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DS2438 Schematic ( PDF Datasheet ) - Maxim Integrated

Teilenummer DS2438
Beschreibung Smart Battery Monitor
Hersteller Maxim Integrated
Logo Maxim Integrated Logo 




Gesamt 29 Seiten
DS2438 Datasheet, Funktion
AVAILABLE
DS2438
Smart Battery Monitor
FEATURES
§ Unique 1-Wire® interface requires only one
port pin for communication
§ Provides unique 64-bit serial number
§ 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 fuel gauging
§ Elapsed time meter in binary format
§ 40-byte nonvolatile user memory available
for storage of battery-specific data
§ Reverts to low-power sleep mode on battery
pack disconnect (feature disabled on
DS2438AZ)
§ Operating range -40ºC to +85ºC
§ Applications include portable computers,
portable/cellular phones, consumer
electronics, and handheld instrumentation
PIN ASSIGNMENT
GND
VSENS+
VSENS-
VAD
1
2
3
4
8 DQ
7 NC
6 NC
5 VDD
DS2438Z, DS2438AZ
8-Pin SOIC (150-mil)
PIN DESCRIPTION
DQ - Data In/Out
VAD - General A/D input
VSENS+ - Battery current monitor input (+)
VSENS- - Battery current monitor input (-)
VDD - Power Supply (2.4V to 10.0V)
GND - Ground
NC - No connect
DESCRIPTION
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that are
number,
desirable to carry
a direct-to-digital
in a battery
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, an elapsed time meter, and 40 bytes of nonvolatile EEPROM
memory for storage of important parameters such as battery chemistry, battery capacity, charging
methodology and assembly date. Information is sent to/from the DS2438 over a 1-Wire interface, so that
only one wire (and ground) needs to be connected from a central microprocessor to a DS2438. This
means that battery packs need only have three output connectors: battery power, ground, and the 1-Wire
interface.
Because each DS2438 contains a unique silicon serial number, multiple DS2438s can exist on the same
1-Wire bus. This allows multiple battery packs to be charged or used in the system simultaneously.
Applications for the smart battery monitor include portable computers, cellular telephones, and handheld
instrumentation battery packs in which it is critical to monitor real-time battery performance. Used in
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the DS2438 provides a complete smart battery
customization for a particular battery chemistry
and capacity is realized in the code programmed into the microcontroller and DS2438 EEPROM, and
only a software revision is necessary should a designer wish to change battery pack chemistry.
For pricing, delivery, and ordering information,1polfe2a9se contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
070605






DS2438 Datasheet, Funktion
CURRENT REGISTER FORMAT Table 3
(This register actually stores the voltage measured across current sense resistor RSENS.
This value can be used to calculate battery pack current using the equation below.)
DS2438
27 26
MSb
SS
25 24 23 22 21 20 LSB
(unit = 0.2441mV) LSb
S S S S 29 28 MSB
The battery pack current is calculated from the Current Register value using the equation:
I = Current Register / (4096 * RSENS)
(where RSENS is in W)
For example, if 1.25A is flowing into the pack, and the pack uses a 0.025W sense resistor, the DS2438
will write the value 12810 to the Current Register. From this value, battery pack current can be calculated
to be:
I = 128 / ( 4096 * 0.025) = 1.25A
Because small current ADC offset errors can have a large cumulative effect when current is integrated
over time, the DS2438 provides a method for canceling offset errors in the current ADC. After each
current measurement is completed, the measured value is added to the contents of the Offset Register and
the result is then stored in the Current Register. The Offset Register is a two-byte nonvolatile read/write
register formatted in two’s-complement format. The four MSb’s of the register contain the sign of the
offset, as shown in Table 4.
OFFSET REGISTER FORMAT Table 4
24 23
MSb
XX
22 21 20
0
(unit = 0.2441 mV)
X S 28 27
0 0 LSB
LSb
26 25 MSB
The following process can be used to calibrate the current ADC:
1. Write all zeroes to the Offset Register
2. Force zero current through RSENS
3. Read the Current Register value
4. Disable the current ADC by setting the IAD bit in the Status/Configuration Register to “0”
5. Change the sign of the previously-read Current Register value by performing the two’s complement
and write the result to the Offset Register
6. Enable the current ADC by setting the IAD bit in the Status/Configuration Register to “1”
NOTE:
When writing to the Offset Register, current measurement MUST be disabled (IAD bit set to “0”).
The current ADC calibration process is done for each DS2438 device prior to shipment. However, for
best results, battery pack manufacturers should calibrate the current ADC during initial battery pack
testing, and the host system should calibrate whenever possible (during battery charging, for example).
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DS2438 pdf, datenblatt
ROM FUNCTIONS FLOWCHART Figure 5
DS2438
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