LTC4124 going into Ship mode again and again

Hi EngrZunuran01 ,

I wonder, how did you confirm that the chip goes into "Ship mode" and not into "Battery Disconnect mode"? However, whichever the mode is, the chip should wake up once there is a proper voltage at ACIN (which should be there if your wireless charging setup is functional). I could not fully understand why you are not able to apply >2.7V to ACIN pin. Please explain your setup.

Cheers, heke

Ok thanks for your answer sir. Actually its not ship mode. its battery disconnect mode. We are using DC2769A-A's transmitter module to charge battery once its voltage is less than 2.7V. But our system does not start charging(charge indication led does not blink) automatically until we apply external power to ACIN pin. When we apply <2.7V on ACIN pin then transmitter starts charging and system gains power again. Its very weird situation for us. We are using CP9440-A4 Coin cell battery (4.35V, 35mAH) and Lithium-ion battery (40mA, 4.2V). Both batteries have almost similar power rating but CP9440-A4 drains like 3times more quickly than Lithium-ion battery. However both batteries are getting charged properly when we connect them separately to DC2769A-A Kit. Also We are using MMSZ5226B this diode with battery terminal(copied from DC2769A-A manual). Can you explain me what exactly this diode does? is this diode also consuming power from battery? because we are designing very power efficient device that takes not more than 8mA at full working. so we need to optimize design in all aspects. Thanks

Hi EngrZunuran01 ,

Thank you for the info.

I suspect that the problem here is that your receiving resonator is not in tune with the transmitter or the coils are too far apart. The LTC4124 does not receive enough power to boot up properly. Finding the best values for the receiving resonator components can be a bit tricky and may require experimenting.

The diode Z1 at the battery terminal is a zener. As it may have some leakage current, I'd leave it out in an ultra-low power application. I think it's role is to provide some "batterish" load at BAT in a case that the battery is removed.

Cheers, heke

Thanks for your response. There is one more thing i am observing, We connect battery to our PCB and PCB runs fine. As soon as battery reaches 3.2V we connect the transmitter to our PCB and battery starts charging and system is also keep running. But issue is rather than increasing the battery voltage, its voltage decreases and it does not increase if we run the system at same time while charging. Charge LED sometimes blink very fast in this time, sometime its mix of fast blink and slow blink(i did not see this behaviour explained in datasheet). Can you advice us some solution for that?

I also removed the diode but battery did not charge more than 3.9V if i remove the diode. thats also an issue i am facing. I am using same diode as used in DC2769A-A design

Hi EngrZunuran01 ,

Thank you for your further observations.

It indeed sounds like the wireless energy transfer coupling is not working. If you have an oscilloscope at hand, compare the ACIN waveform on your board versus the evaluation kit board. I'd say that you need to ensure that the received waveform is as it should be. That's the highest priority IMHO.

Please share any oscilloscope captures of ACIN pins and other observations with the forum.

Cheers, heke

i think we are sometimes achieving good coupling of coils. Because i tested today after removing the diode and system is working fine. But with the diode attached battery keeps dropping voltage while system is on(Coils are coupled). So maybe its better to remove diode for now, Will we have any drawback of removing this Zener diode connected parallel to the battery? 

Hi EngrZunuran01 ,

OK. Sounds logical. I'd say you can safely remove the diode. The datasheet does not mention it, thus it is not required. I suspect that it is placed there on the evaluation kit to allow sane functionality when there is no battery. If you have the battery always connected, the diode is obsolete.

Cheers, heke

Heke currently we have removed the diode and testing is underway. We are facing another very strange issue. When we connect fully charge battery to our system then it works fine. But when voltage drops to 3.45V and we connect transmitter to battery then voltage of battery is not getting recovered. Its always decreasing (System is also on at same time). And we get fast flashing at that point. Only when battery voltage is greater than 3.45V and we connect transmitter then battery starts charging and its voltage increases with time(System is also on at that time). 

We are unable to figure out why battery voltage is not increasing if its voltage is 3.45V or less. Do you have any suggestion for that? Coupling seems fine because charging works fine if battery voltage is greater than 3.45V at the time of transmitter connected. 

Hi EngrZunuran01 ,

Thank you for your update.

The issue with battery not charged at Vbat <3.45V is probably due to the precharge mode. Do you have the precharge mode pin PRECHG (Pin 3) tied to VCC or GND? If your system current consumption is greater than the precharge current, then the battery keeps on being depleted.

Cheers, heke