BQ24800: Layout review

Fred Cheng

Expert 5770 points

Part Number: BQ24800

would you help check if our layout has any serious placement or routing problem

below is the schematic (PUA801)

TI-P105_108.pdf

red circle is AGND pin

Regards,

Fred

over 3 years ago

0 Pengzhao Zhu over 3 years ago

TI__Genius 11385 points

Hi Fred,

Please refer to the following FAQ.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1040652/faq-how-do-i-ensure-the-charger-layout-is-satisfactory-is-there-a-guideline-for-bq24780s-bq24800

Feel free to let me know if you have any specific questions.

Thanks,

Peng

0 Fred Cheng over 3 years ago in reply to Pengzhao Zhu

TI__Expert 5770 points

Hi Pengzhao,

the connection of AGND and PGND is little far from thermal pad shown below, about 300mil

is that a issue?

0 Pengzhao Zhu over 3 years ago in reply to Fred Cheng

TI__Genius 11385 points

Hi Fred,

I don't see any copper under the IC power pad? It is better to have copper under the IC power pad for better thermal performance.

For AGND and PGND, we kept them separated on the EVM but have a narrow net-tie connecting them right next to the IC. Please see attached images below.

We recommend referring to the EVM as much as possible.

Thanks,

Peng

0 Fred Cheng over 3 years ago in reply to Pengzhao Zhu

TI__Expert 5770 points

there're vias on the thermal pad so there must be a copper,

BTW, would you elaborate what would happen if the PGND AGND connection is far from thermal pad?

0 Pengzhao Zhu over 3 years ago in reply to Fred Cheng

TI__Genius 11385 points

Hi Fred,

Can you show where they made the connection between AGND and PGND? Please highlight AGND, PGND, and the connection between the 2.

Pin 22 is AGND and we recommend connecting it to power ground through the pad underneath the IC.

Here is the section on the datasheet talking about this:

Thanks,

Peng

0 Fred Cheng over 3 years ago in reply to Pengzhao Zhu

TI__Expert 5770 points

I already show you before..., see red circle ( above is PGND ,below is AGND)

I know what datasheet said , but I simply curious what would happen if the connection is not below the pad?

thanks

+1 Tiger Zhou over 3 years ago in reply to Fred Cheng

TI__Mastermind 33525 points

Hi, Fred,

Based on our past experience, the charger will operate just fine, however, the regulation accuracy may be slightly worse, for example, by 1%. This is caused by the layout ground offset.

Regards,

Tiger

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BQ24800: Layout review