SN74AHC245: Schematic detail of SN74AHC245PWR

Kento Sato

Intellectual 850 points

Part Number: SN74AHC245

Hi team,

I have some questions on the schematic of SN74AHC245PWR datasheet.

Are there any diodes inside of IC between input and power?
Are there any protestation inside of IC? Or need to restrict the input current?
If none of any protestation inside of IC,
- How much is the current limit (mA)?
- Do you recommend to use an external diode?

Best regards,

Kento

over 3 years ago

0 Emrys Maier over 3 years ago

TI__Guru* 96752 points

Hello Sato-san,

The diode can be determined as explained here:

[FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?

The answer is: no, there is no diode between the input and Vcc.

I don't know what you mean by "protestation" -- but if you mean a current limiter, no the device does not include any internal current limiting. The current limits are listed in the datasheet absolute maximum ratings table.

If you'd like to get my recommendation regarding external diodes, I will need to know about the application.

0 Clemens Ladisch over 3 years ago

Guru 276480 points

When the input voltage goes above V_CC, no current flows, so no external current limiting is needed.

If the input voltage goes above the absolute maximum rating (7 V), the device might get damaged. The only way to prevent this would be to clamp the voltage, for example, with a diode (and current limiting to protect this diode).

Logic

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SN74AHC245: Schematic detail of SN74AHC245PWR