TPS40305: IC becomes hot at no load

user5131028

Part Number: TPS40305
Other Parts Discussed in Thread: TPS40304

Hi,

We have the following circuit on several boards and we have heating issues coming from the TPS40305.

With our current board configuration, only 1.8mA of output current is used on the 5V rail. However, we have 100mA of input current if only the 5V circuit is used. Vin is at 12V and both MOSFETs are IRLHS6342TRPBF.

We were able to get a picture from a Thermal Imager and as soon as the card is powered, the TPS40305 gets hot. The inductor doesn't appear hot on the Thermal Imager but heat is produced from it. Ambiant temperature is at 25C.

Is there a design flaw that make the TPS40305 heats up?

Regards,

Julien Gagnon-Bourassa

Hardware Designer

over 6 years ago

0 user5131028 over 6 years ago

Prodigy 20 points

0 Mathew Jacob1 over 6 years ago

TI__Expert 5910 points

Julien,

What is the input voltage?

Regards,

Mathew

0 Mathew Jacob1 over 6 years ago in reply to user5131028

TI__Expert 5910 points

Please have a look at the BP5 voltage and see if its dropping. At 1.2Mhz and these fets you are taking 26mA or more from the BP5 while its rated for 25mA. Also you can have a look at the spreadsheet to calculate temp rise. It could be that you dont have the DAP on the bottom connected and so the RthetaJA is much higher than 45c/w. is there a specific reason to operate at 1.2Mhz? TPS40304 operates at 600khz and you can use the same inductor.

Regards,
Mathew

0 Mathew Jacob1 over 6 years ago in reply to Mathew Jacob1

TI__Expert 5910 points

TPS40305_E2E.xls

0 Mathew Jacob1 over 6 years ago

TI__Expert 5910 points

Julien,]
Also take the switch pin waveforms without bandwidth limit on scope,just to make sure the voltage spikes dont exceed abs max ratings of the FET and TPS40305..

Regards,
Mathew

Power management

Power management forum

TPS40305: IC becomes hot at no load