Texas Instruments EV2050, BQ2050SN-D119TR, BQ2050SN-D119 Datasheet

1

Features

➤

Conservative and repeatable
measurement of available capac

­ity in Lithium Ion rechargeable
batteries

➤

Designed for battery pack inte

­gration

-

120µA typical operating
current

-

Small size enables imple­mentations in as little as

1

2

square inch of PCB

➤

Integrate within a system or as a
stand-alone device

-

Display capacity via single­wire serial communication
port or direct drive of LEDs

➤ Measurements compensated for

current and temperature

➤ Self-discharge compensation us-

ing internal temperature sensor

➤ 16-pin narrow SOIC

General Description

The bq2050 Lithium Ion Power
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 and rate of charge
or discharge are applied to the
charge, discharge, and self-discharge
calculations to provide available ca

­pacity information across a wide
range of operating conditions. Bat

­tery capacity is automatically recali

­brated, 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. These seg­ments are used to graphically indi­cate available capacity. The bq2050

supports a simple single-line bidi

­rectional serial link to an external
processor (common ground). The
bq2050 outputs battery information
in response to external commands
over the serial link.

The bq2050 may operate directly
from one cell (V

BAT

> 3V). With the

REF output and an external transis

­tor, a simple, inexpensive regulator
can be built for systems with more
than one series cell.

Internal registers include available
capacity, temperature, scaled avail

­able energy, 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 bq2050
power gauge data registers.

LCOM LED common output

SEG

1

/PROG1LED segment 1/

program 1 input

SEG

2

/PROG2LED segment 2/

program 2 input

SEG

3

/PROG3LED segment 3/

program 3 input

SEG

4

/PROG4LED segment 4/

program 4 input

SEG

5

/PROG5LED segment 5/

program 5 input

PROG

6

Program 6 input

1

PN205001.eps

16-Pin Narrow SOIC

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

V

CC

REF

N/C

DQ

RBI

SB

DISP

SR

LCOM

SEG1/PROG

1

SEG2/PROG

2

SEG3/PROG

3

SEG4/PROG

4

SEG5/PROG

5

PROG

6

V

SS

REF Voltage reference output

N/C No connect

DQ Serial communications

input/output

RBI Register backup input

SB Battery sense input

DISP

Display control input

SR Sense resistor input

V

CC

3.0–6.5V

V

SS

System ground

Pin Connections Pin Names

bq2050

9/96 C

Lithium Ion Power Gauge™ IC

Pin Descriptions

LCOM

LED common output

Open-drain output switches V

CC

to source

current for the LEDs. The switch is off dur

­ing initialization to allow reading of the soft
pull-up or pull-down program resistors.
LCOM is also high impedance when the dis

­play is off.

SEG

1

–

SEG

5

LED display segment outputs (dual func

­tion with PROG

1

–PROG6)

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

PROG

1

–

PROG

2

Programmed full count selection inputs
(dual function with SEG

1

–SEG2)

These three-level input pins define the pro

­grammed full count (PFC) thresholds de

­scribed in Table 2.

PROG

3

–

PROG

4

Power gauge rate selection inputs (dual
function with SEG

3

–SEG4)

These three-level input pins define the scale
factor described in Table 2.

PROG

5

Self-discharge rate selection (dual func­tion with SEG

5

)

This three-level input pin defines the
selfdischarge and battery compensation fac­tors as shown in Table 1.

PROG

6

Capacity initialization selection

This three-level pin defines the battery state
of charge at reset as shown in Table 1.

N/C

No connect

SR

Sense resistor input

The voltage drop (V

SR

) across the sense re

-

sistor R

S

is monitored and integrated over

time to interpret charge and discharge activ

-

ity. The SR input is tied between the nega

-

tive terminal of the battery and the sense re

-

sistor. V

SR<VSS

indicates discharge, and V

SR

>VSSindicates charge. The effective voltage
drop, V

SRO

, as seen by the bq2050 is VSR+

V

OS

.

DISP

Display control input

DISP

high disables the LED display. DISP
tied to VCCallows PROGXto connect directly
to V

CC

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.

SB

Secondary battery input

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

RBI

Register backup input

This pin is used to provide backup potential to
the bq2050 registers during periods when
V

CC

≤ 3V. A storage capacitor or a battery

can be connected to RBI.

DQ

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.

V

CC

Supply voltage input

V

SS

Ground

2

bq2050

Functional Description

General Operation

The bq2050 determines battery capacity by monitor

­ing the amount of current input to or removed from a
rechargeable battery. The bq2050 measures dis

­charge and charge currents, measures battery volt

­age, estimates self-discharge, monitors the battery
for low battery voltage thresholds, and compensates
for temperature and charge/discharge rates. The cur

­rent measurement is made by monitoring the voltage
across a small-value series sense resistor between the
negative battery terminal and ground. The estimate of
scaled available energy is made using the remaining
average battery voltage during the discharge cycle
and the remaining nominal available charge. The

scaled available energy measurement is corrected for
the environmental and operating conditions.

Figure 1 shows a typical battery pack application of the
bq2050 using the LED display capability as a charge­state indicator. The bq2050 is configured to display ca

­pacity 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 bq2050 monitors the charge and discharge currents
as a voltage across a sense resistor (see R

S

in Figure 1).
A filter between the negative battery terminal and the
SR pin may be required if the rate of change of the bat

-

tery current is too great.

3

bq2050

FG205001.eps

PROG

6

SEG5/PROG

5

SEG4/PROG

4

SEG3/PROG

3

SEG2/PROG

2

SEG1/PROG

1

SR

DISP

SB

V

CC

REF

bq2050

Power Gauge IC

LCOM

V

SS

RBI

DQ

V

CC

C1

0.1 F

Q1
ZVNL110A

R

1

R

S

RB

1

RB

2

Load

Charger

Indicates optional.

Directly connect to VCC across 1 cell (V

BAT

> 3V).

Otherwise, R1, C1, and Q1 are needed for regulation of > 1 cell.

Programming resistors (6 max.) and ESD-protection diodes are not shown.

R-C on SR may be required, application-specific.

A series Zener may be used to limit discharge current at low voltages
in desi

g

ns using 3 or more cells.

V

CC

C2

1M

PSTAT

Figure 1. Battery Pack Application Diagram—LED Display

Voltage Thresholds

In conjunction with monitoring VSRfor charge/discharge
currents, the bq2050 monitors the battery potential
through the SB pin. The voltage is determined through
a resistor-divider network per the following equation:

RB1
RB2

2N=−1

where N is the number of cells, RB1 is connected to the
positive battery terminal, and RB2 is connected to the
negative battery terminal. The single-cell battery volt

­age is monitored for the end-of-discharge voltage (EDV).
EDV threshold levels are used to determine when the
battery has reached an “empty” state.

Two EDV thresholds for the bq2050 are programmable
with the default values fixed at:

EDV1 (early warning) = 1.52V

EDVF (empty) = 1.47V

If V

SB

is below either of the two EDV thresholds, the as

­sociated flag is latched and remains latched, independ­ent of V

SB

, until the next valid charge. The VSBvalue is

also available over the serial port.

During discharge and charge, the bq2050 monitors V

SR

for various thresholds used to compensate the charge
and discharge rates. Refer to the count compensation
section for details. EDV monitoring is disabled if the
discharge rate is greater than 2C (typical) and resumes

1

2

second after the rate falls below 2C.

RBI Input

The RBI input pin is intended to be used with a storage ca

­pacitor or external supply to provide backup potential to the
internal bq2050 registers when V

CC

drops below 3.0V. V

CC

is output on RBI when VCCis above 3.0V. A diode is re

­quired to isolate the external supply.

Reset

The bq2050 can be reset either by removing VCCand
grounding the RBI pin for 15 seconds or by writing 0x80
to register 0x39.

Temperature

The bq2050 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 incre

­ments as shown in the following table:

Layout Considerations

The bq2050 measures the voltage differential between
the SR and V

SS

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

n

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

CC

and SB pins,

respectively, and their paths to V

SS

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

CC

.

n

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

n

The sense resistor (RS) should be as close as possible to
the bq2050.

4

bq2050

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

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates
the operation of the bq2050. The bq2050 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 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 (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
bq2050 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 al

­lows the gas gauge to be charger-independent and com

­patible 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

CC

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 capac

-

ity transfer from the DCR to the LMD register. The
LMD also serves as the 100% reference threshold
used by the relative display mode.

5

bq2050

FG205002.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

Register

(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

Compensated
Available Charge
LED Display, etc.

Figure 2. Operational Overview

2. Programmed Full Count (PFC) or initial bat

-

tery capacity:

The initial LMD and gas gauge rate values are pro

-

grammed by using PROG

1

–PROG4. The bq2050 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 bq2050 “learns” a new capacity reference.

Example: Selecting a PFC Value

Given:

Sense resistor = 0.05

Ω

Number of cells = 2
Capacity = 1000mAh, Li-Ion battery, coke-anode
Current range = 50mA to 1A
Relative display mode
Serial port only
Self-discharge =

NAC

512

per day @ 25°C
Voltage drop over sense resistor = 2.5mV to 50mV
Nominal discharge voltage = 3.6V

Therefore:

1000mAh*0.05Ω= 50mVh

6

bq2050

PROG

x

Pro-

grammed

Full

Count

(PFC)

PROG

4

= 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/sec. (nom.)

90 45 22.5 11.25 5.6 2.8 mV

Table 2. bq2050 Programmed Full Count mVh Selections

Pin

Connection

PROG5Compensation/

Self-Discharge

PROG

6

NAC on Reset

DISP

Display State

H Table 4/Disabled PFC LEDs disabled

Z Table 4/

NAC

512

0 LEDs on when charging

L Table 3/

NAC

512

0 LEDs on for 4 sec.

Note: PROG5and PROG6states are independent.

Table 1. bq2050 Programming

Select:

PFC = 30720 counts or 48mVh
PROG

1

= float

PROG

2

= low

PROG

3

= high

PROG

4

= float

PROG

5

= float

PROG

6

= float

The initial full battery capacity is 48mVh (960mAh)
until the bq2050 “learns” a new capacity 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.

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 = 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 charge initiations (charges greater than
256 NAC counts, where V

SRO>VSRQ

) occurred dur

­ing the period between NAC = LMD and EDV1 de

­tected.

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.

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 a mWh value using the following
formula:

E(mWh) =

(* *SAEH SAEL)256 +

24.)∗∗+

∗

SCALE (R R

RR

B1 B2

SB2

where RB1,RB2and RSare resistor values in ohms.
SCALE is the selected scale from Table 2. SAEH
and SAEL are digital values read via DQ.

6. Compensated Available Capacity (CAC)

CAC counts similar to NAC, but contains the avail

­able capacity compensated for discharge rate and
temperature.

Charge Counting

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

SR

input. If charge activity is detected, the

bq2050 increments NAC at a rate proportional to V

SR

and,

if enabled, activates an LED display. Charge actions in

-

crement the NAC after compensation for temperature.

The bq2050 determines charge activity sustained at a
continuous rate equivalent to V

SRO>VSRQ

. A valid
charge equates to sustained charge activity greater
than 256 NAC counts. Once a valid charge is detected,
charge counting continues until V

SRO(VSR+VOS

) falls

below V

SRQ

.V

SRQ

is 210µV, and is described in the

Digital Magnitude Filter section.

Discharge Counting

Discharge activity is detected based on a negative voltage
on the V

SR

input. All discharge counts where V

SRO<VSRD

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

SRD

is -200µV, and is described in the

Digital Magnitude Filter section.

Self-Discharge Estimation

The bq2050 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

1

512

*

NAC per day or disabled. This is the rate for a bat

­tery whose temperature is between 20°–30°C. The NAC
register cannot be decremented below 0.

Count Compensations

Discharge Compensation

Corrections for the rate of discharge, temperature, and anode
type are made by adjusting an internal compensation factor.
This factor is based on the measured rate of discharge of the
battery. Tables 3A and 3B outline the correction factor typi

­cally used for graphite anode Li-Ion batteries, and Tables 4A
and 4B outline the factors typically used for coke anode
Li-Ion batteries. The compensation factor is applied to
CAC and is based on discharge rate and temperature.

7

bq2050