PCA9546A: VOH levels

Vidhya J

Intellectual 475 points

Part Number: PCA9546A

Tool/software:

HI Team,

For PCA9546, what is the VOH and VOL level for I2C lines (with VDD=3.3V)?

Thanks and Regards,

Vidhya

3 months ago

0 Clemens Ladisch 3 months ago

Guru 288250 points

V_OL is specified (as test condition for I_OL). V_OH is determined not by the AND gate but by the pull-up resistor (if there is any), so the datasheet cannot tell you about it.

0 Nir Gilgur 3 months ago

TI__Genius 10205 points

Hello Vidhya,

I2C is an open drain protocol, so the mux doesn't output a high voltage signal. Instead it is determined by the PU resistors.

As Clemens mentioned, VOL can only be found as the test condition for IOL.

Thanks,

Nir

0 Vidhya J 3 months ago in reply to Nir Gilgur

Intellectual 475 points

HI Clemens, Nir,

VOL =0.4V for IOL 3mA to 7mA

VOL=0.6V for IOL 6mA to 10mA.

Our case, IOL is < 3mA. will consider VOL =0.4V

For VOH, Pull up voltage is 3.3V. will consider VOH=3.3V?

Please confirm.

Thanks,

Vidhya

0 Rami Mooti1 3 months ago in reply to Vidhya J

TI__Mastermind 28608 points

Hey Vidhya,

The VOH would be around 3.3V here. When your open drain output isn't driving low, you'll simply pull up the line to your Vpu.
You'll need to size the pullup appropriately though. See I2C Bus Pullup Resistor Calculation

So for example here at 1mA IOL and 0.4V VOL, with Vpu of 3.3V your minimum pullup would be (3.3-0.4)/0.001 = 2.9kohms. That would be the strongest pullup resistor you can use. If you start going higher, you'll likely struggle pulling the line low in your logic low driving conditions

Thanks,
Rami

0 Vidhya J 3 months ago in reply to Rami Mooti1

Intellectual 475 points

Thanks Rami

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PCA9546A: VOH levels