DEMO CIRCUIT 383B QUICK START GUIDE LT1930ES5/LT1931ES5 1.2MHz, SOT-23 DC/DC CONVERTER DESCRIPTION Demonstration Circuit 383B is multipurpose demon- frequency, 1A integrated switch, small circuit size, stration board featuring the LT1930 and LT1931. The and low component count makes the LT1930 and demo board offers three separate DC/DC converters. LT1931 suitable for use in many other applications, The Boost circuit is designed to convert 5V input to such as PC cards, miniature disk drives, xDSL power 12V output at 300mA maximum load. The SEPIC cir- supplies, flash memory products and local 5V or 12V cuit generates constant 12V/300mA output with supplies. The LT1930/LT1931 datasheets give complete 10V~16V variable input. The Inverter circuit is de- descriptions of the parts, their operation and application signed for applications requiring negative 12V/350mA information. The datasheets must be read in conjunction from a positive 12V input. All three circuits are de- with this quick start guide for working on or modifying signed to demonstrate the advantages of the 1.2MHz any circuit on the demo circuit 383B. switching frequency, the internal 36V/1A switch, wide input voltage range and small circuit size. These cir- Design files for this circuit board are available. Call cuits are intended for space-conscious applications the LTC factory. such as digital cameras, cellular phones, palmtop LT is a trademark of Linear Technology Corporation computers and LCD displays. The 1.2MHz switching Table 1. Performance Summary SPECIFICATIONS ARE AT TA = 25C SYMBOL PARAMETER FOR BOOST CONVERTER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 5 V IN V Output Voltage Accuracy V = 5V, I = 300mA 11.76 12 12.24 V OUT IN LOAD Ripple V = 5V, I = 300mA 50 mV IN LOAD Fs Switching Frequency 1.2 MHz SYMBOL PARAMETER FOR SEPIC CONVERTER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 10 16 V IN V Output Voltage Accuracy V = 10V, I = 300mA 11.76 12 12.24 V OUT IN LOAD Ripple V =105V, I = 300mA 50 mV IN LOAD Fs Switching Frequency 1.2 MHz SYMBOL PARAMETER FOR INVERTING CONVERTER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 12 V IN V Output Voltage Accuracy V = 12V, I = 350mA -11.76 -12 -12.24 V OUT IN LOAD Ripple V = 12V, I = 350mA 40 mV IN LOAD Fs Switching Frequency 1.2 MHz 1 QUICK START PROCEDURES Refer to Figures 14 for proper measurement age will drop drastically. Return to normal operation equipment setup and follow the procedure outlined by removing the load. below: The equipment setup for the three circuits is very Quick Start for the SEPIC Circuit: similar. They all have three pins marked Vin, Gnd and Vout, and a jumper marked on/off 1. Before turning on the power, connect a 16V, 1A for demonstrating the shutdown function. bench supply to the Vin and Gnd terminals and connect the output loads (up to 300mA). When an For the best accuracy it is important to connect true electronic load is used, decrease load current set- RMS reading voltmeters directly to the PCB termi- ting to less than 100mA until the output voltage has nals, where the input and output voltage are con- stabilized. Connect oscilloscope and meters to the nected. True RMS reading ammeters should be Vout and Gnd terminals, as shown in Figure 2. used for current measurements. 2. Turn on the input power supply and observe the The SHUTDOWN function is tested by placing the output. The DC383 SEPIC Circuit is programmed to jumper in the off position. This will short the generate 12V from a 10V16V input. Vary the input shutdown pin to ground and turn off the internal voltage to test the line regulation. The circuit is de- switch of the LT1930/LT1931. Placing the jumper in signed to deliver up to 300mA at a 12V output. the on position will return the circuit to normal operation. 3. The current limit is tested by increasing the load past 400mA. The current limit will take effect when the peak switch current becomes higher than ~1A. Quick Start for the Boost Circuit: When the current limit is exceeded, the output volt- age will drop drastically. Return to normal operation 1. Before turning on the power, connect a 5V, 1A by removing the load. bench supply to the Vin and Gnd terminals and connect the output loads (up to 300mA). When an electronic load is used, decrease load current set- Quick Start for the Inverter Circuit: ting to less than 100mA until the output voltage has stabilized. Connect an oscilloscope and meters to 1. Before turning on the power, connect a 12V, 1A the Vout and Gnd terminals, as shown in Figure 1. bench supply to the Vin and Gnd terminals and connect the output loads (up to 300mA). When an 2. Turn on the input power supply and observe the electronic load is used, decrease load current set- output. The DC383 Boost converter is programmed ting to less than 100mA until the output voltage has to generate 12V from 5V input. The circuit will de- stabilized. Connect oscilloscope and meters to the liver up to 300mA at 12V. Vout and Gnd terminals, as shown in Figure 3. 3. The current limit is tested by increasing the load 2. Turn on the input power supply and observe the past 400mA. The current limit will take effect when output. The DC383 Inverter Circuit is programmed the peak switch current becomes higher than ~1A. to generate 12V from a +12V input. The circuit will When the current limit is exceeded, the output volt- deliver up to 300mA at 12V. 2