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1
Features
Accurate measurement of available
charge in rechargeable batteries
Designed for electric assist bicycles
and other applications
Measures a wide dynamic current
range
Supports NiCd, NiMH or lead acid
Designed for battery pack inte-
gration
-
120
A typical standby current
(self-discharge estimation mode)
-
Small size enables imple-
mentations in as little as
1
2
square inch of PCB
Direct drive of LEDs for capacity
display
Automatic charge and self-
discharge compensation using in-
ternal temperature sensor
Simple single-wire serial commu-
nications port for subassembly
testing
16-pin narrow SOIC
General Description
The bq2013H 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 resis-
tor connected in series between the
negative battery terminal and ground
to determine charge and discharge ac-
tivity of the battery. The bq2013H is
designed for high cpaacity battery
packs used in high-discharge rate sys-
tems.
Battery self-discharge is estimated
based on an internal timer and tem-
perature sensor. Compensations for
battery temperature, rate of charge,
and self-discharge are applied to the
charge counter to provide available
capacity information across a wide
range of operating conditions. Initial
battery capacity, self-discharge rate,
display mode, and charge compensa-
tion are set using the PROG
1-6
pins.
Actual battery capacity is automati-
cally "learned" in the course of a dis-
charge cycle from full to empty.
Nominal available charge may be
directly indicated using a five-seg-
ment LED display. These segments
are used to graphically indicate
nominal available charge.
The bq2013H supports a simple
single-line bi-directional serial link to
an external processor (common
ground). The bq2013H outputs bat-
tery information in response to exter-
nal commands over the serial link. To
support battery pack testing, the
outputs may also be controlled by
command. The external processor
may also overwrite some of the
bq2013H gas gauge data registers.
The bq2013H may operate directly
from four nickel cells or three lead
acid. With the REF output and an
external transistor, a simple, inexpen-
sive 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
/PROG
1
LED segment 1/ Program
1 input
SEG
2
/PROG
2
LED segment 2 / Program
2 input
SEG
3
/PROG
3
LED segment 3/ Program
3 input
SEG
4
/PROG
4
LED segment 4/ Program
4 input
SEG
5
/PROG
5
LED segment 5/ Program
5 input
PROG
6
Program 6 input
REF
Voltage reference output
DONE
Fast charge complete
input
HDQ
Serial communications
input/output
RBI
Register backup input
SB
Battery sense input
DISP
Display control input
SR
Sense resistor input
V
CC
Supply voltage
bq2013H
Pin Connections
Pin Names
1
PN2013.eps
16-Pin Narrow SOIC
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VCC
REF
DONE
HDQ
RBI
SB
DISP
SR
LCOM
SEG1/PROG1
SEG2/PROG2
SEG3/PROG3
SEG4/PROG4
SEG5PROG5
PROG6
VSS
Gas Gauge IC for Power-
Assist Applications
SLUS120MAY 1999 B
Pin Descriptions
LCOM
LED common
This open-drain output switches V
CC
to source
current for the LEDs. The switch is off during
initialization to allow reading of PROG
1-5
pull-up or pull-down program resistors. LCOM
is also high impedance when the display is off.
SEG
1
SEG
5
LED display segment outputs (dual func-
tion with PROG
1
PROG
5
Each output may activate an LED to sink
the current sourced from LCOM.
PROG
1
PROG
6
Programmed full count selection inputs
(dual function with SEG
1
- SEG
5
)
These three-level input pins define the pro-
grammed full-count (PFC), display mode,
self-discharge
rate,
offset
compensation,
overload threshold, and charge compensa-
tion.
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 (see Figure 1) is connected
between the negative terminal of the battery
and ground. V
SR
> V
SS
indicates charge, and
V
SR
< V
SS
indicates discharge. The effective
voltage drop, V
SRO
, as seen by the bq2013H
is V
SR
+ V
OS.
DONE
Charge complete input
This input/output is used to communicate
the status of an external charge controller to
the bq2013H.
DISP
Display control input
DISP pulled high disables the display.
DISP floating allows the LED display to
be active during certain charge and dis-
charge conditions. Transitioning DISP
low activates the display.
SB
Secondary battery input
This input monitors the scaled battery volt-
age through a high-impedance resistive di-
vider network for the end-of-discharge volt-
age (EDV) thresholds.
RBI
Register backup input
This input is used to provide backup poten-
tial to the bq2013H registers during periods
when V
CC
< 3V. A storage capacitor can be
connected to RBI.
HDQ
Serial I/O pin
This is an open-drain bidirectional commu-
nications port.
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
bq2013H
Functional Description
General Operation
The bq2013H determines battery capacity by monitoring
the amount of charge input to or removed from a recharge-
able battery. The bq2013H measures discharge and charge
currents, estimates self-discharge, monitors the battery for
low-battery voltage thresholds, and compensates for tem-
perature and charge rates. The charge measurement is
made by monitoring the voltage across a small-value se-
ries sense resistor between the battery's negative terminal
and ground. The available battery charge is determined
by monitoring this voltage over time and correcting the
measurement for the environmental and operating condi-
tions.
Figure 1 shows a typical battery pack application of the
bq2013H using the LED display.
The bq2013H can be
configured to display capacity in either a relative or an
absolute display mode. The relative display mode uses
the last measured discharge capacity of the battery as
the battery "full" reference. The absolute display mode
uses the programmed full count (PFC) as the full refer-
ence, forcing each segment of the display to represent a
fixed amount of charge. A push-button display feature
is available for enabling the LED display.
The bq2013H 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 is required.
3
bq2013H
FG2013H1.eps
PROG6
SEG5/PROG5
SEG4/PROG4
SEG3/PROG3
SEG2/PROG2
SEG1/PROG1
VSS
DISP
SB
VCC
REF
bq2013H
Gas Gauge IC
LCOM
RBI
HDQ
DONE
100K
Q1
ZVNL110A
R1
C1
RS
H, Z, or L
To
C
RB1
0.1
F
RB2
Load
Charger
To
C or
Fast Charger
2. The battery stack voltage can be directly connect to VCC across 4 nickel cells
(4.8V nominal and should not exceed 6.5V) with a resistor and a zener diode
to limit voltage during charge. Otherwise, R1and Q1 are needed for
regulation of > 4 nickel cells.
3. Programming resistors and ESD-protection diodes are not shown.
4. R-C on SR is required.
SR
1. Indicates optional.
Notes:
Figure 1. Application Diagram: LED Display
Register Backup
The bq2013H RBI input pin is intended to be used with
a storage capacitor to provide backup potential to the in-
ternal bq2013H registers when V
CC
momentarily drops be-
low 3.0V. V
CC
is output on RBI when V
CC
is above 3.0V.
After V
CC
rises above 3.0V, the bq2013H 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 V
SR
for charge/discharge
currents, the bq2013H monitors the battery potential
through the SB pin for the end-of-discharge voltage (EDV)
thresholds.
The EDV threshold levels are used to determine when
the battery has reached an "empty" state.
The EDV thresholds for the bq2013H are set as follows:
EDV1 (first) = 1.00V
EDVF (final) = EDV1 - 100mV
The battery voltage divider (RB1 and RB2 in Figure 1) is
used to scale these values to the desired threshold.
If VSB is below either of the two EDV thresholds for the
specified delay times in Table 1, the associated flag is
latched and remains latched, independent of VSB, until
the next valid charge. EDV monitoring is disabled if the
OVLD bit in FLGS2 is set.
Table 1. Delay Time in Seconds
Capacity
Temperature
< 10
C
10
C to 30C
> 30
C
> 40%
7
6
5
20% to 40%
4
3
2
< 20%
2
2
2
Reset
The bq2013H can be reset by removing V
CC
and ground-
ing the RBI pin for 15 seconds or with a command over
the serial port. The serial port reset command sequence
requires writing 00h to register PPFC (address = leh)
and the writing 00h to register LMD (address = 05h.)
Temperature
The bq2013H internally determines the temperature in
10C steps centered from -35C to +85C. The tempera-
ture steps are used to adapt charge rate compensations
and self-discharge counting. The temperature range is
available over the serial port in 10C increments as
shown in the following table:
TMPGG (hex)
Temperature Range
0x
< -30C
1x
-30C to -20C
2x
-20C to -10C
3x
-10C to 0C
4x
0C to 10C
5x
10C to 20C
6x
20C to 30C
7x
30C to 40C
8x
40C to 50C
9x
50C to 60C
Ax
60C to 70C
Bx
70C to 80C
Cx
> 80C
Layout Considerations
The bq2013H measures the voltage differential between
the SR and V
SS
pins. V
OS
(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:
I
The capacitors should be placed as close as possible
to the SB and V
CC
pins and their paths to V
SS
should
be as short as possible. A high-quality ceramic
capacitor of 0.1
f is recommended for V
CC
.
I
The sense resistor (R
S
) should be as close as possible
to the bq2013H.
I
The R-C on the SR pin should be located as close as
possible to the SR pin. The maximum R should not
exceed 100K.
Gas Gauge Operation
The operational overview diagram in Figure 2 illus-
trates the operation of the bq2013H. The bq2013H ac-
cumulates a measure of charge and discharge currents,
as well as an estimation of self-discharge. The bq2013H
compensates charge current for charge rate and tem-
4
bq2013H
perature. Discharge current is load compensated based
on the value stored in location LCOMP (address = 0eh).
LCOMP allows the bq2013H to automatically adjust for
continuous small discharge currents. The bq2013H com-
pensates self discharge for the load value as well as tem-
perature.
The main counter, Nominal Available Capacity (NAC),
represents the available battery capacity at any given
time.
Battery charging increments the NAC register,
while battery discharging, self-discharge decrement the
NAC register and increment the DCR (Discharge Count
Register). NAC is also corrected automatically for offset
error based on the value in the offset location OFFSET
(address = 0bh.)
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
bq2013H 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 2.
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. The maximum decrease in LMD because of a
DCR update is 25% of LMD. 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 dis-
play 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
bq2013H is configured for a given application by se-
lecting a PFC value from Table 2. 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 () =
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.
5
bq2013H
FG2013H2.eps
Load and
Temperature
Compensation
Charge
Current
Discharge
Current
Self-Discharge
Timer
Temperature
Translation
Nominal
Available
Charge
(NAC)
(offset corrected)
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
-
+
Load
Compensation
Figure 2. Operational Overview
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