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Original question:

UC2845: UC2845 will generate very low duty cycle PWM pulse when ISENSE reaches 1V

UC2845: current limit for ISENSE pin

Brian Li
Genius 10790 points
Part Number: UC2845

Hi team,

My customer is using our UC2845. They find in their application the UC2845 and the MOS will all broken.

And they find there's burn mark on the Rcs.

So could you please help check the current limit for the ISENSE pin and if the device will be broken when this current out of range?

Thanks,

Brian

  • 0
    TI__Mastermind 44770 points

    Hi Brian,


    ISENSE is an input pin with an absolute maximum voltage rating of 6.3V.  This is a high-impedance input.

    If the RCS has a burn mark it was likely dissipating more power than it is rated for. Without more details, I can only make some suggestions:

    1. The ISENSE voltage is 1V. Are you setting this up per equation 6 where ISENSE = VISENCE/RCS where VISENCE=1?

    2. Are you sure the resistor is rated properly? If you select 1A for ISENSE, this is a 1Ohm resistor which would have to be rated for 1W. 

    3. Do you have a filer on the ISENSE pin as suggested in Figure 8-3? This won't protect an under-power rated resistor but it may save the IC.

    I hope this helps you get started.