“Avoid power pins” for BQ24616?

Zhang Hui

Other Parts Discussed in Thread: BQ24616

Hi,

In the PCB layout guide of bq24616, “Just beneath the IC, use the copper pour for analog ground, but avoid the power pins to reduce inductive and capacitive noise coupling … A star connection under the thermal pad is highly recommended”. What does “power pins” mean?

Hui

over 10 years ago

0 Smriti B over 10 years ago

TI__Expert 5565 points

Hui,

The datasheet is saying to avoid the power GND pins of the device when putting the copper pour underneath the device. Connect the copper pour underneath the device to the power GND pin of the device through a star connection.

0 Zhang Hui over 10 years ago in reply to Smriti B

Intellectual 625 points

The original wording on the datasheet sound that central area of thermal pad, which also connects to GND, should be avoided when pouring polygon. In PCB layout this is achieved through adding keep-out region or polygon cut.

0 Smriti B over 10 years ago in reply to Zhang Hui

TI__Expert 5565 points

It should be just a single tied "neck" to the GND pin and the copper pour under the thermal pad. The copper pour under the thermal pad should be analog ground. The datasheet does not say you can't have ground layers beneath the charger IC. You will need ground beneath the charger IC because you will need thermal vias to conduct the heat away from the IC via ground planes.

0 Zhang Hui over 10 years ago in reply to Smriti B

Intellectual 625 points

But in gerber the thermal vias are clearly in power (converter) ground, not analog?

0 Smriti B over 10 years ago in reply to Zhang Hui

TI__Expert 5565 points

Could you provide a link to where this reference design is?

0 Zhang Hui over 10 years ago in reply to Smriti B

Intellectual 625 points

this should be in layout drawing of SLUU396A and HPA603 user guide, both show thermal pad via enclosed in convert(power) ground.

0 Zhang Hui over 10 years ago in reply to Smriti B

Intellectual 625 points

this should be in layout drawing of SLUU396A and HPA603 user guide, both show thermal pad via enclosed in convert(power) ground.

0 Zhang Hui over 10 years ago in reply to Zhang Hui

Intellectual 625 points

Dear Smriti,

Could this be verified?

0 Smriti B over 10 years ago in reply to Zhang Hui

TI__Expert 5565 points

The guideline in the datasheet is there to ensure that there are no high frequency current flow below the IC (through the thermal pad). The high frequency ground switching noise happens between source of low side FET and the ground of the input capacitors. Since the thermal vias for the battery charger IC is not directly in the ground path between the input capacitors and the low side buck converter FET, there is very little high frequency switching noise in the thermal pad of the battery charger.

0 Zhang Hui over 10 years ago in reply to Smriti B

Intellectual 625 points

Yes, thanks.

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“Avoid power pins” for BQ24616?