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UCC29002: High Voltage, High-side Current Sensing Application for Load Share Controller

Chester N.
Prodigy 120 points
Part Number: UCC29002
Other Parts Discussed in Thread: INA139, TL431, UCC25600

Hi,

I am working on a project that will be using the UCC29002 on a 24V power stage. Referring from the datasheet, figure 5 suggests a circuit configuration for high voltage application, however this recommended circuit is not applicable in my project because the 24V power stage shares the same ground with the 5.1V and 3.3V power stages. That means I have to place the sense resistor along the positive 24V rail and I need to do some workaround to maintain safe voltage levels on the CS+, CS- and ADJ pins. I have a couple of questions:

1. Can you give me a recommendation on a circuit configuration that will input safe voltage levels on CS+ and CS- from a sense resistor along the positive 24V rail? I am planning to insert the INA139 current shunt monitor across the sense resistor and make its output enter the current sense amplifier of the UCC29002 in non-inverting amplifier configuration. Is this a good idea?

2. The 24V power stage has a feedback circuit based on TL431 and an optocoupler combination. I would like to ask on how to effectively attach the ADJ pin on this kind of high voltage feedback circuit. Is there a way to do this?

Thanks,
Chester

  • 0
    TI__Mastermind 34465 points

    Hello Chester

    Attached is a reference document that details suggestions for application issues with the UCC29002 load share controller..
    Page 8 shows a recommended circuit for high side current sensing with a high voltage output.

    You can set the CS+,CS- input levels to be within the operating voltage range for the CS amplifier and there should be no need to use a part like the INA1139.
    All of the applications I am familiar with use a resistor current shunt with the internal current sense amplifier.

    I dont understand your second question. The power module you are controlling is required to have separate output and sense lines.
    There is a small resistor (usually 100 Ohms or so) between Vout and Sense +.
    The UCC29002 controls the signal on S+ .
    This controls the feedback signal within the power module and raises or lowers Vout accordingly.
    Using a TL431 with optocoupler may be part of this feeback loop and the UCC290002 is designed to operate in such a system.

    Regards

    John0726.UCC29002_REF.pdf 

  • 0 in reply to John Griffin1
    Prodigy 120 points

    Hi John,

    Thanks for the suggestion on the input of the CS+ and CS- pins. I tried the configuration shown on page8 before but the voltage from the resistor dividers are higher than 4V. Since the voltage on CS pins must not exceed 4V as recommended, I will try this again with around 2V from the dividers and check the response. I hope I will get a better result this time.

    Referring to page8 circuit, can you please enlighten me about the following:

    1. What is the purpose of the NPN BJT connected to ADJ pin5?

    2. How will the trace +SENSE connect to the power module? In my project's case, the 24V power stage (full-bridge LLC) being controlled by UCC25600.

    3. Is there a load share controller more suitable for high voltage application available in your portfolio of products that is similar in pin configuration?

    Thanks and regards,

    Chester

  • 0 in reply to Chester N.
    TI__Mastermind 34465 points

    Hi Chester ,

    This transistor limits the voltage on ADJ to be equal to VDD-0.7v and so buffers ADJ from Vout

    If you refer to the schematic of UCC2500 EVM  you can connect +SENSE to TP21

    There is no better load share controller for the application you described than the UCC29002.

    Regards

    John