LMR14050-Q1: V out = V in

Rod Brick

Part Number: LMR14050-Q1
Other Parts Discussed in Thread: LMR14050

I have a LMR14050 installed in a power supply I am building. This is designed for 5.0V output. V_in = 26.79V. R_fbt = 124.7K and R_fbb = 22K. I am getting 26.72V at the output and measuring 4.01V, not 0.75V at the FB pin. Any ideas what might be wrong, or does it seem I zapped the chip somehow?

over 5 years ago

0 Arief Hernadi over 5 years ago

TI__Mastermind 23845 points

Hi,

Could you check the connection on RFBT to VOUT and the value of RFBT, It seems like you dont have a regulation.

When VIN goes down to 12V, does VOUT also goes down to close to 12V?

Thanks

-Arief

0 Rod Brick over 5 years ago in reply to Arief Hernadi

Intellectual 580 points

The connection of RFBT to VOUT is soldered and fine. I nonetheless re-soldered and replaced RFBT. The power supply is fed with line voltage through a power transformer and VIN cannot be changed.

Don't know of it helps but here are the 5V LMG14050's updated pin voltages: VIN = 24.93; VOUT = 24.68; BOOT = 24.78; EN = 3.72; FB = 3.7; and Freq = 0.0 (maybe a multimeter problem??) The 3.7 FB voltage calculates to a VOUT = 24.67. If the FB pin voltage was 0.75, as it is supposed to be, it calculates to a VOUT = 5.00