Texas Instruments EV2014X, EV2014, BQ2014SN-D120TR, BQ2014SN-D120 Datasheet

Features

➤

Conservative and repeatable measurement of available charge in rechargeable batteries

➤

Charge control output operates an external charge controller such as the bq2004 Fast Charge IC

➤

Designed for battery pack inte

gration

120µA typical standby current

➤

Display capacity via single-wire serial communication port or di

rect drive of LEDs

➤

Measurements compensated for current and temperature

➤ Self-discharge compensation using

internal temperature sensor

➤ User-selectable end-of-discharge

threshold

➤ Battery voltage, nominal avail-

able charge, temperature, etc. available over serial port

➤

16-pin narrow SOIC

General Description

The bq2014 Gas Gauge IC is in

tended for battery-pack or in-system installation to maintain an accurate record of available battery charge. The IC monitors the voltage drop across a sense resistor connected in series between the negative battery terminal and ground to determine charge and discharge activity of the battery.

Self-discharge of NiMH and NiCd batteries is estimated based on an internal timer and temperature sen

sor. Compensations for battery tem

perature and rate of charge or dis

charge are applied to the charge, dis

charge, and self-discharge calculations to provide available charge information across a wide range of operating conditions. Battery capacity is automatically recalibrated, or “learned,” in the course of a discharge cycle from full to empty.

The bq2014 includes a charge control output that controls an external Fast Charge IC such as the bq2004.

Nominal Available Charge (NAC) may be directly indicated using a five-segment LED display.

The bq2014 supports a simple singleline bidirectional serial link to an ex

ternal processor (with a common ground). The bq2014 outputs battery information in response to external commands over the serial link.

Internal registers include available charge, temperature, capacity, bat

tery voltage, battery ID, battery status, and programming pin set

tings. To support subassembly test

ing, the outputs may also be con

trolled. The external processor may also overwrite some of the bq2014 gas gauge data registers.

The bq2014 may operate directly from three or four cells. With the REF output and an external transistor, a simple, inexpensive regulator can be built to provide V

across a

greater number of cells.

LCOM LED common output

SEG

/PROG1LED segment 1/

program 1 input

SEG

/PROG2LED segment 2/

program 2 input

SEG

/PROG3LED segment 3/

program 3 input

SEG

/PROG4LED segment 4/

program 4 input

SEG

/PROG5LED segment 5/

program 5 input

DONE Fast charge complete

PN201401.eps

16-Pin Narrow SOIC

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

DONE

REF

CHG

EMPTY

DISP

REF Voltage reference output

CHG Charge control output

DQ Serial communications

input/output

EMPTY Empty battery indicator

output

SB Battery sense input

DISP

Display control input

SR Sense resistor input

3.0–6.5V

System ground

12/95 C

Pin Connections Pin Names

bq2014

Gas Gauge IC with External Charge Control

Pin Descriptions

LCOM

LED common output

Open-drain output switches V

to source

current for the LEDs. The switch is off dur

ing initialization to allow reading of the soft pull-up or pull-down programming resistors. LCOM is also in a high impedance state when the display is off.

SEG

–

SEG

LED display segment outputs (dual func

tion with PROG

—PROG5)

Each output may activate an LED to sink the current sourced from LCOM.

PROG

–

PROG

Programmed full count selection imputs (dual function with SEG

—SEG5)

These three-level input pins define the pro

grammed full count (PFC) thresholds de

scribed in Table 2.

PROG

–

PROG

Gas gauge rate selection inputs (dual function with SEG

—SEG4)

These three-level input pins define the programmed full count (PFC) thresholds described in Table 2.

PROG

Self-discharge rate selection (dual function with SEG

)

This three-level input pin defines the selfdischarge compensation rate shown in Table 1.

CHG

Charge control output

This open-drain output becomes active high when charging is allowed.

DONE

Fast charge complete

This input is used to communicate the status of an external charge controller such as the bq2004 Fast Charge IC. Note: This pin must be pulled down to V

using a

200KΩ resistor.

Sense resistor input

The voltage drop (V

) across the sense re

sistor R

is monitored and integrated over

time to interpret charge and discharge activ

ity. The SR input is tied to the high side of the sense resistor. V

SR<VSS

indicates dis

charge, and V

SR>VSS

indicates charge. The

effective voltage drop V

SRO

, as seen by the

bq2014, is V

SR+VOS

(see Table 5).

DISP

Display control input

DISP

high disables the LED display. DISP

tied to VCCallows PROGXto connect di

rectly to V

or VSSinstead of through a

pull-up or pull-down reistor. DISP

floating allows the LED display to be active during a valid charge or during discharge if the NAC register is updated at a rate equiva

lent to V

SRO

≤ -4mV. DISP low activates

the display. See Table 1.

Secondary battery input

This input monitors the single-cell voltage potential through a high-impedance resistive divider network for the end-of-discharge voltage (EDV) thresholds,maximum charge voltage (MCV), and battery removed.

EMPTY

Battery empty output

This open-drain output becomes highimpedance on detection of a valid final endof-discharge voltage (V

EDVF

) and is low fol

lowing the next application of a valid charge.

Serial I/O pin

This is an open-drain bidirectional pin.

REF

Voltage reference output for regulator

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

Supply voltage input

Ground

bq2014

Functional Description

General Operation

The bq2014 determines battery capacity by monitoring the amount of charge input to or removed from a re

chargeable battery. The bq2014 measures discharge and charge currents, estimates self-discharge, monitors the battery for low-battery voltage thresholds, and compen

sates for temperature and charge/discharge rates. The charge measurement is made by monitoring the voltage across a small-value series sense resistor between the battery’s negative terminal and ground. The available battery charge is determined by monitoring this voltage over time and correcting the measurement for the envi

ronmental and operating conditions.

Figure 1 shows a typical battery pack application of the bq2014 using the LED display capability as a chargestate indicator. The bq2014 is configured to display ca

pacity in a relative display mode. The relative display mode uses the last measured discharge capacity of the battery as the battery “full” reference. The LED seg

ments output a percentage of the available charge based on NAC and LMD. A push-button display feature is available for momentarily enabling the LED display.

The bq2014 monitors the charge and discharge currents as a voltage across a sense resistor (see R

in Figure 1). A filter between the negative battery terminal and the SR pin is required.

bq2014

Figure 1. Battery Pack Application Diagram—LED Display,

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge currents, the bq2014 monitors the single-cell battery po

tential through the SB pin. The single-cell voltage po

tential is determined through a resistor/divider network per the following equation:

R R

2 3

1=−

where N is the number of cells, R2 is connected to the positive battery terminal, and R3 is connected to the negative battery terminal. The single-cell battery volt

age is monitored for the end-of-discharge voltage (EDV) and for maximum cell voltage (MCV). EDV threshold levels are used to determine when the battery has reached an “empty” state, and the MCV threshold is used for fault detection during charging.

Two EDV thresholds for the bq2014 are programmable with the default values fixed at:

EDV1 (early warning) = 1.05V

EDVF (empty) = 0.95V

If V

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

, until the next valid charge (as defined in the

section entitled “Gas Gauge Operation”). The V

value

is also available over the serial port.

During discharge and charge, the bq2014 monitors V

for various thresholds. These thresholds are used to compensate the charge and discharge rates. Refer to the count compensation section for details. EDV monitoring is disabled if V

≤ -250mV typical and resumes ½ sec

ond after V

> -250mV.

EMPTY Output

The EMPTY output switches to high impedance when V

SB<VEDF

and remains latched until a valid charge oc

curs.

Reset

The bq2014 recognizes a valid battery whenever VSBis greater than 0.1V typical. V

rising from below 0.25V

or falling from above 2.25V (V

MCV

) resets the device. Re

set can also be accomplished with a command over the serial port as described in the Reset Register section.

Temperature

The bq2014 internally determines the temperature in 10°C steps centered from -35°C to +85°C. The tempera

ture steps are used to adapt charge and discharge rate

compensations, self-discharge counting, and available charge display translation. The temperature range is available over the serial port in 10°C increments as shown below:

Layout Considerations

The bq2014 measures the voltage differential between the SR and V

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

The capacitors (C2 and C3) should be placed as close as possible to the SB and V

pins, respectively, and their

paths to V

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

The sense resistor (R1, C1) should be placed as close as possible to the SR pin.

The sense resistor (R16) should be as close as possible to the bq2014.

bq2014

TMPGG (hex) Temperature Range

0x < -30°C

1x -30°C to -20°C

2x -20°C to -10°C

3x -10°C to 0°C

4x 0°C to 10°C

5x 10°C to 20°C

6x 20°C to 30°C

7x 30°C to 40°C

8x 40°C to 50°C

9x 50°C to 60°C

Ax 60°C to 70°C

Bx 70°C to 80°C

Cx > 80°C

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates the operation of the bq2014. The bq2014 accumulates a measure of charge and discharge currents, as well as an estimation of self-discharge. Charge and discharge cur

rents are temperature and rate compensated, whereas self-discharge is only temperature compensated.

The main counter, Nominal Available Charge (NAC), represents the available battery capacity at any given time. Battery charging increments the NAC register, while battery discharging and self-discharge decrement the NAC register and increment the DCR (Discharge Count Register).

The Discharge Count Register (DCR) is used to update the Last Measured Discharge (LMD) register only if a complete battery discharge from full to empty occurs without any partial battery charges. Therefore, the bq2014 adapts its capacity determination based on the actual conditions of discharge.

The battery's initial capacity is equal to the Pro

grammed Full Count (PFC) shown in Table 2. Until LMD is updated, NAC counts up to but not beyond this threshold during subsequent charges. This approach allows the gas gauge to be charger-independent and compatible with any type of charge regime.

Many actions in the bq2014 are triggered by detection of a “valid charge.” NAC is stored in an asynchronous, 2byte counter; the lower byte is NACL and the upper byte is NACH. A valid charge has occurred anytime the

charge lasts long enough to cause an increment in NACH. Small increments of charging are not consid

ered “valid” if they result in counts in NACL but do not generate a roll-over (carry) that increments NACH. NACL is reset anytime the counter direction changes from down to up, so the number of counts required to cause a roll-over and a valid charge is always 256. The counter may be incrementing by 2, 4, 8, or more counts per increment, however, depending on the scaling fac

tors selected. Therefore, a valid charge may be consti

tuted by a smaller number of counter increments.

1. Last Measured Discharge (LMD) or

learned battery capacity:

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

or bat

tery replacement), LMD = PFC. During subsequent discharges, the LMD is updated with the latest measured capacity in the Discharge Count Register (DCR) representing a discharge from full to below EDV1. A qualified discharge is necessary for a ca

pacity transfer from the DCR to the LMD register. The LMD also serves as the 100% reference thresh

old used by the relative display mode.

2. Programmed Full Count (PFC) or initial

battery capacity:

The initial LMD and gas gauge rate values are programmed by using PROG

—PROG4. The bq2014 is configured for a given application by selecting a PFC value from Table 2. The correct PFC may be

bq2014

FG201002.eps

Rate and

Temperature

Compensation

Temperature

Compensation

Charge Current

Discharge

Current

Self-Discharge

Timer

Temperature

Translation

Nominal

Available

Charge

(NAC)

Last

Measured

Discharged

(LMD)

Discharge

Count

(DCR)

Qualified Transfer

Rate and

Temperature

Compensation

Rate and

Temperature

Compensation

Temperature Step, Other Data

Inputs

Main Counters

and Capacity

Reference (LMD)

Outputs

Serial

Port

Chip-Controlled

Available Charge

LED Display

Figure 2. Operational Overview

determined by multiplying the rated battery capac

ity in mAh by the sense resistor value:

Battery capacity (mAh)*sense resistor (Ω) =

PFC (mVh)

Selecting a PFC slightly less than the rated capac

ity for absolute mode provides capacity above the full reference for much of the battery's life.

Example: Selecting a PFC Value

Given:

Sense resistor = 0.1Ω Number of cells = 6 Capacity = 2200mAh, NiCd battery Current range = 50mA to 2A

Relative display mode Serial port only Self-discharge =

Voltage drop over sense resistor = 5mV to 400mV

Therefore:

2200mAh ∗ 0.1Ω= 220mVh

Select:

PFC = 33792 counts or 211mVh PROG

= float

PROG

= float

PROG

= float

PROG

= low

PROG

= float

DONE = low

bq2014

PROG

Programmed

Full

Count

(PFC)

PROG

= L PROG4= Z

Units

1 2 PROG3 = H PROG3 = Z PROG3 = L PROG3 = H PROG3 = Z PROG3 = L

-- -

Scale =

1/80

Scale =

1/160

Scale =

1/320

Scale =

1/640

Scale =

1/1280

Scale =

1/2560

mVh/ count

H H 49152 614 307 154 76.8 38.4 19.2 mVh

H Z 45056 563 282 141 70.4 35.2 17.6 mVh

H L 40960 512 256 128 64.0 32.0 16.0 mVh

Z H 36864 461 230 115 57.6 28.8 14.4 mVh

Z Z 33792 422 211 106 53.0 26.4 13.2 mVh

Z L 30720 384 192 96.0 48.0 24.0 12.0 mVh

L H 27648 346 173 86.4 43.2 21.6 10.8 mVh

L Z 25600 320 160 80.0 40.0 20.0 10.0 mVh

L L 22528 282 141 70.4 35.2 17.6 8.8 mVh

VSR equivalent to 2

counts/s (nom.)

90 45 22.5 11.25 5.6 2.8 mV

Table 2. bq2014 Programmed Full Count mVh Selections

Pin Connection PROG5Self-Discharge Rate DISP Display State

H Disabled LED disabled

NAC

LED enabled on discharge when

SRO

< -4mV or during a valid charge

NAC

LED on

Table 1. bq2014 Programming

The initial full battery capacity is 211mVh (2110mAh) until the bq2014 “learns” a new capacity with a qualified discharge from full to EDV1.

3. Nominal Available Charge (NAC):

NAC counts up during charge to a maximum value of LMD and down during discharge and selfdischarge to 0. NAC is reset to 0 on initialization and on the first valid charge after EDV = 1. To pre

vent overstatement of charge during periods of over

charge, NAC stops incrementing when NAC = LMD.

4. Discharge Count Register (DCR):

The DCR counts up during discharge independent of NAC and could continue increasing after NAC has decremented to 0 until V

< EDV1. Prior to NAC = 0 (empty battery), both discharge and selfdischarge increment the DCR. After NAC = 0, only discharge increments the DCR. The DCR resets to 0 when NAC = LMD. The DCR does not roll over but stops counting when it reaches FFFFh.

The DCR value becomes the new LMD value on the first charge after a valid discharge to V

EDV1

if:

No valid charges have occurred during the period between NAC = LMD and EDV1 detected.

n The self-discharge count is not more than 4096

counts (8% to 18% of PFC, specific percentage threshold determined by PFC).

The temperature is ≥ 0°C when the EDV1 level is reached during discharge.

The valid discharge flag (VDQ) indicates whether the present discharge is valid for LMD update.

Charge Counting

Charge activity is detected based on a positive voltage on the V

input. The bq2014 determines charge activ

ity sustained at a continuous rate equivalent to V

SRO

(VSR+VOS)>V

SRQ

. Once a valid charge is detected,

charge counting continues until V

SRO

falls below V

SRQ

is a programmable threshold (as described in the Digital Magnitude Filter section) and has a default value of 375µV. If charge activity is detected, the bq2014 increments the NAC at a rate proportional to V

SRO

.If enabled, the bq2014 then activates an LED display. Charge actions increment the NAC after compensation for charge rate and temperature.

Charge Control

Charge control is provided by the CHG output. This out

put is asserted continuously when NAC > 0.94 ∗ LMD. CHG is also asserted when a valid charge is detected (CHGS in the FLGS1 register is also set). CHG is low when NAC < 0.94 ∗ LMD and there is no valid charge ac

tivity.

DONE Input

When the bq2014 detects a valid charge complete with an active-high signal on the DONE input, NAC is set to LMD for

NAC

(NiCd) self-discharge setting. NAC is set

to 94% of LMD (if NAC is below 94%) for

NAC

(NiMH)

self-discharge setting. VDQ is set along with DONE.

Discharge Counting

All discharge counts where V

SRO<VSRD

cause the NAC register to decrement and the DCR to increment if EDV1 = 0. Exceeding the fast discharge threshold (FDQ) if the rate is equivalent to V

SRO

< -4mV activates the display, if enabled. The display becomes inactive after V

SRO

rises above -4mV. V

SRD

is a programmable threshold as described in the Digital Magnitude Filter section. The default value for V

SRD

is -300µV.

Self-Discharge Estimation

The bq2014 continuously decrements NAC and increments DCR for self-discharge based on time and temperature. The self-discharge count rate is programmed to be a nominal

NAC or

∗

NAC per day or disabled as se-

lected by PROG

. This is the rate for a battery whose temperature is between 20°C–30°C. The NAC register cannot be decremented below 0.

Count Compensations

The bq2014 determines fast charge when the NAC up

dates at a rate of ≥ 2 counts/sec. Charge and discharge activity is compensated for temperature and charge/dis

charge rate before updating the NAC and/or DCR. Selfdischarge estimation is compensated for temperature before updating the NAC or DCR.

Charge Compensation

Two charge efficiency compensation factors are used for trickle charge and fast charge. Fast charge is defined as a rate of charge resulting in ≥ 2 NAC counts/sec (≥ 0.15C to 0.32C depending on PFC selections; see Table 2). The compensation defaults to the fast charge factor until the actual charge rate is determined.

bq2014

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