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1
Features
S a f e m a n a g e m e n t o f f a s t
charge for NiCd, NiMH, or Li-
Ion 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
T/t
m i n i m u m
c u r r e n t
(Li-Ion), maximum tempera-
ture, and maximum charge
time
Selectable top-off mode for
achieving maximum capacity in
NiMH batteries
Programmable trickle-charge
mode for reviving deeply dis-
charged batteries and for post-
charge maintenance
Built-in battery removal and
insertion detection
S l e e p m o d e f o r l o w p o w e r
consumption
General Description
The bq2000T 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
bq2000T detects the battery chemis-
try and proceeds with the optimal
charging and termination algorithms.
This process eliminates undesirable
undercharged or overcharged condi-
tions and allows accurate and safe
termination of fast charge.
Depending on the chemistry, the
bq2000T provides a number of
charge termination criteria:
n
Rate of temperature rise,
T/t (for
NiCd and NiMH)
n
Minimum charging current (for
Li-Ion)
n
Maximum temperature
n
Maximum charge time
For safety, the bq2000T inhibits fast
charge until the battery voltage and
temperature are within user-defined
limits. If the battery voltage is below
t h e l o w - v o l t a g e t h r e s h o l d , t h e
bq2000T uses trickle-charge to
condition the battery.
For NiMH
batteries, the bq2000T provides an
optional top-off charge to maximize
the battery capacity.
The integrated high-frequency com-
parator allows the bq2000T to be the
basis for a complete, high-efficiency
power-conversion circuit for both
nickel-based and lithium-based
chemistries.
bq2000T
SNS
Current-sense input
V
SS
System ground
LED
Charge-status
output
BAT
Battery-voltage
input
1
PN-2000.eps
8-Pin DIP or Narrow SOIC
or TSSOP
2
3
4
8
7
6
5
SNS
LED
BAT
VSS
MOD
VCC
TS
RC
Pin Connections
Pin Names
Programmable Multi-Chemistry
Fast-Charge Management IC
SLUS149AFEBRUARY 2000
TS
Temperature-sense
input
RC
Timer-program input
V
CC
Supply-voltage input
MOD
Modulation-control
output
2
Pin Descriptions
SNS
Current-sense input
Enables the bq2000T to sense the battery
current via the voltage developed on this pin
by an external sense-resistor connected in
series with the battery pack
V
SS
System Ground
LED
Charge-status output
Open-drain output that indicates the charg-
ing status by turning on, turning off, or
flashing an external LED
BAT
Battery-voltage input
Battery-voltage sense input. A simple resistive
divider, across the battery terminals, generates
this input.
TS
Temperature-sense input
Input for an external battery-temperature
monitoring circuit. An external resistive di-
vider network with a negative tempera-
ture-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
rate during the charge cycle, and to disable
or enable top-off charge
V
CC
Supply-voltage input
MOD
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 bq2000T is a versatile, multi-chemistry battery-
charge control device. See Figure 1 for a functional block
diagram and Figure 2 for the state diagram.
bq2000T
BD2000T.eps
Voltage
Reference
Internal
OSC
Clock
Phase
Generator
ADC
OSC
SNS
TS
MOD
RC
BAT
LED
V
CC
V
SS
Timer
T/t
ALU
Voltage
Comparator
Voltage
Comparator
Charge
Control
Figure 1. Functional Block Diagram
3
bq2000T
Charge
Initialization
4.0V < V
CC
< 6.0V
Sleep
Mode
Charge
Suspended
Battery
Conditioning
Current
Regulation
Voltage
Regulation
Current Taper
or
Time = MTO
Time < MTO
and
V
BAT
> V
MCV
Maintenance
Charge
Done
Top-Off
Yes
No
V
CC
Reset or Battery Replacement or Capacity Depletion (Li-Ion)
V
CC
Reset
V
BAT
> V
MCV
Time = MTO or
V
TS
< V
TCO
T/t (after hold-off period),
or V
TS
< V
TCO
or
Time = MTO
Battery Voltage
(checked at all times)
Battery Temperature
(checked at all times)
Top-Off
Selected?
V
BAT
< V
SLP
V
BAT
< V
MCV
V
TS
> V
HTF
V
BAT
< V
LBAT
or
V
TS
> V
LTF
V
LBAT
< V
BAT
< V
MCV
and
V
HTF
< V
TS
< V
LTF
V
LBAT
< V
BAT
< V
MCV
and
V
HTF
< V
TS
< V
LTF
V
TS
< V
HTF
V
SLP
< V
BAT
< V
CC
V
MCV
< V
BAT
< V
SLP
SD2000T.eps
V
BAT
> V
MCV
Figure 2. State Diagram
Initiation and Charge Qualification
The bq2000T initiates a charge cycle when it detects
n
Application of power to V
CC
n
Battery replacement
n
Exit from sleep mode
n
Capacity depletion (Li-Ion only)
Immediately following initiation, the IC enters a
charge-qualification mode. The bq2000T charge qualifi-
cation is based on battery voltage and temperature. If
voltage on pin BAT is less than the internal threshold,
V
LBAT
, the bq2000T enters the charge-pending state.
This condition indicates the possiblility of a defective or
shorted battery pack. In an attempt to revive a fully
depleted pack, the bq2000T 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 pin blinks at a 1Hz rate,
indicating the pending status of the charger.
Similarly, the bq2000T suspends fast charge if the battery
temperature is outside the V
LTF
to V
HTF
range. (See Table
4.) For safety reasons, however, it disables the pulse
trickle, in the case of a battery over-temperature condition
(i.e., V
TS
< V
HTF
). Fast charge begins when the battery
temperature and voltage are valid.
Battery Chemistry
The bq2000T detects the battery chemistry by monitor-
ing the battery-voltage profile during fast charge. If the
voltage on BAT input rises to the internal V
MCV
refer-
ence, the IC assumes a Li-Ion battery. Otherwise the
bq2000T assumes NiCd/NiMH chemistry.
As shown in Figure 6, a resistor voltage-divider between
the battery pack's positive terminal and V
SS
scales the
b a t t e r y v o l t a g e m e a s u r e d a t p i n BAT. I n 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 bq2000T
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 NiMH Batteries
Following qualification, the bq2000T 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 termina-
tion 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
4
bq2000T
GR2000CA.eps
I
MAX
I
MIN
Trickle
V
LBAT
V
MCV
Current
Voltage
Qualification
Time
Phase 1
Phase 2
Fast Charge
Voltage
Current
Figure 3. Lithium-Ion Charge Algorithm
with a trickle maintenance-charge that continues as
long as the voltage on pin BAT remains below V
MCV
.
Lithium-Ion Batteries
The bq2000T uses a two-phase fast-charge algorithm for
Li-Ion batteries (Figure 3). In phase one, the bq2000T
regulates constant current until V
BAT
rises to V
MCV
. The
bq2000T then moves to phase two, regulates the battery
with constant voltage of V
MCV
, and terminates when the
charging current falls below the I
MIN
threshold. A new
charge cycle is started if the cell voltage falls below the
V
RCH
threshold.
During the current-regulation phase, the bq2000T
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 bq2000T sets the maximum charge-time through
pin RC. With the proper selection of external resistor
and capacitor, various time-out values may be achieved.
Figure 4 shows a typical connection.
The following equation shows the relationship between
the R
MTO
and C
MTO
values and the maximum charge
time (MTO) for the bq2000T:
MTO = R
MTO
C
MTO
35,988
MTO is measured in minutes, R
MTO
in ohms, and C
MTO
in farads. (Note: R
MTO
and C
MTO
values also determine
other features of the device. See Tables 2 and 3 for de-
tails.)
For Li-Ion cells, the bq2000T resets the MTO when the
battery reaches the constant-voltage phase of the
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 V
SS
and
placed in thermal contact with the battery, may be used
as a temperature-sensing device. Figure 5 shows a typi-
cal temperature-sensing circuit.
During fast charge, the bq2000T compares the battery
temperature to an internal high-temperature cutoff
threshold, V
TCO
. As shown in Table 4, high-temperature
termination occurs when voltage at pin TS is less than
this threshold.
T/t (NiCd, NiMH)
When fast charging, the bq2000T monitors the voltage
at pin TS for rate of temperature change detection,
T/t. The bq2000T samples the voltage at the TS pin
every 16s and compares it to the value measured 2 sam-
ples earlier. This feature terminates fast charge if this
voltage declines at a rate of
V
161
V
Min
CC
Figure 5 shows a typical connection diagram.
Minimum Current (Li-Ion Only)
The bq2000T monitors the charging current during the
voltage-regulation phase of Li-Ion batteries. Fast charge
is terminated when the current is tapered off to 7% of
the maximum charging current. Please note that this
threshold is different for the bq2000.
Initial Hold-Off Period
The values of the external resistor and capacitor con-
nected to pin RC set the initial hold-off period. During
this period, the bq2000T avoids early termination by
disabling the
T/t feature. This period is fixed at the
5
Battery Chemistry
Charge Algorithm
NiCd or NiMH
1. Charge qualification
2. Trickle charge, if required
3. Fast charge (constant current)
4. Charge termination (
T/t, time)
5. Top-off (optional)
6. Trickle charge
Li-Ion
1. Charge qualification
2. Trickle charge, if required
3. Two-step fast charge (constant current followed by constant voltage)
4. Charge termination (minimum current, time)
Table 1. Charge Algorithm
bq2000T
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