TEXAS INSTRUMENTS bq2000 Technical data

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bq2000

Programmable Multi-Chemistry

Fast-Charge Management IC

Features

Safe management of fast

➤

charge for NiCd, NiMH, or Li­Ion battery packs

High-frequency switching con

➤

troller for efficient and simple
charger design

Pre-charge qualification for

➤

detecting shorted, damaged, or
overheated cells

Fast-charge termination by

➤

peak voltage (PVD), minimum
current (Li-Ion), maximum
temperature, and maximum
charge time

➤ Selectable top-off mode for

achieving maximum capacity in
NiMH batteries

➤ Programmable trickle-charge

mode for reviving deeply dis­charged batteries and for post­charge maintenance

➤ Built-in battery removal and

insertion detection

➤

Sleep mode for low power
consumption

General Description

The bq2000 is a programmable,
monolithic IC for fast-charge manage
ment of nickel cadmium (NiCd),
nickel metal-hydride (NiMH), or lith

-

ium-ion (Li-Ion) batteries in single- or
multi-chemistry applications. The
bq2000 detects the battery chemistry
and proceeds with the optimal charg
ing and termination algorithms. This
process eliminates undesirable under
charged or overcharged conditions
and allows accurate and safe termi
nation of fast charge.

Depending on the chemistry, the
bq2000 provides a number of charge
termination criteria:

Peak voltage, PVD (for NiCd and

n

NiMH)

n Minimum charging current (f or

Li-Ion)

n

Maximum temperature

n

Maximum charge time

For safety, the bq2000 inhibits fast
charge until the battery voltage and
temperature are within user-defined

-

limits. If the battery voltage is
below the low-voltage threshold, the

-

bq2000 uses trickle-charge to
condition the battery. For NiMH
batteries, the bq2000 provides an
optional top-off charge to maximize

-

the battery capacity.
The integrated high-frequency com

­parator allows the bq2000 to be the

basis for a complete, high-efficiency

­power-conversion circuit for both

nickel-based and lithium-based
chemistries.

-

Pin Connections

or TSSOP

8

7

6

5

PN-2000.eps

SNS

V

LED

BAT

SLUS138B–FEBRUARY 2001 F

1

2

SS

3

4

8-Pin DIP or Narrow SOIC

MOD

V

CC

RC

TS

Pin Names

SNS Current-sense input
V

SS

LED

BAT Battery-voltage

System ground
Charge-status

output

input

1

TS Temperature-sense

RC Timer-program input
V

CC

MOD Modulation-control

input

Supply-voltage input

output

bq2000

Pin Descriptions

SNS

V

SS

LED

BAT

TS

Current-sense input

Enables the bq2000 to sense the battery cur
rent via the voltage developed on this pin by
an external sense-resistor connected in se
ries with the battery pack

System Ground
Charge-status output

Open-drain output that indicates the charg
ing status by turning on, turning off, or
flashing an external LED

Battery-voltage input

Battery-voltage sense input. A simple resistive
divider, across the battery terminals, generates
this input.

T emperature-senseinput

Input for an external battery-temperature
monitoring circuit. An external resistive di­vider network with a negative tempera­ture-coefficient thermistor sets the lower
and upper temperature thresholds.

RC

Timer-program input

RC input used to program the maximum
charge-time, hold-off period, and trickle

-

-

V

CC

MOD

rate during the charge cycle, and to disable
or enable top-off charge

Supply-voltage input
Modulation-control output

Push-pull output that controls the charging
current to the battery. MOD switches high

-

to enable charging current to flow and low to
inhibit charging- current flow .

Functional Description

The bq2000 is a versatile, multi-chemistry battery­charge control device. See Figure 1 for a functional block
diagram and Figure 2 for a state diagram.

TS

BAT

RC

Voltage

Reference

PVD
ALU

Timer

OSC

ADC

Clock

Phase

Generator

Internal

OSC

Figure 1. Functional Block Diagram

2

SNS

Voltage

Comparator

Charge
Control

Voltage

Comparator

V

CCVSS

LED

MOD

bq2000BD.eps

bq2000

Figure 2. State Diagram

3

bq2000

Initiation and ChargeQualification

The bq2000 initiates a charge cycle when it detects

Application of power to V

n

Battery replacement

n

Exit from sleep mode

n

Capacity depletion (Li-Ion only)

n

Immediately following initiation, the IC enters a
charge-qualification mode. The bq2000 charge qualifica
tion is based on battery voltage and temperature. If
voltage on pin BAT is less than the internal threshold,
V

, the bq2000 enters the charge-pending state. This

LBAT

condition indicates the possiblility of a defective or
shorted battery pack. In an attempt to revive a fully
depleted pack, the bq2000 enables the MOD pin to
trickle-charge at a rate of once every 1.0s. As explained
in the section “Top-Off and Pulse-Trickle Charge,” the
trickle pulse-width is user-selectable and is set by the
value of the resistance connected to pin RC.

During this period, the LED
indicating the pending status of the charger.

Similarly, the bq2000 suspends fast charge if the battery
temperature is outside the V

4.) For safety reasons, however, it disables the pulse
trickle, in the case of a battery over-temperature condition
(i.e., V

TS<VHTF

). Fast charge begins when the battery

temperature and voltage are valid.

CC

pin blinks at a 1Hz rate,

LTF

to V

range. (See Table

HTF

Battery Chemistry

The bq2000 detects the battery chemistry by monitoring
the battery-voltage profile during the initial stage of the
fast charge. If the voltage on BAT input rises to the in
ternal V

reference, the IC assumes a Li-Ion battery.

MCV

Otherwise the bq2000 assumes NiCd/NiMH chemistry.
As shown in Figure 6, a resistor voltage-divider between

the battery pack’s positive terminal and V

scales the

SS

battery voltage measured at pin BAT. In a
mixed-chemistry design, a common voltage-divider is
used as long as the maximum charge voltage of the

­nickel-based pack is below that of the Li-Ion pack. Oth

erwise, different scaling is required.
Once the chemistry is determined, the bq2000 completes

the fast charge with the appropriate charge algorithm
(Table 1). The user can customize the algorithm by
programming the device using an external resistor and
a capacitor connected to the RC pin, as discussed in
later sections.

NiCd and NiMHBatteries

Following qualification, the bq2000 fast-charges NiCd or
NiMH batteries using a current-limited algorithm. Dur­ing the fast-charge period, it monitors charge time, tem­perature, and voltage for adherence to the termination
criteria. This monitoring is further explained in later
sections. Following fast charge, the battery is topped off,
if top-off is selected. The charging cycle ends with a
trickle maintenance-charge that continues as long as
the voltage on pin BATremainsbelowV

MCV

.

-

-

I

MAX

Trickle

I

MIN

Current

Voltage

Qualification

Fast Charge

Phase 1 Phase 2

Current

Time

Figure 3. Lithium-Ion Charge Algorithm

4

GR2000CA.eps

V

MCV

V

LBAT

Voltage

Table 1. Charge Algorithm

Battery Chemistry Charge Algorithm

1. Charge qualification

2. Trickle charge, if required

NiCd or NiMH

Li-Ion

3. Fast charge (constant current)

4. Charge termination (peak voltage, maximum charge time)

5. Top-off (optional)

6. Trickle charge

1. Charge qualification

2. Trickle charge, if required

3. Two-step fast charge (constant current followed by constant voltage)

4. Charge termination (minimum current, maximum charge time)

bq2000

Lithium-Ion Batteries

The bq2000 uses a two-phase fast-charge algorithm for
Li-Ion batteries (Figure 3). In phase one, the bq2000
regulates constant current until V

BAT

rises to V

MCV

. The
bq2000 then moves to phase two, regulates the battery
with constant voltage of V
charging current falls below the I

, and terminates when the

MCV

threshold. A new

MIN

charge cycle is started if the cell voltage falls below the
V

threshold.

RCH

During the current-regulation phase, the bq2000
monitors charge time, battery temperature, and battery
voltage for adherence to the termination criteria. During
the final constant-voltage stage, in addition to the
charge time and temperature, it monitors the charge
current as a termination criterion. There is no
post-charge maintenance mode for Li-Ion batteries.

Charge Termination
Maximum Charge Time (NiCD, NiMH, and

Li-Ion)

The bq2000 sets the maximum charge-time through pin
RC. With the proper selection of external resistor and
capacitor, various time-out values may be achieved. Fig
ure 4 shows a typical connection.

The following equation shows the relationship between
the R
time (MTO) for the bq2000:

MTO is measured in minutes, R
in farads. (Note: R
other features of the device. See Tables 2 and 3 for de
tails.)

For Li-Ion cells, the bq2000 resets the MTO when the
battery reaches the constant-voltage phase of the

MTO

and C

MTO=R

values and the maximum charge

MTO

∗ C

∗ 35,988

MTO

in ohms, and C

MTO

values also determine

MTO

MTO

MTO

and C

MTO

charge. This feature provides the additional charge time
required for Li-Ion cells.

Maximum Temperature(NiCd, NiMH, Li-Ion)

A negative-coefficient thermistor, referenced to VSSand
placed in thermal contact with the battery, may be used
as a temperature-sensing device. Figure 5 shows a typi­cal temperature-sensing circuit.

During fast charge, the bq2000 compares the battery
temperature to an internal high-temperature cutoff
threshold, V

. As shown in Table 4, high-temperature

TCO

termination occurs when voltage at pin TS is less than
this threshold.

Peak Voltage(NiCd, NiMH)

The bq2000 uses a peak-voltage detection (PVD) scheme
to terminate fast charge for NiCd and NiMH batteries.
The bq2000 continuously samples the voltage on the
BAT pin, representing the battery voltage, and triggers
the peak detection feature if this value falls below the
maximum sampled value by as much as 3.8mV (PVD).
As shown in Figure 6, a resistor voltage-divider between
the battery pack’s positive terminal and V
battery voltage measured at pin BAT.

-

For Li-Ion battery packs, the resistor values R
R

are calculated by the following equation:

B2

R

B1
B2

R

V




N

=∗



V

CELL

MCV






where N is the number of cells in series and V
manufacturer-specified charging voltage. The end-to­end input impedance of this resistive divider network
should be at least 200kΩ and no more than 1MΩ.

-

A NiCd or NiMH battery pack consisting of N series­cells may benefit by the selection of the R
N-1 times larger than the R

B2

value.

In a mixed-chemistry design, a common voltage-divider
is used as long as the maximum charge voltage of the

− 1

SS

CELL

value to be

B1

scales the

and

B1

is the

5

bq2000

2

V

SS

bq2000

7

V

CC

C

MTO

6

RC

R

MTO

F2000 RCI.eps

Figure 4. Typical Connection for the RC Input

V

CC

2

V

SS

bq2000

7

V

CC

R

T1

5

TS

N

R

T2

Battery

T

C

F2000TMC.eps

Pack

Figure 5. Temperature Monitoring Configuration

R

B1

R

B2

BAT+

F2000BVD.eps

2

V

SS

bq2000

4

BAT

Figure 6. Battery Voltage Divider

6