sn74lvc2g04: What's the output logic when power down

Brian Wang0928

Part Number: SN74LVC2G04

What's the behavior for the output rail of the inverting logic when power VCC is shutdown (it means the VCC is dropping down to below UVLO threshold point)?

In the motor gate driver application, when there are some unexpected events happened, the VCC of the inverting logic should be connected to grounding to disable the gate driver.

Regards,

Brian

over 7 years ago

0 Clemens Ladisch over 7 years ago

Guru 275330 points

The datasheet says:

This device is fully specified for partial-power-down applications using I_off. The I_off circuitry disables the outputs, preventing damaging current backflow through the device when it is powered down.

As shown by the I_off specification in section 6.5, disabled outputs have high impedance.

0 Michael J Schultis over 7 years ago in reply to Clemens Ladisch

TI__Mastermind 24805 points

Hello Brian,

Clemens is correct. The outputs are disabled when the device is powered down.

Best,
Michael

0 Brian Wang0928 over 7 years ago in reply to Michael J Schultis

TI__Genius 12680 points

I'm a little confused with this.

You said that the output is disable with high impedance after power down. does it mean the output is floating or pull-down to grounding with high impedance.

In customer PWM motor application, we expected that the output behavior during power down is pulling dow to grounding via resistance. Please advice. thanks.

0 Clemens Ladisch over 7 years ago in reply to Brian Wang0928

Guru 275330 points

"High impendace" means "almost infinite impedance". At 5 V, the specified worst-case leakage current of 10 µA would imply a resistance of 500 kΩ, but the actual leakge current will be much smaller, so expect MΩ or GΩ.

For practical purposes, it is floating. (The stated purpose of the Ioff feature is to prevent any current from flowing.)

If you want to pull the output down, you have to add a pull-down resistor that is as strong as you want it to be.

0 Michael J Schultis over 7 years ago in reply to Clemens Ladisch

TI__Mastermind 24805 points

Brian,

Clemens is correct, it is essentially a floating node.

Best,
Michael

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sn74lvc2g04: What's the output logic when power down