Datasheet BQ2945SN-C409TR, BQ2945SN-C409, BQ2945SN-C307TR, BQ2945SN-C307, BQ2945SN Datasheet (Texas Instruments)

1

Features

➤

Provides accurate measurement
of available charge in NiCd,
NiMH, and Li-Ion batteries

➤

Supports SBS v1.0 data set and
two-wire interface

➤

Two programmable general
purpose output ports for added
flexibility

➤

Designed for battery pack inte

-

gration

-

Low operating current

-

Complete circuit can fit on less
than ¾ square inch of PCB
space

➤ Supports SBS charge control

commands for NiCd, NiMH, and
Li-Ion

➤ Drives a five-segment LED dis-

play for remaining capacity
indication

➤ 16-pin narrow SOIC

General Description

The bq2945 Gas Gauge IC With
SMBus Interface is intended for
battery-pack or in-system installa

­tion to maintain an accurate record
of available battery charge. The
bq2945 directly supports capacity
monitoring for NiCd, NiMH, and
Li-Ion battery chemistries.

The bq2945 uses the System Man

­agement Bus v1.0 (SMBus) protocol
and supports the Smart Battery
Data (SBData) commands. The
bq2945 also supports the SBData
charge control functions. Battery
state-of-charge, remaining capacity,
remaining time, and chemistry are
available over the serial link.
Battery-charge state can be directly
indicated using a five-segment LED
display to graphically depict battery
full-to-empty in 20% increments.

The bq2945 estimates battery self­discharge based on an internal
timer and temperature sensor and
user-programmable rate informa

­tion stored in external EEPROM.
The bq2945 also automatically re

­calibrates or “learns” battery capac

­ity in the full course of a discharge
cycle from full to empty.

The bq2945 may operate directly
from three nickel chemistry cells.
With the REF output and an exter

­nal transistor, a simple, inexpensive
regulator can be built to provide V

CC

for other battery cell configurations.

An external EEPROM programs
initial values into the bq2945 and is
necessary for proper operation.

bq2945

Gas Gauge IC with SMBus Interface

V

CC

3.0–6.5V

LED

1

LED segment 1/
EEPROM clock

LED

2

LED segment 2/
EEPROM data

LED

3

LED segment 3

LED

4

LED segment 4

LED

5

LED segment 5

CP

1

Control pin 1

V

SS

System ground

1

PN294501.eps

16-Pin Narrow SOIC

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

V

OUT

REF

SMBC

SMBD

CP

2

SB

DISP

SR

V

CC

LED1/ESCL

LED2/ESDA

LED

3

LED

4

LED

5

CP

1

V

SS

SR Sense resistor input

DISP

Display control input

SB Battery sense input

CP

2

Control pin 2

SMBD SMBus data input/output

SMBC SMBus clock

REF Voltage reference output

V

OUT

EEPROM supply output

6/99 C

Pin Connections Pin Names

Pin Descriptions

V

CC

Supply voltage input

LED

1

–

LED

5

LED display segment outputs

Each output may drive an external LED.

ESCL

Serial memory clock

Output used to clock the data transfer be

-

tween the bq2945 and the external non

-

volatile configuration memory.

ESDA Serial memory data and address

Bidirectional pin used to transfer ad

­dress and data to and from the bq2945
and the external nonvolitile configura

­tion memory.

CP

1

–

CP

2

Control pins 1 and 2

These open-drain outputs can be con­trolled by an SMBus command from the
host. CP

2

can also act as a digital input.

V

SS

Ground

SR

Sense resistor input

The voltage drop (V

SR

) across pins SR and

V

SS

is monitored and integrated over time
to interpret charge and discharge activity.
The SR input is connected to the sense re­sistor and the negative terminal of the
battery. V

SR<VSS

indicates discharge, and

V

SR>VSS

indicates charge. The effective

voltage drop, V

SRO

, as seen by the bq2945

is V

SR+VOS

. (See Table 3.)

DISP

Display control input

DISP

high disables the LED display. DISP
floating allows the LED display to be active
during charge if the rate is greater than
100mA. DISP

low activates the display for

4 seconds.

SB

Secondary battery input

Monitors the pack voltage through a high­impedance resistor divider network. The
pack voltage is reported in the SBD register
function Voltage (0x09) and is monitored for
end-of-discharge voltage and charging volt

-

age parameters.

SMBD

SMBus data

Open-drain bidirectional pin used to trans

­fer address and data to and from the
bq2945.

SMBC

SMBus clock

Open-drain bidirectional pin used to clock
the data transfer to and from the bq2945.

REF Reference output for regulator

REF provides a reference output for an op­tional FET-based micro-regulator.

V

OUT

Supply output

Supplies power to the external EEPROM
configuration memory.

2

bq2945

Functional Description

General Operation

The bq2945 determines battery capacity by monitoring
the amount of charge put into or removed from a re

­chargeable battery. The bq2945 measures discharge
and charge currents, estimates self-discharge, and
monitors the battery for low-battery voltage thresholds.
The charge is measured by monitoring the voltage
across a small-value series sense resistor between the
battery's negative terminal and ground. The available
battery charge is determined by monitoring this voltage
over time and correcting the measurement for the envi

­ronmental and operating conditions.

Figure 1 shows a typical battery pack application of the
bq2945 using the LED capacity display, the serial port,
and an external EEPROM for battery pack program

­ming information. The bq2945 must be configured and
calibrated for the battery-specific information to ensure
proper operation. Table 1 outlines the configuration in

­formation that must be programmed in the EEROM.

An internal temperature sensor eliminates the need
for an external thermistor—reducing cost and compo

­nents. An internal, temperature-compensated time­base eliminates the need for an external resonator,
further reducing cost and components. The entire cir

­cuit in Figure 1 can occupy less than

3

4

square inch of

board space.

3

bq2945

100K

100K

100K

100K

100K

100K

100K

86.5K

BSS138

BSS138

BSS138

2N7002

BSS138

2N7002

2N7002

2N7002

R5R4 R11Q1

No. of Cells

Chart 1

Li-IonNiMH

3

2

4

6

8

9

10

12

499K

301K

499K

499K

499K

698K

698K

806K

806K

806K

604K

604K

604K

909K

909K

909K

See Chart 1 for resistor values and
Q1 FET selection

Figure 1. Battery Pack Application Diagram—LED Display

Notes: R4, R5, and R11 values depend on the battery voltage.

R12 and R13 nominal values must be 10k

4

bq2945

Parameter Name Address Description Length Units

EEPROM length 0x00

Number of EEPROM data locations
must = 0x64

8 bits NA

EEPROM check1 0x01

EEPROM data integrity check byte
must = 0x5b

8 bits NA

Remaining time alarm 0x02/0x03 Sets RemainingTimeAlarm (0x02) 16 bits minutes

Remaining capacity alarm 0x04/0x05 Sets RemainingCapacityAlarm (0x01) 16 bits mAh

Reserved 0x06/0x07 Reserved for future use 16 bits NA

Initial charging current 0x08/0x09 Sets the initial charging current 16 bits mA

Charging voltage 0x0a/0x0b Sets ChargingVoltage (0x15) 16 bits mV

Battery status 0x0c/0x0d Initializes BatteryStatus (0x16) 16 bits NA

Cycle count 0x0e/0x0f Initializes and stores CycleCount (0x17) 16 bits cycles

Design capacity 0x10/0x11 Sets DesignCapacity (0x18) 16 bits mAh

Design voltage 0x12/0x13 Sets DesignVoltage (0x19) 16 bits mV

Specification information 0x14/0x15 Programs SpecificationInfo (0x1a) 16 bits NA

Manufacturer date 0x16/0x17 Programs ManufactureDate (0x1b) 16 bits NA

Serial number 0x18/0x19 Programs SerialNumber (0x1c) 16 bits NA

Fast-charging current 0x1a/0x1b Sets ChargingCurrent (0x14) 16 bits mA

Maintenance-charge current 0x1c/0x1d Sets the trickle current request 16 bits mA

Reserved 0x1e/0x1f Reserved must = 0x0000 16 bits mAh

Manufacturer name 0x20-0x2b Programs ManufacturerName (0x20) 96 bits NA

Current integration gain 0x2c/0x2d Programs the sense resistor scale 16 bits NA

Reserved 0x2e/0x2f Reserved for future use 16 bits NA

Device name 0x30-0x37 Programs DeviceName (0x21) 64 bits NA

Li-Ion taper current 0x38/0x39

Sets the upper limit of the taper current for charge
termination

16 bits mA

Maximum overcharge limit 0x3a/0x3b Sets the maximum amount of overcharge 16 bits NA

Reserved 0x3c Reserved must = 0x00 8 bits NA

Access protect 0x3d Locks commands outside of the SBS data set 8 bits NA

FLAGS1 0x3e Initializes FLAGS1 8 bits NA

FLAGS2 0x3f Initializes FLAGS2 8 bits NA

Device chemistry 0x40-0x47 Programs DeviceChemistry (0x22) 64 bits NA

Battery voltage offset 0x48 Voltage calibration value 8 bits NA

Temperature offset 0x49 Temperature calibration value 8 bits NA

Maximum temperature and
∆T step

0x4a

Sets the maximum charge temperature and the ∆T
step for ∆T/∆t termination

8 bits NA

Table 1. Configuration Memory Map

5

bq2945

Parameter Name Address Description Length Units

Charge efficiency 0x4b Sets the high/low charge rate efficiencies 8 bits NA

Full-charge percentage 0x4c

Sets the percent at which the battery is consid

-

ered fully charged

8 bits NA

Digitial filter 0x4d Sets the minimum charge/discharge threshold 8 bits NA

Reserved 0x4e Reserved for future use 8 bits NA

Self-discharge rate 0x4f Sets the battery’s self-discharge rate 8 bits NA

Manufacturer data 0x50-0x55 Programs ManufacturerData (0x23) 48 bits NA

Voltage gain1 0x56/0x57 Battery divider calibration value 16 bits NA

Reserved 0x58-0x59 Reserved 16 bits NA

Current measurement gain 0x5a/0x5b Sense resistor calibration value 16 bits NA

End of discharge voltage1 0x5c/0x5d Sets EDV1 16 bits NA

End of discharge voltage final 0x5e/0x5f Sets EDVF 16 bits NA

Full-charge capacity 0x60/0x61 Initializes and stores FullChargeCapacity (0x10) 16 bits mAh
∆t step

0x62

Sets the ∆t step for ∆T/∆t termination

8 bits NA

Hold-off time 0x63

Sets ∆T/∆t hold-off timer

8 bits NA

EEPROM check 2 0x64

EEPROM data integrity check byte
must = 0xb5

8 bits NA

Reserved 0x65-0x7f Reserved for future use NA

Table 1. Configuration Memory Map (Continued)

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge
currents, the bq2945 monitors the battery potential
through the SB pin. The voltage potential is deter

-

mined through a resistor-divider network per the fol

-

lowing equation:

R
R

MBV

2.25

5

4

1=−

where MBV is the maximum battery voltage, R

5

is con

-

nected to the positive battery terminal, and R

4

is con

-

nected to the negative battery terminal. R

5/R4

should be

rounded to the next higher integer. R

5

and R4should be

sized so that the voltage at the SB pin (V

SB

) should

never exceed 2.4V.

The battery voltage is monitored for the end-of­discharge voltages (EDV1 and EDVF) and for alarm
warning conditions. EDV threshold levels are used to de

­termine when the battery has reached an “empty” state.
The bq2945 generates an alarm warning when the bat

­tery voltage exceeds the maximum charging voltage by
5% or if the voltage is below EDVF. The battery voltage
gain, the two EDV thresholds, and the charging voltage
are programmable in the EEPROM.

If V

SB

is below either of the two EDV thresholds, the associ­ated flag is latched and remains latched, independent of
V

SB

, until the next valid charge.

EDV monitoring may be disabled under certain condi­tions. If the discharge current is greater than approxi­mately 6A, EDV monitoring is disabled and resumes af­ter the current falls below 6A.

Reset

The bq2945 is reset when first connected to the battery
pack. On power-up, the bq2945 initializes and reads the
EEPROM configuration memory. The bq2945 can also
be reset with a command over the SMBus. The software
reset sequence is the following: (1) write MaxError
(0x0c) to 0x0000; (2) write the reset register (0x64) to
0x8009. A software reset can only be performed if the
bq2945 is in an unlocked state as defined by the value in
location 0x3d of the EEPROM (EE 0x3d) on power-up.

Temperature

The bq2945 monitors temperature sensing using an in

­ternal sensor. The temperature is used to adapt charge
and self-discharge compensations as well as to monitor
for maximum temperature and∆T/∆t during a bq2945
controlled charge. Temperature may also be accessed
over the SMBus with command 0x08.

Layout Considerations

The bq2945 measures the voltage differential between
the SR and V

SS

pins. VOS(the offset voltage at the SR
pin) is greatly affected by PC board layout. For optimal
results, the PC board layout should follow the strict rule
of a single-point ground return. Sharing high-current
ground with small signal ground causes undesirable
noise on the small signal nodes. Additionally, in refer

-

ence to Figure 1:

n

The capacitors (C1 and C2) should be placed as close as
possible to the SB and V

CC

pins, and their paths to V

SS

should be as short as possible. A high-quality ceramic
capacitor of 0.1µf is recommended for V

CC

.

n

The sense resistor capacitor (C3) should be placed as
close as possible to the SR pin.

n

The bq2945 should be in thermal contact with the
cells for optimum temperature measurement.

n

An optional zener (D9) may be necessary to ensure that
V

CC

is not above the maximum rating during

operation.

Gas Gauge Operation

The operational overview diagram in Figure 2 illus­trates the operation of the bq2945. The bq2945 accumu­lates a measure of charge and discharge currents, as
well as an estimation of self-discharge. Charge currents
are compensated for temperature and state-of-charge of
the battery. Self-discharge is temperature-compensated.

The main counter, RemainingCapacity (RM), represents
the available battery capacity at any given time. Battery
charging increments the RM register, whereas battery dis

­charging and self-discharge decrement the RM register
and increment the internal Discharge Count Register
(DCR).

The Discharge Count Register is used to update the
FullChargeCapacity (FCC) register only if a complete
battery discharge from full to empty occurs without any
partial battery charges. Therefore, the bq2945 adapts
its capacity determination based on the actual condi

­tions of discharge.

The battery's initial full capacity is set to the value stored
in EE 0x60-0x61. Until FCC is updated, RM counts up to,
but not beyond, this threshold during subsequent charges.

1. FullChargeCapacity or learned-battery

capacity:

FCC is the last measured discharge capacity of the
battery. On initialization (application of V

CC

or reset),

FCC is set to the value stored in the EEPROM. Dur

-

ing subsequent discharges, FCC is updated with the

6

bq2945

latest measured capacity in the Discharge Count Reg­ister, representing a discharge from full to below
EDV1. A qualified discharge is necessary for a capac­ity transfer from the DCR to the FCC register. Once
updated, the bq2945 writes the new FCC to the EE­PROM. The FCC also serves as the 100% reference
threshold used by the relative state-of-charge calcula­tion and display.

2. DesignCapacity (DC):

The DC is the user-specified battery capacity and is
programmed from external EEPROM. The DC also
provides the 100% reference for the absolute dis

-

play mode.

3. RemainingCapacity (RM):

RM counts up during charge to a maximum value of
FCC and down during discharge and self-discharge to

0. RM is set to 000Ah after the EDV1 threshold has
been reached and a valid charge has been detected.
To prevent overstatement of charge during periods
of overcharge, RM stops incrementing when RM =
FCC. RM may optionally be written to a user­defined value when fully charged if the battery
pack is under bq2945 charge control. On initializa

­tion, RM is set to the value stored in EE
0x1e—0x1f.

4. Discharge Count Register (DCR):

The DCR counts up during discharge independent
of RM and can continue increasing after RM has
decremented to 0. Prior to RM = 0 (empty battery),

both discharge and self-discharge increment the
DCR. After RM = 0, only discharge increments
the DCR. The DCR resets to 0 when RM = FCC.
The DCR does not roll over but stops counting
when it reaches FFFFh.

The DCR value becomes the new FCC value on the
first charge after a qualified discharge to EDV1. A
qualified discharge to EDV1 occurs if all of the fol­lowing conditions exist:

n

No valid charge initiations (charges greater than
10mAh), where V

SRO

>+V

SRD

occurred during

the period between RM = FCC and EDV1 de

-

tected.

n

The self-discharge count is not more than
256mAh.

n

The temperature is≥273°K (0°C) when the
EDV1 level is reached during discharge.

The valid discharge flag (VDQ) in FLAGS1 indi

­cates whether the present discharge is valid for an
FCC update. FCC cannot be reduced by more than
256mAh during any single cycle.

Charge Counting

Charge activity is detected based on a positive voltage
on the SR input. If charge activity is detected, the
bq2945 increments RM at a rate proportional to V

SRO

and, if enabled, activates an LED display. Charge ac

-

tions increment the RM after compensation for charge
state and temperature.

7

bq2945

FG294501.eps

Temperature

Compensation

Charge
Current

Discharge

Current

Self-Discharge

Timer

Remaining

Capacity

(RM)

Full

Charge

Capacity

(FCC)

Discharge

Count

Register

(DCR)

<

Qualified

Transfer

+

Temperature, Other Data

+

--

+

Inputs

Main Counters

and Capacity

Reference (FCC)

Outputs

Two-Wire

Serial Interface

Chip-Controlled

Available Charge

LED Display

State-of-charge

and

Temperature

Compensation

Figure 2. Operational Overview

The bq2945 determines charge activity sustained at a
continuous rate equivalent to V

SRO

>+V

SRD

. A valid

charge equates to sustained charge activity
greater than 10 mAh. Once a valid charge is detected,

charge threshold counting continues until V

SRO

falls be

-

low V

SRD

.V

SRD

is a programmable threshold as de

-

scribed in the Digital Magnitude Filter section.

Discharge Counting

All discharge counts where V

SRO

<-V

SRD

cause the RM

register to decrement and the DCR to increment. V

SRD

is a programmable threshold as described in the Digital
Magnitude Filter section.

Self-Discharge Estimation

The bq2945 continuously decrements RM and incre

-

ments DCR for self-discharge based on time and tem

­perature. The bq2945 self-discharge estimation rate is
programmed in EE 0x4f and can be set from 0 to 25%
per day for 20–30°C. This rate doubles every 10°C
from 30°C to 70°C and halves every 10°C from 20°Cto
0°C.

Charge Control

The bq2945 supports SBS charge control by broadcast­ing the ChargingCurrent and the ChargingVoltage to
the Smart Charger address. The bq2945 broadcasts
charging commands every 10 seconds; the broadcasts
can be disabled by writing bit 14 of BatteryMode to 1.
On reset, the initial charging current broadcast to the
charger is set to the value programmed in EE 0x08­0x09. The bq2945 updates the value used in the charg­ing current broadcasts based on the battery’s state of
charge, voltage, and temperature.

The bq2945 internal charge control is compatible with
nickel-based and Li-Ion chemistries. The bq2945 uses
current taper detection for Li-Ion primary charge termi

­nation and ∆T/∆t for nickel based primary charge termi

­nation. The bq2945 also provides a number of safety
terminations based on battery capacity, voltage, and
temperature.

Current Taper

For Li-Ion charge control, the ChargingVoltage must be
set to the desired pack voltage during the constant volt

­age charge phase. The bq2945 detects a current taper
termination when it measures the pack voltage to be
within 128mV of the requested charging voltage and
when the AverageCurrent is between the programmed
threshold in EE 0x38—0x39 and 100 mA for at least 40s.

∆T/∆t

The ∆T/∆t used by the bq2945 is programmable in both
the temperature step (1.6°C–4.6°C) and time step (20

seconds–320seconds). Typical settings for 1°C/min in

-

clude 2°C over 120 seconds and 3°C over 180 seconds.
Longer times are required for increased slope resolution.

∆∆T

t

is set by the formula:

∆∆T

t

=

[]

[' (

(lower nibble of EE 0x4a) 2 + 16 / 10

EE 0x62)

∗

2 s

20]

C

s∗











o

In addition to the ∆T/∆t timer, there is a hold-off timer,
which starts when the battery is being charged at more
than 255mA and the temperature is above 25°C. Until
this timer expires, ∆T/∆t is suspended. If the tempera

-

ture falls below 25°C, or if charging current falls below
255mA, the timer is reset and restarts only if these con

­ditions are once again within range. The hold-off time is
programmed in EE 0x63.

Charge Termination

Once the bq2945 detects a valid charge termination, the
Fully_Charged, Terminate_Charge_Alarm, and the
Over_Charged_Alarm bits are set in BatteryStatus, and
the requested charge current is set to zero. Once the ter­minating conditions cease, the Terminate_Charge_Alarm
and the Over_Charged_Alarm are cleared, and the re­quested charging current is set to the maintenance rate.
The bq2945 requests the maintenance rate until RM falls
below 95% of full-charge percentage. Once this occurs,
the Fully_Charged bit is cleared, and the requested
charge current and voltage are set to the fast-charge rate.

Bit 4 (CC) in FLAGS2 determines whether RM is modi­fied after a ∆T/∆t or current taper termination occurs. If
CC = 1, RM may be set from 0 to 100% of the FullChar

­geCapacity as defined in EE 0x4c. If RM is below the
full-charge percentage, RM is set to the full-charge per

­centage of FCC. If RM is above the full-charge percent

­age, RM is not modified.

Charge Suspension

The bq2945 may temporarily suspend charge if it de

­tects a charging fault. The charging faults include the
following conditions:

n

Maximum Overcharge: If charging continues for
more than the programmed maximum overcharge
limit as defined in EE 0x3a—0x36 beyond RM=FCC,
the Fully_Charged bit is set, and the requested
charging current is set to the maintenance rate.

n

Overvoltage: An over-voltage fault exists when the
bq2945 measures a voltage more than 5% above the
ChargingVoltage. When the bq2945 detects an
overvoltage condition, the requested charge current
is set to 0 and the Terminate_Charge_Alarm bit is
set in Battery Status. The alarm bit is cleared when

8

bq2945

the current drops below 256mA and the voltage is
less than 105% of ChargingVoltage.

n

Overcurrent: An overcurrent fault exists when the
bq2945 measures a charge current more than 25%
above the ChargingCurrent. If the ChargingCurrent
is less than 1024mA, an overcurrent fault exists if the
charge current is more than 256mA above the
ChargingCurrent. When the bq2945 detects an
overcurrent condition, the requested charge current
is set to 0 and the Terminate_Charge_Alarm bit is set
in Battery Status. The alarm bit is cleared when the
current drops below 256mA.

n

Maximum Temperature: When the battery
temperature exceeds the programmed maximum
temperature, the requested charge current is set to
zero and the Over_Temp_Alarm and the
Terminate_Charge_Alarm bits are set in Battery
Status. The alarm bits are cleared when the
temperature drops below 50°C.

n

Low Temperature: When the battery temperature
is less than 0°C, the requested charge current is set
to the maintenance rate. Once the temperature is
above 5°C, the requested charge current is set to the
fast rate.

n

Undervoltage: When the battery voltage is below
the EDVF threshold, the requested charge current is
set to the maintenance rate. Once the voltage is
above EDVF, the requested charge current is set to
the fast rate.

Count Compensations

Charge activity is compensated for temperature and
state-of-charge before updating the RM and/or DCR.
Self-discharge estimation is compensated for tempera

-

ture before updating RM or DCR.

Charge Compensation

Charge efficiency is compensated for state-of-charge,
temperature, and battery chemistry. The charge effi

-

ciency is adjusted using the following equations:

1.)

RM RM * Q Q

EFC ET

=−()

where RelativeStateOfCharge < FullChargePercentage,
and

Q

EFC

is the programmed fast-charge efficiency vary

-

ing from 0.75 to 1.0.

2.)

RM RM Q Q

ETC ET

=−*( )

where RelativeStateOfCharge ≥ FullChargePercentage
and

Q

ETC

is the programmed maintenance (trickle)

charge efficiency varying from 0.75 to 1.0.

Q

ET

is used to adjust the charge efficiency as the battery

temperature increases according to the following:

QifT

ET

=<030

°C

QCTC

ET

=°≤<°002 30 40.if

QTC

ET

=≥°005 40.if

Q

ET

is 0 over the entire temperature range for Li-Ion.

Digital Magnitude Filter

The bq2945 has a programmable digital filter to elimi

­nate charge and discharge counting below a set
threshold, V

SRD

. Table 2 shows typical digital filter

settings. The proper digital filter setting can be calcu

­lated using the following equation.

DMF =

45

V

SRD

Error Summary

Capacity Inaccurate

The FCC is susceptible to error on initialization or if no
updates occur. On initialization, the FCC value includes
the error between the design capacity and the actual ca

­pacity. This error is present until a qualified discharge
occurs and FCC is updated (see the DCR description).
The other cause of FCC error is battery wear-out. As
the battery ages, the measured capacity must be ad

­justed to account for changes in actual battery capacity.
Periodic qualified discharges from full to empty will
minimize errors in FCC.

Current-Sensing Error

Table 3 illustrates the current-sensing error as a function
of V

SR

. A digital filter eliminates charge and discharge

counts to the RM register when -V

SRD<VSRO

<+V

SRD

.

Display

The bq2945 can directly display capacity information
using low-power LEDs. The bq2945 displays the battery
charge state in either absolute or relative mode. In rela

­tive mode, the battery charge is represented as a per

­centage of the FCC. Each LED segment represents 20%
of the FCC.

9

bq2945

DMF DMF Hex. V

SRD

(mV)

75 4B

0.60

100 64 0.45

150 96 0.30

175 AF 0.26

200 C8 0.23

Table 2. Typical Digital Filter Settings

In absolute mode, each segment represents a fixed
amount of charge, 20% of the DesignCapacity. As the
battery wears out over time, it is possible for the FCC to
be below the design capacity. In this case, all of the
LEDs may not turn on in absolute mode, representing
the reduction in the actual battery capacity.

When DISP

is tied to VCC, the LED

1-5

outputs are inac

-

tive. When DISP

is left floating, the display becomes ac

­tive whenever the bq2945 detects a charge rate of
100mA or more. When pulled low, the segment outputs
become active immediately for a period of approximately
4 seconds. The DISP

pin must be returned to float or

V

CC

to reactivate the display.

LED

1

blinks at a 4Hz rate whenever VSBhas been de­tected to be below EDV1 (EDV1 = 1), indicating a low­battery condition. V

SB

below EDVF (EDVF = 1) disables

the display output.

Microregulator

The bq2945 can operate directly from three nickel chem

­istry cells. To facilitate the power supply requirements
of the bq2945, an REF output is provided to regulate an
external low-threshold n-FET. A micropower source for
the bq2945 can be inexpensively built using a 2N7002 or
BSS138 FET and an external resistor. (See Figure 1.)
The value of R11 depends on the battery pack’s nominal
voltage.

Communicating with the bq2945

The bq2945 includes a simple two-pin (SMBC and
SMBD) bi-directional serial data interface. A host proc

-

essor uses the interface to access various bq2945 regis

-

ters; see Table 4. This method allows battery character

­istics to be monitored easily. The open-drain SMBD and
SMBC pins on the bq2945 are pulled up by the host sys

­tem, or may be connected to V

SS

, if the serial interface is

not used.

The interface uses a command-based protocol, where the
host processor sends the battery address and an eight­bit command byte to the bq2945. The command directs
the bq2945 to either store the next data received to a
register specified by the command byte or output the
data specified by the command byte.

bq2945 Data Protocols

The host system, acting in the role of a Bus master, uses
the read word and write word protocols to communicate
integer data with the bq2945. (See Figure 3.)

Host-to-bq2945 Message Protocol

The Bus Host communicates with the bq2945 using one
of three protocols:

n

Read word

n

Write word

n

Read block

The particular protocol used is a function of the com

­mand. The protocols used are shown in Figure 3.

Host-to-bq2945 Messages

(see Table 4)

ManufacturerAccess() (0x00)

This function is used to control CP1and CP2. (See Table

7.)

10

bq2945

Symbol Parameter Typical Maximum Units Notes

V

OS

Offset referred to V

SR

±

75

±

150

µ

V DISP

= VCC.

INL

Integrated non-linearity
error

±

1

±

4

%

Add 0.1% per °C above or below 25°C
and 1% per volt above or below 4.25V.

INR

Integrated non­repeatability error

±

0.5

±

1

%

Measurement repeatability given
similar operating conditions.

Table 3. bq2945 Current-Sensing Errors

RemainingCapacityAlarm() (0x01)

This function sets or returns the low-capacity alarm
value. When RM falls below the RemainingCapac­ityAlarm value initialized from the external EE­PROM, the Remaining_Capacity_Alarm bit is set in
BatteryStatus. The system may alter this alarm dur­ing operation.

Input/Output: unsigned integer. This sets/returns
the value where the Remaining_Capacity_Alarm
bit is set in Battery Status.

Units: mAh

Range: 0 to 65,535mAh

RemainingTimeAlarm() (0x02)

This function sets or returns the low remaining time
alarm value. When the AverageTimeToEmpty falls be

-

low this value, the Remaining_Time_Alarm bit in Bat

­teryStatus is set. The default value for this register is
programmed in EE 0x02-0x03. The system may alter
this alarm during operation.

Input/Output: unsigned integer. This sets/returns
the value where the Remaining_Time_Alarm bit is
set in Battery Status.

Units: minutes

Range: 0 to 65,535 minutes

BatteryMode() (0x03)

This read/write word selects the various battery opera­tional modes. The bq2945 supports the battery capacity
information specified in mAh. This function also deter­mines whether the bq2945 charging values are broad­casted to the Smart Battery Charger address.

Writing bit 14 to 1 disables voltage and current Master
Mode broadcasts to the Smart Battery Charger. Bit 14 is
automatically reset to 0 if SMBC and SMBD = 0 for
greater than 2 seconds (i.e.pack removal).

Writing bit 13 to 1 disables all Master Mode broadcasts
including alarm messages to the Smart Battery Charger
and Host. The bit remains set until overwritten. Pro

­gramming bit 3 of FLAGS2 in the EEPROM (EE0x3f)
initializes this bit to a 1.

Bit 7 is the condition request flag. It is set when the
bq2945 is initialized from the EEPROM and reset when
a learning cycle has been completed. It is also set to a 1
if CycleCount increases by 32 without a new learning
cycle.

AtRate() (0x04)

This read/write word is the first half of a two-function
set used to set the AtRate value used in calculations
made by the AtRateTimeToFull and AtRateTime

­ToEmpty.

n

When the AtRate value is positive, the
AtRateTimeToFull function returns the predicted
time to full-charge at the AtRate value of charge.

11

bq2945

FG294501.eps

S

Battery Address

0001011

0 A Command Code A Data byte low A Data byte high AP

11818181171

S

Battery Address

0001011

0 A Command Code A Battery Address A1

117181171

S

1

AA

1818

P

Data byte low Data byte high

S

Battery Address

0001011

0

A Command Code A Battery Address A1

117181171

S

1

AA

1818

Byte Count =N Data byte 1

AA

1818

P

Data byte 2 Data byte N

1

bq2945

System Host

Block Read

Read Word

Write Word

A – ACKNOWLEDGE
A – NOT ACKNOWLEDGE
S – START
P – STOP

Figure 3. Host Communication Protocols

12

bq2945

Function Code Access Units Defaults

1

ManufacturerAccess 0x00 read/write - -

Remaning_Capacity_Alarm 0x01 read/write mAh E

2

Remaining_Time_Alarm 0x02 read/write minutes E

2

BatteryMode 0x03 read/write bit flag -

AtRate 0x04 read/write mA -

AtRateTimeToFull 0x05 read minutes -

AtRateTimeToEmpty 0x06 read minutes -

AtRateOK 0x07 read Boolean -

Temperature 0x08 read 0.1°K 2930

Voltage 0x09 read mV E

2

Current 0x0a read mA 0

AverageCurrent 0x0b read mA 0

MaxError 0x0c read percent 100

RelativeStateOfCharge 0x0d read percent -

AbsoluteStateOfCharge 0x0e read percent -

RemainingCapacity 0x0f read mAh E

2

FullChargeCapacity 0x10 read mAh E

2

RunTimeToEmpty 0x11 read minutes -

AverageTimeToEmpty 0x12 read minutes -

AverageTimeToFull 0x13 read minutes -

ChargingCurrent 0x14 read mA E

2

ChargingVoltage 0x15 read mV E

2

Battery Status 0x16 read bit flags E

2

CycleCount 0x17 read cycle E

2

DesignCapacity 0x18 read mAh E

2

DesignVoltage 0x19 read mV E

2

Specification Info 0x1a read - E

2

ManufactureDate 0x1b read - E

2

SerialNumber 0x1c read integer E

2

Reserved 0x1d - 0x1f - - -

ManufacturerName 0x20 read string E

2

DeviceName 0x21 read string E

2

Note: 1. Defaults after reset or power-up.

Table 4. bq2945 Register Functions

13

bq2945

Function Code Access Units Defaults

1

DeviceChemistry 0x22 read string E

2

ManufacturerData 0x23 read string E

2

FLAG1 and FLAG2 0x2f read bit flags E

2

End of Discharge Voltage 1 (EDV1) 0x3e read - E

2

End of Discharge Voltage Final
(EDVF)

0x3f read - E

2

Note: 1. Defaults after reset or power-up.

Table 4. bq2945 Register Functions (Continued)

n

When the AtRate value is negative, the
AtRateTimeToEmpty function returns the predicted
operating time at the AtRate value of discharge.

Input/Output: signed integer. AtRate is positive
for charge and negative for discharge.

Units: mA

Range: -32,768mA to 32,767mA

AtRateTimeToFull() (0x05)

This read-only word returns the predicted remaining
time to fully charge the battery at the AtRate value
(mA) and is valid only if read immediately after an
AtRate command.

Output: unsigned integer. Returns the predicted
time to full charge.

Units: minutes

Range: 0 to 65,534min

Granularity: 2 min or better

Invalid Data Indication: 65,535 indicates that the
AtRate value is negative.

AtRateTimeToEmpty() (0x06)

This read-only word returns the predicted remaining op­erating time if the battery is discharged at the AtRate
value and is valid only if read immediately after an
AtRate command.

Output: unsigned integer. Returns the predicted
time to empty.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid Data Indication: 65,535 indicates that the
AtRate value is not negative.

AtRateOK() (0x07)

This read-only word returns a Boolean value that indi

-

cates whether or not the EDVF flag has been set.

Boolean: Indicates if the battery can supply addi

-

tional energy.

Units: Boolean

Range: TRUE ≠ 0, FALSE = 0

Temperature() (0x08)

This read-only word returns the cell-pack's internal
temperature.

Output: unsigned integer. Returns the cell tem

-

perature in tenths of degrees Kelvin increments.

Units: 0.1°K

Range: 0 to +500.0°K

Granularity: 0.5°K or better

Accuracy:±3°K after calibration

Voltage() (0x09)

This read-only word returns the cell-pack voltage (mV).

Output: unsigned integer. Returns the battery ter

-

minal voltage in mV.

Units: mV

Range: 0 to 65,535mV

Granularity: 0.2% of DesignVoltage

Accuracy:±1% of DesignVoltage after calibration

Current() (0x0a)

This read-only word returns the current through the
battery's terminals (mA).

Output: signed integer. Returns the charge/dis­charge rate in mA, where positive is for charge
and negative is for discharge

Units: mA

Range: 0 to 32,767mA for charge or 0 to
–32,768mA for discharge

Granularity: 0.2% of the DesignCapacity or better

Accuracy:±1% of the DesignCapacity after calibration

AverageCurrent() (0x0b)

This read-only word returns a rolling average of the cur

­rent through the battery's terminals. The AverageCur

­rent function returns meaningful values after the bat

­tery's first minute of operation.

Output: signed integer. Returns the charge/dis

­charge rate in mA, where positive is for charge
and negative is for discharge

Units: mA

Range: 0 to 32,767mA for charge or 0 to
–32,768mA for discharge

Granularity: 0.2% of the DesignCapacity or better

Accuracy:±1% of the DesignCapacity after cali

­bration

14

bq2945

MaxError() (0x0c)

Returns the expected margin of error (%) in the state of
charge calculation.

Output: unsigned integer. Returns the percent un

-

certainty for selected information.

Units: %

Range: 0 to 100%

RelativeStateOfCharge() (0x0d)

This read-only word returns the predicted remaining
battery capacity expressed as a percentage of FullChar

-

geCapacity (%). RelativeStateOfCharge is only

valid for battery capacities more than 1504mAh
and less than 10,400mAh.

Output: unsigned integer. Returns the percent of re

-

maining capacity.

Units: %

Range: 0 to 100%

Granularity: 1%

Accuracy: ±MaxError after circuit and capacity
calibration

AbsoluteStateOfCharge() (0x0e)

This read-only word returns the predicted remaining
battery capacity expressed as a percentage of DesignCa­pacity (%). Note that AbsoluteStateOfCharge can return
values greater than 100%. Absolute StateOfCharge

is only valid for battery capacities more than
1504mAh and less than 10,400mAh.

Output: unsigned integer. Returns the percent of
remaining capacity.

Units: %

Range: 0 to 65,535%

Granularity: 1%

Accuracy: ±MaxError after circuit and capacity
calibration

RemainingCapacity() (0x0f)

This read-only word returns the predicted remaining
battery capacity. The RemainingCapacity value is ex

-

pressed in mAh.

Output: unsigned integer. Returns the estimated re

-

maining capacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

Granularity: 0.2% of DesignCapacity or better

Accuracy: ±MaxError ∗ FCC after circuit and ca

­pacity calibration

FullChargeCapacity() (0x10)

This read-only word returns the predicted pack capacity
when it is fully charged. FullChargeCapacity defaults
to the value programmed in the external EEPROM until
a new pack capacity is learned. The new FCC is stored
to EEPROM within 400ms of a valid charge after a
qualified discharge.

Output: unsigned integer. Returns the estimated full
charge capacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

Granularity: 0.2% of DesignCapacity or better

Accuracy: ±MaxError ∗ FCC after circuit and ca

­pacity calibration

RunTimeToEmpty() (0x11)

This read-only word returns the predicted remaining
battery life at the present rate of discharge (minutes).
The RunTimeToEmpty value is calculated based on
Current.

Output: unsigned integer. Returns the minutes of
operation left.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid data indication: 65,535 indicates battery is
not being discharged.

AverageTimeToEmpty() (0x12)

This read-only word returns the predicted remaining
battery life at the present average discharge rate (min

­utes). The AverageTimeToEmpty is calculated based on
AverageCurrent.

Output: unsigned integer. Returns the minutes of
operation left.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid data indication: 65,535 indicates battery
is not being discharged.

15

bq2945

AverageTimeToFull() (0x13)

This read-only word returns the predicted time until the
Smart Battery reaches full charge at the present aver

-

age charge rate (minutes).

Output: unsigned integer. Returns the remaining
time in minutes to full.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Invalid data indication: 65,535 indicates battery
is not being charged.

ChargingCurrent() (0x14)

If enabled, the bq2945 sends the desired charging rate in
mA to the Smart Battery Charger.

Output: unsigned integer. Transmits/returns the
maximum charger output current in mA.

Units: mA

Range: 0 to 65,534mA

Granularity: 0.2% of the design capacity or better

Invalid data indication: 65,535 indicates that the
Smart Charger should operate as a voltage source
outside its maximum regulated current range.

ChargingVoltage() (0x15)

If enabled, the bq2945 sends the desired voltage in mV
to the Smart Battery Charger.

Output: unsigned integer. Transmits/returns the
charger voltage output in mV.

Units: mV

Range: 0 to 65,534mV

Granularity: 0.2% of the DesignVoltage or better

Invalid data indication: 65,535 indicates that the
Smart Battery Charger should operate as a cur

-

rent source outside its maximum regulated volt

-

age range.

BatteryStatus() (0x16)

This read-only word returns the battery status word.

Output: unsigned integer. Returns the status reg­ister with alarm conditions bitmapped as shown in
Table 5.

Some of the BatteryStatus flags (Remaining_Capac­ity_Alarm and Remaining_Time_Alarm) are calculated
based on current. See Table 8 and 9 for definitions.

CycleCount() (0x17)

This read-only word returns the number of charge/dis

­charge cycles the battery has experienced. A charge/dis

­charge cycle starts from a base value equivalent to the
battery's state-of-charge on completion of a charge cycle.
The bq2945 increments the cycle counter during the cur

­rent charge cycle if the battery has been discharged 15%
below the state-of-charge at the end of the last charge cy

­cle. This prevents false reporting of small charge/discharge
cycles. The cycle count is stored in EEPROM within
400ms of an update.

Output: unsigned integer. Returns the count of
charge/discharge cycles the battery has
experienced.

Units: cycles

Range: 0 to 65,535 cycles; 65,535 indicates battery
has experienced 65,535 or more cycles.

Granularity: 1 cycle

DesignCapacity() (0x18)

This read-only word returns the theoretical capacity of a
new pack. The DesignCapacity value is expressed in
mAh at the nominal discharge rate.

16

bq2945

Alarm Bits

0x8000 Over_Charged_Alarm

0x4000 Terminate_Charge_Alarm

0x2000 Reserved

0x1000 Over_Temp_Alarm

0x0800 Terminate_Discharge_Alarm

0x0400 Reserved

0x0200 Remaining_Capacity_Alarm

0x0100 Remaining_Time_Alarm

Status Bits

0x0080 Initialized

0x0040 Discharging

0x0020 Fully_Charged

0x0010 Fully_Discharged

Error Code

0x0000-

0x000f

Reserved for error codes

Table 5. Status Register

Output: unsigned integer. Returns the battery ca

-

pacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

DesignVoltage() (0x19)

This read-only word returns the theoretical voltage of
a new pack in mV.

Output: unsigned integer. Returns the battery's
normal terminal voltage in mV.

Units: mV

Range: 0 to 65,535mV

Specification Info() (0x1a)

This read-only word returns the specification re­vision the bq2945 supports.

ManufactureDate() (0x1b)

This read-only word returns the date the cell was manu

-

factured in a packed integer word. The date is packed
as follows: (year - 1980) ∗ 512 + month ∗ 32+day.

SerialNumber() (0x1c)

This read-only word returns a serial number. This
number, when combined with the ManufacturerName,
the DeviceName, and the ManufactureDate, uniquely
identifies the battery.

Output: unsigned integer

ManufacturerName() (0x20)

This read-only string returns a character string where the
first byte is the number of characters available. The maxi

­mum number of characters is 11. The character string con

­tains the battery manufacturer's name. For example,
“Unitrode” identifies the battery pack manufacturer as
Unitrode.

Output: string or ASCII character string

DeviceName() (0x21)

This read-only string returns a character string where the
first byte is the number of characters available. The maxi­mum number of characters is 7. The 7-byte character string
contains the battery's name. For example, a DeviceName of
“bq2945” indicates that the battery is a model bq2945.

Output: string or ASCII character string

DeviceChemistry() (0x22)

This read-only string returns a character string where
the first byte is the number of characters available. The
maximum number of characters is 5. The 5-byte charac

­ter string contains the battery's chemistry. For example,
if the DeviceChemistry function returns “NiMH,” the
battery pack contains nickel-metal hydride cells.

Output: string or ASCII character string

ManufacturerData() (0x23)

This read-only string allows access to an up to 5-byte
manufacturer data string.

Output: block data—data whose meaning is as

-

signed by the Smart Battery's manufacturer.

End of Discharge Voltage1 (0x3e)

This read-only word returns the first end-of-discharge
voltage programmed for the pack.

Output: two’s complemented unsigned integer.
Returns battery end-of-discharge voltage pro

-

grammed in EEPROM in mV.

17

bq2945

(MSB) 7 6543210 (LSB)

FLAGS2 DMODE CP2 DI CHM CC - OV LTF OC

FLAGS1 - - VQ - VDQ SEDV EDV1 EDVF

Note: - = Reserved

Table 6. Bit Descriptions for FLAGS1 and FLAGS2

Field

Bits

Used Format Allowable Value

Day 0–4

5-bit binary

value

1–31 (corresponds to
date)

Month 5–8

4-bit binary

value

1–12 (corresponds to
month number)

Year 9–15

7-bit binary

value

0*127 (corresponds
to year biased by

1980)

End of Discharge VoltageF (0x3f)

This read-only word returns the final end-of-discharge
voltage programmed for the pack.

Output: two’s complemented unsigned integer.
Returns battery final end-of-discharge voltage pro

-

grammed in EEPROM in mV.

FLAGS1&2() (0x2f)

This read-only register returns an unsigned integer rep

­resenting the internal status registers of the bq2945.
The MSB represents FLAGS2, and the LSB represents
FLAGS1. See Table 6 for the bit description for FLAGS1
and FLAGS2.

FLAGS2

The Display Mode flag (DMODE), bit 7 determines
whether the bq2945 displays Relative or Absolute capac

­ity.

The DMODE values are:

Where DMODE is:

0 Selects Absolute display

1 Selects Relative display

Bit 6 reflects the high/low state of CP2.

The Chemistry flag (CHM), bit 5, selects Li-Ion or nickel
compensation factors.

The CHM values are:

Where CHM is:

0 Selects Nickel

1 Selects Li-Ion

Bit 4, the Charge Control flag (CC), determines whether
a bq2945-based charge termination will set RM to a
user-defined programmable full charge capacity.

The CC values are:

Where CC is:

0 RM is not modified on valid bq2945

charge termination

1 RM is set to a programmable percentage of

the FCC when a valid bq2945 charge termi

-

nation occurs

Bit 3 is reserved.

Bit 2, the Overvoltage flag (OV), is set when the bq2945
detects a pack voltage 5% greater than the programmed
charging voltage. This bit is cleared when the pack volt

-

age falls 5% below the programmed charging voltage.

The OV values are:

Where OV is:

0 Voltage < 1.05∗ChargingVoltage

1 Voltage≥1.05∗ChargingVoltage

Bit 1, the Low Temperature Fault flag (LTF), is set when
temperature < 0°C and cleared when temperature >
5°C.

The LTF values are:

Where LTF is:

0 Temperature > 5°C

1 Temperature < 0°C

Bit 0, the Overcurrent flag (OC), is set when the average
current is 25% greater than the programmed charging
current. If the charging current is programmed less than
1024mA, overcurrent is set if the average current is
256mA greater than the programmed charging current.

18

bq2945

FLAGS2 Bits

76 5 43210

- - - - -OV- -

FLAGS2 Bits

76 5 43210

-- - CC----

FLAGS2 Bits

7 6543210

DMODE -------

FLAGS2 Bits

76 5 43210

--CHM-----

FLAGS2 Bits

76 5 43210

-- - ---LTF-

FLAGS2 Bits

7 6 5 43210

- CP2DI - -----

This flag is cleared when the average current falls below
256mA.

The OC values are:

Where OC is:

0 AverageCurrent is less than 1.25 ∗ Charg

­ingCurrent or less than 256mA if charging
current is programmed less than 1024mA

1 AverageCurrent exceeds 1.25 ∗ Charg

-

ingCurrent or 256mA if the charging cur

­rent is programmed less than 1024mA.
This bit is cleared if average current <
256mA.

FLAGS1

Bits 7 and 6 are reserved.

The Valid Charge flag (VQ), bit 5, is set when V

SRO

≥

|V

SRD

| and 10mAh of charge has accumulated. This bit

is cleared during a discharge and when V

SRO

≤

|V

SRD

|.

The VQ values are:

Where VQ is:

0V

SRO

≤

|V

SRD

|

1V

SRO

≥

|V

SRD

| and 10mAh of charge has

accumulated

Bit 4 is reserved.

The Valid Discharge flag (VDQ), bit 3, is set when a
valid discharge is occurring (discharge cycle valid for
learning new full charge capacity) and cleared if a par

­tial charge is detected, EDV1 is asserted when T < 0°C,
or self-discharge accounts for more than 256mAh of the
discharge.

The VDQ values are:

Where VDQ is:

0 Self-discharge is greater than 256mAh,

EDV1 = 1 when T < 0°C or VQ = 1

1 On first discharge after RM=FCC

The Stop EDV flag (SEDV), bit 2, is set when the dis

­charge current > 6.15A and cleared when the discharge
current falls below 6.15A.

The SEDV values are:

Where SEDV is:

0 Current < 6.15A

1 Current > 6.15A

The First End-of-Discharge Voltage flag (EDV1), bit 1, is
set when Voltage < EDV1 and SEDV = 0 and cleared
when VQ = 1 and Voltage > EDV1.

The EDV1 values are:

Where EDV1 is:

0 VQ = 1 and Voltage > EDV1

1 Voltage < EDV1 and SEDV = 0

The Final End-of-Discharge Voltage flag (EDVF), bit 0,
is set when Voltage < EDVF and SEDV = 0 and cleared
when VQ = 1 and Voltage > EDVF.

The EDVF values are:

Where EDVF is:

0 VQ = 1 and Voltage > EDVF

1 Voltage < EDVF and SEDV = 0

Error Codes and Status Bits

Error codes and status bits are listed in Table 8 and Ta

­ble 9, respectively.

19

bq2945

FLAGS1 Bits

7654321 0

- - - - - - - EDVF

FLAGS1 Bits

76543 2 10

- - - - - SEDV - -

FLAGS1 Bits

765432 1 0

- - - - - - EDV1 -

FLAGS1 Bits

76 5 43210

--VQ -----

FLAGS1 Bits

7654 3 210

- - - - VDQ - - -

FLAGS2 Bits

765432 1 0

------ - OC

Control Pins 1 and 2 (CP1, CP2)

CP1and CP2are open drain outputs that are controlled
by host command. Since they are under the control of
the host, their use can be defined by the pack designer.
Some uses for these pins are charger control, control of
current path (charge FET, discharge FET, or fuse), or
special LED function. CP

1

and CP2are controlled by the

host writing a command to the battery’s Manufactur

-

erAccess slave function. Table 7 describes the com

-

mands that are available to control CP

1

and CP2.

The CP

2

can also act as a digital input. The logical

status can be monitored in bit 6 of the FLAGS2 register.

SBD Seal

The bq2945 address space can be “locked” to enforce the
SBS specified access to each command code. To lock the
address space, the bq2945 must be initialized with EE
0x3d set to 00h. Once this is done, only commands
0x00-0x04 may be written. Attempting to write to any
other address will cause a “no acknowledge” of the data.
Reading will only be permitted from the command codes
listed in the SBD specification plus the five locations
designated as optional manufacturing functions 1—5
(0x2f, 0x3c—0x3f).

Programming the bq2945

The bq2945 requires the proper programming of an ex

­ternal EEPROM for proper device operation. Each mod

­ule can be calibrated for the greatest accuracy, or gen

­eral “default” values can be used. An EV2200-45 pro

­gramming kit (interface board, software, and cable) for
an IBM-compatible PC is available from Unitrode.

The bq2945 uses a 24LC01 or equivalent serial EE

­PROM (capable of read operation to 2.0V) for storing the
various initial values, calibration data, and string infor

­mation. Table 1 outlines the parameters and addresses
for this information. Tables 10 and 11 detail the various
register contents and show an example program value
for an 2400mAh 4-series Li-Ion battery pack, using a
50mΩsense resistor.

20

bq2945

Table 7. ManufactureAccess Commands

CMD (0x00) = Action

0x0505 CP

1

set to hi-Z

0x051b CP

1

set low

0x0536 CP

2

set to hi-Z

0x054e CP

2

set low

0x0563 CP

1

and CP2set to hi-Z

0x057d CP

1

and CP2set low

21

bq2945

Error Code Access Description

OK 0x0000 read/write bq2945 processed the function code without detecting any errors.

Busy 0x0001 read/write bq2945 is unable to process the function code at this time.

ReservedCommand 0x0002 read/write

bq2945 cannot read or write the data at this time—try again
later.

UnsupportedCommand 0x0003 read/write bq2945 does not support the requested function code.

AccessDenied 0x0004 write

bq2945 detected an attempt to write to a read-only function
code.

Overflow/Underflow 0x0005 read/write bq2945 detected a data overflow or underflow.

BadSize 0x0006 write

bq2945 detected an attempt to write to a function code with an
incorrect size data block.

UnknownError 0x0007 read/write bq2945 detected an unidentifiable error.

Note: Reading the bq2945 after an error clears the error code.

Table 8. Error Codes (BatteryStatus() (0x16))

22

bq2945

Alarm Bits

Bit Name Set When: Reset When:

OVER_CHARGED_ALARM

The bq2945 detects a ∆T/∆t or cur

-

rent taper termination. (Note:

∆T/∆t and current taper are valid
charge terminations.)

A discharge occurs or when the
∆T/∆t or current taper termination
condition ceases during charge.

TERMINATE_CHARGE_ALARM

The bq2945 detects an over-current,
over-voltage, over-temperature,
∆T/∆t, or current taper condition
during charge.

A discharge occurs or when all condi

-

tions causing the event cease.

OVER_TEMP_ALARM

The bq2945 detects that its internal
temperature is greater than the pro

-

grammed value.

Internal temperature falls below
50°C.

TERMINATE_DISCHARGE_ALARM

The bq2945 determines that it has
supplied all the charge that it can
without being damaged (Voltage <
EDVF).

Voltage > EDVF signifies that the
battery has reached a state of charge
sufficient for it to once again safely
supply power.

REMAINING_CAPACITY_ALARM

The bq2945 detects that the Remain­ingCapacity is less than that set by
the RemainingCapacityAlarm func­tion.

Either the value set by the Remain­ingCapacityAlarm function is lower
than the Remaining Capacity or the
RemainingCapacity is increased by
charging.

REMAINING_TIME_ALARM

The bq2945 detects that the esti­mated remaining time at the present
discharge rate is less than that set
by the RemainingTimeAlarm func­tion.

Either the value set by the Remain­ingTimeAlarm function is lower than
the AverageTimeToEmpty or a valid
charge is detected.

Status Bits

Bit Name Set When: Reset When:

INITIALIZED

The bq2945 has completed a “learn”
cycle.

Battery detects that power-on or
user-initiated reset has occurred.

DISCHARGING

The bq2945 determines that it is not
being charged.

Battery detects that it is being
charged.

FULLY_CHARGED

The bq2945 determines a valid
charge termination or a maximum
overcharge state.

RM discharges below 95% of the full
charge percentage.

FULLY_DISCHARGED

bq2945 determines that it has
supplied all the charge that it can
without being damaged.

RelativeStateOfCharge is greater
than or equal to 20%

Table 9. BatteryStatus Bits

23

bq2945

Description

EEPROM

Address

EEPROM

Hex Contents

Example

Values Notes

Low

Byte

High
Byte

Low

Byte

High

Byte

EEPROM
length

0x00 64 100 Must be equal to 0x64.

EEPROM check
1

0x01 5b 91 Must be equal to 0x5b.

Remaining time
alarm

0x02 0x03 0a 00 10 minutes Sets the low time alarm level.

Remaining
capacity
alarm

0x04 0x05 f0 00 240mAh Sets the low capacity alarm level.

Reserved 0x06 0x07 00 00 0 Not currently used by the bq2945.

Initial charg

-

ing current

0x08 0x09 60 09

2400mA

Sets the initial charge request.

Charging
voltage

0x0a 0x0b d8 40 16600mV

Used to set the fast-charge voltage for the Smart
Charger.

Battery status 0x0c 0x0d 80 00 128 Initializes BatteryStatus.

Cycle count 0x0e 0x0f 00 00 0

Contains the charge cycle count and can be set to zero
for a new battery.

Design
capacity

0x10 0x11 60 09 2400mAh Nominal battery pack capacity.

Design
voltage

0x12 0x13 40 38 14400mV Nominal battery pack voltage.

Specification
information

0x14 0x15 10 00 1.0 Default value for this register in a 1.0 part.

Manufacturer
date

0x16 0x17 a1 20

May 1, 1996

= 8353

Packed per the ManufactureDate description.

Serial number 0x18 0x19 12 27 10002 Contains the optional pack serial number.

Fast-charging
current

0x1a 0x1b 60 09 2400mA

Used to set the fast-charge current for the Smart
Charger.

Maintenance
charge
current

0x1c 0x1d 00 00 0mA

Contains the desired maintenance current after fast­charge termination by the bq2945.

Reserved 0x1e 0x1f 00 00 0 Must be programmed to 0x00.

Current inte

-

gration gain

1

0x2c 0x2d 40 00 3.2/0.05

Represents the following: 3.2/sense resistor in ohms.
It is used by the bq2945 to scale the measured voltage
values on the SR pin in mA and mAh. This register
also compensates for variations in the reported sense
resistor value.

Note: 1. Can be adjusted to calibrate the battery pack.

Table 10. Example Register Contents

24

bq2945

Description

EEPROM

Address

EEPROM

Hex

Contents

Example

Values Notes

Low
Byte

High
Byte

Low

Byte

High

Byte

Reserved 0x2e 0x2f 00 00 0 Not currently used by the bq2945.

Li-Ion taper
current

0x38 0x39 10 ff 240mA

Sets the upper taper limit for Li-Ion charge termina

-

tion. Stored in 2’s complement.

Maximum
overcharge
limit

0x3a 0x3b 9c ff 100mAh

Sets the maximum amount of overcharge before a
maximum overcharge charge suspend occurs.
Stored in 2’s complement.

Reserved 0x3c 00 0 Should be programmed to 0.

Access protect 0x3d 00 SBD access only

If the bq2945 is reset and this location is 0, the
bq2945 locks access to any command outside of the
SBD data set. Program to 0x08 for full R/W access.

FLAGS1 0x3e 00 0 Initializes FLAGS1

FLAGS2 0x3f b0

Relative display

Li-Ion chemistry

bq2945 charge

control

Initializes FLAGS2.

Battery voltage
offset

1

0x48 fe -2mV

Used to adjust the battery voltage offset according to
the following:
Voltage = (V

SB

(mV) + V

OFF

) ∗ Voltage gain

Temperature
offset

1

0x49 8a

13.8°C

The default value (zero adjustment) for the offset is

12.8°C or 0x80.
TOFF

NEW

= TOFF

CURRENT

+

(TEMP

ACTUAL

- TEMP

REPORTED

)∗ 10

Maximum tem

-

perature and
∆T step

0x4a 8f

Maximum

temperature =

61.2°C

∆T step = 4.6°C

Maximum charge temperature is 74 - (mt ∗ 1.6)°C (mt
= upper nibble). The ∆T step is (dT ∗ 2 + 16)/10°C
(dT = lower nibble)

Charge
efficiency

0x4b ff

Maintenance

compensation =

100%

Fast compensa

-

tion = 100%

Sets the fast-charge (high) and maintenance charge
(low) efficiencies. The upper nibbles sets the low ef

-

ficiency and the lower nibble adjusts the high effi

-

ciency according to the equation:
Nibble = (efficiency% ∗ 256 - 196)/4

Full-charge
percentage

0x4c 9c 100%

This packed field is the two’s complement of the de

­sired value in RM when the bq2945 determines a
full-charge termination. If RM is below this value,
RM is set to this value. If RM is above this value,
then RM is not adjusted.

Note: 1. Can be adjusted to calibrate the battery pack.

Table 10. Example Register Contents (Continued)

25

bq2945

Description

EEPROM

Address

EEPROM

Hex

Contents

Example

Values Notes

Low

Byte

High

Byte

Low

Byte

High
Byte

Digital filter 0x4d 96 0.30mV

Used to set the digital magnitude filter as described in
Table 2.

Reserved 0x4e 00 0 Not currently used by the bq2945.

Self-discharge rate 0x4f 2d 0.25%

This packed field is the two’s complement of (52.73/x)
where x is the desired self-discharge rate per day (%)
at room temperature.

Voltage gain

1

0x56 0x57 17 07 7.09

Voltage gain is packed as two units. For example,
(R4 + R5)/R4 = 7.09 would be stored as: whole number
stored in 0x57 as 7 and the decimal component stored
in 0x56 as 256 x 0.09 = 23 (= 17h).

Reserved 0x58 0x59 00 00 0 Should be programmed to 0.

Current measure­ment gain

1

0x5a 0x5b ee 02 750

The current gain measurement and current integra­tion gain are related and defined for the bq2945 cur­rent measurement. This word equals 37.5/sense resis­tor value in ohms.

End of discharge
voltage1

0x5c 0x5d 20 d1 12000mV

The value programmed is the two’s complement of the
threshold voltage in mV.

End of discharge
voltage final

0x5e 0x5f 40 d4 11200mV

The value programmed is the two’s complement of the
threshold voltage in mV.

Full charge
capacity

0x60 0x61 d0 07 2000mA This value sets the initial estimated pack capacity.

∆t step

0x62 ff 20s

The ∆t step for ∆T/∆t termination equals 20s ∗ the
two’s complement of the byte value.

Hold-off time 0x63 f0 320s hold-off

The hold-off time is 20s ∗ the two’s complement of the
byte value.

EEPROM check 2 0x64 b5 181 Must be equal to 0xb5.

Reserved 0x65 0x7f NA Not currently used by the bq2945.

Note: 1. Can be adjusted to calibrate the battery pack.

Table 10. Example Register Contents (Continued)

26

bq2945

String Description Address0xX00xX10xX20xX30xX40xX50xX60xX70xX80xX9-Xf0xxa0xxb

Manufacturer name

0x20­0x2b

09

42B45E4eN43C48H4dM41A52R51

Q

--

Device name

0x30­0x37

06

42B51Q32239934435

5

-

Device chemistry

0x40­0x47

04

6cL69I4fO4e

N

-

Manufacturer data

0x50­0x55

05

42B51Q32230032

2

Table 11. Example Register Contents (String Data)

27

bq2945

Absolute Maximum Ratings

Symbol Parameter Minimum Maximum Unit Notes

V

CC

Relative to V

SS

-0.3 +7.0 V

All other pins Relative to V

SS

-0.3 +7.0 V

REF Relative to V

SS

-0.3 +8.5 V Current limited by R1 (See Figure 1.)

V

SR

Relative to V

SS

-0.3 +7.0 V

Minimum 100Ωseries resistor should
be used to protect SR in case of a
shorted battery.

T

OPR

Operating tempera

-

ture

0 +70 °C Commercial

Note: Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional opera

-

tion should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Expo

-

sure to conditions beyond the operational limits for extended periods of time may affect device reliability.

DC Voltage Thresholds (T

A=TOPR

; V = 3.0 to 5.5V)

Symbol Parameter Minimum Typical Maximum Unit Notes

E

VSB

Battery voltage error relative to SB -50mV - 50mV V See note

Note: The accuracy of the voltage measurement may be improved by adjusting the battery voltage offset and

gain, stored in external EEPROM. For best operation, V

CC

should be 1.5V greater than VSB.

28

bq2945

Recommended DC Operating Conditions (T

A

= T

OPR

)

Symbol Parameter Minimum Typical Maximum Unit Notes

V

CC

Supply voltage 3.0 4.25 6.5 V

V

CC

excursion from < 2.0V to

≥

3.0V initializes the unit.

V

REF

Reference at 25°C 5.7 6.0 6.3 V I

REF

= 5µA

Reference at -40°C to +85°C 4.5 - 7.5 V I

REF

= 5µA

R

REF

Reference input impedance 2.0 5.0 - MΩV

REF

= 3V

I

CC

Normal operation

- 90 135

µ

AV

CC

= 3.0V

- 120 180

µ

AV

CC

= 4.25V

- 170 250

µ

AV

CC

= 5.5V

V

SB

Battery input 0 - V

CC

V

R

SBmax

SB input impedance 10 - - MΩ0 < VSB< V

CC

I

DISP

DISP input leakage - - 5

µ

AV

DISP

= V

SS

I

LVOUT

V

OUT

output leakage -0.2 - 0.2

µ

A EEPROM off

V

SR

Sense resistor input -0.3 - 2.0 V

V

SR<VSS

= discharge;

V

SR

> VSS= charge

R

SR

SR input impedance 10 - - MΩ-200mV < VSR< V

CC

V

IH

Logic input high

0.5 ∗ V

CC

-

V

CC

V ESCL, ESDA

1.4 - 5.5 V SMBC, SMBD

V

IL

Logic input low

0-

0.3 ∗ V

CC

V ESCL, ESDA

-0.5 0.6 V SMBC, SMBD

V

OL

Data, clock output low - - 0.4 V IOL=350µA, SMBC, SMBD

I

OL

Sink current 100 - 350

µ

AV

OL

≤

0.4V, SMBC, SMBD

V

OLSL

LEDX,CP1,CP2output low,
low V

CC

- 0.1 - V

V

CC

= 3V, I

OLS

≤

1.75mA

LED

1

–LED5,CP1,CP

2

V

OLSH

LEDX,CP1,CP2output low,
high V

CC

- 0.4 - V

V

CC

= 6.5V, I

OLS

≤

11.0mA

LED

1

–LED5,CP1,CP

2

V

OHVL

V

OUT

output, low V

CC

VCC- 0.3 - - V VCC= 3V, I

VOUT

= -5.25mA

V

OHVHVOUT

output, high V

CC

VCC- 0.6 - - V VCC= 6.5V, I

VOUT

= -33.0mA

I

VOUT

V

OUT

source current -33 - - mA At V

OHVH

= VCC- 0.6V

I

OLS

LEDX,CP1,CP2sink current 11.0 - mA At V

OLSH

= 0.4V

Note: All voltages relative to VSS.

29

bq2945

Symbol Parameter Min Max Units Notes

F

SMB

SMBus operating frequency 10 100 KHz

T

BUF

Bus free time between stop and
start condition

4.7

µ

s

T

HD:STA

Hold time after (repeated) start
condition

4.0

µ

s

T

SU:STA

Repeated start condition setup time 4.7

µs

T

SU:STO

Stop condition setup time 4.0

µ

s

T

HD:DAT

Data hold time 300 ns

T

SU:DAT

Data setup time 250 ns

T

LOW

Clock low period 4.7

µ

s

T

HIGH

Clock high period 4.0

µ

s

T

F

Clock/Data fall time 300 ns

T

R

Clock/data rise time 1000 ns

T

LOW:SEXT

Cumulative clock low extend time
(slave)

25 ms

T

TIMEOUT

25 35 ms

AC Specifications

TD294501.eps

t

SU:STA

SMBC

SMBD

t

SU:STO

t

BUF

t

HD:STA

t

LOW

t

SU:DAT

t

R

t

F

t

HIGH

t

HD:DAT

Bus Timing Data

30

bq2945

16-Pin SOIC Narrow (SN)

16-Pin SN(SOIC Narrow

)

Dimension Minimum Maximum

A 0.060 0.070

A1 0.004 0.010

B 0.013 0.020
C 0.007 0.010
D 0.385 0.400
E 0.150 0.160

e 0.045 0.055
H 0.225 0.245
L 0.015 0.035

All dimensions are in inches.

A

A1

.004

C

B

e

D

E

H

L

31

bq2945

Ordering Information

bq2945

Package Option:

SN = 16-pin narrow SOIC

Device:

bq2945 Gas Gauge IC With SMBus Interface

Temperature Range:

blank = Commercial (0 to 70°C)

ChangeNo. Page No. Description of Change

1 All “Final” changes from “Preliminary” version

2 6 Added V

SB

should not exceed 2.4V

2 11 Changed cycle count increase from 30 to 32 for condition request

2 14 Changed AtRateOK() indication from EDV1 to EDVF

2 25 Changed self discharge programming from 52.75/x to 52.73/x

Notes: Change 1 = June 1998 B changes from Sept. 1997 “Preliminary.”

Change 2 = June 1999 C changes from June 1998.

Data Sheet Revision History

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