Vref_A

VCCB

EN

200 k

A1

A2

B1

B2

GND

LSF0108-Q1

Vref_B

3.3 V

Device

3.3 V

RB1

0.1 μF

1.8 V

Device

1.8 V

VCCA

B8

A8

.

.

.

.

.

.

Figure 8-3. Up Translation Example Schematic with Push-Pull and Open Drain Configuration

Up translation with the LSF requires attention to two important factors: maximum data rate and sink current.

Maximum data rate is directly related to the rising edge of the output signal. Sink current depends on supply

values and the chosen pull-up resistor values. Equation 1 shows the maximum data rate formula, and Equation

2 presents the maximum sink current formula, both of which are estimations. A low RC value is needed to reach

high speeds, which also require strong drivers. For estimated data rate and sink current calculations based on

circuit component, see the Up Translation with the LSF Family video.

1

3 × 2RB1CB1 =  16RB1CB1  bitssecond

(1)

IOL ≅ VCCARA1+ VCCBRB1 A

(2)

Down Translation: When the signal is being driven HIGH from the Bn port to An port, the switch will be OFF,

clamping the voltage on the An port to the voltage set by Vref_A. A pull-up resistor can be added on either side

of the device. There are special circumstances that allow the removal of one or both of the pull-up resistors. If

the signal is always going to be down translated from a push-pull transmitter, then the resistor on the B-side

can be removed. If the leakage current into the receiver on the A-side is less than 1 µA, then the resistor on

the A-side can also be removed. This arrangement, with no external pull-up resistors, can be used when down

translating from a push-pull output to a low-leakage input. For an open drain transmitter, the pull-up resistor on

the B-side is necessary because an open drain output cannot drive high by itself. Table 9-2 lists a summary

of device operation. For additional details on the functional operation of the LSF family of devices, see the Up

Translation with the LSF Family and Down Translation with the LSF Family videos.

LSF0108-Q1

SDLS967E – MAY 2016 – REVISED NOVEMBER 2022

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