LSF0204, LSF0204D

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SLVSCP5D – JULY 2014 – REVISED DECEMBER 2015

Typical Applications (continued)

Table 3. Application Operating Condition

SYMBOL

PARAMETER

MIN

TYP

MAX

UNIT

Vref_A

Reference voltage (A)

0.8

4.5

V

Vref_B

Reference voltage (B)

Vref_A + 0.8

5.5

V

(1)

Input voltage on EN terminal

0

Vref_A

V

Vpu

Pull-up supply voltage

0

Vref_B

V

(1)

Also Vref_B is recommended to be at 1.0 V higher than Vref_A for best signal integrity.

The LSF Family is able to set different voltage translation level on each channel.

NOTE

Vref_A must be set as lowest voltage level.

11.2.1.2 Detailed Design Procedure

11.2.1.2.1

Bidirectional Translation

The master output driver may 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).

NOTE

However, if either output is push-pull, data must be unidirectional or the outputs must be

3-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 9, the reference supply voltage (Vref_A) is connected to the processor core power supply voltage.

When Vref_B is connected through to a 3.3 V Vpu power supply, and Vref_A is set 1.0V. 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.

11.2.1.2.1.1

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 Equation 1.

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.

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