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TL494: TL494 CC Mode

MS
Prodigy 10 points
Part Number: TL494
Other Parts Discussed in Thread: CSD19538Q3A, TPS2816, TPS2828, TPS2818

Tool/software:

Hello,

I have a VDD = 46V which supplies a system (load). This load tries to draw more than 10A, and I want to limit the current. For this, I wanted to use a TL494 and P-channel MOSFET.

My plan is: TL494 controls the MOSFET through PWM. When the load requires, for example, 14A, the TL494 reduces the PWM width so that the load gets a maximum of 10A without interrupting the supply. 

Is this TL494 suitable for my case?

Best regards,

  • 0
    TI__Guru 73495 points

    Hi,

    Yes, you can set up the current feedback loop and make set point 10A so the current will stay at this value after the load intends to demand more current. This is similar to make output voltage constant when you make the circuit to sense the output voltage, now you sense the output current to ask the feedback loop to regulate current at 10A. When load < 10A, I think your application is still to regulate the output voltage constant. So you need to have two feedback loops, one for output voltage and one for output current, so < 10A, voltage loop in regulation, and > 10A current loop in regulation.

  • 0 in reply to Hong Huang
    Prodigy 10 points

    Hi Hong,

    Thank you for the quick answer.

    • For current regulation I will use Error-Amplifier2, connect 2IN- with 1V as reference voltage. A 0.1 ohm resistor connected to GND, which is in series with the load. The voltage of the resistor will be connected to 2IN+.

    • For this part of my circuit I don't need voltage regulation. What should be the state of PIN 1IN-, 1IN+ and FEEDBACK of Error-Amplifier1 now, e.g. connect to GND, floating...?

    • Thank you for your support!
  • 0 in reply to MS
    TI__Guru 73495 points

    Hi,

    If not using that amplifier, then need to keep IN+ < IN-.

  • 0 in reply to Hong Huang
    Prodigy 10 points

    Hi Hong,

    For controlling the high-side P-channel MOSFET CSD19538Q3A through PWM (for current regulation), I have connected a MOSFET driver TPS2818DBVR to pin C2 (pin 11) of the TL494, see the attached schematic. Is this driver stage suitable for this current limitation?

    Best regards,

  • 0 in reply to MS
    TI__Guru 73495 points

    Hi,

    As you use C2 to control, C2 is inversed output based on the datasheet below, so when a positive duty cycle pulse produced, C2 is low, Q2 pin 1 = low, Q2 pin 3 = high, Q2 turns off, but Q2 should turn on, so it looks your control timing needs to adjust.

    Please have a look and see if you agree. If you agree, you would need to use TPS2816, 18 or TPS2828.

  • 0 in reply to Hong Huang
    Prodigy 10 points

    Hi Hong,

    When a PWM is generated by TL494 and there is a positive duty cycle, does this mean that during this time the transistor that controls the current and is connected to the load (Q3, P-channel MOSFET) must turn on?

    If yes: In my circuit, C2 is low when a duty cycle is positive. Pin 4 (OUT) of U2 (TPS2818), which is connected to the gate of Q2 (N-channel MOSFET), is high because U2 (TPS2818) is an inverted gate driver. This turns Q2 on. When Q2 is on, Q3 is also on.

    This should normally be correct, or am I missing something?

    Thank you for your help, your support is highly appreciated.

  • 0 in reply to MS
    TI__Guru 73495 points

    Hi,

    If TPS2818 is used in your design, then ok. TPS2818 output is inversed but your drawing does not show this inverse. I think that is why I am asking.