SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
t FEATURES
D Reports Accurate State-of-Charge in Li-Ion
D
D
D
D
D
D
D
D
and Li-Pol Cells, No System Processor
Calculations Needed
Communicates Directly With the Integrated
HDQ Engine in TI OMAPt Processors
Reports Cell Temperature and Voltage
High-Accuracy Coulometric Charge and
Discharge Current Integration with
Automatic Offset Cancellation
Requires No Offset Calibration
Programmable Input/Output Port
Internal Time-Base Eliminates External
Crystal Oscillator
Four Automatic Low-Power Operating Modes
− Active: < 100 µA
− Sleep: < 2.5 µA
− Ship: < 1.7 µA
− Hibernate: < 1.5 µA
Small 8-Pin TSSOP Package
APPLICATIONS
D PDAs
D Smart Phones
D MP3 Players
D Digital Cameras
D Internet Appliances
D Handheld Devices
DESCRIPTION
SIMPLIFIED APPLICATION
PACK+
+
Li-Ion
or
Li-Pol
bq26501
1 RBI
GPIO 8
2 VCC
SRP 7
3 VSS
SRN 6
4 HDQ
BAT 5
The bq26501, the first in the bqJUNIORt family
of advanced gas gauge device for handhald
applications, is a highly accurate standalone
single-cell Li-Ion and Li-Pol battery capacity
monitoring and reporting device targeted at space
limited portable applications. The device monitors
a voltage drop across a small current sense
resistor connected in series with the battery to
determine charge and discharge activity of the
battery. Compensations for battery temperature,
self-discharge, and rate of discharge are applied
to the charge counter to provide available capacity
across a wide range of operating conditions.
Battery capacity is automatically recalibrated, or
learned, in the course of a discharge cycle from full
to empty. Internal registers include available
capacity, cell temperature and voltage,
state-of-charge, and status and control registers.
The bq26501 can operate directly from single-cell
Li-Ion and Li-Pol batteries and communicates to
the system over a simple one-wire bi-directional
serial interface. The 5-kbits/s HDQ bus interface
reduces communication overhead in the external
microcontroller.
HDQ
Protection
Controller
PACK−
Battery Pack
UDG−03038
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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)('"/'%/ 3'%%'"(40 %$/+*(!$" -%$*,))!"5 /$,) "$( ",*,))'%!.4 !"*.+/,
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Copyright 2003−2004, Texas Instruments Incorporated
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1
SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range unless otherwise noted(1)
bq26501
Supply voltage range, VCC (all with respect to VSS)
−0.3 to 7.0
Input voltage range at SRP, SRN, RBI, and BAT (all with respect to VSS)
Input voltage
UNIT
−0.3 to VCC + 0.3 V
HDQ, GPIO (with respect to VSS)
−0.3 to 7.0
GPIO (with respect to VSS) during EEPROM programming only
−0.3 to 22.0
Output sink current at GPIO, HDQ
5
Operating free-air temperature range, TA
V
mA
−20 to 70
Storage temperature range, Tstg
65°C to 150°C
Junction temperature range, TJ
−40°C to 125°C
°C
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds
300
(1) Stresses beyond those listed under ”absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated under ”recommended operating conditions” is
not implied. Exposure to Absolute Maximum Rated conditions for extended periods may affect device reliability
RECOMMENDED OPERATING CONDITIONS
MIN
Supply voltage, VCC
NOM
2.6
MAX
UNIT
4.5
V
Operating free-air temperature, TJ
−20
70
°C
Input voltage range at SRP and SRN, (with respect to VSS)
−100
100
mV
ELECTRICAL CHARACTERISTICS
TJ = −20°C to 70°C, TJ = TA, 2.6 V ≤ VCC ≤ 4.5 V (unless otherwise noted)
TEST CONDITIONS
PARAMETER
MIN
TYP
MAX
UNIT
INPUT CURRENTS
ICC(ACT)
ICC(SLP)
Active current
60
90
Sleep current
1.2
2.5
ICC(SHP)
ICC(POR)
Ship current
0.9
1.7
0.6
1.5
V(POR)
VCC > VCC(min)
Hibernate current
0 V < VCC < V(POR)
RBI current
RBI pin only,
VCC < V(POR)
POR threshold
20
2.05
POR threshold hysteresis
2.55
100
Input impedance on BAT pin
10
Input impedance on SRP, SRN pins
10
µA
A
nA
V
mV
MΩ
VOLTAGE MEASUREMENT
Measurement range
VCC = VI(BAT)
2.6
Reported voltage resolution
4.5
V
1
Reported accuracy
−20
Voltage update time
20
2
mV
s
TEMPERATURE MEASUREMENT
Reported temperature resolution
0.25
Reported temperature accuracy
−3
Temperature update time
2
3
2
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°K
s
SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
ELECTRICAL CHARACTERISTICS(continued)
TJ = −20°C to 70°C, TJ = TA, 2.6 V ≤ VCC ≤ 4.5 V (unless otherwise noted)
TEST CONDITIONS
PARAMETER
MIN
TYP
MAX
UNIT
CAPACITY MEASUREMENT
Voltage-to-frequency converter offset
15
Voltage-to-frequency converter gain
Voltage-to-frequency converter gain
variabilty(3)
0°C ≤ TA ≤ 50°C
Voltage-to-frequency input
(VSRP − VSRN)
µV
µVH
3
2%
−100
100
mV
100
ms
EEPROM PROGRAMMING (VCC ≥ 3.0 V, 20°C ≤ TA ≤ 35°C)(1)
tRISE
tPROG
Programming voltage rise time
tFALL
VPROG
Programming voltage fall time
Programming voltage high time
Programming voltage
1
VPROG = 21 V
20
1
Applied to GPIO pin
20
IPROG
EEPROM programming current
Current into GPIO pin
IO PORT (GPIO) AND SERIAL INTERFACE (HDQ)
VIH
VIL
High-level input voltage
VOL
VOL
GPIO low-level output voltage
V
3
mA
1.9
Low-level input voltage
HDQ low-level output voltage
22
0.7
IOL = 0.3 mA
IOL = 2 mA
0.4
V
0.4
IHDQPD HDQ internal pull-down current
STANDARD SERIAL COMMUNICATION (HDQ) TIMING(2)
4.5
t(B)
t(BR)
Break timing
t(CYCH)
t(HW1)
Host bit window timing
190
Host sends 1 time
0.5
50
t(HW0)
t(RSPS)
Host sends 0 time
86
145
bq26501 to host response time
190
320
t(CYCD)
t(DW1)
bq26501 bit window timing
190
260
µA
190
Break recovery time
40
bq26501 sends 1 time
32
t(DW0)
bq26501 sends 0 time
80
(1) Maximum number of programming cycles on the EEPROM is 10 and data retention time is 10 years at TA=85°C
(2) See Figure 1.
(3) Not a production tested parameter.
µs
50
145
The following timing diagrams describe break and break recovery timing (a), host transmitted bit timing (b),
bq26501 transmitted bit timing (c), and bq26501 to host response timing (d).
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3
SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
(a)
t(BR)
t(B)
(c)
(b)
t(HW1)
t(DW1)
t(HW0)
t(CYCH)
t(DW0)
t(CYCD)
(d)
1−bit
7−Bit Address
Break
8−Bit Data
R/W
UDG−03039
t(RSPS)
Figure 1. HDQ Bit Timing Diagrams
PIN ASSIGNMENTS
TERMINAL
NAME
NO.
I/O
DESCRIPTION
BAT
5
I
GPIO
8
I/O
Battery voltage sense input
General-purpose input/output port
HDQ
4
I/O
Single-wire HDQ serial interface
RBI
1
I
Register back-up input
SRN
6
I
Current sense input (negative)
SRP
7
I
Current sense input (positive)
VCC
2
I
VSS
3
I
VCC supply input
Ground input
PW PACKAGE
(TOP VIEW)
RBI
VCC
VSS
HDQ
1
2
3
4
8
7
6
5
GPIO
SRP
SRN
BAT
AVAILABLE OPTIONS
TA
PACKAGED
DEVICES(1)
MARKINGS
−20°C to 70°C
bq26501PW
26501
(1) The PW package is available taped and reeled. Add R suffix to device type (e.g. bq26501PWR) to
order quantities of 2,000 devices per reel.
4
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
PACK+
R5
1 MΩ
1 RBI
C4
0.1 µF
bq26501
2 VCC
ESD Protection
HDQ
+
GPIO 8
R1
100 kΩ
SRP 7
C3
0.1 µF
R4
R3
100 Ω
100 Ω
Autocalibration and
Autocompensating
VFCD1
5.6 V
Li-Ion
or
Li-Pol
C1
0.1 µF
3 VSS
SRN 6
4 HDQ
BAT 5
RS
0.02Ω
R2
100 kΩ
Protection
Controller
C2
0.1 µF
PACK−
Battery Pack
UDG−03041
Figure 2. Typical Application Circuit
VCC 2
Bandgap
Reference and
Bias
Temperature
Compensated
Precision Oscillator
Clock
Generator
4 HDQ
EEPROM
System I/O
and Control
8 GPIO
SCPU
SRP 7
SRN 6
Autocalibrating and
Autocompensating
VFC
Temperature
Sensor
RAM
1 RBI
3 VSS
ADC
BAT 5
UDG−03040
Figure 3. Functional Block Diagram
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
FUNCTIONAL DESCRIPTION
The bq26501 determines battery capacity by monitoring the amount of charge input to or removed from a Li-Ion
or Li-Pol battery. The bq26501 measures discharge and charge currents, monitors the battery for low voltage
thresholds, and compensates for temperature and self-discharge rate. Current is measured across a small
value series resistor between the negative terminal of the battery and the pack ground (see RS in Figure 2).
Available capacity is reported with a resolution of 0.003/RS(mAh). Time-to-empty (TTE) reporting in minutes
at host-provided at-rate currents allow the requirements for host based calculations to be greatly reduced or
eliminated; reading a single register pair provides useful and meaningful information to the application’s end
user.
Figure 2 shows a typical application circuit. Differential sense of the voltage across the current sense resistor,
RS, improves device performance, leading to an improvement in reported time-to-empty accuracy. In the typical
application, the GPIO pin can be used as a general-purpose programmable I/O port. An internal pull-down on
the HDQ line ensures that the device detects a logic “0” on the HDQ line and automatically enters the low power
sleep mode when the system power is switched off or the pack is removed. A 100-kΩ pull-up to VCC can be
added to the HDQ line to disable this feature. The bq26501 can operate directly from a single Li-Ion or Li-Pol
cell.
Measurements
As shown in the Figure 3, the bq26501 uses a fully differential, dynamically balanced voltage-to-frequency
converter (VFC) for charge and discharge counting and an analog-to-digital converter (ADC) for battery voltage
and temperature measurement. Both VFC and ADC are automatically compensated for offset. No user
calibration or compensation is required.
Charge and Discharge Counting
The bq26501 uses a voltage-to-frequency converter (VFC) to perform a continuous integration of the voltage
waveform across a small value sense resistor in the negative lead of the battery, as shown in Figure 2. The
integration of the voltage across the sense resistor is the charge added or removed from the battery. Since the
VFC directly integrates the waveform, the shape of the current waveform through the sense resistor has no
effect on the measurement accuracy. The low-pass filter that feeds the sense resistor voltage to the bq26501
SRP and SRN inputs serves to filter out system noise and does not affect the measurement accuracy, since
the low-pass filter does not change the integrated value of the waveform.
Offset Calibration
The offset voltage of the VFC measurement must be very low to be able to measure small signal levels
accurately. The bq26501 provides an auto-compensation feature to cancel the internal voltage offset error
across SRP and SRN for maximum charge measurement accuracy.
NOTE:NO CALIBRATION IS REQUIRED. See the Layout Considerations section for details on
minimizing PCB induced offset across the SRP and SRN pins.
6
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Digital Magnitude Filter
The digital magnitude filter (DMF) threshold can be set in EEPROM to indicate a threshold below which any
charge or discharge accumulation is ignored. This allows setting a threshold above the maximum VFC offset
expected from the device and PCB combination. This ensures that when no charge or discharge current is
present, the measured capacity change by the bq26501 is zero. Note that even a small PCB offset can add up
to a large error over a long period. In addition to setting the threshold above the largest offset expected, the DMF
should be set below the minimum signal level to be measured. Since the measured signal can only be measured
as accurately as the VFC offset induced from the PCB, the sense resistor value should be large enough to allow
the minimum current level to provide a signal level substantially higher than the maximum offset voltage.
Conversely, the sense resistor must be small enough to meet the system requirement for insertion loss as well
as keep the maximum voltage across the sense resistor below the ±100-mV maximum that the VFC can
accurately measure.
The DMF threshold is programmed in EEPROM in increments of 6 µV. Programming a zero in the DMF value
disables the DMF function and no VFC counts are ignored.
Voltage
The bq26501 monitors the battery voltage through the BAT pin and reports an offset corrected value through
the internal registers. The bq26501 also monitors the voltage for the end-of-discharge voltage (EDV) thresholds.
The EDV threshold levels are used to determine when the battery has reached an empty state.
Temperature
The bq26501 uses an integrated temperature sensor to monitor the pack temperature. The temperature
measurements reported through the internal registers are used to adjust charge and discharge rate
compensations, and self-discharge capacity loss estimation.
RBI Input
The register back-up input pin, RBI, is used with an external capacitor to provide backup potential to the internal
registers when VCC drops below the power-on-reset voltage V(POR). VCC is output on RBI when VCC is above
V(POR), charging the capacitor. Figure 2 shows an optional 1-MΩ resistor from RBI pin to VCC. This allows the
device to maintain RAM register data when the battery voltage is below V(POR) and above 1.3 V. The bq26501
checks for RAM corruption by storing redundant copies of the high bytes of NAC and LMD. After a reset, the
bq26501 compares the redundant NAC and LMD values and verifies the accuracy of 2 checkbyte values. If the
redundant copies match and the checkbytes are correct, NAC and LMD are retained and the CI bit in FLAGS
is left unchanged. If these checks are not correct, NAC is cleared, LMD is initialized from EEPROM, and the
CI bit in FLAGS is set to “1”. All other RAM is initialized on all resets.
Layout Considerations
The auto-compensating VFC approach effectively cancels the internal offset voltage within the bq26501, but
any external offset caused by PCB layout is not cancelled. This makes it critical to pay special attention to the
PCB layout. To obtain optimal performance, the decoupling capacitor from VCC to VSS and the filter capacitors
from SRP and SRN to VSS should be placed as closely as possible to the bq26501, with short trace runs to both
signal and VSS pins. All low-current VSS connections should be kept separate from the high-current discharge
path from the battery and should tie into the high current trace at a point directly next to the sense resistor. This
should be a trace connection to the edge or inside of the sense resistor connection, so that no part of the VSS
interconnections carry any load current and no portion of the high-current PCB trace is included in the effective
sense resistor (i.e. Kelvin connection).
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7
SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Gas Gauge Operation
Figure 4 illustrates an operational overview of the gas gauge function.
INPUTS
Discharge Current
Charge Current
Self-Discharge Timer
Temperature
Compensation
+
COMPUTATIONS
_
_
_
Nominal Available
Charge (NAC)
Last Measured
Discharge (LMD)
Rate and
Temperature
Compensation
Qualified
Transfer
+
+
Learning Count
Register (LCR)
Temperature, Voltage,
Average Current,
Other Data
OUTPUTS
Compensated
Available Charge
HDQ Interface
UDG−03042
Figure 4. Operational Overview
The bq26501 measures the capacity of the battery during actual use conditions and updates the last measured
discharge (LMD) register with the latest measured value. The bq26501 retains the learned LMD value unless
a full reset occurs. By measuring the capacity that the battery delivers as it is discharged from full to the EDV1
threshold without any disqualifying events, the bq26501 learns the capacity of the battery. During normal use
conditions, the bq26501 should learn a new capacity only after a full discharge. Learning cycles are disqualified
by several abnormal conditions (see list at end of section). In the event that a learning cycle occurs with a
significant reduction in learned capacity, the new LMD value is restricted to a maximum LMD reduction during
any single learning discharge of LMD/8. The capacity inaccurate (CI) bit in FLAGS is cleared after the first
learning cycle. This bit remains cleared unless a full reset occurs.
The battery-full condition is defined as nominal available capacity (NAC) = LMD. The valid discharge flag (VDQ)
in the FLAGS register is set when this condition occurs and remains set until the learning discharge cycle
completes or an event occurs that disqualifies the learning cycle.
The learning discharge cycle completes when the battery is discharged to the condition where VOLT ≤ EDV1
threshold. The EDV1 threshold should be set at a voltage that guarantees at least 6.25% of battery capacity
below that threshold. The EDVF threshold should be set at a voltage that the system sees as the zero capacity
battery voltage.
The bq26501 does not learn the capacity between EDV1 and EDVF thresholds, but assumes that the capacity
is 6.25% of LMD, so care should be taken to set EDV1 based on the characteristics of the battery. The measured
LMD value is determined by measuring the capacity delivered from the battery from NAC=LMD until
VOLT ≤ EDV1, plus LMD/16 to account for the 6.25% capacity remaining below the EDV1 threshold.
8
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
VDQ is cleared and a capacity learning cycle is disqualified by any of the following conditions:
1. Cold temperature: Temperature less than or equal to the TOFF value programmed in the TCOMP register
when the EDV1 threshold voltage is reached.
2. Light load: Average current is less than or equal to 2 times the initial standby load (ISLC) when the EDV1
threshold voltage is reached.
3. Fast voltage drop: VOLT ≤ (EDV1 − 256 mV) when EDV1 is set.
4. Excessive charging: Cumulative charge added is greater than 255 mAh during a learning discharge cycle
(alternating discharge-charge-discharge before EDV1 is set).
5. Reset: VDQ is cleared on reset.
6. Excessive self-discharge: NAC reduction from self−discharge estimate exceeds 12.48%.
7. Self-discharge at termination of learning cycle. If self-discharge estimate reduces NAC until NAC ≤ LMD/16.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Register Interface for bq26501
The bq26501 stores all calculated information in RAM, which is backed up by the voltage present on the RBI
pin. EEPROM registers store permanent user data. The memory map for bq26501 is shown in Table 1.
Table 1. bq26501 Memory Map
HDQ ADDRESS
NAME
FUNCTION (256 x High Byte + Low Byte)
EEPROM Registers
0x7F
TCOMP
Temperature compensation constants, OR, ID#1
0x7E
DCOMP
Discharge rate compensation constants, OR, ID#2
0x7D
ID3
ID#3
0x7C
PKCFG
Pack configuration values
0x7B
TAPER
Charge termination taper current
0x7A
DMFSD
Digital magnitude filter and self-discharge rate constants
0x79
ISLC
Initial standby load current
0x78
SEDV1
Scaled EDV1 threshold
0x77
SEDVF
Scaled EDVF threshold
0x76
ILMD
Initial last measured discharge high byte
RAM Registers
0x6F − 0x75
−
RESERVED
0x6E
EE_EN
EEPROM program enable
0x14 − 0x6D
−
RESERVED
0x13 − 0x12
LMD
Last measured discharge high − low byte
0x11 − 0x10
CACT
Temperature compensated CACD high – low byte
0x0F − 0x0E
CACD
Discharge compensated NAC high − low byte
0x0D − 0x0C
NAC
Nominal available capacity high − low byte
0x0B
RSOC
Relative state of charge
0x0A
FLAGS
Status flags
0x09 − 0x08
VOLT
Reported voltage high − low byte
0x07 − 0x06
TEMP
Reported temperature high − low byte
0x05 − 0x04
ARTTE
At rate time-to-empty high − low byte
0x03 − 0x02
AR
At rate high − low byte
0x01
MODE
Device mode register
0x00
CTRL
Device control register
(1) Divide by RS(mΩ) to convert µV to mA or µVh to mAh.
10
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LSB VALUE
192 µV(1)
6 µV(1)
768 µVh(1)
3 µVh(1)
3 µVh(1)
3 µVh(1)
3 µVh(1)
1%
1 mV
0.25°K
1 minute
3 µV(1)
SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
REGISTER DESCRIPTIONS
Device Control Register (CTRL) − Address 0x00
The device control register is used by the host system to request special operations by the bq26501. The highest
priority command set in the MODE register performs when the host writes data 0xA9 to the control register. The
CTRL register is cleared when the action is complete. Note that writing any value other than 0xA9 has no effect.
Mode Register (MODE) − Address 0x01
NAME
MODE
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
GPIEN
GPSTAT
WRTNAC
DONE
PRST
POR
FRST
SHIP
DESCRIPTION
GPIEN
GPIEN sets the state of the GPIO pin. A “1” configures the GPIO pin as input, while a “0” configures the GPIO pin
as an open-drain output. This bit is initialized to the value of bit 7 of the PKCFG register in the EEPROM
GPSTAT
GPSTAT sets the state of the open drain output of the GPIO pin (GPIEN = 0). A “1” turns off the open drain output while a “0” turns the output on. This bit is set to 1 on POR. When the GPIO pin is an input (GPIEN=1), this bit
returns the logic state of the GPIO pin.
WRTNAC
WRTNAC is used to transfer data from the AR registers to the NAC registers. Other registers are updated as
appropriate. This command is useful during the pack manufacture and test to initialize the gauge to match the
estimated battery capacity. This bit is cleared on all resets.
DONE
DONE is used to write NAC to LMD. Useful if the host uses a charge termination method that does not allow the
monitor to detect the taper current. The host system could use this command when the charging is complete to
force update of internal registers to a full battery condition. This bit is cleared on all resets.
PRST
Partial reset. This command requests a full reset, except that the NAC, LMD, and the CI bit in FLAGS should not
be restored to their initial values. This command is intended for manufacturing use. This bit is cleared on all resets.
POR
The POR status bit is set to “1” by the bq26501 following a power-on-reset (POR). This is a flag to the host that
VCC was less than V(POR) and caused a reset. The bit is cleared to “0” by the bq26501 when a full charge condition is reached or it may be cleared by the host. The host may set this bit, but it has no effect on the bq26501
operation.
FRST
Full reset. This command bit requests a full reset. A full reset re-initializes all RAM registers, including the NAC,
LMD, and FLAGS registers. This command is intended for manufacturing use. This bit is cleared on all resets.
SHIP
This command bit requests that the device should be put in ship mode. See the Power Modes section for a description of the ship mode. This command is intended for manufacturing use. This bit is cleared on all resets.
WRTNAC, DONE, PRST, FRST, and SHIP commands are prioritized in bit order. This means that WRTNAC
(bit 5) has higher priority than DONE (bit 4); PRST (bit 3) has higher priority than FRST (bit 1), and so on. Only
the highest priority mode set is enabled each time the CTRL register is written with data 0xA9, and the firmware
clears all other mode bits and the CTRL register when that action is complete. The host system must make two
writes for every mode to be enabled, one write to the mode register to set the appropriate bit and a second write
to the CTRL register to signal that the mode should be enabled.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
At Rate Registers (ARH/ARL) − Address 0x02/0x03
For the bq26501, the host writes the current value to this register for predictive calculation of time-to-empty. The
device uses this value to predict the time-to-empty at any desired current. The current value written into this
register pair is always assumed to be a discharge current. The value written to AR should be the predicted
voltage across the sense resistor expressed in units of 3 µV per count.
This register is also used during pack manufacturing to input a nominal available charge (NAC) value to set the
NAC registers to the approximate initial pack capacity value.
At Rate Time to Empty Registers (ARTTEL/ARTTEH) − Address 0x04/0x05
Predicted time-to-empty, in minutes, at user entered discharge rate. The discharge current used in the
calculation is entered by the host system in the at-rate (AR) registers. The at-rate capacitance (ARCAP) value
used may be larger or smaller than CACT. It is computed using the same formulas as CACT, except the
discharge compensation is computed using AR, instead of average discharge current (AI), for the discharge
rate. The equation used to predict at rate time-to-empty is:
ARTTE + 60
ARCAP
AR
(1)
The host system has read only access to this register pair.
Reported Temperature Registers (TEMPL/TEMPH) − Address 0x06/0x07
The TEMPH and the TEMPL registers contain the reported die temperature. The temperature is expressed in
units of 0.25°K per count and updated every 2 seconds. The equation to calculate reported pack temperature
is:
T PACK + 0.25
(256
TEMPH ) TEMPL)
(2)
The host system has read-only access to this register pair.
Reported Battery Voltage Registers (VOLTL/VOLTH) − Address 0x08/0x09
The VOLTH and the VOLTL low-byte registers contain the reported battery voltage measured on the BAT pin.
Voltage is expressed in mV and is updated every two seconds. Reported voltage cannot exceed 5000 mV. The
host system has read only access to this register pair.
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APPLICATION INFORMATION
Status Flag Register (FLAGS) − Address 0x0A
NAME
POR STATUS
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
CHGS
NOACT
IMIN
CI
RSVD
VDQ
EDV1
EDVF
0
0
0
1
0
0
0
0
MODE
DESCRIPTION
REGISTER
CHGS
Charge-state flag. A “1” in the CHGS indicates a charge current (VSRP > VSRN). A “0” indicates a lack of charge
activity. This bit should be read when the host system reads the average current register pair to determine the
sign of the average current magnitude. This bit is cleared to “0” on all resets.
NOACT
No-activity flag. A “1” indicates that the voltage across RS is less than the digital magnitude filter. See the Digital
Magnitude Filter section for more information. This bit is cleared to ”0” on all resets.
IMIN
Li-ion taper current detection flag. A “1” indicates that the charge current has tapered to less than the taper value
set in EEPROM and that the battery voltage is greater than or equal to the value selected by the QV0 and QV1
bits in the PKCFG register (see EEPROM Data Registers description for more details). This bit is cleared to “0” on
all resets.
CI
Capacity Inaccurate flag. A ”1” indicates that the firmware has not been through a valid learning cycle and is basing all calculations on design values programmed into EEPROM. This bit will be set on a full reset and will only be
cleared on a LMD update following a learning cycle.
RSVD
Reserved bit.
VDQ
Valid-discharge flag. A “1” indicates that the bq26501 has met all necessary requirements for a capacity learning
discharge cycle. This bit clears to “0” on a LMD update or condition that disqualifies a learning cycle. This bit is
cleared to “0” on all resets.
EDV1
End-of-discharge-voltage-1 flag. A “1” indicates that voltage on the BAT pin is less than or equal to the EDV1
voltage programmed in EEPROM and the battery has less than or equal to 6.25% of LMD capacity remaining.
LMD updates immediately if the VDQ bit is set when this bit transitions from 0 to 1. This bit is cleared to ”0” on all
resets or when charging.
EDVF
End-of-discharge-voltage-final flag. A “1” indicates that the battery has discharged fully based on design capacity
programmed in EEPROM. Used to define the empty capacity threshold. This bit is cleared to ”0” on all resets or
when charging.
The host system has read-only access to this register.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Relative State of Charge (RSOC) – Address 0x0B
RSOC reports the battery charge as a percentage of the last measured discharge value (LMD). This value
should be used if the end equipment reports percentage rather than time-to-empty. The equation is:
RSOC(%) + 100
NAC
LMD
(3)
The host system has read-only access to this register.
Nominal Available Capacity Registers (NACL/NACH) – Address 0x0C/0x0D
Uncompensated available capacity in the battery. NAC is reported in counts of 3 µVh. This register pair
increments during charge (VSRP > VSRN) and decrements during discharge (VSRP < VSRN). The NAC registers
are cleared when the BAT voltage is less than or equal to EDVF while discharging. The NAC registers are
cleared during reset or power-on-reset (POR), if RAM corruption is detected. The register value is retained after
a reset if RAM corruption is not detected. The host system has read only access to this register pair.
Discharge Rate Compensated Available Capacity Registers (CACDL/CACDH) – Address 0x0E/0x0F
Available capacity in the battery, compensated for discharge rate. CACD is reported in counts of 3 µVh. This
register pair follows NAC during charge and discharge by an amount computed from the measured discharge
rate and the discharge rate compensation value programmed into EEPROM. CACD is not allowed to increase
while discharging, so that if the discharge rate decreases, the available capacity does not increase. CACD
equals NAC if the CHGS bit is “1”. If CHGS is “0”, CACD is the smaller of the previous and new computed
values. The host system has read-only access to this register pair.
Temperature Compensated CACD Registers (CACTL/CACTH) – Address 0x10/0x11
Available capacity in the battery, compensated for discharge rate and temperature. CACT is reported in counts
of 3 µVh. This register pair follows CACD during both charge and discharge unless the temperature is less than
the threshold programmed into EEPROM. Once the temperature falls below the programmed threshold, the
CACT value is reduced from CACD by an amount computed from ILMD and the temperature compensation
constants programmed into EEPROM. The host system has read only access to this register pair.
Last Measured Discharge Registers (LMDL/LMDH) – Address 0x12/0x13
Last measured discharge, used as a measured full reference, is based on the measured discharge capacity
of the battery from full to empty. LMD is reported in counts of 3 µVh.The firmware updates LMD on a valid
capacity learning cycle, which is defined as the battery reaching the EDV1 level while the VDQ bit is set. Used
with NAC register values to calculate relative state of charge (RSOC). The host system has read only access
to this register pair.
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APPLICATION INFORMATION
Reserved Registers
The addresses 0x14 – 0x6D and addresses 0x6F – 0x75 are reserved and cannot be written by the host.
EEPROM Enable Register (EE_EN) – Address 0x6E
Register used to enable host writes to EEPROM data locations (addresses 0x76 – 0x7F). Host must write data
0xDD to this register to enable EEPROM programming. See the Programming the EEPROM section for further
information on programming the EEPROM bytes.
EEPROM Data Registers (EE_DATA) – Address 0x76 – 0x7F
The EEPROM data registers contain information vital to the performance of the device. These registers are to
be programmed during pack manufacturing to allow flexibility in the design values of the battery to be monitored.
The EEPROM data registers are listed in Table 2. Detailed descriptions of what should be programmed follows.
See Programming the EEPROM for detailed information on writing the values to EEPROM.
Table 2. bq26501 EEPROM Memory Map
ADDRESS
NAME
0x7F
TCOMP
Temperature compensation constants, OR, ID#1
FUNCTION
0x7E
DCOMP
Discharge rate compensation constants, OR, ID#2
0x7D
ID3
0x7C
PKCFG
ID#3
Pack configuration values
0x7B
TAPER
Charge termination taper current
0x7A
DMFSD
Digital magnitude filter and self-discharge rate constants
0x79
ISLC
Initial standby load current
0x78
SEDV1
Scaled EDV1 threshold
0x77
SEDVF
Scaled EDVF threshold
0x76
ILMD
Initial last measured discharge high byte
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Initial Last Measured Discharge High Byte (ILMD) – Address 0x76
This register contains the scaled design capacity of the battery to be monitored. The equation to calculate the
initial LMD is:
ILMD +
Design Capacity (mAh) R S(mW)
(256 3 mVh)
(4)
where RS is the value of the sense resistor used in the system. This value is used as the high byte for the initial
LMD values. The initial low byte value is “0”.
Scaled EDVF Threshold (SEDVF) – Address 0x77
This register contains the scaled value of the threshold for zero battery capacity. To calculate the value to
program, use the following equation:
SEDVF +
Design EDVF (mV)
* 256
8
(5)
Scaled EDV1 Threshold (SEDV1) – Address 0x78
This register contains the scaled value of the voltage when the battery has 6.25% remaining capacity. When
the battery reaches this threshold during a valid discharge, the device learns the full battery capacity, including
the remaining 6.25%. To calculate the value to program, use the following equation:
SEDV1 +
Design EDV1 (mV)
* 256
8
(6)
Initial Standby Load Current (ISLC) – Address 0x79
This register contains the scaled end equipment design standby current. A capacity learning cycle is disqualified
if average current is less than or equal to two times the initial standby load when the EDV1 threshold voltage
is reached. The equation for programming this value is:
ISLC +
Design Standby Current (mA)
6 (mV)
R S (mW)
(7)
where RS is the value of the sense resistor used in the system.
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APPLICATION INFORMATION
Digital Magnitude Filter and Self-Discharge Values (DMFSD) – Address 0x7A
NAME
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DMF[3]
DMF[2]
DMF[1]
DMF[0]
SD[3]
SD[2]
SD[1]
SD[0]
MODE
DESCRIPTION
REGISTER
DMF[3]
Sets the digital magnitude filter (DMF) threshold. See Digital Magnitude Filter section for more information on the
function of the DMF. The value to be programmed is:
DMF[2]
DMF[1]
DMF[0]
DMF[3 : 0] +
Design Threshold
, mV
6
Sets the self-discharge rate %/day value at 25°C. NAC is reduced with an estimated self-discharge correction to
adjust for the expected self-discharge of the battery. This estimation is only performed when the battery is not
being charged. The rate programmed in EEPROM for DMFSD determines the self-discharge when 20°C
≤ TEMP < 30°C. The self-discharge estimation is doubled for each 10°C decade hotter than the 20°C−30°C
decade, up to a maximum of 16 times the programmed rate for TEMP ≥ 60°C and is halved for each 10°C
decade colder than the 20°C−30°C decade, down to a minimum of one-quarter the programmed rate for TEMP <
0°C. The self-discharge estimation is performed by reducing NAC by NAC/512 at a time interval that achieves
the desired estimation. If DMFSD is programmed with 12 decimal, the self-discharge rate is 0.195% per day in
the 20°C−30°C decade. This is accomplished by reducing NAC by NAC/512 (100/512 = 0.195%) a single time
every 24 hours. If temperature rises by 10°C, the 0.195% NAC reduction is made every 12 hours. The value to
be programmed is:
SD[3]
SD[2]
SD[1]
SD[3 : 0] +
SD[0]
2.34
, %/day
Design SD
Taper Current (TAPER) − Address 0x7B
This register contains the scaled end equipment design charge taper current. This value, in addition to battery
voltage, is used to determine when the battery has reached a full charge state. The equation for programming
this value is:
TAPER +
I TAPER (mA) R S (mW)
192 (mV)
(8)
where RS is the value of the sense resistor used in the system.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Pack Configuration (PKCFG) − Address 0x7C
NAME
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
GPIEN
QV1
QV0
RSVD
RSVD
RSVD
DCFIX
TCFIX
PKCFG
DESCRIPTION
REGISTER
GPIEN
Allows the pack manufacturer to set the state of the GPIO pin on initial power up. If the bit is “0”, the GPIEN bit is
cleared on reset and the GPIO pin acts as a high impedance output. If the bit is “1”, the GPIEN bit is set on reset
and the GPIO pin acts as an input. The state of the GPIO pin can then be read through the GPSTAT bit in the
MODE register.
QV1
QV2
These bits set the end voltage for charge termination. The terminating voltage is set as shown in Table 3.
RSVD
No function.
DCFIX
Fixed discharge compensation. Normal discharge rate compensation (DCOMP register) is used if this bit is set to
“0”. If this bit is set to “1”, the device assumes a fixed value of 0x42 for DCOMP, giving a discharge rate
compensation gain of 6.25% with a compensation threshold of C/4. Setting the bit to “1” frees the EEPROM
location of 0x7E for use as a programmable identification byte.
TCFIX
Fixed temperature compensation. Normal temperature compensation (TCOMP register) is used if this bit is set to
“0”. If this bit is set to “1”, the device assumes a fixed value of 0x7C for TCOMP, giving a temperature
compensation gain of 0.68% of Design Capacity/°C with an offset of 12°C. Setting this bit to “1” frees the
EEPROM location of 0x7F for use as a programmable identification byte.
Table 3. Charge Termination Voltage Settings
18
QV1
QV2
VOLTAGE (mV)
0
0
3968
0
1
4016
1
0
4064
1
1
4112
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Identification Byte #3 (ID3) − Address 0x7D
This register may be programmed to any desired value.The contents do not affect the operation of the bq26501.
Discharge Rate Compensation Constants (DCOMP) or ID2 − Address 0x7E
This register is used to set the compensation coefficients for discharge rate. These coefficients are applied to
the nominal available charge (NAC) to more accurately predict capacity at high discharge rates.
NAME
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DCGN[5]
DCGN[4]
DCGN[3]
DCGN[2]
DCGN[1]
DCGN[0]
DCOFF[1]
DCOFF[0]
MODE
DESCRIPTION
REGISTER
DCGN[5]
DCGN[4]
DCGN[3]
DCGN[2]
DCGN[1]
Discharge rate compensation gain. Used to set the slope of the discharge capacity compensation as a
percentage of discharge current. The gain factor adjustment is in increments of 0.39% of discharge current in
excess of the DCOFF value. The equation for programming the value is:
DCGN[5:0] = 2.56 × design discharge compensation gain %
DCGN[0]
DCOFF[1]
DCOFF[0]
These bits set the discharge threshold of compensating the nominal available charge for discharge rate. The
threshold is set as shown in Table 4.
Table 4. Discharge Rate Compensation Thresholds
DCOFF
THRESHOLD
DCOFF[1]
DCOFF[0]
0
0
0
0
1
LMD/2
1
0
LMD/4
1
1
LMD/8
Discharge compensation, DCMP, is computed from these coefficients as follows:
DCMP +
DCGN
(AI * DCOFF)
256
(9)
where DCMP is restricted to ≥ 0. AI is the average discharge current. The CACD register then takes on the value:
CACD + NAC * (DCMP * DCMPADJ), if DCMP u DCMPADJ or
(10)
CACD + NAC, if DCMP v DCMPADJ
(11)
where DCMPADJ is the value of DCMP at a previous EDV1 detection. This allows the compensation for CACD
to adapt as the LMD value is learned.
If PKCFG[1]=1, the device assumes a fixed value of 0x42 for DCOMP, giving a discharge rate compensation
gain of 6.25% with a compensation threshold of C/4. This frees the EEPROM location of 0x7E for a user-defined
identification byte, ID2.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Temperature Compensation Constants (TCOMP) or ID1 – Address 0x7F
This register is used to set the compensation coefficients for temperature. These coefficients are applied to the
discharge rate compensated available charge (CACD) to more accurately predict capacity available at cold
temperature.
NAME
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TCGN[3]
TCGN[2]
TCGN[1]
TCGN[0]
TOFF[3]
TOFF[2]
TOFF[1]
TOFF[0]
MODE
DESCRIPTION
REGISTER
TCGN[3]
TCGN[2]
TCGN[1]
TCGN[0]
TOFF[3]
TOFF[2]
TOFF[1]
TOFF[0]
Temperature compensation gain. Used to set the slope of the compensation as a percentage of design capacity
(DC) decrease per °C.
C. The equation for programming the value is:
TCGN[3:0] = 10.24 × design temp compensation gain % DC/°C
Temperature compensation offset. Used to set the offset of the compensation. The temperature threshold is also
used as the cold temperature disqualification for learning cycle even if TCGN=0. The equation for programming
the value is:
TOFF[3:0] = design temp compensation offset (°K) − 273
Temperature compensation, TCMP, is computed from these coefficients as follows:
TCMP + TCGN
ILMD
(273 ) TOFF * T)
4
(12)
where T is the temperature in °K and T < 273 + TOFF. TCMP = 0 if T ≥ 273 + TOFF. CACT is then computed
as follows:
CACT + CACD * (TCMP * TCMPADJ)
(13)
where TEMPADJ is the value of TCMP at EDV1 or is equal to zero, depending on whether the EDV1 condition
or full condition respectively, occurred last.
If PKCFG[0]=1, the device assumes a fixed value of 0x7C for TCOMP, giving a temperature compensation gain
of 0.68% DC/°C with an offset of 12°C. This frees the EEPROM location of 0x7F for a user-defined identification
byte, ID1.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
POWER MODES
The bq26501 has four power modes: active, sleep, ship, and hibernate. Figure 5 shows the flow that moves the
device between the active, sleep, and ship modes. Hibernate is a special mode not included in the flow. Detailed
explanations of each mode follow the diagram.
Active Mode
HDQ low for
16 seconds?
NO
YES
NO
Ship Enabled?
NO
YES
YES
Sleep Mode
Ship Mode
HDQ pulled
high?
YES
VRs
below DMF
threshold?
NO
HDQ pulled
high?
4 hour wake?
NO
YES
NO
YES
Device enters
active mode for
16 seconds
1st, 4th, 7th, etc.
wakeup?
NO
YES
Figure 5. Power Mode Flow Chart
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
Active Mode
During normal operation, the device is in active mode, which corresponds to the highest power consumption.
Normal gas gauging is performed in this mode. If system requirements mandate that bq26501 should not enter
sleep or ship modes then an external pull-up resistor between VCC and HDQ is required on the bq26501 side
of the system. The resistor value chosen should be small enough to force a logic “1” on HDQ even with the HDQ
internal pull-down current and any external ESD protection circuitry loading.
Sleep Mode
This low power mode is entered when the HDQ line is pulled low for at least 16 seconds and the charge or
discharge activity is below the digital magnitude filter. It may take up to 30 minutes to determine the no-activity
condition after charge or discharge current is removed. Normal gas gauging ceases, but battery self-discharge,
based on the temperature when the device entered sleep mode, is maintained internally. The device wakes
every 4 hours to perform a temperature conversion and will go back to sleep after 16 seconds if the HDQ line
is still low. bq26501 has an internal pull-down device that sinks less than IHDQPD, allowing the device to enter
sleep mode if the battery pack is pulled from the system and there is not a pull-up mechanism present.
When the device wakes the first time to perform a temperature update, it stays in active mode long enough to
confirm that the charge or discharge activity is still below the digital magnitude filter threshold. This is meant
to minimize possible error if the battery pack is removed from the end equipment and is later re-inserted without
a transition on the HDQ line. This is only an issue if the system has some current drain from the battery even
though HDQ is pulled low. The activity check will take 15 minutes to complete. The device reenters sleep mode
if the activity is below the digital magnitude filter threshold. The device repeats the activity check every 3
wakeups (12 hours).
When the HDQ line is pulled high, the device leaves the sleep mode. The device enters the sleep mode again
only after the HDQ line is pulled low for at least 16 seconds and the charge/discharge activity is below the digital
magnitude filter threshold. If the DMF threshold is set to zero and HDQ line is pulled low, the device enters sleep
mode if the VFC activity is less than 2 counts in 15 minutes. This is equivalent to approximately 24 µV across
the current-sense resistor.
A 100-kΩ pull-up resistor from HDQ to VCC can be added in the battery pack to disable the sleep function.
Ship Mode
This low power mode is to be used when the pack manufacturer has completed assembly and test of the pack.
The ship mode is enabled by setting the SHIP bit in the MODE register and issuing the control command (data
0xA9 to register 0x00). Ship mode is entered only after the ship mode is enabled and the HDQ line has been
pulled low for 16 seconds. This allows the pack manufacturer to enable the ship mode and pull the pack from
the test equipment without any additional overhead. After the ship mode has been enabled but before the device
has entered ship mode, transients on the HDQ line do not cause the device to stay in active mode.
All device functionality stops in ship mode and it does not start again until the HDQ line is pulled high (by plugging
it into the end equipment) or the battery voltage drops below and then rises above the V(POR) threshold. Care
should be taken to ensure that there are no glitches on the HDQ line after the device enters ship mode or else
the device enters the active mode. It enters sleep if HDQ remains low, but does not re-enter ship mode unless
another ship mode command is sent.
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APPLICATION INFORMATION
Hibernate Mode
The device enters hibernate mode when VCC drops below V(POR) and there is a voltage source connected to
the RBI pin. VCC must be raised above V(POR) in order to exit the hibernate mode. This mode retains RAM
integrity and allows retention of remaining capacity, learned LMD, and the CI flag.
PROGRAMMING THE EEPROM
The bq26501 has 10 bytes of EEPROM that are used for firmware control and application data (see the Register
Descriptions section for more information). Programming the EEPROM through the HDQ pin should take place
during pack manufacturing, as a 21-V pulse is needed on the GPIO pin. The programming mode must be
enabled prior to writing any values to the EEPROM locations. The programming mode is enabled by writing to
the EE_EN register (address 0x6E) with data 0xDD. Once the programming mode is enabled, the desired data
can be written to the appropriate address. Figure 6 shows the method for programming all locations.
Host enables EEPROM programming
mode / write data 0xDD to address 0x6E
Host writes data addresses
0x76 to 0x7F
Host reads data
address to be programmed
V(PROG) pulse applied to
GPIO pin for t(PROG)
Host increments
address and reads
No
Programmed
0x7F?
Yes
Write data 0x00 to address 0x6E
Figure 6. EEPROM Programming Flow Chart
It is not required that addresses 0x76 − 0x7F be programmed at the same time or in any particular order. The
programming method illustrated in Figure 6 can be used to program any of the bytes as long as the sequence
of enable, write, read, apply programming pulse, and disable is followed.
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SLUS586B − OCTOBER 2003 − REVISED MARCH 2004
APPLICATION INFORMATION
COMMUNICATING WITH THE bq26501
The bq26501 includes a single-wire HDQ serial data interface. Host processors, configured for either polled or
interrupt processing, can use the interface to access various bq26501 registers. The HDQ pin is an open drain
device, which requires an external pull-up resistor. The interface uses a command-based protocol, where the
host processor sends a command byte to the bq26501. The command directs the bq26501 to either store the
next eight bits of data received to a register specified by the command byte, or to output the eight bits of data
from a register specified by the command byte.
The communication protocol is asynchronous return-to-one and is referenced to VSS. Command and data bytes
consist of a stream of eight bits that have a maximum transmission rate of 5 Kbits/s. The least-significant bit
of a command or data byte is transmitted first. Data input from the bq26501 may be sampled using the
pulse-width capture timers available on some microcontrollers. A UART can also be configured to communicate
with the bq26501.
If a communication time-out occurs (for example, if the host waits longer than t(RSPS) for the bq26501 to
respond) or if this is the first access command, then a BREAK should be sent by the host. The host may then
resend the command. The bq26501 detects a BREAK when the HDQ pin is driven to a logic-low state for a time
t(B) or greater when the bus is free. If the host sends a BREAK when the bq26501 is transmitting a bit, it is
possible that the BREAK would be ignored. Best practice is to hold all BREAK transmissions for twice the
minimum time listed in the HDQ specification table. The HDQ pin then returns to its normal ready-high logic state
for a time t(BR).The bq26501 is then ready for a command from the host processor.
The return-to-one data-bit frame consists of three distinct sections:
1. The first section starts the transmission by either the host or the bq26501 taking the HDQ pin to a logic-low
state for a period equal to t(HW1) or t(DW1).
2. The next section is the actual data transmission, where the data should be valid for t(HW0)− t(HW1) or t(DW0)−
t(DW1).
3. The final section stops the transmission by returning the HDQ pin to a logic-high state and holding it high
until the time from bit start to bit end is equal to t(CYCH) or t(CYCD).
The HDQ line may remain high for an indefinite period of time between each bit of address or between each
bit of data on a write cycle. After the last bit of address is sent on a read cycle, the bq26501 starts outputting
the data after t(RSPS) with timing as specified. The serial communication timing specification and illustration
sections give the timings for data and break communication. Communication with the bq26501 always occurs
with the least-significant bit being transmitted first.
Plugging in the battery pack may be seen as the start of a communication due to contact bounce. It is
recommended that each communication or string of communications be preceded by a break to reset the HDQ
engine.
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APPLICATION INFORMATION
Command Byte
The command byte of the bq26501 consists of eight contiguous valid command bits. The command byte
contains two fields: W/R command and address. The command byte values are shown in the following table:
NAME
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
W/R
AD6
AD5
AD4
AD3
AD2
AD1
AD0
MODE
DESCRIPTION
REGISTER
W/R
W/R indicates whether the command bytes is a read or write command. A “1” indicates a write command and
that the following eight bits should be written to the register specified by the address field of the command byte,
while a “0” indicates that the command is a read. On a read command, the bq26501 outputs the requested
register contents specified by the address field portion of the command Byte.
AD[6]
AD[5]
AD[4]
AD[3]
The seven bits labeled AD6 through AD0 containing the address portion of the register to be accessed
AD[2]
AD[1]
AD[0]
Reading 16 bit Registers
Since 16-bit values are only read 8 bits at a time with the HDQ interface, it is possible that the device may update
the register value between the time the host reads the first and second bytes. To prevent any system issues,
any 16-bit values read by the host should be read using the following protocol. The entire read sequence should
complete in less than 0.8 s, the fastest rate at which any register pair is updated.
1. Read high byte (H0)
2. Read low byte (L0)
3. Read high byte (H1)
4. If H1 = H0, then valid result is H0, L0
5. Otherwise, read low byte (L1) and valid result is H1, L1.
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25
MECHANICAL DATA
MTSS001C – JANUARY 1995 – REVISED FEBRUARY 1999
PW (R-PDSO-G**)
PLASTIC SMALL-OUTLINE PACKAGE
14 PINS SHOWN
0,30
0,19
0,65
14
0,10 M
8
0,15 NOM
4,50
4,30
6,60
6,20
Gage Plane
0,25
1
7
0°– 8°
A
0,75
0,50
Seating Plane
0,15
0,05
1,20 MAX
PINS **
0,10
8
14
16
20
24
28
A MAX
3,10
5,10
5,10
6,60
7,90
9,80
A MIN
2,90
4,90
4,90
6,40
7,70
9,60
DIM
4040064/F 01/97
NOTES: A.
B.
C.
D.
All linear dimensions are in millimeters.
This drawing is subject to change without notice.
Body dimensions do not include mold flash or protrusion not to exceed 0,15.
Falls within JEDEC MO-153
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