LSF0102: Vref_A power supply voltage changes when communication starts.

dai_sakamoto

Prodigy 90 points

Part Number: LSF0102
Other Parts Discussed in Thread: TS5A23157, SN74LVC2G66, TCA9543A

Please contact us by e-mail because the contents cannot be disclosed such as circuit diagrams.

over 1 year ago

0 dai_sakamoto over 1 year ago

Prodigy 90 points

As a rough outline of the application, I want to communicate individually with two units that have the same slave address, so I use two LSF0102 units and perform I2C communication while switching the EN signal.

The problem is that the voltage of Vref_A rises only during communication.

0 Clemens Ladisch over 1 year ago

Guru 268760 points

I cannot help you with your circuit without seeing the schematic.

The primary purpose of the LSF is to be used as a level translator.

If you just want to switch I²C devices, use an I²C switch like the TCA9543A (to control the switch through I²C), or a general-purpose 2:1 switch like the TS5A23157, or multiple general-purpose 1:1 switches like the SN74LVC2G66.

0 dai_sakamoto over 1 year ago in reply to Clemens Ladisch

Prodigy 90 points

Dear Clemens Ladisch

Could you please let me know your email address?
I will send you the password for the attached file.

There is a schematic and detailed documentation there.

0 Clemens Ladisch over 1 year ago in reply to dai_sakamoto

Guru 268760 points

The schematic as shown is wrong; EN must be connected to Vref_B, and the I2C_BUFFx_EN signals must be driven by open-drain outputs.

Check that the voltage at pin Vref_A is 3.3 V, and that the voltage at pins Vref_B and EN is roughly 0.6 V above Vref_A.

0 dai_sakamoto over 1 year ago in reply to Clemens Ladisch

Prodigy 90 points

Open-drain output, changed EN and V_refB to short. Communication was fine. Since the EN signal is open-drain, the rise time is slow, so it was possible to wait about 50ms before starting communication.

The 3.3V power supply stabilized the 3.3V waveform by changing the program so that EN is set to LOW immediately after communication ends. It seems that 3.3V of V_refA is affected when EN is HIGH. I don't know why.

+1 Clemens Ladisch over 1 year ago in reply to dai_sakamoto

Guru 268760 points

During normal operation, a small curent flows into Vref_B and out of Vref_A. (It is limited by the 200 kΩ resistor.)

To make startup faster, use a smaller capacitor at EN.

0 dai_sakamoto over 1 year ago in reply to Clemens Ladisch

Prodigy 90 points

I've got it. thank you very much.

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LSF0102: Vref_A power supply voltage changes when communication starts.