SS4002AG
Smart Li-Ion Battery Gas Gauge
PRODUCT SUMMARY
Accurately measures available charge in Li-Ion batteries
Provides 14-bit resolution for voltage, temperature, and current measurements
Controls the MOSFETs used in the Li-Ion protection circuit
FEATURES
Supports SBS Smart Battery Data Specification v1.1
Supports the 2- wire SMBus v1.1 interface with PEC
Reports individual cell voltages
Monitors and provides control to charge and
discharge the MOSFETs used in a Li- Ion
protection circuit
Provides cell balance control output for charge
control.
Consumes less than 1.5mW during operation
Drives a 4- or 5-segment LED display for indication
of remaining capacity
Narrow (150-mil) SSOP-28
Pb-free, RoHS compliant.
GENERAL DESCRIPTION
The SS4002AG is an SBS-compliant gas gauge IC for
battery pack or in-system installation. It maintains an
accurate record of available charge in rechargeable
batteries. The SS4002AG is designed specifically for Li-Ion
batteries, and monitors capacity and other critical
battery parameters. The SS4002AG uses an A-to- D
converter with automatic offset error correction for
voltage, temperature, and cur rent reporting. The
cumulated charge into (or discharge from) the battery is
continuously calculated. The onboard ADC also
monitors individual cell voltages in the battery pack and
allows the SS4002AG to generate control signals that may
be used in conjunction with a pack supervisor to enhance
pack safety.
The SS4002AG supports the smart battery data
(SBData) commands and charge -control functions. It
communicates
data using the 2- wire System
Management Bus (SMBus). The data available includes
the battery’s remaining capacity, temperature, voltage,
current, and remaining run -time predictions.
The SS4002AG provides drive pins for LEDs to depict
remaining battery capacity from full to empty in 20% or
25% increments with a 4 or 5-segment display.
The SS4002AG work s with an external EEPROM. The
EEPROM stores the configuration information for the
SS4002AG, such as the self-discharge rate, measurement
calibration, and design voltage and capacity.
The SS4002AG uses the programmable self-discharge
rate and other compensat ion factors stored in the
EEPROM to accurately adjust remaining capacity for
use and standby conditions based on time, rate, and
temperature. The SS4002AG also automatically calibrates
or learns the true battery capacity in the course of a
discharge cycle from near full to near empty levels.
The VREF output regulates the operating voltage for
the SS4002AG from the battery cell stack using an
external MOSFET.
12/16/2005 Rev.3.01
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SS4002AG
PIN CONFIGURATION
V2
V2
V1
ADJ1
ADJ2
ADJ3
ADJ4
DCHG
AVDD
DVDD
VP
ESCL
ESDA
SDA
SCL
V3
V4
T
I
IGND
VREF
CHG
AGND
DGND
LED1
LED2
LED3
LED4
LED5
V1
ADJ1
ADJ2
ADJ3
ADJ4
DCHG
AVDD
DVDD
VP
ESCL
ESDA
SDA
SCL
Voltage from tip of cell 2
Voltage from tip of cell 1
Cell1 bypass control
Cell2 bypass control
Cell3 bypass control
Cell 4 bypass control
Discharge FET control output
Analog VDD
Digital VDD (4.5V~5.5V)
EEPROM supply output
EEPROM clock (output)
EEPROM data (input/output)
SMB data (input/output)
SMB clock (input/output)
V3
V4
T
I
IGND
VREF
CHG
AGND
DGND
LED1
LED2
LED3
LED4
LED5
Voltage from tip of cell 3
Voltage from tip of cell 4
Temperature sense resistor input
Current sense resistor input
Current sense resistor ground port
Voltage reference output
Charge FET control output
Analog Ground
Digital ground
LED segment (MSB)
LED segment
LED segment
LED segment
LED segment (LSB)
28-Pin Narrow SOIC
SS4002AG
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SS4002AG
PIN DESCRIPTION
Pin Name
ADJ1
ADJ2
ADJ3
ADJ4
AGND
AVDD
CHG
DCHG
DGND
DVDD
ESCL
ESDA
I
IGND
LED1
LED2
LED3
LED4
LED5
SCL
SDA
T
V1
V2
V3
V4
VP
VREF
3
4
5
6
21
8
22
7
20
9
11
12
25
24
19
18
17
16
15
14
13
26
2
1
28
27
10
23
Pin No
I/O
Input/Output
Output
Output
Output
Input
Input
Output
Output
Input
Input
Output
Input/Output
Input
Input
Output
Output
Output
Output
Output
4
4
4
4
4
2
1
1
1
1
Description
Cell balance bypass control for cell 1 (Timer in for calibration)
Cell balance bypass control for cell 2
Cell balance bypass control for cell 3
Cell balance bypass control for cell 4
Analog ground
Analog positive supply
Charge MOSFET control output. High output to terminate charge
Discharge MOSFET control output. High output to terminate discharge
Digital ground
Digital positive supply
EEPROM I C clock line
EEPROM I C data line
Current sense resistor battery negative terminal
Current sense resistor ground (pack negative) terminal
LED display segment (MSB)
LED display segment
LED display segment
LED display segment
LED display segment (LSB)
SMbus clock line
SMbus data line
Temperature sense resistor voltage divider circuits terminal
Divided voltage input from cell 1 (the cell connect to battery negative
terminal)
Divided voltage input from cell 2
Divided voltage input from cell 3
Divided voltage input from cell 4 (highest voltage)
EEPROM positive supply
Voltage regulator’s voltage reference output
2
2
Input/Output
Input/Output
Input
Input
Input
Input
Input
3
3
3
3
3
Output
Output
Note 1: Input/outputs are TTL compatible level.
Note 2: Input voltage range is –160mV to +80mV.
Note 3: Divided voltage input range should be from 0.5V to 3.5V.
Note 4: Open drain output.
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SS4002AG
Voltage Thresholds
In conjunction with monitoring the voltage at the I pin for
charge/discharge currents, the SS4002AG also monitors
the battery potential through the V pin. The voltage
potential is determined through a resistor- divider
network on tips of cells. The dividing factors of networks
are calculated during calibration and saved in the
EEPROM. The battery voltage is obtained by measuring
the input voltages on tips of cells and dividing factors
stored in EEPROM. The battery voltage is monitored for
battery LOW and battery EXHAUSTED (PLV and PEV).
An alarm warning will be sent to the host when battery
voltage is lower than PLV or PEV. Both PLV and PEV
are dynamically adjusted according to present load and
temperature. Exhausting charge threshold levels are
used to determine when the battery has reached a
programmable “empty” state. If the discharge current is
greater than the overload current value stored in the
EEPROM, PLV monitoring is disabled and resumes
after the current falls below the programmed value.
FCCAP is updated, RCAP counts up to, but not beyond,
this threshold during subsequent charges. The battery’s
empty state is also programmed in the EEPROM. The
battery -low percentage stores the percentage of FCCAP
while the battery voltage drops to the PLV threshold.
1. Full Charge Capacity (FCC AP ):
FCCAP is the lat est measured discharge capacity of the
battery. On initialization, FCCAP is set to the value
stored in the EEPROM. During subsequent discharges,
FCCAP is updated with the latest recognized complete
discharging (or learning cycle), representing a discharge
from full to PLV, plus the battery low amount. A learning
cycle is necessary to updat e the FCCAP register. The
FCCAP also serves as the 100% reference threshold
used by the relative state-of-charge calculation and
display.
2. Design Capacity (DCAP ):
The DCAP is the user-specified battery capacity and is
programmed in the external EEPROM. The DCAP also
provides the 100% reference for the absolute state- of -
charge calculation.
3. Remaining Capacity (RCAP ):
RCAP counts up during charge to a maximum value of
FCCAP and counts down to 0 during discharge and self-
discharge. RCAP is set to the battery low amount after
the PLV threshold has been reached. If RCAP is equal
to the battery low amount , RCAP keeps until voltage
drops below PLV threshold. To prevent overstatement of
charge during periods of overcharge, RCAP stops
incrementing when RCAP = FCCAP.
4. Cumulated Discharge Count (CDC):
The Cumulated Discharge Count is used to record the
usage of the battery which relates to the life of battery.
The CDC counts up during discharge independent of
RCAP and can continue increasing after RCAP has
decremented to 0. The CDC resets to 0 when CDC =
DCAP and the Cycle Count will be increased by 1.
Reset
The SS4002AG is in reset state when either first
connected to the battery pack or receiving a RESET
command from SMBus. Two categories of reset
command, hard reset and soft reset, are acceptable
from the SMBus. On hard reset, the SS4002AG initializes
and reads the EEPROM to configur e the battery pack.
On soft reset, the SS4002AG keeps the current state of
battery. The soft -RESET command is a byte command
with command code 0xF5. The hard- RESET command
is sent through manufacture r access data 0404.
Sleep mode
The SS4002AG switches into sleep mode after detecting
no charge flow-through for more than 24 0 seconds . In
the sleep mode, most of the logic circuitry in the chip is
turned off to minimize the power consumption. SS4002AG
will be a wakened by either receiving an SBD command
or detecting a current flow through the sense resistor.
Measurement Operation
The SS4002AG accumulates a measure of charge and
discharge currents, and estimates self- discharge.
Charge currents are compensated for temperature and
state-of -charge of the battery. The battery capacity,
denoted as Remaining Capacity (RCAP) in terms of
either current or power, represents the available battery
capacity at any given time. The charging increments the
RCAP, while the discharging and self- discharging
decrement the RCAP. An internal register is used to
accumulate the amount of discharge to adjust the Full
Charge Capacity (FCCAP). FCCAP is updated only if a
complete battery discharges from full to empty occurs
without any partial battery charges. Therefore, the
SS4002AG adapts its capacity determination based on
the actual conditions of discharge. The battery's initial
full capacity is set to the value stored in EEPROM. Until
12/16/2005 Rev.3.01
Charge Counting
Charge activity is detected based on a positive voltage
on the I input. The voltage input at the I input is
measured and converted into current through the sense
resistor. If charge activity is detected, the SS4002AG
increases the RCAP. Charge actio ns increment the
RCAP according to the cumulated charge counts. If the
measured current is lower than the threshold of the
digital filter and the digital filter is enabled, the charge
current is set as zero.
Discharge Counting
Discharge activity is detected based on a negative
voltage on the I input. The voltage input at the I input is
measured and converted into current through the sense
resistor. If discharge activity is detected, the SS4002AG
decre ases the RCAP. If the measured current is lower
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SS4002AG
than the threshold of the digital filter and both SMD and
SMC are high, the discharge current is set to light
discharge load. The threshold of the digital filter and
light discharge load are stored in EEPROM.
broadcasting
the
ChargingCurrent ()
and
the
ChargingVoltage () to the Smart Charger every 60
seconds. Broadcasting can be either suspended by
set ting bit 14 of BatteryMode to 1 or turned off in the
Master functionality by clearing bit 2 of ControlMode.
The SS4002AG updates the charging current
broadcasting based on the battery’s state of charge,
voltage, and temperature. The SS4002AG uses current
taper detection for Li- Ion primary charge termination and
over voltage detection to suspend charging. The
SS4002AG also provides a number of safety terminations
based on battery capacity, voltage, temperature and
conditions of individual cells.
Self-Discharge Estimation
The SS4002AG periodically decre ments RCAP for self-
discharge, until the charge - full or charge- empty
condition is detected. The estimated self-discharge rate
is programmed in EEPROM. The SS4002AG also adjusts
the self- discharge rate based on the pack temperature.
Charge Control
The SS4002AG supports SBS charge control by
Trickle Charge
CC charge
CV charge
Finished
V
CV
V
CC
∆V
V
RESUME
Capacity
V
LOW
I
CC
I
CV
I
TC
Figure 1. Charging control
Alarm Mode
If any of the bits 8- 15 is set , SS4002AG broadcasts an
AlarmWarning() message to the SMBus host. If any of
the bits 12- 15 is set, the AlarmWarning message is
broadcast to the Smart Charger as well. The message
sent by the AlarmWarning() function is the same as the
message returned by the BatteryStatus() function,
except for the lowest nibble (4 bits). The Smart Battery
will continue
broadcasting the AlarmWarning()
messages at 10 second intervals until the critical
condition(s) has been corrected. The AlarmWarning()
message broadcasting can be suspended by setting bit
13 (AlarmMode) of BatteryMode or turned off by clearing
bit 0 of ControlMode..
threshold. Depending upon the control circuit in the gas
gauge
module,
the
cell
balancing
can
be
enabled/disabled through a control bit in the control
mode register in
EEPROM.
Digital Filter
The SS4002AG does not measure charge or discharge
counts below the digital filter threshold. The digital filter
threshold is programmed in the
EEPROM
and should be
set sufficiently high to prevent false signal detection with
no charge or discharge flowing through the sense
resistor.
Current
The SS4002AG uses the voltage drops across the sense
resistor to measure and calculate the battery charge and
discharge current , and reports Current() in the data
register.
Cell Balancing
The SS4002AG balances the cells during charge by
partially bypassing the charges through the bypass
resistors for those cells above the bypass charge
threshold set in
EEPROM.
The cell balanc ing ceases
when voltages of all cells are over the bypass charge
12/16/2005 Rev.3.01
Voltage
While monitoring charge and discharge currents, the
SS4002AG monitors the individual series cell voltages .
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