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TPS3838: TPS3838 filter against inrush voltage spikes on the Vcc

Alfred Logico
Expert 4170 points
Part Number: TPS3838
Other Parts Discussed in Thread: TPS3899

Hi Team,

My customer is using our TPS3838 in their application to monitor a 3.3V Vcc supply. In their application, they face some inrush current coming from outside of their application and causes the VCC to have negative pulses but the pulse are in the µs level. Please see below image for the pulse:

 

These pulses will sometimes cause the reset IC to trigger and generate the reset pulse to MCU.

Customer wants to check if we have some idea on how to filter this kind of disturbance, or if we have other products which support longer TpHL to be able to not prematurely trigger during this condition? 

For their design, they connected the CT pin to GND for 10ms delay. 

Thanks!

Best Regards,

Alfred

  • 0
    TI__Mastermind 27625 points

    Hi Alfred,

    They can add a simple RC network on the input of the VDD to filter out the pulse noise.  Do you know if they have a capacitor near the VDD pin for some kind of local bypass?

    We do have a new part (TPS3899 - www.ti.com/.../tps3899.pdf) that has programmable sense delay that provides/support longer TpHL.

    Ben 

  • 0 in reply to Ben C
    TI__Expert 4170 points

    Hi Ben,

    Thanks for the feedback! They are using a 10nFand 1uF cap on the Vcc before the TPS3838. Any recommended RC network component to add?

    I will share also the new part to them.

    Thanks! 

    BR,

    Alfred

  • 0 in reply to Alfred Logico
    TI__Mastermind 27625 points

    Hi Alfred, 

    Is it possible that the customer can use a 0.1uF instead of the 10nF capacitor?  Also, how far are the capacitors from the TPS3838?  Good practice is to have the capacitors as close as possible to the TPS3838 pin.

    Since this part consumes very little IDD current, they can try and place a resistor of 1Kohms to 10Kohms.  Using a 1Kohm resistor will result in a time constant greater than 1ms which should filter out the VDD transient noise given that the pulses are in the microsecond range.

    Just curious, can they give us a scope shot of a zoomed in view of the transient noise?  Do you know if this voltage rail has any bulk capacitance on it besides the 1uF and 10nF capacitors?  Thanks!

    Ben