DEMO MANUAL DC239 NO-DESIGN SWITCHER LTC1502-3.3 Single Cell to 3.3V Regulated Charge Pump DC/DC Converter DESCRIPTIO U Demonstration Circuit DC239 is a quadrupler charge pump DC/DC converter that produces a regulated 3.3V output from a single alkaline cell input. The circuit requires only five small external capacitors and no inductors. Low supply current (40A typ) and minimal external component area make this power supply ideal for space and power conscious single-cell applications. The maximum output load is 10mA for input voltages greater than or equal to 1V. A jumper is available to put the circuit into shutdown mode, which reduces input quiescent current to 5A (typ) and disconnects VOUT from VIN. Gerber files for this circuit are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. W U WW PERFOR A CE SU ARY PARAMETER Operating Temperature Range 0C to 70C CONDITIONS VIN Operating Voltage MIN TYP MAX UNITS 1.8 V 0.75 0.9 V 3.3 3.43 V 40 90 A 5 15 0.9 Minimum VIN Start-Up Voltage 100k VOUT Load VOUT IOUT 10mA, 1V VIN 1.8V VIN Operating Current IOUT = 0mA, 0.9V VIN 1.8V VIN Shutdown Current C1 -/SHDN Output Ripple IOUT = 10mA, VIN = 1.25V 50 mVP-P Efficiency VIN = 1V, IOUT = 10mA 77 % 3.17 = 0V, 0.9V VIN 1.8V A W U U TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO Component Side Output Voltage vs Input Voltage 3.5 TA = 25C OUTPUT VOLTAGE (V) 3.4 IOUT = 1mA 3.3 IOUT = 10mA IOUT = 15mA 3.2 3.1 3.0 0.8 1.0 1.4 1.6 1.2 INPUT VOLTAGE (V) 1.8 1502-3.3 TA02 1 DEMO MANUAL DC239 NO-DESIGN SWITCHER W W U SCHE ATIC A D PACKAGE DIAGRA S Demo Board Schematic U1 1 C2 10F R1 100 C2 VOUT 8 2 7 C3 + C1+ C1 LTC1502-3.3 1F 3 6 C1-/SHDN C3 - 4 5 GND VIN JP1 ON C3 1F TOP VIEW J2 VOUT COUT 3.3V/10mA 10F C2 C1+ - C1 /SHDN GND J1 VOUT C3 + C3 - VIN MS8 PACKAGE 8-LEAD PLASTIC MSOP J3 VIN CIN 10F 8 7 6 5 1 2 3 4 LTC1502CMS8-3.3 J4 SHDN DC239 SCHEM PARTS LIST REFERENCE DESIGNATOR C1, C3 QUANTITY 2 PART NUMBER DESCRIPTION VENDOR 0603ZG105ZAT1A 1F 10V Y5V Capacitor AVX TELEPHONE (843) 946-0362 C2, COUT, CIN 3 1206ZG106ZAT1A 10F 10V Y5V Capacitor AVX (843) 946-0362 JP1 1 2802S-03G2 3-Pin, 2mm Jumper Comm Con (626) 301-4200 J1, J2, J3, J4 4 2501-2 0.090 Turret Testpoint Mill-Max (516) 922-6000 R1 1 CR16-101JM 100 1/16W 5% Chip Resistor TAD (800) 508-1521 U1 1 LTC1502CMS8-3.3 MSOP Step-Up DC/DC IC LTC (408) 432-1900 1 CCIJ2mm-138-G 2-Pin 2mm Shunt Comm Con (626) 301-4200 U OPERATIO The LTC1502-3.3 uses a switched capacitor quadrupler charge pump 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 2-phase clock that 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 flying capacitors (CP1 and CP2) continues at the free running oscillator frequency (500kHz typ) until the output is in regulation. Regulation is achieved by comparing the divided output voltage to a fixed voltage reference. The charge pump 2 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 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 part's output (VOUT) is connected to a load. Hysteresis in COMP2 forces CP2 to be turned ON and OFF while COUT is charged DEMO MANUAL DC239 NO-DESIGN SWITCHER U OPERATIO LTC1502-3.3 Block Diagram C2 C1 C3 SHUTDOWN C1-/SHDN 3 2 C1+ C3- C2 1 6 7 C3+ VIN CP1 5 CP2 2.5A CIN 8 COUT 400k - VIN VOUT - HIZ2 + + COMP3 + 0.55V HIZ1 U2 2.1M COMP2 1M 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 to prevent a lock-up 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 demo circuit provides a jumper that selects either the ON or SHDN state. In the ON state, the 100 external pull-down resistor is left floating. In the SHDN state, the resistor is shorted to ground through the jumper. The center pin of the jumper can be driven with an external, open-drain device to test the AC start-up and shutdown characteristics. The shutdown feature can be used to prevent charge pump switching during noise sensitive intervals. 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. During shutdown, VOUT is disconnected from VIN. Short-Circuit Protection When the output pin is shorted to ground, the LTC15023.3 will continuously charge the C2 capacitor 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 trip voltage, the output charge pump will be forced Hi-Z while C2 charges 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 30mA (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. 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. 3 DEMO MANUAL DC239 NO-DESIGN SWITCHER W U PCB LAYOUT A D FIL Component Side Silkscreen Copper Layer 1 (Top) Component Side Solder Mask Component Side Paste Mask Copper Layer 2 Solder Side Solder Mask U PC FAB DRAWI G 2.00 NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL DIMENSIONS ARE IN INCHES 2. FINISHED MATERIAL IS FR4, 0.062 THICK 2 OZ COPPER, 2 LAYERS. PLATED HOLE WALL THICKNESS 0.001 MIN 3. PROCESS: SMOBC B A 2.00 B NUMBER OF HOLES PLTD SYMBOL DIAMETER A 0.030 3 PLTD B 0.094 4 PLTD TOTAL HOLES 7 DC239 FAB DWG 4 Linear Technology Corporation dc239f LT/TP 0799 500 * 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