Programmable NiCd/NiMH Fast-Charge Management IC bq24400 FEATURES GENERAL DESCRIPTION

Programmable NiCd/NiMH Fast-Charge Management IC bq24400 FEATURES GENERAL DESCRIPTION
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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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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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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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<VLTF, fast
charge restarts and the timer resumes from where it left off with no change in total fast charge time.
Maximum Temperature
A negative-coefficient thermistor, referenced to VSS and placed in thermal contact with the battery, may be used
as a temperature-sensing device. Figure 4 shows a typical temperature-sensing circuit.
VCC
2
VCC 7
VSS
RT1
bq24400
TS
5
RT2
N Battery
T Pack
C
Figure 4. Temperature Monitoring Configuration
During fast charge, the bq24400 compares the battery temperature to an internal high-temperature cutoff
threshold, VTCO, and a low-temperature threshold, VLTF. During fast charge only, the VHTF fault comparator is
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disabled. When the voltage at the TS pin is lower than VTCO, the bq24400 terminates fast charge, moves to the
charge suspended state, and turns off the LED. When VTS rises above VHTF, the bq24400 will resume charging in
the trickle maintenance charge state, per Figure 2. In fast charge, when the voltage on the TS pin is higher than
VLTF, the charger enters the battery conditioning state, as described in the previous section. Fast charge is
resumed when VTS is less than VLTF.
Peak Voltage
The bq24400 uses a peak-voltage detection (PVD) scheme to terminate fast charge for NiCd and NiMH
batteries. The bq24400 continuously monitors the voltage on the BAT pin, representing the battery voltage, to
ensure that it never exceeds VMCV (maximum cell voltage). In addition, it also samples, at a rate of MTO/128, the
voltage on the BAT pin and triggers the peak detection feature if this value falls below the maximum sampled
value by as much as 3.8mV (PVD). In preparation for sampling the BAT pin voltage, the bq24400 briefly turns off
most circuits (the MOD and RC pins will both go low) in order to get the cleanest possible, noise-free
measurement. While the monitoring of the BAT pin voltage is continuous, the sampling of the BAT pin voltage
with the internal ADC only occurs during fast charge. As shown in Figure 5, a resistor voltage-divider between
the battery pack's positive terminal and VSS scales the battery voltage measured at the BAT pin. A low-pass filter
then smooths out this voltage to present a clean signal to the BAT pin.
BAT+
2
VSS
bq24400
4
RB1
BAT
RB2
Figure 5. Battery Voltage Divider and Filter
The resistor values RB1 and RB2 are calculated by the following equation:
RB1
= N -1
RB2
(3)
where N is the number of cells in series. RB1 + RB2 should be at least 200kΩ and no more than 1MΩ.
Top-Off and Pulse-Trickle Maintenance Charge
Once constant-current fast charge has ended, the bq24400 measures the value of the CMTO capacitor and then
proceeds to either top-off or trickle maintenance charge. Top-off is optional and may be desirable on batteries
that have a tendency to terminate charge before reaching full capacity. To enable this option, the capacitance
value of CMTO connected between the RC pin and VCC (see Figure 3) should be greater than 0.13µF, and the
value of the resistor connected to this pin should be less than 250kΩ. To disable top-off, the capacitance value
should be less than 0.07µF. The tolerance of the capacitor needs to be taken into account in component
selection.
Once top-off is started, the timer is reset and top-off proceeds until the timer expires, VMCV is reached, or there is
a temperature fault. During top-off, current is delivered to the battery in pulses that occur each second. The fixed
pulse width allows an average current of 1/16 of the fast charge current to be delivered to the battery every
second. The LED is always off during top-off and trickle maintenance charge.
During top-off, there are three different temperature faults that can occur. If VTS > VLTF, top-off is suspended, the
timer is paused, and trickle charge is started. When VTS falls below VLTF, top-off is resumed. If VTS < VHTF, all
charging stops, but the timer keeps counting. When VTS > VHTF, top-off is resumed, if there is still time remaining
on the timer. If there is not time left, trickle maintenance charge is entered. If VTS < VTCO, all charging stops. Only
trickle maintenance charge may resume after VTS > VHTF.
8
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Pulsewidth - ms
Following top-off, the bq24400 trickle-charges the battery by enabling the MOD pin to charge at a rate of once
every 1.0 second. The trickle pulse-width is user-selectable and is set by the value of the resistor RMTO,
connected between the RC pin and VSS. Figure 6 shows the relationship between the trickle pulse-width and the
value of RMTO. The typical tolerance of the pulsewidth below 150kΩ is ±10%.
200
180
160
140
120
100
80
60
40
20
4
3
2
1
Shows Tolerance
2
4
6
8
10
50
100
RMTO - kW
150
200
250
Figure 6. Relationship Between Trickle Pulse-Width and Value of RMTO
Note that with an RMTO value around 150 kΩ, the trickle charge pulse width is nearly identical to the top-off pulse
width of 62.5 ms (1/16 of a second for a 1A fast charge current). With RMTO values near 150 kΩ, it can be difficult
to tell which state the IC is in (top-off or trickle charge). The best way to tell if the bq24400 is in top-off or trickle
charge is to look at the RC pin when the temperature is between the LTF and HTF. In top-off, the RC pin is
counting and has a sawtooth waveform on it. In trickle charge, there is no timer and the RC pin is at a DC value.
The RC pin contains valuable information in determining what state the bq24400 is in, since it always operates in
one of three modes. If the RC pin is low (around VSS potential), the IC is in sleep mode. (If the RC pin is low for
brief instants during fast charge, the bq24400 is sampling the BAT pin for PVD). If the RC pin is at some DC
value (usually around 1-2V), then the IC has paused the timer or the timer is inactive. If the RC pin is a sawtooth
waveform (similar to Figure 14), then the timer is running and the RC pin is considered “active.” Lastly, the RC
pin can be loaded by too large of a C or too small of an R. This will sometimes make the usual sawtooth
waveform look like a triangle waveform on an oscilloscope (the rise time is lengthened), or the RC signal could
have the appearance of being clipped (flat top or bottom). The timer is unreliable under these conditions and the
bq24400 should not be operated in this manner. Table 2 summarizes the different states of the RC pin.
Table 2. RC Pin Status
bq24400 CHARGE STATE
TS PIN STATE
RC PIN BEHAVIOR
Battery absent
N/A
1-2V DC level
Sleep mode
N/A
Ground (Vss)
Charge qualification (including battery
conditioning (trickle charge) and charge
suspended)
N/A
1-2V DC level
VTS < VLTF
Active
VTS > VLTF (in battery conditioning state)
1-2V DC level (timer is paused and will
resume when VTS < VLTF)
VTS > VLTF (in trickle maintenance charge
state)
1-2V DC level (timer is paused and will
resume when VTS < VLTF)
VLTF > VTS > VHTF
Active
VHTF > VTS > VTCO
Active (timer is still counting, even though
charging is suspended)
Trickle maintenance charge (after fast charge)
N/A
1-2V DC level
Charge complete
N/A
Active
Fast charge (current regulation)
Top-off charge
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Both top-off and trickle maintenance charge are terminated and the pack never receives any more charge (until a
charge initialization occurs) if the voltage on the BAT pin reaches VMCV. During trickle maintenance charge,
charging is suspended if VTS < VHTF. It resumes when VTS > VHTF. The bq24400 is designed to remain in trickle
maintenance charge forever (excluding the two faults just mentioned) in order to keep the Nickel pack full.
Charge Current Control
The bq24400 implements a hysteretic control loop that regulates the current being delivered to the battery pack
to a user programmable value that is set by the value of the RSNS resistor. A second, outer control loop reduces
the average current delivered to the pack in order to clamp the voltage at the BAT pin to a maximum of VMCV.
The bq24400 controls the MOD pin to regulate the current and voltage of the pack. The bq24400 monitors
charge current at the SNS input by sensing the voltage drop across a sense-resistor, RSNS, in series with the
battery pack. See Figure 7 for a typical current-sensing circuit.
Rf
RSNS
1 SNS
Cf
2
BAT-
VSS
bq24400
Power supply ground
bq24400 ground and BAT-
Figure 7. Current-Sensing Circuit
RSNS is sized to provide the desired fast-charge current (IMAX).
0.05
IMAX =
RSNS
(4)
If the voltage at the SNS pin is greater than VSNSLO or less than VSNSHI, the bq24400 switches the MOD output
high to pass charge current to the battery. When the SNS voltage is less than VSNSLO or greater than VSNSHI, the
bq24400 switches the MOD output low to shut off charging current to the battery. A hysteresis capacitor (CHYS) is
required between the CMOD pin and the SNS pin to add a healthy amount of hysteresis to the current sense
signal (see Figure 8). Typical hysteresis values are between 5 and 25 mV. The amount of hysteresis can be
calculated by examining the capacitive divider formed by CHYS and Cf.
CHYS
Hysteresis (V) = VCC ´
(C HYS + Cf )
(5)
10
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Q1
FMMT718
D4
DC+
S1A
D3
MMSD914LT
C6
47 mF
D5
MMSD914LT
L1
BAT+
47 mH
Q2
MMBT3904LT1
D2
ZHCS1000
R12
120 W
C9
R10
1 KW
1000 PF
Q3
MMBT3904LT1
VCC
R2
2 KW
D6
BZT52-C5V1
C3
10 mF
R11
220 W
C7
C4
4.7 PF
0.0022 mF
R1
D1
RED
C2
0.1 mF
U1
1 SNS
2 VSS
3 LED
4
BAT
C8
0.33 mF
R4
12.4 KW
R6
210 KW
C5
10 mF
100 KW
8
7
6
5
MOD
VCC
RC
TS
THERM
bq24400
C1
0.1 mF
R8
6.81 KW
R5
20 KW
BATR7
105 KW
R13
1.1 KW
R3
0.05 W
DCNOTES:
1. DC input voltage: 9–16V
2. Charge current: 1A
3. L1: 3L Global P/N PKSMD-1005-470K-1A
Figure 8. 3-Cell NiCd/NiMH 1A Charger
Being a hysteretic controller, the switching frequency of the bq24400 is determined by the values of several of
the external circuit components. The components that affect the switching frequency are: input voltage, RSNS
value, inductor value, hysteresis capacitor value (CHYS), and the value of the filter on the current sense signal (Rf
and Cf values). Rf and Cf have the most impact on the switching frequency and are also the components that are
easiest to change to adjust the frequency, as they do not affect anything else in the circuit (besides, of course,
the cleanliness and quality of the current sense signal being fed to the bq24400). In general, increasing the input
voltage and/or inductor value or decreasing CHYS and/or the Rf × Cf filter corner frequency will increase the
switching frequency. Figure 9 and Figure 10 show empirical data on the variation in switching frequency based
on adjusting Rf and Cf. This data was taken with an input voltage of 12V, inductor value of 220 µH, RSNS value of
50 mΩ, and CHYS value of 4.7 pF. Typical switching frequencies for the bq24400 are between 100 and 200 kHz,
though it is possible to achieve switching frequencies in excess of 300kHz.
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180
160
fs - Switching Frequency - kHz
Rf = 748W
140
120
100
80
60
40
20
0
220
720 1220 1720 2220 2720 3220 3720 4220
Cf - pF
Figure 9. Switching Frequency vs Capacitance
210
fs - Switching Frequency - kHz
190
Cf = 1000pF
170
150
130
110
90
70
50
200 300 400 500 600 700 800 900 1000 1100 1200
Rf - W
Figure 10. Switching Frequency vs Resistance
12
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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
TEMPERATURE MONITORING
The bq24400 measures the temperature by the voltage at the TS pin. This voltage is typically generated by a
negative-temperature-coefficient thermistor. The bq24400 compares this voltage against its internal threshold
voltages to determine if charging is safe. These thresholds are the following:
• High-temperature cutoff voltage: VTCO = 0.225 × VCC. This voltage corresponds to the maximum temperature
(TCO) at which any charging is allowed. The bq24400 terminates charging if the voltage on the TS pin falls
below VTCO.
• High-temperature fault voltage: VHTF = 0.25 × VCC. This voltage corresponds to a maximum allowed pack
temperature (HTF) in all states except for fast charge. During fast charge, HTF faults are disabled to allow for
a normal increase in pack temperature.
• Low-temperature fault voltage: VLTF = 0.5 × VCC. This voltage corresponds to the minimum temperature (LTF)
at which fast charging or top-off is allowed. If the voltage on the TS pin rises above VLTF, the bq24400
suspends either fast charge or top-off and begins a trickle charge. When the voltage falls back below VLTF,
fast charge or top-off resumes from the point where suspended. If VTS > VLTF, the charger will always be in
trickle charge.
Table 3 summarizes these various conditions.
Table 3. Temperature-Monitoring Conditions and Actions
TEMPERATURE
CONDITION
ACTION
During charge qualification, no effect
VTS > VLTF
Cold battery – checked at all times
VHTF < VTS < VLTF
Optimal charging range
During fast charge, suspends fast charge and moves into charge
qualification, pauses timer, and flashes LED
During top-off, suspends top-off and moves into trickle maintenance
charge and pauses timer
During trickle maintenance charge, no effect
Allows all stages of charging
During charge qualification, stops charging
VTS < VHTF
Hot battery – checked at all times,
except during fast charge
During fast charge, no effect
During top-off, stops charging
During trickle maintenance charge, stops charging
During charge qualification, stops charging
VTS < VTCO
Battery exceeding maximum
allowable temperature – checked at
all times
During fast charge, terminates fast charge and stops charging, turns off
LED
During top-off, terminates top-off and stops charging
During trickle maintenance charge, stops charging
Table 4. Summary of NiCd or NiMH Charging Characteristics
VALUE (1)
PARAMETER
Maximum cell voltage (VMCV)
2V
Minimum pre-charge qualification voltage (VLBAT)
950 mV
High-temperature cutoff voltage (VTCO)
0.225 × VCC
High-temperature fault voltage (VHTF)
0.25 × VCC
Low-temperature fault voltage (VLTF)
0.5 × VCC
bq24400 fast-charge maximum time out (MTO)
RMTO × CMTO × 35,988
Fast-charge charging current (IMAX)
0.05/RSNS
Hold-off period
MTO/32
Top-off charging current (optional)
IMAX/16
Top-off period (optional)
MTO
Trickle-charge frequency
1Hz
Trickle-charge pulse-width
(1)
See Figure 6
See the DC Thresholds Specification for details.
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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
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Charge Status Display
The charge status is indicated by open-drain output LED. Table 5 summarizes the display output of the bq24400.
A temperature fault or timer expiring changes the charge state immediately (according to Figure 2) and will thus
change the LED status immediately and accordingly.
Table 5. Charge Status Display
bq24400 CHARGE STATE
LED STATUS
Charge qualification (including battery conditioning and charge suspended)
1 Hz flash
Fast charge (current regulation)
Low
Top-off charge
Trickle maintenance charge (after fast charge)
Charge complete
High impedance
Battery absent
Sleep mode
Sleep Mode
The bq24400 features a sleep mode for low power consumption. This mode is enabled when the voltage at the
BAT pin is above the low-power-mode threshold, VSLP. During sleep mode, the bq24400 shuts down all
unnecessary internal circuits, drives the LED output to high-impedance state, and drives the MOD pin low.
Restoring BAT below the VMCV threshold initiates the IC and starts a fast-charge cycle. Normally, the bq24400
only enters sleep mode when there is no battery connected on the output and the charger is idling with nothing to
charge. In addition, VIN needs to be high enough such that when VIN is present on the output, VBAT would be
greater than VSLP. In sleep mode, the output voltage will decay to VMCV at which point the bq24400 turns on and
pulses the MOD pin several times. With no battery connected, the output will rise to near VIN at which point the
bq24400 re-enters sleep mode. During sleep mode, the RC pin will be at VSS potential. A typical sleep mode
waveform is shown in Figure 17.
14
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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
TYPICAL CHARACTERISTICS
CH1 = RC pin, 2V/div
CH1 = RC pin, 2V/div
1
CH2 = MOD pin, 5V/div
CH2 = MOD pin, 5V/div
Voltage - V
Voltage - V
2
CH3 = VO, 5V/div
2
CH3 = VI, 5V/div
3
CH4 = LED pin, 5V/div
1
CH4 = LED pin, 5V/div
4
3
4
Time - 0.2s/div
Time - 0.2s/div
Figure 11. bq24400 Start-up on Battery Insertion
Figure 12. bq24400 Start-up on Vin
CH1 = VO, 5V/div
CH2 = RC pin, 1V/div
CH1 = VO, 5V/div
1
Voltage - V
Voltage - V
1
CH2 = BAT pin, 1V/div
CH3 = MOD pin, 5V/div
3
2
CH3 = MOD pin, 5V/div
3
2
CH4 = LED pin, 1V/div
Time - 0.5s/div
4
Time - 0.5ms/div
Figure 13. Battery Removal During Fast Charge
Figure 14. bq24400 in Fast Charge
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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
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TYPICAL CHARACTERISTICS (continued)
CH1 = VO, 5V/div
1
CH2 = RC pin, 1V/div
CH1 = SNS pin, 20mV/div
CH3 = MOD pin, 5V/div
2
Voltage - V
Voltage - V
1
CH2 = MOD pin, 5V/div
3
2
4
CH4 = LED pin, 1V/div
Time - 2ms/div
Time - 10ms/div
Figure 15. bq24400 in Fast Charge
Figure 16. bq24400 Fast Charge SNS and MOD Waveforms
CH1 = VO, 10V/div
Voltage - V
1
CH2 = BAT pin, 1V/div
CH3 = RC pin, 2V/div
2
3
4
CH4 = MOD pin, 5V/div
Time - 1s/div
Figure 17. bq24400 Cycling In and Out of Sleep Mode (No battery present)
16
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SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010
REVISION HISTORY
Changes from Revision September 2001 (*) to Revision A
•
Page
Changed the data sheet format. The data sheet was originally from Benchmark Products. In revision A, the data
sheet was converted to the TI format, and a re-write of the data sheet was implemented .................................................. 1
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17
PACKAGE OPTION ADDENDUM
www.ti.com
10-Jun-2014
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
BQ24400D
ACTIVE
SOIC
D
8
75
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
-20 to 70
24400
BQ24400DG4
ACTIVE
SOIC
D
8
75
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
-20 to 70
24400
BQ24400DR
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
-20 to 70
24400
BQ24400DRG4
ACTIVE
SOIC
D
8
2500
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
-20 to 70
24400
BQ24400PW
ACTIVE
TSSOP
PW
8
150
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-20 to 70
24400
BQ24400PWR
ACTIVE
TSSOP
PW
8
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-20 to 70
24400
BQ24400PWRG4
ACTIVE
TSSOP
PW
8
2000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-20 to 70
24400
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
10-Jun-2014
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Jun-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
BQ24400DR
SOIC
D
8
2500
330.0
12.4
6.4
5.2
2.1
8.0
12.0
Q1
BQ24400PWR
TSSOP
PW
8
2000
330.0
12.4
7.0
3.6
1.6
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Jun-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
BQ24400DR
SOIC
D
8
2500
367.0
367.0
35.0
BQ24400PWR
TSSOP
PW
8
2000
367.0
367.0
35.0
Pack Materials-Page 2
PACKAGE OUTLINE
PW0008A
TSSOP - 1.2 mm max height
SCALE 2.800
SMALL OUTLINE PACKAGE
C
6.6
TYP
6.2
SEATING PLANE
PIN 1 ID
AREA
A
0.1 C
6X 0.65
8
1
3.1
2.9
NOTE 3
2X
1.95
4
5
B
4.5
4.3
NOTE 4
SEE DETAIL A
8X
0.30
0.19
0.1
C A
1.2 MAX
B
(0.15) TYP
0.25
GAGE PLANE
0 -8
0.15
0.05
0.75
0.50
DETAIL A
TYPICAL
4221848/A 02/2015
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not
exceed 0.15 mm per side.
4. This dimension does not include interlead flash. Interlead flash shall not exceed 0.25 mm per side.
5. Reference JEDEC registration MO-153, variation AA.
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EXAMPLE BOARD LAYOUT
PW0008A
TSSOP - 1.2 mm max height
SMALL OUTLINE PACKAGE
8X (1.5)
8X (0.45)
SYMM
1
8
(R0.05)
TYP
SYMM
6X (0.65)
5
4
(5.8)
LAND PATTERN EXAMPLE
SCALE:10X
SOLDER MASK
OPENING
METAL
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
0.05 MAX
ALL AROUND
0.05 MIN
ALL AROUND
SOLDER MASK
DEFINED
NON SOLDER MASK
DEFINED
SOLDER MASK DETAILS
NOT TO SCALE
4221848/A 02/2015
NOTES: (continued)
6. Publication IPC-7351 may have alternate designs.
7. Solder mask tolerances between and around signal pads can vary based on board fabrication site.
www.ti.com
EXAMPLE STENCIL DESIGN
PW0008A
TSSOP - 1.2 mm max height
SMALL OUTLINE PACKAGE
8X (1.5)
8X (0.45)
SYMM
(R0.05) TYP
1
8
SYMM
6X (0.65)
5
4
(5.8)
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
SCALE:10X
4221848/A 02/2015
NOTES: (continued)
8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
9. Board assembly site may have different recommendations for stencil design.
www.ti.com
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