BQ25120A: TS fault error

Hi Jenitt,

It appears that the TS voltage detected is above or below the TS warm and TS cool voltage thresholds, though this is being read at 25C. Can you confirm your NTC's properties (Beta value and calibrated resistance) so that I can calculate the expected behavior across temperature?

If you force a voltage on TS you shouldn't see any TS fault between 20.8% of VIN and 35.4% of VIN. Can you confirm this is the case on your charger?

Best Regards,

Juan Ospina

Hi Juan, 

Thank you for your prompt response.

Above is the Electrical characteristics for B-Value 
Calibrated resistance are RHI=30k and RLow=64.9K and NTC=10K

Case-1
                         We removed NTC and used Fixed 10k Resistor 
But we still see the Fault state i.e.. 0x02h =e8 or a8 and TS Pin we see voltage variation between 0.2v to 0.9v or Greater than 1.8V

Case -2
We mounted NTC Outside our board and connected using a wire (suspected NTC Issue but not)
But we still see the same fault state and TS Pin we see voltage variation between 0.2v to 0.9v or Greater than 1.8V

Case-3
We tried disabling the TS using Register change 0x02h(7th bit) here We removed ntc 10k DNM and mounted only Rhi=30k and Rlow=68.1K(voltage calculated divider output should be 3.44v and VIN=5v) But we see voltage varying from 3v to 4v. TS is disabled but there is voltage variation at TS pin point. 

Case-4
We tried disabling TS pin by only resistors(Rhi=30k and Rlow=68.1K expecting output of divider be 3.44v which is more than 60% of Vin)NTC is DNM
But we see voltage here at the varying from 3v to 4v.

Can you please go through the above cases and please let us know what might the issue ? 


Thanks, 
Muhafeez

Hi Muhafeez,

The TS pin only has voltage sampling circuitry so voltage variation is due to your pull up rail (VIN) and resistor values. Can you share a waveform of VTS and your Input voltage as well?

Best Regards

Hi Juan,

Thanks for your reply, 
Please find attached waveforms-


Green- VTS PIN(500mV/Div)
Yellow- 5v VIN(1V/Div)

Our Vin is regulated and it is stable at 5V and resistor(Rhi=24.9k and Rlow=40.2K with NTC 10K) we also checked the resistor values and We removed thermistor mounted Fixed 10K, The Behavior is same. 
We notice VTS Drop from 1.26V to 300mV after keeping the device on and in charging state for 15 mins 
We suspect something is going wrong on BQ25120A TS. 

Kindly Let us know your inputs and suggestions.  

Thanks, 
Muhafeez 

Hi Juan, 

Any update? Can you please let us know?


Thanks,
Muhafeez

Hi Mahesh,

Apologies for the delay. The VTS behavior is certainly unexpected since voltage at TS should be purely determined by your VIN and the resistors used across the resistor divider. The BQ25120A should not be exerting any kind of voltage or current on the TS pin, only sampling the voltage. This is especially unexpected with a fixed resistor since voltage should never really change. If there are no other paths to this node via which this it can be biased, and if there isn't a possible soldering or contact issue then I would suspect the device may be damaged. 

Is this behavior you are seeing on multiple devices and boards?

Best Regards,

Juan Ospina

Hi, 

We have cross checked  the board and there is no issue with soldering. All boards  are assembled at PCB SMT factory only. 

Also noted this in  issue  multiple boards. 

Hi Mahesh,

Are you able to have IC's re-balled and soldered? I'd like to check this behavior with one of these units on an EVM to confirm that it is something caused by the ICs. 

Best Regards.

Hi, 

Now onwards I am taking responsibility of this case. 

IC's re-balling is not possible at my SMT assembly house because of limitation. Moreover, soldering more than two times is not possible because, the Rigid flex PCB thickness is 0.4MM only. 

For do failure analysis, we had shipped ICs ( 2 nos) to Texas Instruments, Germany. 

In between, I have one query.

1. What is the current consumption of BQ25120A TS pin? 

2. With divider network resistors of 24.9K and 40.2K, the current allowed flow is =5V/65.1K =77uA only. Is this okay for TS pin functionality? 

Regards

Sudheer