7.3.2 VBIAS/ Enable

To enable the I/O pins, the VBIAS input should be referenced towards the lower power supply (in the following

example, VEXT,A) during voltage translation. To be in the high impedance state during power-up, power-down, or

during operation, the VBIAS pin must be pulled low and at GND or disabled by an open-drain driver without

a pullup resistor. Use the VBIAS pin to properly bias the I/O channels. A filter capacitor on VBIAS is also

recommended for a stable supply at the device.

1.8 V

A1

VBIAS

B1

3.3 V

A2

B2

0.1

F

1.8 V

VEXT,A

VEXT,B

1kΩ

1kΩ

Figure 7-1. VBIAS Tied to Lower Power Supply

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 7-1. Enable Pin Function Table

INPUT VBIASPIN

Data Port State

Tied directly to VBIAS

An = Bn

L

Hi-Z

7.4 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 7-1 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 7-2. 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 VEXT,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 VEXT,A and then pulled up to the VEXT,B

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 VEXT,A for additional current drive capability or may also be pulled above VEXT,A with a pullup resistor.

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

LSF0002

SDLS975 – APRIL 2024

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