About SN74HC595 output status after power on

Bell Ye

Other Parts Discussed in Thread: SN74HC595

Hi Apps team,

Could you kindly help on the below questions, please? Many thanks!

We are using TI SN74HC595 (shift register) in our design, and we connect OE_L to GND directly, want to check with you what’ the output status after power on, will they have a low output after power on? Since we are using the HC595 to control some power controller, so want to make sure HC595 has a low output.

regards,

Bell

over 8 years ago

0 Clemens Ladisch over 8 years ago

Guru 283700 points

As shown in the timing diagram, the state after power on is undefined. Even with SRCLR, an RCLK edge is required.

0 Dennis Eichmann over 8 years ago in reply to Clemens Ladisch

Guru 74080 points

Agree to Clemens, although my personal experience is all outputs low after startup, never seen anything different so far for the 595. But you cannot rely on that, of course, especially when having some power switching connected to the outputs.

0 ShreyasRao over 8 years ago in reply to Dennis Eichmann

TI__Guru 58720 points

Bell ,

please refer to the app note on power up behavior of clocked devices. Unless there is a valid input , the output is undefined / indeterminate.
www.ti.com/.../scha005a.pdf

0 Bell Ye over 8 years ago in reply to ShreyasRao

TI__Intellectual 1135 points

Hi,

Thanks for all of your answers. Now this question is clear to me. Thank you!

regards,
Bell

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About SN74HC595 output status after power on