bq24400
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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
Programmable NiCd/NiMH Fast-Charge Management IC
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FEATURES
1
•
•
•
•
•
•
•
•
Safe Management of Fast Charge for NiCd and
NiMH 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), 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
•
•
Nickel Charger
High-Power, Multi-Cell Charger
8-Pin DIP or Narrow SOIC or TSSOP
GENERAL DESCRIPTION
The bq24400 is a programmable, monolithic IC for
fast-charge management of nickel cadmium (NiCd)
and nickel metal-hydride (NiMH) in single or multi-cell
applications.
The bq24400 provides these charge termination
criteria:
• Peak voltage, PVD
• Maximum temperature
• Maximum charge time
For safety, the bq24400 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
bq24400
uses
trickle-charge to condition the battery. For NiMH
batteries, the bq24400 provides an optional top-off
charge to maximize the battery capacity.
The integrated high-speed comparator allows the
bq24400 to be the basis for a complete,
high-efficiency battery charger circuit for nickel-based
chemistries.
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
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
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 © 2001–2010, Texas Instruments Incorporated
bq24400
SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
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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 bq24400 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 capacitor 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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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
FUNCTIONAL DESCRIPTION
The bq24400 is a versatile, NiCd and NiMH 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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bq24400
SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
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VCC Reset
or
Battery Replacement at any time
4.0 V < VCC < 6.0 V
Charge
Initialization
VBAT < VSLP
Battery Voltage (Voltage at BAT pin
checked continuously. PVD checked
at rate of MTO/128.)
Sleep
Mode
VMCV < VBAT < VSLP
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
Fast Charge State
Top-Off
Selected?
VTS > VLTF
YES
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
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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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
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
±2.5%
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
(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 = VSLP
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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Initiation and Charge Qualification
The bq24400 initiates a charge cycle when it detects
• Application of power to VCC
• Battery replacement
• Exit from sleep mode
Immediately following initiation, the IC enters a charge-qualification mode. The bq24400 charge qualification is
based on battery voltage and temperature. If the voltage on the BAT pin is less than the internal threshold, VLBAT,
the bq24400 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 bq24400 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 bq24400 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.
Fast Charge (Current Regulation)
Following charge qualification (which includes trickle charge, if required), the bq24400 begins fast charge fast
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. While in the fast
charge state, the LED pin is pulled low (the LED is on). 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.
Table 1 summarizes the charging process.
Table 1. Charge Algorithm
BATTERY CHEMISTRY
CHARGE ALGORITHM
1. Charge qualification
2. Trickle charge, if required
NiCd or NiMH Batteries
(VBAT < VMCV always)
3. Fast charge (constant current)
4. Fast charge termination (peak voltage, maximum charge time = 1 MTO)
5. Top-off (optional)
6. Trickle charge
FAST CHARGE TERMINATION
Initial Hold-Off Period
The bq24400 incorporates a user programmable hold-off period to avoid premature fast charge termination that
can occur with brand new nickel 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 bq24400 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.
MTO
hold-off period =
32
(1)
6
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Maximum Charge Time
The bq24400 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 fast charge, the
bq24400 proceeds to top-off charge (if top-off is enabled) or trickle maintenance charge. If top-off is enabled, the
timer is reset on the completion of fast charge before beginning top-off charge. Figure 3 shows a typical
connection.
2
VSS
VCC
7
bq24400
CMTO
RC
6
RMTO
Figure 3. 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 bq24400:
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 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