QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1389A DEMO CIRCUIT 1389A QUICK START GUIDE LTC3521EUF Synchronous 1A Buck-Boost DC/DC Converter and Dual 600mA Buck DC/DC Converters DESCRIPTION Demonstration circuit 1389A is high efficiency triple out- switch to PWM mode at higher loads. The Buck-Boost put DC/DC power supply featuring the LTC3521. The IC converter will also operate in burst mode but the avail- includes a 4-switch synchronous Buck-Boost DC/DC able load current is reduced considerably, to approxi- converter with 1A switch ratings and two synchronous mately 50mA. No load BURST mode quiescent current is 600mA Buck converters. The board will accept an input approximately 50A. When all three converters are shut- voltage between 2.4V and 5V, and provide fixed output down, the quiescent current drops to less than 1A. voltages of 3.3V 800mA for the Buck-Boost converter The Power Good output terminals pull low if the output and 1.2V & 1.8V 600mA for the Buck converters. voltage is 8% or more below the regulation voltage. The board includes jumpers for shutdown for each con- The LTC3521 datasheet gives a complete description of verter, one jumper for PWM or BURST operation and the part, operation and application information. The data- terminals to monitor each converters Power Good out- sheet must be read in conjunction with this quick start put signal. Other features are 1A shutdown current, guide. integrated soft start, thermal and over current protection, Design files for this circuit board are available. Call under voltage lockout, 100% duty cycle for the Buck the LTC factory. converter and a 1MHz switching frequency that allows small L and C components to be used. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation. With BURST mode selected, the buck converters operate in BURST mode at low load current and automatically o Performance Summary ( T = 25 C ) A PARAMETER CONDITION VALUE Input Voltage Range 2.4V to 5V Buck-Boost Output Voltage (Vout 1) Vin = 2.4V, Vout Load = 100mA 3.3V +/- 2.5% Buck Output Voltage (Vout 2) Vin = 2.4V, Vout Load = 100mA 1.2V +/- 2.5% Buck Output Voltage (Vout 3) Vin = 2.4V, Vout Load = 100mA 1.8V +/- 2.5% Maximum Output Current (Buck-Boost) Vin = 2.4V, PWM mode 800mA Maximum Output Current (Buck) Vin = 2.4V 600mA Input Supply Current All Converters Shutdown, Vin = 2.4V <1A Input Supply Current (no load) All Converters Enabled, BURST Mode, Vin = 2.4V, No Load 50A, typ. Input Supply Current (no load) All Converters Enabled, PWM Mode, Vin = 2.4V, No Load 8.5mA, typ. Table 1. Circuit Specifications QUICK START PROCEDURE This Demonstration circuit 1389A can be evaluated using the setup 1. Place all Shutdown jumpers in the ON position and the shown in Figure 1. MODE jumper to the PWM position. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1389A 2. With AC power off, connect the input power supply to Vin and current is limited to approximately 50mA if the Mode jumper is GND. set for BURST. 3. Connect voltmeters to Vin and ground terminals and each 8. When measuring the input or output voltage ripple, care must Vout and Ground terminals. be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the 4. With the input voltage turned down, switch on the input power probe tip directly across the Vin or Vout and GND terminals. supply and raise the input voltage to 1.8V. See Figure 2 for proper scope probe technique. 5. Verify that each output voltage meets the values as shown in 9. The Power Good terminals can be monitored with a voltmeter Table 1. or an oscilloscope. The Power Good outputs pull low if the 6. Increase the input voltage to 2.5V and connect suitable load output voltage is 8% or more below the regulation voltage, resistors between each output and ground. otherwise they are pulled up to their respective output voltage through a 1M pull-up resistor. 7. Verify each output voltage. If an output is low, temporarily dis- connect the load to make sure that the load current is not set 10. To measure no load input current, connect a mA/A meter in too high. Also, monitor the input voltage at the board terminals series with the input supply, adjust for 2.4V and read meter. to verify that the input voltage has not dropped due to the in- Both BURST and PWM quiescent current can be verified by creased input current. Note: The Buck-Boost converter output moving JP1 to the appropriate position. Power Mode Good Shutdown Outputs + + Power RL2 V 2 out Supply - - + RL2 V 3 out - + - RL1 V 1 out Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Voltage Ripple 2