# SN74AVC2T244: VOH and VOL

Part Number: SN74AVC2T244

Hello Experts,

I would like to understand VOH and VOL at VCCA=1.8V/VCCB=3.3V condition. According to datasheet, VOH and VOL vary by output current and power supply voltage. How can I understand VOH/VOL? VOH(min)=VCCB-2V, VOL(max)=0.2V even if output current is not 500uA?

Best Regards,
Fujiwara

• The test conditions show the maximum current at which the behaviour is guaranteed. At a fixed supply voltage, the output resistance is constant, so for currents that are smaller than the test condition, the voltage drop also is smaller by the same factor. See [FAQ] What is the output voltage (VOH or VOL) when the output current is X or the supply voltage is Y?

• The FAQ is one power supply voltage but SN74AVC2T244 has two power supply voltage, VCCA and VCCB. To calculate VOH and VOL, VCCA voltage need to be considered? Or it considers VCCB voltage only?
If it need to consider VCCB only, below calculation is reasonable?
[conditions]
VCCA=1.8V, VCCB=3.3V, Iout=20mA

[VOH]
used condition: IOH = –24 mA; VI=VH.
Output resistance: (3.0V-2.2V)/24mA=33.3ohm.
Voltage drop: 33.3ohm x 20mA=0.67V
VOH: 3.3V-0.67V=2.63V
[VOL]
used condition: IOH = 24 mA; VI=VH.
Output resistance: 0.55V/24mA=22.9ohm.
VOL: 22.9ohm x 20mA=0.46V

Best Regards,
Fujiwara

• The voltages at the outputs are independent from the input supply voltage.

Your calculations are correct. (The specified values are for the worst case; the typical output resistance might be roughly half that.)