• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 33 subscribers
  • Views 849 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TCA9509: High Impedance SDA and SCL when powered off - where is this specified in the data sheet specifications?

Paul Eason
Prodigy 50 points
Part Number: TCA9509
Other Parts Discussed in Thread: TCA9803

I specifically need a part that has a high impedance on SDA and SCL when the power is removed from Vcca and Vccb.  The "Features" section of the datasheet (SCPS225C - August 2011) indicates "Powered-Off High-Impedance I2C Bus Pins."  However, I cannot find a specification in the data sheet that indicates parametrically that high impedance on SDA and SCL will occur when the power is removed. 

My application is an SMBus where the master processor on board will be powered off (on the Vcca power rail) and a programming tool will power up the circuit subsection for SMBus (Vccb side) but I do not wish to power Vccb on this device. 

My rationale for not powering Vccb while programming is that I have limited power available when the SMBus is operating (Vccb) and if I power Vccb from the power rail that my programming device uses, under normal operating conditions I may draw too much power from the isolated power rail that I have available for Vccb.

I believe that the part will meet my needs but I want to be sure before I spin a very expensive FPGA board with this part on it.  If I cannot program the SMBus enabled power supply manager with my programming tool when the power is removed from Vcca and Vccb, I will not be able to power up my board without removing this voltage translation device.

If there is another part that parametrically specifies the condition that I'm considering, please inform me.  My needs are simple: 400Khz max Vcca = 1.8V, Vccb=3.3V, and SDA and SCL on the Vccb side must be high impedance when power is removed from Vcca and Vccb.

Regards,

Paul Eason

  • 0
    Guru 317390 points

    Section 11 says that it "includes a power-up circuit that keeps the output drivers turned off until VCCB is above 2.5 V and the VCCA is above 0.8 V."

    The TCA9803 uses less power when idle. (It has the current source on its B side, so you might want to switch A/B.) And if your bus does not have a high capacitance, you can use another TCA980x with lower current.

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points
    Understood, I re-read section 11 and got the point. When powered, I'm using the 3.3V rail... it has 10A behind it there won't be a problem powering the device ;)

    Thank you for your prompt reply.

    Best regards,
    Paul Eason