SN74LS244: Input and output impedance range

[FAE] Andrew Wang

Part Number: SN74LS244

Hi Team,

Customer is asking for device input.output impedance range of this device, can any expert help? Please help to correct or add if I miss anything.

Thanks.

VOH: (max & typ)

In Sat Region: Ro (min): VOH min / IOH max = 2V / 15mA = 133.3 Ω

In Active Region: Ro (typ): VOH typ / IOH typ = 3.4V / 3mA = 1133 Ω

VOL: (max)

In Sat Region: Ro (max): VOL max / IOL max = 0.5V / 24mA = 20.8 Ω

In Active Region: No Info.

VIH: (max)

Vi / IIH (max) = 2.7V / 20uA = 135K Ω

VIL: (max)

Vi / IIL (max) = 0.4V / 0.2mA = 2K Ω

Andrew

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 300430 points

Dividing the voltage drop by the current works only if the output behaves like a resistor, which is the case for MOSFETs in CMOS devices, but not necessarily for the BJTs used in LS family devices. And for high logic levels, the voltage drop is V_CC − V_xH.

The typical input and output impedances can be derived from the slope of the curves in figures 2 and 17 of Input and Output Characteristics of Digital Integrated Circuits at 5-V Supply Voltage:

For the input and output circuits, see figures 19 and 21 in the datasheet.

What is the actual problem the customer is trying to solve? For bipolar devices, the I/Os are usually characterized by their drive strength, i.e., the current.

0 [FAE] Andrew Wang over 5 years ago in reply to Clemens Ladisch

TI__Genius 10685 points

Thanks a lot! -)

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SN74LS244: Input and output impedance range