L7987L problems

[RGais.1]

Hello!

I use L7987L DC-DC as step-down regulator with input voltage range 9-60V. output 5V , 2A max.

Online design offers schematic i use (see image).

I have a trouble with dc-dc stability with IC.

With some input voltage and loads It is instable. With load less than 100 - 150 mA and loads with more than 1.5 - 2 Amperes. Somtimes with 100 - 150 mA output voltage drops to 0 and regulator can't normaly start while input voltage less than 17-18 volts. Rarely with 1.5 - 2 A load i have big sin wawe pulses in output voltage 

Is schematic correct?

[Peter BENSCH]

Essentially the values of your circuit correspond to those calculated with eDesignSuite. However, with Vin = max 60V for D1 you should choose a Schottky diode that has a VWRM or VRRM higher than 60V and thus offers some margin. The eDesignSuite also suggests a 100V Schottky to have a margin in case of any spikes on the input voltage line.

The stability of switching regulators like this buck converter depends not only on the components used, but also very much on the layout. Can you please share a picture of your design?

Regards

/Peter