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BQ51013B: Do we really need parallel caps

Dennis Saputelli
Prodigy 80 points
Part Number: BQ51013B
Other Parts Discussed in Thread: BQ51003

Hello.  Referring to the schematic on EVM-764 Figure 4.1.

We have successfully replicated the core circuit shown there and everything seems to be working OK on a prototype.

We stripped out all the dev features not relevant to us.

Our charging requirement is very light, about 100mA max.

Now we need to do an extreme size shrink on the design and the many parts are not all fitting well.

Here is the main question:

What is the reason for the 3 parallel caps C1, C2, C3 ?  Net value is 0.18uF.

Can't we use a single cap 0.2uF?

All of the many caps in that section are 50V, is that really necessary, I am referring to more than C1-C3, there are 11 caps in that area.

C5 is tweaking C4 but is close to tolerance of C4, what will I lose if I delete C5 considering that power is low and efficiency not a priority.

I need any tips to make this as small as possible and reduce component count please.

I can send my schematic but I don't want to post it here

Thanks !

  • 0
    TI__Guru* 76076 points

    Hello

    "Can't we use a single cap 0.2uF?" -- Bill J - The advantage of using parallel capacitor is reduced ESR and higher efficiency.  But at lower currents loss in the Cs (C1, C2 and C3) is less of a factor.

    "All of the many caps in that section are 50V," -- Bill J - Yes min recommended is 25V and 50V is better.  The concern is voltage transients during start up, moving the device or similar.

     "C5 is tweaking C4 but is close to tolerance of C4," -- Bill J -- This is the Cd capacitor and used with moving coil transmitters, not a lot of them on the market now.  If you are going to Qi certify the device accuracy would be important.  If not then single capacitor solution may be enough.

    If you output current is 100mA and you want a small solution the BQ51003 may be a good alternate for BQ51013B.