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Modifying LTC4282 circuit

We were checking DC2422(LTC4282) reference schematic and how our existing schematic with ADM1278 can be modified for LTC4282. We have a few doubts, about whether we can reuse few components such as FETs and sense resistors from ADM1278 schematic in the new schematics with LTC4282. This is because we have already ordered FETs and other discretes and it would be great if we can reuse the same in new schematics.

Please find link for our schematic with ADM1278

https://drive.google.com/file/d/1Ulf4H7BKmHEu_XGa3QP635v0RiZxZ4lg/view?usp=sharing

  1. The FETs in our original schematic are PSMN0R9-25YLC. We are using total 4 FETs assuming 140A current limit. DC2422 reference schematic has total 9 FETs with gate2 connected to 8 FETs with MPN PSMN0R9-30YLD and gate1 connected to single FET with MPN PSMN011-30YL. We understand that the DC2422 schematic is using 'low stress staged start' configuration. We would like to know whether we can use the same 4 FETs from ADM1278 schematic? And whether any other changes would be required in the schematic to use only 4 FETs with MPN PSMN0R9-25YLC? Should we short gate1 and gate2 and go for single MOSFET configuration?
  2. We are using 3 sense resistors with 0.0005 ohm in ADM1278 schematic to get current limit of 140A. As per the formula given for LTC4282, we have calculated that we would need 6 sense resistors instead of 3 which would give 150 A current limit. (Rsense= 12.5mv/current limit). But it is also mentioned in the datasheet that the default value of 12.5 mv for Vsense can be adjusted through I2C interface. Considering the step size of 3.1mV if we adjust Vsense to 24.9mV through I2C then the 3 sense resistors of 0.0005 ohm would be sufficient for 150A current limit. Is this approach correct?

Thanks,

Avani

  • Hi,

    Your approach is correct. 

    The correct part number for the 200A reference design is DC2442A. This was designed a few years ago and MOSFETs have improved, lower RDS(on). It is to be expected that you can use a smaller number.

    Check that I x I x RDS(on 100C) per MOSFET is around 1 to 1.5W

    I suggest that you get the DC2442A demo board and modify by replacing the Sense resistors and MOSFETs. 

    You may also want to get the DC1613A dongle so that you can use the GUI software LTpowerPlay.

    You can also use the LTspice model.

    JayBee