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PTH08T2xx input Cap selection

Jamie Maxwell
Expert 1530 points

We are currently using two Texas Instruments DC-DC Converters, PTH08T221WAZ and PTH08T250WAZ. We are currently using the TDK C5750Y5V1C107Z(CAP CER 100UF 16V Y5V 5750) on the input rails of both converters but the capacitor is an EOL component. Our current suggested replacement and the only one suited to the design is the TDK C5750X5R1C476M230KA(CAP CER 47UF 16V 20% X5R 5750). The current one is a Y5V 100 uF ceramic capacitor while the suggested replacement is a X5R 47 uF ceramic capacitor.

The PTH08T221WAZ datasheet explicitly states that the input should have a minimum of 300 uF of ceramic input capacitance. Currently the three PTH08T221WAZ chips on our board use four of the 100 uF ceramic capacitors on each of their input rails and satisfy the requirement. The PTH08T250WAZ uses seven of the 100 uF capacitors on its input rail.  

However, the suggested 47 uF replacement does not meet the data sheet specified requirement.

The question I am hoping to get answered is whether the minimum specified requirement is flexible or will our suggested replacement suffice. 

Thanks

  • 0
    TI__Mastermind 38230 points

    JMax:

    I reviewed the application using Y5V very poor temperature  range. Y5V at 65°C   temperature  coefficient versus capacitance change   is about  -60% of 100uF with effective capacitance degraded to 40uF or less.

    47uF (K) X5R temperature coefficient  or capacitance change  is  about 5-10% at 65°C effective capacitance is about 44°C. 

    Tom

    Send me an e-mail off line at tguerin@ti.com to discuss this change in this  minimum input capacitance.