TLV704: Regulator burning up during short circuit

Alex N

Part Number: TLV704
Other Parts Discussed in Thread: BQ40Z50

Hello,

I am currently using a TLV704 series regulator in a BMS circuit to power an EEPROM. The regulator functions as expected until we attempt to do short circuit testing with the BMS. When shorting the battery pack outputs, the voltage regulator goes straight to outputting around 8.0Vdc instead of 3.3Vdc.

I have tried putting a diode in series with the voltage input of the regulator, but it did not work.

What am I missing to keep the regulator from burning up during an short circuit on its input?

over 5 years ago

0 Jason Song over 5 years ago

TI__Mastermind 23361 points

Hi Alex,

Can you include a schematic of your BMS with the LDO? Will you also capture some waveforms that shows the Vin, Vout and output current?

Regards,
Jason

0 Chito Tapia over 5 years ago

TI__Intellectual 825 points

Hi Alex,

Could you send the partial schematic of your circuit just for me to better understand what's connected to the input and output of the TLV704?

What I understood from your post is that the TLV704 started to burn when the "IN" pin of the device is shorted to ground (GND pin). In this case, adding an external diode (preferably schlocky for faster switching) between the IN and OUT pins should protect the device from excessive reverse current/voltage. Connect the diode's cathode to IN pin and anode to OUT pin.

By the way, how big is the capacitance connected to the OUT pin?

Regards,

Chito

0 Alex N over 5 years ago in reply to Chito Tapia

Prodigy 240 points

Attached is the schematic of the BMS with the regulator (U3). The regulator in the schematic is an Ablic. I was originally going to use the ablic ship, however, upon short circuit between Vin and GND, the regulator smoked and sparked.

I then started looking around for a more robust solution and came across the TLV704. I replaced the ablic with the TLV704 and while it didn't smoke and spark, it lost the ability to regulate.

I then suspected reverse current and placed a diode between Vin and B+ ,but this did not work either. I dont have a capture of the event, but observed that the voltage did dip from 12.8Vdc to around 7 to 8Vdc during the uS it took for the BQ40Z50 to stop the short circuit.4846.Schematic Prints.pdf

0 Chito Tapia over 5 years ago in reply to Alex N

TI__Intellectual 825 points

Hi Alex,

I suggest adding a schottky diode as shown below to protect the regulator's IN and OUT pins from reverse voltage and current thus prevent it from damage. It would be really helpful if you can send us waveform that shows the Vin, Vout and output/input current during the short circuit test.

Just for clarification, which nets exactly are you shorting during this test?