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CSD97395Q4M: Output not enabling

Part Number: CSD97395Q4M

I'm having issues with the output being disabled (100% DUC on PWM input, with no output). I think the chip might be going into UVLO mode or something else. My main culprit is the 5V line. It's a 1.5A supply, but on bootup, at 50mS in, there is some ripple.

Pin connection

  1. Pullup 10K to 3.3V
  2. 5V, 4.7uF bypass cap
  3. GND
  4. Out
  5. In (15V)
  6. 100nF cap, to boot
  7. 100nF cap, to boot_r
  8. PWM input

I don't know why this would be happening the supply is fine and can be loaded with no ripple. Any suggestions?

  • Hello,

    5V/1.5A supply should be enough to power the boot circuit. The scope picture shows that 5V supply is dropping at power up. There is a sign of damage on pin 5.

    1- Did you measure the 5V current?

    2- Is there another circuit connected to 5V supply?

    3- What do you mean by "100% DUC on PWM input"?

    4- Is the problem with only one part?

    Regards

  • Supplying from an external 5V supply doesn't change anything so we can rule that out.

    I've tried several chips with the same issues. 100% DUC mean the PWM pin is high, so the control fet should be on, and sync fet should be off. However, I'm not seeing the voltage (15V) on Vin at Vsw. It's worth noting that after power on, there is a large current jump for a split second, and Vsw jumps to around 7V, then it slowly bleeds down.

    This is why I think the output is getting disabled somehow.

  • Hi Rayan,

    It is normal if the PWM is 100%. The upper FET can not be turned on at 100% duty cycle because the boot capacitor will be discharged within few micro-seconds. In order to refresh the boot capacitor, lower FET must be no for a minim time. I hope this explains the issue. Please close the thread as resolved if your question is answered and let me know for further support.

    Regards