TCA9406 Datasheet, PDF (10/19 Pages) Texas Instruments – 2-BIT BIDIRECTIONAL 1MHz, I2C BUS AND SMBUS VOLTAGE-LEVEL TRANSLATOR

TCA9406
SCPS221 – JULY 2010
PRINCIPLES OF OPERATION
www.ti.com
Application Notes
The TCA9406 A-Port I/O has open-drain outputs with an internal 10-kΩ pullup resistor to V_CCA, and B-Port I/O
has an internal 10-kΩ pullup resistor to V_CCB. If a smaller value of pullup resistor is required, an external resistor
must be added from the I/O to V_CCA or V_CCB (in parallel with the internal 10-kΩ resistors). Adding lower value
pullup resistors changes V_OL levels. When the OE pin is set low, the internal pullups of the TCA9406 are
disabled for power saving caused by pullup resistors.
Figure 1. Typical Design Example
The TCA6406 has a V_CC isolation feature known as I_off partial power down and backdrive protection. If a cable is
connected, and the connected external system is still powered own, the system can be put into standby mode by
shutting down the power rail. In this state, the TCA6406 has a leakage current of approximately 2 µA caused by
current flow from powered-on system.
Power Up, Power Down
One advantage of the TCA9406 translator is that either power supply can be ramped up first. Another advantage
is that either power supply can be set to 0 V, and the outputs are in high-impedance state.
The recommended power up sequence is:
1. Apply power to the first V_CC and apply the second V_CC
2. Drive the OE input high to enable the device
The recommended power down sequence is:
1. Drive OE input low to disable the device
2. Switch Off the power from either V_CC and remove power from other V_CC.
Enable/Disable
The TCA9406 han an OE input that is used to disable the device by setting OE low, which place all I/Os in the
high-impedance state. The control OE is referenced to the V_CCA supply. A pulldown resistor tying OE to ground
should be used to ensure that bus contention, excessive currents, or oscillations do not occur during power up
and power down. The value of resistor is based upon the current sinking capability of the device.
10
Submit Documentation Feedback
Product Folder Link(s): TCA9406
Copyright © 2010, Texas Instruments Incorporated