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TPS784-Q1: TPS78418QDBVRQ1

yang leo
Prodigy 30 points
Part Number: TPS784-Q1
Other Parts Discussed in Thread: TPS784,

Dear team

I have 2 questions about TPS78418QDBVRQ1.

1) The recommended input capacitor is 1uF at least, but currently in our PCBA , the input capacitor is 100nF, and the input power is supplied by SBC with a 10uF output capacitors. 

Is this 100nF ok for the application? 

2) Do we have the CSR curve? There is a 1ohm resistor in series with 4.7uF output capacitor, is it in the range of stable region.?

(The above questions caused by the end-of-life of TPS76318QDBVRQ1, and TPS784 will replace it，and we don't want to change our PCB design.)

Thank you!

  • 0
    TI__Expert 6570 points

    Hi Yang, 

    1. 100nF or 0.1uF is the minimum recommended capacitance for TPS784-Q1. 

    2. We do not have a CSR curve, but as long as the output capacitor ESR is below 1Ω, you are operating within recommended conditions. 

    BR,

    Erin

  • 0 in reply to Erin Thibeault
    Prodigy 30 points

    Hi Erin

    Thank you so much for the quickly reply!

    1. Do we have the guide about the effect of input capacitor on LDO?

    2. "ESR is below 1ohm", it doesn't include 'external adding resistor' right?  Because we do have a resistor in series with output capacitor as below.

  • 0 in reply to yang leo
    TI__Expert 6570 points

    Hi Yang, 

    Of course, I'm happy to support your questions as you work to incorporate a new device. 

    1. A higher value input capacitor can improve LDO load or line transient responses. 

    2. Correct, this refers to total ESR on output. Does your capacitor datasheet list ESR? 

    I found the ESR vs. Cout curve  (Figure 6-82) in the datasheet. 

    BR,

    Erin