Texas Instruments EV2010, BQ2010SN-D107TR, BQ2010SN-D107 Datasheet

Features
Conservative and repeatable measurement of available charge in rechargeable batteries
Designed for battery pack inte
-
gration
120µA typical standby current
Small size enables imple­mentations in as little as
1
2
square inch of PCB
Integrate within a system or as a stand-alone device
Display capacity via single­wire serial communication port or direct drive of LEDs
Measurements compensated for
current and temperature
Self-discharge compensation us-
ing internal temperature sensor
Accurate measurements across a
wide range of current (> 500:1)
16-pin narrow SOIC
General Description
The bq2010 Gas Gauge IC is intended for battery-pack or in-system installa
­tion to maintain an accurate record of a battery's available charge. The IC monitors a voltage drop across a sense resistor connected in series be
­tween the negative battery terminal and ground to determine charge and discharge activity of the battery.
NiMH and NiCd battery self-dis
­charge is estimated based on an inter
­nal timer and temperature sensor. Compensations for battery tempera
­ture and rate of charge or discharge are applied to the charge, discharge, and self-discharge calculations to pro
­vide available charge information across a wide range of operating con­ditions. Battery capacity is automati­cally recalibrated, or “learned,” in the course of a discharge cycle from full to empty.
Nominal available charge may be directly indicated using a five- or six-segment LED display. These seg­ments are used to indicate graphi­cally the nominal available charge.
The bq2010 supports a simple single-line bidirectional serial link to an external processor (common ground). The bq2010 outputs battery information in response to external commands over the serial link.
The bq2010 may operate directly from 3 or 4 cells. With the REF out
-
put and an external transistor, a sim
­ple, inexpensive regulator can be built to provide V
CC
across a greater
number of cells.
Internal registers include available charge, temperature, capacity, battery ID, battery status, and programming pin settings. To support subassembly testing, the outputs may also be con
­trolled. The external processor may also overwrite some of the bq2010 gas gauge data registers.
1
LCOM LED common output
SEG
1
/PROG1LED segment 1/
program 1 input
SEG
2
/PROG2LED segment 2/
program 2 input
SEG
3
/PROG3LED segment 3/
program 3 input
SEG
4
/PROG4LED segment 4/
program 4 input
SEG
5
/PROG5LED segment 5/
program 5 input
SEG
6
/PROG6LED segment 6/
program 6 input
1
PN201001.eps
16-Pin Narrow SOIC
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
CC
REF
NC
DQ
EMPTY
SB
DISP
SR
LCOM
SEG1/PROG
1
SEG2/PROG
2
SEG3/PROG
3
SEG4/PROG
4
SEG5/PROG
5
SEG6/PROG
6
V
SS
REF Voltage reference output
NC No connect
DQ Serial communications
input/output
EMPTY Empty battery indicator
output
SB Battery sense input
DISP
Display control input
SR Sense resistor input
V
CC
3.0–6.5V
V
SS
System ground
bq2010
Pin Connections
Pin Names
4/95 D
Gas Gauge IC
Pin Descriptions
LCOM
LED common output
Open-drain output switches V
CC
to source
current for the LEDs. The switch is off dur
­ing initialization to allow reading of the soft pull-up or pull-down program resistors. LCOM is also high impedance when the dis
­play is off.
SEG
1
SEG
6
LED display segment outputs (dual func
­tion with PROG
1
–PROG6)
Each output may activate an LED to sink the current sourced from LCOM.
PROG
1
PROG
2
Programmed full count selection inputs (dual function with SEG
1
–SEG2)
These three-level input pins define the pro
­grammed full count (PFC) thresholds de
­scribed in Table 2.
PROG
3
PROG
4
Gas gauge rate selection inputs (dual function with SEG
3
–SEG4)
These three-level input pins define the scale factor described in Table 2.
PROG
5
Self-discharge rate selection (dual func­tion with SEG
5
)
This three-level input pin defines the selfdischarge compensation rate shown in Ta­ble 1.
PROG
6
Display mode selection (dual function with SEG
6
)
This three-level pin defines the display op
­eration shown in Table 1.
NC
No connect
SR
Sense resistor input
The voltage drop (V
SR
) across the sense re
-
sistor R
S
is monitored and integrated over
time to interpret charge and discharge activ
­ity. The SR input is tied to the high side of the sense resistor. V
SR<VSS
indicates dis
­charge, and V
SR>VSS
indicates charge. The
effective voltage drop, V
SRO
, as seen by the
bq2010 is V
SR+VOS
(see Table 5).
DISP
Display control input
DISP
high disables the LED display. DISP tied to VCCallows PROGXto connect directly to V
CC
or VSSinstead of through a pull-up or
pull-down resistor. DISP
floating allows the LED display to be active during discharge or charge if the NAC registers update at a rate equivalent to |V
SRO
|≥4mV. DISP low acti
-
vates the display. See Table 1.
SB
Secondary battery input
This input monitors the single-cell voltage potential through a high-impedance resis­tive divider network for end-of-discharge voltage (EDV) thresholds, maximum charge voltage (MCV), and battery removed.
EMPTY
Battery empty output
This open-drain output becomes high-impedance on detection of a valid end-of-discharge voltage (V
EDVF
) and is low following the next application
of a valid charge.
DQ
Serial I/O pin
This is an open-drain bidirectional pin.
REF
Voltage reference output for regulator
REF provides a voltage reference output for an optional micro-regulator.
V
CC
Supply voltage input
V
SS
Ground
2
bq2010
Functional Description
General Operation
The bq2010 determines battery capacity by monitoring the amount of charge input to or removed from a re
­chargeable battery. The bq2010 measures discharge and charge currents, estimates self-discharge, monitors the battery for low-battery voltage thresholds, and compen
­sates for temperature and charge/discharge rates. The charge measurement derives from monitoring the voltage across a small-value series sense resistor between the negative battery terminal and ground. The available bat
­tery charge is determined by monitoring this voltage over time and correcting the measurement for the environ
­mental and operating conditions.
Figure 1 shows a typical battery pack application of the bq2010 using the LED display capability as a charge­state indicator. The bq2010 can be configured to display capacity in either a relative or an absolute display mode. The relative display mode uses the last measured dis
-
charge capacity of the battery as the battery “full” refer
­ence. The absolute display mode uses the programmed full count (PFC) as the full reference, forcing each seg
­ment of the display to represent a fixed amount of charge. A push-button display feature is available for momentarily enabling the LED display.
The bq2010 monitors the charge and discharge currents as a voltage across a sense resistor (see R
S
in Figure 1). A filter between the negative battery terminal and the SR pin may be required if the rate of change of the bat
-
tery current is too great.
3
bq2010
FG201001.eps
SEG6/PROG
6
SEG5/PROG
5
SEG4/PROG
4
SEG3/PROG
3
SEG2/PROG
2
SEG1/PROG
1
SR
DISP
SB
V
CC
REF
bq2010
Gas Gauge IC
LCOM
V
SS
EMPTY
DQ
V
CC
C1
0.1 F
µ
Q1 ZVNL110A
R
1
R
S
RB
1
RB
2
Load
Charger
Indicates optional.
Directly connect to VCC across 3 or 4 cells (3 to 5.6V nominal) with a resistor and a Zener diode to limit voltage during charge. Otherwise, R1, C1, and Q1 are needed for regulation of >4 cells. The value of R1 depends on the number of cells.
Programming resistors (6 max.) and ESD-protection diodes are not shown.
R-C on SR ma
y
be required, application-specific.
V
CC
Figure 1. Battery Pack Application Diagram—LED Display
Voltage Thresholds
In conjunction with monitoring VSRfor charge/discharge currents, the bq2010 monitors the single-cell battery potential through the SB pin. The single-cell voltage potential is determined through a resistor/divider net
-
work according to the following equation:
RB
RB
N
1
2
1=−
where N is the number of cells, RB
1
is connected to the
positive battery terminal, and RB
2
is connected to the
negative battery terminal. The single-cell battery volt
­age is monitored for the end-of-discharge voltage (EDV) and for maximum cell voltage (MCV). EDV threshold levels are used to determine when the battery has reached an “empty” state, and the MCV threshold is used for fault detection during charging.
Two EDV thresholds for the bq2010 are fixed at:
V
EDV1
(early warning) = 1.05V
V
EDVF
(empty) = 0.95V
If V
SB
is below either of the two EDV thresholds, the as­sociated flag is latched and remains latched, indepen­dent of V
SB
, until the next valid charge. EDV monitoring may be disabled under certain conditions as described in the next paragraph.
During discharge and charge, the bq2010 monitors V
SR
for various thresholds. These thresholds are used to compensate the charge and discharge rates. Refer to the count compensation section for details. EDV monitoring is disabled if V
SR
-250mV typical and resumes
1
2
second
after V
SR
> -250mV.
EMPTY Output
The EMPTY output switches to high impedance when V
SB<VEDVF
and remains latched until a valid charge
occurs. The bq2010 also monitors V
SB
relative to V
MCV
,
2.25V. V
SB
falling from above V
MCV
resets the device.
Reset
The bq2010 recognizes a valid battery whenever VSBis greater than 0.1V typical. V
SB
rising from below 0.25V or falling from above 2.25V resets the device. Reset can also be accomplished with a command over the serial port as described in the Reset Register section.
Temperature
The bq2010 internally determines the temperature in 10°C steps centered from -35°C to +85°C. The tempera
­ture steps are used to adapt charge and discharge rate compensations, self-discharge counting, and available
charge display translation. The temperature range is available over the serial port in 10°C increments as shown below:
Layout Considerations
The bq2010 measures the voltage differential between the SR and V
SS
pins. VOS(the offset voltage at the SR pin) is greatly affected by PC board layout. For optimal results, the PC board layout should follow the strict rule of a single-point ground return. Sharing high-current ground with small signal ground causes undesirable noise on the small signal nodes. Additionally:
n
The capacitors (SB and VCC) should be placed as close as possible to the SB and V
CC
pins, respectively,
and their paths to V
SS
should be as short as possible. A high-quality ceramic capacitor of 0.1µf is recommended for V
CC
.
n
The sense resistor capacitor should be placed as close as possible to the SR pin.
n
The sense resistor (R
SNS
) should be as close as
possible to the bq2010.
4
bq2010
TMPGG (hex) Temperature Range
0x < -30°C
1x -30°C to -20°C
2x -20°C to -10°C
3x -10°C to 0°C
4x 0°C to 10°C
5x 10°C to 20°C
6x 20°C to 30°C
7x 30°C to 40°C
8x 40°C to 50°C
9x 50°C to 60°C
Ax 60°C to 70°C
Bx 70°C to 80°C
Cx > 80°C
Gas Gauge Operation
The operational overview diagram in Figure 2 illustrates the operation of the bq2010. The bq2010 accumulates a measure of charge and discharge currents, as well as an estimation of self-discharge. Charge and discharge cur
­rents are temperature and rate compensated, whereas self-discharge is only temperature compensated.
The main counter, Nominal Available Charge (NAC), represents the available battery capacity at any given time. Battery charging increments the NAC register, while battery discharging and self-discharge decrement the NAC register and increment the DCR (Discharge Count Register).
The Discharge Count Register (DCR) is used to update the Last Measured Discharge (LMD) register only if a complete battery discharge from full to empty occurs without any partial battery charges. Therefore, the bq2010 adapts its capacity determination based on the actual conditions of discharge.
The battery's initial capacity is equal to the Programmed Full Count (PFC) shown in Table 2. Until LMD is updated, NAC counts up to but not beyond this threshold during subsequent charges. This approach allows the gas gauge to be charger-independent and compatible with any type of charge regime.
1.
Last Measured Discharge (LMD) or learned battery capacity:
LMD is the last measured discharge capacity of the battery. On initialization (application of V
CC
or bat
­tery replacement), LMD = PFC. During subsequent discharges, the LMD is updated with the latest measured capacity in the Discharge Count Register (DCR) representing a discharge from full to below EDV1. A qualified discharge is necessary for a ca
­pacity transfer from the DCR to the LMD register. The LMD also serves as the 100% reference thresh
­old used by the relative display mode.
2.
Programmed Full Count (PFC) or initial bat
­tery capacity:
The initial LMD and gas gauge rate values are pro
­grammed by using PROG
1
–PROG4. The PFC also
provides the 100% reference for the absolute dis
­play mode. The bq2010 is configured for a given ap
­plication by selecting a PFC value from Table 2. The correct PFC may be determined by multiplying the rated battery capacity in mAh by the sense re
­sistor value:
Battery capacity (mAh)*sense resistor (Ω) =
PFC (mVh)
Selecting a PFC slightly less than the rated capac­ity for absolute mode provides capacity above the full reference for much of the battery's life.
5
bq2010
FG201002.eps
Rate and
Temperature
Compensation
Temperature
Compensation
Charge Current
Discharge
Current
Self-Discharge
Timer
Temperature
Translation
Nominal
Available
Charge
(NAC)
Last
Measured
Discharged
(LMD)
Discharge
Count
Register
(DCR)
<
Qualified Transfer
+
Rate and
Temperature
Compensation
Rate and
Temperature
Compensation
Temperature Step, Other Data
+
--
+
Inputs
Main Counters
and Capacity
Reference (LMD)
Outputs
Serial
Port
Chip-Controlled
Available Charge
LED Display
Figure 2. Operational Overview
Example: Selecting a PFC Value
Given:
Sense resistor = 0.1
Number of cells = 6 Capacity = 2200mAh, NiCd battery Current range = 50mA to 2A Absolute display mode Serial port only Self-discharge =
C
64
Voltage drop over sense resistor = 5mV to 200mV
Therefore:
2200mAh*0.1Ω= 220mVh
Select:
PFC = 33792 counts or 211mVh PROG
1
= float
PROG
2
= float
PROG
3
= float
PROG
4
= low
PROG
5
= float
PROG
6
= float
The initial full battery capacity is 211mVh (2110mAh) until the bq2010 “learns” a new capac
­ity with a qualified discharge from full to EDV1.
6
bq2010
PROG
x
Pro-
grammed
Full
Count
(PFC)
PROG
4
= L PROG4= Z
Units
1 2 PROG3 = H PROG3 = Z PROG3 = L PROG3 = H PROG3 = Z PROG3 = L
-- -
Scale =
1/80
Scale =
1/160
Scale =
1/320
Scale =
1/640
Scale =
1/1280
Scale =
1/2560
mVh/ count
H H 49152 614 307 154 76.8 38.4 19.2 mVh
H Z 45056 563 282 141 70.4 35.2 17.6 mVh
H L 40960 512 256 128 64.0 32.0 16.0 mVh
Z H 36864 461 230 115 57.6 28.8 14.4 mVh
Z Z 33792 422 211 106 53.0 26.4 13.2 mVh
Z L 30720 384 192 96.0 48.0 24.0 12.0 mVh
L H 27648 346 173 86.4 43.2 21.6 10.8 mVh
L Z 25600 320 160 80.0 40.0 20.0 10.0 mVh
L L 22528 282 141 70.4 35.2 17.6 8.8 mVh
VSR equivalent to 2
counts/sec. (nom.)
90 45 22.5 11.25 5.6 2.8 mV
Table 2. bq2010 Programmed Full Count mVh Selections
Pin
Connection
PROG
5
Self-Discharge Rate
PROG
6
Display Mode
DISP
Display State
H Disabled
Absolute
NAC = PFC on reset
LED disabled
Z
NAC
64
Absolute
NAC = 0 on reset
LED-enabled on discharge or charge
when equivalent |V
SRO
|≥4mV
L
NAC
47
Relative
NAC = 0 on reset
LED on
Note: PROG5and PROG6states are independent.
Table 1. bq2010 Programming
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