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DRV8844: maximum voltage rating for charge pump capacitor

Jan vercammen
Prodigy 10 points
Part Number: DRV8844

hi,

I have a question about pins CP1 and CP2 of DRV8844, TI recommends a 10nF 100V rated CER CAP. The capacitor is used 

in a charge pump circuit to make a voltage higher than the power supply VM

We have a design that uses VM=24V+/-5%, single supply and use a CP1-CP2 capacitor 10nF +/- 10%, 50V rating and X7R material

We do not meet the 100V rating as stated in the data sheet, but I wonder how to calculate the voltage difference between CP1 and CP2

when the power supply voltage is 24V and not the maximum voltage of 60V? Is it correct to assume that the maximum voltage is more

or less the double of VM?

Also the use of an XR7 material is not the most optimal choice because the X7R makes the capacitance voltage dependent.

Make note that we do not experience any production problems!

  • 0
    TI__Guru 56650 points

    Jan,

    If the VM voltage is only 24V, the capacitor between CP1 and CP2 pin doesn't need 100V.  It only needs to handle VM + VCP voltage . A 50V rating capacitor is good for VM=24V+/-5% power source.

    All ceramic capacitor's capacitance is voltage dependent. The 0.1uF, 50V rate, X7R capacitor should be OK for this application. If you have a voltage dependent concern, you can pick a relevant large size ceramic capacitor, such as 0603 or 0805 size.