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TCA9534: High current draw

Prodigy 30 points

Replies: 3

Views: 190

Part Number: TCA9534

Hello,

I have assembled a board with a TCA9534 and when I power it with 2.85V the part pulls the supply down to 0.95V. I can confirm that the TCA9534 is the issue because it gets warm to the touch and no other parts are connected to the 2.85V rail. The datasheet does not specify anything about floating pins and I currently have the INT and one of the port pins floating - could that be the issue? 

  • Hey Mguirg,

    You are saying when you power on the device, you see that drop to ~1V? Or after you've powered it and then did an I2C transaction?

    Can you provide a scopeshot of the Vcc when it is GND, then when you power it on, then when it drops to ~1V?

    Does this happen with only one device or have you replaced the device and then power on again and see the same issue?

    What is your power source for the 2.85V? An LDO, a switching regulator? A lab power supply?

    It seems highly unusual for one floating input to cause this kind of voltage drop and temperature change. I have seen some floating pins draw mAs of current but your case seems like something is shorting.

    The other possibility I can think of is that you soldering the device on 180 degrees off resulting in the GND being at Vcc and the Vcc being at GND and you are back biasing internal body diodes of the device. Please double check to see if the pin 1 of the device is connected correctly.

    -Bobby

  • In reply to BOBBY:

    Hi Bobby,

    Thank you for your reply. 

    The device drops to 1V instantly on power on. It is being powered by an LDO designed to output 250mA (TPS727285DSER). Attached is a screenshot of the power on sequence.

    I have not tried replacing the part yet, but can do that and let you know if it fixes the issue. It does not appear that Vcc and Gnd are shorted.

    Thanks.

  • In reply to mguirg:

    I replaced the part and now I am not longer seeing high current draw and voltage is steady at 2.85V. Thanks for your help.

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