QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 822 DUAL SYNCHRONOUS, 800MA/400MA, 2.25 MHZ STEP-DOWN DC/DC REGULATOR LTC3548 DESCRIPTION Demonstration circuit DC822 is a Dual channel Syn- and consumes less than 1uA in shutdown. The chronous, 2.25MHz Step-Down DC/DC Regulator fea- LTC3548 comes in a small 10-Pin DFN package, turing the LTC 3548. The DC822 has an input volt- which has an exposed pad on the bottom-side of the age range of 2.5V to 5.5V. The 2.5V output is capable IC for good thermal performance. These features, of delivering up to 400mA of output current The plus the nominal operating frequency of 2.25MHz (al- jumper selective 1.2V/1.5V/1.8V output is capable of lowing the exclusive use of low profile surface mount delivering up to 800mA of current. In Burst Mode components), make the DC822 demo board an ideal operation, the LTC3548 requires only 40uA of quies- reference circuit for battery-powered, hand-held cent current, as a result, the DC822 provides good applications. efficiency at light load currents. In Pulse Skip mode, Design files for this circuit board are available. Call the DC822 provides lower output ripple voltage at the LTC factory. light load currents than in Burst Mode. In either LTC is a trademark of Linear Technology Corporation mode, the DC822 can provide up to 95% efficiency Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V 1.2V 2% Output Voltage V V = 2.5V to 5.5V, I = 0A to 800mA 1.5V 2% OUT1 IN OUT1 1.8V 2% Typical Output Ripple V V = 5V, I = 800mA (20MHz BW) 20mV OUT1 IN OUT1 PP Line 1% Output Regulation Load 1% Output Voltage V V = 2.5V to 5.5V, I = 0A to 800mA 2.5V 2% OUT2 IN OUT2 Typical Output Ripple V V = 5V, I = 400mA (20MHz BW) 20mV OUT2 IN OUT2 PP Line 1% Output Regulation Load 1% Nominal Switching Frequency 2.25MHz 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 822 DUAL SYNCHRONOUS, 800MA/400MA, 2.25 MHZ STEP-DOWN DC/DC REGULATOR QUICK START PROCEDURE Demonstration circuit 822 is easy to set up to evalu- right-side of the board. Refer to Figure 1 for the ate the performance of the LTC3548. Refer to Figure 1 proper measurement equipment setup. for proper measurement equipment setup and follow 2. Before proceeding to operation, insert jumpers JP1 the procedure below. and JP2 into the OFF positions, jumper JP3 into Note: When measuring the input or output voltage the Vout1 voltage position of choice (1.2V, 1.5V, ripple, care must be taken to avoid a long ground lead and 1.8V), and jumper JP4 into the desired mode on the oscilloscope probe. Measure the input or out- of operation: Pulse Skip or Burst Mode. put voltage ripple by touching the probe tip directly 3. Apply 3.3V at Vin. Measure both Vouts they across the Vin or Vout and GND terminals. See Figure should read 0V. The supply current will be ap- 2 for proper scope probe technique. proximately 33uA in shutdown, with roughly 32uA Note: The POR pin is an open-drain output which due to the optional 100kW pull-up resistor of the Power-On Reset (POR) feature. This resistor can pulls low when either regulator is out of regulation. be removed to measure the actual shutdown sup- When both output voltages are within ---8.5% of regu- 18 ply current (of approx. 1uA). lation, a timer is started which releases POR after 2 clock cycles. This delay can be significantly longer in 4. Turn on Vout1 and Vout2 by changing jumpers JP1 Burst Mode operation with low load currents, since and JP2 from the OFF position(s) to the ON posi- the clock cycles only occur during a burst and there tion(s). Vary the input voltage from 2.5V to 5.5V could be milliseconds of time between bursts. This and adjust each load current from 0 to full load. can be bypassed by tying the POR output to the Both output voltages should be regulating. The MODE/SYNC input to force pulse skipping mode dur- regulated error is less than 2% of rated voltage. ing a reset (JP4 needs to be removed when connect- 5. Set the load current of outputs between 25% to ing POR to MODE/SYNC). 100% load range, and measure both output ripple voltages they should measure less than 20mV each. The switching frequencies should be between 1. Connect the input power supply to the Vin and 1.8MHz and 2.7MHz (T = 0.555 us and 0.37 us) GND terminals on the left-side of the board. Do not hot-plug Vin or increase Vin over the rated maximum supply voltage of 5.5V. Connect the loads between the Vout and GND terminals on the 2