TPS63805EVM-026: Changing the input voltage

Hi Paul,

Thanks for reaching out.

The TPS63805 can support more than 1 A at Vout = 4.9 V, Vin = 2.5 V, unless it is damaged or something else is not functioning.

1. Is your EVM not working anymore, even at higher input voltages?
2. Does the input acts as a short and the output voltage is 0 V?
3. Can you confirm that there is no switching action on L1 and L2 pins?

Best regards,
Milos

Hi Milos,

1. The EVM is not working anymore, even at higher input voltages.

2. Yes, the input is acting as a short to ground and the output is 0V.

3. I measured the switching on the L1 and L2 pins and there is no action.

Thanks very much,

Paul

Hi Paul,

It seems that the device got damaged for some reason. That should't happened, since it can deliver more than 1 A under your conditions.

1. What did you have connected on the output as the load?
2. Did you have a current limit turned on on your power supply, and are you using short wires between the power supply and the EVM? The only thing that should have changed while you reduced your input voltage from 3 V to 2.5 V is the input current, approximately from 1.8 A to 2.2 A. 
3. Are you able to replace the unit on the EVM with another one?

Best regards,
Milos

Hi Milos,

For the load, I had a 5F capacitor as well as an electronic load that was set to pull 4.9W (so the output current was about 1A from the EVM).

The current limit on my power supply was set to 3A, and I have fairly short wires in my system.

That is what I was expecting as well. I turned the input voltage down expecting to see a rise in input current.

I have a spare EVM that I am using right now at 3V and it is working. Later I will attempt to turn the system on with the input already set to 2.5V, instead of me dialing it down manually.

Thanks,

Paul

Hi Paul,

In one of our tests we ramp the input voltage up and down. This is for Iout = 1 A, Vout = 5.2 V, which is close to your case:


So, yes, please check another device under the same conditions. I can't see any reason why the device would fail.

Best regards,
Milos

Milos,

I tested another device but the same thing happened. Is it possible that the presence of the supercapacitor (5F) on the output of my system is drawing too much inrush current and hurting the device?

Thanks,

Paul 

Hi Paul,

Just to check, you changed the input voltage down in a step, not gradually? Also, was it set to PFM or PWM mode?

Best regards,
Milos

Hi Milos,

I turned the voltage down on  my power supply from 3V to 2.5V gradually, over the span of a few seconds or so. At the time of the anomaly it was set to PWM mode, though my plan was to test both modes.

Thanks,

Paul

Hi Paul,

Thank you for the info. My guess is that the decrease in input voltage forces the inductor current in reverse initially. If your power supply cannot sink current, this would ramp up the input voltage. However, the device has an overvoltage protection that should prevent the input voltage from rising above 5.7 V. 

We will have to try reproducing this in the lab. It might take a few days due to the outbreak and limited lab access, please excuse the delay.

Best regards,
Milos

Milos,

No problem - thank you very much for the continued support. Please let me know what you find.

Paul

Hello Paul,

Thank you for your patience. Please excuse that the answer will take some days especially because of Easter.

No problem, I understand.

Paul

Hi Paul,

Please excuse the delay, we will do the bench test in the following few days. In the meantime, if you have any updates from your bench, please share.

Best regards,
Milos

Hi Paul,

Please excuse the delay.

We did tests with a supercapacitor on the output, and with a power supply that can sink current or with an added diode so that the reverse current cannot be sunk. In neither case were we able to reproduce the failure that you experienced, regardless of the speed of change of the input voltage. There would be just a small overshoot on the input. The simulations showed similar results as well. 

Have you maybe tried another power supply? It could have happened that your power supply does not like reverse current, causing an overvoltage on the output. Could you please also show us your setup?

Best regards,
Milos

Hi Milos,

No worries about the delay. I have not tried another power supply, but I was using the GPE4323 bench power supply, which was connected directly to the input of the dev board. The output of the dev board was connected to two Tecate PC10 capacitors which were arranged in series.

For reasons unrelated to this issue I had to change dc converters, and I am using a different TI part. I have therefore not explored this issue further. 

I am still curious as to what happened in my situation, but it is not a pressing matter. I do appreciate the work that you have put into this.

Thanks,
Paul