SN74LVC1G34: Ioff function

masahiko shimizu

Part Number: SN74LVC1G34

Hi,

My cusotmer is using SN74LVC1G34 in below circuit.
Customer want to avoid to pump VccB when VccB is not supplied.
But customer has a issue of pump of VccB after VccB power down.
We think that VccB is pumped by source current from VccA.
Can SN74LVC1G34 do Ioff when the slope of power down VccB voltage is gentle?

Best reagrds,
Shimizu

over 6 years ago

0 Emrys Maier over 6 years ago

TI__Guru* 96591 points

Hello Shimizu-san,
The SN74LVC1G34 does not have positive input clamp diodes, so there is no path for the input at 1A to drive the VccB pin. Perhaps there is a different cause for the issue?

0 masahiko shimizu over 6 years ago in reply to Emrys Maier

Guru 11235 points

Hi Emrys,

Thank you for your reply.
How about is the case of using input-line to MCU as below?

Best regards,
Shimizu

0 Emrys Maier over 6 years ago in reply to masahiko shimizu

TI__Guru* 96591 points

Hello Shimizu-san,
When VccB = 0V, the SN74LVC1G34's output will go into a high-impedance mode. That means the input to the MCU will register 5V.

This is not true if VccB is not 0V -- for example, if VccB were turned off but still had ~1V for some reason, then the device would try to operate at 1V. and the output would either drive to 0V or 1V depending on the value at the input.

0 masahiko shimizu over 6 years ago in reply to Emrys Maier

Guru 11235 points

Hi Emrys-san,

If pull-up resistor is removed from board, this issue doesn't occur.
But If pull-up resistor is mounted in board, this issue occur.

Can SN74LVC1G34 be used with pullup at outline?

Best regards,
Shimizu

0 Emrys Maier over 6 years ago in reply to masahiko shimizu

TI__Guru* 96591 points

Can you get a scope shot of VccB and the output when this is happening both with and without the pull-up resistor?

I think that the VccB pin is not being driven to 0V, so the device's Ioff protection is not being turned on.

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SN74LVC1G34: Ioff function