BQ21040: Review of the implemented design

SHYAM THILLAINATHAN

Prodigy 220 points

Part Number: BQ21040

Hi,

Would like to get the following design reviewed, especially the thermistor section:

Capture.rtf

over 8 years ago

0 Diana Bodenmiller over 8 years ago

TI__Prodigy 640 points

Hello.

Following the schematic on the datasheet,

there should be no resistor from VOUT to VBATT.
and there should be another resistor, RTS, from TS pin to ground

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

Thanks for the reply. Here are some questions:

The 0 OHM from VOUT to VBATT is for debugging.
When you say "another resistor between TS pin and GND", do you mean to add a fixed resistor, or a thermistor, if so may I know the value. Right now we are using: ERT-J0EG103FA (NTC THERMISTOR 10K OHM 1% 0402).

Please do advise us as to how to proceed.

0 Diana Bodenmiller over 8 years ago in reply to SHYAM THILLAINATHAN

TI__Prodigy 640 points

Hello,

Sorry for the delay. I believe the RTS resistor in the datasheet schematic is only there to indicate the 237k Ohm resistor that you can place from TS to ground if you wish to disable TTDM upon battery removal. (See section 8.4.6 for more info)

If you do not wish to disable TTDM, you do not need this resistor, and your schematic looks good.

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

Thanks for the reply, if our battery doesn't have an inbuild thermistor and we don't want the TTDM feature and don't want to monitor the temperature or in other words, don't want to use TTDM or TS feature, can I leave this pin floating or should I add a resistor from TS to GND?

0 Diana Bodenmiller over 8 years ago in reply to SHYAM THILLAINATHAN

TI__Prodigy 640 points

Shyam,

If TS feature is not needed, a fixed 10kΩ resistor can be placed between TS and VSS to allow normal operation.

Section 8.4.5 in the BQ21040 datasheet has further information on the TS feature. Hope this helps.

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

I did go through the datasheet, however, our pack has no thermistor and we'll be placing one(a 10K NTC, ERT-J0EG103FA) on the board topside center next to the battery as an approximation. This will provide some degree of temperature monitoring and allow for 'normal' charger operation. While not ideal, this is our plan of record. Do you see a specific problem with this approach?

As the design above shows, the 10K NTC is implemented, will there be a issue with this?

0 Diana Bodenmiller over 8 years ago in reply to SHYAM THILLAINATHAN

TI__Prodigy 640 points

Shyam,

I am getting a second opinion regarding your specific thermistor setup. Thank you for your patience.

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

Thank you so much for the reply. I appreciate your effort, will it be possible to get a feedback by EOD today, since this design is going to FAB by EOD today.

0 Diana Bodenmiller over 8 years ago in reply to SHYAM THILLAINATHAN

TI__Prodigy 640 points

Shyam,

I am very sorry we missed your deadline.

Your thermistor set-up should be alright. Placing thermistor as close as possible to battery will allow best performance.

And if you did want to enable TS feature, you can expect your Low temperature CHG pending and High temperature CHG disable (mV) will differ somewhat from the datasheet, and can be calculated using the values for the ERT-J0EG103FA.

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

Thank you so much for the feedback. Will it be possible to get TS (Low temperature CHG pending and High temperature CHG disable (mV)) values for ERT-J0EG103FA. This way we can take a educated decision.

0 Diana Bodenmiller over 8 years ago in reply to SHYAM THILLAINATHAN

TI__Prodigy 640 points

Hello Shyam,

Yes, I calculate the Low temperature CHG pending (VTS-0C) to be 1411 mV and the High temperature CHG disable (VTS-45C) to be 245 mV for the ERT-J0EG103FA.

In the datasheet they are 1250mV and 275 mV. However, I recalculated these using values from the recommended thermistors (SEMITEC 103AT-2 or Mitsubishi TH05-3H103F), and they are somewhat different.
Please compare to Low temperature CHG pending of 1360 mV and High temperature CHG disable of 245 mV, rather than values listed in the data sheet.

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

Thank you, so my understanding is:

According to datasheet:
0 degree C: 1250mV
45 degree C: 275mV

For ERT-J0EG103FA:
A little higher than 0 degree C: 1411mV
A little higher than 45 degree C: 245mV

For SEMITEC 103AT-2 or Mitsubishi TH05-3H103F:
A little lower than 0 degree C: 1360mV
A little higher than 45 degree C: 245mV

Would like to validate my understanding. Since there is no actual temperature margins mentioned here, it would be great if I can get a temperature range of operation for ERT-J0EG103FA.

0 Diana Bodenmiller over 8 years ago in reply to SHYAM THILLAINATHAN

TI__Prodigy 640 points

Shyam,

All the values listed above correspond to 0 and 45 degrees C.

Good question. Since we have to recommend a temperature range based on the data sheet, the temperature range for ERT-J0EG103FA should be 2.7 - 41.6 degrees C

(these values correspond to 1250 mV and 275 mV for the ERT-J0EG103FA)

0 SHYAM THILLAINATHAN over 8 years ago in reply to Diana Bodenmiller

Prodigy 220 points

Hi Diana,

This is great. This is exactly what we were looking for. Thanks for the information. Much appreciated for the help and the patience.

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BQ21040: Review of the implemented design