LSF0108: Push Pull Driver into A1 with Voltage higher than VREF_A

Stephen Kennedy

Part Number: LSF0108

Hi,

I am working on a schematic where I am using a LSF0108 with VREF_B = 3.3 V and V_REF_A = 1.2 V.

I have a Push-Pull driven signal that could have high levels in the range 3.3-5.2 V, and I would like to connect this as an input to A1 and convert it to a 3.3V signal at B1.

I have watched the video 'Single Supply Translation with the LSF Family' - which has a situation where an input is higher than VREF_A and a resistor divider is used to create VREF_A; however it appeared that the signal in the video was an open drain signal with a pullup to a voltage higher than VREF_A.

My question is - is there a way to connect a 5.2 V push-pull input signal with VREF_A =1.2 V to convert it to 3.3 V on the B side?

Thanks for looking into it.

3 months ago

0 Clemens Ladisch 3 months ago

Guru 267510 points

Just connect it.

The pull-up voltages at the I/O pins are not required to be the same as the Vref voltages; the only restriction is that Vref_A must be the lowest voltage.

0 Stephen Kennedy 3 months ago in reply to Clemens Ladisch

Prodigy 30 points

This is a push-pull driven signal, there is no pull-up resistor. The device will drive 5V into pin A1 with low impedance output.

0 Clemens Ladisch 3 months ago in reply to Stephen Kennedy

Guru 267510 points

It makes no difference whether the high voltage comes from a pull-up resistor or from an active output.

The LSF is a passive, analog switch; for voltages of Vref_A and higher, the switch is open, and the pin is high impedance.

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LSF0108: Push Pull Driver into A1 with Voltage higher than VREF_A