QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1008 600MA SYNCHRONOUS STEP-DOWN REGULATOR WITH PLL, SOFT-START AND SPREAD SPECTRUM LTC3543 DESCRIPTION Demonstration circuit 1008 is a step-down converter, continuous mode, or large load current applications, the using the LTC3543 monolithic synchronous buck regu- DC1008 is a high efficiency circuit - over 90% in some lator. The DC1008 has an input voltage range of 2.5V to cases. The DC1008A consumes only 40 uA during 5.5V, and is capable of delivering up to 600 mA of out- sleep mode operation, and during shutdown, it con- put current in a small 2mm x 3mm DFN package. The sumes less than 1 uA. Because of the high switching output voltage of the DC1008 can be set as low as 0.6V, frequency of the LTC3543 - 2.25 MHz - the DC1008 the reference voltage of the LTC3543. At low load cur- uses low profile surface mount components. These rents, the DC1008 can operate in either applications features, plus the LTC3543 coming in a tiny 6-Lead DFN requiring high efficiency, due to the capability of the package, make the DC1008A an ideal circuit for use in LTC3543 to operate in Burst Mode, or in noise sensitive battery-powered, hand-held applications. applications, because the LTC3543 can also operate in Design files for this circuit board are available. Call pulse-skipping mode. Also in noise sensitive applica- the LTC factory. tions, since the LTC3543 has Spread Spectrum capabil- ity, the DC1008 can provide low noise on the input, as well as a lower noise regulated output. Of course, in Table 1. Performance Summary (T = 25C) A PARAMETER CONDITIONS VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V GND = Shutdown Run/Shutdown V = Run IN Output Voltage V V = 2.5V to 5.5V, I = 0A to 600 mA 1.8V 4% (1.728V 1.872V) OUT IN OUT Typical Output Ripple V V = 5V, I = 600 mA (20 MHz BW) < 20mV OUT IN OUT PP Line 1% (1.782V 1.818V) Output Regulation Load 1% (1.782V 1.818V) Nominal Switching Frequency 2.25 MHz Burst Mode - V = 3.3V, V = 1.8V ~75 mA 10 mA IN OUT Operation Modes Pulse-Skip - V = 3.3V, V = 1.8V ~75 mA 10 mA IN OUT Spread Spectrum See Photo 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1008 600MA SYNCHRONOUS STEP-DOWN REGULATOR WITH PLL, SOFT-START AND SPREAD SPECTRUM QUICK START PROCEDURE Demonstration Circuit 1008 is easy to set up to evalu- Turn on the circuit by inserting the shunt in header ate the performance of the LTC3543. For proper JP1 into the ON position. The output voltage should measurement equipment configuration, set up the be regulating. Measure Vout - it should measure circuit according to the diagram in Figure 2. Before 1.8V +/- 2% (1.764V to 1.836V). proceeding to test, insert shunts into the OFF position Vary the input voltage from 2.5V to 5.5V and adjust of header JP1, which connects the RUN pin to ground the load current from 0 to 600 mA. Vout should read (GND), and thus, shuts down the circuit, and the between 1.8V +/- 4% (1.728V to 1.872V). pulse-skip position (PS) of header JP2. Measure the output ripple voltage at any output cur- When measuring the input or output ripple voltage, rent level it should measure less than 20 mVAC. care must be taken to avoid a long ground lead on the Observe the voltage waveform at the switch node. oscilloscope probe. Measure the input or output rip- Verify the switching frequency is between 1.8 MHz ple voltage by touching the probe tip directly across and 2.7 MHz (T = 0.555 us and 0.37 us), and that the the Vin or Vout and GND terminals. See Figure 1 for switch node waveform is rectangular in shape in con- proper scope probe measurement technique. tinuous mode at Iout > 75 mA. The circuit (and IC) With the DC1008 set up according to the proper should be in pulse-skip mode at Iout < 75 mA. Move equipment measurement configuration in Figure 2, the shunt in header JP2 to Burst Mode (BM): the cir- apply 3.3V at Vin (Do not hot-plug Vin or increase Vin cuit (and IC) should be in Burst Mode at Iout < 75 over the rated maximum supply voltage of 5.5V, or mA. Move the shunt in header JP2 to spread spec- the part may be damaged.). Measure Vout it should trum mode (SS): the circuit (and IC) should be in read 0V. If desired, one can measure the shutdown spread spectrum operation at any and all output cur- supply current at this point. The supply current will rent levels (see scope photo). be approximately 1 uA, or less, in shutdown. When finished, turn off the circuit by inserting the shunt in header JP1 into the OFF position. Figure 1. Measuring Input or Output Ripple Voltage 2