MP2651 behavior during pulsed load on BATT pin while charging

Battery Management
1

Hi,

I have a question about the MP2651 behavior when a load is connected to the battery at the same time the MP2651 is charging it.

The system has no NVDC and no separate system rail. The MP2651 charges the battery, and an independent load is also connected directly to the battery terminals:

VIN ──► [MP2651] ──► BATT+ ──┬── Load+
                     BATT- ──┴── Load-
                     (4S Li-ion pack)

So at the same time:

  • The MP2651 pushes current into the battery (charging at a fixed ICC via I2C)
  • The load pulls current out of the battery (can be few Amps during seconds and mA rest of the time)

The MP2651 and the load are completely independent circuits — the load is not connected to VIN.

My questions:

  1. The load pulse causes a transient voltage dip across the battery terminals. Will the MP2651 react to this dip in any way — for example, interpreting it as a low battery condition, restarting the charge cycle, reducing charge current, or triggering a fault?

  2. Is there any general issue with the MP2651 charging a battery while that same battery is simultaneously discharged by an independent load connected directly to its terminals?

  3. One workaround we are considering is to disable charging via I2C (CHG_EN=0) just before the load is activated, and re-enable it (CHG_EN=1) once the load pulse is over. Would this be a safe and reliable approach?

  4. Alternatively, is there any feature in the MP2651 that could handle this automatically — for example, detecting a discharge condition on BATT and pausing the charge cycle on its own?

Thank you.

2

Hello, apologies for the delayed response. I will answer your questions in the order asked:

  1. How drastic is the transient that you see when the load pulls current? The response of the charger is entirely dependent on the voltage protection settings and charge current settings.
  2. This would generally stress the battery itself, which would likely reduce it’s overall lifetime.
  3. Disabling CHG_EN before the load is activated and re-enabling when the pulse is over seems good on paper. Have you tried this out? Alternatively (or additionally, depending on the space you have), you can add a system of switches that can enable paths for charging the battery, load, or both when you would like that would also help with avoiding the transient events and stressing your battery out.
  4. Depending on the charging and discharging characteristics of the battery and the nature of your load, you can always adjust the timing via the registers of the MP2651 to adapt accordingly. We also have chargers with a separate SYS output that can be detected through the load and manages the power path between the input and the battery in order to sustain the load.

Have there been any updates since you last posted? Let us know.

Best,

Krishan