DS2740
High-Precision Coulomb Counter
www.maxim-ic.com
FEATURES
15-Bit Bidirectional Current Measurement
(DS2740U)
1.56μV LSB and ±51.2mV Dynamic
Range
78μA LSB and ±2.56A Dynamic
Range with External 20mΩ Sense
Resistor (R
SNS
)
156μA LSB and ±5.12A Dynamic
Range with External 10mΩ Sense
Resistor (R
SNS
)
13-Bit Bidirectional Current Measurement
(DS2740BU)
6.25μV LSB and ±51.2mV Dynamic
Range
312μA LSB and ±2.56A Dynamic
Range with External 20mΩ Sense
Resistor (R
SNS
)
625μA LSB and ±5.12A Dynamic
Range with External 10mΩ Sense
Resistor (R
SNS
)
Analog Input Filter (IS1, IS2) Extends
Dynamic Range for Pulse-Load
Applications
Current Accumulation Register
Resolution
6.25μVhr (Both DS2740U and
DS2740BU)
0.3125mAhr with External 20mΩ
R
SNS
0.6250mAhr with External 10mΩ
R
SNS
Dallas 1-Wire
®
Interface
Unique 64-Bit Device Address
Standard and Overdrive Timings
(OVD)
Low Power Consumption:
Active Current: 65μA max
Sleep Current: 1μA max
1-Wire is a registered trademark of Dallas Semiconductor.
PIN CONFIGURATION
OVD
PIO
SNS
IS2
1
2
3
4
8
7
6
5
V
DD
DQ
V
SS
IS1
μMAX
(DS2740U, DS2740BU)
See Table 1 for Ordering Information.
See Table 2 for Detailed Pin Descriptions.
PIN DESCRIPTION
OVD - 1-Wire Bus Speed Select
PIO - Programmable I/O Pin
SNS - Sense Resistor Input
IS2 - Current-Sense Input
IS1 - Current-Sense Input
V
SS
- Device Ground, Current-Sense Resistor
Return
DQ - Data Input/Output
V
DD
- Power-Supply Input (2.7V to 5.5V)
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051805
DS2740
Table 1. ORDERING INFORMATION
DESCRIPTION
15-Bit Current Resolution, 8-Pin
μMAX
15-Bit Current Resolution, Lead-Free 8-Pin
μMAX
15-Bit Current Resolution, 8-Pin
μMAX,
Tape-and-Reel
15-Bit Current Resolution, Lead-Free 8-Pin
μMAX,
Tape-
DS2740U+T&R
D2740 (see note)
and-Reel
DS2740BU
2740B
13-Bit Current Resolution, 8-Pin
μMAX
DS2740BU+
2740B (see note) 13-Bit Current Resolution, Lead-Free 8-Pin
μMAX
DS2740BU/T&R
2740B
13-Bit Current Resolution, 8-Pin
μMAX,
Tape-and-Reel
13-Bit Current Resolution, Lead-Free 8-Pin
μMAX,
Tape-
DS2740BU+T&R
2740B (see note)
and-Reel
Note: A “+” will also be marked on the package next to the pin 1 indicator.
PART
DS2740U
DS2740U+
DS2740U/T&R
MARKING
D2740
D2740 (see note)
D2740
DESCRIPTION
The DS2740 provides high-precision current-flow measurement data to support battery-capacity
monitoring in cost-sensitive applications. Current is measured bidirectionally over a dynamic range of 15
bits (DS2740U) or 13 bits (DS2740BU), with the net flow accumulated in a separate 16-bit register.
Through its 1-Wire interface, the DS2740 allows the host system read/write access to status and current
measurement registers. Each device has a unique factory-programmed 64-bit net address that allows it to
be individually addressed by the host system, supporting multibattery slot operation. The interface can be
operated with standard or overdrive timing.
Although the DS2740 is primarily intended for location on the host system, it is also suited for mounting
in the battery pack. The DS2740 and FuelPack™ algorithms, along with host measurements of
temperature and voltage, form a complete and accurate solution for estimating remaining capacity.
FuelPack is a trademark of Dallas Semiconductor.
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DS2740
Figure 1. BLOCK DIAGRAM
V
DD
STATUS/CONTROL
PIO
DQ
1-WIRE
INTERFACE
AND
ADDRESS
ACCUMULATED
CURRENT
TIMEBASE
CURRENT
15-Bit + Sign
ADC
CHIP
GROUND
R
IS
10 k
Ω
R
IS
10 k
Ω
C
F
SNS
IS2
IS1
V
SS
R
SNS
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DS2740
Table 2. DETAILED PIN DESCRIPTIONS
PIN
SYMBOL
DESCRIPTION
1-Wire Bus Speed Control.
Input logic level selects the speed of the 1-
Wire bus. Logic 1 selects overdrive (OVD) and Logic 0 selects standard
timing (STD). On a multidrop bus, all devices must operate at same
speed.
Programmable I/O Pin.
Programmed as input or output through internal
registers. Open-drain output sufficient for LED or vibrator activation.
Current-Sense Resistor Input
Current-Sense Input.
Connected to SNS through a 10kΩ resistor to
allow filtering of the current waveform by an external capacitor.
Current-Sense Input.
Connected to V
SS
through a 10kΩ resistor to allow
filtering of the current waveform through an external capacitor.
Device Ground, Current-Sense Resistor Return.
Connect directly to
the negative terminal of the battery cell.
Data I/O Pin.
Operates bidirectionally with open-drain output driver.
Internal 1µA pulldown aids in sensing pack removal and Sleep-mode
activation.
Power-Supply Input.
Connects to system voltage supply or positive
terminal of battery cell.
OVD
1
PIO
SNS
IS2
IS1
V
SS
DQ
V
DD
2
3
4
5
6
7
8
Figure 2. APPLICATION EXAMPLE
2.7V to 5.5V
System Supply
or
Battery Pack
Positive
DATA
150
DQ
VDD
150
PIO
330
PIO
SNS
*
*
IS2
DS2740
OVD
VSS
IS1
104
System
GND
104
Connection
To
Battery
Negative
R
SNS
* 5.6V zener recommended for ESD protection when DATA or PIO
contacts exposed, such as a removable battery pack application
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DS2740
POWER MODES
The DS2740 has two power modes: Active and Sleep. While in Active mode, the DS2740 operates as a
high-precision coulomb counter with current and accumulated current measurement blocks operating
continuously and the resulting values updated in the measurement registers. Read and write access is
allowed to all registers. PIO pin is active. In Sleep mode, the DS2740 operates in a low-power mode with
no current measurement activity. Serial access to current, accumulated current, and status/control
registers is allowed if V
DD
> 2V.
The DS2740 operating mode transitions from SLEEP to ACTIVE when:
1)
DQ > V
IH
, and V
DD
> UV threshold, or
2)
V
DD
rises from below UV threshold to above UV threshold.
The DS2740 operating mode transitions from ACTIVE to SLEEP when:
1)
V
DD
falls to UV threshold, or
2)
SMOD = 1 and DQ < V
IL
for 2s.
CURRENT MEASUREMENT
In the Active mode of operation, the DS2740 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
. To extend the input
range for pulse-type load currents, the voltage signal can be filtered by adding a capacitor between the
IS1 and IS2 pins. The external capacitor and two internal resistors form a lowpass filter at the input of the
ADC. The voltage-sense range at IS1 and IS2 is ±51.2mV. The input converts peak signal amplitudes up
to 102mV as long as the continuous or average signal level (post filter) does not exceed ±51.2mV over
the conversion cycle period. The ADC samples the input differentially at IS1 and IS2 with an 18.6kHz
sample clock and updates the current register at the completion of each conversion cycle. Conversion
times for each resolution option are listed in the tables below. Two resolution options are available.
Figure 3 describes the current measurement register format and resolution for each option. “S” indicates
the sign bit(s).
Figure 3. CURRENT REGISTER FORMAT
DS2740U
: Units: 1.5625
μ
V/R
SNS
, 15-bit + sign resolution, 3.5s conversion period.
DS2740BU
: Units: 6.250
μ
V/R
SNS
, 13-bit + sign resolution, 0.875s conversion period.
MSB—Address 0Eh
S
2
14
2
13
2
12
2
11
2
10
2
9
2
8
LSb
2
7
MSb
2
6
LSB—Address 0Fh
2
5
2
4
2
3
2
2
2
1
2
0
LSb
MSb
Full-scale magnitude: ±51.2mV
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