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SN7407: output low when POR

Gary Zeng
Intellectual 1810 points

Part Number: SN7407
Other Parts Discussed in Thread: SN74LS07

Hi team,

My customer is using SN7407. 

They use 5V pullup on input signals and 12V pullup on output signal.

SN7407 uses same 5V on VCC.

Now the issue is when 5V power up on both input signal and VCC pin. There will be a low on output.

mmexport1767664130934.jpginput VCC output.jpg

Yellow is input signal with 5V pull-up. Blue is 5V VCC for SN7407.

Green is output signal with 12V pull-up.

You can see there is a output low when SN7407 POR.

How to solve it? Is SN74LS07 helpful for it?

  • 0
    TI__Mastermind 31950 points

    Hi Gary,

    Unfortunately you might see this on most logic devices before the supply voltage hits the minimum recommended operating voltage, especially TTL/bipolar output devices due to the nature of that technology. The best way would be to use a CMOS output device, but we don't have any CMOS open-drain devices that support 12V outputs.

    For you solution, you will probably need a FET low side driver.

    Best,

    Malcolm