DEMO CIRCUIT 1896A LTC3633AEFE-3 DEMO BOARD MANUAL LTC3633AEFE-3 DUAL CHANNEL 3A 20V MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR BOARD DESCRIPTION Demonstration circuit DC1896 is a dual output regulator 90%. The DC1896 uses the 28 Pin QFN LTC3633AEFE-3 consisting of two constant-frequency step-down convert- package, which has an exposed pad on the bottom-side ers, based on the LTC3633A-3 monolithic dual channel of the IC for better thermal performance. These features, synchronous buck regulator. The DC1896 has an input plus a programmable operating frequency range from voltage range of 3.6V to 20V, with each regulator capable 500 kHz to 4 MHz (2 MHz switching frequency with the of delivering up to 3A of output current. The DC1896 can RT pin connected to INTVcc), make the DC1896 demo operate in either Burst Mode or forced continuous board an ideal circuit for use industrial or distributed mode. In shutdown, the DC1896 can run off of less than power applications. Design files for this circuit are 15 uA total. The DC1896 is a very efficient circuit: up to available at www.linear.com/demo. QUICK START PROCEDURE The DC1896 is easy to set up to evaluate the soft-start (SS) positions of headers JP3 and JP4, shunt XJP8 into the forced continuous performance of the LTC3633A-3. For a proper mode (FCM) position of MODE header JP8, measurement equipment configuration, set up shunt XJP14 into the 1 MHz position of the the circuit according to the diagram in Figure frequency (FREQ) header JP14, shunts 1. XJP12 and XJP13 into the external (EXT) NOTE: When measuring the input or output compensation positions of headers JP12 and voltage ripple, care must be taken to avoid a JP13, and shunt XJP6 into the Vout1 voltage long ground lead on the oscilloscope probe. options of choice of header JP6: 1.5V, 1.8V, or Measure the input or output voltage ripple by 2.5V, and a shunt into the Vout2 voltage option touching the probe tip directly across the Vin of choice: 2.5V (header JP15), 3.3V (header or Vout and GND terminals. See the proper JP5), or 5V (header JP7). scope probe technique in figure 2. 2. Apply 5.5V at Vins 1 & 2. Measure both Please follow the procedure outlined below for Vouts they should read 0V. If desired, one proper operation. can measure the shutdown supply current at 1. Connect the input power supply to the this point. The supply current will be less than Vin1/Vin2 and GND terminals (Vin1 and Vin2 15 uA in shutdown. are separate nodes.). Connect the loads be- tween the Vout and GND terminals. Refer to 3. Turn on Vout1 and Vout2 by shifting shunts figure 1 for the proper measurement equip- XJP1 and XJP2 from the OFF positions to the ment setup. ON positions. Both output voltages should be within a tolerance of +/- 2%. Before proceeding to operation, insert jumper shunts XJP1 and XJP2 into the OFF positions 4. Vary the input voltages from 5.8V (the min. of headers JP1 and JP2, shunt XJP11 into the Vin is dependent on Vout) to 20V, and the load ON position (180out-of-phase) of PHASE currents from 0 to 3A. Both output voltages header JP11, shunts XJP3 and XJP4 into the should be within +/- 3% tolerance. 1 L TC3633AEFE-3 5. Set the load current of both outputs to 3A and the input voltages to 20V, and then measure each output ripple voltage (refer to figure 2 for proper measurement technique) they should each measure less than 30 mVAC. Also, observe the voltage waveform at either switch node (pins 23 & 24 for reg.1 and 13 & 14 for reg.2) of each regulator. The switching frequencies should be between 800 kHz and 1.2 MHz (T = 1.25 us and 0.833 us). To attain 2 MHz operation, change the shunt position on header JP14. In all cases, both switch node waveforms should be rectangular in shape, and 180 out- of-phase with each other. Change the shunt position on header JP11 to set the switch waveforms in phase with respect to each other. To operate the ckt.s in Burst Mode, change the shunt in header JP8 to the Burst Mode position. When finished, insert shunts XJP1 and XJP2 to the OFF position(s) and disconnect the power. 6. Regulators 1 (VIN1) and 2 (VIN2) are completely separated from each other thus, they can be powered from different individ- ual input supplies, as can the signal input supply. Of course, all the voltage requirements still must be met: 1.5V to 20V for the PVin pins and 3.6V to 20V for the SVin pin. Warning - If the power for the demo board is carried in long leads, the input voltage at the part could ring, which could affect the operation of the circuit or even exceed the maximum voltage rating of the IC. To eliminate the ringing, a small tantalum capacitor (for instance, AVX part TPSY226M035R0200) is inserted on the pads between the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum capacitor will dampen the (possible) ringing voltage caused by the long input leads. On a normal, typical PCB, with short traces, this capacitor is not needed. Table 1. Performance Summary (T = 25C) A PARAMETER CONDITIONS VALUE Minimum Input Voltages 3.6V Maximum Input Voltages 20V RUN Pin = GND Shutdown Run RUN Pin = V Operating IN 1.5V 3% (1.455V - 1.545V) Output Voltage V Regulation V = 3.6V to 20V, I = 0A to 3A 1.8V 3% (1.746V 1.854V) OUT1 IN1 OUT1 2.5V 3% (2.425V 2.575V) Typical Output Ripple V V = 12V, I = 3A (20 MHz BW) < 30mV OUT1 IN1 OUT1 PP 2.5V 3% (2.425V 2.575V) Output Voltage V Regulation V = 3.6V to 20V, I = 0A to 3A 3.3V 3% (3.201V 3.399V) OUT2 IN2 OUT2 5V 3% (4.85V 5.15V) Typical Output Ripple V V = 12V, I = 3A (20 MHz BW) < 30mV OUT2 IN2 OUT2 PP RT Pin connected to 324k 1 MHz Nominal Switching Frequencies RT Pin = INTV 2 MHz CC Channel 1: Vin = 12V, Vout1 = 1.8V, Fsw = 1 MHz Iout1 < 1.5A Burst Mode Operation Channel 2: Vin = 12V, Vout2 = 3.3V, Fsw = 1 MHz Iout2 < 1.25A Output Current Thresholds Channel 1: Vin = 12V, Vout1 = 1.8V, Fsw = 2 MHz Iout1 < 1A Channel 2: Vin = 12V, Vout2 = 3.3V, Fsw = 2 MHz Iout2 < 0.75 A Phase Pin = INTV Out-of-Phase CC Phase Phase Pin = GND In Phase INTV 3.3V 6% CC 2