MP2731 Battery Disconnection Function


I use a MP2731 on a client project and we cannot disconnect the
battery from the system (for shipping mode) with the DISC pin.

If I read the register REG0Ah ( BATFET Configuration ) I have the value 0x40.
So SYSRST_SEL = 0 -> hardware reset and Tdisc_l = 0 -> 8s holding to turn off the BATFET.

Here is a screenshot of Vbat, Vsys and Vdisc:

As you can see, Vbat and Vsys are around 4.1V, Vdisc = Vref around 3.3V and Vbus is not connected so 0V.
If Vdisc is held low during 8s or even more than 18s, nothing happens on Vsys…

Am I missing something? The datasheet only refers REG0Ah for this option, maybe something else needs to be set?

Thanks for your help!

Hello Geoffrey,
Everything looks in order with the signals, timing appears to be OK, levels should work as well. You may double check the reg 0Ah to make sure the settings are as expected. Let us know what state the device is in - charging with input connected or discharging. I’m not sure of the effect of fault signals, but you can check that register to make sure no faults triggered such as NTC. Also is there any load on SYS or disconnected? Possibly the output cap is holding up the SYS voltage.

Hello James,
I am sorry for this very late response. I made more tests. I read registers 0A (Config), 0C (Status) and 0D (fault) while waiting for shipping mode:

-> Config = 0x40, which is the proper configuration
-> Status = 0x01, which is the default value for a system without USB plugged in and a full battery
-> Fault = 0x20, which means "INPUT_FAULT : Input over-voltage protection or no input’ (It is my case: I have no input)

I have not found yet why the chip is not going in shipping mode. I can wait forever with the DISC pin connected to GND, nothing happens. This is the same thing for MP2731 and MP2723.

As you wrote, there is a capacitor of 22uF on VCC. But the load requires around 1.5A. It cannot hold voltage for more than few ms.

However, if I set the chip in shipping mode by setting BATFET_DIS ( bit 5 of 0x0A register), I can get out from it by holding DISC pin low few seconds…

Only entering in shipping mode with DISC pin seems to not working properly…

Here is the whole I2C settings when I am trying to set shipping mode:
Reg 0x00 : 0x7F
Reg 0x01 : 0x08
Reg 0x02 : 0x54
Reg 0x03 : 0x50
Reg 0x04 : 0x00
Reg 0x05 : 0x88
Reg 0x06 : 0x22
Reg 0x07 : 0xA0
Reg 0x08 : 0x85
Reg 0x09 : 0x00
Reg 0x0A : 0x40
Reg 0x0B : 0xC0
Reg 0x0C : 0x01
Reg 0x0D : 0x20
Reg 0x0E : 0x00
Reg 0x0F : 0xD1
Reg 0x10 : 0x80
Reg 0x11 : 0x16
Reg 0x12 : 0x00
Reg 0x13 : 0x00
Reg 0x14 : 0x3F
Reg 0x15 : 0x60
Reg 0x16 : 0xEE
Reg 0x17 : 0x00

Best regards

7 months later, the problem remains :sweat_smile: