QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 432 HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN REGULATOR LTC1875 or LTC1879 DESCRIPTION Demonstration circuit 432 is a step-down converter, fea- ICs to deliver high(er) power to small, low-profile appli- turing either the LTC1875 or LTC1879 high frequency cations. While the standard operating frequency of both monolithic switching regulators. With an input voltage parts is 550 kHz, the switching can be externally set as range from 2.65V to 6V, the LTC1875 is ideal for Li-Ion high as 750 kHz. All these features make the LTC1879 applications, such as PDAs, cellular phones, and digital (DC432A) or LTC1875 (DC432B) perfectly suited for bat- cameras. For applications with higher input voltages, the tery-powered, surface mount applications. LTC1879 is the choice with its maximum input voltage Design files for this circuit board are available. Call limit of 10V. Both devices have switch current limits over the LTC factory. 1A (LTC1875-1.6A, LTC1879-1.8A), which allows these Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage 2.65V Maximum Input Voltage (LTC1875) 6V Maximum Input Voltage (LTC1879) 10V V (LTC1875) I = 0A to 1.5A 0.8V 2% to V 2% OUT OUT IN V (LTC1879) I = 0A to 1.2A 0.8V 2% to V 2% OUT OUT IN I (LTC1875) 1.5A OUT I (LTC1879) 1.2A OUT Nominal Switching Frequency 550kHz QUICK START PROCEDURE Demonstration circuit 432 is easy to set up to evaluate 3. Connect the load between the Vout and GND termi- the performance of the LTC1875 or LTC1879. Refer to nals on the bottom right-side of the board. Figure 1 for proper measurement equipment setup and 4. With power off, connect the input power supply to Vin follow the procedure below: and GND (which are at the bottom left-side of the When measuring the input or output voltage ripple, care board). Turn on the power at the input. must be taken to avoid a long ground lead on the oscil- NOTE: If evaluating the LTC1875, do not exceed 6V in- loscope probe. Measure the input or output voltage rip- put if evaluating the LTC1879, do not exceed 10V in. ple by touching the probe tip directly across the Vin or 5. Place jumper JP2 in the RUN position. Vout and GND terminals. Refer to Figure 2 for proper placement of the scope probe. 6. Check for the proper output voltages. 1. Place jumper JP2 in the SHDN position. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 2. Select the desired output voltage, using jumper JP3. The fixed output options are 1.8V, 2.5V, and 3.3V. Too 7. Once the proper output voltages are established, ad- set the output voltage to a custom value, insert a re- just the loads within the operating range and observe sistor into RFB5. the output voltage regulation, ripple voltage, efficiency and other parameters. 1GND VIN QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 432 HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN REGULATOR + + + LOAD Figure 1. Proper Measurement Equipment Setup for both versions of the board: LTC1879 (DC432A) and LTC1875 (DC432B) Figure 2. Scope Probe Placement for Measuring Input or Output Ripple 2 + + +