LM2676: LM2676 OUTPUT NOT STABLE IN 5V

user5902858

Part Number: LM2676

Hi all,
I have made a small plate with an lm2676-5 following the data of the datasheets to make a power supply of 5v 3A and when measuring the output voltage gives 5v but when the input voltage goes up from 16v the output voltage varies to 6v and more
Could someone tell me what happens to the circuit?
Thank you

over 5 years ago

0 Ambreesh Tripathi over 5 years ago

TI__Expert 6860 points

Hello ,

Can you please post the circuit .

--Ambreesh

0 user5902858 over 5 years ago in reply to Ambreesh Tripathi

Prodigy 30 points

hi, the circuit is the same as the datasheet, the coil is 33uf.

0 Ambreesh Tripathi over 5 years ago in reply to user5902858

TI__Expert 6860 points

What is the make of the output capacitor ? It's a voltage mode device and selection of an output capacitor, with an associated equivalent series resistance (ESR), impacts both the amount of output ripple voltage and stability of the control loop.Are you using the cap given in page 15 and 16 of the datasheet .
Also how is the switch node looking at below 16V and above 16V input(share the waveform) ? Can you also share the layout of the design .

---Ambreesh

0 user5902858 over 5 years ago in reply to Ambreesh Tripathi

Prodigy 30 points

hello again, thanks for answering.
I sent you the scheme
The capacitors are panasonic with low ESR
the coil is 33uH of colicraft
Thank you

0 Ambreesh Tripathi over 5 years ago in reply to user5902858

TI__Expert 6860 points

Hello ,

Please remove the 10nF snubber capacitance to 330pF or so . Also the ESR of the output cap forms a Zero and is critical for closed loop performance of the device . What is the ESR of the output cap used ? Can you please use 180uF cap with ESR of around 125mohm or so .

---Ambreesh

Power management

Power management forum

LM2676: LM2676 OUTPUT NOT STABLE IN 5V