bq2000
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SLUS138D – JANUARY 2008 – REVISED DECEMBER 2009
Programmable Multi-Chemistry Fast-Charge Management IC
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FEATURES
1
•
•
•
•
•
•
•
•
Safe Management of Fast Charge for NiCd,
NiMH, or Li-Ion Battery Packs
High-Frequency Switching Controller for
Efficient and Simple Charger Design
Pre-Charge Qualification for Detecting
Shorted, Damaged, or Overheated Cells
Fast-Charge Termination by Peak Voltage
(PVD) for Nickel chemistries, Minimum Current
for Li-Ion chemistries, 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
APPLICATIONS
•
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Multi-Chemistry Charger
Nickel Charger
High-Power, Multi-Cell Charger
GENERAL DESCRIPTION
The bq2000 is a programmable, monolithic IC for
fast-charge management of nickel cadmium (NiCd),
nickel metal-hydride (NiMH), or lithium-ion (Li-Ion)
batteries in single- or multi-chemistry applications.
The bq2000 chooses the proper battery chemistry
(either nickel or lithium) and proceeds with the
optimal charging and termination algorithms. This
process eliminates undesirable, undercharged, or
overcharged conditions, and allows accurate and safe
termination of fast charge
Depending on the chemistry, the bq2000 provides a
number of charge termination criteria:
• Peak voltage, PVD (for NiCd and NiMH)
• Minimum charge current (for Li-Ion)
• Maximum temperature
• 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-speed comparator allows the
bq2000 to be the basis for a complete, high-efficiency
battery charger circuit for both nickel-based and
lithium-based chemistries.
8-Pin DIP or Narrow SOIC or TSSOP
spacer between para and illustration
Pin Names
SNS
Current-sense input
SNS
1
8
MOD
VSS
System ground
VSS
2
7
VCC
LED
Charge-status output
BAT
Battery-voltage input
LED
3
6
RC
TS
Temperature-sense input
BAT
4
5
TS
RC
Timer-program input
VCC
Supply-voltage input
MOD
Modulation-control output
1
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Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2009, Texas Instruments Incorporated
bq2000
SLUS138D – JANUARY 2008 – REVISED DECEMBER 2009
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
PIN DESCRIPTIONS
SNS
Current-sense input
Enables the bq2000 to sense the battery current via the voltage developed on this pin by an external
sense-resistor connected in series with the battery pack
VSS
System Ground
Connect to the battery’s negative terminal
LED
Charge-status output
Open-drain output that indicates the charging status by turning on, turning off, or flashing an external
LED, driven through a resistor.
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 divider network with
a negative temperature-coefficient thermistor sets the lower and upper temperature thresholds.
RC
Timer-program input
Used to program the maximum fast charge-time, maximum top-off charge-time, hold-off period, trickle
charge rate, and to disable or enable top-off charge. A capcitor from VCC and a resistor to ground
connect to this pin.
VCC
Supply-voltage input
Recommended bypassing is 10µF + 0.1µF to 0.22µF of decoupling capacitance near the pin.
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.
2
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FUNCTIONAL DESCRIPTION
The bq2000 is a versatile, multi-chemistry battery charge control device. See Figure 1 for a functional block
diagram and Figure 2 for a state diagram.
TS
Voltage
Reference
BAT
OSC
Voltage
Comparators 3x
ADC
PVD
ALU
Clock
Phase
Generator
Timer
Charge
Control
LED
Voltage
Comparators
MOD
RC
Internal
OSC
SNS
VCC
VSS
Figure 1. Functional Block Diagram
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VCC Reset
or
Battery Replacement at any time
4.0 V < VCC < 6.0 V
Charge
Initialization
VBAT < VSLP
VMCV < VBAT < VSLP
Battery Voltage (Voltage at BAT pin
checked continuously. PVD checked
at rate of MTO/128.)
Sleep
Mode
Charge
Qualification
State
VSLP < VBAT < VCC
VBAT < VMCV
VTS > VHTF
Charge
Suspended
Battery Temperature
(Temperature at TS pin checked
continuously)
VTS < VHTF
VTS < VHTF
VLBAT < VBAT < VMCV and
VHTF < VTS < VLTF
VBAT < VLBAT or
VTS > VLTF
VTS > VLTF
Battery
Conditioning
Current
Regulation
VLBAT < VBAT and
VHTF < VTS < VLTF
PVD (after hold-off period),
or VTS < VTCO or
Time = MTO
NO
Trickle
Maintenance
Charge
Top-Off
Selected?
VTS > VLTF
Fast Charge State
VTS > VLTF
Time < MTO
and
VBAT reaches VMCV
Voltage
Regulation
YES
Current Taper (IBAT < Imin).
or
Time = 2 x MTO or VTS < VTCO
VTS < VLTF and
Time < MTO
VTS > VHTF
Top-Off
Time = MTO
VBAT ≥ VMCV
Done
VBAT ≥ VMCV
VTS < VHTF
Charge
Suspended
(See Note)
VTS < VHTF
VTS > VHTF
and Time < MTO
VCC Reset or Battery Replacement or Capacity Depletion (Li-lon)
NOTE: If VTS < VTCO at any time, may only return to Trickle Maintenance Charge state and not to Top-Off.
Figure 2. State Diagram
4
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ABSOLUTE MAXIMUM RATINGS (1)
VALUE
UNIT
–0.3 to 7
V
–0.3 to VCC
V
Operating ambient temperature
–20 to 70
°C
Storage temperature
–40 to 125
°C
260
°C
VCC
VCC relative to VSS
VT
DC voltage applied on any pin, relative to VSS
TOPR
TSTG
TSOLDER
Soldering temperature (10 s max.)
(1)
Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional operation should be limited to the
Recommended DC Operating Conditions detailed in this data sheet. Exposure to conditions beyond the operational limits for extended
periods of time may affect device reliability.
DC THRESHOLDS (1)
TA = TOPR; VCC = 5V ±20% (unless otherwise specified)
PARAMETER
TEST CONDITIONS
TYPICAL
TOLERANCE
UNIT
VTCO
Temperature cutoff
Voltage at the TS pin
0.225 × VCC
±5%
V
VHTF
High-temperature fault
Voltage at the TS pin
0.25 × VCC
±5%
V
VLTF
Low-temperature fault
Voltage at the TS pin
0.5 × VCC
±5%
V
VMCV
Maximum cell voltage
Voltage at the BAT pin
2.00
±0.75%
VLBAT
Minimum cell voltage
Voltage at the BAT pin
950
±5%
mV
PVD
BAT input change for PVD detection
Voltage at the BAT pin
3.8
±20%
mV
VSNSHI
High threshold at SNS
Voltage at the SNS pin
50
±10
mV
VSNSLO
Low threshold at SNS
Voltage at the SNS pin
–50
±10
mV
VSLP
Sleep-mode input threshold
Voltage at the BAT pin
VCC–1
±0.5
V
VRCH
Recharge threshold
Voltage at the BAT pin
VMCV–0.1
±0.02
V
(1)
V
All voltages are relative to VSS except as noted.
RECOMMENDED DC OPERATING CONDITIONS
over operating free-air temperature range (unless otherwise noted)
TEST CONDITIONS
VCC
Supply voltage
ICC
Supply current
Exclusive of external loads
ICCS
Sleep current
VBAT = VSLPM
VTS
Thermistor input
VTS < 0.5 V prohibited
VOH
Output high input
MOD, IOH = 10 mA
VOL
Output low input
MOD, LED, IOL = 10 mA
IOZ
High-impedance leakage current
LED
Isnk
Sink current
MOD, LED
RMTO
Charge timer resistor
CMTO
Charge timer capacitor
MIN
TYP
MAX
4
5
6
V
0.5
1
mA
5
µA
VCC
V
0.5
UNIT
VCC–0.4
V
0.2
V
5
µA
20
mA
2
250
kΩ
0.001
1
µF
IMPEDANCE
PARAMETER
MIN
TYP
MAX
UNIT
RBAT
Battery input impedance
10
MΩ
RTS
TS input impedance
10
MΩ
RSNS
SNS input impedance
10
MΩ
TIMING
TA = TOPR; VCC = 5 V ±20% (unless otherwise noted)
PARAMETER
dMTO
MTO time-base variation
fTRKL
Pulse-trickle frequency
MIN
TYP
–5%
0.9
MAX
UNIT
5%
1
1.1
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bq2000
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Initiation and Charge Qualification
The bq2000 initiates a charge cycle when it detects
• Application of power to VCC
• Battery replacement
• Exit from sleep mode
• Capacity depletion (Li-Ion only)
Immediately following initiation, the IC enters a charge-qualification mode. The bq2000 charge qualification is
based on battery voltage and temperature. If the voltage on the BAT pin is less than the internal threshold, VLBAT,
the bq2000 enters the battery conditioning state. This condition indicates the possibility 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 Maintenance Charge," the trickle
pulse-width is user-selectable and is set by the value of the resistance connected between the RC pin and VSS.
During charge qualification, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger.
Once battery conditioning (trickle charge) has raised the voltage on the BAT pin above VLBAT, the IC enters fast
charge, if the battery temperature is within the VLTF to VHTF range. The BQ2000 will stay in the battery
conditioning state indefinitely and will not progress to fast charge until the voltage on the BAT pin is above VLBAT
and the temperature is within the VLTF and VHTF range. No timer is implemented during battery conditioning.
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 the BAT pin rises to the internal VMCV reference, the IC assumes a Li-Ion battery.
Otherwise, the bq2000 assumes a NiCd/NiMH chemistry. While in the fast charge state, the LED pin is pulled low
(the LED is on).
As shown in Figure 3, a resistor voltage-divider between the battery pack's positive terminal and VSS scales the
battery voltage. A low-pass filter then smooths out this voltage to present a clean signal to the BAT pin. 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. Otherwise, different scaling is required.
BAT+
2
VSS
bq2000
4
RB1
BAT
RB2
Figure 3. Battery Voltage Divider and Filter
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 NiMH Batteries
Following charge qualification (which includes trickle charge, if required ), 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 the BAT pin remains below VMCV.
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Lithium-Ion Batteries
The bq2000 uses a two-phase fast-charge algorithm for Li-Ion batteries (Figure 4). In phase one, the bq2000
regulates constant current until VBAT rises to VMCV. Once VBAT = VMCV, the device identifies the cell as a Li-ion,
and changes the termination method from PVD to minimum current. The bq2000 then moves to phase two,
regulates the battery with constant voltage of VMCV, and terminates when the charging current falls below the IMIN
threshold or the timer expires (whichever happens first). A new charge cycle is started if the cell voltage falls
below the VRCH threshold.
Current
IMAX
Charge
Qualification
VMCV
Voltage
Fast
Charge
Phase 1
VLBAT
Phase 2
Voltage
Trickle
Current
IMIN
Time
Figure 4. Lithium-Ion Charge Algorithm
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.
Table 1 summarizes the charging process for both Nickel and Li-Ion batteries.
Table 1. Charge Algorithm
BATTERY CHEMISTRY
CHARGE ALGORITHM
1. Charge qualification
2. Trickle charge, if required
NiCd or NiMH
(VBAT < VMCV always)
3. Fast charge (constant current)
4. Charge termination (peak voltage, maximum charge time = 1 MTO)
5. Top-off (optional)
6. Trickle charge
1. Charge qualification
2. Trickle charge, if required
Li-Ion
(VBAT ≤ VMCV )
3. Fast charge (constant current)
4. Fast charge (constant voltage)
5. Charge termination (minimum current, maximum charge time = 2 MTO)
FAST CHARGE TERMINATION
Initial Hold-OFF Period
The bq2000 incorporates a user programmable hold-off period to avoid premature fast charge termination that
can occur with brand new cells at the very beginning of fast charge. The values of the external resistor and
capacitor connected to the RC pin set the initial hold-off period. During this period, the bq2000 avoids early
termination due to an initial peak in the battery voltage by disabling the peak voltage-detection (PVD) feature.
This period is fixed at the programmed value of the maximum charge time (MTO) divided by 32.
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hold-off period =
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MTO
32
(1)
Maximum Charge Time (NiCD, NiMH, and Li-Ion)
The bq2000 sets the maximum charge-time through the RC pin. With the proper selection of external resistor and
capacitor values, various time-out values may be achieved. If the timer expires while still in constant-current
charging, the bq2000 assumes a Nickel chemistry and proceeds to top-off charge (if top-off is enabled) or trickle
maintenance charge. Figure 5 shows a typical connection.
2
VSS
VCC
7
bq2000
CMTO
RC
6
RMTO
Figure 5. Typical Connection for the RC Input
The following equation shows the relationship between the RMTO and CMTO values and the maximum charge time
(MTO) for the bq2000:
MTO = RMTO ´ CMTO ´ 35,988
(2)
MTO is measured in minutes, RMTO in ohms, and CMTO in farads. (Note: RMTO and CMTO values also determine
other features of the device. See Table 4 and Table 5 for details.
If, during fast charge, VTS > VLTF, then the timer is paused and the IC enters battery conditioning charge until VTS
< VLTF. Since the IC is in the battery conditioning state, the LED flashes at the 1 Hz rate. Once VTS