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Solar LIPO charger with LT8490 not charging

Question asked by Patrik on Feb 22, 2018
Latest reply on Mar 22, 2018 by Tage

Hi there

this is my first time here. Please be forbearing if i am doing anything wrong. :-) I am developing a solar charger to charge an 48V LIPO battery with a solar module using the LT8490. By now i am testing the (selfmade) board and it is not looking good. :-(

 

Testresults: The LT8490 seems to work as the status LED is blinking once (0.25s) every 3.5s. The fault LED is off. I tested the fault LED by using a 12V battery and then the fault LED showed an under-voltage fault as expected in the datasheet. The problem is, that the LT8490 is not charging although the status LED suggests stage 1 charging.

I can not measure any clock signal at the CLKOUT-pin.

 

Here are the facts:

Battery Voltage: 36.97V

SolarPanelVoltage: 35.36V (I am using a power supply for the tests as the solar panels have not arrived yet)

(MPP is supposed at 37V, open circuit is supposed at 48V)

 

INTVCC = 6.34V

SWEN = 0.72V

IMON_OUT = 0.7V (but there is no current. Actually imon_out is a pwm-signal from 0V-3.3V with a period of 27.4ms and a high-time of 6ms)

IMON_IN = 0.146V (i think this is normal as the imon_in circuit has an measurement offset of 7mV and there is no current flowing)

CSPOUT = 36.97V

CSNOUT = 36.97V

CSPIN = 35.36V

CSNIN = 35.36V

VBAT = 36.97V

VIN = 35.36V

TG1 = 0V

BG1 = 6.34V

TG2 = 0V

BG2 = 0V

FBIR/FBIN = 1.54V

FBOUT/FBOR = 1.2V

BOOST2 = 5.92V

BOOST1 = 5.92V

FBIW = 2.53V

 

 

I am using 4 pieces of IPT007N06N FET's.

I am using 2 CMMR1U-02 TR diodes between GATEVCC and BOOST1/2

MODE is tied to an external 3.3V source.

The input feedback network is configured for 60V using the resistor / capacitor values from the datasheet.

The stage 2 voltage limit (Vs2) is set to 48V.

Charge current limit is set by a poti to 4.8A.

Input current is limited to 20A.

TempSense is not used. (11.5k and 10k resistors)

 

I attached the essential part of the schematic as the hole board contains way more than just this circuit. Please be aware that i canceled some parts from the schematic for the tests. You will know once you take a look at the schematic.

 

Please help me finding the bug. I am searching for days and cant find it. It is getting really depressing. I think i am making some very basic mistakes because of some misunderstanding. (My English could be much better) Thanks a lot for every helpful comment!

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