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LM25119Q: There is no output of 5V.

Lian Wu
Genius 5250 points
Part Number: LM25119Q

Dears:

Could you kindly help to check the schematic?

Since there is no output of 5V, and there is no signal testing Nmos' G pot and S pot.

There is no voltage testing FB PIN.

How is the state of PIN31 and PIN32?

Pls. give some advice. 

  • 0
    TI__Mastermind 24075 points
    HI Luck,

    Can you check below items?
    1. Check if UVLO pin is higher than 1.25V
    2. Check if VCC1 and VCC2 voltage are normal.
    3. Check if HO1 and HO2 are switching.

    Btw, usually R-C-R filter is needed to filter noise on current sensing resistor. Please refer to reference design on datasheet page 21.

    Thanks
    Qian
  • 0 in reply to Qian Chen
    Genius 5250 points

    Hi Qian：

    Pls. kindly refer the below information:

    1. Check if UVLO pin is higher than 1.25V

    Luck: Yes, it's higher than 1.25V


    2. Check if VCC1 and VCC2 voltage are normal. 

    Luck: Yes, they are normal.


    3. Check if HO1 and HO2 are switching. 

    Luck: Between HO and Switch's wave as follows:

    Btw: the below picture is about between Io and CS1's wave:

  • 0 in reply to Lian Wu
    TI__Mastermind 24075 points
    Hi Luck,

    A few things to look into:

    1. The high-side FET is turned on each period, there should be some output voltage. What is output voltage?

    2. DEMB is floating in your design. The pin is pulled low internally and the part work at diode emulation mode at no load or light load condition. Refer to pin description in datasheet page 3 for more information.

    3. There is no RCR filter for current sense in our design. If the voltage between CS and CSG pin is above 120mV, high-side pulse will be terminated and Vout will be lower than setting value. Can you use small loop probe to measure the voltage between CS and CSG pins? If possible, modify the board and insert RCR filter in current board.

    Thanks
    Qian
  • 0 in reply to Qian Chen
    TI__Mastermind 24075 points
    Hi Luke

    We don't hear from for two weeks.
    Please let us know if you need further support.

    Thanks
    Qian
  • 0 in reply to Qian Chen
    Genius 5250 points
    Hi Qian:
    Sorry for my delay reply, and customer has handled it.
    Many thanks!