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TPS60120: RC filter on Vin to filter out EMI from long cable to batteries

Frits Jan van Kempen
Prodigy 215 points
Part Number: TPS60120


I am using the TPS60120 booster for a battery powered project (2x AA batteries).
The cable to the batteries is approx 30cm long.
Should I protect the Vin from EMI pickup in the cable with an RC filter?
And what would you recommend the values be.
See this schematic:

C3 is the input capacitor for the TPS, R10 and C9 are the RC filter.
I placed the RC filter AFTER this capacitor, or should I place it BEFORE?

- What would you recommend the cutoff frequency to be for filtering emi from wire pickup?
- Which RC values would you recommend? The power draw at around 3V wil be on average 20mA with short tops of 180mA.
- I am confused if I should keep R10 low for less power draw by the RC filter or C9 low...?
- Is it neccecary at all to use an RC filter here?

thanks for answering my questions!

  • 0
    TI__Guru 59755 points

    Hello Frits,

    The input capacitor needs to be directly on the IC input, so place the filter on the battery side.

    I expect EMI is not the biggest issue, but the moment when the battery is exchanged. Then you get inductive ringing. You need to test this at real circuit. 

    For the spikes to 180mA, you might be able to use a higher output capacitor. But then you might need to increase the flying cap as well.

    Best regards, 

    Brigitte 

  • 0 in reply to Brigitte
    Prodigy 215 points

    Hi Brigitte, 

    thanks for answering.

    So I would not need a EMI filter? 
    When the battery is exchanged, the device will be powered off (enable pin will be low).
    So I cannot imagine any ringing there... 
    Only after the batteries are replaced, the power can be turned on again (only by bottonpress).

    As for the spikes:
    I am now using 10uF input, 22uF output and 2.2uF flying caps. 
    According to the datasheet this should be sufficient for 200mA and a Vpp of 35mV

    Or should I use higher capacitors?

  • 0 in reply to Frits Jan van Kempen
    TI__Guru 59755 points

    Hello Frits,

    You need to make sure that the inductive ringing when the batteries are put in, does not get through to the IC if the voltage is above abs max.

    You need to check if a single input cap is able to block it.

    Best regards, 

    Brigitte