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UCD74120: + UCD9244, current sense problem, reads the same ~3.8 A independent of load

Michael Slade
Prodigy 30 points
Part Number: UCD74120
Other Parts Discussed in Thread: UCD9244,

UCD74120 design driven by UCD9244. UCD9244 says the current on the output is about 3.8 amps no matter what the actual load is.

Design was done with Fusion Digital Power Designer 1.9.78

Design specs are: discrete components, current sense = DCR, input voltage = 12V, switching frequency = 751 kHz, output voltage = 0.9V, rated current = 25A

SRE_MD is connected to BP3
SRE is connected to BP3

Some of the values in the design:
Rdly = 8.06 k
L = 100 nH
Rs1 = 169 k
Rs2 = 0 ohm
Cs = 1 nF
Ratt = 475 ohm
Rcs = 2.49 k
Ccs = 10 nF

  • 0
    TI__Genius 9845 points

    The controller needs to know the gain and offset of the current sense signal in order to calculate output current value. Please make sure the IOUT_CAL_GAIN and IOUT_CAL_OFFSET parameters are correctly configured to reflect the sensing gain of the DCR sensing circuit and UCD74120 amplifier .

    Also check if the DCR sensing circuit of UCD74120 is working correctly.

    Regards,

    Zhiyuan