DEMO MANUAL DC2123B LT3790 60V Four-Switch Synchronous Buck-Boost Controller DESCRIPTION The DC2123B is a 60V four-switch synchronous buck-boost pcb has large copper planes and extensive vias for thermal controller that demonstrates the high power capability performance. of the LT 3790. The output is 24V and the maximum The CLKOUT output and the SYNC input can be used to output current is 5A. The switching frequency is 200kHz synchronize switching between two or more DC2123B and efficiency is as high as 98% for a 24V input. circuits. A resistor from SYNC to ground must be removed The LT3790 is capable of high power operation. DC2123B prior to using the SYNC input. can be altered for increased output power with higher SHORT and C/10 are open-collector status flag outputs and minimum input voltage. If V remains always above IN are pulled up to the INTV pin voltage. A resistor shorts CC + 20V, I can be increased to 12A (for 290W output) by OUT the CCM pin to C/10 and causes the circuit to change to changing RS2 to 4m. discontinuous conduction mode (DCM) when C/10 is active The operating input voltage range of DC2123B is from 8V at light load currents. CCM can also be connected with a to 56V. The output voltage, EN/UVLO, and OVLO are all resistor to INTV instead of C/10 for continuous conduc- CC programmed by resistor dividers. EN/UVLO is set so the tion mode (CCM) operation over the entire load range. circuit will turn off when the input voltage falls below 8V The CTRL input is pulled up to the V pin through a 0 REF and will turn on when the input voltage rises above 9.6V. resistor to set the output current limit to its maximum, OVLO is set to engage for input voltages above 57V. and an external voltage on CTRL can be used to lower the Current sense resistors program input and output current current limit if the resistor is removed. A capacitor at the limits and also determine the monitoring voltages that SS pin programs soft-start and additionally SS is pulled indicate input and output current. IVINMON provides a up to the V pin through a 100k resistor. The switching REF 30mV/1A voltage that is used to monitor the input cur- frequency is adjustable with a resistor. rent. Input current limit occurs at 33.3A and is set by The demo circuit is designed to be easily reconfigured to RIN1. ISMON provides a 160mV/1A voltage that is used many other applications, including the example schemat- to monitor the output current. The output current limit is ics in the data sheet. Consult the factory for assistance. 7.5A and is set by RS2. High power operation, four-switch buck-boost topology, The demo circuit features MOSFETs that compliment the fault protection and full monitoring make the LT3790 5V gate drive of the LT3790 to achieve high efficiency. 60V attractive for high power voltage regulator circuits and MOSFETs are used on the input side of the four-switch also circuits that require output current regulation such topology while 40V MOSFETs are used on the output side. as battery chargers. The LT3790EFE is available in a Ceramic capacitors are used at both the circuit input and thermally enhanced 38-lead TSSOP package. The LT3790 output because of their small size and high ripple current data sheet must be read in conjunction with this demo capability. In addition to ceramic capacitors, there is an manual to properly use or modify demo circuit DC2123B. aluminum polymer capacitor on the output that assures Design files for this circuit board are available at feedback loop stability, even at low temperatures. The DEMO MANUAL DC2123B PERFORMANCE SUMMARY Specifications are at T = 25C A PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage, V V = 24V I 5A 8 V PVIN OUT OUT Maximum Input Voltage, V V = 24V I 5A 56 V PVIN OUT OUT Maximum Output Current 8V < V < 56V, CTRL = V 5 A PVIN REF Input EN Voltage, V R3 = 88.7k, R4 = 499k, V Rising 9.6 V PVIN(EN) PVIN Input UVLO Voltage, V R3 = 88.7k, R4 = 499k, V Falling 8.0 V PVIN(UVLO) PVIN Input OVLO Turn-Off Voltage, V R11 = 27.4k, R1 = 499k, V Rising 57.6 V PVIN(OVLO turn-off) PVIN Input OVLO Turn-On Voltage, V R11 = 27.4k, R1 = 499k, V Falling 56.2 V PVIN(OVLO turn-on) PVIN Output Voltage V R19 = 71.5k, R34 = 1.37k, R20 = 3.83k 23.5 24.5 V OUT Efficiency V = 24V, I = 5A 98 % PVIN OUT Switching Frequency R18 = 147k 200 kHz Input Current Limit RIN1 = 0.0015 33 A Output Current Limit RS2 = 0.008 7.5 A QUICK START PROCEDURE It is easy to set up demonstration circuit DC2123B to 2. After all connections are made, turn on the input power evaluate the performance of the LT3790. Refer to Figure1 and verify that the input voltage is between 8V and56V. for the proper measurement equipment setup and follow 3. Remove the clip-on lead from EN/UVLO. Verify that the the procedure below: output voltage is 24V. NOTE: Make sure that the voltage applied to PV does IN NOTE: If the output voltage is low, temporarily disconnect not exceed the absolute maximum voltage rating of 60V the load to make sure that it is not set too high. for the LT3790. 4. Once the proper output voltage is established, adjust 1. Connect the EN/UVLO terminal to ground with a clip-on the input voltage and load within the operating ranges lead. Connect the power supply (with power off), load, and observe the output voltage regulation, ripple volt- and meters as shown. age, efficiency and other parameters. dc2123bfa 2