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[FAQ] BQ25120A: Schematics Questions: What capacitor ratings should I pick? How do I pick the right inductor for the DC-DC converter? Do I need to tie the PGND and GND together? Is there a schematic checklist?

Part Number: BQ25120A

What capacitor ratings should I pick?

For choosing the capacitor voltage we recommend looking into Pins Functions section of the BQ25120A datasheet, where the recommended capacitor value will be mentioned. For selecting the right voltage ratings, refer to the Recommended Operating Conditions and Absolute Maximum Rating of the datasheet. As a rule of thumb, you want your voltage rating to be ~2X of your operating voltage, or refer to the derating percentage of your capacitor. While placing your components on your board, you want your bypass capacitor be as close to the pin as possible, you can refer to Section 12.2 Layout Example of the datasheet for a guideline on how to place and route your capacitors.

How do I pick the right inductor for the DC-DC converter?

For picking the right inductor for the DC-DC converter of the BQ25120A, you want to look into the maximum inductor current of your applications. You can use Equation 8 of the datasheet to calculate your current. Additionality Table 7 of the datasheet shows recommended inductors from different suppliers you can use.

IL(max) = ISYS(max) + ΔIL / 2                                                                       Equation 8

Where

ΔIL = Peak to Peak inductor ripple current

 Do I need to tie the PGND and GND together?

Yes, both PGND and GND needs to be tight together on your printed circuit board (PCB). Based on your design needs and grounding methodology, you can keep them isolated on separate nets and connect all your grounds (AGND, PGDN, DGND, etc..) later on a star ground connection, or you can tight them both together to the same ground plane of your PCB.

Is there a schematic checklist?

Yes, the BQ25120A setup guide tool includes a schematic checklist that will help getting starting on designing your application with the charger.

BQ25120A Setup Guide Link: https://www.ti.com/lit/zip/sluc696