BQ79616: NTC must be isolated from GND by 10 ohms

Alex Wu

Part Number: BQ79616

Tool/software:

Hi TI Expert

Our design used two TMUX1308 devices to multiplex 16 Negative Temperature Coefficient (NTC) thermistors to one BQ79616 or BQ79718.
We found in the BQ79718 circuit that the NTC must be isolated from GND by 10 ohms.
For this situation , we need layout routing independent trace on cell FPC for NTC GND ,what is the reason for this design?

11 months ago

0 Benjamin Luty 11 months ago

TI__Expert 6770 points

Alex,

I am unfamiliar with the design that you are talking about. Could you provide the documents that you are referencing?

Regards,

Ben

0 Alex Wu 11 months ago in reply to Benjamin Luty

Prodigy 140 points

CSU_sch_E1.PDF

Hi Ben,

Please refer to the attachment and

The following link talks about our design architecture

e2e.ti.com/.../bq79616-ntc

0 Benjamin Luty 11 months ago in reply to Alex Wu

TI__Expert 6770 points

Alex,

Looking at the schematic, it seems like the resistors are there to help protect the GPIO pins. If you were to actually connect the jumpers in J23, you could "turn off" the temperature sensing by grounding the GPIO pin. However, it is not recommended to let the GPIO pins measure below 0 V, so the resistor keeps the pin just above zero volts to allow for any fluctuation in the system.

I am not sure why the J23 jumpers are necessary, as they are not normally on our EVMs. The use case is probably specific to the engineer who created it.

Regards,

Ben

Power management

Power management forum

BQ79616: NTC must be isolated from GND by 10 ohms