ST2149B Supplementary notes
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 maximum current of (V
CC
/4) mA to/from the weak 4 k Ω output buffer.
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.
Table 3.
Truth table
Enable
OE
H
(1)
H
(1)
L
1.
High level V
L
power supply referred.
2.
High level V
CC
power supply referred.
3.
Z = high impedance.
I/O
VCC
H
(2)
L
Z
(3)
Bi-directional input/output
I/O
VL
H
(1)
L
Z
(3)
Doc ID 023310 Rev 1 9/23
