Post Go back to editing

ADP8140 PWM control with VT pin

Hi,

Would you let me know how to connect the MODE, MIN, DIM and VT pin on ADP8140CP-EVALZ when the board is set to PWM dimming mode using VT pin?

The current setting on the board is as follows:

  • MODE pin is connected to REG
  • MIN pin is connected to REG
  • VT pin is connected to PWM signal (0 and 3.3V) which is generated by my custom board.
  • DIM pin is open.

This setting did not work at all. there are no description on the datasheet how to use PWM mode with VT pin in detail.

It worked when the board was set to PWM mode with DIM pin. However, P-ch MOSFET became too hot ( it read around 80 C deg on case).

To prevent this heat condition, I' d like to apply a PWM current sink mode with using VT pin (I'm not sure how to call).

I'm wondering if the board does not work as a PWM mode with VT pin on ADP8140CP-EVAL.

Please let me know if I'm missing anything about pin setting on ADP8140CP-EVAL.

Regards,

ytak

  • Hi 

    To set VT as a PWM input. Please set the Pins  as shown below.

    MODE pin to GND

    MIN pin to REG

    VT pin PWM input

    DIM pin connect to POT

    DIM pin still needs to connect to the POT since this will be used to set the max current per channel.

    If it is left open it would just default to min value. To control via VT pin alone turn the POT fully clockwise 

    Regards,

  • Hi,

    Thank you for your response.

    it worked with VT PWM mode as you suggested.

    I got nother questions. I'm assuming that the current limit should be defined by a resistor on ISET pin, not the voltage of DIM pin. meanwhile, you mentioned DIM pin for setting maximum current per channel.

    Would you let me know the role of DIM pin and ISET pin on VT PWM mode?

    I'd like to sink the maximum current of 150mA per SINK at 100% on-duty.

    In this case, I'm assuming that the value of RSET is around 17 k ohms and the voltage of DIM pin sets to VREG.

    Would you let me know if the above setting is correct or not?

    Thankks, 

  • Hi

    In VT PWM mode,  ISET and DIM pins dictates the max value of the sink current. 

    DIM pin will still scale the maximum current set by the Rset in VT PWM mode. that is why you will need to set the DIM pin to max current to achieve the target current 

    Yes configuration you suggest is correct 

    Regards