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052699
FEATURES
Provides all identification, information,
instrumentation and protection functions
needed in a lithium-ion battery pack
Supports one-cell battery packs
Protects cell from:
overvoltage (overcharge)
undervoltage (overdischarge)
overcurrent (charging and discharging)
high temperatures (thermal runaway)
Current accumulator tracks remaining battery
capacity in 0.5% increments
Voltage measurement with 10 mV accuracy
Temperature measurement with
2
C
accuracy eliminates need for thermistor
32-byte user memory stores battery data
64-bit ROM ID uniquely identifies each
battery pack
1-WireTM interface carries all commands and
data via a single wire
Programmable alarm warns when cell is
nearly discharged
Programmable I/O pin supports LEDs,
vibration motors and other features
Operating temperature range: -40
C to +85
C
10kV ESD rating
PIN ASSIGNMENT
PIN DESCRIPTION
GND
Ground
PIO
Programmable I/O pin
ISENS
Current sense input
VM
not used, connect to GND
V
DD
Power supply input (2.4V to 10V)
CHG
Charge control output
DCHG
Discharge control output
DQ
Data I/O (1-Wire interface)
DESCRIPTION
The DS2441 1-Cell Li-Ion Battery Manager provides all essential functions for monitoring, protecting
and managing one-cell lithium-ion battery packs. The DS2441 constantly measures cell voltage, current,
and temperature, and automatically takes action to disable charging and/or discharging of the cell to
protect it when undesirable conditions arise.
Via its 1-Wire interface, the DS2441 provides the host system access to identification information, status
data, configuration and control settings, instrumentation registers, and general purpose data storage. Each
DS2441 has a factory-programmed 64-bit ROM ID which allows the host system to verify the
authenticity of the battery pack as well as a factory-programmed 16-bit manufacturing ID which can be
used to encode assembly location, cell chemistry and other information. A full set of status information
in the DS2441 keeps the host informed about protection conditions, remaining capacity and other matters.
Configuration and control fields in the device allow the host to disable charging and/or discharging, put
the battery pack in a low-power mode, and set various timing parameters. In addition, instrumentation
DS2441
1-Cell Li-Ion Battery Manager
www.dalsemi.com
PRELIMINARY
DS2441
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registers on the chip present the host with high-accuracy temperature, voltage, and current measurements
as well as information on remaining capacity and cycle life. Thirty-two bytes of general purpose memory
in the DS2441 are available for storing pack-specific information.
When the cell voltage reaches the undervoltage cutoff, the DS2441 automatically enters a low-power
mode in which it consumes only 1A of battery current. When a battery charger is applied to the pack,
the DS2441 automatically leaves its low-power mode to support charging. A refresh feature in the
DS2441 allows even the most severely discharged battery packs to be refreshed and recharged. The
DS2441 also features a programmable I/O pin that allows the host system to sense and control other
electronics in the pack, such as vibration motors, speakers and LEDs.
DETAILED PIN DESCRIPTION Table 1
Pin
Symbol
Description
1
GND
Ground. System voltage reference. Connect this pin to the negative terminal
of the cell and to one side of the current sense resistor.
2
PIO
Programmable Digital I/O. Use this user-definable pin to control features
such as a vibration motor or an LED driver, or to monitor an input signal such
as a tamper-sensing circuit.
3
ISENS
Current Sense Input. The DS2441 measures the voltage between this pin
and GND to calculate the current flowing through the external sense resistor.
Connect this pin through an RC low-pass filter to the PACK- side of the sense
resistor.
4
VM
Voltage Monitor Input. Not used on the DS2441. Connect to GND.
5
V
DD
Power Supply Input. The DS2441 draws operating power through this pin
and uses this pin and the GND pin to monitor the voltage of the cell. Voltage
on this pin must be between 2.4V and 10V for proper operation.
6
CHG
Charge Control Output. Controls an external p-channel charge protection
FET. Open-drain output driver.
7
DCHG
Discharge Control Output. Controls an external p-channel discharge
protection FET. Push-pull output driver.
8
DQ
Data Input/Output. 1-Wire data line. Parasite power supply for memory
read/write operations. DS2441 power supply in Refresh Mode. Open-drain
output driver. Connect this pin to the DATA terminal of the battery pack. In
the host system, connect a 5 k
pullup from the DATA terminal to the
PACK+ terminal.
DS2441
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BLOCK DIAGRAM Figure 1
APPLICATION EXAMPLE Figure 2
The circuit in Figure 2 depicts the DS2441 in a one-cell battery pack application. The circuit employs two
p-channel power MOSFETs as charge and discharge protection switches along with a 1 M
pullup
resistor to PACK+ to turn off the charge FET. The DS2441 tracks current in and out of the pack by
measuring the voltage across sense resistor R
SENS
(i.e., the voltage on ISENS with respect to GND). The
0.1
F capacitor and 2.2 k
resistor on the ISENS pin form a low-pass filter to aid current measurement
and accumulation. The diagram shows how the PIO pin can be used to drive an LED to implement a
state-of-charge display. A zener diode limits the maximum voltage at the DQ terminal in the event that
the pullup voltage is higher than the specified maximum DQ input voltage. Although the DS2441 has a
10kV ESD rating, this diode is recommended to clamp ESD events safely outside the IC.
Cell
DS2441
2.2K
0.025
1K
1M
0.1
F
0.1
F
CHG
DCHG
PACK+
PACK
-
DATA
6.2V
R
SENS
VDD
VM
GND
PIO
1
2
3
4
5
6
7
8
VREG
MUX
Temp
Sensor
Voltage A/D
Current A/D
1-Wire I/O
and
64-bit
ROM ID
Control
Logic
Registers
32-Byte
User
Memory
DQ
VDD
GND
ISENS
DCHG
CHG
PIO
DQ
DCHG
CHG
VDD
GND
PIO
ISENS
VM
DS2441
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OVERVIEW
The DS2441 Block Diagram in Figure 1 shows the six major components of the DS2441:
1-Wire I/O port and 64-bit ROM ID
Battery voltage A/D converter and monitor logic
Battery current A/D converter and monitor logic
Temperature sensor
Registers and memory
Control logic and outputs
POWER-ON RESET
The DS2441 executes a power-on reset (POR) whenever the voltages on both the VDD and DQ pins are
below V
POR
and then one or both voltages rise above V
POR
. This includes the case where a lithium-ion
cell is first attached to the DS2441 with DQ low or unconnected. During a POR, the DS2441 sets the
POR
bit in the Configuration Register to logic 0, locks Page 0 memory against accidental overwrite, and
loads default values into the following registers from laser ROM:
-
Control Register
-
Delay Timing Register
-
Discharge Termination Warning Register
-
Manufacturing ID Register
-
Configuration Register
Also during a POR, the DS2441 sets the Temperature, Voltage, and Current registers to their most
negative values, as shown in Table 2.
POR Register Values Table 2
Value
Register
decimal
hex
Temperature
-128
C
80h
Voltage
0 mV
0000h
Current
-5.12C
FE00h
After reloading and resetting all of the registers mentioned above, the DS2441 enters its normal mode of
operation, measuring voltage, current and temperature and reacting accordingly.
DS2441
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LI-ION PROTECTION CIRCUITRY
During normal operation, the DS2441 constantly monitors cell voltage, current and temperature to protect
the cell from overcharge (overvoltage), overdischarge (undervoltage), excessive charge and discharge
currents (overcurrent), and thermal runaway (overtemperature). The DS2441 monitors for and protects
against each of these conditions with separate circuitry in order to properly protect the lithium-ion cell
from any single condition or combination of conditions that can arise. Conditions and DS2441 responses
are described in the sections below and summarized in Table 3 and Figure 3.
LI-ION PROTECTION CONDITIONS AND DS2441 RESPONSES Table 3
Activation
Release
Condition
Name
Threshold
Delay
Response
Threshold
Delay
Overvoltage
V
CELL
> V
OV
t
OVD
CHG
off
V
CELL
< V
CE
0
Undervoltage
V
CELL
< V
UV
t
UVD
CHG
off,
DCHG
high,
Low Power
Mode
exit Low Power Mode
AND V
CELL
> V
UV
0
Overcurrent,
Charge
V
ISENS
< -V
OC
t
OCD
CHG
off
none
t
REL
V
ISENS
> V
OC
t
OCD
Overcurrent,
Discharge
V
ISENS
> V
SC
t
SCD
DCHG
high
none
t
REL
Overtemp
T
MEAS
> T
TRIP
0
CHG
off,
DCHG
high
T
MEAS
< T
TRIP
- T
HYS
0
(V
CELL
= VDD. T
MEAS
= measured temperature.)
Overvoltage. If the voltage of the cell exceeds overvoltage threshold V
OV
for a period longer than
overvoltage delay t
OVD
, the DS2441 shuts off the external charge FET and sets the overvoltage protection
flag, OV, in the Status Register. When the cell voltage falls below charge enable threshold V
CE
, the
DS2441 clears the OV flag and enables the charge FET (unless another protection condition prevents it).
Except when a discharge protection condition also occurs, discharging remains enabled during
overvoltage, with the discharge path consisting of the channel of the discharge FET and the body diode of
the charge FET.
Undervoltage. If the voltage on the cell drops below undervoltage threshold V
UV
for a period longer
than undervoltage delay t
UVD
, the DS2441 shuts off the charge and discharge FETs, asserts the
undervoltage protection flag, UV, in the Status Register and enters Low Power Mode to minimize the
load it presents to the cell. See the section on Low Power Mode for more details.
Overcurrent, Charge Direction. The voltage on the I
SENS
pin with respect to GND (V
ISENS
) is the
voltage across current sense resistor R
SENS
. If V
ISENS
is less than -V
OC
(V
OC
is the overcurrent threshold)
for a period longer than overcurrent delay t
OCD
, the DS2441 shuts off the external charge FET and sets the
overcurrent protection flag, OC, in the Status Register. After the expiration of release delay t
REL
, the
DS2441 clears the OC flag and enables the charge FET (unless another protection condition prevents it).
If the overcurrent condition persists for t
OCD
after the charge FET is enabled, the DS2441 responds again.
If the overcurrent condition persists indefinitely, the DS2441 cycles between protecting and releasing
until an overvoltage condition arise. Except when a discharge protection condition also occurs,
discharging remains enabled during charge-direction overcurrent, with the path consisting of the channel
of the discharge FET and the body diode of the charge FET.
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