QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 397 2.2MHZ, SOT-23 DC/DC CONVERTER LT1930A and LT1931A DESCRIPTION Demonstration circuit 397 is a multipurpose DC/DC (2.2Mhz), an internal 36V/1A switch, wide input range, switching regulator using the LT1930A and LT1931A, the and small circuit size. These circuits are designed for industrys fastest and highest power voltage regulator in space-conscious low profile applications such as cellular a SOT-23 package. The demo board offers three sepa- phones, palm top computers, digital cameras, and LCD rate DC/DC converters for different applications needs. displays. The 2.2MHz switching frequency, 1A integrated The boost circuit is designed to convert a 5V input to switch, small circuit size, and low component count 12V output at 250mA maximum load. The SEPIC circuit makes the LT1930A and LT1931A also suitable for PC generates a constant 12V/250mA (max load) output with cards, miniature disk drives, xDSL power supplies, flash a 10V~16V variable input. The inverter circuit is de- memory products, and local 5V or 12V supplies. signed for applications requiring negative 12V/250mA Design files for this circuit board are available. Call (max load) from a positive 12V input. All three circuits the LTC factory. are designed to demonstrate fast switching frequency QUICK START PROCEDURE Demonstration circuit 397 is easy to set up to evaluate 2. Turn on the input power supply and observe the out- the performance of the LT1930A and LT1931A. Refer to put. The DC397 boost circuit is programmed to gen- Figure 1, Figure 2 and Figure 3 for proper measurement erate 12V from a 5V input. The circuit will deliver up equipment setup and follow the procedures below: to 250mA at 12V. NOTE: When measuring the output ripple, see Figure 4 3. With the 250mA load at the output observe the for proper scope probe technique. switching frequency ripple at the output using the os- cilloscope. The typical switching frequency is around The equipment setup for the three circuits is very simi- 2.2MHz. See Figure 4 for proper measurement tech- lar. They all have three pins marked Vin, Gnd, Vout nique. and a jumper marked on and off for demonstrating the shutdown function. 4. The current limit is tested by increasing the load past 300mA. The current limit will take effect when the peak switch current becomes higher than ~1A. When BOOST CIRCUIT (LEFT SIDE OF BOARD) the current limit is exceeded, the output voltage will 1. Before turning on the power, connect a 5V, 1A bench drop drastically. Return to normal operation by re- supply to the Vin and Gnd terminals and connect the moving the load. output loads (up to 250mA). 5. The SHUTDOWN function is tested by placing the When an electronic load is used, connect the load jumper in the off position. This will short the shut- AFTER turning on the input supply and the output down pin to ground and turn off the internal switch of voltage has stabilized. the LT1930A. Placing the jumper in the on position will return the circuit to normal operation. Connect the oscilloscope and meters to the Vout and Gnd terminals, as shown in Figure 1. For the best ac- curacy it is important to connect true RMS reading SEPIC CIRCUIT (MIDDLE OF BOARD) voltmeters directly to the PCB terminals where the in- 1. Before turning on the power, connect a 16V, 1A bench put and output voltage are connected. True RMS read- supply to the Vin and Gnd terminals and connect the ing ammeters should be used for current measure- output load (up to 250mA). ments. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 397 2.2MHZ, SOT-23 DC/DC CONVERTER When an electronic load is used, connect the load INVERTER CIRCUIT (RIGHT SIDE OF BOARD) AFTER turning on the input supply and the output 1. Before turning on the power, connect a 12V, 1A bench voltage has stabilized. supply to the Vin and Gnd terminals and connect the Connect the oscilloscope and meters to the Vout and output load (up to 250mA). Gnd terminals, as shown in Figure 2. For the best ac- When an electronic load is used, connect the load curacy it is important to connect true RMS reading AFTER turning on the input supply and the output voltmeters directly to the PCB terminals where the in- voltage has stabilized. put and output voltage are connected. True RMS read- Connect the oscilloscope and meters to the Vout and ing ammeters should be used for current measure- Gnd terminals, as shown in Figure 3. For the best ac- ments. curacy it is important to connect true RMS reading 2. Turn on the input power supply and observe the out- voltmeters directly to the PCB terminals where the in- put. The DC397 SEPIC Circuit is programmed to gen- put and output voltage are connected. True RMS read- erate 12V from a 10V~16V input. Vary the input volt- ing ammeters should be used for current measure- age to test the line regulation. The circuit is design to ments. deliver up to 250mA at the 12V output. 2. Turn on the input power supply and observe the out- 3. With the 250mA load at the output, observe the put. The DC397 inverter circuit is programmed to switching frequency ripple at the output using the os- generate 12V from a +12V input. The circuit will de- cilloscope. The typical switching frequency is around liver up to 250mA at 12V. 2.2Mhz. See Figure 4 for proper measurement tech- 3. With the 250mA load at the output, observe the nique. switching frequency ripple at the output using the os- 4. The current limit is tested by increasing the load past cilloscope. The typical switching frequency is around 300mA. The current limit will take effect when the 1.2MHz. See Figure 4 for proper measurement tech- peak switch current becomes higher than ~1A. When nique. the current limit is exceeded, the output voltage will 4. The current limit is tested by increasing the load past drop drastically. Return to normal operation by re- 300mA. The current limit will take effect when the moving the load. peak switch current becomes higher than ~1A. When 5. The SHUTDOWN function is tested by placing the the current limit is exceeded, the output voltage will jumper in the off position. This will short the shut- drop drastically. Return to normal operation by re- down pin to ground and turn off the internal switch of moving the load. the LT1930A. Placing the jumper in the on position 5. The SHUTDOWN function is tested by placing the will return the circuit to normal operation. jumper in the off position. This will short the shut- down pin to ground and turn off the internal switch of the LT1931A. Placing the jumper in the on position will return the circuit to normal operation. 2