TPS7A47-Q1: Voltage regulator damage on Vin=25V from battery source.

Hi Riya, 

I would use a digital multi-meter to check empty board connections to each pin of the LDO. This is to make sure the PCB layout and connections are good. Since this is a 36V LDO, and most of the pins can tolerate 36V, the most likely cause for the part to damage is that the pins may have been exposed to negative voltage due to either board layout or unintentional connections. 

Will you please permform the check and let me know you find out, and we will go from there.

Regards, 
Jason

Hello jason,

I found the solution of regulator getting damaged.The input capacitor voltage rating was 25V only.So i replaced it with 50V ceramic capacitor.

The Regulator output voltage is not coming 3.3V.Sometimes it shows 3.7V or 7V or 16V.I have tried using Regulator as a standalone Circuit in Any out programing mode but the output is never 3.3V.

I am working on a very critical project of company but i am just stuck because of this Regulator.

Please help me as soon as possible.

Hi Riya, 

Besides checking on the output voltage, will you please also check the voltage on the NR pin? It seems to me that the LDO is already damaged. Do you think you could replace the LDO after you changed the input capacitor? 

Regards, 
Jason

Jason,I have replaced the LDO multiple times assuming it might be damaged but still no regulation of 3.3V.The voltage on NR is input voltage.What could be the issue now.

If you are using ANY-OUTS, the NR voltage will be the same as the output. I would check for any shorts between Vin and NR. In addtion, will you please post your schematic here?

I have attached the schematic here.

One time LDO was regulating 3.3V continuously.To test its relaibility I was switching input on off many times.Thats when the regulation stopped and output generated was 7V 10V 25V.

Hi Riya, 

Thanks for providing the details. As we can see, there is a 47uF output capacitor at the output, when the Vin is suddenly pulled down, we need to make sure the output voltage is higher than Vin otherwise there will be reverse current flowing back from the output to the input of the LDO through body diode and it may damage the LDO. 

Will you check the input and output waveform and see if the output is higher than the input during your tests? 

Regards, 
Jason Song

Hi jason,

Thanks for the solution.I will observe the waveforms on oscilloscope and get back to you. Could you please tell me why the external diode is not added in application circuit of LDO datasheet?

The external diode from the output to the input is optional and it's only needed if the application expects to see sudden Vin drops that could potentially bring the input voltage down faster than the output. 

Jason,but whenever we will Power off the LDO the input voltage will go down In that case external diode must be compulsory then. 

Hi jason,

When I removed all the capacitor of the circuit the LDO was working fine.After that i added 47uf/16v capacitor on output and same issue was observed output voltage was equal to input voltag

Can you suggest a LDO with input maxiumum voltage of 60v and regulates to 3.3V?

Hi Riya, 

Not always, if the input voltage drops slowly, the output is likely to follow once in dropout, and due to the fact that there could be an extra load on the output, the output could be lower than Vin by a dropout at the load current. But during the test environment, the input can be brought down quickly and faster than the output could respond, and if the application does have the possibility for reverse current, you will need to add a diode between the output to the input. 

Regards, 
Jason Song