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TCAN11623-Q1: high ripple out of LDO inside LDO + CAN transceiver

thomas b
Intellectual 285 points
Part Number: TCAN11623-Q1

Tool/software:

Hello,

I'm using a TCAN11623DMTRQ1  (CAN transceiver + LDO 3.3V) with a 10uF connected on VLD03 pin GCJ31CR71C106KA15L

A 10uF with same reference is connected on VFLT

Input capacitors are 220 + 100nF with a 10R in series with Vbat (12V)

I can see a ripple of 76mV (regular ripple is more like 45mW but I can see asynchonous peaks

As a consequence I can see some oscillations on the ADC output captured by the TI microcontroler powered by this LDO

Average consumption of the PCB is around 60mA/12V, on 3.3V side there is a load of around 45mA that is switched on 60ms every 100ms

Would it be possible to know if the chosen capacitor is too low or if a parameter is wrong, please?

Thanks

BR. T.

  • 0
    TI__Mastermind 28030 points

    Hi Thomas,

    Typically it requires a 4.7uF capacitor as close to the VLDO3 pin as possible, can you try to use that value?

    Regards,

    Sean

  • 0 in reply to Sean Guo
    Intellectual 285 points

    Hello Sean, thanks a lot - would the ripple decreases if I reduce the capacitor from 10 to 4.7 uF?

    I confirm it's placed as close as possible to the pin (less than 10mm)

    I'll try to check what happens if I remove the 10R in serial with power supply, I suppose that load switch result in input voltage ripple that is hard to compensate.

    What happens if for a short time 70mA is exceeded?

    Thanks

    BR. T.

  • 0 in reply to thomas b
    TI__Mastermind 28030 points

    Hi Thomas,

    The 4.7uF is required per datasheet, as it is designed to accommodate that LDO. Using smaller or larger value may cause instability.

    The device has the capability to output a little bit higher than 70mA, with a voltage drop, but the normal operation is not expected to beyond 70mA. Do you know what exact current it's going to exceed?

    Regards,

    Sean