DEMO MANUAL DC1958 LTC3633AEUFD-2 Dual Channel 3A 20V Monolithic Synchronous Step-Down Regulator Board Description Demonstration circuit DC1958 is a dual output regulator the bottom side of the IC for better thermal performance. consisting of two constant-frequency step-down convert- These features, plus a programmable operating frequency ers, based on the LTC3633A-2 monolithic dual-channel range from 500kHz to 4MHz (2MHz switching frequency synchronous buck regulator. The DC1958 has an input with the R pin connected to INTV ), make the DC1958 T 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 DC1958 power applications. can operate in either Burst Mode or forced continuous Design files for this circuit board are available at mode. In shutdown, the DC1958 can run off of less than DEMO MANUAL DC1958 Quick s Dp Demonstration circuit 1958 is easy to set up to evaluate the 4. Vary the input voltages from 5.8V (the min. V is de- IN performance of the LTC3633A-2. For a proper measure- pendent on V ) to 20V, and the load currents from OUT ment equipment configuration, set up the circuit according 0A to 3A. Both output voltages should be within 3% to the diagram in Figure 1. tolerance. NOTE: When measuring the input or output voltage ripple, 5. Set the load current of both outputs to 3A and the care must be taken to avoid a long ground lead on the input voltages to 20V, and then measure each output oscilloscope probe. Measure the input or output voltage ripple voltage (refer to figure 2 for proper measure- ripple by touching the probe tip directly across the V ment technique) they should each measure less than IN or V and GND terminals. See the proper scope probe 30mVAC. Also, observe the voltage waveform at either OUT technique in figure 2. switch node (pins 23 & 24 for reg.1 and 13 & 14 for reg.2) of each regulator. The switching frequencies Please follow the procedure outlined below for proper should be between 800kHz and 1.2MHz (T = 1.25 s operation. and 0.833s). To realize 2MHz operation, change the 1. Connect the input power supply to the V /V and GND shunt position on header JP14. In all cases, both switch IN1 IN2 terminals (V and V are separate nodes.). Connect node waveforms should be rectangular in shape, and IN1 IN2 the loads between the V and GND terminals. Refer to 180out-of-phase with each other. Change the shunt OUT Figure 1 for the proper measurement equipment setup. position on header JP11 to set the switch waveforms in phase with respect to each other. To operate the ckt.s in Before proceeding to operation, insert jumper shunts XJP1 Burst Mode, change the shunt in header JP8 to the Burst and XJP2 into the OFF positions of headers JP1 and JP2, Mode position. When finished, insert shunts XJP1 and shunt XJP11 into the ON position (180 out-of-phase) XJP2 to the OFF position(s) and disconnect the power. of PHASE header JP11, shunts XJP3 and XJP4 into the soft-start (ss) positions of headers JP3 and JP4, shunt 6. Regulators 1 (V ) and 2 (V ) are completely sepa- IN1 IN2 XJP8 into the forced continuous mode (FCM) position of rated from each other thus, they can be powered from MODE header JP8, shunt XJP14 into the 1MHz position different individual input supplies, as can the signal of the frequency (FREQ) header JP14, shunts XJP12 and input supply. Of course, all the voltage requirements XJP13 into the external (EXT) compensation positions of still must be met: 1.5V to 20V for the PV pins and IN headers JP12 and JP13, and shunt XJP6 into the V 3.6V to 20V for the SV pin. OUT1 IN voltage options of choice of header JP6: 1.2V, 1.5V, or Warning: If the power for the demo board is carried in 1.8V, and a shunt into the V voltage option of choice: OUT2 long leads, the input voltage at the part could ring, which 2.5V (header JP15), 3.3V (header JP5), or 5V (header JP7). could affect the operation of the circuit or even exceed the 2. Apply 5.5V at V 1 & 2. Measure both V they maximum voltage rating of the IC. To eliminate the ring- INS OUTS should read 0V. If desired, one can measure the shut- ing, a small tantalum capacitor (for instance, AVX part down supply current at this point. The supply current TPSY226M035R0200) is inserted on the pads between will be less than 15A in shutdown. the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum capacitor 3. Turn on V and V by shifting shunts XJP1 and OUT1 OUT2 will dampen the (possible) ringing voltage caused by the XJP2 from the OFF positions to the ON positions. Both long input leads. On a normal, typical PCB, with short output voltages should be within a tolerance of 2%. traces, this capacitor is not needed. dc1958f 2 ure roce tart