Hello,

First post on this forum.

I am designing a circuitry which is capable of charging a Li-ion battery (2 cells), and to do that, I am using an IC from Linear.
The IC is: LTC4162EUFD-LADM.
Because that IC is not able to measure the coulombs, I have added another IC: LTC2943, to measure the same sense resistor, as the LTC4162 at the battery side.


My problem is, that when I write and read data through the I2C bus, the coulomb counter (LTC2943) is not responsive, if I get to charge more than 500 mA into the battery.

I have uploaded the schematic. Hope that clears is out.

I have a suspicion that it maybe could be the output ripple of the buck converter. But I have measured it with a scope, and the ripple is only 100 mV (peak-to-peak).

Meanwhile you guys think about the problem, I will the to add a 1 uF capacitor to the SENSE+ pin, to see if that sort out the ripple, and too see if that is the cause of the problem.

Thanks!

 

What is the current ripple (ripple voltage across R59)?

To suppress any curent ripple, add a 1kΩ resistor in series with each LTC2943 sense input, and add the capacitor across the input pins.

 

Hi @crutschow

I dont think it is the current ripple, that is the problem.

SENSE+ is connected directly to the LTC2943' power supply. And I think maybe that is drawn below the minimum voltage (3.6V) to function correctly (the IC is turning off because of the ripple).

I just mounted a capacitor (1uF) on SENSE+ to gnd. I will let you know, if that works.

 

After adding the 1 uF capacitor on SENSE+ to GND, I tried to charge the battery again.
It is working now! The coulomb counter has no communication problems even at high current charge.

 

New thing came up.

If I slowly increase the current from 0 to 2 amps from mains to the battery, the I2C bus is NOT getting disrupted.
But if I draw a around 2 amps of current through mains and into the battery, without delaying or slowly increasing the current, the I2C bus is no longer working. The SDA pin is pulling low.

Any clue?