ST2349 datasheet(7/23 Pages) STMICROELECTRONICS

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ST2349

Supplementary notes

7/23

Supplementary notes

3.1

Driver requirement

The ST2349 may be driven by an open drain or totem pole driver and the nature of the

device’s output is “open drain”. It must not be used to drive a pull-down resistor since the

impedance of the output at HIGH state depends on the pull-up resistor placed at the I/Os.

As the device has pull-up resistors on both the I/OVCC and I/OVL ports, the user needs to

ensure that the driver is able to sink the required amount of current. For example, if the

settings are VCC =5.5 V, VL = 4.3 V and the pull-up resistor is 10 kΩ, then the driver must be

able to sink at least (5.5 V/10 k

Ω) + (4.3 V/10 kΩ)

= 1 mA and still meet the V

requirements of the ST2349.

3.2

Load driving capability

To support the open drain system, the one-shot transistor is turned on only during state

transition at the output side. When it drives a high state, after the one-shot transistor is

turned off, only the pull-up resistor is able to maintain the state. In this case, the resistive

load is not recommended.

3.3

Power off feature

In some applications where it might be required to turn off one of the power supplies

powering up the level translator, the user may turn off the VCC only when the OE pin is low

(device is disabled). There will be no current consumption in VL due to floating gates or

other causes, and the I/Os are in a high-impedance state in this mode.

3.4

Truth table

Table 3.

Truth table

Enable

Bi-directional Input/Output

I/OVCC

I/OVL

H (1)

High level VL power supply referred

H (2)

High level VCC power supply referred

H(1)

Z (3)

Z = high impedance

Z(3)

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