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UCC2805-Q1: UCC2805-Q1: OVC

Nobukazu Tsukiji
Prodigy 50 points
Part Number: UCC2805-Q1
Other Parts Discussed in Thread: UCC2805

I have a question regarding the UCC2805 Over Current function. 

Since the COMP pin is clamped at 1V when the secondary output is in an over-current state, the PWM is always reset when CS reaches 1V in each switching cycle. However, the data sheet block diagram shows a circuit that detects over-current when CS reaches 1.5V.

Could you please explain under what operating conditions OVC with 1.5V threshold is detected?

Best Regards,
Nobukazu Tsukiji

  • 0
    TI__Mastermind 34465 points

    Hello Nobukazu Tsukiji

    CS and COMP are separate control pins to the UCC2805.

    In most applications CS is on the primary side and an overcurrent on the primary side may not be due to an over current in the secondary.

    In this situation CS will limit to 1.5V and the secondary never limits COMP.

    If your circuit controls an overcurrent on the secondary then how the system behaves depends on where the overcurrent first occurs.

    Regards

    John 

  • 0 in reply to John Griffin1
    TI__Prodigy 50 points

    Hi John,

    CS is compared to the voltage on the internal COMP node, but internal COMP voltage is clamped to a maximum of 1V. Therefore, if the CS voltage exceeds 1V, the switching FET will be turned off, so the CS voltage will not reach 1.5V in normal operation. 

    In what situation does CS reach 1.5V and the overcurrent detection circuit works?
    What kind of state is this protection circuit to prevent in flyback application?

    Best Regards,
    Nobukazu Tsukiji

  • 0 in reply to Nobukazu Tsukiji
    TI__Mastermind 34465 points

    Hello Nobukazu Tsukiji,

    That is not correct.
    You can see on the data sheet that the error amplifier is characterised at values of COMP = 2.5V, 2V and 1V
    COMP and CS are independent signals.

    I am sorry if  I cannot explain this in any simpler terms

    Regards

    John