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LSF0101, LSF0102, LSF0108

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SDLS966G – DECEMBER 2013 – REVISED FEBRUAURY 2016

Product Folder Links: LSF0101 LSF0102 LSF0108

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Typical Application (continued)

(1)

Vref_A have to be the lowest voltage level across all of inputs and outputs.

Table 3. Application Operating Condition

PARAMETER

MIN

TYP

MAX

UNIT

reference voltage (A)

0.95

4.5

V

Vref_B

reference voltage (B)

Vref_A + 0.8

5.5

V

input voltage on EN pin

Vref_A + 0.8

5.5

V

Vpu

pull-up supply voltage

0

Vref_B

V

(1)

(2)

(3)

The 200 k

Ω, pull-up resistor is required to allow Vref_B to regulate the EN input. A filter capacitor on

signal integrity.

9.2.1.2 Detailed Design Procedure

9.2.1.2.1

Bidirectional Translation

For the bidirectional clamping configuration (higher voltage to lower voltage or lower voltage to higher voltage),

the EN input must be connected to Vref_B and both pins pulled to HIGH side Vpu through a pull-up resistor

(typically 200 k

Ω). This allows Vref_B to regulate the EN input. A filter capacitor on Vref_B is recommended. The

master output driver can be push-pull or open-drain (pull-up resistors may be required) and the slave device

output can be push-pull or open-drain (pull-up resistors are required to pull the Bn outputs to Vpu).

If either output is push-pull, data must be unidirectional or the outputs must be tri-state and be

controlled by some direction-control mechanism to prevent HIGH-to-LOW contentions in either direction.

If both outputs are open-drain, no direction control is needed.

In Figure 6, the reference supply voltage (Vref_A) is connected to the processor core power supply voltage.

When Vref_B is connected through a 200 k

Ω resistor to a 3.3 V Vpu power supply, and Vref_A is set 1.0 V. The

output of A3 and B4 has a maximum output voltage equal to Vref_A, and the bidirectional interface (Ch1/2,

MDIO) has a maximum output voltage equal to Vpu.

9.2.1.2.2

Pull-up Resistor Sizing

The pull-up resistor value needs to limit the current through the pass transistor when it is in the ON state to about

15 mA. This ensures a pass voltage of 260 mV to 350 mV. If the current through the pass transistor is higher

than 15 mA, the pass voltage also is higher in the ON state. To set the current through each pass transistor at 15

mA, to calculate the pull-up resistor value use the following equation:

Rpu = (Vpu – 0.35 V) / 0.015 A

(1)

Table 4 summarizes resistor values, reference voltages, and currents at 15 mA, 10 mA, and 3 mA. The resistor

value shown in the +10% column (or a larger value) should be used to ensure that the pass voltage of the

transistor is 350 mV or less. The external driver must be able to sink the total current from the resistors on both

sides of the LSF family device at 0.175 V, although the 15 mA applies only to current flowing through the LSF

family device.

15 mA

10 mA

3 mA

NOMINAL (

Ω)

Ω)

NOMINAL (

Ω)

Ω)

NOMINAL (

Ω)

Ω)

5 V

310

341

465

512

1550

1705

3.3 V

197

217

295

325

983

1082

2.5 V

143

158

215

237

717

788

1.8 V

97

106

145

160

483

532

1.5 V

77

85

115

127

383

422

1.2 V

57

63

85

94

283

312