SN74HCS125: Input Threshold Voltage

Brian Wang0928

Part Number: SN74HCS125
Other Parts Discussed in Thread: SN74LV4T125, SN74AHCT125, SN74AHCT541, SN74AHCT1G125, TXU0104

We're looking for the 4ch buffer with VCC=5V, and the Input Voltage is from MCU 3.3V.

It looks SN74HCS125 is able to meet this requirement. But we'd like to double check with you the input threshold.

in the d/s, it says:

In the application, the 3.3V input (+/-5% tolerance) is applied to the buffer. Is this input threshold able to meet? Is the design margin of the input voltage good enough?

If it's not suited one, is there other device you suggest to use with this conditions?

over 3 years ago

+1 Emrys Maier over 3 years ago

TI__Guru* 97016 points

No, the SN74HCS125 will not support 3.3V input signals. The threshold of 3.15V (max) is measured at 4.5V supply. Increasing the supply will increase this value to 3.5V.

I would recommend using SN74LV4T125.

+1 Clemens Ladisch over 3 years ago

Guru 303640 points

For converting 3.3 V to 5 V, you can use any buffer with TTL-compatible inputs, such as the SN74AHCT125 or SN74AHCT541.

0 Brian Wang0928 over 3 years ago in reply to Emrys Maier

TI__Genius 13460 points

Hello Emrys,

Is there 3ch or 4ch buffer with TTL logic and the all inputs are at left side of the package and outputs are at right side of the package? It's better for the FMEA on the safety requirement. Very thanks.

0 Clemens Ladisch over 3 years ago in reply to Brian Wang0928

Guru 303640 points

All 3-channel and 4-channel buffers have the 'wrong' pinout (for historical reasons). You have the choice between one channel (SN74AHCT1G125) and eight channels.

If you also have a 3.3 V supply, you can use the TXU0104.

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SN74HCS125: Input Threshold Voltage