L7986ta Regulation issue at high voltage and light load

[Harshwardhana]

Hi..

I have used L7986ta ic for 10.8V to 34V vin and Output 3.7Vdc, during light load conditions my 3.7v dips and ic skips the pulses. What i can do??

[Peter BENSCH]

Welcome @Harshwardhana, to the community!

This is the normal behavior of a voltage-more PWM regulator. To prevent pulse skipping, you can only increase the base load.

Does it answer your question?

Regards
/Peter

[Harshwardhana]

Thanks peter..

what does base load means..?

do you mean Iout?

also is it possible to resolve this by tuning compensation network..?

[Harshwardhana]

Peter, due to pulse skipping at light load and 32 volts, the voltage ripple increases to 0.5V for 15secs. How i can overcome this issue ?

[Peter BENSCH]

Increasing the base load means increasing the minimum load current flowing. As already mentioned, this is typical behaviour of voltage mode regulators, but COT (constant on-time) regulators also require some minimum load. You cannot change this inherent behaviour by changing the compensation.

Linear regulators do not have this problem, but they burn up the entire voltage difference.

[AScha.3]

>what does base load means..?

Put something on your circuit, that needs some current:

a LED + resistor , or just a resistor , to burn some mA .

[Harshwardhana]

Peter, i tried increasing the load to 37mA still same issue is there.. it gets resolved at significant load like 100mA. is it okay to set such high pre loads?

[Peter BENSCH]

It depends on your requirements: the L7986TA is a 3amps regulator, usually used for output loads in the range of 0.1-3A.

Please have a look at the efficiency curves in the data sheet, fig. 25 and 26.

[Harshwardhana]

Thanks Peter.

The graphs are given for 5V, 12V and 24V Vin and 250khz frequency… in my case the fsw is 400K and vin is 32V

[Harshwardhana]

Peter, will this issue occur if wrong values selected for compensation network and regulation network..?