LSF0102DCTR datasheet(22/53 Pages) TI

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9.2.4 Voltage Translation for Vref_B < Vref_A + 0.8 V

As described in the Enable, Disable, and Reference Voltage Guidelines section, it is generally recommended

that Vref_B > Vref_A + 0.8 V; however, the device can still operate in the condition where Vref_B < Vref_A + 0.8

V as long as additional considerations are made for the design.

Typical Operation (Vref_B > Vref_A + 0.8 V): in this scenario, pullup resistors are not required on the A-side for

proper down-translation as is shown for channels 1 and 2 of Figure 9-4. The typical operating mode of the device

ensures that when down translating from B to A, the A-side I/O ports will clamp at Vref_A to provide proper

voltage translation. For further explanation of device operation, see the Down Translation with the LSF Family

video.

Requirements for Vref_B < Vref_A + 0.8 V Operation: in this scenario, there is not a large enough voltage

difference between Vref_A and Vref_B to ensure that the A side I/O ports will be clamped at Vref_A, but rather at

a voltage approximately equal to Vref_B – 0.8 V. For example, if Vref_B = 1.8 V and Vref_A = 1.2 V, the A-side

I/Os will clamp to a voltage around 1.0 V. Therefore, to operate in such a condition, the following additional

design considerations must be met:

• Vref_B must be greater than Vref_A during operation (Vref_B > Vref_A)

• Pullup resistors should be populated on A-side I/O ports to ensure the line will be fully pulled up to the

desired voltage

Figure 9-6 shows an example of this setup, where 1.2 V ↔ 1.8 V translation is achieved with the LSF0108. This

type of setup also applies for other voltage nodes such as 1.8 V ↔ 2.5 V, 1.05 V ↔ 1.5 V, and others as long as

the Recommended Operating Conditions table is followed.

1.8 V

1.8 V Device

1.2 V Device

200 kΩ

Vref_B

RPU(B1)

Vref_A

1.2 V

RPU(B2)

RPU(A2)

RPU(A1)

0.1 μF

Figure 9-6. 1.2 V to 1.8 V Level Translation with LSF0108

LSF0108

SDLS966L – DECEMBER 2013 – REVISED DECEMBER 2022

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LSF0102DCTR датащи(PDF) 22 Page - Texas Instruments