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Original question:

Why is UCC27200's HO always keep VDD ?

UCC27200: High Side Output keep high state

Dalton Vono17
Prodigy 10 points
Part Number: UCC27200

I'm having the pulses in LO pin but HO keeps in high state. The VDD is 12V, the capacitor betwen HS and HB is 0.1uF and switch frequency is 5kHz. First I measured with the LO and HO openned.

After, I tryed load LO and HO with a 10k resistor, like described in a typical application in datasheet (pag. 5, Figure 22). Loaded, the pulses appeared in HO pin but it doesn't drop to 0V. The pulses vary betwen 5 and 12V. 

Can anybody help me?

  • 0
    TI__Mastermind 20950 points
    Hello Dalton,
    Thank you for the interest in the UCC27200. The first item to determine in your test results is to confirm if you are looking at HO relative to ground with the probe, or HO relative to the HS pin. The HS pin is the ground reference for the HO output, so if HS is high relative to ground, the HO signal relative to ground will be high as well even if there is no potential from HO to HS.
    Can you record a scope plot of LO, HS, and HO to HS with a differential probe on the HO-HS? If there is not a differential probe available, measure HS to ground, and HO to ground with the same V/division and same ground reference. In this way you can clearly see when HO is higher than HS.
    Please confirm if this helps, or need to ask additional questions.

    Regards,
    Richard Herring