PCA9306: PCA9306 2.9V coming at lower side even after removing the pullup

HARI T O1

Expert 1645 points

Part Number: PCA9306

Dear Team,

Below is my schematic for PC9306.The high side is connected to 5V and it is going to an Arduino Nano.

SDA from our ASIC is coming to J113(SMA Connector Marked in RED) .The voltage at this side is 2.9V.

I removed all the pull ups connected to SDA.

5V side is R3,R4,R5 and low voltage side is R6,R7,R8.

What I onserved is even after removing the pull ups from both side the lower side am observing a voltage of 2.9V at SD1.(Low voltage side).

May I know why.

Regards

HARI

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 316470 points

Yes, this device clamps voltages to VREF1. See [FAQ] How do the LSF translators work?

0 HARI T O1 over 2 years ago in reply to Clemens Ladisch

Expert 1645 points

Thank you..

But without pull-up how that clamping happens.

I am seeing this voltage after the pull-up removal

+1 Clemens Ladisch over 2 years ago in reply to HARI T O1

Guru 316470 points

This is explained in the application note linked from the FAQ. The gate voltage of the MOSFET between the SDA1 and SDA2 pins is just high enough to allow voltages between 0 V and 2.9 V to pass. When SDA1 tries to go higher than 2.9 V, the gate-to-source voltage of the MOSFET would become to small to allow any current. So the SDA1 output cannot float higher than 2.9 V.

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PCA9306: PCA9306 2.9V coming at lower side even after removing the pullup