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TPS3840: RESET pin voltage

Yuto Sakai
Mastermind 6100 points
Part Number: TPS3840

Hi,

The VDD and RESET pins have the same pull-up power supply.
The TPS3840 has VPOR specifications.
When VDD is lower than VPOR, the voltage shown in Figure 5 can be seen on the RESET pin.


Could you tell me how to suppress this voltage?
Since it is better to keep the reset signal level unchanged, I would like to avoid placing a resistor between RESET and GND to divide the voltage.
Or is there a device that can fix the RESET pin to low level when VDD is lower than VPOR?

Best regards,
Yuto Sakai

  • 0
    TI__Genius 10951 points

    Hi Yuto 

    In case of open drain configuration, RESET will go to pullup voltage level for VDD< VPOR for VDD slew rate <= 100mV/us

    1- If RESET pull up resistor and VDD are shorted the you can have a pull down resistor  on RESET pin (RESET to GND) same as pullup resistor. VPOR will be reduced by half. It will increase your total power consumption. 

    2- IF reset is pulled up to fixed voltage(VF) then RESET voltage will be VF for VDD< VPOR. In that case you have to use very small resistor compare to pullup (1/10 times) for proper operation but that will burn lot of power. Hence it may not be recommended. 

    In case of Push pull configuration, RESET will follow VDD for VDD<VPOR for VDD slew rate <=100 mV/us

    You can put a pull down resistance of 100k. POR will reduce significantly. 

    Regards

    Trailokya

     

  • 0 in reply to Trailokya Rai
    Mastermind 6100 points

    Hi Tarailokya-san,

    Thank you for your reply.
    Our customer use an open drain configuration.
    The RESET pull-up resistor and VDD are shorted.
    Placing a pull-down resistor changes the signal level when the reset pin is high.
    Our customers want to avoid that.
    Is there any other way? Or is there an IC that is fixed low when the RESET signal starts up?

    Best regards,
    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 10951 points

    Hi Yuto- San 

    Please refer app note http://www.ti.com/lit/an/snva845/snva845.pdf to minimize the POR for portland. 

    Regards

    Trailokya