BQ27520-G4
SLUSB20C – NOVEMBER 2012 – REVISED NOVEMBER 2021
BQ27520-G4 System-Side Impedance Track™ Fuel Gauge With Integrated LDO
1 Features
3 Description
•
The Texas Instruments BQ27520-G4 system-side Liion battery fuel gauge is a microcontroller peripheral
that provides fuel gauging for single-cell Li-ion
battery packs. The device requires little system
microcontroller firmware development. The fuel gauge
resides on the main board of the system and
manages an embedded battery (non-removable) or a
removable battery pack.
•
•
•
Single-series cell Li-ion battery fuel gauge resides
on system board
– Integrated 2.5 VDC LDO
– External low-value 10-mΩ sense resistor
Patented Impedance Track™ technology
– Adjusts for battery aging, self-discharge,
temperature, and rate changes
– Reports remaining capacity, state-of-charge
(SOC), and time-to-empty
– Optional smoothing filter
– Battery state-of-health (aging) estimation
– Supports embedded or removable packs with
up to 14500-mAh capacity
– Accommodates pack swapping with two
separate battery profiles
Microcontroller peripheral supports
– 400-kHz I2C serial interface
– 32 bytes of scratch-pad FLASH NVM
– Battery low digital output warning
– Configurable SOC interrupts
– External thermistor, internal sensor, or hostreported temperature options
Tiny 15-pin, 2610 × 1956 µm, 0.5-mm pitch
NanoFree™ (DSBGA) package
The fuel gauge uses the patented Impedance Track™
algorithm for fuel gauging, and provides information
such as remaining battery capacity (mAh), state-ofcharge (%), run-time to empty (minimum), battery
voltage (mV), temperature (°C), and state of health
(%).
Battery fuel gauging requires only PACK+ (P+),
PACK– (P–), and optional Thermistor (T) connections
to a removable battery pack or embedded battery
circuit. The device uses a 15-ball NanoFree™
(DSBGA) package in the nominal dimensions of
2610 × 1956 µm with 0.5-mm lead pitch. It is ideal for
space-constrained applications.
Device Information
PART NUMBER
2 Applications
BQ27520-G4
•
•
•
•
(1)
Smartphones, feature phones, and tablets
Digital still and video cameras
Handheld terminals
MP3 or multimedia players
PACKAGE(1)
DSBGA (15)
BODY SIZE (NOM)
2.610 mm × 1.956 mm
For all available packages, see the orderable addendum at
the end of the data sheet.
Host System
Single Cell Li-lon
Battery Pack
VCC
CE
Power
Management
Controller
I2C
LDO
PACK+
Battery
Low
Voltage
Sense
DATA
Temp
Sense
BAT_GD
PROTECTION
IC
T
PACK-
FETs
CHG
DSG
Current
Sense
SOC_INT
Typical Application Diagram
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
BQ27520-G4
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SLUSB20C – NOVEMBER 2012 – REVISED NOVEMBER 2021
Table of Contents
1 Features............................................................................1
2 Applications..................................................................... 1
3 Description.......................................................................1
4 Revision History.............................................................. 2
5 Device Comparison Table...............................................3
6 Pin Configuration and Functions...................................3
7 Specifications.................................................................. 5
7.1 Absolute Maximum Ratings ....................................... 5
7.2 ESD Ratings............................................................... 5
7.3 Recommended Operating Conditions.........................5
7.4 Thermal Information....................................................5
7.5 Electrical Characteristics: Supply Current...................6
7.6 Digital Input and Output DC Characteristics............... 6
7.7 Power-on Reset.......................................................... 6
7.8 2.5-V LDO Regulator.................................................. 6
7.9 Internal Clock Oscillators............................................ 6
7.10 ADC (Temperature and Cell Measurement)
Characteristics...............................................................7
7.11 Integrating ADC (Coulomb Counter)
Characteristics...............................................................7
7.12 Data Flash Memory Characteristics..........................7
7.13 I2C-Compatible Interface Communication
Timing Requirements.................................................... 8
7.14 Typical Characteristics.............................................. 9
8 Detailed Description......................................................10
8.1 Overview................................................................... 10
8.2 Functional Block Diagram......................................... 11
8.3 Feature Description...................................................12
8.4 Device Functional Modes..........................................12
8.5 Programming............................................................ 17
9 Application and Implementation.................................. 21
9.1 Application Information............................................. 21
9.2 Typical Application.................................................... 22
10 Power Supply Recommendations..............................26
10.1 Power Supply Decoupling.......................................26
11 Layout........................................................................... 26
11.1 Layout Guidelines................................................... 26
11.2 Layout Example...................................................... 27
12 Device and Documentation Support..........................28
12.1 Third-Party Products Disclaimer............................. 28
12.2 Documentation Support.......................................... 28
12.3 Receiving Notification of Documentation Updates..28
12.4 Support Resources................................................. 28
12.5 Trademarks............................................................. 28
12.6 Electrostatic Discharge Caution..............................28
12.7 Glossary..................................................................28
13 Mechanical, Packaging, and Orderable
Information.................................................................... 28
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (December 2015) to Revision C (November 2021)
Page
• Updated 32 Ahr to 14500-mAh .......................................................................................................................... 1
• Updated the data sheet to the latest Texas Instruments data sheet standards.................................................. 1
Changes from Revision A (August 2013) to Revision B (December 2015)
Page
• Changed 32 Ahr to 14500-mAh ......................................................................................................................... 1
• Deleted minimum and maximum values for Power-on reset hysteresis............................................................. 6
• Added Device Information table, ESD Ratings table, Feature Description section, Device Functional Modes,
Programming section, Application and Implementation section, Power Supply Recommendations section,
Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information...........12
• Changed Figure 8-1 .........................................................................................................................................13
• Added Figure 8-2 ............................................................................................................................................. 13
Changes from Revision * (November 2012) to Revision A (August 2013)
Page
• Aligned package description throughout datasheet............................................................................................1
2
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5 Device Comparison Table
PRODUCTION
PART NO.(2)
BQ27520YZFR-G4
BQ27520YZFT-G4
(1)
PACKAGE(1)
TA
COMMUNICATION
FORMAT
DSBGA-15
–40°C to 85°C
I2C(2)
TAPE AND REEL
QUANTITY
3000
250
For the most current package and ordering information, see the Package Option Addendum at the end of this document; or, see the TI
website at www.ti.com.
BQ27520-G4 is shipped in I2C mode.
(2)
6 Pin Configuration and Functions
(TOP VIEW)
B3
C3
D3
E3
E3
D3
C3
B3
A3
A2
B2
C2
D2
E2
E2
D2
C2
B2
A2
A1
B1
C1
D1
E1
E1
D1
C1
B1
A1
A3
E
(BOTTOM VIEW)
xx
xx
Pin A1
Index Area
D
DIM
MIN
TYP
MAX
D
2580
2610
2640
E
1926
1956
1986
UNITS
m
Figure 6-1. YZF Package 15-Pin DSBGA
Table 6-1. Pin Functions
PIN
NAME
NO.
TYPE1
DESCRIPTION
BAT
E2
I
Cell-voltage measurement input. ADC input. Recommend 4.8 V maximum for conversion
accuracy.
BAT_GD
B2
O
Battery Good push-pull indicator output. Active low and output disabled by default. Polarity
is configured via Op Config [BATG_POL] and the output is enabled via OpConfig C
[BATGSPUEN].
BAT_LOW
C3
O
Battery Low push-pull output indicator. Active high and output enabled by default. Polarity
is configured via Op Config [BATL_POL] and the output is enabled via OpConfig C
[BATLSPUEN].
BI/TOUT
E3
IO
Battery-insertion detection input. Power pin for pack thermistor network. Thermistormultiplexer control pin. Use with pullup resistor >1 MΩ (1.8 MΩ, typical).
CE
D2
I
Chip Enable. Internal LDO is disconnected from REGIN when driven low.
Note: CE has an internal ESD protection diode connected to REGIN. Recommend
maintaining VCE ≤ VREGIN under all conditions.
REGIN
E1
P
Regulator input. Decouple with 0.1-μF ceramic capacitor to VSS.
SCL
A3
I
Slave I2C serial communications clock input line for communication with system (Master).
Open-drain IO. Use with 10-kΩ pullup resistor (typical).
SDA
B3
IO
Slave I2C serial communications data line for communication with system (Master). Opendrain IO. Use with 10-kΩ pullup resistor (typical).
SOC_INT
A2
O
SOC state interrupts output. Generates a pulse under the conditions specified in the
BQ27520-G4 Technical Reference Manual. Open drain output.
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Table 6-1. Pin Functions (continued)
PIN
NAME
NO.
TYPE1
DESCRIPTION
SRN
B1
IA
Analog input pin connected to the internal coulomb counter with a Kelvin connection where
SRN is nearest the VSS connection. Connect to 5-mΩ to 20-mΩ sense resistor.
SRP
A1
IA
Analog input pin connected to the internal coulomb counter with a Kelvin connection where
SRP is nearest the PACK– connection. Connect to 5-mΩ to 20-mΩ sense resistor.
TS
D3
IA
Pack thermistor voltage sense (use 103AT-type thermistor). ADC input
VCC
D1
P
Regulator output and BQ27520-G4 processor power. Decouple with 1-μF ceramic capacitor
to VSS.
VSS
C1, C2
P
Device ground
1. IO = Digital input-output, IA = Analog input, P = Power connection
4
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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
VREGIN
Regulator input
MIN
MAX
UNIT
–0.3
5.5
V
–0.3
6.0
(1)
V
VCE
CE input pin
–0.3
VREGIN + 0.3
V
VCC
Supply voltage
–0.3
2.75
V
VIOD
Open-drain I/O pins (SDA, SCL, SOC_INT)
–0.3
5.5
V
VBAT
BAT input pin
–0.3
5.5
V
–0.3
6.0 (1)
V
VI
Input voltage to all other pins
(BI/TOUT, TS, SRP, SRN, BAT_LOW, BAT_GD)
–0.3
VCC + 0.3
V
TA
Operating free-air temperature
–40
85
°C
Tstg
Storage temperature
–65
150
°C
(1)
Condition not to exceed 100 hours at 25°C lifetime.
7.2 ESD Ratings
VALUE
VESD
(1)
Electrostatic discharge
Human-body model (HBM) (1)
All pins except E2
2000
Pin E2
1500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
TA = –40°C to 85°C, VREGIN = VBAT = 3.6 V (unless otherwise noted)
MIN
No operating restrictions
VREGIN
Supply voltage
CREGIN
External input capacitor for internal
LDO between REGIN and VSS
CLDO25
External output capacitor for internal
LDO between VCC and VSS
tPUCD
Power-up communication delay
No flash writes
Nominal capacitor values specified.
Recommend a 5% ceramic X5R-type
capacitor located close to the device.
NOM
MAX
2.8
4.5
2.45
2.8
0.47
UNIT
V
0.1
μF
1
μF
250
ms
7.4 Thermal Information
over operating free-air temperature (unless otherwise noted)
BQ27520-G4
THERMAL METRIC(1)
YZF (DSBGA)
UNIT
15 PINS
RθJA
Junction-to-ambient thermal resistance
70
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
17
°C/W
RθJB
Junction-to-board thermal resistance
20
°C/W
ψJT
Junction-to-top characterization parameter
1
°C/W
ψJB
Junction-to-board characterization parameter
18
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
NA
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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7.5 Electrical Characteristics: Supply Current
TA = 25°C and VREGIN = VBAT = 3.6 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ICC (1)
Normal operating mode current
Fuel gauge in NORMAL mode
ILOAD > Sleep current
118
μA
ISLP+ (1)
Snooze operating mode current
Fuel gauge in SNOOZE mode
ILOAD < Sleep current
62
μA
ISLP (1)
Low-power storage mode current
Fuel gauge in SLEEP mode
ILOAD < Sleep current
23
μA
IHIB (1)
Hibernate operating mode current
Fuel gauge in HIBERNATE mode
ILOAD < Hibernate current
8
μA
(1)
Specified by design. Not production tested.
7.6 Digital Input and Output DC Characteristics
TA = –40°C to 85°C, typical values at TA = 25°C and VREGIN = 3.6 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
Output voltage, low (SCL, SDA,
SOC_INT, BAT_LOW, BAT_GD)
VOL
VOH(PP)
VOH(OD)
IOH = –1 mA
VCC – 0.5
Output voltage, high (SDA, SCL,
SOC_INT)
External pullup resistor connected to
VCC
VCC – 0.5
BAT INSERT CHECK mode active
Input voltage, high (SDA, SCL)
VIH
Input voltage, high (BI/TOUT)
VIL(CE)
Input voltage, low (CE)
VIH(CE)
Input voltage, high (CE)
Ilkg (1)
Input leakage current (IO pins)
MAX
0.4
Output voltage, high (BAT_LOW,
BAT_GD)
Input voltage, low (BI/TOUT)
TYP
IOL = 3 mA
Input voltage, low (SDA, SCL)
VIL
(1)
MIN
–0.3
0.6
–0.3
0.6
1.2
VCC + 0.3
0.8
VREGIN = 2.8 to 4.5 V
V
V
1.2
BAT INSERT CHECK mode active
UNIT
2.65
0.3
V
V
V
μA
Specified by design. Not production tested.
7.7 Power-on Reset
TA = –40°C to 85°C, typical values at TA = 25°C and VREGIN = 3.6 V (unless otherwise noted)
PARAMETER
VIT+
Positive-going battery voltage input at VCC
VHYS
Power-on reset hysteresis
MIN
TYP
MAX
2.05
2.15
2.20
115
UNIT
V
mV
7.8 2.5-V LDO Regulator
TA = –40°C to 85°C, CLDO25 = 1 μF, VREGIN = 3.6 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
2.8 V ≤ VREGIN ≤ 4.5 V, IOUT ≤ 16
VREG25
(1)
Regulator output voltage (VCC)
mA(1)
2.45 V ≤ VREGIN < 2.8 V (low battery),
IOUT ≤ 3 mA
MIN
TYP
MAX
2.3
2.5
2.6
2.3
UNIT
V
V
LDO output current, IOUT, is the total load current. LDO regulator should be used to power internal fuel gauge only.
7.9 Internal Clock Oscillators
TA = –40°C to 85°C, 2.4 V < VCC < 2.6 V; typical values at TA = 25°C and VCC = 2.5 V (unless otherwise noted)
PARAMETER
fOSC
6
High frequency oscillator
MIN
TYP
8.389
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MAX
UNIT
MHz
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7.9 Internal Clock Oscillators (continued)
TA = –40°C to 85°C, 2.4 V < VCC < 2.6 V; typical values at TA = 25°C and VCC = 2.5 V (unless otherwise noted)
PARAMETER
fLOSC
MIN
Low frequency oscillator
TYP
MAX
32.768
UNIT
kHz
7.10 ADC (Temperature and Cell Measurement) Characteristics
TA = –40°C to 85°C, 2.4 V < VCC < 2.6 V; typical values at TA = 25°C and VCC = 2.5 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VADC1
Input voltage range (TS)
VSS – 0.125
2
V
VADC2
Input voltage range (BAT)
VSS – 0.125
5
V
VIN(ADC)
Input voltage range
GTEMP
Internal temperature sensor
voltage gain
tADC_CONV
Conversion time
0.05
Resolution
VOS(ADC)
ZADC1
ZADC2 (1)
Effective input resistance (BAT)
Ilkg(ADC) (1)
Input leakage current
(1)
125
ms
15
bits
1
Effective input resistance (TS)
Device not measuring cell voltage
V
mV/°C
14
Input offset
(1)
1
–2
mV
8
MΩ
8
MΩ
Device measuring cell voltage
100
kΩ
0.3
μA
Specified by design. Not tested in production.
7.11 Integrating ADC (Coulomb Counter) Characteristics
TA = –40°C to 85°C, 2.4 V < VCC < 2.6 V; typical values at TA = 25°C and VCC = 2.5 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
VSR
Input voltage range,
V(SRP) and V(SRN)
VSR = V(SRP) – V(SRN)
tSR_CONV
Conversion time
Single conversion
Resolution
TYP
–0.125
MAX
UNIT
0.125
V
1
s
14
VOS(SR)
Input offset
INL
Integral nonlinearity error
ZIN(SR) (1)
Effective input resistance
Ilkg(SR) (1)
Input leakage current
(1)
MIN
15
10
±0.007
bits
μV
±0.034
2.5
% FSR
MΩ
0.3
μA
Specified by design. Not tested in production.
7.12 Data Flash Memory Characteristics
TA = –40°C to 85°C, 2.4 V < VCC < 2.6 V; typical values at TA = 25°C and VCC = 2.5 V (unless otherwise noted)
PARAMETER
tDR
(1)
Data retention
Flash-programming write cycles(1)
MIN
TYP
MAX
UNIT
10
Years
20,000
Cycles
tWORDPROG (1) Word programming time
2
ms
10
mA
ICCPROG (1)
Flash-write supply current
tDFERASE (1)
Data flash master erase time
200
ms
tIFERASE (1)
Instruction flash master erase time
200
ms
20
ms
tPGERASE
(1)
(1)
5
Flash page erase time
Specified by design. Not production tested
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7.13 I2C-Compatible Interface Communication Timing Requirements
TA = –40°C to 85°C, 2.4 V < VCC < 2.6 V; typical values at TA = 25°C and VCC = 2.5 V (unless otherwise noted)
MIN
NOM
MAX
UNIT
tr
SCL or SDA rise time
300
ns
tf
SCL or SDA fall time
300
ns
tw(H)
SCL pulse duration (high)
600
ns
tw(L)
SCL pulse duration (low)
1.3
μs
tsu(STA)
Setup for repeated start
600
ns
td(STA)
Start to first falling edge of SCL
600
ns
tsu(DAT)
Data setup time
100
ns
th(DAT)
Data hold time
0
ns
tsu(STOP)
Setup time for stop
t(BUF)
Bus free time between stop and start
fSCL
Clock frequency (1)
(1)
600
ns
66
μs
400
kHz
If the clock frequency (fSCL) is > 100 kHz, use 1-byte write commands for proper operation. All other transactions types are supported
at 400 kHz. (See Section 8.5.3.1 and Section 8.5.3.3).
Figure 7-1. I2C-Compatible Interface Timing Diagrams
8
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7.14 Typical Characteristics
8.8
VREGIN = 2.7 V
VREGIN = 4.5 V
2.6
fOSC - High Frequency Oscillator (MHz)
VREG25 - Regulator Output Voltage (V)
2.65
2.55
2.5
2.45
2.4
2.35
-40
-20
0
20
40
Temperature (°C)
60
8.6
8.5
8.4
8.3
8.2
8.1
8
-40
80
33.5
4
Reported Temperature Error (qC)
5
33
32.5
32
31.5
31
30.5
-20
0
20
40
Temperature (qC)
0
20
40
Temperature (qC)
60
80
60
80
100
D002
Figure 7-3. High-Frequency Oscillator Frequency
vs. Temperature
34
30
-40
-20
D001
Figure 7-2. Regulator Output Voltage vs.
Temperature
fLOSC - Low Frequency Oscillator (kHz)
8.7
100
3
2
1
0
-1
-2
-3
-4
-5
-30
-20
D003
Figure 7-4. Low-Frequency Oscillator Frequency
vs. Temperature
-10
0
10
20
30
Temperature (qC)
40
50
60
D004
Figure 7-5. Reported Internal Temperature
Measurement vs. Temperature
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8 Detailed Description
8.1 Overview
The BQ27520-G4 fuel gauge accurately predicts the battery capacity and other operational characteristics of a
single Li-based rechargeable cell. It can be interrogated by a system processor to provide cell information, such
as time-to-empty (TTE), state-of-charge (SOC), and SOC interrupt signal to the host.
Information is accessed through a series of commands, called Standard Commands. Further capabilities are
provided by the additional Extended Commands set. Both sets of commands, indicated by the general format
Command( ), are used to read and write information contained within the device control and status registers, as
well as its data flash locations. Commands are sent from system to gauge using the I2C serial communications
engine, and can be executed during application development, system manufacture, or end-equipment operation.
Cell information is stored in the device in non-volatile flash memory. Many of these data flash locations are
accessible during application development. They cannot generally be accessed directly during end-equipment
operation. Access to these locations is achieved by either use of the companion evaluation software, through
individual commands, or through a sequence of data-flash-access commands. To access a desired data flash
location, the correct data flash subclass and offset must be known.
The key to the high-accuracy gas gauging prediction is Texas Instruments proprietary Impedance Track™
algorithm. This algorithm uses cell measurements, characteristics, and properties to create state-of-charge
predictions that can achieve less than 1% error across a wide variety of operating conditions and over the
lifetime of the battery.
The fuel gauge measures charge and discharge activity by monitoring the voltage across a small-value series
sense resistor (5 mΩ to 20 mΩ, typical) located between the system VSS and the battery PACK– terminal. When
a cell is attached to the device, cell impedance is learned based on cell current, cell open-circuit voltage (OCV),
and cell voltage under loading conditions.
The external temperature sensing is optimized with the use of a high-accuracy negative temperature coefficient
(NTC) thermistor with R25 = 10.0 kΩ ±1%. B25/85 = 3435K ± 1% (such as Semitec NTC 103AT). Alternatively,
the fuel gauge can also be configured to use its internal temperature sensor or receive temperature data from
the host processor. When an external thermistor is used, a 18.2-kΩ pullup resistor between the BI/TOUT and TS
pins is also required. The fuel gauge uses temperature to monitor the battery-pack environment, which is used
for fuel gauging and cell protection functionality.
To minimize power consumption, the device has different power modes: NORMAL, SNOOZE, SLEEP,
HIBERNATE, and BAT INSERT CHECK. The fuel gauge automatically changes modes depending upon the
occurrence of specific events, though a system processor can initiate some of these modes directly.
For complete operational details, see the BQ27520-G4 Technical Reference Manual (SLUUA35).
Note
The following formatting conventions are used in this document:
Commands: italics with parentheses( ) and no breaking spaces, for example, Control( ).
Data Flash: italics, bold, and breaking spaces, for example, Design Capacity.
Register bits and flags: italics with brackets [ ], for example, [TDA]
Data flash bits: italics, bold, and brackets [ ], for example, [LED1]
Modes and states: ALL CAPITALS, for example, UNSEALED mode.
10
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8.2 Functional Block Diagram
REGIN
LDO
POR
2.5 V
VCC
HFO
BAT
CC
HFO
SRN
LFO
HFO/128
4R
HFO/128
SRP
MUX
ADC
R
Wake
Comparator
TS
Internal
Temp
Sensor
BI/TOUT
HFO/4
SDA
SOCINT
22
I2C Slave
Engine
Instruction
ROM
22
CPU
VSS
SCL
I/O
Controller
Instruction
FLASH
BAT_LOW
8
Wake
and
Watchdog
Timer
GP Timer
and
PWM
8
BAT_GD
Data
SRAM
Data
FLASH
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8.3 Feature Description
The BQ27520-G4 measures the voltage, temperature, and current to determine battery capacity and state-ofcharge (SOC) based on the patented Impedance Track™ algorithm (refer to the Theory and Implementation
of Impedance Track Battery Fuel-Gauging Algorithm Application Report [SLUA450] for more information). The
BQ27520-G4 monitors charge and discharge activity by sensing the voltage across a small-value resistor
(5 mΩ to 20 mΩ typical) between the SRP and SRN pins and in series with the battery. By integrating
charge passing through the battery, the battery’s SOC is adjusted during battery charge or discharge. Battery
capacity is found by comparing states of charge before and after applying the load with the amount of
charge passed. When a system load is applied, the impedance of the battery is measured by comparing the
open circuit voltage (OCV) obtained from a predefined function for present SOC with the measured voltage
under load. Measurements of OCV and charge integration determine chemical state-of-charge and chemical
capacity (Qmax). The initial Qmax values are taken from a cell manufacturers' data sheet multiplied by the
number of parallel cells. It is also used for the value in Design Capacity. The BQ27520-G4 acquires and
updates the battery-impedance profile during normal battery usage. It uses this profile, along with SOC and
the Qmax value, to determine FullChargeCapacity( ) and StateOfCharge( ), specifically for the present load
and temperature. FullChargeCapacity() is reported as capacity available from a fully charged battery under
the present load and temperature until Voltage( ) reaches the Terminate Voltage. NominalAvailableCapacity()
and FullAvailableCapacity() are the uncompensated (no or light load) versions of RemainingCapacity() and
FullChargeCapacity(), respectively. The BQ27520-G4 has two Flags( ) bits and two pins to warn the host if the
battery’s SOC has fallen to critical levels. If RemainingCapacity() falls below the first capacity threshold specified
by SOC1 Set Threshold, the Flags() [SOC1] bit is set and is cleared if RemainingCapacity() rises above the
SOC1 Clear Threshold. If enabled via OpConfig C [BATLSPUEN], the BAT_LOW pin reflects the status of
the [SOC1] flag bit. If enabled by OpConfig B [BL_INT], the SOC_INT will toggle upon a state change of the
[SOC1] flag bit. As Voltage() falls below the SysDown Set Volt Threshold, the Flags() [SYSDOWN] bit is set
and SOC_INT will toggle once to provide a final warning to shut down the system. As Voltage() rises above
SysDown Clear Voltage the [SYSDOWN] bit is cleared and SOC_INT toggles once to signal the status change.
Additional details are found in the BQ27520-G4 Technical Reference Manual (SLUUA35).
8.4 Device Functional Modes
8.4.1 Power Modes
The fuel gauge has different power modes:
•
•
•
•
•
BAT INSERT CHECK: The BAT INSERT CHECK mode is a powered-up, but low-power halted, state where
the fuel gauge resides when no battery is inserted into the system.
NORMAL: In NORMAL mode, the fuel gauge is fully powered and can execute any allowable task.
SLEEP: In SLEEP mode, the fuel gauge turns off the high-frequency oscillator and operates in a reducedpower state, periodically taking measurements and performing calculations.
SLEEP+: In SLEEP+ mode, both low-frequency and high-frequency oscillators are active. Although the
SLEEP+ mode has higher current consumption than the SLEEP mode, it is also a reduced power mode.
HIBERNATE: In HIBERNATE mode, the fuel gauge is in a low power state, but can wake up by
communication or certain I/O activity.
The relationship between these modes is shown in Figure 8-1 and Figure 8-2.
8.4.1.1 BAT INSERT CHECK Mode
This mode is a halted-CPU state that occurs when an adapter, or other power source, is present to power the
fuel gauge (and system), but no battery has been detected. When battery insertion is detected, a series of
initialization activities begin, which include: OCV measurement, setting the Flags() [BAT_DET] bit, and selecting
the appropriate battery profiles.
Some commands, issued by a system processor, can be processed while the fuel gauge is halted in this mode.
The gauge wakes up to process the command, then returns to the halted state awaiting battery insertion.
12
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8.4.1.2 NORMAL Mode
The fuel gauge is in NORMAL mode when not in any other power mode. During this mode, AverageCurrent() ,
Voltage() , and Temperature() measurements are taken, and the interface data set is updated. Decisions to
change states are also made. This mode is exited by activating a different power mode.
Because the gauge consumes the most power in NORMAL mode, the Impedance Track algorithm minimizes the
time the fuel gauge remains in this mode.
8.4.1.3 SLEEP Mode
SLEEP mode is entered automatically if the feature is enabled (Op Config [SLEEP] = 1) and AverageCurrent()
is below the programmable level Sleep Current. Once entry into SLEEP mode has been qualified, but prior to
entering it, the fuel gauge performs a coulomb counter autocalibration to minimize offset.
During SLEEP mode, the fuel gauge periodically takes data measurements and updates its data set. However, a
majority of its time is spent in an idle condition.
The fuel gauge exits SLEEP mode if any entry condition is broken, specifically when:
•
•
AverageCurrent() rises above Sleep Current, or
A current in excess of IWAKE through RSENSE is detected.
In the event that a battery is removed from the system while a charger is present (and powering the gauge),
Impedance Track updates are not necessary. Hence, the fuel gauge enters a state that checks for battery
insertion and does not continue executing the Impedance Track algorithm.
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Exit From HIBERNATE
Battery Removed
POR
BAT INSERT CHECK
Exit From HIBERNATE
Communication Activity
AND Comm address is for bq27531
bq27531 clears CONTROL_STATUS
[HIBERNATE] = 0
Recommend Host also set
CONTROL_STATUS
[HEBERNATE] = 0
Check for battery insertion
from HALT state.
No gauging
Entry To NORMAL
Flags [BAT_DET] = 1
Exit From NORMAL
Flags [BAT_DET] = 0
NORMAL
Entry To SLEEP+
Operation Configuration [SLEEP] = 1
AND
CONTROL_STAUS [SNOOZE] = 1]
AND
Ι AverageCurrent ( ) Ι < Sleep Current
Flags [BAT_DET] = 0
Fuel gauging and data
updated every second
Exit From SLEEP
Flags [BAT_DET] = 0
Exit From SLEEP
Ι AverageCurrent ( ) Ι > Sleep Current
OR
Current is detected above Ι WAKE
Exit From SLEEP+
Any communication to the gauge
OR
Ι AverageCurrent ( ) Ι > Sleep Current
OR
Current is detected above Ι WAKE
SLEEP+
Entry To SLEEP+
Operation Configuration [SLEEP] = 1
AND
Ι AverageCurrent ( ) Ι < Sleep Current
Fuel gauging and data
updated every 20 seconds.
Both LFO and HFO are ON.
AND
CONTROL_STAUS [SNOOZE] = 0
Entry to SLEEP+
CONTROL_STATUS [SNOOZE] = 1
Entry to SLEEP
CONTROL_STATUS [SNOOZE] = 0
SLEEP
Exit From WAIT_HIBERNATE
Host must set CONTROL_STATUS
[HIBERNATE] = 0
AND
VCELL < Hibernate Voltage
Fuel gauging and data
updated every 20 seconds.
(LFO ON and HFO OFF)
To WAIT_HIBERNATE
System Sleep
Exit From SLEEP
Host has set CONTROL_STATUS
[HIBERNATE] = 1
OR
VCELL < Hibernate Voltage
Figure 8-1. Power Mode Diagram—System Sleep
14
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POR
Exit From HIBERNATE
Battery Removed
Exit From HIBERNATE
Communication Activity
AND Comm address is for bq27531
bq27531 clears CONTROL_STATUS
[HIBERNATE] = 0
Recommend Host also set
CONTROL_STATUS
[HEBERNATE] = 0
Exit From SLEEP
Flags [BAT_DET] = 0
BAT INSERT CHECK
Check for battery insertion
from HALT state.
No gauging
Entry To NORMAL
Flags [BAT_DET] = 1
Flags [BAT_DET] = 0
Exit From NORMAL
Flags [BAT_DET] = 0
NORMAL
Fuel gauging and data
updated every second.
HIBERNATE
Disable all bq27531
subcircuits.
Wakeup From HIBERNATE
Communication Activity
AND
Comm address is not for
bq27531
Exit From WAIT_HIBERNATE
Host must set CONTROL_STATUS
[HIBERNATE] = 0
AND
VCELL < Hibernate Voltage
To SLEEP
WAIT_HIBERNATE
Exit From WAIT_HIBERNATE
Cell relaxed
AND
Ι AverageCurrent () Ι < Hibernate
Current
OR
Cell relaxed
AND
VCELL < Hibernate Voltage
Fuel gauging and data
updated every 20 seconds.
Exit From SLEEP
Host has set CONTROL_STATUS
[HIBERNATE] = 1
OR
VCELL < Hibernate Voltage
System Shutdown
Figure 8-2. Power Mode Diagram—System Shutdown
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8.4.2 SLEEP+ Mode
Compared to the SLEEP mode, SLEEP+ mode has the high-frequency oscillator in operation. The
communication delay could be eliminated. The SLEEP+ mode is entered automatically if the feature is enabled
(CONTROL_STATUS [SNOOZE] = 1) and AverageCurrent() is below the programmable level Sleep Current.
During SLEEP+ mode, the fuel gauge periodically takes data measurements and updates its data set. However,
a majority of its time is spent in an idle condition.
The fuel gauge exits SLEEP+ mode if any entry condition is broken, specifically when:
•
•
•
Any communication activity with the gauge, or
AverageCurrent() rises above Sleep Current , or
A current in excess of IWAKE through RSENSE is detected.
8.4.3 HIBERNATE Mode
HIBERNATE mode should be used when the system equipment needs to enter a low-power state, and minimal
gauge power consumption is required. This mode is ideal when system equipment is set to its own HIBERNATE,
SHUTDOWN, or OFF mode.
Before the fuel gauge can enter HIBERNATE mode, the system must set the CONTROL_STATUS [HIBERNATE]
bit. The gauge waits to enter HIBERNATE mode until it has taken a valid OCV measurement and the magnitude
of the average cell current has fallen below Hibernate Current. The gauge can also enter HIBERNATE mode
if the cell voltage falls below Hibernate Voltage and a valid OCV measurement has been taken. The gauge
remains in HIBERNATE mode until the system issues a direct I2C command to the gauge or a POR occurs. Any
I2C communication that is not directed to the gauge does not wake the gauge.
It is the responsibility of the system to wake the fuel gauge after it has gone into HIBERNATE mode. After
waking, the gauge can proceed with the initialization of the battery information (OCV, profile selection, and so
forth).
16
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8.5 Programming
8.5.1 Standard Data Commands
The fuel gauge uses a series of 2-byte standard commands to enable system reading and writing of battery
information. Each standard command has an associated command-code pair, as indicated in Table 8-1. Because
each command consists of two bytes of data, two consecutive I2C transmissions must be executed both to
initiate the command function and to read or write the corresponding two bytes of data. Additional options
for transferring data are described in Section 8.5.2. Read and write permissions depend on the active access
mode, SEALED or UNSEALED. For details, see the BQ27520-G4 Technical Reference Manual (SLUUA35). See
Section 8.5.3 for I2C details.
Table 8-1. Standard Commands
NAME
COMMAND CODE
UNIT
SEALED
ACCESS
Control( )
CNTL
0x00 and 0x01
NA
RW
AtRate( )
AR
0x02 and 0x03
mA
RW
AtRateTimeToEmpty( )
ARTTE
0x04 and 0x05
Minutes
R
Temperature( )
TEMP
0x06 and 0x07
0.1°K
RW
Voltage( )
VOLT
0x08 and 0x09
mV
R
FLAGS
0x0A and 0x0B
NA
R
NominalAvailableCapacity( )
NAC
0x0C and 0x0D
mAh
R
FullAvailableCapacity( )
FAC
0x0E and 0x0F
mAh
R
RemainingCapacity( )
RM
0x10 and 0x11
mAh
R
FullChargeCapacity( )
FCC
0x12 and 0x13
mAh
R
AI
0x14 and 0x15
mA
R
TTE
0x16 and 0x17
Minutes
R
SI
0x18 and 0x19
mA
R
Flags( )
AverageCurrent( )
TimeToEmpty( )
StandbyCurrent( )
StandbyTimeToEmpty( )
STTE
0x1A and 0x1B
Minutes
R
StateOfHealth( )
SOH
0x1C and 0x1D
% / num
R
CC
0x1E and 0x1F
num
R
SOC
0x20 and 0x21
%
R
CycleCount( )
StateOfCharge( )
InstantaneousCurrent( )
InternalTemperature( )
0x22 and 0x23
mA
R
INTTEMP
0x28 and 0x29
0.1°K
R
Op Config
0x2C and 0x2D
NA
R
0x2E and 0x2F
mAh
R
UFRM
0x6C and 0x6D
mAh
R
ResistanceScale( )
OperationConfiguration( )
0x2A and 0x2B
DesignCapacity( )
UnfilteredRM( )
FilteredRM( )
UnfilteredFCC( )
FilteredFCC( )
TrueSOC( )
R
FRM
0x6E and 0x6F
mAh
R
UFFCC
0x70 and 0x71
mAh
R
FFCC
0x72 and 0x73
mAh
R
UFSOC
0x74 and 0x75
%
R
8.5.2 Extended Data Commands
Extended commands offer additional functionality beyond the standard set of commands. They are used in the
same manner; however, unlike standard commands, extended commands are not limited to 2-byte words. The
number of command bytes for a given extended command range in size from single to multiple bytes is specified
in Table 8-2. See BQ27520-G4 Technical Reference Manual (SLUUA35) for details on accessing the data flash.
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Table 8-2. Extended Data Commands
NAME
Reserved
COMMAND
CODE
UNIT
0x34 to 0x3D
NA
R
R
0x3E
NA
NA
RW
DataFlashClass( ) (2)
DataFlashBlock( ) (2)
SEALED
ACCESS(1) (2)
UNSEALED
ACCESS(1) (2)
0x3F
NA
RW
RW
0x40 to 0x5F
NA
R
RW
BlockDataCheckSum( )
0x60
NA
RW
RW
BlockDataControl( )
0x61
NA
NA
RW
0x6A
NA
R
R
0x6B to 0x7F
NA
R
R
BlockData( )
ApplicationStatus( )
Reserved
(1)
(2)
SEALED and UNSEALED states are entered via commands to Control( ) 0x00 and 0x01.
In SEALED mode, data flash cannot be accessed through commands 0x3E and 0x3F.
8.5.3 Communications
8.5.3.1 I2C Interface
The BQ27520-G4 fuel gauge supports the standard I2C read, incremental read, quick read, one byte write, and
incremental write functions. The 7-bit device address (ADDR) is the most significant 7 bits of the hex address
and is fixed as 1010101. The first 8-bits of the I2C protocol is, therefore, 0xAA or 0xAB for write or read,
respectively.
Host generated
S
ADDR[6:0]
0 A
Gauge generated
CMD [7:0]
A
DATA [7:0]
A P
S
ADDR[6:0]
(a) 1-byte write
S
ADDR[6:0]
0 A
1 A
DATA [7:0]
N P
(b) quick read
CMD [7:0]
A Sr
ADDR[6:0]
1 A
DATA [7:0]
N P
(c) 1- byte read
S
ADDR[6:0]
0 A
CMD [7:0]
A Sr
ADDR[6:0]
1 A
DATA [7:0]
A ...
DATA [7:0]
N P
(d) incremental read
S
ADDR[6:0]
0 A
CMD[7:0]
A
DATA [7:0]
A
DATA [7:0]
A
...
A P
(e) incremental write
(S = Start , Sr = Repeated Start , A = Acknowledge , N = No Acknowledge , and P = Stop).
Figure 8-3. I2C Read, Incremental Read, Quick Read, One Byte Write, and Incremental Write Functions
The “quick read” returns data at the address indicated by the address pointer. The address pointer, a register
internal to the I2C communication engine, increments whenever data is acknowledged by the fuel gauge or the
I2C master. “Quick writes” function in the same manner and are a convenient means of sending multiple bytes to
consecutive command locations (such as two-byte commands that require two bytes of data).
The following command sequences are not supported:
Attempt to write a read-only address (NACK after data sent by master):
Figure 8-4. Invalid Write
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Attempt to read an address above 0x6B (NACK command):
Figure 8-5. Invalid Read
8.5.3.2 I2C Time Out
The I2C engine releases both SDA and SCL if the I2C bus is held low for 2 seconds. If the fuel gauge was
holding the lines, releasing them frees them for the master to drive the lines. If an external condition is holding
either of the lines low, the I2C engine enters the low-power sleep mode.
8.5.3.3 I2C Command Waiting Time
To ensure proper operation at 400 kHz, a t(BUF) ≥ 66 μs bus free waiting time must be inserted between all
packets addressed to the fuel gauge. In addition, if the SCL clock frequency (fSCL) is > 100 kHz, use individual
1-byte write commands for proper data flow control. The following diagram shows the standard waiting time
required between issuing the control subcommand the reading the status result. An OCV_CMD subcommand
requires 1.2 seconds prior to reading the result. For read-write standard command, a minimum of 2 seconds is
required to get the result updated. For read-only standard commands, there is no waiting time required, but the
host should not issue all standard commands more than two times per second. Otherwise, the fuel gauge could
result in a reset issue due to the expiration of the watchdog timer.
S
ADDR [6:0]
0 A
CMD [7:0]
A
DATA [7:0]
A P
66ms
S
ADDR [6:0]
0 A
CMD [7:0]
A
DATA [7:0]
A P
66ms
S
ADDR [6:0]
0 A
CMD [7:0]
A Sr
ADDR [6:0]
1 A
DATA [7:0]
A
DATA [7:0]
N P
66ms
N P
66ms
Waiting time inserted between two 1-byte write packets for a subcommand and reading results
(required for 100 kHz < fSCL £ 400 kHz)
S
ADDR [6:0]
0 A
CMD [7:0]
A
DATA [7:0]
S
ADDR [6:0]
0 A
CMD [7:0]
A Sr
ADDR [6:0]
A
1 A
DATA [7:0]
DATA [7:0]
A P
A
66ms
DATA [7:0]
Waiting time inserted between incremental 2-byte write packet for a subcommand and reading results
(acceptable for fSCL £ 100 kHz)
S
ADDR [6:0]
DATA [7:0]
0 A
A
CMD [7:0]
DATA [7:0]
A Sr
N P
ADDR [6:0]
1 A
DATA [7:0]
A
DATA [7:0]
A
66ms
Waiting time inserted after incremental read
Figure 8-6. Standard I2C Command Waiting Time Required
8.5.3.4 I2C Clock Stretching
A clock stretch can occur during all modes of fuel gauge operation. In SLEEP and HIBERNATE modes, a short
clock stretch occurs on all I2C traffic as the device must wake-up to process the packet. In the other modes (BAT
INSERT CHECK, NORMAL, SNOOZE) clock stretching only occurs for packets addressed for the fuel gauge.
The majority of clock stretch periods are small as the I2C interface performs normal data flow control. However,
less frequent yet more significant clock stretch periods may occur as blocks of Data Flash are updated. The
following table summarizes the approximate clock stretch duration for various fuel gauge operating conditions.
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Table 8-3. Approximate Clock Stretch Duration
GAUGING
MODE
SLEEP
HIBERNATE
BAT INSERT
CHECK,
NORMAL,
SNOOZE
20
APPROXIMATE
DURATION
OPERATING CONDITION or COMMENT
Clock stretch occurs at the beginning of all traffic as the device wakes up.
5 ms
Clock stretch occurs within the packet for flow control (after a start bit, ACK or first data bit).
100 µs
Normal Ra table Data Flash updates.
24 ms
Data Flash block writes.
72 ms
Restored Data Flash block write after loss of power.
116 ms
End of discharge Ra table Data Flash update.
144 ms
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9 Application and Implementation
Note
Information in the following applications sections is not part of the TI component specification, and
TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining
suitability of components for their purposes. Customers should validate and test their design
implementation to confirm system functionality.
9.1 Application Information
The BQ27520-G4 system-side Li-ion battery fuel gauge is a microcontroller peripheral that provides fuel gauging
for single-cell Li-ion battery packs. The device requires minimal system microcontroller firmware development.
The fuel resides on the main board of the system and manages an embedded battery (nonremovable) or an up
to 14500-mAhr capacity removable battery pack. To allow for optimal performance in the end application, special
considerations must be taken to ensure minimization of measurement error through proper printed circuit board
(PCB) board layout. Section 9.2.1 details these requirements.
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9.2 Typical Application
U1
BQ27520
Figure 9-1. BQ27520-G4 System-Side Li-Ion Battery Fuel Gauge Typical Application Schematic
22
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9.2.1 Design Requirements
Several key parameters must be updated to align with a given application's battery characteristics. For highest
accuracy gauging, it is important to follow-up this initial configuration with a learning cycle to optimize resistance
and maximum chemical capacity (Qmax) values prior to sealing and shipping systems to the field. Successful
and accurate configuration of the fuel gauge for a target application can be used as the basis for creating a
"golden" gas gauge (.fs) file that can be written to all gauges, assuming identical pack design and Li-ion cell
origin (chemistry, lot, and so on). Calibration data is included as part of this golden GG file to cut down on
system production time. If going this route, it is recommended to average the voltage and current measurement
calibration data from a large sample size and use these in the golden file. Table 9-1, Key Data Flash Parameters
for Configuration, shows the items that should be configured to achieve reliable protection and accurate gauging
with minimal initial configuration.
Table 9-1. Key Data Flash Parameters for Configuration
NAME
DEFAULT
UNIT
RECOMMENDED SETTING
Design Capacity
1000
mAh
Set based on the nominal pack capacity as interpreted from cell manufacturer's
datasheet. If multiple parallel cells are used, should be set to N × Cell Capacity.
Design Energy Scale
1
—
Set to 10 to convert all power values to cWh or to 1 for mWh. Design Energy is
divided by this value.
Reserve Capacity-mAh
0
mAh
Set to desired runtime remaining (in seconds / 3600) × typical applied load
between reporting 0% SOC and reaching Terminate Voltage, if needed.
Should be configured using TI-supplied Battery Management Studio software.
Default open-circuit voltage and resistance tables are also updated in
conjunction with this step. Do not attempt to manually update reported Device
Chemistry as this does not change all chemistry information! Always update
chemistry using the appropriate software tool (that is, BQSTUDIO).
Chem ID
0100
hex
Load Mode
1
—
Set to applicable load model, 0 for constant current or 1 for constant power.
Load Select
1
—
Set to load profile which most closely matches typical system load.
Qmax Cell 0
1000
mAh
Set to initial configured value for Design Capacity. The gauge will update this
parameter automatically after the optimization cycle and for every regular Qmax
update thereafter.
Cell0 V at Chg Term
4200
mV
Set to nominal cell voltage for a fully charged cell. The gauge will update this
parameter automatically each time full charge termination is detected.
Terminate Voltage
3200
mV
Set to empty point reference of battery based on system needs. Typical is
between 3000 and 3200 mV.
Ra Max Delta
44
mΩ
Set to 15% of Cell0 R_a 4 resistance after an optimization cycle is completed.
Charging Voltage
4200
mV
Set based on nominal charge voltage for the battery in normal conditions (25°C,
etc). Used as the reference point for offsetting by Taper Voltage for full charge
termination detection.
Taper Current
100
mA
Set to the nominal taper current of the charger + taper current tolerance to
ensure that the gauge will reliably detect charge termination.
Taper Voltage
100
mV
Sets the voltage window for qualifying full charge termination. Can be set tighter
to avoid or wider to ensure possibility of reporting 100% SOC in outer JEITA
temperature ranges that use derated charging voltage.
Dsg Current Threshold
60
mA
Sets threshold for gauge detecting battery discharge. Should be set lower than
minimal system load expected in the application and higher than Quit Current.
Chg Current Threshold
75
mA
Sets the threshold for detecting battery charge. Can be set higher or lower
depending on typical trickle charge current used. Also should be set higher than
Quit Current.
Quit Current
40
mA
Sets threshold for gauge detecting battery relaxation. Can be set higher or
lower depending on typical standby current and exhibited in the end system.
Avg I Last Run
–299
mA
Current profile used in capacity simulations at onset of discharge or at all times
if Load Select = 0. Should be set to nominal system load. Is automatically
updated by the gauge every cycle.
Avg P Last Run
–1131
mW
Power profile used in capacity simulations at onset of discharge or at all times
if Load Select = 0. Should be set to nominal system power. Is automatically
updated by the gauge every cycle.
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Table 9-1. Key Data Flash Parameters for Configuration (continued)
NAME
DEFAULT
UNIT
RECOMMENDED SETTING
Sleep Current
15
mA
Sets the threshold at which the fuel gauge enters SLEEP mode. Take
care in setting above typical standby currents else entry to SLEEP may be
unintentionally blocked.
CC Gain
10
mΩ
Calibrate this parameter using TI-supplied BQSTUDIO software and calibration
procedure in the TRM. Determines conversion of coulomb counter measured
sense resistor voltage to current.
CC Delta
10
mΩ
Calibrate this parameter using TI-supplied BQSTUDIO software and calibration
procedure in the TRM. Determines conversion of coulomb counter measured
sense resistor voltage to passed charge.
CC Offset
–1418
Counts
Calibrate this parameter using TI-supplied BQSTUDIO software and calibration
procedure in the TRM. Determines native offset of coulomb counter hardware
that should be removed from conversions.
Board Offset
0
Counts
Calibrate this parameter using TI-supplied BQSTUDIO software and calibration
procedure in the TRM. Determines native offset of the printed circuit board
parasitics that should be removed from conversions.
Pack V Offset
0
mV
Calibrate this parameter using TI-supplied BQSTUDIO software and calibration
procedure in the TRM. Determines voltage offset between cell tab and ADC
input node to incorporate back into or remove from measurement, depending
on polarity.
9.2.2 Detailed Design Procedure
9.2.2.1 BAT Voltage Sense Input
A ceramic capacitor at the input to the BAT pin is used to bypass AC voltage ripple to ground, greatly reducing
its influence on battery voltage measurements. It proves most effective in applications with load profiles that
exhibit high-frequency current pulses (that is, cell phones) but is recommended for use in all applications to
reduce noise on this sensitive high-impedance measurement node.
9.2.2.2 SRP and SRN Current Sense Inputs
The filter network at the input to the coulomb counter is intended to improve differential mode rejection of
voltage measured across the sense resistor. These components should be placed as close as possible to the
coulomb counter inputs and the routing of the differential traces length-matched to best minimize impedance
mismatch-induced measurement errors.
9.2.2.3 Sense Resistor Selection
Any variation encountered in the resistance present between the SRP and SRN pins of the fuel gauge will affect
the resulting differential voltage, and derived current, it senses. As such, it is recommended to select a sense
resistor with minimal tolerance and temperature coefficient of resistance (TCR) characteristics. The standard
recommendation based on best compromise between performance and price is a 1% tolerance, 100 ppm drift
sense resistor with a 1-W power rating.
9.2.2.4 TS Temperature Sense Input
Similar to the BAT pin, a ceramic decoupling capacitor for the TS pin is used to bypass AC voltage ripple
away from the high-impedance ADC input, minimizing measurement error. Another helpful advantage is that the
capacitor provides additional ESD protection since the TS input to system may be accessible in systems that use
removable battery packs. It should be placed as close as possible to the respective input pin for optimal filtering
performance.
9.2.2.5 Thermistor Selection
The fuel gauge temperature sensing circuitry is designed to work with a negative temperature coefficient-type
(NTC) thermistor with a characteristic 10-kΩ resistance at room temperature (25°C). The default curve-fitting
coefficients configured in the fuel gauge specifically assume a 103AT-2 type thermistor profile and so that is the
default recommendation for thermistor selection purposes. Moving to a separate thermistor resistance profile (for
example, JT-2 or others) requires an update to the default thermistor coefficients in data flash to ensure highest
accuracy temperature measurement performance.
24
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9.2.2.6 REGIN Power Supply Input Filtering
A ceramic capacitor is placed at the input to the fuel gauge internal LDO to increase power supply rejection
(PSR) and improve effective line regulation. It ensures that voltage ripple is rejected to ground instead of
coupling into the internal supply rails of the fuel gauge.
9.2.2.7 VCC LDO Output Filtering
A ceramic capacitor is also needed at the output of the internal LDO to provide a current reservoir for fuel gauge
load peaks during high peripheral utilization. It acts to stabilize the regulator output and reduce core voltage
ripple inside of the fuel gauge.
9.2.3 Application Curves
8.8
VREGIN = 2.7 V
VREGIN = 4.5 V
2.6
fOSC - High Frequency Oscillator (MHz)
VREG25 - Regulator Output Voltage (V)
2.65
2.55
2.5
2.45
2.4
2.35
-40
-20
0
20
40
Temperature (°C)
60
8.6
8.5
8.4
8.3
8.2
8.1
8
-40
80
33.5
4
Reported Temperature Error (qC)
5
33
32.5
32
31.5
31
30.5
-20
0
20
40
Temperature (qC)
0
20
40
Temperature (qC)
60
80
60
80
100
D002
Figure 9-3. High-Frequency Oscillator Frequency
vs. Temperature
34
30
-40
-20
D001
Figure 9-2. Regulator Output Voltage vs.
Temperature
fLOSC - Low Frequency Oscillator (kHz)
8.7
100
3
2
1
0
-1
-2
-3
-4
-5
-30
-20
D003
Figure 9-4. Low-Frequency Oscillator Frequency
vs. Temperature
-10
0
10
20
30
Temperature (qC)
40
50
60
D004
Figure 9-5. Reported Internal Temperature
Measurement vs. Temperature
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10 Power Supply Recommendations
10.1 Power Supply Decoupling
Both the REGIN input pin and the VCC output pin require low equivalent series resistance (ESR) ceramic
capacitors placed as closely as possible to the respective pins to optimize ripple rejection and provide a stable
and dependable power rail that is resilient to line transients. A 0.1-µF capacitor at the REGIN and a 1-µF
capacitor at VCC will suffice for satisfactory device performance.
11 Layout
11.1 Layout Guidelines
11.1.1 Sense Resistor Connections
Kelvin connections at the sense resistor are just as critical as those for the battery terminals themselves.
The differential traces should be connected at the inside of the sense resistor pads and not anywhere along
the high-current trace path to prevent false increases to measured current that could result when measuring
between the sum of the sense resistor and trace resistance between the tap points. In addition, the routing of
these leads from the sense resistor to the input filter network and finally into the SRP and SRN pins needs
to be as closely matched in length as possible else additional measurement offset could occur. It is further
recommended to add copper trace or pour-based "guard rings" around the perimeter of the filter network and
coulomb counter inputs to shield these sensitive pins from radiated EMI into the sense nodes. This prevents
differential voltage shifts that could be interpreted as real current change to the fuel gauge. All of the filter
components need to be placed as close as possible to the coulomb counter input pins.
11.1.2 Thermistor Connections
The thermistor sense input should include a ceramic bypass capacitor placed as close to the TS input pin as
possible. The capacitor helps to filter measurements of any stray transients as the voltage bias circuit pulses
periodically during temperature sensing windows.
11.1.3 High-Current and Low-Current Path Separation
For best possible noise performance, it is extremely important to separate the low-current and high-current loops
to different areas of the board layout. The fuel gauge and all support components should be situated on one side
of the boards and tap off of the high-current loop (for measurement purposes) at the sense resistor. Routing the
low-current ground around instead of under high-current traces will further help to improve noise rejection.
26
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11.2 Layout Example
Battery power
connection to
system
Use copper
pours for battery
power path to
minimize IR
losses
SCL
To system host
processor
SDA
BAT_LOW
BATTERY PACK
CONNECTOR
BAT_GD
C1
PACK+
Kelvin connect the
BAT sense line right
at positive terminal to
battery pack
C2
BI/TOUT
BAT
REGIN
C3
THERM
CE
VCC
VSS
VSS
SDA
BAT_GD
SRN
SCL
SOC_INT
SRP
TS
BAT_LOW
SOC_INT
PACK –
10 mΩ 1%
Via connects to Power Ground
Ground return to
system
Kelvin connect SRP
and SRN
connections right at
Rsense terminals
Figure 11-1. Layout Recommendation
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12 Device and Documentation Support
12.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
12.2 Documentation Support
12.2.1 Related Documentation
•
BQ27520-G4 Technical Reference Manual (SLUUA35)
12.3 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. Click on
Subscribe to updates to register and receive a weekly digest of any product information that has changed. For
change details, review the revision history included in any revised document.
12.4 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
12.5 Trademarks
Impedance Track™, NanoFree™, TI E2E™ are trademarks of Texas Instruments.
All trademarks are the property of their respective owners.
12.6 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric changes could cause the device not to meet its published
specifications.
12.7 Glossary
TI Glossary
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
28
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PACKAGE OPTION ADDENDUM
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19-Oct-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
BQ27520YZFR-G4
ACTIVE
DSBGA
YZF
15
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
BQ27520
Samples
BQ27520YZFT-G4
ACTIVE
DSBGA
YZF
15
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
BQ27520
Samples
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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