DS2437
Smart Battery Monitor
www.dalsemi.com
FEATURES
Unique 1-Wire interface requires only one
port pin for communication
Provides unique 64-bit serial number to
battery packs
Eliminates thermistors by sensing battery
temperature on-chip
On-board A/D converter allows monitoring of
battery voltage for end-of-charge and end-of-
discharge determination
On-board integrated current accumulator
facilitates gas gauging
Real-time clock in binary format
40-byte nonvolatile user memory available for
storage of user data such as gas gauge and
manufacturing information
Operating range -40°C to +85°C
Applications include portable computers,
portable/cellular phones, consumer
electronics, and handheld instrumentation
®
PIN ASSIGNMENT
DQ
NC
VAD
NC
VSENS+
VSENS-
NC
AGND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VDD
NC
NC
X1
NC
X2
NC
GND
16-PIN SSOP
See Mech. Drawings Section
PIN DESCRIPTION
DQ
VAD
VSENS+
VSENS-
NC
GND
AGND
X2
X1
V
DD
- Data In/Out
- General A/D input
- Battery current monitor input (+)
- Battery current monitor input (-)
- No connect
- Digital Ground
- Analog Ground
- Connection for 32.768 kHz XTAL
- Connection for 32.768 kHz XTAL
- Power Supply (2.7V to 10.0V)
DESCRIPTION
The DS2437 Smart Battery Monitor provides several functions that are desirable to carry in a battery
pack: a means of tagging a battery pack with a unique serial number; a direct-to-digital temperature
sensor which eliminates the need for thermistors in the battery pack; an A/D converter which measures
the battery voltage and current; an integrated current accumulator, which keeps a running total of all
current going into and out of the battery; a real-time clock; and 40 bytes of nonvolatile EEPROM
memory for storage of important parameters such as battery capacity, capacity remaining, and indication
of battery cycling.
Information is sent to/from the DS2437 over a 1-Wire interface, so that only one wire (and ground) needs
to be connected from a central microprocessor to a DS2437. This means that battery packs need only
have three output connectors: battery power, ground, and the 1-Wire interface.
Because each DS2437 contains a unique silicon serial number, multiple DS2437s can exist on the same
1-Wire bus. This allows multiple battery packs to be charged or used in the system simultaneously.
1 of 31
070600
DS2437
Applications for the smart battery pack monitor include portable computers, portable/cellular telephones,
and handheld instrumentation battery packs in which it is critical to monitor real-time battery
performance. Used in conjunction with a microcontroller in the battery pack or host system, the DS2437
provides a complete smart battery pack solution that is fully chemistry-independent. The customization
for a particular battery chemistry and capacity is realized in the code programmed into the
microcontroller and DS2437 EEPROM, and only a software revision is necessary should a designer wish
to change battery pack chemistry.
DETAILED PIN DESCRIPTION
PIN
1
3
5
6
8
9
11
13
16
2, 4, 7, 10,
12, 14, 15
SYMBOL
DQ
VAD
VSENS+
VSENS-
AGND
GND
X2
X1
V
DD
NC
DESCRIPTION
Data Input/Out:
for 1-Wire operation: open drain
ADC Input:
input for general purpose A/D
Battery Input:
connection for battery current to be monitored (see text)
Battery Input:
connection for battery current to be monitored (see text)
Analog Ground:
must be at the same potential as GND
Digital Ground:
must be at the same potential as AGND
Crystal Input:
connection for 32.768 kHz for RTC operation
Crystal Input:
connection for 32.768 kHz for RTC operation
V
DD
Pin:
input supply voltage
No Connect
OVERVIEW
The block diagram of Figure 1 shows the seven major components of the DS2437:
1.
2.
3.
4.
5.
6.
7.
64-bit lasered ROM
temperature sensor
battery voltage A/D
battery current A/D
current accumulators
real-time clock
40-byte nonvolatile user memory
Each DS2437 contains a unique 64-bit lasered ROM serial number so that several battery packs can be
charged/monitored by the same host system. Furthermore, other Dallas products featuring the same
1-Wire bus architecture with a 64-bit ROM can reside on the same bus; refer to the Dallas "Automatic
Identification Data Book" for the specifications of these products.
Communication to the DS2437 is via a 1-Wire port. With the 1-Wire port, the memory and control
functions will not be available until the ROM function protocol has been established. The master must
first provide one of four ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, or 4)
Skip ROM. These commands operate on the 64-bit lasered ROM portion of each device and can singulate
a specific device if many are present on the 1-Wire line as well as indicate to the bus master how many
and what types of devices are present. After a ROM function sequence has been successfully executed,
the memory and control functions are accessible and the master may then provide any one of the six
memory and control function commands.
2 of 31
DS2437
Control function commands may be issued which instruct the DS2437 to perform a temperature
measurement or battery voltage A/D conversion. The result of these measurements will be placed in the
DS2437’s memory map, and may be read by issuing a memory function command which reads the
contents of the temperature and voltage registers. Additionally, the charging/discharging battery current is
measured without user intervention, and again, the last completed result is stored in DS2437 memory
space. The DS2437 uses these current measurements to update three current accumulators: one stores net
charge for gas gauge calculations, the second accumulates the total charging current over the life of the
battery, and the remaining accumulator tallies battery discharge current. The real time clock data, which
can be used in calculating battery self-discharge or time-related charge termination limits, also resides in
the DS2437 memory map and can be extracted with a control function command. The nonvolatile user
memory of the DS2437 consists of 40 bytes of EEPROM. These locations may be used to store any data
the user wishes and are written to using a memory function command. All data and commands are read
and written least significant bit first.
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power
whenever the DQ pin is high. DQ will provide sufficient power as long as the specified timing and
voltage requirements are met (see the section titled “1-Wire Bus System”). The advantage of parasite
power is that the ROM may be read in absence of normal power, i.e., if the battery pack is completely
discharged.
DS2437 BLOCK DIAGRAM
Figure 1
3 of 31
DS2437
OPERATION – MEASURING TEMPERATURE
The DS2437 measures temperatures through the use of an onboard proprietary temperature measurement
technique.
The temperature reading is provided in a 13-bit, two’s complement reading, which provides 0.03125°C of
resolution. Table 1 describes the exact relationship of output data to measured temperature. The data is
transmitted serially over the 1-Wire interface. The DS2437 can measure temperature over the range of
-55°C to +125°C in 0.03125°C increments. For Fahrenheit usage, a lookup table or conversion factor
must be used.
Note that temperature is represented in the DS2437 in terms of a 0.03125°C LSb, yielding the following
13-bit format. The 3 least significant bits of the temperature register will always be 0. The remaining 13
bits contain the two’s complement representation of the temperature in
°C,
with the MSb holding the sign
(S) bit. See “Memory Map” section for the TEMPERATURE REGISTER address location.
Temperature/Data Relationships
Table 1
TEMPERATURE
+125°C
+25.0625°C
+1/2°C
0°C
-1/2°C
-25.0625°C
-55°C
DIGITAL OUTPUT (Binary)
01111101 00000000
00011001 00010000
00000000 10000000
00000000 00000000
11111111 10000000
11100110 11110000
11001001 00000000
DIGITAL OUTPUT (Hex)
7D00h
1910h
0080h
0000h
FF80h
E6F0h
C900h
OPERATION – MEASURING BATTERY VOLTAGE
The on-board analog-to-digital converter (ADC) has 10 bits of resolution and will perform a conversion
when the DS2437 receives a command protocol (Convert V) instructing it to do so. The result of this
measurement is placed in the 2-byte VOLTAGE REGISTER. The range for the DS2437 ADC is 0V to
10V; this range is suitable for NiCd or NiMH battery packs up to six cells and for lithium ion battery
packs of two cells. The full-scale range of the ADC is scaled to 10.23V, resulting in a resolution of 10
mV.
While the ADC has a range that extends to 0V, it is important to note that the battery voltage can also be
the supply voltage to the DS2437. As such, the accuracy of the ADC begins to degrade below battery
voltages of 2.7V, and the ability to make conversions is limited by the operating voltage range of the
DS2437.
4 of 31
DS2437
Voltage is expressed in this register in scaled binary format, as outlined in Table 2. Note that while codes
exist for values below 2.7V, accuracy of the ADC and the limitation on the DS2437’s supply voltage
make it unlikely that these values would be used in actual practice. See “Memory Map” section for the
VOLTAGE REGISTER address location.
Voltage/Data Relationships
Table 2
BATTERY
VOLTAGE
0.01V
2.7
3.6V
5V
7.2V
9.99V
10V
DIGITAL OUTPUT (Binary)
0000 0000 0000 0001
0000 0001 0000 1110
0000 0001 0110 1000
0000 0001 1111 0100
0000 0010 1101 0000
0000 0011 1110 0111
0000 0011 1110 1000
DIGITAL OUTPUT (Hex)
0001h
010Eh
0168h
01F4h
02D0h
03E7h
03E8h
For applications requiring a general purpose voltage A/D converter, the DS2437 can be configured so that
the result of a Convert V command will place the scaled binary representation of the voltage on the V
AD
input (as opposed to the V
DD
input) into the VOLTAGE REGISTER in the same format described in
Table 2. Depending upon the state of the configuration register, either (but not both) the V
DD
or V
AD
voltage will be stored in the VOLTAGE REGISTER upon receipt of the Convert V command. Refer to
the description of the Configuration Register in the Memory Map section for details. If the V
AD
input is
used as the voltage input, the A/D will be accurate for 0V < V
AD
< 2V
DD
over the range 2.7V < V
DD
<
5.0V. Recall that the battery voltage A/D (V
DD
input) loses accuracy as V
DD
falls below 2.7V. This
feature gives the user the ability to have a voltage A/D that meets spec accuracy for inputs over the entire
range of 0V < V
AD
< 10V for V
DD
= 5.0V.
OPERATION – MEASURING BATTERY CURRENT
The DS2437 features a sigma-delta A/D converter that effectively measures the current flow into and out
of the battery pack. It does so in the background at a rate of 32 measurements/sec; thus, no command is
required to initiate current flow measurements. However, the DS2437 will only perform current A/D
measurements if the IAD bit is set to 1 in the CONFIGURATION REGISTER. The DS2437 measures
current flow in and out of the battery through the VSENS pins; the voltage from the VSENS+ pin to the
VSENS- pin is considered to be the voltage across the current sense resistor, R
SENS
. While the VSENS+
terminal may be tied directly to the cell side of the R
SENS
resistor, we recommend using an RC low pass
filter between the other side of R
SENS
and VSENS-. Using a 47 kΩ=(max) resistor (R
F
) and a 0.1
µF
capacitor (C
F
), the filter cutoff is approximately 32 Hz. The current A/D measures at a rate of 32 times
per second, or once every 31.25 ms. This filter will capture the effect of many current spikes and will thus
allow the current accumulators to accurately reflect the total charge which has gone into or out of the
battery.
5 of 31
京公网安备 11010802033920号
EEWORLD
