[MC33926] Guideline for the capacitors on the VPWR line

[TomasVaverka]

Hi Jim,

Could you please help with the following question regarding the VPWR bypass and charge pump reservoir capacitors?

"In the datasheet of MC33926 rev 15, there are some descriptions for capacitors attached to V_PWR line. In the Figure 15, there are 100uF and 100nF coupling capacitors between the power supply to VPWR terminal and 33nF capacitor between VPWR and CPP terminal. Are there any guidelines for choosing those capacitance values?

I could find that that the capacitor between VPWR-CPP should be 30nF to 100nF in table 2 and section 9.2.8, and the coupling capacitor on the VPWR should be low ESR one. I would like to get more information such as example circuit or calculation method for those capacitors."

Thanks!

T.

[ava121]

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[JimShepard]

Tokai Rika,

For VPWR to ground two caps are listed 100uf low ESR and a 100nf cap for filtering out high frequency noise. Place the smaller of the two caps closest to the VPWR pin. For harsher environment this (100uf)  cap can be substantially larger.

For most applications these values should suffice.

The charge pump provides gate drive for the internal  H-bridge MOSFETs and insures the required bias levels so output MOSFETs turn fully ON when commanded.

For the charge pump reservoir cap the default value of 30 to 100nf has been determined from the switching speed of the pump  (7MHz) and the gate charge required to drive the output FETs. The gate charge of the internal MOFETS should cause <1% movement on VPWR. The actual gate charge of the MOSFETS used in this part is proprietary.

 A reservoir (CCP) cap from 30-100nf has been modeled and tested to deliver a charge pump voltage of 3.5V to 12V over VPWR across the  VPWR range of 5 to 28V.    

[TomasVaverka]

Seems like this info is sufficient for them, thanks Jim!

[Pearce4]

In electric power distribution, capacitor banks are used for power-factor correction. These banks are needed to counteract inductive loading from devices like electric motors and transmission lines, thus making the load appear to be mostly resistive.

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