MP2722: REG12 VSYS_STAT behavior when VIN is absent and battery is below VSYS_MIN

Battery Management
1

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Hello,

I am using the MP2722 in a single-cell Li-Po application. The system is powered from SYS, the battery is connected to BATT/BATTSNS,

I would like to use the MP2722 status registers to detect a low battery condition and put my host MCU into deep sleep.

My configuration:

REG06h SYS_MIN[2:0] = 100b
VSYS_MIN = 3.588 V, default setting

VIN is absent:
REG12h = 0b00000110
VIN_GD = 0
VIN_RDY = 0
VSYS_STAT = 1
WATCHDOG_FAULT = 1

Measured voltages:

BATT pin: approximately 3.20 V
BATTSNS pin: approximately 3.20 V
SYS pin: approximately 3.15 V

According to the datasheet, REG12h.VSYS_STAT is described as:

0: VBATT < VSYS_MIN
1: VBATT > VSYS_MIN

Since the measured battery voltage is around 3.20 V and VSYS_MIN is configured to 3.588 V, I expected VSYS_STAT to be 0. However, it remains 1 (V_IN is absent)

I also found in the datasheet that when the input source is absent, the BATTFET turns fully on and passes battery power to the system through a low-impedance path. The VSYS_MIN + VTRACK regulation seems to apply when an input source is present and the buck converter has started.

Could you please clarify the intended behavior of VSYS_STAT?

My questions are:

  1. Is REG12h.VSYS_STAT valid only when VIN is present and the buck converter is operating?

  2. Should VSYS_STAT be ignored when VIN_GD = 0?

  3. Is it expected that VSYS_STAT = 1 even when VBATT < VSYS_MIN, if the system is running only from the battery?

  4. What is the recommended register/status bit for detecting low battery in battery-only operation?

  5. Should I use REG16h.BATT_LOW_STAT instead, or is an external ADC measurement of VBATT recommended for host deep-sleep decisions?