Tool/software:
Hi, we are using two LM7480 ideal diode controllers to connect two batteries in parallel to a system. I have attached a schematic of 1 input below, it is the same for the other battery.
The behaviour we expect is the following:
- If a battery voltage is higher than the other, all current should be drawn from that battery
- If both batteries have the same (within some tolerance) voltage, current should be drawn from both equally
- If a battery is below the UVLO threshold, it should stay off
Unfortunately, we are having the following problems:
- The controllers are not load sharing correctly, instead majority power is being drawn from the lower voltage
- In one test with a load of 10A, Supply 1 had 4A drawn @ 13.9V and Supply 2 had 6A @ 13.06V
- This can be demonstrated easily by starting Supply 2 at 14.5V and then lowering the voltage in 100mV increments
- The MOSFETs for the ideal diodes on supply 1 end up dropping all the voltage between Supply 1 and Supply 2 and heat up to 120C
- Current sharing not working at low loads (normally less than 500mA)
- Random failing open
- Occasionally a diode controller will fail such that it no longer turns on the MOSFETS. We have not been able to find a root cause for this issue. Are there any obvious things we are missing?
- Oscillations of the MOSFET when using a current limited supply with a load connected.
- On startup, the ideal diode oscillates between on and off due to the UVLO. This causes the MOSFET to heat up and emit an audible whine.
- Ideally the soft start should avoid this but it doesn't work.
- The attached oscilloscope pictures show startup
- Purple is DGate
- Blue is VBatt
- Yellow is Vbus (output)
Lastly, do you have any more information on MOSFET selection?
- Is there a minimum Rds(on)?
- Is there a maximum gate charge that is appropriate?
- Is there a specific range of appropriate gate thresholds?
- We are using 2x BSZ025N04LS in parallel, this means the Rds(on) can be as low as 1mOhm.
/resized-image/__size/320x240/__key/communityserver-discussions-components-files/196/Oscilloscope1.jpg
