8.3.2 Output Enable

To enable the I/O pins, the EN input should be tied directly to Vref_B during operation and both pins must be

pulled up to the HIGH side (Vpu or VCCB) through a pull-up resistor (typically 200 kΩ). To ensure the high

impedance state during power-up, power-down, or during operation, the EN pin must be LOW. The EN pin

should always be tied directly to the Vref_B pin and is recommended to be disabled by an open-drain driver

without a pullup resistor. This allows Vref_B to regulate the EN input and bias the channels for proper translation.

A filter capacitor on Vref_B is recommended for a stable supply at the device.

1.8 V

Vref_A

VCCB

EN

200 kΩ

Vref_B

3.3 V

A1

B1

0.1 μF

Figure 8-1. Enable Pin Tied to Vref_B Directly and to VCCB Through a Pull-Up Resistor

The supply voltage of open drain I/O devices can be completely different from the supplies used for the LSF and

has no impact on the operation. For additional details on how to use the enable pin, see the Using the Enable

Pin with the LSF Family video.

Table 8-1. Enable Pin Function Table

INPUT EN(1) PIN

Data Port State

Tied directly to Vref_B

An = Bn

L

Hi-Z

(1)

EN is controlled by Vref_B logic levels.

8.4 Device Functional Modes

For each channel (n), when either the An or Bn port is LOW, the switch provides a low impedance path between

the An and Bn ports; the corresponding Bn or An port will be pulled LOW. The low RON of the switch allows

connections to be made with minimal propagation delay and signal distortion.

Table 8-1 provides a summary of device operation. For additional details on the functional operation of the LSF

family of devices, see the Down Translation with the LSF Family and Up Translation with the LSF Family videos.

Table 8-2. Device Functionality

Signal Direction(1)

Input State

Switch State

Functionality

B to A (Down Translation)

B = LOW

ON

(Low Impedance)

A-side voltage is pulled low through the switch to the B-side voltage

B = HIGH

OFF

(High Impedance)

A-side voltage is clamped at Vref_A (2)

A to B (Up Translation)

A = LOW

ON

(Low Impedance)

B-side voltage is pulled low through the switch to the A-side voltage

A = HIGH

OFF

(High Impedance)

B-side voltage is clamped at Vref_A and then pulled up to the Vpu#

supply voltage

(1)

The downstream channel should not be actively driven through a low impedance driver, or else bus contention may occur.

(2)

The A-side can have a pullup to Vref_A for additional current drive capability or may also be pulled above Vref_A with a pullup resistor.

Specifications in the Recommended Operating Conditions section should always be followed.

LSF0108

SDLS966L – DECEMBER 2013 – REVISED DECEMBER 2022

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