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UCC2818: IAC pin voltage

Pol REYMOND
Intellectual 1540 points
Part Number: UCC2818
Other Parts Discussed in Thread: , , UC2854, UC2854B, UC2854A, UC3854A,

Hi team,

Customer has a question regarding the UCC2818 (and its equivalents like UCC2818-EP and UCC2818A-Q1):
What is the voltage at the IAC input?

This pin needs to be connected to the input voltage of the converter through a resistor, in order to get an IAC current proportional to the input voltage.

On other controller like the UC2854 and UC2854A / UC2854B, the value of this voltage is specified.

In particular, it has been the subject of improvements, as highlighted in the Application Report SLUA177A:


thanks in advance for your help on this topic

Regards,

Pol

  • 0
    TI__Genius 9790 points

    Hi, Pol

    I assigned expert to go through your question. please give some time to investigate.

    BR,

    Yunsheng

  • 0 in reply to Yunsheng Qu
    TI__Genius 9140 points

    Hi Pol,

    unfortunately there is not clear define of the voltage in the datasheet. My experience is it should be the same as UCC3854A/B.

    Actually whether or nor we have the IAC pin volatage value do not influence the design of this controller.

    IAC pin is an input current pin, not input votlage pin, customer needs to limit the input current to below 10mA to avoid over current on this pin, and 500uA is recommended to select the resistor between the sampling point after Bridge and IAC pin.

    hope this help you.

  • 0 in reply to David Huang33
    Prodigy 20 points

    Hello M. Huang,

    we plan to use UCC2818 to implement a bridgless PFC boost. Then we do not have rectifier bridge at converter input. We use analog amplifiers to create the image of rectified input voltage and we inject it in the IAC pin using a howland current source.

    We need to know the IAC pin voltage because it impacts the howland current source supply voltage.

    With UC3854A/B, given that IAC voltage is 0.5V(typ), a 5V supply is sufficient.

    Is it the same case with UCC2818? Do we have the same improvement as for UC3854A/B with a reduced IAC voltage?

    Best Regards,

    François KLEIN

  • 0 in reply to Francois KLEIN
    TI__Genius 9140 points

    Hi Francois,

    below link I add is a post about IAC in UCC2818A.

    One of our expert list that the voltage is 6V for UCC2818A, and UCC2818 is the same with UCC2818A except the driver circuit.

    So I suggest customer to use a voltage at least higher than 6V to supply.

    sorry about the confusion.

    e2e.ti.com/.../462323

  • 0 in reply to David Huang33
    Prodigy 20 points

    I do not have access to the post, but I understand that IAC typical voltage of UCC2818 and UCC2818A is 6V(typ).

    Thank you for your answer.

    Best regards,

    François KLEIN