SPV1050 very bad efficiency with solar panel. In same condition charge current is 15mA with spv1050 and 50mA with battery directly connect to solar panel. Help need

[Efian.1]

I use a solar panel ref SM141k08l from IXOLAR and the sp1050 schematic from eval board ISV020V1 in a buck boost version. Just change some resistor to adjust Vppm to 4.8v (I got it in my test, but only 15mA is push to my Lipo battery, lipo voltage is 3.8v and Veoc and Vuvp are correct).. I could share my schematic. I need help because I didn't understand what's happen. Emmanuel from GEO2I

[Jostikas]

Is your battery already close to the EOC voltage? SPV1050 has a 7 Ohm pass transistor between STORE and BATT, and in buck-boost mode you have a typical 1.5 Ohms in the switching elements and 360 mOhms in the inductor. At 15 mA, you will drop 0.14 V in the circuit, and that might well be the difference between the needed voltages for the relevant charge currents.

The chip is meant for harvesting energy from very weak sources. There's a reason the datasheet graphs stop at 20 mA: to keep quiescent current low, they've really undersized the MOSFETs. It'll happily MPPT-optimize a 100 uA source, especially in boost mode, but anything above 10 mA runs into the pass transistor drop like a brick wall.

[Efian.1]

My god an answer! Many thanks Jostikas!

EOC voltage is at 4.5v and battery is a single lipo.

my solar cell best power output is around 40mA..

So with your explanation I understand why it's not working...

But this is not clearly visible when you look to demo board...

Even if I was not see these, anyway I stay very desapointed by this circuit which promised a lot!

So I switch to the Chinese CN3065, who make the job !

(That's a shame!)