SN74LVCC3245A: VOHB meaning

Motoyasu Hattori

Genius 10965 points

Part Number: SN74LVCC3245A
Other Parts Discussed in Thread: SN74LVC8T245

Hi,

Customer thinks the following.

On the case of IOL=-24mA, VCCA=2.7V, VCCB=4.5V, VOHB is Min 3.2V.

This means that High output voltage is only increased by 3.2V (Min case) under the above condition.

In other words, Vob does not reach 4.5V for long time later under the above condition.

Is it correct?

Thanks and best regards,
M.HATTORI.

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316760 points

When the output pin outputs a high signal, there is a P-channel MOSFET that connects the pin to V_CC. The V_OHB specification tells you that, when drawing 24 mA out of the pin, the voltage at the pin is at least 3.2 V. This means that the voltage drop over the transistor is at most 1.3 V, i.e., its R_DS(on) is at most 54.2 Ω.

The actual V_OH is likely to be higher than the minimum V_OH, and stays pretty much constant for a specific current and temperature.

Also see [FAQ] What is the output voltage (VOH or VOL) when the output current is X or the supply voltage is Y?

0 ShreyasRao over 5 years ago in reply to Clemens Ladisch

TI__Guru 62080 points

Hattori san,

Agree with Clemens on this. Datasheet guarantees a minimum high level under the loading conditions. if the loading decreases, the Voh will tend to reach the Vcc level.

Please refer to http://www.ti.com/lit/an/szza036c/szza036c.pdf for more on various datasheet parameters.

You could also consider SN74LVC8T245 as this device has dual Vcc rails across 1.65 to 5.5V.

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SN74LVCC3245A: VOHB meaning