LM2676 / about "ADDITIONAL APPLICATION INFORMATION" of datasheet

Ryuji

Guru 20090 points

Other Parts Discussed in Thread: LM2676

Hello,

Please let me know about LM2676.

(1) long start up time

In our customer , LM2676 need long start up time about 8 minutes.

Could you please let me know this reason and countermeasure ?

I think that this is caused of "ADDITIONAL APPLICATION INFORMATION" from datasheet P.12.

Our customer conditions are as following.

Vin:24V

Vout:11.4V

Iout:1.7A

Cout :164uF

L : 69uH

(2) external components

I found the description that "Cout=47uF and L=22uH will work in this specific condition" in the datasheet P13.
However , LM2676 external parts recommendation values are decided by Inductor Selection GUides and Capacitor Selection Guides.
Should we select 47uF and 22uH for above condition ?

Best Regards,

Ryuji Asaka

over 10 years ago

0 Marc Davis-Marsh over 10 years ago

TI__Genius 10095 points

I will forward this to the applications engineer for this part.

Regards,

Marc

0 Marc Davis-Marsh over 10 years ago

TI__Genius 10095 points

Looking through the datasheet, it looks like the part might be hitting current limit during start up. This would then fall under the ADDITIONAL APPLICATION INFORMATION section describing recovery from the current limit.

At this time I would recommend following the 47uF and 22uH recommendation..

Regards,

MArc

0 Frank De Stasi over 10 years ago in reply to Marc Davis-Marsh

TI__Guru 57555 points

I agree with Marc; use the recomended values.

Waiting 8 minutes to start-up means the part never starts-up.

The only thing I could think of is a very large output capacitor and/or a very heavy load.

Do you have more than 164uF downstream ??

0 Ryuji over 10 years ago in reply to Frank De Stasi

Guru 20090 points

Hello Frank san, Mark san,

Our customer said that there is WI ramp as load.

And there is not more than 164uF downstream.

I will check again their downstream and load.

Best Regards,

Ryuji

Power management

Power management forum

LM2676 / about "ADDITIONAL APPLICATION INFORMATION" of datasheet