Problem with L5973D

ari2399 · ‎2011-01-11

Posted on January 11, 2011 at 09:52

I am designing a circuit with a L5973D switching regulator to provide 3.8v and am facing a peculiar problem. The circuit is as per the design reference in the datasheet and the feedback resistors are given to provide 3.8v output (10K and 4.7K). Initially, I get 3.8v. But while leaving the circuit connected, it starts inching up about 10mV every 10 minutes or so. Furthermore, powering down the circuit and then back up does not cause it to provide 3.8v again. Wondering what's going on....

mallik.ranajay · ‎2011-01-21

Posted on January 21, 2011 at 15:59

Hi,

To better understand could you let me know:

1) What is the output current from the 5973? Is it heating up significantly?

2) After you turn off: do you wait for some time before measuring again?

3) The feed back resistors: what type are they? CFR, MFR? Could you substirute with a lower tempco type and repeat?

Regards

mallik.ranajay · ‎2011-01-21

Posted on January 21, 2011 at 16:01

And one more query: what is the application scenario?

coetzeec · ‎2012-06-26

Posted on June 26, 2012 at 17:14

Hi ,

out of my past experience in switch mode power supplies there is a couple of key points to follow when doing these designs.

1. Ensure all resistors are 1% type, this limits the the change over temperature which in turn will limit the output change variations.

2. ensure the the track from the switching point is close as possible to the coil and does not add resistance to the coil.

3. output capacitors need to have a low ESR type

hope some of this helps.

coetzeec · ‎2012-06-26

Posted on June 26, 2012 at 17:21

Hi,

I have a question on this device regarding the input voltage. The data sheet says it can handle up to 35V input and 40V max. This is all good if the the power supplied is ramped up slowly. However if the input voltage is at a instance of 20V or more the chip seems to literally blow its top of. i presume this is because the inrush current to the device. In my attempt to curb this inrush current i used a 5ohm 8mm disc NTC in series with the input power. This caused a whole new problem by blowing the external TANT caps and the chip which confusing. any ideas?

regards