Texas Instruments BQ2011KSN-D121TR, BQ2011KSN-D121 Datasheet

1
Features
Conservative and repeatable measurement of available charge in rechargeable batteries
Designed for portable equipment such as power tools with high dis
-
Designed for battery pack inte
-
gration
-
120µA typical standby current (self-discharge estimation mode)
-
Small size enables imple­mentations in as little as
1
2
square inch of PCB
Direct drive of LEDs for capacity
display
Self-discharge compensation us-
ing internal temperature sensor
Simple single-wire serial commu-
nications port for subassembly testing
16-pin narrow SOIC
General Description
The bq2011K Gas Gauge IC is in
­tended for battery-pack installation to maintain an accurate record of a bat
­tery’s available charge. The IC moni
­tors a voltage drop across a sense re
­sistor connected in series between the negative battery terminal and ground to determine charge and discharge ac
­tivity of the battery. The bq2011K is designed for systems such as power tools with very high discharge rates.
Battery self-discharge is estimated based on an internal timer and tem
­perature sensor. Compensations for battery temperature and rate of charge or discharge are applied to the charge, discharge, and selfdischarge calculations to provide available charge information across a wide range of operating conditions. Initial battery capacity is set using the PROG
1-4
and SPFC pins. Actual battery capacity is automatically “learned” in the course of a dis­charge cycle from full to empty and may be displayed depending on the display mode.
Nominal available charge may be di
-
rectly indicated using a five-seg
­ment LED display. These segments are used to graphically indicate nominal available charge.
The bq2011K supports a simple single-line bidirectional serial link to an external processor (common ground). The bq2011K outputs bat
­tery information in response to exter
­nal commands over the serial link. To support subassembly testing, the outputs may also be controlled by command. The external processor may also overwrite some of the bq2011K gas gauge data registers.
The bq2011K may operate directly from four cells. With the REF out­put and an external transistor, a simple, inexpensive regulator can be built to provide V
CC
from a greater
number of cells.
Internal registers include available charge, temperature, capacity, battery ID,and battery status.
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
LED segment 5
SPFC Programmed full count
selection input
REF Voltage reference output
NC No connect
DQ Serial communications
input/output
RBI Register backup input
SB Battery sense input
DISP
Display control input
SR Sense resistor input
V
CC
3.0–6.5V
V
SS
Negative battery terminal
Gas Gauge IC for
High Discharge Rates
bq2011K
10/97 B
Pin Connections Pin Names
1
PN2011JK.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
RBI
SB
DISP
SR
LCOM
SEG1/PROG
1
SEG2/PROG
2
SEG3/PROG
3
SEG4/PROG
4
SEG
5
SPFC
V
SS
Pin Descriptions
LCOM
LED common
Open-drain output switches V
CC
to source cur
-
rent for the LEDs. The switch is off during ini
-
tialization to allow reading of PROG
1-4
pull-up or pull-down program resistors. LCOM is high impedance when the display is off.
SEG
1
SEG
5
LED display segment outputs
Each output may activate an LED to sink the current sourced from LCOM, the battery, or V
CC
.
PROG
1
PROG
4
Programmed full count selection inputs (dual function with SEG
1
- SEG4)
These three-level input pins define the pro
­grammed full count (PFC) in conjunction with SPFC pin, define the display mode and enable or disable self-discharge.
SPFC
Programmed full count selection input
This three-level input pin along with PROG
1-3
define the programmed full count (PFC) thresholds described in Table 1. The state of the SPFC pin is only read immediately after a reset condition.
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 low side of the sense resistor and battery pack ground (see Figure 1). V
SR>VSS
indicates discharge,
and V
SR<VSS
indicates charge. The effec
­tive voltage drop, V
SRO
, as seen by the
bq2011K is V
SR+VOS
(see Table 4).
NC
No connect
DISP
Display control input
DISP
floating allows the LED display to
be active during certain charge and dis
­charge conditions. Transitioning DISP low activates the display for 4±0.5 seconds.
SB
Secondary battery input
This input monitors the single-cell voltage potential through a high-impedance resis
­tive divider network for the end-of-discharge voltage (EDV) threshold and maximum cell voltage (MCV).
RBI
Register backup input
This input is used to provide backup poten
­tial to the bq2011K registers during periods when V
CC
< 3V. A storage capacitor should
be connected to RBI.
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
bq2011K
Functional Description
General Operation
The bq2011K determines battery capacity by monitoring the amount of charge input to or removed from a recharge
­able battery. The bq2011K measures discharge and charge currents, estimates self-discharge, monitors the battery for low-battery voltage thresholds, and compensates for tem
­perature and charge/discharge rates. The charge measure
­ment is made by monitoring the voltage across a small­value series sense resistor between the battery’s negative terminal and ground. The available battery charge is de
­termined by monitoring this voltage over time and correct
­ing the measurement for the environmental and operating conditions.
Figure 1 shows a typical battery pack application of the bq2011K using the LED display with absolute mode as a charge-state indicator. The absolute display mode uses the programmed full count (PFC) as the full reference, forcing each segment of the display to represent a fixed amount of charge. A push-button display feature is available for momentarily enabling the LED display.
The bq2011K monitors the charge and discharge cur
-
rents as a voltage across a sense resistor (see R
S
in Fig
­ure 1). A filter between the negative battery terminal and the SR pin may be required if the rate of change of the battery current is too great.
Register Backup
The bq2011K RBI input pin is intended to be used with a storage capacitor to provide backup potential to the in
-
3
bq2011K
FG201103.eps
SPFC
SEG
5
SEG4/PROG
4
SEG3/PROG
3
SEG2/PROG
2
SEG1/PROG
1
V
SS
DISP
SB
V
CC
REF
bq2011K
Gas Gauge IC
LCOM
SR
RBI
DQ
V
CC
C1
0.1 F
Q1 ZVNL110A
R
1
R
S
RB
1
RB
2
Load
Charger
Indicates optional.
Directly connect to VCC across 4 cells (4.8V nominal and should not exceed 6.5V) with a resistor and a Zener diode to limit voltage during charge. Otherwise, R1, C1, and Q1 are needed for regulation of >4 cells.
Programming resistors and ESD-protection diodes are not shown.
R-C on SR may be required (application-specific), where the maximum R should not exceed 20K.
Figure 1. Application Diagram: LED Display, Absolute Mode
ternal bq2011K registers when VCCmomentarily drops be
-
low 3.0V. V
CC
is output on RBI when VCCis above 3.0V.
After V
CC
rises above 3.0V, the bq2011K checks the internal registers for data loss or corruption. If data has changed, then the NAC register is cleared, and the LMD register is loaded with the initial PFC.
Voltage Thresholds
In conjunction with monitoring VSRfor charge/discharge currents, the bq2011K monitors the single-cell battery po
-
tential through the SB pin. The single-cell voltage poten
­tial is determined through a resistor-divider network per 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). The EDV thresh
­old level is used to determine when the battery has reached an “empty” state, and the MCV threshold is used for fault detection during charging. The MCV threshold for the bq2011K is fixed at:
V
MCV
= 2.00V
The EDV threshold varies as a function of discharge cur­rent as follows:
Reset
Reset can be accomplished with a command over the se
­rial port as described on page 13.
Temperature
The bq2011K 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 bq2011K 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:
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
.
The sense resistor (RS) should be as close as possible to the bq2011K.
The R-C on the SR pin should be located as close as possible to the SR pin. The maximum R should not exceed 20K.
Gas Gauge Operation
The operational overview diagram in Figure 2 illus
-
trates the operation of the bq2011K. The bq2011K accu
­mulates a measure of charge and discharge currents, as well as an estimation of self-discharge. Charge currents are temperature and rate compensated, whereas self­discharge 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
4
bq2011K
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
V
SRO
(mV) V
EDV
(V)
010<≤V
SRO
1.160
10 20<≤V
SRO
1.124
20 40<≤V
SRO
1.060
40 60<≤V
SRO
0.960
V
SRO
> 60
0 (OVLD)
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 bq2011K adapts its capacity determination based on the actual conditions of discharge.
The battery’s initial capacity is equal to the Pro
­grammed Full Count (PFC) shown in Table 1. Until LMD is updated, NAC counts up to but not beyond this threshold during subsequent charges. This approach al
­lows the gas gauge to be charger-independent and com
­patible 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 EDV. A qualified discharge is necessary for a ca­pacity transfer from the DCR to the LMD register. The LMD also serves as the 100% reference thresh­old 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 PFC. The PFC also provides the 100% reference for the absolute display mode. The bq2011K is configured for a given application by se
­lecting a PFC value from Table 1. The correct PFC may be determined by multiplying the rated bat
­tery capacity in mAh by the sense resistor value:
Battery capacity (mAh)*sense resistor (Ω) =
PFC (mVh)
Selecting a PFC slightly less than the rated capac
­ity for absolute mode provides capacity above the full reference for much of the battery’s life.
Example: Selecting a PFC Value
Given:
Sense resistor = 0.002
Number of cells = 6 Capacity = 1800mAh, NiCd cells Current range = 1A to 80A Absolute display mode Self-discharge =
C
80
Voltage drop across sense resistor = 2mV to 160mV
5
bq2011K
FG201104.eps
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
Therefore:
1800mAh*0.002Ω= 3.6mVh
Select:
PFC = 35840 counts or 3.39mVh SPFC = Z (float) PROG1, PROG2=HorZ PROG3 = L PROG4=HorZ
The initial full battery capacity is 3.39mVh (1695mAh) un
­til the bq2011K “learns” a new capacity with a qualified discharge from full to EDV.
3. Nominal Available Charge (NAC):
NAC counts up during charge to a maximum value of LMD and down during discharge and self dis
­charge to 0. NAC is reset to 0 on initialization and on the first valid charge following discharge to EDV. To prevent overstatement of charge during periods of overcharge, NAC stops incrementing when NAC = LMD.
Note: NAC is set to the value in LMD when PROG
4
is pulled low during a reset.
6
bq2011K
Programmed
Full Count (PFC) mVh Scale
Display
Mode SPFC PROG
1
PROG
2
PROG
3
40192 3.81
1
10560
Absolute
H H or Z H or Z H or Z
32256 3.05
1
10560
Z H or Z H or Z H or Z
28928 2.74
1
10560
L H or Z H or Z H or Z
25856 2.45
1
10560
H L H or Z H or Z
35840 3.39
1
10560
Z L H or Z H or Z
23296 2.21
1
10560
L L H or Z H or Z
Table 1. bq2011K Programmed Full Count mVh Selections
PROG
4
NAC Reset Value Self-Discharge
H or Z NAC = 0 Enabled
L NAC = PFC Disabled
Table 2. Programmed Self-Discharge
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