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LTC4020 Output voltage regulation not working

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freeelectron

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Hi there,

I have designed the LI-ion battery charger module with LTC4020 control. Module designed with below given configuration.

Vout max : 14.2V

Vout min : 10.97V

VBatt : 13.05V

Battery Type : Rechargeable BATT LI-ION 11.25V / 6400mAh

Maximum inductor current : 12.5A

Battery charging current : 5A

Inductor Used : IHLP5050EZER4R7M01 / PWR IND 4.7uH 15mE 20% 27Asat Shld 2-SMD 13.2x13x5 RoHs

All components & layout were desided based on the recommendation available in datasheet. Now the issue is, Without load, module outvoltage observed ~14V as expected. But when the load is connected (570ohm Varible rheostat - at about 80ohm resistive load - 180mA) the output voltage is getting reduced to 3 to 4 Volts. (Battery not connected)

while debugging it is foud that, TG2 voltage is getting reduced in increasing load current.

Load was increased linearly from maximum load resistance (570Ohm). As given in datasheet, Duty cycle is increasing with incresing in current, that i visualize in DSO. once the continuous switching is observed, further incresing in load cause the reduction in output voltage.

Voltage at INTVCC -5V exist in all cases. from which I hope that the LTC4020 not malfunctioning.

Request your kind advice to overcome the issue. awaiting for reply and thanks in advance.
 

Hi,

A battery is far away from being a resistive load.

Thus, maybe a "resistive" load is not suitable to test this circuit.

You may try to add high value elecrolytic capacitors in parallel to your resistive load.

****
Some charger circuits (I didn´t go through the datasheet) require a minimum battery voltage to work properly.
Otherwise the controller may assume this is not a battery or a defective (old) battery.

****
Btw:
We often see this statement:
All components & layout were desided based on the recommendation available in datasheet
Sometimes it is true.
If you show us your design we are able to verify it.
In many cases we detect some issues.

Klaus
 

Dear Klaus,
LTC4020 can charge the battery and provide the supply to the load simultaniously. plz find the attached functional block diagram for understanding. LTC4020 is like a smart chip for charging LI-ion / Lead Acid / some other battery types and can operate cc/cv, 3 stage 4 step / cc operation. buck -boost operation duty cycle will be automatically control by internal algorithms. input voltage range 4.5 to 55V and Output range till 55V.
 

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Hi,

Now the issue is, Without load, module outvoltage observed ~14V as expected. But when the load is connected (570ohm Varible rheostat - at about 80ohm resistive load - 180mA) the output voltage is getting reduced to 3 to 4 Volts. (Battery not connected)
At this situation, what is:
* V_IN, best to be mesured with a scope to see it moves

while debugging it is foud that, TG2 voltage is getting reduced in increasing load current.
How did you mesure it? A DVM is not useful, because this is a switching node
Use a scope...and the (most) interesting value is the gate-source-voltage for the according MOSFET.
It is a sensitive node, capacitive loading (scope probe) may modify the behaviour.

Can you show us your inductor value calculations?
To me it seems a bit low, especially with your high input voltage .. (but I did not calculate it for now)

I think it´s a good idea to show your actual schematic with your used values. Otherwise we have to guess your I_limit setup, switching frequency setup, and so on...

Klaus
 

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