DS2438

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DETAILED PIN DESCRIPTION

PIN

SYMBOL

DESCRIPTION

1

GND

Ground

Battery Input: connection for battery current to be monitored (see text)

Battery Input: connection for battery current to be monitored (see text)

ADC Input: input for general purpose A/D

6, 7

NC

No Connect

8DQ

Data Input/Out: for 1-Wire operation: Open drain

OVERVIEW

The block diagram of Figure 1 shows the seven major components of the DS2438:

1. 64-bit lasered ROM

2. temperature sensor

3. battery voltage A/D

4. battery current A/D

5. current accumulators

6. elapsed time meter

7. 40-byte nonvolatile user-memory

Each DS2438 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 DS2438 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 to 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.

Control function commands may be issued which instruct the DS2438 to perform a temperature

measurement or battery voltage A/D conversion. The result of these measurements will be placed in the

DS2438’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 DS2438 memory

space. The DS2438 uses these current measurements to update three current accumulators; the first stores

net charge for fuel gauge calculations, the second accumulates the total charging current over the life of

the battery, and the remaining accumulator tallies battery discharge current. The elapsed time meter data,

which can be used in calculating battery self-discharge or time-related charge termination limits, also

resides in the DS2438 memory map and can be extracted with a memory function command. The

nonvolatile user memory of the DS2438 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.