I've put together a PCB based directly on the second application circuit in the LTC4412 datasheet. This seems to work as intended for a power path circuit with an 18.5V (16-21V working range) lithium ion battery as the primary input and a 24V DC PSU as the auxiliary. I chose this application circuit because using a schottky diode for my auxiliary supply would result in a large amount of power dissipation (this circuit is designed to operate up to 20A with FDS6681 MOSFETs).
Here is the page of the datasheet explaining the circuit operation (I have used figure 2 for the circuit, connecting the charger as is done so in figure 3).
https://i.imgur.com/62cdOHY.png
However, when I connect a charger (CC/CV board based on XL4015, from eBay) between the 24V input and the battery in the circuit, the 24V PSU immediately hits current limit and the voltage sags significantly.
If I connect the charger to the circuit with a separate 24V supply powering it, all is fine and dandy, I can charge the battery, switch the source powering the load and so on no problems.
I'm really stumped by this. The only thing I can think of is that the difference in the way the sense pin is configured between the 2nd and 3rd application circuits is what's causing my issue, but I've run a multimeter through the circuit checking the voltages at various points in the circuit against the datasheet in the different states of operation and it seems to check out for the most part.
Could anyone explain to me the behavior I'm experiencing? I can conduct any further tests and give any more information needed to diagnose the problem.
Thanks.
Here is the page of the datasheet explaining the circuit operation (I have used figure 2 for the circuit, connecting the charger as is done so in figure 3).
https://i.imgur.com/62cdOHY.png
However, when I connect a charger (CC/CV board based on XL4015, from eBay) between the 24V input and the battery in the circuit, the 24V PSU immediately hits current limit and the voltage sags significantly.
If I connect the charger to the circuit with a separate 24V supply powering it, all is fine and dandy, I can charge the battery, switch the source powering the load and so on no problems.
I'm really stumped by this. The only thing I can think of is that the difference in the way the sense pin is configured between the 2nd and 3rd application circuits is what's causing my issue, but I've run a multimeter through the circuit checking the voltages at various points in the circuit against the datasheet in the different states of operation and it seems to check out for the most part.
Could anyone explain to me the behavior I'm experiencing? I can conduct any further tests and give any more information needed to diagnose the problem.
Thanks.