SN74HCS09: Different Output Pull-up Voltage

Jejomar Ildefonso

Part Number: SN74HCS09

Hi Team,

Would it be fine to use different output pull-up voltage for the channels of SN74HCS09? We are currently using SN74HCS09 with 5V Vcc.

Three of its channels will be receiving signals with 3.3V level. Output pull-up will be at 3.3V. While the other channel would also receive 3.3V levels, but with an output pull-up at 1.8V. Would this work?

Thanks in advance!

Kind Regards,

Jejomar

over 2 years ago

+1 Sebastian Muriel over 2 years ago

TI__Genius 13620 points

Hi Jejomar,

Yes this will work. Since this device has positive clamp diodes as long as the output voltages are less than or equal to Vcc, the device will function correctly.

Regards,

Sebastian

0 Jejomar Ildefonso over 2 years ago in reply to Sebastian Muriel

TI__Expert 8590 points

Hello Sebastian,

Many thanks! Just a follow-up question, what would be the device's output (Y) state if the inputs (A and B) are as follows?

A	B	Y
Z	H	?
H	Z	?
Z	Z	?

Z = High Impedance

Kind Regards,

Jejomar

+1 Clemens Ladisch over 2 years ago in reply to Jejomar Ildefonso

Guru 243220 points

CMOS inputs always have a high impedance.

If you are not driving an input, it is floating, and its voltage is random. This can have bad effects; see [FAQ] How does a slow or floating input affect a CMOS device?

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SN74HCS09: Different Output Pull-up Voltage