ST2149B

Supplementary notes

Doc ID 023310 Rev 1

9/23

4

Supplementary notes

4.1

Driver requirement

For proper operation, the driver from each side of the device must be able to source and

sink a minimum of 1 mA current. The device architecture requires the driver to source/sink

4.2

Load driving capability

To support the architecture that allows level translation without the direction pin, the

one-shot transistor is turned ON only during state transition at the output side. After the

one-shot transistor is turned OFF, only the 4 k

Ω resistor maintains the output logic state.

So, a resistive load or pull-up resistor less than 50 k

Ω is not recommended for proper

operation.

4.3

Truth table

Table 3.

Truth table

Enable

Bi-directional input/output

OE

1.

2.

H(1)

H(1)

LL

3.

Z = high impedance.

Z(3)