DEMO BOARD MANUAL DC324 LTC1876 High Efficiency, Low Cost, 3-Output Power Supply DESCRIPTION Demonstration Board DC324 is a high efficiency, low cost design using the LTC 1876. This demo board provides three regulated outputs from a single IC: 3.3V/5A, 5V/5A and 12V/200mA, along with two LDO outputs at 3.3V and 5V. Using only a small number of surface mount components, this design is ideal for network equipment, notebook computers and other portable applications that require low profile, small board area and minimum system cost. High efficiency and low EMI are also achieved by operating the two main power stages 180 out of phase, which, in turn, results in long battery life and smaller input capacitors. All three main outputs can be adjusted externally and the 12V regulator is configured to receive its input from the 3.3V output, the 5V output or an external supply. DC324 highlights the capabilities of the LTC1876, which incorporates a dual out-of- phase, step-down switching controller and a step-up regulator with an internal 1A, 36V switch. It uses a constant frequency, current mode architecture to provide excellent line and load regulation for all three outputs. The operating frequency of the step-down controller is DC programmable from 150kHz to 300kHz and the frequency of the step-up regulator is fixed at 1.2MHz, allowing the use of tiny, low cost capacitors and inductors. Protection features of the controller include an overvoltage soft latch, an overcurrent latch-off (which can be externally defeated) and internal current foldback for overload situations. At low output currents, two modes of operation are available: Burst Mode operation to maintain high efficiency and burst disable mode to maintain constant frequency operation. The controller is also capable of very low dropout operation, with a 99% maximum duty cycle. To be compatible with battery operation, the input range of this demo board is 7.5V to 24V for the 3.3V and 5V outputs and from 3V to10V for the 12V output. Gerber files for this circuit board are available. Call the LTC factory. PERFORMANCE SUMMARY (Operating Temperature Range: 0 C to 50 C) PARAMETERS CONDITIONS VALUE Input Voltages Step-Down Channels (V = 5V and 3.3V) Limited by 5.2V to 30V OUT External MOSFET Drive and Breakdown Requirement Step-Up Channel (V = 12V) 2.6V to 11V OUT Output Voltages Step-Down Channel 1 Externally Adjustable 5.00V 0.10V Step-Down Channel 2 Externally Adjustable 3.30V 0.07V Step-Up Channel Externally Adjustable 12.00V 0.24V 5V Linear Regulator 5.00V 4% 3.3V Linear Regulator 3.30V 4% Load Currents Step-Down Channels 0 to 5A, 6A Peak Step-Up Channel V = 3.3V 200mA IN2 V = 10V 600mA IN2PARAMETERS CONDITIONS VALUE Frequencies Step-Down Channels Externally Adjustable FREQSET Pin 300kHz Tied to INTV CC Step-Up Channel Fixed 1.2MHz Output Ripple Voltages Step-Down Channel 1 20MHz BW V = 15V I = 5A 60mV IN O P-P Step-Down Channel 2 20MHz BW V = 15V I = 5A 60mV IN O P-P Step-Up Channel 20MHz BW V = 5V I = 200mA 50mV IN2 O P-P Line Regulation Step-Down Channel 1 V = 7.5V to 24V 5mV IN Step-Down Channel 2 V = 7.5V to 24V 5mV IN Step-Up Channel V = 3.3V to 10V 5mV IN Load Regulation Step-Down Channel 1 V = 15V V = 5.00V I = 0 to 5A - 60mV IN OUT1 O Step-Down Channel 2 V = 15V V = 3.30V I = 0 to 5A - 60mV IN OUT2 O Step-Up Channel V = 5V V = 12.00V I = 0 to 200mA - 10mV IN OUT3 O Supply Current V = 15V All Three Channels On EXTV = V 80m A* IN CC OUT1 Shutdown Current V = 15V STBYMD = 0 20m A IN Standby Current V = 15V 1MW Resistor from STBYBD to V 5V INTV and 170m A IN IN CC 3.3V LDO On RUN/SS1 = RUN/SS2 = AUXSD = 0 Efficiency V = 15V V = V 4A Load at 5V Channel (Not Including 90% IN IN2 OUT1 the Supply Current to 12V Channel) 5A Load at 3.3V Channel 200mA at 12V Channel *400m A including the supply current from EXTV . Dynamic supply current is higher CC due to the gate charge being delivered at the switching frequency. See the LTC1876 data sheet for more information. TYPICAL PERFORMANCE CHARACTERISTICS 1 5V Channel (Both 3.3V and 12V Channels are OFF) Vin(V) Iin(A) Vout(V) Iout(A) Eff.(%) 15 0.004 5.02 0 0 15 0.01 5.01 0.015 50.1 15 0.023 5 0.052 75.36232 15 0.041 4.99 0.102 82.76098 15 0.182 4.99 0.496 90.66081 15 0.356 4.98 1.004 93.63146 15 0.706 4.98 2.003 94.19207 15 1.066 4.98 3.002 93.49568 15 1.44 4.98 4.002 92.26833 15 1.822 4.97 4.99 90.74387