Hello!
I build the MP2459 default circuit from datasheet, and work fine, when Vin = 12V.
Now, I like use this circuit lower Vin voltage, 8V.
At 8.8V work fine, but if Vin drop to 8V, switch off the regulator.
Can you help me? The datashhet say the limits: Vin*0.95 = Vout
Thank you,
Laszlo
My circuit:
Hi Laszlo, welcome to the forum!
A probably culprit in this circuit is the EN pin, since it is referenced to the input voltage. The MP2459 requires the EN pin to be pulled above 1.2V to operate. You can derive the voltage on the EN pin in your circuit as below, where V is the input voltage, U is R12, and D is R13.
If we plug V = 8 into the equation, the EN pin drops to about 1.3V, which is closer to the cutoff.
You can confirm this issue by taking a scope capture where you monitor the EN pin voltage and the SW node as you lower Vin from 12V to 8V and see if the point the regulator stops switching coincides to a particular EN pin voltage.
Hi Kareem!
Thank you very much, that was the problem. I was blind not to notice.
I remove R13 and work fine! 
Laszlo
Hi,
is it possible to connect the EN pin directly to IN pin please?
I would like to use it for replacement of LM2842 XMK-ADJ in my design and there are these two pin connectet together with no R12 (as the design mentionet here).
Of course I count with modification of the divider.
Best regards
Jaroslav
absolute max of all other pins ( EN thus) 6V so no
