SN74LXC8T245: SN74LXC8T245, Unwanted spike on power on time on I/O

Hardik Sheth

Prodigy 10 points

Part Number: SN74LXC8T245

Tool/software:

Hi, Below is the my circuit with SN74LXC8T245.

1. VCCB ( 5V ) power one first.

2. After ~35 ms VCCA ( 3.3 ) Power ON )

What we observed that initial spike on I/O which are on VCCB power rail while VCCA ( 3.3V ) not power on. Datasheet mentioned that there is no need for power on sequence but still we are getting initial spike on I/O with VCCB power rail.

Sample Schmatic

Any suggestion or correction in my circuit, please help.

Regards,

Hardik

4 months ago

0 Joshua Salinas 4 months ago

TI__Mastermind 23020 points

Hello Hardik,

Just to clarify, are you observing spikes on A-port or B-port I/Os? This type of issue generally happens when we power up the internal output buffers before the input buffers. There is a possibility spikes will be observed when data flows from A -> B (DIR = H) and VCCB powers up.

The glitch-free power sequencing feature, however, should eliminate these types of spikes. Are the I/Os being driven or pulled-up to the supply?

Regards,

Josh

0 Hardik Sheth 4 months ago in reply to Joshua Salinas

Prodigy 10 points

Hi Joshua,

We are observing the spike on Port B' I/O. VCCB power on first while VCCA after 30ms.

Regards,

Hardik

0 Joshua Salinas 4 months ago in reply to Hardik Sheth

TI__Mastermind 23020 points

Hello Hardik,

Can you confirm if I/Os are pulled-up to the supply?

Regards

Josh

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SN74LXC8T245: SN74LXC8T245, Unwanted spike on power on time on I/O