ST2189 datasheet(6/21 Pages) STMICROELECTRONICS

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Supplementary notes

ST2189

6/21

Doc ID 15918 Rev 1

Supplementary notes

3.1

Driver requirement

It must be ensured that the driver is able to source and sink a minimum of 1mA current on

both sides of the device. The device requires the driver to source/sink a maximum current of

(VCC/4) mA to/from the weak 4 kΩ output buffer in order to change the state of the output.

3.2

Load driving capability

To support the level translation without direction pin architecture, the one-shot transistor at

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

turned OFF, only the 4 k

Ω pull-up/down resistor maintains the state of the output. As a

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

Ω is not recommended.

3.3

Ensuring low current consumption during off state

The OE pin can be tied to the enable signal which is driving the enable pin of the slave

device to ensure that the device will turn off and put all I/Os to tri-state mode whenever the

slave device is not needed. On the event that the enable signal driving into the slave device

is active low, the signal going into the OE pin for ST2189 (active high) needs to be inverted

accordingly.

Alternatively, a pull-down resistor can be added to the VCCB supply. This will ensure that the

VCCB supply does not float whenever the supply is turned off. All the I/Os go to high

impedance automatically when this happens.

3.4

Truth table

Table 3.

Truth table

Enable

Bidirectional Input/Output

I/OVCCB

I/OVCCA

H(1)

High level VCCA power supply referred.

H(2)

High level VCCB power supply referred.

H(1)

High-Z(3)

Z = High impedance.

High-Z(3)

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