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PDF DS2438 Data sheet ( Hoja de datos )

Número de pieza DS2438
Descripción Smart Battery Monitor
Fabricantes Maxim Integrated 
Logotipo Maxim Integrated Logotipo



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No Preview Available ! DS2438 Hoja de datos, Descripción, Manual

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

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DS2438 pdf
VOLTAGE REGISTER FORMAT Table 2
27 26 25 24 23 22 21 20 LSB
MSb
(unit = 10 mV)
LSb
0 0 0 0 0 0 29 28 MSB
DS2438
BATTERY
VOLTAGE
0.05V
2.7V
3.6V
5V
7.2V
9.99V
10V
DIGITAL OUTPUT (Binary)
0000 0000 0000 0101
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)
0005h
010Eh
0168h
01F4h
02D0h
03E7h
03E8H
For applications requiring a general purpose voltage A/D converter, the DS2438 can be configured so that
the result of a Convert V command will place the scaled binary representation of the voltage on the VAD
input (as opposed to the VDD input) into the Voltage Register in the same format described in Table 2.
Depending upon the state of the Status/Configuration Register, either (but not both) the VDD or VAD
voltage will be stored in the Voltage Register upon receipt of the Convert V command. Refer to the
description of the Status/Configuration Register in the Memory Map section for details. If the VAD input
is used as the voltage input, the A/D will be accurate for 1.5V < VAD < 2VDD over the range 2.4V < VDD <
5.0V. This feature gives the user the ability to have a voltage A/D that meets spec accuracy for inputs
over the entire range of 1.5V < VAD < 10V for VDD = 5.0V.
OPERATION - MEASURING BATTERY CURRENT
The DS2438 features an A/D converter that effectively measures the current flow into and out of the
battery pack by measuring the voltage across an external sense resistor. It does so in the background at a
rate of 36.41 measurements/sec; thus, no command is required to initiate current flow measurements.
However, the DS2438 will only perform current A/D measurements if the IAD bit is set to “1” in the
Status/Configuration Register. The DS2438 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, RSENS. The VSENS+ terminal may be tied directly to the RSENS resistor, however, for
VSENS-, we recommend use of an RC low pass filter between it and the GND end of RSENS (see the block
diagram in Figure 1). Using a 100 kW (min) resistor (RF) and a 0.1 mF tantalum capacitor (CF), the filter
cutoff is approximately 15.9 Hz. The current A/D measures at a rate of 36.41 times per second, or once
every 27.46 ms. This filter will capture the effect of most current spikes, and will thus allow the current
accumulators to accurately reflect the total charge which has gone into or out of the battery.
The voltage across current sense resistor RSENS is measured by the ADC and the result is placed in the
Current Register in two’s complement format. The sign (S) of the result, indicating charge or discharge,
resides in the most significant bit of the Current Register, as shown in Table 3. See “Memory Map” in
Figure 7 for the Current Register address location.
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DS2438 arduino
64-BIT LASERED ROM FORMAT Figure 3
DS2438
8-BIT CRC CODE
48-BIT SERIAL NUMBER
8-BIT FAMILY CODE (26h)
MSb
LSb MSb
LSb MSb
LSb
CRC Generation
The DS2438 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master can
compute a CRC value from the first 56 bits of the 64-bit ROM and compare it to the value stored within
the DS2438 to determine if the ROM data has been received error-free by the bus master. The equivalent
polynomial function of this CRC is:
CRC = X8 + X5 + X4 +1
The DS2438 also generates an 8-bit CRC value using the same polynomial function shown above and
provides this value to the bus master to validate the transfer of data bytes. In each case where a CRC is
used for data transfer validation, the bus master must calculate a CRC value using the polynomial
function given above and compare the calculated value to either the 8-bit CRC value stored in the 64-bit
ROM portion of the DS2438 (for ROM reads) or the 8-bit CRC value computed within the DS2438
(which is read as a 9th byte when a scratchpad is read). The comparison of CRC values and decision to
continue with an operation are determined entirely by the bus master. There is no circuitry inside the
DS2438 that prevents a command sequence from proceeding if the CRC stored in or calculated by the
DS2438 does not match the value generated by the bus master. Proper use of the CRC as outlined in the
flowchart of Figure 6 can result in a communication channel with a very high level of integrity.
The 1-Wire CRC can be generated using a polynomial generator consisting of a shift register and XOR
gates as shown in Figure 4. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is
available in Application Note 27 entitled “Understanding and Using Cyclic Redundancy Checks with
Dallas Semiconductor Touch Memory Products.”
The shift register bits are initialized to 0. Then starting with the least significant bit of the family code,
1 bit at a time is shifted in. After the 8th bit of the family code has been entered, the serial number is
entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC
value.
1-WIRE CRC CODE Figure 4
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