I'm using an lmz21700 in our product.
I saw a bad behavior on low input voltage.
In our application we supply the board with a rechargable lithium battery, the input range is 3.3 to 4.1V, the output voltage is fixed to 3.3V.
Some board works perfectly like an evaluation board of the switching that we bought, other in the range from 3.3V to 3.6 - 4.0 Volt, the switching works in continuos mode and the consumption rise to few mA, when it work correctly the switching goes in burst mode and the consumption decrease to 20uA.
The switchings that no work correctly, if we increase the input above 4V it starts to work ok.
This is the track on the inductance when the switching work correctly, the current of the load is 20 uA and Vin is 3.6V:
This is the track when the switching not work correctly, the current of the load is 20 uA and Vin is 3.6V:
Can anyone help us?
We tried descrese the resistance on FB (the same diveded for 2), the result was the same.
We tried connect an electolytic capacitor on Vin and Vout, the result was the same.
We tried connect a condensator in parallel to R1 or in parallel to R2, the result was the same.
If We tried to fix Vout to 3.0V the problem is shifted in low from 3.0V to 3.5 - 3.6V.
We tried switch LMZ21700 from a board that works and vice versa, the behavior was switched between the two boards
Thaks
