Texas Instruments BQ2040SN-C408TR, BQ2040SN-C408 Datasheet

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bq2040

Gas Gauge IC With SMBus Interface

Features

Provides accurate measurement

➤

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

Supports SBS v1.0 data set and

➤

two-wire interface

Monitors charge FET in Li-Ion

➤

pack protection circuit

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 four-segment LED dis-

play for remaining capacity

General Description

The bq2040 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 bq2040 directly supports capacity monitoring for NiCd, NiMH, and LiIon battery chemistries.

The bq2040 uses the System Man

agement Bus v1.0 (SMBus) protocol

and supports the Smart Battery Data (SBData) commands. The bq2040 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 four-segment LED display to graphically depict battery full-to-empty in 25% increments.

indication

➤ 16-pin narrow SOIC

Pin Connections Pin Names

The bq2040 estimates battery selfdischarge based on an internal timer and temperature sensor and user-programmable rate informa tion stored in external EEPROM.

The bq2040 also automatically re

calibrates or “learns” battery capac ity in the full course of a discharge cycle from full to empty.

The bq2040 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

for other battery cell configu

rations.

An external EEPROM is used to program initial values into the bq2040 and is necessary for proper operation.

ESCL

ESDA

LED

SLUS005–JUNE 1999 E

16-Pin Narrow SOIC

OUT

REF

SMBC

SMBD

PSTAT

DISP

PN204001.eps

ESCL EEPROM clock ESDA EEPROM data LED V SR Sense resistor input DISP Display control input

1-4

3.0–6.5V

LED segment 1-4 System ground

SB Battery sense input PSTAT Protector status input SMBD SMBus data input/output SMBC SMBus clock REF Voltage reference output V

EEPROM supply output

OUT

bq2040

Pin Descriptions

ESCL

ESDA Serial memory data and address

LED LED

Supply voltage input

Serial memory clock

Output used to clock the data transfer be tween the bq2040 and the external non volatile configuration memory.

Bidirectional pin used to transfer address and data to and from the bq2040 and the ex ternal nonvolitile configuration memory.

LED display segment outputs

–

Each output may drive an external LED.

Ground

Sense resistor input

The voltage drop (V

) across pins SR and

VSSis 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. VSR<VSSindicates discharge, and VSR>VSSindicates charge. The effective voltage drop, V

, as seen by the bq2040

SRO

is VSR+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.

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.

PSTAT

Protector status input

Provides overvoltage status from the Li-Ion protector circuit and can initiate a charge sus pend request.

SMBD

SMBus data

Open-drain bidirectional pin used to transfer address and data to and from the bq2040.

SMBC

SMBus clock

Open-drain bidirectional pin used to clock the data transfer to and from the bq2040.

REF Reference output for regulator

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

OUT

Supply output

Supplies power to the external EEPROM con figuration memory.

bq2040

Functional Description

General Operation

The bq2040 determines battery capacity by monitoring the amount of charge put into or removed from a re chargeable battery. The bq2040 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.

ESCL

SMBC

ESDA

SMBD

LED1 LED2

PS TAT LED3 LED4 V

bq2040

Figure 1 shows a typical battery pack application of the bq2040 using the LED capacity display, the serial port, and an external EEPROM for battery pack program ming information. The bq2040 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 EEPROM.

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

board space.

(Optional)

OUT REF

DISP

square inch of

No. of Cells

Li-IonNiMH

Chart 1

For bq2040 With No D8

R5 R4 Q1R11

301K BSS138

499K

3 4

698K

499K

698K

806K

909K

Figure 1. Battery Pack Application Diagram—LED Display

604K 806K 604K

499K 806K 499K 604K 909K

100K 100K 100K

100K 100K 100K 100K

86.5K

BSS138 2N7002

BSS138 BSS138 2N7002 2N7002 2N7002

(Optional)

2040LED.eps

bq2040

Table 1. Configuration Memory Map

Parameter Name Address Description Length Units

EEPROM length 0x00

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

Manufacture 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 overload 0x2c/0x2d Sets the overload current threshold 16 bits mA

Battery low % 0x2e Sets the battery low amount 8 bits %

Reserved 0x2f Reserved for future use 8 bits NA

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

Li-Ion taper current 0x38/0x39

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 0x40-0x45 Programs DeviceChemistry (0x22) 48 bits NA

Current measurement gain 0x46/0x47 Sense resistor calibration value 16 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

Number of EEPROM data locations must = 0x64

Sets the upper limit of the taper current for charge termination

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

8 bits NA

16 bits mA

8 bits NA

bq2040

Table 1. Configuration Memory Map (Continued)

Parameter Name Address Description Length Units

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

Full charge percentage 0x4c

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

Current integration gain 0x4e

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

EDVF charging current 0x5a/0x5b

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

Hold-off time 0x63

EEPROM check 2 0x64

Reserved 0x65-0x7f Reserved for future use NA

0x62

Sets the percent at which the battery is consid ered fully charged

Programs the current integration gain to the sense resistor value

Sets the charge current request when the battery voltage is less than EDVF

Sets the ∆t step for ∆T/∆t termination Sets ∆T/∆t hold-off timer

EEPROM data integrity check byte must = 0xb5

8 bits NA

16 bits NA

8 bits NA

bq2040

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge currents, the bq2040 monitors the battery potential through the SB pin. The voltage potential is deter mined through a resistor-divider network per the fol lowing equation:

MBV

2.25

where MBV is the maximum battery voltage, R

1=−

is 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. The voltage at the SB pin (VSB) 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 a programmable “empty” state. The bq2040 generates an alarm warning when the battery 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.

is below either of the two EDV thresholds, the associ-

If V

ated flag is latched and remains latched, independent of VSB, until the next valid charge.

EDV monitoring may be disabled under certain conditions. If the discharge current is greater than the value stored in location 0x2c and 0x2d in the EEPROM (EE 0x2c/0x2d), EDV monitoring is disabled and resumes after the current falls below the programmed value.

Reset

The bq2040 is reset when first connected to the battery pack. On power-up, the bq2040 initializes and reads the EEPROM configuration memory. The bq2040 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 bq2040 is in an unlocked state as defined by the value in location 0x3d of the EEPROM (EE 0x3d) on power-up.

Temperature

The bq2040 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 bq2040 controlled charge. Temperature may also be accessed over the SMBus with command 0x08.

Layout Considerations

The bq2040 measures the voltage differential between the SR and VSSpins. 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:

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

possible to the SB and VCCpins, and their paths to V should be as short as possible. A high-quality ceramic capacitor of 0.1µf is recommended for VCC.

The sense resistor capacitor (C3) should be placed as

close as possible to the SR pin.

The bq2040 should be in thermal contact with the

cells for optimum temperature measurement.

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates the operation of the bq2040. The bq2040 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 discharging 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 bq2040 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.

The battery’s empty state is also programmed in the EEPROM. The battery low percentage (EE 0x2e) stores

the percentage of FCC that will be written to RM when the battery voltage drops below the EDV1 threshold.

1. FullChargeCapacity or learned-battery

capacity:

FCC is the last measured discharge capacity of the battery. On initialization (application of V FCC is set to the value stored in the EEPROM. Dur

or reset),

bq2040

Inputs

Main Counters

and Capacity

Reference (FCC)

Outputs

Charge Current

State-of-charge

Temperature

Compensation

Figure 2. Operational Overview

ing subsequent discharges, FCC is updated with the latest measured capacity in the Discharge Count Register plus the battery low amount, 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 bq2040 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 the battery low amount after the EDV1 threshold has been reached. If RM is already equal to or less than the battery low amount, RM is not modified. If RM reaches the battery low amount before the battery voltage falls below EDV1 on dis charge, RM stops counting down until the EDV1 threshold is reached. RM is set to 0 when the battery voltage reaches EDVF. To prevent overstatement of charge during periods of overcharge, RM stops in crementing when RM = FCC. RM may optionally be written to a user-defined value when fully charged if the battery pack is under bq2040 charge control. On initialization,RM is set to 0.

and

Remaining

Chip-Controlled

Available Charge

LED Display

Capacity

(RM)

Discharge

Current

Serial Interface

Full

Charge

Capacity

(FCC)

Two-Wire

Self-Discharge

Timer

Temperature

Compensation

Discharge

Count

Qualified

Transfer

(DCR)

Temperature, Other Data

FG294501.eps

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, both discharge and self-discharge increment the DCR. After RM = 0, only discharge increments the DCR. The DCR resets to 0 when RM = FCC and stops counting at EDV1 on discharge. The DCR does not roll over but stops counting when it reaches FFFFh.

FCC is updated on the first charge after a qualified discharge to EDV1. The updated FCC equals the battery low percentage times the current FCC plus

the DCR value. A qualified discharge to EDV1 oc curs if all of the following conditions exist:

No valid charge initiations (charges greater than 10mAh, where V the period between RM = FCC and EDV1 de tected.

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

The low temperature fault bit in FLAGS2 is not set when the EDV1 level is reached during dis charge.

Battery voltage is not more than 256mV below the EDV1 threshold when EDV1 is set.

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.

SRO

>+V

occurred during

SRD

bq2040

Charge Counting

Charge activity is detected based on a positive voltage on the SR input. If charge activity is detected, the bq2040 increments RM at a rate proportional to V and, if enabled, activates an LED display. Charge ac tions increment the RM after compensation for charge state and temperature.

The bq2040 determines charge activity sustained at a continuous rate equivalent to V

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

charge threshold counting continues until V low V scribed in the Digital Magnitude Filter section.

SRD

is a programmable threshold as de

SRO

>+V

SRD

SRO

. A valid

falls be

Discharge Counting

All discharge counts where V register to decrement and the DCR to increment. V is a programmable threshold as described in the Digital Magnitude Filter section.

SRO

<-V

cause the RM

SRD

Self-Discharge Estimation

The bq2040 continuously decrements RM and increments DCR for self-discharge based on time and temperature provided that the discharge flag in BatteryStatus is set (charge not detected). The bq2040 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 approximately doubles for every 10°C increase until the temperature is ≥ 70°C or halves every 10°C decrease until the temperature is < 10°C.

Charge Control

The bq2040 supports SBS charge control by broadcast ing the ChargingCurrent and the ChargingVoltage to the Smart Charger address. The bq2040 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 bq2040 updates the value used in the charg ing current broadcasts based on the battery’s state of charge, voltage, and temperature.

The bq2040 internal charge control is compatible with nickel-based and Li-Ion chemistries. The bq2040 uses current taper detection for Li-Ion primary charge termi nation and ∆T/∆t for nickel based primary charge termi nation. The bq2040 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 bq2040 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 less than the programmed threshold in EE 0x38—0x39 and non-zero for at least 100s.

∆T/∆t

The ∆T/∆t used by the bq2040 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.

∆

is set by the formula:

∆

[]

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

[(

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 temperature falls below 25°C, or if charging current falls below 255mA, the timer is reset and restarts only if these conditions are once again within range. The hold-off time is programmed in EE 0x63.

EE 0x62

−320

∆

) 20)]

∗

Charge Termination

Once the bq2040 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 Termi nate_Charge_Alarm and the Over_Charged_Alarm are cleared, and the requested charging current is set to the maintenance rate. The bq2040 requests the mainte nance rate until RM falls below the amount determined

by the programmable full- charge percentage. Once this

occurs, the Fully_Charged bit is cleared, and the re quested charge current and voltage are set to the fast-charge rate.

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.









s∗





bq2040

Charge Suspension

The bq2040 may temporarily suspend charge if it detects a charging fault. The charging faults include the follow ing conditions:

Maximum Overcharge: If charging continues for

more than the programmed maximum overcharge limit as defined in EE 0x3a—0x3b beyond RM=FCC, the Fully_Charged bit is set, and the requested charging current is set to the maintenance rate.

Overvoltage: An over-voltage fault exists when the

bq2040 measures a voltage more than 5% above the ChargingVoltage. When the bq2040 detects an overvoltage condition, the requested charge current is set to 0 and the Terminate_Charge_Alarm bit is set in BatteryStatus. The alarm bit is cleared when the current drops below 256mA and the voltage is less than 105% of ChargingVoltage.

Overcurrent: An overcurrent fault exists when the

bq2040 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 1mA above the lowest multiple of 256mA that exceeds the ChargingCurrent. When the bq2040 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.

Maximum Temperature: When the battery temperature equals 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 Over_Temp_Alarm bit is cleared when the temperature drops to 43°C below the maximum temperature threshold minus 5°C.

PSTAT: When the PSTAT input is ≥1.5V, the requested charge current is set to 0 and the Terminate_Charge_Alarm bit is set in BatteryStatus if the Discharging flag is not set. The alarm bit is cleared when the PSTAT input is <1.0V or the Discharging flag is set.

Low Temperature: When the battery temperature is less than 12°C (LTF bit in FLAGS2 set), the requested charge current is set to the maintenance rate. Once the temperature is above 15°C, the requested charge current is set to the fast rate.

Undervoltage: When the battery voltage is below the EDVF threshold, the requested charge current is set to the EDVF rate stored in EE0x5a/0x5b. Once the voltage is above EDVF, the requested charge current is set to the fast or maintenance rate depending on the state of the LTF bit.

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 ing from 0.75 to 1.0.

is the programmed fast-charge efficiency vary

EFC

2.)

RM RM Q Q

=−*( )

ETC ET

where RelativeStateOfCharge ≥ FullChargePercentage and charge efficiency varying from 0.75 to 1.0.

temperature increases according to the following:

QifT

QCTC

QTC

is the programmed maintenance (trickle)

ETC

is used to adjust the charge efficiency as the battery

=<030

=°≤<°002 30 40.if

=≥°005 40.if

°C

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

Digital Magnitude Filter

The bq2040 has a programmable digital filter to elimi nate charge and discharge counting below a set threshold, V

. Table 2 shows typical digital filter

SRD

settings. The proper digital filter setting can be calcu lated using the following equation.

DMF =

SRD

Table 2. Typical Digital Filter Settings

DMF DMF Hex. V

75 4B

100 64 0.45

150 96 0.30

175 AF 0.26

200 C8 0.23

SRD

(mV)

0.60

bq2040

Table 3. bq2040 Current-Sensing Errors

Symbol Parameter Typical Maximum Units Notes

INL

INR

Offset referred to V

Integrated non-linearity error

Integrated nonrepeatability error

0.5

150

V DISP

= VCC.

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

Measurement repeatability given similar operating conditions.

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 adjusted 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 VSR. A digital filter eliminates charge and discharge counts to the RM register when -V +V

SRD

Display

The bq2040 can directly display capacity information using low-power LEDs. The bq2040 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 25% of the FCC.

In absolute mode, each segment represents a fixed amount of charge, 25% 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 tive. When DISP is left floating, the display becomes ac tive whenever the bq2040 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 VCCto reactivate the display.

LED1blinks at a 4Hz rate indicating a low battery con dition whenever the display is active, EDVF is not set,

SRD<VSRO

outputs are inac

1-4

and Remaining_Capacity_Alarm is set. V (EDVF = 1) disables the display output.

below EDVF

Microregulator

The bq2040 can operate directly from three nickel chem

istry cells. To facilitate the power supply requirements of the bq2040, an REF output is provided to regulate an external low-threshold n-FET. A micropower source for the bq2040 can be built inexpensively 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 bq2040

The bq2040 includes a simple two-pin (SMBC and SMBD) bi-directional serial data interface. A host proc-

essor uses the interface to access various bq2040 registers; see Table 4. This method allows battery characteristics to be monitored easily. The open-drain SMBD and SMBC pins on the bq2040 are pulled up by the host system, or may be connected to VSS, 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 bq2040. The command directs the bq2040 to either store the next data received to a register specified by the command byte or output the data specified by the command byte.

bq2040 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 bq2040. (See Figure 3).

Host-to-bq2040 Message Protocol

The Bus Host communicates with the bq2040 using one of three protocols:

Read word

Write word

bq2040

Battery Address

0001011

Battery Address

0001011

Battery Address

0001011

Byte Count =N Data byte 1

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

Write Word

0 A Command Code A Battery Address A1

Read Word

A Command Code A Battery Address A1

1818

Block Read

1818

PData byte low Data byte high

Figure 3. Host Communication Protocols

Read block

The particular protocol used is a function of the command. The protocols used are shown in Figure 3.

Host-to-bq2040 Messages

(see Table 4)

ManufacturerAccess() (0x00)

This read/write word is an open location.

Input/Output: word.

RemainingCapacityAlarm() (0x01)

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.

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.

11818181171

117181171

System Host

117181171

1818

PData byte 2 Data byte N

bq2040

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

FG204001.eps

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 bq2040 supports the battery capacity information specified in mAh. This function also determines whether the bq2040 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 bq2040 is initialized from the EEPROM and reset when a learning cycle has been completed. It is also set toa1if 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.

bq2040

Table 4. bq2040 Register Functions

Function Code Access Units Defaults

ManufacturerAccess 0x00 read/write - -

RemaningCapacityAlarm 0x01 read/write mAh E

RemainingTimeAlarm 0x02 read/write minutes E

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

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

FullChargeCapacity 0x10 read mAh E

RunTimeToEmpty 0x11 read minutes -

AverageTimeToEmpty 0x12 read minutes -

AverageTimeToFull 0x13 read minutes -

ChargingCurrent 0x14 read mA E

ChargingVoltage 0x15 read mV E

Battery Status 0x16 read bit flags E

CycleCount 0x17 read cycle E

DesignCapacity 0x18 read mAh E

DesignVoltage 0x19 read mV E

SpecificationInfo 0x1a read - E

ManufactureDate 0x1b read - E

SerialNumber 0x1c read integer E

Reserved 0x1d - 0x1f - - -

ManufacturerName 0x20 read string E

DeviceName 0x21 read string E

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

bq2040

Table 4. bq2040 Register Functions (Continued)

Function Code Access Units Defaults

DeviceChemistry 0x22 read string E

ManufacturerData 0x23 read string E

FLAG1 and FLAG2 0x2f read bit flags E

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

End of Discharge Voltage Final (EDVF)

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

0x3f read - E

bq2040

When the AtRate value is positive, the

AtRateTimeToFull function returns the predicted time to full-charge at the AtRate value of charge.

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

bq2040

Accuracy:±1% of the DesignCapacity after cali bration

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 remaining 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.

bq2040

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.

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 bq2040 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 bq2040 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 voltage range.

BatteryStatus() (0x16)

This read-only word returns the battery status word.

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

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

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

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 bq2040 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

bq2040

Table 6. Bit Descriptions for FLAGS1 and FLAGS2

(MSB) 7 6543210 (LSB)

FLAGS2 DMODE PSTAT CHM CC - OV LTF OC

FLAGS1

Note: - = Reserved

∆T/∆t

MIN

VQ - VDQ OVLD EDV1 EDVF

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.

Output: unsigned integer. Returns the battery capacity 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

SpecificationInfo() (0x1a)

This read-only word returns the specification re vision the bq2040 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.

Field

Month 5–8

Year 9–15

Bits

Used Format Allowable Value

Day 0–4

5-bit binary

value

4-bit binary

value

7-bit binary

value

1–31 (corresponds to date)

1–12 (corresponds to month number)

0–127 (corresponds to year biased by 1980)

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 maximum number of characters is 11. The character string contains the battery manufacturer's name. For example, “Benchmarq” identifies the battery pack manufacturer as Benchmarq.

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 “bq2040” indicates that the battery is a model bq2040.

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.

bq2040

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.

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 bq2040. 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 bq2040 displays Relative or Absolute capacity.

The DMODE value is:

FLAGS2 Bits

7 6543210

DMODE -------

Where DMODE is:

0 Selects Absolute display

1 Selects Relative display

Bit 6 reflects the high/low state of PSTAT. PSTAT ≥1.5V generates a charge suspend condition.

The PSTAT value is:

FLAGS2 Bits

7 6 543210

-PSTAT------

Where PSTAT is:

0 PSTAT input < 1.0V 1 PSTAT input ≥ 1.5V

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

The CHM value is:

FLAGS2 Bits

76 5 43210

--CHM-----

Where CHM is:

0 Selects Nickel

1 Selects Li-Ion

Bit 4, the Charge Control flag (CC), determines whether a bq2040-based charge termination will set RM to a user-defined programmable full charge capacity.

The CC value is:

FLAGS2 Bits

76 5 43210

-- - CC----

Where CC is:

0 RM is not modified on valid bq2040

charge termination

1 RM is set to a programmable percentage of

the FCC when a valid bq2040 charge termination occurs

Bit 3 is reserved. Bit 2, the Overvoltage flag (OV), is set when the bq2040

detects a pack voltage 5% greater than the programmed charging voltage. This bit is cleared when the pack voltage falls 5% below the programmed charging voltage.

The OV value is:

FLAGS2 Bits

76 5 43210

- - - - -OV- -

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 is < 12°C and cleared when Temperature is ≥ 15°C.

The LTF value is:

FLAGS2 Bits

76 5 43210

-- - ---LTF-

bq2040

Where LTF is:

0 Temperature > 15°C

1 Temperature < 12°C

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

The OC value is:

FLAGS2 Bits

765432 1 0

------ - OC

Where OC is:

0 Current is less than 1.25 ∗ ChargingCur

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

1 Current exceeds 1.25 ∗ ChargingCurrent or

256mA if the charging current is programmed less than 1024mA. This bit is cleared if Current < 256mA.

FLAGS1

Bits 7 indicates that a ∆T/∆t termination condition exists.

The ∆T/∆t value is:

FLAGS1 Bits

7 6 5 43210

∆T/∆t

Where ∆T/∆t is:

Bit 6 indicates that a current taper termination condi tion exists.

7 6 5 43210

- - -----

0 The ∆T/∆t rate drops below the pro

grammed rate.

1 The ∆T/∆t rate exceeds the programmed

rate.

FLAGS1 Bits

-I

MIN

- -----

The I

Where I

MIN

value is:

is:

MIN

0 A valid current taper termination condition

is not present.

1 Valid current taper termination condition

detected.

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

| and 10mAh of charge has accumulated. This bit

SRD

is cleared during a discharge and when V

SRO

≤

FLAGS1 Bits

76 5 43210

--VQ -----

The VQ value is:

Where VQ is:

SRO

SRD

≤

≥

| and 10mAh of charge has

SRD

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

FLAGS1 Bits

7654 3 210

- - - - VDQ - - -

The VDQ value is:

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 Overload flag (OVLD), bit 2, is set when the dis charge current is greater than the programmed rate and

cleared when the discharge current falls below the pro grammed rate.

FLAGS1 Bits

76543 2 10

- - - - - OVLD - -

SRD

SRO

≥

bq2040

The OVLD value is:

Where OVLD is:

0 Current < programmed rate

1 Current > programmed rate

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

FLAGS1 Bits

765432 1 0

- - - - - - EDV1 -

The EDV1 value is:

Where EDV1 is:

0 VQ = 1 and Voltage > EDV1

1 Voltage < EDV1 and OVLD = 0

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

FLAGS1 Bits

7654321 0

- - - - - - - EDVF

The EDVF value is:

Where EDVF is:

0 VQ = 1 and Voltage > EDVF

1 Voltage < EDVF and OVLD = 0

SBD Seal

The bq2040 address space can be “locked” to enforce the SBS specified access to each command code. To lock the address space, the bq2040 must be initialized with EE 0x3d set to b0h. 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 bq2040

The bq2040 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 EV2200-40 pro gramming kit (interface board, software, and cable) for an IBM-compatible PC is available from Benchmarq.

The bq2040 uses a 24LC01 or equivalent serial EEPROM (capable of read operation to 2.0V) for storing the various initial values, calibration data, and string information. 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.

Error Codes and Status Bits

Error codes and status bits are listed in Table 8 and Ta ble 9, respectively.

bq2040

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

Error Code Access Description

OK 0x0000 read/write bq2040 processed the function code without detecting any errors.

Busy 0x0001 read/write bq2040 is unable to process the function code at this time.

ReservedCommand 0x0002 read/write

UnsupportedCommand 0x0003 read/write bq2040 does not support the requested function code.

AccessDenied 0x0004 write

Overflow/Underflow 0x0005 read/write bq2040 detected a data overflow or underflow.

BadSize 0x0006 write

UnknownError 0x0007 read/write bq2040 detected an unidentifiable error.

Note: Reading the bq2040 after an error clears the error code.

bq2040 cannot read or write the data at this time—try again later.

bq2040 detected an attempt to write to a read-only function code.

bq2040 detected an attempt to write to a function code with an incorrect size data block.

bq2040

Bit Name Set When: Reset When:

OVER_CHARGED_ALARM

TERMINATE_CHARGE_ALARM

OVER_TEMP_ALARM

TERMINATE_DISCHARGE_ALARM

REMAINING_CAPACITY_ALARM

REMAINING_TIME_ALARM

Bit Name Set When: Reset When:

INITIALIZED

DISCHARGING

FULLY_CHARGED

FULLY_DISCHARGED

Table 9. BatteryStatus Bits

Alarm Bits

The bq2040 detects a ∆T/∆t or cur rent taper termination. (Note:

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

The bq2040 detects an over-current, over-voltage, over-temperature, ∆T/∆t, or current taper condition during charge.

The bq2040 detects that its internal temperature is greater than the pro grammed value.

The bq2040 determines that it has supplied all the charge that it can without being damaged (Voltage < EDVF).

The bq2040 detects that the RemainingCapacity is less than that set by the RemainingCapacityAlarm function.

The bq2040 detects that the estimated remaining time at the present discharge rate is less than that set by the RemainingTimeAlarm function.

Status Bits

The bq2040 loads from the EEPROM (bit 7 set in EE0x0c).

The bq2040 determines that it is not being charged.

The bq2040 determines a valid charge termination or a maximum overcharge state.

bq2040 determines that it has supplied all the charge that it can without being damaged.

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

A discharge occurs or when all condi tions causing the event cease.

Internal temperature falls to 43°C or the maximum temperature threshold minus 5°C.

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

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

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

A bad EEPROM load is detected.

Battery detects that it is being charged.

RM discharges below the full charge percentage.

RelativeStateOfCharge is greater than or equal to 20%

Table 10. Example Register Contents

bq2040

EEPROM

Address

Low

Description

EEPROM length

EEPROM check 1 0x01 5b 91 Must be equal to 0x5b.

Remaining time alarm

Remaining capacity alarm

Reserved 0x06 0x07 00 00 0 Not currently used by the bq2040.

Initial charging current

Charging voltage 0x0a 0x0b d8 40 16600mV

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

Cycle count 0x0e 0x0f 00 00 0

Design capacity 0x10 0x11 60 09 2400mAh Normal battery pack capacity.

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

Specification information

Manufacture date

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

Fast-charging current

Maintenance charge current

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

Current overload

Battery low % 0x2e 08 3%

High

Byte

0x00 64 100 Must be equal to 0x64.

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

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

0x08 0x09 60 09

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

0x16 0x17 a1 20

0x1a 0x1b 60 09 2400mA

0x1c 0x1d 00 00 0mA

0x2c 0x2d 70 17 6000mA

EEPROM

Hex Contents

Low

High

Byte

Example

Values Notes

2400mA

May 1, 1996

= 8353

Sets the initial charge request.

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

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

Packed per the ManufactureDate description.

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

Contains the desired maintenance current after fastcharge termination by the bq2040.

Sets the discharge current at which EDV threshold monitoring is disabled.

Sets the battery capacity that RemainingCapacity is reduced to at EDV1. The value equals 2.56 ∗ (%RM at EDV1)

bq2040

Table 10. Example Register Contents (Continued)

EEPROM

Address

Low

High

Byte

Description

Byte

Reserved 0x2f 00 0 Not currently used by the bq2040.

Li-Ion taper current

0x38 0x39 10 ff 240mA

Maximum overcharge

0x3a 0x3b 9c ff 100mAh

limit

Reserved 0x3c 00 0 Must be programmed to 0.

Access protect 0x3d b0 SBD access only

FLAGS1 0x3e 00 0 Initializes FLAGS1

FLAGS2 0x3f b0

Current measurement

gain

Battery voltage

offset

Temperature

offset

0x46 0x47 00 0f 3840

0x48 fe -2mV

0x49 8a

Maximum temperature

0x4a 5f

and ∆T step

Charge efficiency

Full-charge percentage

0x4b ff

0x4c 9c

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

Hex

Contents

Low

Byte

High Byte

Relative display Li-Ion chemistry

bq2040 charge

temperature =

∆T step = 4.6°C

Maintenance

compensation =

Fast compensa

Example

Values Notes

Sets the upper taper limit for Li-Ion charge termina tion. Stored in 2’s complement.

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

If the bq2040 is reset and bit 3 of this location is 0, the bq2040 locks access to any command outside of the SBS data set. Program to 0xb8 for full R/W access, 0xb0 for SBD access only.

Initializes FLAGS2.

control

The current gain measurement and current integration gain are related and defined for the bq2040 current measurement. This word equals 192/sense resistor value in ohms.

Used to adjust the battery voltage offset according to the following: Voltage = (VSB(mV) + V

The default value (zero adjustment) for the offset is

13.8°C

Maximum

61.0°C

12.8°C or 0x80. TOFF (TEMP

NEW

ACTUAL

= TOFF

- TEMP

CURRENT

Maximum charge temperature is 69- (mt ∗ 1.6)°C (mt = upper nibble). The ∆T step is (dT ∗ 2 + 16)/10°C (dT = lower nibble).

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

100%

tion = 100%

ciency and the lower nibble adjusts the high effi ciency according to the equation:

Nibble = (efficiency% ∗ 256 - 196)/4

This packed field is the two’s complement of the de sired value in RM when the bq2040 determines a

100%

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.

) ∗ Voltage gain

OFF

REPORTED

)∗ 10

Table 10. Example Register Contents (Continued)

EEPROM

Address

Low

Description

Digital filter 0x4d 96 0.30mV

Current integra tion gain

Self-discharge rate 0x4f 2d 0.25%

Voltage gain

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

EDVF charging current

End of discharge voltage 1

End-of-discharge voltage final

Full charge capacity

∆t step

Hold-off time 0x63 00 320s hold-off

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

Reserved 0x65 0x7f NA Not currently used by the bq2040.

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

High

Byte

0x4e 40 0 3.2/0.05

0x56 0x57 17 07 7.09

0x5a 0x5b 64 00 100mA Contains the desired charge current below EDVF.

0x5c 0x5d 20 d1 12000mV

0x5e 0x5f 40 d4 11200mV

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

0x62 0f 20s

Hex

Contents

Low

Byte

High Byte

Example

Values Notes

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

Represents the following: 3.2/sense resistor in ohms. It is used by the bq2040 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.

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 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).

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

The ∆t step for ∆T/∆t termination equals 320 - (byte value ∗ 20).

The hold-off time is 320 - (byte value ∗ 20).

bq2040

Table 11. Example Register Contents (String Data)

String Description Address0xX00xX10xX20xX30xX40xX50xX60xX70xX80xX90xXa0xXb

Manufacturer name

Device name

Device chemistry

Manufacturer data

0x200x2b

0x300x37

0x400x45

0x500x55

42B45E4eN43C48H4dM41A52R51

42B51Q32230034430

6cL69I4fO4e

42B51Q32230032

bq2040

Absolute Maximum Ratings

Symbol Parameter Minimum Maximum Unit Notes

All other pins Relative to V

REF Relative to V

OPR

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

Relative to V

-0.3 +7.0 V

-0.3 +8.5 V Current limited by R11 (see Figure 1)

Minimum 100Ωseries resistor should

Relative to V

-0.3 +7.0 V

be used to protect SR in case of a shorted battery.

Operating tempera ture

0 +70 °C Commercial

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

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, VCCshould be 1.5V greater than VSB.

bq2040

Recommended DC Operating Conditions (T

= T

OPR

)

Symbol Parameter Minimum Typical Maximum Unit Notes

REF

SBmax

DISP

LVO UT

OLSL

OLSH

OHVL

OHVH

VOUT

OLS

Supply voltage 3.0 4.25 6.5 V

Reference at 25°C 5.7 6.0 6.3 V I

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

Reference input impedance 2.0 5.0 - MΩV

- 90 135

Normal operation

- 120 180

- 170 250

Battery input 0 - V

SB input impedance 10 - - MΩ0 < VSB< V

DISP input leakage - - 5

output leakage -0.2 - 0.2

OUT

Sense resistor input -0.3 - 2.0 V

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

Logic input high

0.5 ∗ V

1.4 - 5.5 V SMBC, SMBD

Logic input low

0.3 ∗ V

-0.5 0.6 V SMBC, SMBD

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

Sink current 100 - 350

LEDXoutput low, low V

LEDXoutput low, high V

output, low V

OUT

output, high V

OUT

source current -33 - - mA At V

OUT

- 0.1 - V

- 0.4 - V

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

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

LEDXsink current 11.0 - mA At V

VCCexcursion from < 2.0V to

3.0V initializes the unit.

= 5µA

REF

= 5µA

REF

= 3V

REF

= 3.0V

= 4.25V

= 5.5V

A EEPROM off

DISP

= V

VSR<VSS= discharge; VSR> VSS= charge

V ESCL, ESDA

0.4V, SMBC, SMBD

≤

VCC= 3V, I LED

–LED

OLS

VCC= 6.5V, I

–LED

LED

VOUT

= VCC- 0.6V

OHVH

= 0.4V

OLSH

OLS

Note: All voltages relative to VSS.

1.75mA

≤

11.0mA

≤

= -5.25mA

= -33.0mA

≥

AC Specifications

Symbol Parameter Min Max Units Notes

SMB

BUF

HD:STA

SU:STA

SU:STO

HD:DAT

SU:DAT

LOW

HIGH

LOW:SEXT

TIMEOUT

SMBus operating frequency 10 100 KHz

Bus free time between stop and start condition

Hold time after (repeated) start condition

4.7

4.0

Repeated start condition setup time 4.7

Stop condition setup time 4.0

µs

Data hold time 300 ns

Data setup time 250 ns

Clock low period 4.7

Clock high period 4.0

µ µ

Clock/data fall time 300 ns

Clock/data rise time 1000 ns

Cumulative clock low extend time (slave)

25 ms

25 35 ms

bq2040

Bus Timing Data

SU:STO

SU:STA

SMBC

SMBD

BUF

HD:STA

LOW

SU:DAT

HD:DAT

HIGH

TD294501.eps

bq2040

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.

)

.004

Data Sheet Revision History

ChangeNo. Page No. Description of Change

3 3 Updated recommended application schematic.

3 9 Changed overcurrent fault conditon for ChargingCurrent < 1024mA.

3 10 4Hz operation of LED clarification.

3 11 Added descriptions for bits 7 and 13 of BatteryMode.

3 14 AtRateTimeToEmpty and AtRateTimeToFull invalid data indication correction.

3 15, 16

3 23 Changed typical Battery low % value for Li-Ion with EDV1 = 3.0V/cell.

3 24 Li-Ion taper current is stored in 2’s complement.

324

3 25 Voltage gain is (R4 + R5)/R4.

3 25 Changed typical EDV1 and EDVF values for Li-Ion.

4 6 Added V 4 8 The self discharge rate approx imately doubles or halves

4 11 Changed cycle count increase from 30 to 32 for condition request.

4 14 Changed AtRateOK() indication from EDV1 to EDVF

4 25 Changed self-discharge programming from 52.75/x to 52.73/x.

4 25 Changed recommended EDVF charging current from 0mA to 100mA

Notes: Changes 1 and 2 refer to the 1998 Data Book

Change 3 = June1998 D changes from Jan. 1998 C. Change 4 = June 1999 E changes from June 1998 D.

RunTimeToEmpty, AverageTimeToEmpty and AverageTimeToFull invalid data indication corrections.

Changed typical ∆T step and Full-charge percentage for Li-Ion.

should not exceed 2.4V

bq2040

Ordering Information

bq2040

Temperature Range:

blank = Commercial (0 to 70°C)

Package Option:

SN = 16-pin narrow SOIC

Device:

bq2040 Gas Gauge IC With SMBus Interface

IMPORTANT NOTICE

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Texas Instruments BQ2040SN-C408TR, BQ2040SN-C408 Datasheet

Specifications and Main Features

Frequently Asked Questions

User Manual