BUS

MASTER

400 kHz

SDA

SCL

1.65 V

5 k

5 k

EN

SDAA

SCLA

SDAB

SCLB

VCCA

VCCB

TCA980x

SDA

SCL

SLAVE

400 kHz

3.3 V

VCCB

VCCA

FET Based

1.65 V

5 k

5 k

Open Drain

Copyright © 2017, Texas Instruments Incorporated

BUS

MASTER

400 kHz

SDA

SCL

1.65 V

5 k

5 k

EN

SDAA

SCLA

SDAB

SCLB

VCCA

VCCB

TCA980x

SDA

SCL

SLAVE

400 kHz

3.3 V

VCCB

VCCA

FET Based

1.65 V

5 k

5 k

Copyright © 2017, Texas Instruments Incorporated

17

TCA9803

www.ti.com

SCPS267B – MARCH 2017 – REVISED FEBRUARY 2020

Product Folder Links: TCA9803

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Copyright © 2017–2020, Texas Instruments Incorporated

Figure 15. Incorrect B-Side Pass-Gate Based Translator Use Case

Figure 16. A-Side Pass-Gate Based Translator Use Case

As shown in Figure 15, it may appear that this use case is valid, but actually it is not. When either the TCA980x

B-side or the slave pull down on the bus, the FET isolating the bus closes (low RDS_ON) and current from the 5-

kΩ resistor is observed by the TCA980x, violating IEXT-I. See the IEXT-I section for more information.

Figure 16 shows the correct way to pair with a FET base translator (connecting to the A-side).

Rather than using a FET-based translator, it is recommended that a buffered translator be used, such as another

TCA980x or a TCA9517. See the Typical Application section for single device for more information on concerns

with B-side connections to buffered translators.

10.1.2.2 Buffered Translators/Level-shifters

The TCA980x family supports connections with buffered translators, but care must be taken to ensure that no

operating conditions be violated. In a general sense, the following must be avoided on the B-side ports of the

TCA980x:

•

Sources of current other than the individual TCA980x (B-side of the other TCA980x, external pull-up resistors,

current sources, rise time accelerators, etc)

•

Static-voltage offset buffer outputs (B-side of the TCA9517, etc)

•

Outputs with RILC (equivalent pull-down resistance) > 150 Ω