LSF0108: The leakage current is observed when the EN pins are not connected to a pull-up resistor

Yu-Jen Lin

Part Number: LSF0108

Hi There,

I am aware of the requirement that Vref_B during operation and both pins must be pulled up to the HIGH side (VCCB) through a bias resistor (typically 200 kΩ). However, I am curious about why the same requirement applies to the enable pin. As per my understanding, the EN pin should be connected to the MOS gate, which should eliminate any leakage without a pull-up resistor. However, we encountered an issue where there appears to be leakage when we pull the EN pin high without the resistor. Could you please provide the reason behind this?

Thanks,

Louis

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 316700 points

You are correct that no current flows into or out of the EN pin. The EN pin must be connected to Vref_B so that the gate voltage is correct, at Vref_A + V_GS(thr), so that the resulting output voltage is clamped at Vref_A.

When you pull EN higher, the pass transistors allow voltages higher then Vref_A, which makes correct level translation impossible.

See [FAQ] How do the LSF translators work?

0 Yu-Jen Lin over 2 years ago in reply to Clemens Ladisch

Prodigy 20 points

Thank you for the information. I have one more question: I'm curious to know if there is any body diode included as below ?

0 Clemens Ladisch over 2 years ago in reply to Yu-Jen Lin

Guru 316700 points

All MOSFETs have two body diodes. In general, one of them is shorted because the body is connected to the source, but in the LSF, the body is connected to GND, so you have two diodes from GND to the Ax/Bx pins.

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LSF0108: The leakage current is observed when the EN pins are not connected to a pull-up resistor