Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - battery management Battery monitoring Smart batteries SOIC 8 N Surface-mount

AVAILABLE

Functional Diagrams

Pin Configurations appear at end of data sheet.

Functional Diagrams continued at end of data sheet.

UCSP is a trademark of Maxim Integrated Products, Inc.

For pricing, delivery, and

ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

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070605

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

PIN DESCRIPTION

DQ - Data In/Out

VAD - General A/D input

SENS+

- Battery current monitor input (+)

SENS-

- Battery current monitor input (-)

VDD - Power Supply (2.4V to 10.0V)

GND - Ground

NC - No connect

DESCRIPTION

The DS2438 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, 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

conjunction with a microcontroller in the host system, the DS2438 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 DS2438 EEPROM, and

only a software revision is necessary should a designer wish to change battery pack chemistry.

DS2438

Smart Battery Monito

GND

SENS+

SENS-

DS2438Z, DS2438AZ

8-Pin SOIC (150-mil)

Summary of content (29 pages)

PAGE 1
LE AVAILAB 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 endof-discharge determination On-board integrated current accumulator facilitates fuel gauging Elapsed time meter in binary format 40-byte nonvolatile user memory available for storage o
PAGE 2
DS2438 ORDERING INFORMATION PART DS2438Z+ DS2438Z+T&R DS2438AZ+ DS2438AZ+T&R DS2438Z DS2438Z/T&R DS2438AZ DS2438AZ/T&R MARKING DS2438 DS2438 DS2438A DS2438A DS2438 DS2438 DS2438A DS2438A PACKAGE INFORMATION 8-Pin SOIC DS2438Z+ on Tape-and-Reel 8-Pin SOIC DS2438AZ+ on Tape-and-Reel 8-Pin SOIC DS2438Z on Tape-and-Reel 8-Pin SOIC DS2438AZ on Tape-and-Reel + Denotes lead-free package.
PAGE 3
DS2438 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.
PAGE 4
DS2438 OPERATION-MEASURING TEMPERATURE The DS2438 measures temperatures through the use of an on-board temperature measurement technique. The temperature reading is provided in a 13-bit, two’s complement format, 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 DS2438 can measure temperature over the range of -55°C to +125°C in 0.03125°C increments.
PAGE 5
DS2438 VOLTAGE REGISTER FORMAT Table 2 27 26 25 MSb 0 24 23 22 21 (unit = 10 mV) 0 0 0 0 0 20 LSB LSb 29 28 MSB BATTERY VOLTAGE 0.05V DIGITAL OUTPUT (Binary) DIGITAL OUTPUT (Hex) 0000 0000 0000 0101 0005h 2.7V 0000 0001 0000 1110 010Eh 3.6V 0000 0001 0110 1000 0168h 5V 0000 0001 1111 0100 01F4h 7.2V 0000 0010 1101 0000 02D0h 9.
PAGE 6
DS2438 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.) 27 26 25 MSb S 24 23 22 21 (unit = 0.2441mV) S S S S S 20 LSB LSb 29 28 MSB The battery pack current is calculated from the Current Register value using the equation: (where RSENS is in W) I = Current Register / (4096 * RSENS) For example, if 1.
PAGE 7
DS2438 OPERATION - CURRENT ACCUMULATORS The DS2438 tracks the remaining capacity of a battery using the Integrated Current Accumulator (ICA). The ICA maintains a net accumulated total of current flowing into and out of the battery; therefore, the value stored in this register is an indication of the remaining capacity in a battery and may be used in performing fuel gauge functions.
PAGE 8
DS2438 THRESHOLD REGISTER FORMAT Table 6 TH2 TH1 0 0 0 0 0 MSb 0 LSb TH2 TH1 THRESHOLD 0 0 None (default) 0 1 ±2 LSB 1 0 ±4 LSB 1 1 ±8 LSB The Charging Current Accumulator (CCA) is a two-byte nonvolatile read/write counter which represents the total charging current the battery has encountered in its lifetime. It is only updated when current through RSENS, is positive; i.e., when the battery is being charged.
PAGE 9
DS2438 Figure 2 illustrates the activity of the ICA, CCA, and DCA over a sample charge/discharge cycle of a battery pack, assuming the DS2438 is configured for the ICA to function and the CCA/DCA to function and shadow data to EEPROM. To simplify the illustration of the accumulators, they are treated as analog values, although they are digital counters in the DS2438. Note that when the battery becomes fully discharged, i.e., the ICA value reaches 0, the CCA and DCA register values are maintained.
PAGE 10
DS2438 Two other time-related functions are available. The first is the Disconnect Timestamp, which is written to by the DS2438 whenever it senses that the DQ line has been low for approximately 2 seconds.
PAGE 11
DS2438 64-BIT LASERED ROM FORMAT Figure 3 8-BIT CRC CODE MSb 48-BIT SERIAL NUMBER LSb MSb LSb 8-BIT FAMILY CODE (26h) 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.
PAGE 12
DS2438 ROM FUNCTIONS FLOWCHART Figure 5 12 of 29
PAGE 13
DS2438 MEMORY/CONTROL FUNCTIONS FLOWCHART Figure 6 NO 13 of 29 YES
PAGE 14
DS2438 MEMORY/CONTROL FUNCTIONS FLOWCHART Figure 6 (continued) MEMORY MAP The DS2438’s memory is organized as shown in Figure 7. The memory consists of a scratchpad RAM and storage SRAM/EEPROM. The scratchpad helps insure data integrity when communicating over the 1-Wire bus. Data is first written to the scratchpad where it can be read back.
PAGE 15
DS2438 Page 0 (00h) The first page contains the most frequently accessed information of the DS2438, and most locations are volatile read-only bytes with the exception of the Status/Configuration Register (Byte 0) and the Threshold Register (Byte 7). The Status/Configuration Register is a nonvolatile read/write byte which defines which features of the DS2438 are enabled and how they will function.
PAGE 16
DS2438 Page 1 (01h) The second page, Page 1, contains the ICA, elasped time meter, and current offset data. Both the ETM and ICA are volatile read/write locations so that they may be set, changed, or cleared by the host software. Bytes 0-3 contain the ETM data, formatted as described in the “Operation - Elapsed Time Meter” section. Byte 4 contains the 8-bit ICA. Bytes 5 and 6 contain the Offset Register data. Byte 7 is reserved and will read out as all “1”s.
PAGE 17
DS2438 1-Wire BUS SYSTEM The 1-Wire bus is a system which has a single bus master and one or more slaves. The DS2438 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). HARDWARE CONFIGURATION The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time.
PAGE 18
DS2438 ROM FUNCTION COMMANDS Once the bus master has detected a presence, it can issue one of the four ROM function commands. All ROM function commands are 8-bits long. A list of these commands follows (refer to flowchart in Figure 5): Read ROM [33h] This command allows the bus master to read the DS2438’s 8-bit family code (26h), unique 48-bit serial number, and 8-bit CRC. This command can only be used if there is a single DS2438 on the bus.
PAGE 19
DS2438 3. The bus master reads a bit from the 1-Wire bus. Each device will respond by placing the value of the first bit of their respective ROM data onto the 1-Wire bus. ROM1 and ROM4 will place a 0 onto the 1-Wire bus, i.e., pull it low. ROM2 and ROM3 will place a 1 onto the 1-Wire bus by allowing the line to stay high. The result is the logical AND of all devices on the line; therefore the bus master sees a 0. The bus master reads another bit.
PAGE 20
DS2438 16. The bus master writes a 0 bit. This decouples ROM3, and leaving only ROM2. 17. The bus master reads the remainder of the ROM bits for ROM2 and communicates to the underlying logic if desired. This completes the third ROM search pass, in which another of the ROMs was found. 18. The bus master starts a new ROM search by repeating steps 13 through 15. 19. The bus master writes a 1 bit. This decouples ROM2, leaving only ROM3. 20.
PAGE 21
DS2438 Recall Memory [B8hxxh] This command recalls the stored values in EEPROM / SRAM page xxh to the scratchpad page xxh. This command must proceed a Read SPxx command in order to read any page of memory on the DS2438. Valid page numbers are 00h - 07h. Convert T [44h] This command begins a temperature conversion. No further data is required. The temperature conversion will be performed, setting the TB flag in the Status/Configuration register to a “1” during conversion.
PAGE 22
DS2438 NOTES: 1. Temperature conversion takes up to 10 ms. 2. A/D conversion takes up to 4 ms. 3. EEPROM writes take up to 10 ms. SAMPLE COMMAND SEQUENCE Table 12 Example: Bus Master enables the ICA, CCA, and DCA on a single DS2438 and configures it such that the CCA/DCA information is shadowed to EEPROM. The voltage A/D is configured such that the DS2438 will perform voltage measurements on the battery (VDD) voltage.
PAGE 23
DS2438 SAMPLE COMMAND SEQUENCE Table 13 Example: Bus Master issues a temperature and voltage conversion, then reads the temperature, battery voltage, battery current, all on a single DS2438.
PAGE 24
DS2438 SAMPLE COMMAND SEQUENCE Table 14 Example: Assuming a single DS2438 is configured for its current accumulators to function, this sequence allows the Bus Master to read the three current accumulators.
PAGE 25
DS2438 INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 9 RESISTOR MASTER DS2438 480 ms £ tRSTL < ¥ * 480 ms £ tRSTH < ¥ (includes recovery time) 15 ms £ tPDH < 60 ms 60 ms £ tPDL < 240 ms Write Time Slots A write time slot is initiated when the host pulls the data line from a high (inactive) logic level to a low logic level. There are two types of write time slots: Write 1 time slots and Write 0 time slots.
PAGE 26
DS2438 READ / WRITE TIMING DIAGRAM Figure 10 Write-One Time Slot DS2438 SAMPLING WINDOW RESISTOR MASTER 60 ms £ tSLOT < 120 ms 1 ms £ tLOW1 < 15 ms 1 ms £ tREC < ¥ Write-Zero Time Slot DS2438 60 ms £ tLOW0 < tSLOT < 120 ms 1 ms £ tREC < ¥ Read-Data Time Slot RESISTOR MASTER DS2438 60 ms £ tSLOT < 120 ms 1 ms £ tLOWR < 15 ms 0 £ tRELEASE < 45 ms 1 ms £ tREC < ¥ tRDV = 15 ms tSU < 1ms 26 of 29
PAGE 27
DS2438 ABSOLUTE MAXIMUM RATINGS* Voltage on VDD and VAD, Relative to Ground Voltage on VSENS+, VSENS-, Relative to Ground Voltage on Any Other Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -0.3V to + 12V <±300 mV -0.3V to + 7.
PAGE 28
DS2438 ELECTRICAL CHARACTERISTICS: DIGITAL THERMOMETER (-40°C to +85°C; 2.4V £ VDD £ 10.0V) PARAMETER Thermometer Error (TACTUALTMEASURED) Conversion Time SYMBOL CONDITION MIN TYP MAX TERR tCONVT 3 UNITS ±2 °C 10 ms NOTES ELECTRICAL CHARACTERISTICS: VOLTAGE A/D CONVERTER (-40°C to +85°C; 2.4V £ VDD £ 10.0V) PARAMETER A/D Error SYMBOL CONDITION MIN TYP MAX VDDERR VDD input ±10 ±50 VADERR VAD input ±25 ±75 UNITS NOTES mV VAD Input Range VADR 1.5V 10.
PAGE 29
DS2438 AC ELECTRICAL CHARACTERISTICS: NV MEMORY (-40°C to +85°C; 2.4V £ VDD £ 10.0V) PARAMETER NV Write Cycle Time SYMBOL CONDITION MIN tWR TYP MAX 2 10 UNITS NOTES ms EEPROM Writes (copy scratchpad command) NEEWR -20ºC to +55ºC 50k writes EEPROM data retention tEEDR -20ºC to +55ºC 10 years AC ELECTRICAL CHARACTERISTICS: 1-WIRE INTERFACE (-40°C to +85°C; 2.4V £ VDD £ 10.