-1

0

1

2

3

4

0

50

100

150

200

250

300

350

400

450

500

Time (ns)

Input

Output

14

LSF0101, LSF0102, LSF0108

SDLS966H – DECEMBER 2013 – REVISED JUNE 2019

www.ti.com

Product Folder Links: LSF0101 LSF0102 LSF0108

Submit Documentation Feedback

Copyright © 2013–2019, Texas Instruments Incorporated

(1)

(2)

(3)

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 bus contention in either

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

When Vref_B is connected through a 200-k

Ω resistor to a 3.3-V Vpu power supply and Vref_A is set 1.8 V, as

shown in Figure 6, the A1 and A2 channels have a maximum output voltage equal to Vref_A, and the B1 and B2

channels have 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 voltage drop of 260 mV to 350 mV to have a valid LOW signal on the downstream

channel. If the current through the pass transistor is higher than 15 mA, the voltage drop is also higher in the ON

state. To set the current through each pass transistor at 15 mA, calculate the pull-up resistor value using the

following equation:

Rpu = (Vpu – 0.35 V) / 0.015 A

(1)

Table 5 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 voltage drop across 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)

NOMINAL (Ω)

NOMINAL (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

9.2.1.3 Application Curve

Figure 7. Open Drain Translation (1.8 V to 3.3 V at 2.5 MHz)