TPS7A7100: Controlled by PCA9536

Lars Tischendorf

Part Number: TPS7A7100
Other Parts Discussed in Thread: PCA9536, PCA9557

I will controlled the output voltage of TPS7A7100 by i2c iio expander. Discribed in App Note:

http://www.ti.com/lit/an/sbva035a/sbva035a.pdf

I will switch between 1.2 and 1.8V.

So I have connect 100mV and 400mV of TPS7A71000 direct to ground. And 50mV, 1.6V leaved open. 200mV and 800mV connect to i2c IO expander.

If now I configure port P1 or P2 as input (high impedance), the output voltage is 0.0V instead of 1.0V

If P1 and P2 configure as output ('0'), the output voltage is 2V - correct.

if P1 is input and P2 is output, the Vout is 1V instead of 1.8V.

if P1 is output and P2 is input, the Vout is 0V instead of 1.2V.

What can be the problem?

Is the input impedance of PCA9536 not high enough? The app note is for PCA9557.

over 5 years ago

0 Lars Tischendorf over 5 years ago

Prodigy 110 points

0 Ryan Eslinger over 5 years ago in reply to Lars Tischendorf

TI__Guru 55940 points

Hi Lars,

Could you provide a scopeshot with Vin, Vout, 200mV, and 800mV? I am especially curious what the voltage is on the ANYOUT pins. Is it possible that these pins are being driven to a voltage rather than being high impedance?

Very Respectfully,
Ryan

0 Lars Tischendorf over 5 years ago in reply to Ryan Eslinger

Prodigy 110 points

0 Lars Tischendorf over 5 years ago in reply to Ryan Eslinger

Prodigy 110 points

" Is it possible that these pins are being driven to a voltage rather than being high impedance?"
This pins are only driven by PCA9536. I think, that the problem is from PCA9536.
If I remove the PCA9536 and place R1109 or R1110, than it works. But is not longer programable.

0 Ryan Eslinger over 5 years ago in reply to Lars Tischendorf

TI__Guru 55940 points

Hi Lars,

I agree with your conclusion that the issue seems to be tied to the PCA9536. It seems that the outputs are not truly high impedance when you need them to be and are therefore affecting the resistor divider. As you noted we used PCA9557 for our proof of concept. Is it possible for you to switch to PCA9557 for your application?

Very Respectfully,
Ryan

0 Lars Tischendorf over 5 years ago in reply to Ryan Eslinger

Prodigy 110 points

I will not switch to PCA9557. This IC is to big and I do not trust in the functionality with the TPS7A7100. For datasheets of PCA9536 and 9557 are no differences in functionality. I will go another way for my application.

Thank you

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TPS7A7100: Controlled by PCA9536