BQ2945_技术文档

bq2945

Gas Gauge IC with SMBus Interface

The bq2945 estimates battery self-

discharge based on an internal

Features

General Description

timer and temperature sensor and

The bq2945 Gas Gauge IC With

user-programmable rate informa-

SMBus Interface is intended for

tion stored in external EEPROM.

battery-pack or in-system installa-

The bq2945 also automatically re-

tion to maintain an accurate record

calibrates or “learns” battery capac-

of available battery charge. The

ity in the full course of a discharge

bq2945 directly supports capacity

cycle from full to empty.

➤ Provides accurate measurement

of available charge in NiCd,

NiMH, and Li-Ion batteries

➤ Supports SBS v1.0 data set and

two-wire interface

monitoring for NiCd, NiMH, and

➤ Two programmable general

purpose output ports for added

flexibility

Li-Ion battery chemistries.

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.

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.

➤ Designed for battery pack inte-

gration

- ^{Low operating current}

- ^{Complete circuit can fit on less}

than ¾ square inch of PCB

space

An external EEPROM programs

initial values into the bq2945 and is

necessary for proper operation.

➤ 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

Pin Connections

Pin Names

SR

Sense resistor input

Display control input

Battery sense input

Control pin 2

V_CC

3.0–6.5V

DISP

SB

LED₁

LED segment 1/

EEPROM clock

V

1

2

3

4

5

6

16

15

14

13

12

11

V

OUT

CC

LED /ESCL

REF

1

LED₂

LED segment 2/

EEPROM data

CP₂

LED /ESDA

SMBC

SMBD

2

SMBD SMBus data input/output

SMBC SMBus clock

LED₃

LED₄

LED₅

CP₁

LED segment 3

LED segment 4

LED segment 5

Control pin 1

LED

CP

3

4

5

CP

SB

2

REF

Voltage reference output

EEPROM supply output

7

8

10

9

DISP

SR

V_OUT

1

V

SS

V_SS

System ground

16-Pin Narrow SOIC

PN294501.eps

6/99 C

1

bq2945

Display control input

DISP

Pin Descriptions

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.

Supply voltage input

V_CC

LED display segment outputs

LED₁–

LED₅

Each output may drive an external LED.

Secondary battery input

SB

Serial memory clock

ESCL

Monitors the pack voltage through a high-

impedance 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.

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.

SMBus data

SMBD

Open-drain bidirectional pin used to trans-

fer address and data to and from the

bq2945.

Control pins 1 and 2

CP₁–

CP₂

SMBus clock

SMBC

REF

These open-drain outputs can be con-

trolled by an SMBus command from the

host. CP₂can also act as a digital input.

Open-drain bidirectional pin used to clock

the data transfer to and from the bq2945.

Ground

V_SS

SR

Reference output for regulator

Sense resistor input

REF provides a reference output for an op-

tional FET-based micro-regulator.

The voltage drop (V_SR) across pins SR and

V

_SSis monitored and integrated over time

Supply output

V_OUT

to interpret charge and discharge activity.

The SR input is connected to the sense re-

sistor and the negative terminal of the

battery. V_SR< V_SSindicates discharge, and

V_SR> V_SSindicates charge. The effective

voltage drop, V_SRO, as seen by the bq2945

is V_SR+ V_OS. (See Table 3.)

Supplies power to the external EEPROM

configuration memory.

2

bq2945

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.

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.

An internal temperature sensor eliminates the need

for an external thermistor—reducing cost and compo-

nents. An internal, temperature-compensated time-

base eliminates the need for an external resonator,

further reducing cost and components. The entire cir-

3

cuit in Figure 1 can occupy less than square inch of

4

board space.

Chart 1

No. of Cells

Q1

R4

R5

R11

604K

806K

604K

See Chart 1 for resistor values and

Q1 FET selection

2

BSS138

2N7002

301K

499K

698K

100K

3

4

6

8

9

499K

698K

499K

806K

499K

604K

BSS138 100K

Notes:

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

R12 and R13 nominal values must be 10k

2N7002 100K 806K

100K

10

12

2N7002

909K

86.5K

909K

Figure 1. Battery Pack Application Diagram—LED Display

3

bq2945

Table 1. Configuration Memory Map

Parameter Name

Address

Description

Length

Units

Number of EEPROM data locations

must = 0x64

EEPROM length

EEPROM check1

0x00

0x01

8 bits

NA

EEPROM data integrity check byte

must = 0x5b

8 bits

NA

Remaining time alarm

Remaining capacity alarm

Reserved

0x02/0x03 Sets RemainingTimeAlarm (0x02)

0x04/0x05 Sets RemainingCapacityAlarm (0x01)

0x06/0x07 Reserved for future use

16 bits

96 bits

16 bits

64 bits

minutes

mAh

NA

Initial charging current

Charging voltage

Battery status

0x08/0x09 Sets the initial charging current

0x0a/0x0b Sets ChargingVoltage (0x15)

0x0c/0x0d Initializes BatteryStatus (0x16)

0x0e/0x0f Initializes and stores CycleCount (0x17)

0x10/0x11 Sets DesignCapacity (0x18)

mA

mV

NA

Cycle count

cycles

mAh

mV

Design capacity

Design voltage

0x12/0x13 Sets DesignVoltage (0x19)

Specification information

Manufacturer date

Serial number

0x14/0x15 Programs SpecificationInfo (0x1a)

0x16/0x17 Programs ManufactureDate (0x1b)

0x18/0x19 Programs SerialNumber (0x1c)

0x1a/0x1b Sets ChargingCurrent (0x14)

NA

Fast-charging current

mA

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

mA

Reserved

0x1e/0x1f Reserved must = 0x0000

mAh

NA

Manufacturer name

Current integration gain

Reserved

0x20-0x2b Programs ManufacturerName (0x20)

0x2c/0x2d Programs the sense resistor scale

0x2e/0x2f Reserved for future use

NA

Device name

0x30-0x37 Programs DeviceName (0x21)

NA

Sets the upper limit of the taper current for charge

termination

Li-Ion taper current

0x38/0x39

16 bits

mA

Maximum overcharge limit

Reserved

0x3a/0x3b Sets the maximum amount of overcharge

16 bits

8 bits

64 bits

8 bits

NA

0x3c

0x3d

0x3e

0x3f

Reserved must = 0x00

Access protect

Locks commands outside of the SBS data set

Initializes FLAGS1

FLAGS1

FLAGS2

Initializes FLAGS2

Device chemistry

Battery voltage offset

Temperature offset

0x40-0x47 Programs DeviceChemistry (0x22)

0x48

0x49

Voltage calibration value

Temperature calibration value

Maximum temperature and

∆T step

Sets the maximum charge temperature and the ∆T

step for ∆T/∆t termination

0x4a

8 bits

NA

4

bq2945

Table 1. Configuration Memory Map (Continued)

Parameter Name

Charge efficiency

Address

Description

Length

Units

0x4b

Sets the high/low charge rate efficiencies

8 bits

NA

Sets the percent at which the battery is consid-

ered fully charged

Full-charge percentage

0x4c

8 bits

NA

Digitial filter

0x4d

0x4e

0x4f

Sets the minimum charge/discharge threshold

Reserved for future use

8 bits

NA

mAh

NA

Reserved

Self-discharge rate

Manufacturer data

Voltage gain1

Sets the battery’s self-discharge rate

8 bits

0x50-0x55 Programs ManufacturerData (0x23)

0x56/0x57 Battery divider calibration value

0x58-0x59 Reserved

48 bits

16 bits

8 bits

Reserved

Current measurement gain

End of discharge voltage1

0x5a/0x5b Sense resistor calibration value

0x5c/0x5d Sets EDV1

End of discharge voltage final 0x5e/0x5f Sets EDVF

Full-charge capacity

∆t step

0x60/0x61 Initializes and stores FullChargeCapacity (0x10)

0x62

0x63

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

Sets ∆T/∆t hold-off timer

Hold-off time

8 bits

EEPROM data integrity check byte

must = 0xb5

EEPROM check 2

Reserved

0x64

8 bits

NA

0x65-0x7f Reserved for future use

5

bq2945

Voltage Thresholds

Layout Considerations

In conjunction with monitoring V_SRfor 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:

The bq2945 measures the voltage differential between

the SR and V_SSpins. V_OS(the offset voltage at the SR

pin) is greatly affected by PC board layout. For optimal

results, the PC board layout should follow the strict rule

of a single-point ground return. Sharing high-current

ground with small signal ground causes undesirable

noise on the small signal nodes. Additionally, in refer-

ence to Figure 1:

R₅

R₄

MBV

2.25

=

− 1

where MBV is the maximum battery voltage, R₅is con-

nected to the positive battery terminal, and R₄is con-

nected to the negative battery terminal. R₅/R₄should be

rounded to the next higher integer. R₅and R₄should be

sized so that the voltage at the SB pin (V_SB) should

never exceed 2.4V.

n

The capacitors (C1 and C2) should be placed as close as

possible to the SB and V_CCpins, 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.

The battery voltage is monitored for the end-of-

discharge 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.

The bq2945 should be in thermal contact with the

cells for optimum temperature measurement.

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

V_CCis not above the maximum rating during

operation.

Gas Gauge Operation

If V_SBis below either of the two EDV thresholds, the associ-

ated flag is latched and remains latched, independent of

The operational overview diagram in Figure 2 illus-

trates the operation of the bq2945. The bq2945 accumu-

lates 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.

V_SB, until the next valid charge.

EDV monitoring may be disabled under certain condi-

tions. If the discharge current is greater than approxi-

mately 6A, EDV monitoring is disabled and resumes af-

ter the current falls below 6A.

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).

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.

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.

Temperature

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.

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.

1. FullChargeCapacity or learned-battery

capacity:

FCC is the last measured discharge capacity of the

battery. On initialization (application of V_CCor reset),

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

ing subsequent discharges, FCC is updated with the

6

bq2945

Charge

Current

Discharge

Current

Self-Discharge

Timer

Inputs

State-of-charge

and

Temperature

Compensation

Temperature

Compensation

+

-

Full

Charge

Capacity

(FCC)

Discharge

Count

Register

(DCR)

Remaining

Capacity

(RM)

+

<

Main Counters

and Capacity

Reference (FCC)

Qualified

Transfer

Temperature, Other Data

Chip-Controlled

Available Charge Serial Interface

LED Display

Two-Wire

Outputs

FG294501.eps

Figure 2. Operational Overview

latest measured capacity in the Discharge Count Reg-

ister, representing a discharge from full to below

EDV1. A qualified discharge is necessary for a capac-

ity transfer from the DCR to the FCC register. Once

updated, the bq2945 writes the new FCC to the EE-

PROM. The FCC also serves as the 100% reference

threshold used by the relative state-of-charge calcula-

tion and display.

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 fol-

lowing conditions exist:

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.

n

No valid charge initiations (charges greater than

10mAh), where V_SRO> +V_SRDoccurred during

the period between RM = FCC and EDV1 de-

tected.

3. RemainingCapacity (RM):

n

The self-discharge count is not more than

256mAh.

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 user-

defined 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.

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.

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),

7

bq2945

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_SROfalls be-

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

∆T

∆t

is set by the formula:

=

low V_SRD

.

V_SRDis a programmable threshold as de-

scribed in the Digital Magnitude Filter section.

o

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

[2' s(EE 0x62) ∗ 20]

C

s













Discharge Counting

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.

All discharge counts where V_SRO< -V_SRDcause 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°C to

0°C.

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 ter-

minating conditions cease, the Terminate_Charge_Alarm

and the Over_Charged_Alarm are cleared, and the re-

quested 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.

Charge Control

The bq2945 supports SBS charge control by broadcast-

ing 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 0x08-

0x09. The bq2945 updates the value used in the charg-

ing current broadcasts based on the battery’s state of

charge, voltage, and temperature.

Bit 4 (CC) in FLAGS2 determines whether RM is modi-

fied 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.

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.

Charge Suspension

The bq2945 may temporarily suspend charge if it de-

tects a charging fault. The charging faults include the

following conditions:

Current Taper

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.

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.

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

∆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

8

bq2945

the current drops below 256mA and the voltage is

less than 105% of ChargingVoltage.

Q_ET= 0 if

T < 30°C

Q_ET= 0.02 if 30°C ≤ T < 40°C

Q_ET= 0.05 if T ≥ 40°C

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

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

ChargingCurrent.

When the bq2945 detects an

Digital Magnitude Filter

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.

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.

n

Maximum Temperature: When the battery

temperature exceeds the programmed maximum

temperature, the requested charge current is set to

45

DMF =

zero

and

the

Over_Temp_Alarm

and

the

VSRD

Terminate_Charge_Alarm bits are set in Battery

Status. The alarm bits are cleared when the

temperature drops below 50°C.

Table 2. Typical Digital Filter Settings

DMF

75

DMF Hex.

V_SRD(mV)

0.60

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.

4B

64

100

150

175

200

0.45

96

0.30

AF

C8

0.26

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.

0.23

Error Summary

Capacity Inaccurate

Count Compensations

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.

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_EFC− Q_ET

)

Current-Sensing Error

where RelativeStateOfCharge < FullChargePercentage,

and Q_EFCis the programmed fast-charge efficiency vary-

ing from 0.75 to 1.0.

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< V_SRO< + V_SRD

.

2.) RM = RM * (Q_ETC− Q_ET

)

Display

where RelativeStateOfCharge ≥ FullChargePercentage

and Q_ETCis the programmed maintenance (trickle)

charge efficiency varying from 0.75 to 1.0.

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.

Q_ETis used to adjust the charge efficiency as the battery

temperature increases according to the following:

9

bq2945

Table 3. bq2945 Current-Sensing Errors

Symbol

Parameter

Typical

Maximum

Units

Notes

V_OS

Offset referred to V_SR

75

150

µV

DISP = V_CC.

Integrated non-linearity

error

Add 0.1% per °C above or below 25°C

and 1% per volt above or below 4.25V.

INL

1

4

1

%

Integrated non-

repeatability error

Measurement repeatability given

similar operating conditions.

INR

0.5

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.

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.

When DISP is tied to V_CC, the LED_1-5outputs 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

The interface uses a command-based protocol, where the

host processor sends the battery address and an eight-

bit 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.

V_CCto reactivate the display.

LED₁blinks at a 4Hz rate whenever V_SBhas been de-

tected to be below EDV1 (EDV1 = 1), indicating a low-

battery condition. V_SBbelow EDVF (EDVF = 1) disables

the display output.

bq2945 Data Protocols

Microregulator

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.)

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.

Host-to-bq2945 Message Protocol

The Bus Host communicates with the bq2945 using one

of three protocols:

n

Read word

Write word

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

1

7

1

0

1

8

1

8

1

8

1

Battery Address

S

A

Command Code

A

Data byte low

A

Data byte high

A

P

0001011

Write Word

1

7

1

0

1

8

1

7

1

Battery Address

S

A

Command Code

A

S

Battery Address

A

0001011

8

1

8

1

Data byte low

A

Data byte high

A

P

System Host

Read Word

1

7

1

0

1

8

1

7

1

bq2945

Battery Address

0001011

S

A

Command Code

A

S

Battery Address

A

A – ACKNOWLEDGE

A – NOT ACKNOWLEDGE

S – START

8

1

8

1

8

1

8

1

Byte Count =N

A

Data byte 1

A

Data byte 2

A

Data byte N

A

P

P – STOP

Block Read

FG294501.eps

Figure 3. Host Communication Protocols

RemainingCapacityAlarm() (0x01)

BatteryMode() (0x03)

This function sets or returns the low-capacity alarm

value. When RM falls below the RemainingCapac-

ityAlarm value initialized from the external EE-

PROM, the Remaining_Capacity_Alarm bit is set in

BatteryStatus. The system may alter this alarm dur-

ing operation.

This read/write word selects the various battery opera-

tional modes. The bq2945 supports the battery capacity

information specified in mAh. This function also deter-

mines whether the bq2945 charging values are broad-

casted 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).

Input/Output: unsigned integer. This sets/returns

the value where the Remaining_Capacity_Alarm

bit is set in Battery Status.

Units: mAh

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.

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.

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)

Input/Output: unsigned integer. This sets/returns

the value where the Remaining_Time_Alarm bit is

set in Battery Status.

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.

Units: minutes

Range: 0 to 65,535 minutes

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

Table 4. bq2945 Register Functions

Function

Code

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0x09

0x0a

0x0b

0x0c

Access

read/write

read

Units

-

Defaults¹

ManufacturerAccess

Remaning_Capacity_Alarm

Remaining_Time_Alarm

BatteryMode

-

E²

-

mAh

minutes

bit flag

mA

AtRate

-

AtRateTimeToFull

AtRateTimeToEmpty

AtRateOK

minutes

Boolean

0.1°K

mV

-

read

-

read

-

Temperature

read

2930

E²

0

Voltage

read

Current

read

mA

AverageCurrent

MaxError

read

mA

0

read

percent

mAh

100

-

RelativeStateOfCharge

AbsoluteStateOfCharge

RemainingCapacity

FullChargeCapacity

RunTimeToEmpty

AverageTimeToEmpty

AverageTimeToFull

ChargingCurrent

ChargingVoltage

Battery Status

0x0d

0x0e

0x0f

read

-

read

E²

-

0x10

0x11

0x12

0x13

0x14

0x15

0x16

0x17

0x18

0x19

0x1a

0x1b

0x1c

read

mAh

read

minutes

mA

read

-

read

-

read

E²

-

read

mV

read

bit flags

cycle

CycleCount

read

DesignCapacity

DesignVoltage

read

mAh

read

mV

Specification Info

ManufactureDate

SerialNumber

read

-

read

-

read

integer

-

Reserved

0x1d - 0x1f

0x20

0x21

-

ManufacturerName

DeviceName

read

string

E²

read

Note:

1. Defaults after reset or power-up.

12

bq2945

Table 4. bq2945 Register Functions (Continued)

Function

DeviceChemistry

Code

0x22

0x23

0x2f

Access

read

Units

string

bit flags

-

Defaults¹

E²

ManufacturerData

read

FLAG1 and FLAG2

read

End of Discharge Voltage 1 (EDV1)

0x3e

read

End of Discharge Voltage Final

(EDVF)

0x3f

read

-

E²

Note:

1. Defaults after reset or power-up.

13

bq2945

n

When the AtRate value is negative, the

AtRateTimeToEmpty function returns the predicted

operating time at the AtRate value of discharge.

Output: unsigned integer. Returns the cell tem-

perature in tenths of degrees Kelvin increments.

Units: 0.1°K

Input/Output: signed integer. AtRate is positive

for charge and negative for discharge.

Range: 0 to +500.0°K

Granularity: 0.5°K or better

Accuracy: 3°K after calibration

Units: mA

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

Voltage() (0x09)

AtRateTimeToFull() (0x05)

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

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 battery ter-

minal voltage in mV.

Units: mV

Output: unsigned integer. Returns the predicted

time to full charge.

Range: 0 to 65,535mV

Granularity: 0.2% of DesignVoltage

Accuracy: 1% of DesignVoltage after calibration

Units: minutes

Range: 0 to 65,534min

Granularity: 2 min or better

Current() (0x0a)

Invalid Data Indication: 65,535 indicates that the

AtRate value is negative.

This read-only word returns the current through the

battery's terminals (mA).

AtRateTimeToEmpty() (0x06)

Output: signed integer. Returns the charge/dis-

charge rate in mA, where positive is for charge

and negative is for discharge

This read-only word returns the predicted remaining op-

erating time if the battery is discharged at the AtRate

value and is valid only if read immediately after an

AtRate command.

Units: mA

Range: 0 to 32,767mA for charge or 0 to

–32,768mA for discharge

Output: unsigned integer. Returns the predicted

time to empty.

Granularity: 0.2% of the DesignCapacity or better

Accuracy: 1% of the DesignCapacity after calibration

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

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.

Invalid Data Indication: 65,535 indicates that the

AtRate value is not negative.

AtRateOK() (0x07)

Output: signed integer. Returns the charge/dis-

charge rate in mA, where positive is for charge

and negative is for discharge

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: mA

Range: 0 to 32,767mA for charge or 0 to

–32,768mA for discharge

Units: Boolean

Range: TRUE ≠ 0, FALSE = 0

Granularity: 0.2% of the DesignCapacity or better

Accuracy:

bration

1% of the DesignCapacity after cali-

Temperature() (0x08)

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

temperature.

14

bq2945

MaxError() (0x0c)

Granularity: 0.2% of DesignCapacity or better

Returns the expected margin of error (%) in the state of

charge calculation.

Accuracy: MaxError ∗ FCC after circuit and ca-

pacity calibration

Output: unsigned integer. Returns the percent un-

certainty for selected information.

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.

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 estimated full

charge capacity in mAh.

Units: mAh

Range: 0 to 65,535mAh

Output: unsigned integer. Returns the percent of re-

maining capacity.

Granularity: 0.2% of DesignCapacity or better

Units: %

Accuracy: MaxError ∗ FCC after circuit and ca-

pacity calibration

Range: 0 to 100%

Granularity: 1%

RunTimeToEmpty() (0x11)

Accuracy: MaxError after circuit and capacity

calibration

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.

AbsoluteStateOfCharge() (0x0e)

This read-only word returns the predicted remaining

battery capacity expressed as a percentage of DesignCa-

pacity (%). 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 minutes of

operation left.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Output: unsigned integer. Returns the percent of

remaining capacity.

Invalid data indication: 65,535 indicates battery is

not being discharged.

Units: %

AverageTimeToEmpty() (0x12)

Range: 0 to 65,535%

Granularity: 1%

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.

Accuracy: MaxError after circuit and capacity

calibration

Output: unsigned integer. Returns the minutes of

operation left.

RemainingCapacity() (0x0f)

This read-only word returns the predicted remaining

battery capacity. The RemainingCapacity value is ex-

pressed in mAh.

Units: minutes

Range: 0 to 65,534min

Granularity: 2min or better

Output: unsigned integer. Returns the estimated re-

maining capacity in mAh.

Invalid data indication: 65,535 indicates battery

is not being discharged.

Units: mAh

Range: 0 to 65,535mAh

15

bq2945

Invalid data indication: 65,535 indicates that the

Smart Charger should operate as a voltage source

outside its maximum regulated current range.

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).

ChargingVoltage() (0x15)

Output: unsigned integer. Returns the remaining

time in minutes to full.

If enabled, the bq2945 sends the desired voltage in mV

to the Smart Battery Charger.

Units: minutes

Output: unsigned integer. Transmits/returns the

charger voltage output in mV.

Range: 0 to 65,534min

Granularity: 2min or better

Units: mV

Range: 0 to 65,534mV

Invalid data indication: 65,535 indicates battery

is not being charged.

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.

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.

BatteryStatus() (0x16)

This read-only word returns the battery status word.

Units: mA

Output: unsigned integer. Returns the status reg-

ister with alarm conditions bitmapped as shown in

Table 5.

Range: 0 to 65,534mA

Granularity: 0.2% of the design capacity or better

Some of the BatteryStatus flags (Remaining_Capac-

ity_Alarm and Remaining_Time_Alarm) are calculated

based on current. See Table 8 and 9 for definitions.

Table 5. Status Register

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.

Alarm Bits

0x8000

0x4000

0x2000

0x1000

0x0800

0x0400

0x0200

0x0100

Over_Charged_Alarm

Terminate_Charge_Alarm

Reserved

Over_Temp_Alarm

Terminate_Discharge_Alarm

Reserved

Remaining_Capacity_Alarm

Remaining_Time_Alarm

Status Bits

Output: unsigned integer. Returns the count of

charge/discharge cycles the battery has

experienced.

0x0080

0x0040

0x0020

0x0010

Initialized

Units: cycles

Discharging

Range: 0 to 65,535 cycles; 65,535 indicates battery

has experienced 65,535 or more cycles.

Fully_Charged

Fully_Discharged

Error Code

Granularity: 1 cycle

DesignCapacity() (0x18)

0x0000-

0x000f

Reserved for error codes

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

Table 6. Bit Descriptions for FLAGS1 and FLAGS2

(MSB) 7

6

5

4

CC

-

3

-

2

1

0 (LSB)

OC

FLAGS2 DMODE

CP2 DI

-

CHM

VQ

OV

LTF

EDV1

FLAGS1

-

VDQ

SEDV

EDVF

Note: - = Reserved

Output: unsigned integer. Returns the battery ca-

pacity in mAh.

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.

Units: mAh

Range: 0 to 65,535mAh

DesignVoltage() (0x19)

This read-only word returns the theoretical voltage of

a new pack in mV.

Output: string or ASCII character string

DeviceName() (0x21)

Output: unsigned integer. Returns the battery's

normal terminal voltage in mV.

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 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.

Units: mV

Range: 0 to 65,535mV

Specification Info() (0x1a)

Output: string or ASCII character string

This read-only word returns the specification re-

vision the bq2945 supports.

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.

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.

Bits

Used

Output: string or ASCII character string

Field

Format

Allowable Value

ManufacturerData() (0x23)

5-bit binary 1–31 (corresponds to

Day

0–4

value date)

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

manufacturer data string.

4-bit binary 1–12 (corresponds to

Month

Year

5–8

value

month number)

Output: block data—data whose meaning is as-

signed by the Smart Battery's manufacturer.

0

127 (corresponds

*

7-bit binary

value

9–15

to year biased by

1980)

End of Discharge Voltage1 (0x3e)

This read-only word returns the first end-of-discharge

voltage programmed for the pack.

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: two’s complemented unsigned integer.

Returns battery end-of-discharge voltage pro-

grammed in EEPROM in mV.

Output: unsigned integer

17

bq2945

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.

End of Discharge VoltageF (0x3f)

This read-only word returns the final end-of-discharge

voltage programmed for the pack.

The CC values are:

Output: two’s complemented unsigned integer.

Returns battery final end-of-discharge voltage pro-

grammed in EEPROM in mV.

FLAGS2 Bits

7

6

5

4

3

2

1

0

-

CC

-

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.

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

FLAGS2

The Display Mode flag (DMODE), bit 7 determines

whether the bq2945 displays Relative or Absolute capac-

ity.

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 DMODE values are:

FLAGS2 Bits

The OV values are:

7

6

5

4

3

2

1

0

DMODE

-

FLAGS2 Bits

7

6

5

4

3

2

1

0

Where DMODE is:

-

OV

-

0

1

Selects Absolute display

Selects Relative display

Where OV is:

Bit 6 reflects the high/low state of CP2.

0

1

Voltage < 1.05 ChargingVoltage

∗

FLAGS2 Bits

Voltage ≥ 1.05 ChargingVoltage

∗

7

6

5

4

3

2

1

0

Bit 1, the Low Temperature Fault flag (LTF), is set when

temperature < 0°C and cleared when temperature >

5°C.

-

CP2DI

-

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

compensation factors.

The LTF values are:

FLAGS2 Bits

The CHM values are:

7

6

5

4

3

2

1

0

-

LTF

-

FLAGS2 Bits

7

6

5

4

3

2

1

0

Where LTF is:

-

CHM

-

0

1

Temperature > 5°C

Temperature < 0°C

Where CHM is:

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.

0

1

Selects Nickel

Selects Li-Ion

18

bq2945

This flag is cleared when the average current falls below

256mA.

0

1

Self-discharge is greater than 256mAh,

EDV1 = 1 when T < 0°C or VQ = 1

The OC values are:

On first discharge after RM=FCC

FLAGS2 Bits

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.

7

6

5

4

3

2

1

0

-

OC

The SEDV values are:

Where OC is:

FLAGS1 Bits

0

AverageCurrent is less than 1.25 ∗ Charg-

ingCurrent or less than 256mA if charging

current is programmed less than 1024mA

7

6

5

4

3

2

1

0

-

SEDV

-

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.

Where SEDV is:

0

1

Current < 6.15A

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.

FLAGS1

Bits 7 and 6 are reserved.

The EDV1 values are:

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

≥

|V_SRD| and 10mAh of charge has accumulated. This bit

FLAGS1 Bits

is cleared during a discharge and when V_SRO≤ |V_SRD|.

7

6

5

4

3

2

1

0

The VQ values are:

-

EDV1

-

FLAGS1 Bits

Where EDV1 is:

7

6

5

4

3

2

1

0

-

VQ

-

0

1

VQ = 1 and Voltage > EDV1

Voltage < EDV1 and SEDV = 0

Where VQ is:

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.

0

1

V_{SRO ≤}|V_SRD|

V_SRO≥ |V_SRD| and 10mAh of charge has

accumulated

The EDVF values are:

FLAGS1 Bits

Bit 4 is reserved.

7

6

5

4

3

2

1

0

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.

-

EDVF

Where EDVF is:

0

1

VQ = 1 and Voltage > EDVF

Voltage < EDVF and SEDV = 0

The VDQ values are:

FLAGS1 Bits

Error Codes and Status Bits

7

6

5

4

3

2

1

0

-

VDQ

-

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

ble 9, respectively.

Where VDQ is:

19

bq2945

Control Pins 1 and 2 (CP₁, CP₂)

Programming the bq2945

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. CP₁and 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 CP₁and CP₂.

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

50mΩ sense resistor.

The CP₂can also act as a digital input. The logical

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

Table 7. ManufactureAccess Commands

CMD (0x00) =

0x0505

Action

CP₁set to hi-Z

0x051b

CP₁set low

0x0536

CP₂set to hi-Z

0x054e

CP₂set low

0x0563

0x057d

CP₁and CP₂set to hi-Z

CP₁and CP₂set low

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).

20

bq2945

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

Error

Code

Access

Description

OK

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

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

Busy

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

ReservedCommand

UnsupportedCommand

AccessDenied

0x0002 read/write

later.

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

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

0x0004

write

code.

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

Overflow/Underflow

BadSize

bq2945 detected an attempt to write to a function code with an

incorrect size data block.

0x0006

write

UnknownError

0x0007 read/write bq2945 detected an unidentifiable error.

Note:

Reading the bq2945 after an error clears the error code.

21

bq2945

Table 9. BatteryStatus Bits

Alarm Bits

Set When:

Bit Name

Reset When:

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.

OVER_CHARGED_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.

TERMINATE_CHARGE_ALARM

OVER_TEMP_ALARM

The bq2945 detects that its internal

temperature is greater than the pro-

grammed value.

Internal temperature falls below

50°C.

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.

TERMINATE_DISCHARGE_ALARM

Either the value set by the Remain-

ingCapacityAlarm function is lower

than the Remaining Capacity or the

RemainingCapacity is increased by

charging.

The bq2945 detects that the Remain-

ingCapacity is less than that set by

the RemainingCapacityAlarm func-

tion.

REMAINING_CAPACITY_ALARM

REMAINING_TIME_ALARM

The bq2945 detects that the esti-

mated remaining time at the present

discharge rate is less than that set

by the RemainingTimeAlarm func-

tion.

Either the value set by the Remain-

ingTimeAlarm function is lower than

the AverageTimeToEmpty or a valid

charge is detected.

Status Bits

Set When:

Bit Name

Reset When:

The bq2945 has completed a “learn” Battery detects that power-on or

cycle. user-initiated reset has occurred.

INITIALIZED

The bq2945 determines that it is not Battery detects that it is being

DISCHARGING

being charged.

charged.

The bq2945 determines a valid

charge termination or a maximum

overcharge state.

RM discharges below 95% of the full

charge percentage.

FULLY_CHARGED

bq2945 determines that it has

supplied all the charge that it can

without being damaged.

RelativeStateOfCharge is greater

than or equal to 20%

FULLY_DISCHARGED

22

bq2945

Table 10. Example Register Contents

EEPROM

Address

EEPROM

Hex Contents

Example

Values

Low

Byte

High

Byte

Low High

Byte Byte

Description

Notes

EEPROM

length

0x00

64

5b

100

91

Must be equal to 0x64.

Must be equal to 0x5b.

EEPROM check

1

0x01

0x02

Remaining time

alarm

0x03

0x05

0a

f0

00

10 minutes Sets the low time alarm level.

240mAh Sets the low capacity alarm level.

Remaining

capacity

alarm

0x04

Reserved

0x06

0x08

0x07

0x09

00

60

00

09

0

Not currently used by the bq2945.

Sets the initial charge request.

Initial charg-

ing current

2400mA

Charging

voltage

Used to set the fast-charge voltage for the Smart

Charger.

0x0a

0x0b

0x0d

0x0f

d8

80

00

40

00

16600mV

Battery status 0x0c

128

0

Initializes BatteryStatus.

Contains the charge cycle count and can be set to zero

for a new battery.

Cycle count

0x0e

0x10

0x12

0x14

0x16

Design

capacity

0x11

0x13

0x15

60

40

10

09

38

00

2400mAh Nominal battery pack capacity.

14400mV Nominal battery pack voltage.

Design

voltage

Specification

information

1.0

Default value for this register in a 1.0 part.

Manufacturer

date

May 1, 1996

= 8353

0x17

0x19

0x1b

a1

12

60

20

27

09

Packed per the ManufactureDate description.

Contains the optional pack serial number.

Serial number 0x18

10002

Fast-charging

0x1a

Used to set the fast-charge current for the Smart

Charger.

2400mA

current

Maintenance

Contains the desired maintenance current after fast-

charge termination by the bq2945.

charge

0x1c

0x1e

0x1d

0x1f

00

0mA

0

current

Reserved

Must be programmed to 0x00.

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.

Current inte-

gration gain¹

0x2c

0x2d

40

00

3.2/0.05

Note:

1. Can be adjusted to calibrate the battery pack.

23

bq2945

Table 10. Example Register Contents (Continued)

EEPROM

Address

Hex

Contents

Low High Low High

Byte Byte Byte Byte

Example

Values

Description

Notes

Reserved

0x2e 0x2f

0x38 0x39

00

10

00

ff

0

Not currently used by the bq2945.

Li-Ion taper

current

Sets the upper taper limit for Li-Ion charge termina-

tion. Stored in 2’s complement.

240mA

Maximum

overcharge

limit

Sets the maximum amount of overcharge before a

maximum overcharge charge suspend occurs.

Stored in 2’s complement.

0x3a 0x3b

0x3c

9c

00

ff

100mAh

0

Reserved

Should be programmed to 0.

If the bq2945 is reset and this location is 0, the

SBD access only bq2945 locks access to any command outside of the

SBD data set. Program to 0x08 for full R/W access.

Access protect 0x3d

FLAGS1

FLAGS2

0x3e

0x3f

0

Initializes FLAGS1

Relative display

Li-Ion chemistry

bq2945 charge

control

b0

fe

Initializes FLAGS2.

Used to adjust the battery voltage offset according to

the following:

Voltage = (V_SB(mV) + V_OFF) ∗ Voltage gain

Battery voltage

offset¹

0x48

0x49

-2mV

The default value (zero adjustment) for the offset is

Temperature

offset¹

12.8°C or 0x80.

TOFF_NEW= TOFF_CURRENT

8a

13.8°C

+

(TEMP_ACTUAL- TEMP_REPORTED)∗ 10

Maximum

temperature =

61.2°C

Maximum tem-

perature and

∆T step

Maximum charge temperature is 74 - (mt ∗ 1.6)°C (mt

= upper nibble). The ∆T step is (dT ∗ 2 + 16)/10°C

(dT = lower nibble)

0x4a

0x4b

8f

ff

∆T step = 4.6°C

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:

Maintenance

compensation =

100%

Fast compensa-

tion = 100%

Charge

efficiency

Nibble = (efficiency% ∗ 256 - 196)/4

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.

Full-charge

percentage

0x4c

9c

100%

Note:

1. Can be adjusted to calibrate the battery pack.

24

bq2945

Table 10. Example Register Contents (Continued)

EEPROM

Address

Hex

Contents

Example

Values

Low High Low High

Byte Byte Byte Byte

Description

Notes

Used to set the digital magnitude filter as described in

Table 2.

Digital filter

Reserved

0x4d

0x4e

96

00

0.30mV

0

Not currently used by the bq2945.

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.

Self-discharge rate 0x4f

2d

0.25%

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).

Voltage gain¹

Reserved

0x56 0x57 17

0x58 0x59 00

0x5a 0x5b ee

07

00

02

7.09

0

Should be programmed to 0.

The current gain measurement and current integra-

tion gain are related and defined for the bq2945 cur-

rent measurement. This word equals 37.5/sense resis-

tor value in ohms.

Current measure-

ment gain¹

750

End of discharge

voltage1

The value programmed is the two’s complement of the

threshold voltage in mV.

0x5c 0x5d 20

0x5e 0x5f 40

0x60 0x61 d0

d1

d4

07

12000mV

11200mV

2000mA

20s

End of discharge

voltage final

The value programmed is the two’s complement of the

threshold voltage in mV.

Full charge

capacity

This value sets the initial estimated pack capacity.

The ∆t step for ∆T/∆t termination equals 20s ∗ the

two’s complement of the byte value.

0x62

0x63

ff

∆t step

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

byte value.

Hold-off time

f0

320s hold-off

EEPROM check 2 0x64

b5

181

NA

Must be equal to 0xb5.

Reserved

0x65 0x7f

Not currently used by the bq2945.

Note:

1. Can be adjusted to calibrate the battery pack.

25

bq2945

Table 11. Example Register Contents (String Data)

0x

X0

0x

X1

0x

X2

0x

X3

0x

X4

0x

X5

0x

X6

0x

X7

0x

X8

0x

X9-Xf

0x

xa

0x

xb

String Description

Address

0x20-

0x2b

42

B

45

E

4e

N

43

C

48

H

4d

M

41

A

52

R

51

Q

Manufacturer name

09

06

04

05

-

0x30-

0x37

42

B

51

Q

32

2

39

9

34

4

35

5

Device name

-

0x40-

0x47

6c

L

69

I

4f

O

4e

N

Device chemistry

Manufacturer data

-

0x50-

0x55

42

B

51

Q

32

2

30

0

32

2

26

bq2945

Absolute Maximum Ratings

Symbol

V_CC

Parameter

Relative to V_SS

Minimum

-0.3

Maximum

+7.0

Unit

V

Notes

All other pins

REF

-0.3

+7.0

V

-0.3

+8.5

V

Current limited by R1 (See Figure 1.)

Minimum 100Ω series resistor should

be used to protect SR in case of a

shorted battery.

V_SR

Relative to V_SS

-0.3

0

+7.0

+70

V

Operating tempera-

ture

T_OPR

°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 = T

; V = 3.0 to 5.5V)

OPR

A

Symbol

Parameter

Battery voltage error relative to SB

Minimum

Typical

Maximum

Unit

Notes

See note

E_VSB

-50mV

-

50mV

V

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_CCshould be 1.5V greater than V_SB

.

27

bq2945

Recommended DC Operating Conditions (T = T

)

A

OPR

Symbol

Parameter

Supply voltage

Minimum Typical Maximum

Unit

Notes

V_CCexcursion from < 2.0V to ≥

3.0V initializes the unit.

V_CC

3.0

4.25

6.5

V

Reference at 25°C

5.7

4.5

2.0

-

6.0

6.3

7.5

-

V

I_REF= 5µA

V_REF

R_REF

Reference at -40°C to +85°C

Reference input impedance

-

5.0

90

120

170

-

MΩ V_REF= 3V

µA V_CC= 3.0V

µA V_CC= 4.25V

µA V_CC= 5.5V

V

135

180

250

V_CC

-

I_CC

Normal operation

-

V_SB

Battery input

0

R_SBmax

I_DISP

SB input impedance

DISP input leakage

V_OUToutput leakage

10

-

MΩ 0 < V_SB< V_CC

µA V_DISP= V_SS

µA EEPROM off

-

5

I_LVOUT

-0.2

-

0.2

V_SR< V_SS= discharge;

_SR> V_SS= charge

V_SR

R_SR

Sense resistor input

SR input impedance

-0.3

-

2.0

V

10

-

V_CC

MΩ -200mV < V_SR< V_CC

V

ESCL, ESDA

0.5 ∗ V_CC

V_IH

V_IL

Logic input high

Logic input low

1.4

0

5.5

SMBC, SMBD

ESCL, ESDA

0.3 ∗ V_CC

0.6

-0.5

-

SMBC, SMBD

V_OL

I_OL

Data, clock output low

Sink current

-

0.4

I_OL=350µA, SMBC, SMBD

100

350

µA V_OL≤0.4V, SMBC, SMBD

LED_X, CP₁, CP₂output low,

low V_CC

V_CC= 3V, I_OLS≤ 1.75mA

V_OLSL

V_OLSH

-

0.1

0.4

-

V

LED₁–LED₅, CP₁, CP₂

LED_X, CP₁, CP₂output low,

high V_CC

V_CC= 6.5V, I_OLS≤ 11.0mA

LED₁–LED₅, CP₁, CP₂

V

V_OHVL

V_OHVH

I_VOUT

I_OLS

V_OUToutput, low V_CC

V_OUToutput, high V_CC

V_OUTsource current

V_CC- 0.3

V_CC- 0.6

-33

-

V

V_CC= 3V, I_VOUT= -5.25mA

V_CC= 6.5V, I_VOUT= -33.0mA

mA At V_OHVH= V_CC- 0.6V

mA At V_OLSH= 0.4V

LED_X, CP₁, CP₂sink current

11.0

Note:

All voltages relative to V_SS.

28

bq2945

AC Specifications

Symbol

F_SMB

Parameter

Min

Max

Units

Notes

SMBus operating frequency

10

100

KHz

Bus free time between stop and

start condition

µs

T_BUF

4.7

4.0

Hold time after (repeated) start

condition

T_HD:STA

T_SU:STA

T_SU:STO

T_HD:DAT

T_SU:DAT

T_LOW

Repeated start condition setup time

Stop condition setup time

Data hold time

4.7

4.0

300

250

4.7

4.0

µs

ns

µs

ns

Data setup time

Clock low period

T_HIGH

T_F

Clock high period

Clock/Data fall time

Clock/data rise time

300

T_R

1000

Cumulative clock low extend time

(slave)

T_LOW:SEXT

T_TIMEOUT

25

35

ms

25

Bus Timing Data

t_R

t_F

t_HIGH

t_SU:STA

SMBC

t_HD:STA

t_LOW

t_HD:DAT

t_SU:DAT

t_SU:STO

SMBD

t_BUF

TD294501.eps

29

bq2945

16-Pin SOIC Narrow (SN)

(

)

16-Pin SN SOIC Narrow

Dimension

Minimum

0.060

0.004

0.013

0.007

0.385

0.150

0.045

0.225

0.015

Maximum

0.070

0.010

0.020

0.010

0.400

0.160

0.055

0.245

0.035

A

A1

B

D

B

e

C

D

E

e

H

L

H

All dimensions are in inches.

A

C

A1

.004

L

30

bq2945

Data Sheet Revision History

ChangeNo.

Page No.

Description of Change

“Final” changes from “Preliminary” version

Added V_SBshould not exceed 2.4V

1

2

All

6

11

14

25

Changed cycle count increase from 30 to 32 for condition request

Changed AtRateOK() indication from EDV1 to EDVF

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.

Ordering Information

bq2945

Temperature Range:

blank = Commercial (0 to 70°C)

Package Option:

SN = 16-pin narrow SOIC

Device:

bq2945 Gas Gauge IC With SMBus Interface

31

IMPORTANT NOTICE

Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue

any product or service without notice, and advise customers to obtain the latest version of relevant information

to verify, before placing orders, that information being relied on is current and complete. All products are sold

subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those

pertaining to warranty, patent infringement, and limitation of liability.

TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in

accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent

TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily

performed, except those mandated by government requirements.

CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF

DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL

APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR

WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER

CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO

BE FULLY AT THE CUSTOMER’S RISK.

In order to minimize risks associated with the customer’s applications, adequate design and operating

safeguards must be provided by the customer to minimize inherent or procedural hazards.

TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent

that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other

intellectual property right of TI covering or relating to any combination, machine, or process in which such

semiconductor products or services might be or are used. TI’s publication of information regarding any third

party’s products or services does not constitute TI’s approval, warranty or endorsement thereof.


型号：	BQ2945
厂家：	TEXAS INSTRUMENTS
描述：	Gas Gauge IC with SMBus Interface 电量监测计IC ，带有SMBus接口仪表
文件：	总32页 (文件大小：255K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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