUMP
LTC1522 BD
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LTC1522
APPLICATIONS INFORMATION
A ceramic capacitor is recommended for the flying capacitor with a value in the range of 0.1F to 0.22F. Note that a large value flying cap (> 0.22F) will increase output ripple unless COUT is also increased. For very low load applications, CFLY may be reduced to 0.01F to 0.047F. This will reduce output ripple at the expense of efficiency and maximum output current. Output Ripple Normal LTC1522 operation produces voltage ripple on the VOUT pin. Output voltage ripple is required for the LTC1522 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 due to ESR (Equivalent Series Resistance) in the output capacitor. Typical output ripple under maximum load is 50mVP-P with a low ESR 10F output capacitor. The magnitude of the ripple voltage depends on several factors. High input voltages (VIN > 3.3V) increase the output ripple since more charge is delivered to COUT per clock cycle. A large flying capacitor (> 0.22F) also increases ripple for the same reason. 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 1).
LTC1522 3 VOUT
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15F TANTALUM
1F CERAMIC
VOUT 5V
LTC1522 3 VOUT
3.9
+
10F TANTALUM
+
VOUT 5V 10F TANTALUM
1522 F01
Figure 1. Output Ripple Reduction Techniques
In low load or high VIN applications, smaller values for CFLY may be used to reduce output ripple. A smaller flying capacitor (0.01F to 0.047F) delivers less charge per clock cycle to the output capacitor resulting in lower output ripple. However, the smaller value flying caps also reduce the maximum IOUT capability as well as efficiency. Inrush Currents During normal operation, VIN will experience current transients in the 50mA to 100mA range whenever the charge pump is enabled. During start-up, these inrush currents may approach 250mA. For this reason, it is important to minimize the source resistance between the input supply and the VIN pin. Too much source resistance may result in regulation problems or even prevent start-up. Ultralow Quiescent Current (IQ = 2.1A) Regulated Supply The LTC1522 contains an internal resistor divider (refer to the Block Diagram) that draws only 1A (typ) from VOUT. During no-load conditions, the internal load causes a droop rate of only 100mV per second on VOUT with COUT = 10F. Applying a 2Hz to 100Hz, 95% to 98% duty cycle signal to the SHDN pin ensures that the circuit of Figure 2 comes out of shutdown frequently enough to maintain regulation during no-load or low-load conditions. Since the part spends nearly all of its time in shutdown, the no-load quiescent current (see Figure 3a) is approximately equal to (VOUT)(1A)/(VIN)(Efficiency).
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LTC1522
APPLICATIONS INFORMATION
1 VIN 2.7V TO 5V 2 NC VIN VOUT C+ 0.22F VOUT 5V 4% NC SHDN LTC1522 GND C- 8 7 6 5
+
10F 3 10F 4
+
Figure 2. Ultralow Quiescent Current (<2.1A) Regulated Supply
6.0 1000
MAXIMUM SHDN OFF TIME (ms)
SUPPLY CURRENT (A)
4.0
2.0
0.0 2.0
3.0 4.0 INPUT VOLTAGE (V)
5.0
1522 F03a
Figure 3a. No-Load ICC vs Input Voltage for Circuit in Figure 3
The LTC1522 must be out of shutdown for a minimum duration of 200s to allow enough time to sense the output and keep it in regulation. A 2Hz, 98% duty cycle signal will keep VOUT in regulation under no-load conditions. As the VOUT load current increases, the frequency with which the part is taken out of shutdown must also be increased to prevent VOUT from drooping below 4.8V during the OFF phase (see Figure 3b). A 100Hz 98% duty cycle signal on the SHDN pin ensures proper regulation with load currents as high as 100A. When load current greater than 100A is needed, the SHDN pin must be forced low as in normal operation. The typical no-load supply current for this circuit with VIN = 3V is only 2.1A.
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FROM MPU
SHDN PIN WAVEFORMS:
LOW IQ MODE (2Hz TO 100Hz, 95% TO 98% DUTY CYCLE) VOUT LOAD ENABLE MODE IOUT 100A (IOUT = 100A TO 20mA)
1522 F02
SHDN ON PULSE WIDTH = 200s COUT = 10F
100
10
1 1 10 100 OUTPUT CURRENT (A) 1000
1522 F03b
Figure 3b. Maximum SHDN OFF Time vs Output Load Current for Ultralow IQ Operation
Each time the LTC1522 comes out of shutdown, the part delivers a minimum of one clock cycle worth of charge to the output. Under high VIN (> 3.3V) and/or low IOUT (< 10A) conditions, this behavior may cause a net excess of charge to be delivered to the output capacitor if a high frequency signal is used on the SHDN pin (e.g., 50Hz to 100Hz). Under such conditions, VOUT will slowly drift positive and may even go out of regulation. To avoid this potential problem in the low IQ mode, it is necessary to switch the part in and out of shutdown at the minimum allowable frequency (refer to Figure 3b) for a given output load.
LTC1522
APPLICATIONS INFORMATION
General Layout Considerations Due to the high switching frequency and high transient currents produced by the LTC1522, careful board layout is a must. A clean board layout using a ground plane and short connections to all capacitors will improve performance and ensure proper regulation under all conditions (refer to Figure 4).
VIN
VOUT COUT
Figure 4. Suggested Component Placement for LTC1522
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 0.004* (3.00 0.102) 0.040 0.006 (1.02 0.15) 0.034 0.004 (0.86 0.102) 8 76 5
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 0.192 0.004 (4.88 0.10) 0.118 0.004** (3.00 0.102)
* 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
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.
+
CIN
+
4 5
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1 2 3
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8 7 LTC1522 6 GND SHDN
CFLY
1522 F04
0.006 0.004 (0.15 0.102)
MSOP (MS8) 1197
1
23
4
0.050 (1.270) TYP
SO8 0996
1
2
3
4
7
LTC1522
TYPICAL APPLICATION
Programmable 5V/3V SIM Interface Supply for GSM Cellular Phones
D1
3V TRUTH TABLE AB V CC 0 0 NOT USED 0 1 3V 1 0 5V 1 1 SHUTDOWN
GSM CONTROLLER
RELATED PARTS
PART NUMBER LTC1144 LTC1262 LTC1514/15 LTC1516 LTC1517-5 LTC1555/56 LTC660 DESCRIPTION 20mA Switched Capacitor Converter for Up to 20V Inputs 5V to 12V Regulated Switched Capacitor Converter Step-Up/Step-Down Switched Capacitor DC/DC Converters Micropower, Regulated 5V Charge Pump DC/DC Converter Micropower, Regulated 5V Charge Pump DC/DC Converter SIM Power Supply and Level Translator 100mA CMOS Voltage Converter COMMENTS Includes Micropower Shutdown (8A) Up to 30mA at Regulated Output VIN 2V to 10V, VOUT is Fixed or Adjustable, IOUT to 50mA IOUT = 20mA (VIN 2V), IOUT = 50mA (VIN 3V) LTC1522 Without Shutdown and Packaged in SOT-23 Step-Up/Step-Down SIM Power Supply and Level Translators 5V to - 5V Conversion with Low Voltage Loss
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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Q1
A 1 2 B 7
R1 470k
NC VIN SHDN LTC1522
NC VOUT GND C- 0.22F
8 3
+
6 5 10F
+
VCC = 5V OR 3V (SEE TRUTH TABLE) D1 = BAS70-05 Q1 = Si6943DQ
10F 4 C +
VCC RST LEVEL SHIFT CLK I/O GND
1522 TA03
SIM CARD
1522f LT/TP 0198 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1997

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