DEMO MANUAL DC1895A LTC3633A Dual Channel 3A 20V Monolithic Synchronous Step-Down Regulator Board Description Demonstration circuit DC1895 is a dual output regulator the bottom-side of the IC for better thermal performance. consisting of two constant-frequency step-down con- These features, plus a programmable operating frequency verters, based on the LTC3633A monolithic dual channel range from 500kHz to 4MHz (2MHz switching frequency synchronous buck regulator. The DC1895 has an input with the RT pin connected to INTV ), make the DC1895 CC voltage range of 3.6V to 20V, with each regulator capable demo board an ideal circuit for use industrial or distributed of delivering up to 3A of output current. The DC1895 can power applications. operate in either Burst Mode operation or forced continu- Design files for this circuit board are available at ous mode. In shutdown, the DC1895 can run off of less DEMO MANUAL DC1895A Quick s p D The DC1895 is easy to set up to evaluate the performance 3. Turn on V and V by shifting shunts XJP1 and OUT1 OUT2 of the LTC3633A. For a proper measurement equipment XJP2 from the OFF positions to the ON positions. Both configuration, set up the circuit according to the diagram output voltages should be within a tolerance of 2%. in Figure 1. 4. Vary the input voltage from 5.8V (the minimum V is IN NOTE: When measuring the input or output voltage ripple, dependent on V ) to 20V, and the load currents from OUT care must be taken to avoid a long ground lead on the 0A to 3A. Both output voltages should be within 4% oscilloscope probe. Measure the input or output voltage tolerance. ripple by touching the probe tip directly across the V IN 5. Set the load current of both outputs to 3A and the or V and GND terminals. See the proper scope probe OUT input voltage to 20V, and then measure each output technique in Figure 2. ripple voltage (refer to Figure 2 for proper measure- Please follow the procedure outlined below for proper ment technique) they should each measure less than operation. 30mVAC. Also, observe the voltage waveforms at the switch nodes (Pins 23 and 24 for reg.1 and 13 and 14 1. Connect the input power supply to the V and GND IN for reg.2) of each regulator. The switching frequencies terminals. Connect the loads between the V and GND OUT should be between 800kHz and 1.2MHz (t = 1.25s terminals. Refer to Figure 1 for the proper measurement and 0.833s). To realize 2MHz operation, change the equipment setup. shunt position on header JP14. In all cases, both switch Before proceeding to operation, insert jumper shunts node waveforms should be rectangular in shape, and XJP1 and XJP2 into the OFF positions of headers JP1 180out-of-phase with each other. Change the shunt and JP2, shunt XJP11 into the ON position (180 out- position on header JP11 to set the switch waveforms in of-phase) of PHASE header JP11, shunts XJP3 and phase with respect to each other. To operate the ckt.s in XJP4 into the soft-start (ss) positions of headers JP3 Burst Mode Operation, change the shunt in header JP8 and JP4, shunt XJP8 into the forced continuous mode to the Burst Mode position. When finished, insert shunts (FCM) position of MODE header JP8, shunt XJP14 XJP1 and XJP2 to the OFF position(s) and disconnect into the 1MHz position of the frequency (FREQ) header the power. JP14, shunts XJP12 and XJP13 into the external (EXT) Warning: If the power for the demo board is carried in compensation positions of headers JP12 and JP13, and long leads, the input voltage at the part could ring, which shunt XJP6 into the V voltage options of choice of OUT1 could affect the operation of the circuit or even exceed header JP6: 1.2V, 1.5V, or 1.8V, and a shunt into the the maximum voltage rating of the IC. To eliminate the V voltage option of choice: 2.5V (header JP15), OUT2 ringing, a small tantalum capacitor (for instance, AVX 3.3V (header JP5), or 5V (header JP7). part number TPSY226M035R0200) is inserted on the 2. Apply 5.5V at V . Measure both V they should pads between the input power and return terminals on IN OUTs read 0V. If desired, one can measure the shutdown the bottom of the demo board. The (greater) ESR of the supply current at this point. The supply current will be tantalum will dampen the (possible) ringing voltage due less than 100A in shutdown. to the use of long input leads. On a normal, typical PCB, with short traces, this capacitor is not needed. dc1895afb 2 ure roce tart