BQ51050B: TS/CTRL function

Florian Uhlich

Part Number: BQ51050B
Other Parts Discussed in Thread: PCA9536

Tool/software:

Ok, we have the BQ51050B in our design, however we coudn't get the TS/CTRL function to work properly.

Our goal is to control the TS pin from an external I/O pin, as we do already have a precision temperature sensor right next to the battery in our design.

So we connected the TS/CTRL pin to a 10k resistor to ground and have a connection from the TS/CTRL to our host output pin. However, the pin has a 100k internal pull up, that can't be disabled. Therefore, we added an additional external 100k resistor in the trace between the TS/CTRL pin and our output. With it, I achieve a voltage of 0.165V at the TS/CTRL pin, which is above the LOW treshold of 0.1V and below the high trheshold of 0.2V.

However, the power transmission doesn't start at all. If we cut the trace to our host, power transmission works as expected. I assume the resistor measurement is offset by our voltage, but how can we solve our problem?

2 months ago

0 Bill Johns 2 months ago

TI__Guru* 75676 points

Hi Florian

The problem may be TS sense circuit, which is a pulse every 240ms, see figure 31.

Can you send schematic for review?

0 Florian Uhlich 2 months ago in reply to Bill Johns

Prodigy 40 points

Hi Bill,

the TS/CTRL circuit looks like this:

When charging is enabled, the PCA9536 is configured as an input with 100k pull up. We need to be able to control charging as there are situations where charging should not happen. Does the TS mechanism measures the voltage directly at the TS/CTRL pin?

0 Bill Johns 2 months ago in reply to Florian Uhlich

TI__Guru* 75676 points

Hi Florian

Thanks for update, I am looking at this in the lab and will update you tomorrow.

0 Bill Johns 2 months ago in reply to Bill Johns

TI__Guru* 75676 points

Hi Florian

I am duplicating the problem in lab. Suspect the RX is sending EPT00 which is end power transfer unknown.

Something to try is increasing R6 to a higher value.

0 Florian Uhlich 2 months ago in reply to Bill Johns

Prodigy 40 points

Hi Bill,

thanks for the feedback. I think I finally understood the TS_CTRL pin, my circuit won't work. If the TS_CTRL is pulled high (higher than 0.1V it seems), the BQ51050B recognises it as a high input during the high-impedance phase and sends EPT unknown. If it's pulled down, it will sense a low value during the TS-measurement cycle. In my opinion, this is not clearly explained in the data sheet.

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BQ51050B: TS/CTRL function