ADP5350ACBZ-1-R7 datasheet(27/63 Pages) AD

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Data Sheet

ADP5350

Rev. B | Page 27 of 63

(typical) of operation current. In sleep mode, the battery SOC is

updated every 5 min and the battery instant current (IINS) is

updated every 37.5 sec, which reduces the current to typically

4 µA (see Table 15). The ADP5350 automatically switches from

sleep mode to active mode when the current through the

isolation FET is higher than typically 35 mA. The system

current must be less than 35 mA when switching to sleep mode.

Depending on the system load, the mode can be switched to

active mode to achieve better SOC accuracy.

Table 15. Fuel Gauge Operation Mode

Operation

Mode

Current

(Typical)

ADC Sample

Rate

SOC Update

Rate

Shutdown

0.2 µA

None

Sleep

4 µA

37.5 sec

5 min

Active

160 µA

0.125 sec

1 sec

Battery Voltage Compensation

The battery internal resistance impacts the accuracy of a

traditional voltage-based SOC. A higher load current translates

to a higher voltage drop (ΔVDROP) over the internal resistance,

RBAT (see Figure 44).

Figure 44. Discharge Current Sensing Through Battery Isolation FET

The ADP5350 uses the battery isolation FET for battery discharge

current sensing. The device senses the ISOS and ISOB node

voltages to obtain the delta voltage. Divide the delta voltage by

RDSON to achieve the discharge current, which can be used for

SOC calculation compensation.

The voltage reading from the BSNS pin is compensated using

the following equation and can be read in the VBAT_READ_H

and VBAT_READ_L registers.

VBAT = VBSNS + RBAT × IBAT

where:

VBSNS is the voltage on the BSNS pin.

RBAT is the internal resistance of the battery.

IBAT is the current through the battery.

When the battery is charging, IBAT is the charging current.

During the battery discharges, IBAT is calculated by the voltage

sense on the isolated FET.

The internal resistance of the battery has strong temperature

dependency. Figure 45 shows the internal resistance

temperature coefficient using a 280 mAh, 3.7 V Li-Ion cell

battery.

The ADP5350 contains I2C registers to calculate the RBAT value,

where the user can program the battery internal resistance

characterized from the battery at certain temperatures. The

ADP5350 uses this data to calculate the battery internal

resistance at different temperatures.

It is strongly recommended to use the I2C bits, BAT_TEMP, to

obtain an accurate battery temperature if the system has such

temperature sense information. If using the ADP5350 internal

sense circuitry as the temperature source, only four temperature

levels for battery resistance compensation are available, which

may cause errors in the SOC calculation relating to the battery

resistance temperature coefficient.

Figure 45. RBAT Temperature Coefficient vs. Battery Temperature,

Temperature Coefficient of the Li-Ion Battery, Relative to Battery RBAT at 25°C

In addition, the internal resistance of the battery has a remaining

capacity dependency, especially when the SOC is less than 20%.

The ADP5350 allows the user to program different internal

resistance coefficients when the SOC is in the 20% to 0% range

during a discharge by programming the corresponding bits,

K_RBAT_SOC (see Figure 46).

Figure 46. RBAT SOC Coefficient vs. Battery SOC,

SOC Coefficient of the Li-Ion Battery, Relative to Battery RBAT at 25°C

RDSON

ISOB

ISOS

TO SYSTEM

BATTERY RESISTANCE

ΔVDROP = RBAT × IBAT

–

3.0

0.5

1.5

2.5

1.0

2.0

BATTERY TEMPERATURE (°C)

100

BATTERY SOC (%)

1 × 20% SOC

2 × 20% SOC

4 × 20% SOC

8 × 20% SOC

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