TPS709: High reverse current measured.

Hi Yee Yong,

Would you be able to give more detailed conditions on how you are testing this? The datasheet condition has Vin and Ven forced to 0V and then 3V is being applied at the output. What voltage are you forcing at the output and how are you measuring the current flowing into the output?

Regards,
Mark

Hi Mark,

Please ignore case #1. It happens on case #2 where Vin is smaller than Vout.

We used 1ohm 1% tolerance current sense resistor at the output pin to measure the current. With Vin = disconnect, Ven = left floating & Vout = 3.3V, 40uA is measured flowing into OUT pin then gradually drop to 20uA and stay steadily there.

In our case, Ven is left floating instead of 0V. In the datasheet, it mentions enable pin is internally pull-up by 300nA current source & zener clamp to 6.5V. What is the equivalent ipu resistor value? It is equal to 6.5V/300nA = 21.67MOhm?

Under section 7.3.4 reverse current protection, it mentions "Reverse current can flow if the output voltage is less than 1.8 V and if input voltage is less than the output voltage.". What does it mean by "Reverse current can flow if the output voltage is less than 1.8 V"?

Thanks.

- YY

Hi YY,

I will put this on the bench tomorrow and test a couple of configurations and share the results with you.

Section 7.3.4 is saying that the output voltage must be higher than 1.8V for the reverse current protection to be engaged. There is an internal switch that has to have some voltage to be turned on.

Regards,
Mark

Hi Mark,

How's your bench test? Any update?

Thanks.

- YY

Hi Mark,

Can you show me your setup? We will try it again on your setup.

Thanks.

- YY

Hi YY,

As this is being completed over email I am going to close this out.

Regards,
Mark

Hi!

we have similar problem. We have application in where Vin can start floating and we have super cap through serial resistor (500ohm) in Vout side. Idea is that when Vin is floating the super cap gives power to RTC in Vout.

We selected TPS709 because of reverse current protection but we are now measuring very high currents from OUT side to IN side. What is the problem?

Thanks!

Hi BLE,

When you are seeing the part have high reverse current what is the voltage on the EN pin and the IN pin? Are you forcing it to GND? If you arent forcing it to GND you can have a condition where the part thinks that it is in dropout and has a high IQ. If you pull the EN pin to GND when the input is floating this should go away.

Regards,

Mark

Hi Mark,
EN is floating. In this situation Vin is between 3.3V to 0V. And super cap tryes to keep Vout at 3.3V.