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Features
Accurate measurement of avail-
able capacity in NiCd or NiMH
batteries
Low-cost battery management so-
lution for pack integration
-
As little as
1
2
square inch of
PCB for complete circuit
-
Low operating current (120
A
typical)
-
Less than 100nA of data
retention current
High-speed (5kb/s) single-wire
communication interface (HDQ
bus) for critical battery
parameters
Communication with an external
charge controller such as the
bq2004
Direct drive of remaining capacity
LEDs
Automatic rate and temperature
compensation of measurements
16-pin narrow SOIC
General Description
T h e b q 2 0 1 4 H N i C d / N i M H G a s
Gauge IC is intended for battery-
pack or in-system installation to
maintain an accurate record of
available battery capacity. The IC
monitors a voltage drop across a
sense resistor connected in series
between the negative battery termi-
n a l a n d g r o u n d t o d e t e r m i n e
charge and discharge activity of
the battery. Compensations for bat-
tery temperature, self-discharge,
and rate of discharge are applied to
the charge counter to provide avail-
able capacity information across a
wide range of operating conditions.
Battery capacity is automatically re-
calibrated, or "learned," in the
course of a discharge cycle from full
to empty.
Nominal available capacity may be
directly indicated using a five-
segment LED display. The bq2014H
also supports a simple single-line
bidirectional serial link to an exter-
nal processor (common ground). The
5kb/s HDQ bus interface reduces
communications overhead in the
external microcontroller.
Internal registers include available
capacity and energy, temperature,
voltage and current, and battery
status. The external processor may
also overwrite some of the bq2014H
gas gauge data registers.
The bq2014H can operate from the
batteries in the pack. The REF out-
put and an external transistor allow
a simple, inexpensive voltage regu-
lator to supply power to the circuit
from the cells.
1
Preliminary
bq2014H
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
DONE
Charge complete
input
1
PN20140H..eps
16-Pin Narrow SOIC
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LCOM
SEG1/PROG1
SEG2/PROG2
SEG3/PROG3
SEG4/PROG4
SEG5/PROG5
DONE
VSS
VCC
REF
NC
HDQ
RBI
SB
DISP
SR
V
SS
System ground
SR
Sense resistor input
DISP
Display control input
SB
Battery sense input
RBI
Register backup input
HDQ
Serial communications
input/output
NC
No connect
REF
Voltage reference output
V
CC
Supply voltage
Pin Connections
SLUS030JUNE 1999
Low-Cost NiCd/NiMH Gas Gauge IC
Pin Names
Pin Descriptions
LCOM
LED common output
Open-drain output that switches V
CC
to
source current for the LEDs. The switch is
off during initialization to allow reading of
the soft pull-up or pull-down program resis-
tors. 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
)
Outputs that each 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
SEG
2
)
Three-level input pins that define the pro-
grammed full count (PFC) thresholds de-
scribed in Table 2.
PROG
3
PROG
4
Power gauge scale selection inputs (dual
function with SEG
3
SEG
4
)
Three-level input pins that define the scale
factor described in Table 2.
PROG
5
Self-discharge rate selection (dual func-
tion with SEG
5
)
Three-level input pin that defines
the
self-discharge and battery-compensation fac-
tors as shown in Table 1.
DONE
Charge complete input
Communicates the status of an external
charge-controller such as the bq2004 Fast-
Charge IC to the bq2014H. Note: This pin
must be pulled down to V
SS
using a 200k
resistor.
V
SS
Ground
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. V
SR
< V
SS
indicates discharge, and V
SR
>
V
SS
indicates charge. The effective voltage
drop, V
SRO
, as seen by the bq2014H is V
SR
+
V
OS
.
DISP
Display control input
DISP high disables the LED display. DISP
tied to V
CC
allows PROG
X
to connect di-
rectly to V
CC
or V
SS
instead of through a
pull-up or pull-down resistor. DISP floating
allows the LED display to be active during
charge. DISP low activates the display. See
Table 1.
SB
Secondary battery input
Monitors the battery cell-voltage potential
through a high-impedance resistive divider
network for end-of-discharge voltage (EDV)
t h r e s h o l d s a n d f o r b a t t e r y - r e m o v e d
detection.
RBI
Register backup input
Provides backup potential to the bq2014H reg-
isters while V
CC
3V. A storage capacitor or
a battery can be connected to RBI.
HDQ
Serial communication input/output
This is the open-drain bidirectional commu-
nications port.
NC
No connect
REF
Voltage reference output
REF provides a voltage reference output for
an optional microregulator.
V
CC
Supply voltage input
2
bq2014H
Preliminary
Functional Description
General Operation
The bq2014H determines battery capacity by moni-
toring the amount of current input to or removed
from a rechargeable battery.
The bq2014H mea-
sures discharge and charge currents, measures bat-
tery voltage, estimates self-discharge, monitors the
battery for low battery-voltage thresholds, and com-
pensates for temperature and charge/discharge rate.
Current measurement is made by monitoring the
voltage across a small-value series sense resistor be-
tween the negative battery terminal and ground.
The bq2014H compensates the nominal available
capacity register for discharge rate and tempera-
t u r e a n d r e p o r t s t h e c o m p e n s a t e d a v a i l a b l e
capacity. The bq2014H uses the compensated available
capacity to drive the LED display. In addition, the
bq2014H estimates the available energy using the aver-
age battery voltage during the discharge cycle and re-
maining compensated available capacity.
Figure 1 shows a typical battery pack application of the
bq2014H using the LED display capability as a charge-
state indicator. The bq2014H is configured to display
capacity in relative display mode. The relative display
mode uses the last measured discharge capacity of the
battery as the battery "full" reference. A push-button
display feature is available for momentarily enabling
the LED display.
The bq2014H 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
F2014HBP.eps
DONE
SEG5/PROG5
SEG4/PROG4
SEG3/PROG3
SEG2/PROG2
SEG1/PROG1
SR
DISP
SB
VCC
REF
bq2014H
Gas-Gauge IC
LCOM
VSS
RBI
HDQ
VCC
100K
0.1
F
C1
Q1
ZVNL110A
RS
1M
RB1
R1
RB2
See note 4
Load
Charger
1. Indicates optional.
2. Programming resistors (5 max.) and ESD-protection diodes are not shown.
3. RC on SR is required.
4. A series diode is required on RBI if the bottom series cell is used as the backup source.
If the cell is used, the backup capacitor is not required, and the anode is connected to the
positive terminal of the cell.
VCC
C2
Notes:
Figure 1. Battery Pack Application Diagram--LED Display
Preliminary
bq2014H
Voltage Thresholds
In conjunction with monitoring V
SR
for charge/discharge
currents, the bq2014H 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 bq2014H are programmable
with the default values fixed as follows:
EDV1 (first) = 0.76V
EDVF (final) = EDV1 - 0.025V = 0.735V
The battery voltage divider (RB1 and RB2 in Figure 1) is
used to scale these values to the desired threshold.
If V
SB
is below either of the two EDV thresholds, the as-
sociated flag is latched and remains latched, independ-
ent of V
SB
, until the next valid charge.
EDV monitoring is disabled if the discharge rate is
greater than 2C (OVLD Flag = 1) and resumes
1
2
second
after the rate falls below 2C. The V
SB
value is available
over the serial port.
RBI Input
The RBI input pin is used with a storage capacitor or ex-
ternal supply to provide backup potential to the internal
bq2014H registers when V
CC
drops below 3.0V. V
CC
is
output on RBI when V
CC
is above 3.0V. If using an exter-
nal supply (such as the bottom series cell) as the backup
source, an external diode is required for isolation.
Reset
The bq2014H can be reset by removing V
CC
and ground-
ing the RBI pin for 15 seconds or by commands over the
serial port. The serial port reset command sequence re-
quires writing 00h to register PPFC (address = 1Eh) and
then writing 00h to register LMD (address = 05h).
Temperature
The bq2014H internally determines the temperature in
10C steps centered from approximately -35C to +85C.
The temperature steps are used to adapt charge and dis-
charge rate compensations, self-discharge counting, and
available charge display translation.
The temperature range is available over the serial port
in 10C increments, as shown in the following table
Layout Considerations
The bq2014H 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 (C1 and C2) should be placed as
close
as
possible
to
the
V
CC
and
SB
pins,
respectively, 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 capacitor should be placed as close
as possible to the SR pin.
I
The sense resistor (R
S
) should be as close as possible to
the bq2014H.
4
TMP (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
bq2014H
Preliminary
Gas Gauge Operation
The operational overview diagram in Figure 2 illustrates
the operation of the bq2014H. The bq2014H accumu-
lates a measure of charge and discharge currents, as
well as an estimation of self-discharge.
The accumu-
lated charge and discharge currents are adjusted for
temperature and rate to provide the indication of com-
pensated available capacity to the host system or user.
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 and self-discharge decrement
the NAC register and increment the DCR (Discharge
Count Register).
The Discharge Count Register 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 bq2014H adapts
its capacity determination based on the actual condi-
tions of discharge.
The battery's initial capacity equals the Programmed
Full Count (PFC) shown in Table 2. Until LMD is up-
dated, 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
representing a discharge from full to below EDV1.
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.
5
F2014HOO.eps
Temperature
Compensation
Charge
Current
Discharge
Current
Self-Discharge
Timer
Nominal
Available
Charge
(NAC)
Last
Measured
Discharged
(LMD)
Discharge
Count
Register
(DCR)
<
Qualified
Transfer
+
Temperature Step,
Other Data
+
-
-
+
Inputs
Main Counters
and Capacity
Reference (LMD)
Outputs
Serial
Port
Compensated
Available Charge
LED Display, etc.
Rate and
Temperature
Compensation
Rate and
Temperature
Compensation
Figure 2. Operational Overview
Preliminary
bq2014H
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