Datasheet

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DS2746

Low-Cost 2-Wire Battery Monito

with Ratiometric A/D Inputs

1 of 17

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GENERAL DESCRIPTION

The DS2746 provides system-side battery capacity

monitoring in cost-sensitive applications. Voltage,

bidirectional current, and accumulated current

measurement data is provided to the host processor

over a 2-wire interface. Offset bias and offset

blanking features greatly enhance the accuracy of

the coulomb counter. In addition, the DS2746 has

two auxiliary A/D inputs to sample the pack

identification resistor, thermistor, or other voltage

source. The results are reported as a ratiometric

fraction of the supply voltage eliminating error related

to the supply. The DS2746 reduces the total power

consumption of the measurement circuit by enabling

the resistor dividers, through the V

OUT

pin, only while

measurements are made. When the system is

inactive, a low power sleep mode reduces current

consumption while maintaining the coulomb count.

The tiny 3mm × 3mm TDFN package consumes only

9mm

of PCB space.

APPLICATIONS

2.5G/3G Wireless Handsets

PDA/Smartphones

Digital Still and Video Cameras

Handheld Computers and Terminals

TYPICAL OPERATING CIRCUIT

FEATURES

 14-Bit Bidirectional Current Measurement

- 6.25V LSB, ±51.2mV Dynamic Range

- 416.7A LSB, ±3.4A Range (R

SNS

= 15m)

 Current Accumulation Register Resolution

- 6.25Vhr LSB, 409.6mVh Range

- 417Ahr LSB, 27.31Ah Range

 11-Bit Battery Voltage Measurement

- 2.44mV LSB, 0V to 4.5V Input Range

- ±10mV Accuracy at 3.6V Input

 Two 11-Bit Aux Input Voltage Measurements

- Ratiometric Inputs Eliminate Supply Error

- VOUT drives Dividers, Reduces Power

- ±8 LSB Accuracy

 Low Power Consumption:

- Active Current: 70A typical, 100A max

- Sleep Current: 1A typical, 3A max

ORDERING INFORMATION

PART TEMP RANGE PIN-PACKAGE

DS2746G+ -20ºC to +70ºC

10-Pin 3mm×3mm

TDFN

DS2746G+T&R -20ºC to +70ºC

DS2746G+ in Tape-

and-Reel

+ Denotes lead(Pb)-free/RoHS-compliant package.

PIN CONFIGURATION

TOP VIEW

3mm × 3mm TDFN

Summary of content (17 pages)

PAGE 1
9-4632; 5/09 DS2746 Low-Cost 2-Wire Battery Monitor with Ratiometric A/D Inputs www.maxim-ic.com GENERAL DESCRIPTION FEATURES The DS2746 provides system-side battery capacity monitoring in cost-sensitive applications. Voltage, bidirectional current, and accumulated current measurement data is provided to the host processor over a 2-wire interface. Offset bias and offset blanking features greatly enhance the accuracy of the coulomb counter.
PAGE 2
DS2746 Low-Cost 2-Wire Battery Monitor ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to Ground Operating Temperature Range Storage Temperature Range Soldering Temperature -0.3V to +6V -40°C to +85°C -55°C to +125°C See IPC/JEDECJ-STD-020A Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.
PAGE 3
DS2746 Low-Cost 2-Wire Battery Monitor SCL, SDA Input Capacitance: SCL, SDA Bus Low Timeout VPIN = 0.4V CBUS tSLEEP (Note 3) 1.5 50 pF 2.2 S MAX UNITS 400 KHz DC ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (VDD = 2.5V to 4.5V, TA = -20°C to +70°C.) PARAMETER SYMBOL SCL Clock Frequency fSCL Bus Free Time Between a STOP and START Condition Hold Time (Repeated) START Condition tBUF tHD:STA CONDITIONS (Note 4) (Note 5) MIN TYP 0 1.3 µs 0.6 µs Low Period of SCL Clock tLOW 1.
PAGE 4
DS2746 Low-Cost 2-Wire Battery Monitor Figure 1. Valid Range for AINGERR Accuracy Specification AINx Voltage Measurement Error Not Specified C 0° -2 °C 25 °C 70 AINx PIN VOLTAGE AS A PERCENTAGE OF VOUT (%) 100% 67% 57% 48% AINx Voltage Measurement Error ≤ AINGERR Specification 0% 2.5V 3.7 3.86 VOUT PIN VOLTAGE (V) Figure 2. 2-Wire Bus Timing Diagram 4 of 17 4.0 4.
PAGE 5
DS2746 Low-Cost 2-Wire Battery Monitor PIN DESCRIPTION PIN 1 2 NAME AIN1 AIN0 3 SCL 4 SDA 5 6 7 SNS VSS CTG 8 VOUT 9 VIN 10 VDD PAD PAD FUNCTION Aux Voltage Input Number 1. Aux Voltage Input Number 0. Serial Clock Input. Input only 2-wire clock line. Connect this pin to the CLOCK signal of the 2-wire interface. This pin has a 0.2µA typical pulldown to sense disconnection. Serial Data Input / Output. Open drain 2-wire data line. Connect this pin to the DATA signal of the 2-wire interface.
PAGE 6
DS2746 Low-Cost 2-Wire Battery Monitor Figure 3. Block Diagram DETAILED DESCRIPTION The DS2746 operates either in active mode where cell voltage, system current, and auxiliary inputs are monitored, or in a low power sleep mode to conserve energy when the system is idle. While in active mode, the DS2746 contantly measures current flow through an external sense resistor. Each current measurement is reported with sign and magnitude in a two-byte Current register.
PAGE 7
DS2746 Low-Cost 2-Wire Battery Monitor Figure 4. APPLICATION EXAMPLE System VDD Pack+ 150 1K VOUT VIN VDD (1) 5.6V Protection IC (Li+/Polymer) 10nF AIN0 PackID 1K Therm 1K SDA AIN1 SCL VSS CTG SNS System Serial Bus DS2746 RSNS Pack- 1nF 1nF (1) Optional for 8kV/15kV ESD 2.5V (1) System VSS POWER MODES The DS2746 operates in one of two power modes: active and sleep.
PAGE 8
DS2746 Low-Cost 2-Wire Battery Monitor Figure 5. Measurement Timing VOLTAGE MEASUREMENT Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 4.997V (limited by VDD pin voltage) and with a resolution of 2.44mV. The result is updated every 660ms with the average voltage over the last 220ms and placed in the VOLTAGE register in two’s compliment form. Voltages above the maximum register value are reported as 7FFFh. Figure 6.
PAGE 9
DS2746 Low-Cost 2-Wire Battery Monitor AUXILARY INPUT MEASUREMENTS The DS2746 allows for measuring two auxiliary measurement inputs, AIN0 and AIN1, with respect to VSS. These inputs are designed for measuring resistor ratios, particularly useful for measuring thermistor or pack identification resistors.
PAGE 10
DS2746 Low-Cost 2-Wire Battery Monitor Table 1. Current Resolution for Various RSNS Values CURRENT RESOLUTION (1 LSB) VSS - VSNS 6.25V RSNS 20m 312.5µA 15m 416.7µA 10m 625µA 5m 1.25mA 10m ±5.12A 5m ±10.24A Table 2. Current Range for Various RSNS Values CURRENT INPUT RANGE VSS - VSNS ±51.2mV RSNS 20m ±2.56A 15m ±3.41A Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs approximately once per hour.
PAGE 11
DS2746 Low-Cost 2-Wire Battery Monitor Table 3. Accumulated Current Range for Various RSNS Values ACR RANGE VSS - VSNS 409.6mVh RSNS 20m 20.48Ah 15m 27.31Ah 10m 40.96Ah 5m 81.92Ah CURRENT OFFSET BIAS The Current Offset Bias register (COBR) allows a programmable offset value to be added to raw current measurements. The result of the raw current measurement plus the COBR value is displayed as the current measurement result in the CURRENT register, and is used for current accumulation.
PAGE 12
DS2746 Low-Cost 2-Wire Battery Monitor Figure 1. Accumulation Bias Register Format Address 62h S 24 MSb “S”: sign bit 23 22 21 20 X X LSb Units: 6.25Vh/Rsns MEMORY The DS2746 has memory space with registers for instrumentation, status, and control. When the MSB of a twobyte register is read, both the MSB and LSB are latched and held for the duration of the read data command to prevent updates during the read and ensure synchronization between the two register bytes.
PAGE 13
DS2746 Low-Cost 2-Wire Battery Monitor STATUS/CONFIG REGISTER The Status/Config register is read/write with individual bits designated as read only. Bit values indicate status as well as program or select device functionality. Figure 12. Status/Config Register Format ADDRESS 01 BIT 7 X BIT 6 PORF BIT 5 SMOD BIT 4 NBEN BIT 3 VODIS BIT 2 X BIT 1 AIN1 BIT 0 AIN0 X — Reserved. PORF — The Power-On-Reset Flag is set to indicate initial power-up. PORF is not cleared internally.
PAGE 14
DS2746 Low-Cost 2-Wire Battery Monitor Bus Idle The bus is defined to be idle, or not busy, when no master device has control. Both SDA and SCL remain high when the bus is idle. The STOP condition is the proper method to return the bus to the idle state. START and STOP Conditions The master initiates transactions with a START condition (S), by forcing a high-to-low transition on SDA while SCL is high.
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DS2746 Low-Cost 2-Wire Battery Monitor Table 5.
PAGE 16
DS2746 Low-Cost 2-Wire Battery Monitor Data is returned beginning with the most significant bit (msb) of the data in MAddr. Because the address is automatically incremented after the least significant bit (lsb) of each byte is returned, the msb of the data at address MAddr + 1 is available to the host immediately after the acknowledgement of the data at address MAddr. If the bus master continues to read beyond address FFh, the DS2746 outputs data values of FFh.
PAGE 17
DS2746 Low-Cost 2-Wire Battery Monitor REVISION HISTORY REVISION DATE 051209 DESCRIPTION Changed the VDD maximum operating range in the Electrical Characteristics table to 4.5V. Added “VIN pin is limited to VDD voltage” text in the Voltage Measurement section. PAGES CHANGED 2, 3 8 17 of 17 Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied.