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Problem with UCD9248 and UCD7232

Peter Scott
Prodigy 40 points
Other Parts Discussed in Thread: UCD9248, UCD7232

Hi There,

I have a design using the UCD9248 and UCD7232.

There are many problems that I am seeing and cant pin down a hardware reason for the fault.

1:  the UCD7232 regularly reports FLT. the output current is running around 0.5A. The highside current limit is set to be arround 30Amps, and the ilim should be arround about 17Amps. The blanking time is set to 200ns. Looking with an osc it looks like the turn on time of the high side fet is about 40ns. Yet the 7232 still faults.

2: Because of this  I have disabled the fault input to the UCD9248.

After about 15 minutes I see the output voltage drops  about 500mV and then rises again. I have traced this to the PWM signal from the ucd that stops for a period of time.  usually about 10 cycles at 500KHz are missing. Sometimes this causes an UVout fault to be logged by the UCD9248. No other faults are logged. 

I have tried disabling the FAST_OC_LIMIT but the device still drops out.

The UCD is supplied with a stable 3.3V

Can anyone suggest what hardware fault could cause this ? or can you suggest how I should go about finding the cause of the problem.

/Peter

  • 0
    Prodigy 40 points

    Actually I have solved all the problems above, except the 7232s faulting.

    Can someone list the possible causes of a fault signal.

    I know the following reasons for flt

    1: low vin

    2:high voltage drop across the high side fet tblank after its turned on.

    3:the voltage on the cs p&n pins over the ILIM value. Does the 7232 multiply this differential by 49 or 98, I have seen both in the documentation?

    Any other possible causes?

    Many thanks

    /Peter