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UCC28C58: UCC28C58

Sidharth Gupta
Prodigy 50 points
Part Number: UCC28C58
Other Parts Discussed in Thread: UCC28C56EVM-066, UCC28C55

Tool/software:

Hello-

I am using UCC28C58QDRQ1 for my boost converter application.

The controller IC is powered with bench power supply with 18V and is not powered from the high-voltage input. In my design I have a requirement to turn-on the MOSFET in case of zero or reverse MOSFET current. For example, if DC connectors at the input are reversed, I would like to turn on the MOSFET to let the current flow from the MOSFET instead of the body diode of the MOSFET. Based on the functional block diagram of this controller IC, my understading is that both at zero current and negative current, cs pin will zero or negative and that will cause the PWM comparator inside to change state and MOSFET will be turned on with max duty cycle (i.e.. 96~97%)...Is that correct? Further, is their eval board of this controller IC which I can buy and verify this functionality to confirm and put it in my circuit?

Thank you.

  • 0
    TI__Guru 74095 points

    Hi,

    CS pin voltage depends on your external circuit design. CS voltage = 0 does not cause PWM change - each cycle begins with the clock determined by RT/CT. 

    You need to provide your circuit to explain so to help understand.

    We do not have an EVM for UCC28C58 but you can find the EVM of UCC28C56EVM-066.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Thank you. I have sent you my schematic through a private message. Can you please check and let me know.

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    It looks CT1 winding 3-4 should have a resistor in typical applications. CT1 without a resistor on 3-4 pin can make higher noise and also CT1 reset is also concerned.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, circuit has that burden resistor..It's R18 and R45 parallel combination, tied to net label Is_CT...(I needed 6.5ohms, so I habe two 13ohms in parallel)...Ct's reset is also taken care by the D2 and D3 (zener + diode combination)

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    I do not see any 13 ohm resistors. Also the resistors should be on pin 3-4 to help reduce noise or confine the noise locally - instead of after the diode so far from the CT.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, Sorry please ignore the wording of 13ohms. I mean that R18 and R45 parallel combination represents the burden resistir of the CT. These are across pin3 and 4 of the CT, although after diode as you pointed out. Thanks for pinting this out. I will try to put a placeholder there and verify it during testing.  Thank you. 

    In addition, can you please let me know about - In my design I have a requirement to turn-on the MOSFET in case of zero or reverse MOSFET current. For example, if DC connectors at the input are reversed, I would like to turn on the MOSFET to let the current flow from the MOSFET instead of the body diode of the MOSFET. Will the MOSFET be turned on with maximum duty cycle in both these cases?

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    If input voltage connected with wrong polarity, there is no function from the IC UCC28C55 can provide since it is not biased to work. If no current limit in this case, the MOSFET will be burnt to damage. You need to add some circuit like a diode or something to prevent this from happening or limit the current level.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, thanks. In my design, as you can see from schematic VDD of controller IC is independent of the HV supply. My question is about when the HV supply is reversed but controller power supply is intact at 18V (controller should function as normal).

    Now, when HV power supply is reversed , current will flow through the body diode and CT will also measure negative current and voltage at cs pin will also be negative, in this case will the controller turns on the MOSFET with maximum duty cycle?

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    When flow current from MOSFET source to drain with Vgs off, then the current flow through its body diode. There is no current limit and UCC28C58 cannot turn off the body diode, so the current will be continuous and very large as not current limit in the path/loop. This is also the same if flow the current through the N-channel. If no external circuit to stop the current quick enough the MOSFET will be damage.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, Thanks for sharing but the answer to my question is still not clear. Sorry but I would like to know that when the reverse current flows through body diode (let’s assume it’s a constant current from the power supply in this case), will the controller turn on the MOSFET with maximum duty cycle, so the reverse current will flow through MOSFET channel instead of the body diode? I would just like to know that in event of a constant reverse current will the controller turn on the FET with maximum duty cycle or not?

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    More than max duty, it is on all the time since no function can stop the current from source pin to drain pin due to the body diode. The controller only turns off current from drain to source through the N-channel but not from source to drain through the body diode.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, thanks but I think I didn’t state the problem statement clearly. My question is intended for a constant current application like PV, where the short circuit current is quite close to its nominal or MPP current. So, the intent is when the HV power supply of the converter is reversed, and the the current flows from body diode of the FET, we want to turn-on the channel instead. It will not damage the FET as it is a constant current application. 

    So, my understanding is correct that in this case the controller when it senses a negative or reverse current turns on the FET with maximum duty cycle (controller being powered from an independent +18V)? …

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    The MOSFET will flow a current from source to drain through its body diode if the n-channel is off, and will flow through the n-channel if the channel is turned on. The current has to be limited externally through something else other than UCC28C58 which cannot stop the MOSFET reverse current. If you understand this, then ok. 

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, I don’t want to stop the reverse current, just want to ensure that the channel takes over that current from the body diode. It is okay to let the reverse current flow for even hours through the channel (not the body diode), since it is a constant current application. Channel is more reliable than body diode.

    1. So, the controller will ensure to turn on the channel with max duty cycle I think when a reverse current flows?

    2. Can I check this functionality of UCC28C58 in the EVM of other UCC28C56 that you suggested earlier?

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    Please provide your schematics to see if the circuit can do what you want. Note CS pin cannot sustain a negative voltage lower than -0.3V, also other pins same. If the negative current causes further negative than -0.3V then the IC can be damaged or mal-function.

  • 0 in reply to Hong Huang
    Prodigy 50 points

    Hi, Thank you.
    I already shared the schematic over a private message before.

    I missed that it can’t go negative than 0.3V..In that case, I will have to use an external circuit to detect reverse current and turn on the channel permanently.  

  • 0 in reply to Sidharth Gupta
    TI__Guru 74095 points

    Hi,

    I do not know how to get your schematics. Please provide the link to that private message.