SN74HCS14: higher input voltage than VCC

Koji Ikeda

Part Number: SN74HCS14
Other Parts Discussed in Thread: SN74AHC14

Hello support team,

My customer ask if SN74HCS14 can accept 5.5V input voltage when VCC5V. Could you support?

Datasheet "Absolute Maximum Ratings" has notice (2), this looks like to allow Vi > VCC if the current keep less than 20mA. But, "Recommended Operating Conditions " shows Vi range is up to VCC, this looks like not to allow Vi >Vcc....

SN74AHC14 also has same notice (2) on "Absolute Maximum Ratings", but, Vi range is up to 5.5V, not VCC, this looks like to allow Vi >VCC (of cause, if less than 20mA

Thanks,

Koji Ikeda

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 244220 points

When you do this with the HCS device, a current flows from the input into V_CC. (See [FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?) That current must be limited, and the power supply must be able to sink the current (which often is not the case).

The AHC device does not have a current path to V_CC. (The input clamp current rating is for negative voltages.)

0 Koji Ikeda over 2 years ago in reply to Clemens Ladisch

TI__Expert 5335 points

Hello Clemens-san,

Thank you for your support. Do you mean that you recommend AHC device for their usage? Or if current flow is below 20mA from input to VCC, can HCS accept their usage?

Thanks,

Koji Ikeda

+1 Clemens Ladisch over 2 years ago in reply to Koji Ikeda

Guru 244220 points

Yes, just use the AHC device.

Logic

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SN74HCS14: higher input voltage than VCC