Dallas Semiconductor DS2435 Datasheet

www.dalsemi.com

PRELIMINARY

DS2435

Battery Identification Chip

with Time/Temperature Histogram

FEATURES

 Provides unique ID number to battery packs  Eliminates thermistors by sensing battery

temperature on-chip

 Elapsed time counter provides indication of

battery usage/storage time

 Time/temperature histogram function

provides essential information for determining battery self-discharge

 256-bit nonvolatile user memory available for

storage of user data such as gas gauge and manufacturing information.

 Operating range of -40°C to +85°C  Applications include portable computers,

portable/cellular phones, consumer electronics, and handheld instrumentation.

PACKAGE OUTLINE

PR-35 PACKAGE

DALLAS

DS2435

DQ NC

NC NC NC NC NC

GND

VDD

GND

123

See Mech. Drawings Section

BOTTOM VIEW

DS2435S 16-Pin SSOP

NC NC NC NC NC NC GND

PIN DESCRIPTION

GND - Ground DQ - Data In/Out

- Supply Voltage

NC - No Connect

DESCRIPTION

The DS2435 Battery Identification Chip with Time/Temperature Histogram provides a convenient method of tagging and identifying battery packs by manufacturer, chemistry, or other identifying parameters. The DS2435 allows the battery pack to be coded with a unique identification number and also store information regarding the battery life and charge/discharge characteristics in its nonvolatile memory.

The DS2435 performs the essential function of monitoring battery temperature without the need for a thermistor in the battery pack. A time/temperature histogram function stores the amount of time that the battery has been in one of its eight user definable temperature bands, allowing more accurate selfdischarge calculations to be carried out by the user for determining remaining battery capacity. The onboard elapsed time counter provides a method that can even determine the amount of time that a battery pack has been in storage, allowing for a more accurate self-discharge determination.

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DS2435

Information is sent to/from the DS2435 over a 1-Wire interface, reducing the number of battery pack connectors to only three; power, ground, and the 1-Wire interface.

DETAILED PIN DESCRIPTION

16-PIN SSOP

8, 9 1 GND

12DQData Input/Output pin - for 1-Wire communication port.

16 3 V

2-7, 10-15 - NC

PR-35

SYMBOL DESCRIPTION

Ground pin.

Supply pin - input power supply. No Connect

OVERVIEW

The DS2435 has six major components: 1) Scratchpad Memory, 2) Nonvolatile Memory, 3) On-board SRAM, 4) Temperature Sensor, 5) ID Register, and 6) Elapsed Time Counter. All data is read and written least significant bit first.

Access to the DS2435 is over a 1-Wire interface. Charging parameters, battery chemistry, gas gauge information, and other user data would be stored in the DS2435, allowing this information to remain permanently in the battery pack. Nonvolatile (E2) RAM holds information even if the battery goes dead; as long as the battery remains within typical charge/discharge operating range, the SRAM provides battery-backed storage of information.

DS2435 BLOCK DIAGRAM Figure 1

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DS2435

OVERVIEW - TIME/TEMPERATURE HISTOGRAM

Periods of storage are normal for most battery-powered applications. During this storage time, little or no current is actually drawn from the battery; batteries will, however, lose capacity during this storage time due to parasitic side reactions in the cell and other electrochemical mechanisms. This loss of capacity is termed self-discharge.

Since self-discharge is the result of electrochemical reactions, its rate is dependent upon the cell temperature. Knowing the time spent in certain temperature ranges during the storage time of the battery, these temperature effects may be factored into a calculation of self-discharge for the battery. This will allow a more accurate determination of retained battery capacity.

The DS2435 measures, tabulates, and stores this information in the battery pack. It periodically measures the battery temperature, and updates the appropriate temperature “bin” of the time/temperature histogram with the time spent in that temperature range. The resulting histogram data could appear graphically as shown in Figure 2.

The DS2435 allows for eight temperature ranges, or bins, to be specified by fixing the values of the bin limits, TA through TG. Once specified, the time spent in each of the bins (bin 1 being anything less than TA, bin 2 being temperature greater than or equal to TA but less than TB, etc., and bin 8 being anything greater than or equal to TG) is recorded (t1 being the time spent in bin 1, t2 the time spent in bin 2, etc.). Using this information and data from the battery manufacturer regarding retained capacity, the actual battery capacity remaining may be closely approximated by the user.

TIME/TEMPERATURE HISTOGRAM Figure 2

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DS2435

MEMORY

The DS2435’s memory is divided into five pages, each page filling 32 bytes of address space. Not all of the available addresses are used, however. Refer to the memory map of Figure 4 to see actual addresses which are available for use.

The first three pages of memory consist of a scratchpad RAM and then either a nonvolatile RAM (pages 1 and 2) or SRAM (page 3). The scratchpads help insure data integrity when communicating over the 1Wire bus. Data is first written to the scratchpad where it can be read back. After the data has been verified, a copy scratchpad command will transfer the data to the RAM (NV or SRAM). This process insures data integrity when modifying the memory.

The fourth page of memory consists of registers which contain the measured temperature value, time/temperature histogram registers, elapsed time counter, and status registers for the device; these registers are made from SRAM cells.

The fifth page of memory holds the ID number for the device, the cycle count registers and the histogram bin limits in E2 RAM, making these registers nonvolatile under all power conditions.

PAGE 1

The first page of memory has 24 bytes. It consists of a scratchpad RAM and a nonvolatile (E2) RAM. These 24 bytes may be used to store any data the user wishes; such as battery chemistry descriptors, manufacturing lot codes, gas gauge information, etc.

The nonvolatile portion of this page may be locked to prevent data stored here from being changed inadvertently. Both the nonvolatile and the scratchpad portions are organized identically, as shown in the memory map of Figure 4. In this page, these two portions are referred to as NV1 and SP1, respectively.

PAGE 2

The second page of memory has 8 bytes. It consists of a scratchpad RAM and a nonvolatile (E2) RAM. These 8 bytes may be used to store any data the user wishes, such as battery chemistry descriptors, manufacturing lot codes, gas gauge information, etc.

PAGE 3

The third page of memory has a full 32 bytes. It consists of a scratchpad RAM and an SRAM. This address space may be used to store any data the user wishes, such as gas gauge and self-discharge information. Should the battery go dead and power to the DS2435 is lost, this data may also be lost. Data which must remain even if power to the DS2435 is lost should be placed in either Page 1 or Page 2.

PAGE 4

The fourth page of memory is used by the DS2435 to store the converted value of battery temperature, the time/temperature histogram data, and the elapsed time counter. A 2-byte status register is also provided.

TEMPERATURE REGISTERS (60h-61h)

The DS2435 can measure temperature without external components. The resulting temperature measurement is placed into two temperature registers. These registers are SRAM, and therefore will hold the values placed in them until the battery voltage falls below the minimum VDD specified. The first register, at address 60h, provides ½°C resolution for temperatures between 0°C and 127 ½°C, formatted as follows:

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DS2435

The second register, at address 61h, provides 1°C resolution over the -40°C to +85°C range, formatted as follows in the binary two’s complement coding as shown in Table 1:

TEMPERATURE/DATA RELATIONSHIPS Table 1

TEMPERATURE DIGITAL OUTPUT (Binary) DIGITAL OUTPUT (Hex)

+85°C 01010101 55h

+25°C 00011001 19h

1°C 00000001 01h

0°C 00000000 00h

-1°C 11111111 FFh

-25°C 11100111 E7h

-40°C 11011000 D8h

STATUS/CONTROL REGISTER (62h-63h)

The status register is a 2-byte register at addresses 62h and 63h (consisting of SRAM). Address 62h is the least significant byte of the status register, and is currently the only address with defined status bits; the other byte at address 63h is reserved for future use. The status register is formatted as follows:

where

X = Don’t Care

TB = Temperature Busy flag. 1 = temperature conversion in progress; 0 = temperature

conversion complete, valid data in temperature register.

NVB = Nonvolatile memory busy flag. 1 = Copy from scratchpad to NVRAM in progress, 0 =

nonvolatile memory is not busy. A copy to NVRAM may take from 2 ms to 10 ms (taking longer at lower supply voltages).

LOCK = 1 indicates that NV1 is locked; 0 indicates that NV1 is unlocked.

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t1-t8 REGISTERS (64h-73h)

These registers hold the accumulated time values for the time/temperature histogram. t1 corresponds to the time spent in histogram bin 1, t2 the time spent in bin 2, etc., where the bins are defined by the limits set in TA-TG as shown in Figure 2. The format for the time value stored in these two-byte registers depends upon the SAMPLE RATE, and is defined in the paragraph describing the SAMPLE RATE parameter.

t REGISTER (74h-76h)

This 3-byte register is the elapsed time counter, formatted as follows:

The elapsed time counter has an LSB value of 1 minute; the total time which the counter can accommodate is 224 minutes, or 31.92 years.

Issuing any protocol to the DS2435 prevents the incrementing of the elapsed time counter and histogram registers until the protocol is cleared by issuing a reset. Therefore, it is imperative that any protocol issued to the DS2435 be followed by a reset (either after the protocol, if it requires no data, or immediately following the required data). This is necessary to avoid contention between the counter and histogram writing process and external processes.

PAGE 5

The fifth page of memory holds the battery manufacturer ID number, a 2-byte counter for counting the number of battery charge/discharge cycles, histogram bin limits, and sample rate.

ID REGISTER (80h and 81h)

The ID Register is a 16-bit ROM register that can contain a unique identification code, if purchased from Dallas Semiconductor. This ID number is programmed by Dallas Semiconductor, is unchangeable, and is unique to each customer. This ID number may be used to ensure that batteries containing a DS2435 have the same manufacturer ID number as a charger configured to operate with that battery pack. This feature may be used to prevent charging of batteries for which the charging circuit has not been designed.

CYCLE COUNTER (82h and 83h)

The cycle counter register gives an indication of the number of charge/discharge cycles the battery pack has been through. This nonvolatile (E2) register is incremented by the user through the use of a protocol to the DS2435, and is reset by another protocol. The counter is a straight binary counter, formatted as follows:

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TA-TG REGISTERS (84h-8Ah)

These registers define the boundaries for the temperature bins in the time/temperature histogram, as shown in Figure 2. These temperature values are expressed in the same temperature format as shown in

Table 1. These limits therefore may be positive or negative values, expressed with 1°C resolution. The

bin limits must be specified in increasing order (i.e., TA<TB, TB<TC, etc.).

SAMPLE RATE (8Bh)

This register defines the periodic interval at which the DS2435 will take a temperature measurement for updating the histogram data. Note that this does not affect the actual time needed to perform a temperature conversion using the Convert T protocol; this sample rate refers only to the periodic interval at which histogram data is updated.

The sample rate is expressed as follows:

S2 S1 S0 SAMPLE RATE

0 0 0 1/2 minute

0 0 1 1 minute

0 1 0 2 minutes

0 1 1 4 minutes

1 0 0 1/8 hour

1 0 1 1/4 hour

1 1 0 1/2 hour

1 1 1 1 hour

The interval specified in this register determines the LSB value for the time/temperature histogram registers, as shown below. Examples of time expressions for a given sample rate are shown in Table 2.

HISTOGRAM REGISTER DATA GIVEN FOR SAMPLE RATE

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DS2435 MEMORY PARTITIONING Figure 3

DS2435

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