DS2781 Maxim Integrated Products, DS2781 Datasheet

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... GENERAL DESCRIPTION The DS2781 measures voltage, temperature, and current, and estimates available rechargeable Lithium-Ion and Lithium-Ion Polymer batteries. Cell stack characteristics and application parameters used in the calculations are stored in on- chip EEPROM. The available capacity registers report a conservative estimate of the amount of ...

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ABSOLUTE MAXIMUM RATINGS Voltage on VPLS, VIN Relative to VSS Voltage Range on Any Pin Relative to VSS Continuous Sink Current, DQ, PIO Operating Temperature Range Storage Temperature Range Soldering Temperature (10s) Stresses beyond those listed under “Absolute Maximum Ratings” ...

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PARAMETER Voltage Full-Scale Voltage Error Current Resolution Current Full-Scale Current Gain Error Current Offset Error Accumulated Current Offset Timebase Error ELECTRICAL CHARACTERISTICS: 1-WIRE INTERFACE, STANDARD (V = 2.5V to 10V -20°C to +70°C.) PLS A PARAMETER Time Slot ...

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EEPROM RELIABILITY SPECIFICATION (V = 2.5V to 10V -20°C to +70°C, unless otherwise noted. Typical values are at T PLS A PARAMETER EEPROM Copy Time EEPROM Copy Endurance Note 1: All voltages are referenced to VSS. Note 2: ...

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... SNS DETAILED DESCRIPTION The DS2781 operates directly from 2.5V to 10V and supports single or dual cell Lithium-ion battery packs. Nonvolatile storage is provided for cell compensation and application parameters. Host side development of fuel- gauging algorithms is eliminated. On-chip algorithms and convenient status reporting of operating conditions reduce the serial polling required of the host processor ...

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... PMOD SLEEP was high when UVEN SLEEP was entered, then the DS2781 is prepared to receive a 1-Wire reset from the master. In the first two cases with DQ low during SLEEP, the DS2781 does not respond to the first rising edge of DQ with a presence pulse. ...

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... CURRENT MEASUREMENT In the ACTIVE mode of operation, the DS2781 continually measures the current flow into and out of the battery by measuring the voltage drop across a low-value current-sense resistor, R SNS and VSS is ±51.2mV. The input linearly converts peak signal amplitudes up to 102.4mV as long as the continuous signal level (average over the conversion cycle period) does not exceed ± ...

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Figure 5. Current Register Format CURRENT MSB—Address 0Eh MSb “S”: sign bit(s) VSS - VSNS 1.5625mV CURRENT OFFSET CORRECTION Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset ...

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... FSGAIN back into RSGAIN. SENSE RESISTOR TEMPERATURE COMPENSATION The DS2781 is capable of temperature compensating the current sense resistor to correct for variation in a sense resistor’s value over temperature. The DS2781 is factory programmed with the sense resistor temperature coefficient, RSTC, set to zero, which turns off the temperature compensation function ...

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ACR register update period). A write to the ACR forces the ADC to perform an offset correction conversion and update the internal offset correction factor. Current measurement and accumulation begins with the second conversion following a write to the ACR. ...

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... The AB can be used to account for currents that do not flow through the sense resistor, estimate currents too small to measure, estimate battery self-discharge or correct for static offset of the individual DS2781 device. The AB register allows a user programmed constant positive or negative polarity bias to be included in the current accumulation process. The user-programmed two’ ...

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Figure 11. Top Level Algorithm Diagram Voltage (R) Temperature (R) Current (R) Accumulated Current (ACR) (R/W) Average Current (R) Cell Parameters 16 bytes (EEPROM) Aging Cap (AC) (2 bytes EE) Age Scalar (AS) (1 bytes EE) Sense Resistor’ (RSNSP) (1byte ...

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... The charge termination method used in the application is used to determine the table values. The DS2781 reconstructs the Full line from cell characteristic table values to determine the Full capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments. Full values are stored as ppm change per º ...

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... The standby load current and voltage are used for determining the cell characteristics but are not programmed into the DS2781. The DS2781 reconstructs the Standby Empty line from cell characteristic table values to determine the Standby Empty capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments ...

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Figure 13. Lookup Function Diagram Cell Model Parameters (EEPROM) Temperature APPLICATION PARAMETERS In addition to cell model characteristics, several application parameters are needed to detect the full and empty points, as well as calculate results in mAh units. Sense Resistor ...

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... Usually, writing AS by the host is not necessary because AS is automatically saved to EEPROM on a periodic basis by the DS2781. (See the Memory section for details.) The EEPROM stored value recalled on power-up. CAPACITY ESTIMATION UTILITY FUNCTIONS Aging Estimation As discussed above, the AS register value is adjusted occasionally based on cumulative discharge ...

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Active Empty, AE( The Active Empty capacity of the battery at the present ...

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... STATUS REGISTER The STATUS register contains bits that report the device status. The bits can be set internally by the DS2781. The CHGTF, AEF, SEF, LEARNF and VER bits are read only bits that can be cleared by hardware. The UVF and PORF bits can only be cleared via the 1-Wire interface. ...

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CONTROL REGISTER All CONTROL register bits are read and write accessible. The CONTROL register is recalled from Parameter EEPROM memory at power-up. Register bit values can be modified in shadow RAM after power-up. Shadow RAM values can be saved as ...

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... Read Only MEMORY The DS2781 has a 256 byte linear memory space with registers for instrumentation, status, and control, as well as EEPROM memory blocks to store parameters and user information. Byte addresses designated as “Reserved” return undefined data when read. Reserved bytes should not be written. Several byte registers are paired into two- byte registers in order to store 16-bit values ...

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... The ACR (MSB and LSB) and AS registers are automatically saved to EEPROM when the RARC result crosses 4% boundaries. This allows the DS2781 to be located outside the protection FETs. In this manner protection device is triggered, the DS2781 cannot lose more that 4% of charge or discharge data. ...

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Table 2. MEMORY MAP ADDRESS (HEX) 00 Reserved 01 STATUS - Status Register 02 RAAC - Remaining Active Absolute Capacity MSB RAAC - Remaining Active Absolute Capacity LSB 03 04 RSAC - Remaining Standby Absolute Capacity MSB 05 RSAC - ...

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... Each DS2781 has a unique, factory-programmed 1-Wire net address that is 64 bits in length. The first eight bits are the 1-Wire family code (3Dh for DS2781). The next 48 bits are a unique serial number. The last eight bits are a cyclic redundancy check (CRC) of the first 56 bits (see Figure 18). The 64-bit net address and the 1-Wire I/O circuitry built into the device enable the DS2781 to communicate through the 1-Wire protocol detailed in the 1-Wire Bus System section of this data sheet ...

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... To facilitate this, each device attached to the 1-Wire bus must connect to the bus with open-drain or tri-state output drivers. The DS2781 uses an open-drain output driver as part of the bidirectional interface circuitry shown in Figure 20 bidirectional pin is not available on the bus master, separate output and input pins can be connected together ...

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... This command can be used with one or more slave devices on the bus. Skip Net Address [CCh]. This command saves time when there is only one DS2781 on the bus by allowing the bus master to issue a function command without specifying the address of the slave. If more than one slave device is present on the bus, a subsequent function command can cause a data collision when all slaves transmit data at the same time ...

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... EEPROM to the shadow. See the Memory section for more details. Write Data [6Ch, XX]. This command writes data to the DS2781 starting at memory address XX. The LSb of the data to be stored at address XX can be written immediately after the MSb of address has been entered. Because the address is automatically incremented after the MSb of each byte is written, the LSb to be stored at address can be written immediately after the MSb to be stored at address XX ...

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Table 4. Function Commands COMMAND DESCRIPTION Reads data from memory starting at Read Data address XX Writes data to Write Data memory starting at address XX Copies shadow RAM data to EEPROM Copy Data block containing address XX Recalls EEPROM ...

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... COMMAND 55h NO F0h NO SEARCH YES YES DS2781 Tx BIT 0 DS2781 Tx BIT 0 MASTER Tx BIT 0 BIT BIT 0 MATCH ? YES YES DS2781 Tx BIT 1 DS2781 Tx BIT 1 MASTER Tx BIT 1 BIT BIT 1 MATCH ? YES YES DS2781 Tx BIT 63 DS2781 Tx BIT 63 MASTER Tx BIT CCh NO A5h NO SKIP ...

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... A read-time slot is initiated when the bus master pulls the 1-Wire bus line from a logic-high level to a logic-low level. The bus master must keep the bus line low for at least 1ms and then release it to allow the DS2781 to present valid data. The bus master can then sample the data t slot, the DS2781 releases the bus line and allows pulled high by the external pullup resistor ...

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... DS2781 active low t SLOT t LOW0 t REC TYP MAX >1ms 30ms 3ms t SLOT >1ms WRITE 1 SLOT t SLOT t LOW1 DS2781 Sample Window MIN TYP 15ms 15ms 30ms 2ms 1ms 3ms READ 1 SLOT t SLOT t REC Master Sample Window t RDV DS2781 active low Resistor pullup MAX ...