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TCA9802 Datasheet, PDF (17/36 Pages) Texas Instruments – Level-Translating I2C Bus Buffer/Repeater
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1.65 V
3.3 V
TCA9802
SCPS266 – MARCH 2017
1.65 V
5k
BUS
MASTER
400 kHz
SDA
SCL
5k
5k
5k
VCCA VCCB
TCA980x
SDAA SDAB
VCCB VCCA
SDA
SCLA SCLB
EN
FET Based
SCL
SLAVE
400 kHz
Copyright © 2017, Texas Instruments Incorporated
Figure 15. Incorrect B-Side Pass-Gate Based Translator Use Case
1.65 V
3.3 V
1.65 V
BUS
MASTER
400 kHz
5k
5k
5k
5k
SDA
VCCB VCCA
TCA980x
SDAB SDAA
VCCB VCCA
SDA
SCL
SCLB SCLA
EN
Open Drain
FET Based
SCL
SLAVE
400 kHz
Copyright © 2017, Texas Instruments Incorporated
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
Copyright © 2017, Texas Instruments Incorporated
Product Folder Links: TCA9802
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