MP279x CHG MOSFET soft start in separate port configuration

Battery Management
1

Hello team,

We are planning to use MP2790 as MPS controller for the 5S2P Li-ion battery system.
We need a separate charge and discharge port configuration and pre-charge (soft start charge M OSFET) functionality.
And the problem is:

The datasheets for the MP2790 on page 29 says about CHG MOSFET soft start:
“When CHG_SOFTON_EN (see the
FET_MODE (13h) section on page 56) is
enabled and VPACKP exceeds VTOP, the MOSFET
drive circuit automatically uses CHG MOSFET
soft start to control the output current of the CHG
pin, so that VGS rises slowly.”

But in separate port config the PACKP connected to Load path only and condition VPACKP > VTOP impossible when only charger plugged in (MP2790 DS, p.136, Figure 27).
Is that means the CHG MOSFET will never be switchen on slowly in soft start mode?

If yes, is there any way to emulate soft start for the CHG MOSFET?
For example programming 0.5A overcurrent limit and manually on-off CHG MOSFET during let say 500mS using MP2790 registers (and external MCU firmware, of course).

PS. I found out that breaf datasheet for the new product MP3713 described MID pin for charge plug in detection and supposingly DSG MOSFET soft start enabling, so the problem doesn’t exist.
“41 MID P
Protection MOSFET middle point. Used as the charge pump supply input
and charger insert detection.”

Thank you!

2

Hello Eugene, apologies for the delayed response for this request.

I will look into this request regarding the nature of the CHG MOSFET in this setting. I am sure this can be emulated, but I will also look into specifics on this as well and get back to you on this thread.

3

Hey Eugene,

I talked with one of my colleagues about this issue and here is the result of this conversation:

Yes, the soft start could be emulated, though it wouldn’t be as elegant of a solution as native hardware-based behavior. Use an MCU to do the following:

  • First, try manually switching the CHG MOSFET on and off via register control.
  • Use a lower overcurrent limit, perhaps like 0.5A.
  • Then, ramp up the current limit to the normal limit after a short delay, for example perhaps 500ms.

Be sure that your safety timers and watchdogs (if enabled) to allow this staged startup. This workaround has been used by a lot of my Sr. level colleagues where soft-start logic is bypassed by topology constraints.

Hope this provided some insight.

Best,
Krishan