Texas Instruments BQ2014HSN-A309TR, BQ2014HSN-A309 Datasheet

Features

➤

Accurate measurement of avail

able capacity in NiCd or NiMH batteries

➤

Low-cost battery management so

lution for pack integration

As little as

square inch of

PCB for complete circuit

Low operating current (120µA typical)

Less than 100nA of data retention current

➤

High-speed (5kb/s) single-wire communication interface (HDQ bus) for critical battery parameters

➤ Communication with an external

charge controller such as the bq2004

➤ Direct drive of remaining capacity

LEDs

➤ Automatic rate and temperature

compensation of measurements

➤ 16-pin narrow SOIC

General Description

The bq2014H NiCd/NiMH Gas Gauge IC is intended for batterypack or in-system installation to maintain an accurate record of available battery capacity. The IC monitors a voltage drop across a sense resistor connected in series between the negative battery termi

nal and ground to determine charge and discharge activity of the battery. Compensations for bat

tery temperature, self-discharge, and rate of discharge are applied to the charge counter to provide avail

able capacity information across a wide range of operating conditions. Battery capacity is automatically re

calibrated, or “learned,” in the course of a discharge cycle from full to empty.

Nominal available capacity may be directly indicated using a fivesegment LED display. The bq2014H also supports a simple single-line

bidirectional serial link to an exter

nal processor (common ground). The 5kb/s HDQ bus interface reduces communications overhead in the external microcontroller.

Internal registers include available capacity and energy, temperature, voltage and current, and battery status. The external processor may also overwrite some of the bq2014H gas gauge data registers.

The bq2014H can operate from the batteries in the pack. The REF out

put and an external transistor allow a simple, inexpensive voltage regu

lator to supply power to the circuit from the cells.

Preliminary

bq2014H

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 Charge complete

input

PN20140H..eps

16-Pin Narrow SOIC

LCOM

SEG1/PROG

SEG2/PROG

SEG3/PROG

SEG4/PROG

SEG5/PROG

DONE

REF

HDQ

RBI

DISP

System ground

SR Sense resistor input

DISP

Display control input

SB Battery sense input

RBI Register backup input

HDQ Serial communications

input/output

NC No connect

REF Voltage reference output

Supply voltage

Pin Connections

SLUS030–JUNE 1999

Low-Cost NiCd/NiMH Gas Gauge IC

Pin Names

Pin Descriptions

LCOM

LED common output

Open-drain output that switches V

to source current for the LEDs. The switch is off during initialization to allow reading of the soft pull-up or pull-down program resis

tors. LCOM is also high impedance when the display is off.

SEG

–

SEG

LED display segment outputs (dual func

tion with PROG

–PROG5)

Outputs that each may activate an LED to sink the current sourced from LCOM.

PROG

–

PROG

Programmed full count selection inputs (dual function with SEG

–SEG2)

Three-level input pins that define the pro

grammed full count (PFC) thresholds de

scribed in Table 2.

PROG

–

PROG

Power gauge scale selection inputs (dual function with SEG

–SEG4)

Three-level input pins that define the scale factor described in Table 2.

PROG

Self-discharge rate selection (dual function with SEG

)

Three-level input pin that defines the self-discharge and battery-compensation fac

tors as shown in Table 1.

DONE

Charge complete input

Communicates the status of an external charge-controller such as the bq2004 FastCharge IC to the bq2014H. Note: This pin must be pulled down to V

using a 200kΩ

resistor.

Ground

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. V

SR<VSS

indicates discharge, and VSR>

indicates charge. The effective voltage

drop, V

SRO

, as seen by the bq2014H is VSR+

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 resistor. DISP

floating allows the LED display to be active during charge. DISP

low activates the display. See

Table 1.

Secondary battery input

Monitors the battery cell-voltage potential through a high-impedance resistive divider network for end-of-discharge voltage (EDV) thresholds and for battery-removed detection.

RBI

Provides backup potential to the bq2014H reg

isters while V

≤

3V. A storage capacitor or

a battery can be connected to RBI.

HDQ

Serial communication input/output

This is the open-drain bidirectional communications port.

No connect

REF

Voltage reference output

REF provides a voltage reference output for an optional microregulator.

Supply voltage input

bq2014H

Preliminary

Functional Description

General Operation

The bq2014H determines battery capacity by moni

toring the amount of current input to or removed from a rechargeable battery. The bq2014H mea

sures discharge and charge currents, measures bat

tery voltage, estimates self-discharge, monitors the battery for low battery-voltage thresholds, and com

pensates for temperature and charge/discharge rate. Current measurement is made by monitoring the voltage across a small-value series sense resistor be

tween the negative battery terminal and ground. The bq2014H compensates the nominal available capacity register for discharge rate and tempera

ture and reports the compensated available capacity. The bq2014H uses the compensated available

capacity to drive the LED display. In addition, the bq2014H estimates the available energy using the aver

age battery voltage during the discharge cycle and re

maining compensated available capacity.

Figure 1 shows a typical battery pack application of the bq2014H using the LED display capability as a chargestate indicator. The bq2014H is configured to display capacity in relative display mode. The relative display mode uses the last measured discharge capacity of the battery as the battery “full” reference. A push-button display feature is available for momentarily enabling the LED display.

The bq2014H monitors the charge and discharge cur

rents as a voltage across a sense resistor. (See R

in Fig

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

F2014HBP.eps

DONE

SEG5/PROG

SEG4/PROG

SEG3/PROG

SEG2/PROG

SEG1/PROG

DISP

REF

bq2014H

Gas-Gauge IC

LCOM

RBI

HDQ

100K

0.1µF

Q1 ZVNL110A

See note 4

Load

Charger

1. Indicates optional.

2. Programming resistors (5 max.) and ESD-protection diodes are not shown.

3. RC on SR is required.

4. A series diode is required on RBI if the bottom series cell is used as the backup source. If the cell is used, the backup capacitor is not required, and the anode is connected to the positive terminal of the cell.

Notes:

Figure 1. Battery Pack Application Diagram—LED Display

Preliminary

bq2014H

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge currents, the bq2014H monitors the battery potential through the SB pin for the end-of-discharge voltage (EDV) thresholds.

The EDV threshold levels are used to determine when the battery has reached an “empty”state.

The EDV thresholds for the bq2014H are programmable with the default values fixed as follows:

EDV1 (first) = 0.76V

EDVF (final) = EDV1 - 0.025V = 0.735V

The battery voltage divider (RB1 and RB2 in Figure 1) is used to scale these values to the desired threshold.

If V

is below either of the two EDV thresholds, the as

sociated flag is latched and remains latched, independ

ent of V

, until the next valid charge.

EDV monitoring is disabled if the discharge rate is greater than 2C (OVLD Flag = 1) and resumes

second

after the rate falls below 2C. The V

value is available

over the serial port.

RBI Input

The RBI input pin is used with a storage capacitor or external supply to provide backup potential to the internal bq2014H registers when V

drops below 3.0V. VCCis

output on RBI when V

is above 3.0V. If using an external supply (such as the bottom series cell) as the backup source, an external diode is required for isolation.

Reset

The bq2014H can be reset by removing VCCand ground

ing the RBI pin for 15 seconds or by commands over the serial port. The serial port reset command sequence re

quires writing 00h to register PPFC (address = 1Eh) and then writing 00h to register LMD (address = 05h).

Temperature

The bq2014H internally determines the temperature in 10°C steps centered from approximately -35°C to +85°C. The temperature steps are used to adapt charge and dis

charge 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 in the following table

Layout Considerations

The bq2014H 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 (C1 and C2) should be placed as close as possible to the V

and SB 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 capacitor should be placed as close as possible to the SR pin.

■

The sense resistor (RS) should be as close as possible to the bq2014H.

TMP (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

bq2014H

Preliminary

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates the operation of the bq2014H. The bq2014H accumu

lates a measure of charge and discharge currents, as well as an estimation of self-discharge. The accumu

lated charge and discharge currents are adjusted for temperature and rate to provide the indication of com

pensated available capacity to the host system or user.

The main counter, Nominal Available Capacity (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 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 bq2014H adapts its capacity determination based on the actual condi

tions of discharge.

The battery's initial capacity equals the Programmed Full Count (PFC) shown in Table 2. Until LMD is up

dated, 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.

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 representing a discharge from full to below EDV1. A qualified discharge is necessary for a capacity transfer from the DCR to the LMD register. The LMD also serves as the 100% reference threshold used by the relative display mode.

F2014HOO.eps

Temperature

Compensation

Charge Current

Discharge

Current

Self-Discharge

Timer

Nominal

Available

Charge

(NAC)

Last

Measured

Discharged

(LMD)

Discharge

Count

(DCR)

Qualified

Transfer

Temperature Step, Other Data

Inputs

Main Counters

and Capacity

Reference (LMD)

Outputs

Serial

Port

Compensated Available Charge LED Display, etc.

Rate and

Temperature

Compensation

Rate and

Temperature

Compensation

Figure 2. Operational Overview

Preliminary

bq2014H

2. Programmed Full Count (PFC) or initial bat

tery capacity:

The initial LMD and gas gauge rate values are pro

grammed by using PROG

–PROG4. The bq2014H is configured for a given application by selecting a PFC value from Table 2. The correct PFC may be 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 provides a conservative capacity reference until the bq2014H “learns” a new capacity reference.

Example: Selecting a PFC Value

Given:

Sense resistor = 0.05

Ω

Number of cells = 10 Capacity = 3500mAh, NiMH Current range = 50mA to 1A Relative display mode Self-discharge =

NAC

per day @ 25°C Voltage drop over sense resistor = 2.5mV to 50mV Nominal discharge voltage = 1.2V

Therefore:

3500mAh*0.05Ω= 175mVh

PROG

Pro-

grammed

Full

Count

(PFC)

PROG

= L PROG4= Z or H

Units

PROG

= 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

equivalent to 2

counts/s (nom.)

90 45 22.5 11.25 5.6 2.8 mV

Table 2. bq2014H Programmed Full Count mVh, VSRGain Selections

Connection

PROG

Self-Discharge Rate

DISP

Display State

H Disabled LEDs disabled

NAC

LEDs on when charging

NAC

LEDs on for 4s

Table 1. Self-Discharge and Capacity Compensation

bq2014H

Preliminary

Select:

PFC = 27648 counts or 173mVh PROG

= low

PROG

= high

PROG

= float

PROG

= low

PROG

= low

The initial full battery capacity is 173mVh (3460mAh) until the bq2014H “learns” a new capac

ity with a qualified discharge from full to EDV1.

3. Nominal Available Capacity (NAC):

NAC counts up during charge to a maximum value of LMD and down during discharge and self-dis

charge to 0. NAC is reset to 0 on initialization and on the first valid charge following discharge to EDV1. To prevent overstatement of charge during periods of overcharge, NAC stops incrementing when NAC = LMD or 0.94 ∗ LMDifT<0°C.

4. Discharge Count Register (DCR):

The DCR counts up during discharge independent of NAC and could continue increasing after NAC has decremented to 0. Prior to NAC = 0 (empty battery), both discharge and self-discharge increment the DCR. After NAC = 0, only discharge increments the DCR. The DCR resets to 0 when NAC ≥ 0.94 ∗ LMD and a discharge is detected. The DCR does not roll over but stops counting when it reaches FFh.

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

EDV1

if all

the following conditions are met:

■

No valid charge initiations (charges greater than 2 NAC updates where V

SRO>VSRQ

) occurred during the period between NAC ≥ 0.94 ∗ LMD and EDV1.

■

The self-discharge is less than 6.25% of NAC.

■

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

■

The discharge begins when NAC ≥ 0.94 ∗ LMD.

■

VDQ is set.

The valid discharge flag (VDQ) indicates whether the present discharge is valid for LMD update. If the DCR update value is less than 0.94 ∗ LMD, LMD will only be modified by 0.94 ∗ LMD. This pre

vents invalid DCR values from corrupting LMD.

5. Scaled Available Energy (SAE):

SAE is useful in determining the available energy within the battery, and may provide a more useful

capacity reference in battery chemistries with sloped voltage profiles during discharge. SAE may be converted to an mWh value using the following formula:

E(mWh) =

(SAEH SAEL)∗+ ∗256

12. ∗∗

∗

SCALE (R + R )

B1 B2

SB2

where RB1,RB2, and RSare resistor values in ohms, as shown in Figure 1. SCALE is the selected scale from Table 2.

6. Compensated Available Capacity (CACT)

CACT counts similarly to NAC, but contains the available capacity compensated for discharge rate and temperature.

Charge Counting

Charge activity is detected based on a positive voltage on the SR input. If charge activity is detected, the bq2014H increments NAC at a rate proportional to V

and, if enabled, activates the LED display.

The bq2014H counts charge activity when the voltage at theSRinput(V

SRO

) exceeds the minimum charge

threshold (V

SRQ

). A valid charge is detected when NAC has been updated twice without discharging or reaching the digital magnitude filter time-out. Once a valid charge is detected, charge counting continues until V

including offset,falls below V

SRQ

Discharge Counting

Discharge activity is indicated by a negative voltage on the SR input. All discharge counts where V

SRO

is less

than the minimum discharge threshold (V

SRD

) cause the NAC register to decrement and the DCR to increment.

Self-Discharge Counting

The bq2014H continuously decrements NAC and incre

ments DCR for self-discharge on the basis of time and tem

perature.

Charge/Discharge Current

The bq2014H current-scale registers, VSRH and VSRL, can be used to determine the battery charge or dis

charge current. See the Current Scale Register descrip

tion for details.

Preliminary

bq2014H

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