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UCC28711 in TIDA-00173

Premankar Choudhuri
Prodigy 165 points
Other Parts Discussed in Thread: TIDA-00173, UCC28711, UCC28710

TI's reference design TIDA-00173 uses UCC28711 with input voltages of upto 1.2kV DC. Since the HV start-up pin can withstand upto 700V input only, a resistor network along with a TVS diode has been used on the HV pin. I am designing a power supply for a similar input voltage range and wish to use UCC28710. My question is, do we need an additional zener diode to clamp the input voltage at the HV pin? If not, then how is the voltage being regulated at the HV pin? As far as I know, we cannot use TVS diode in continuous breakdown region.

  • 0
    TI__Mastermind 34465 points

    You need to limit the voltage at the HV to 700v or less. You can do this with a zener diode or transient suppressor provided the continuous power dissipation in the zener (or suppressor) is less than its rated power dissipation. I think the word "transient" here is a slight misnomer and I believe a transient suppressor was chosen here because it costs less than an equivalent zener.