Cmos output current flow back

Matth. B.

Other Parts Discussed in Thread: SN74LVC574A

Hello,

For an application, I want to use a SN74LVC574A component. This component will be connected with another one which have differents threshold.

Before to use level shifter or some discret component in interface, I would like to konw why connections like below doesn't work?

The idea is that when the LVC is driving a high level, the Pmos is closed and so voltage at the input of the other IC is 6.65V (between both resistors).

So, it will be a current flow back to the LVC but is this current will damage the Pmos at the output of the LVC?

It is the case, why? is it because output stage is not like a real Pmos?

Thanks

Regards

over 7 years ago

0 Daniel Hartung over 7 years ago

TI__Mastermind 22145 points

Hey Matthieu,

The picture of your connections hasn't seemed to load. To fix this problem you will likely have to re comment. You can add pictures by going to the bottom right of the textbox you use to reply and "Use rich formatting". After that you will have to upload the picture using the paperclip and uploading the picture. Copy paste unfortunately does not work.

Thanks,

Daniel

0 Matth. B. over 7 years ago in reply to Daniel Hartung

Expert 1135 points

Ok thanks, it's right now.

0 Clemens Ladisch over 7 years ago

Guru 243910 points

This device does not have clamp diodes to V_CC.

In any case, the recommended operation conditions do not allow any output to go above V_CC, so even if the device is not damaged, there is no guarantee that it actually works.

0 Matth. B. over 7 years ago in reply to Clemens Ladisch

Expert 1135 points

Thanks Clemens

Just for my knowledge,

So I assume that the output PMOS is not like a simple PMOS, right? Because with a simple PMOS, I think these connections could work.

Regards

0 Clemens Ladisch over 7 years ago in reply to Matth. B.

Guru 243910 points

The transistors on a chip are tiny. If they need to withstand voltages higher than V_CC, they (and all the protection circuits) must be designed for that.

0 Matth. B. over 7 years ago in reply to Clemens Ladisch

Expert 1135 points

Ok thanks for your support, I'll add a level shifter stage in my design.

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Cmos output current flow back