TI BQ24400 Programmable nicd/nimh fast-charge management device Datasheet

bq24400
Programmable NiCd/NiMH
Fast-Charge Management Device
Features
General Description
Ø
Safe management of fast charge
for NiCd and NiMH battery
packs.
Ø
High-frequency switching controller for efficient and simple
charger design
Ø
Ø
Pre-charge qualification for
detecting shorted, damaged, or
overheated cells
Fast-charge termination by
peak voltahge (PVD), maximum
temperature, and maximum
charge time
Ø
Selectable top-off mode for
achieving maximum capacity in
NiMH batteries
Ø
Programmable trickle-charge
mode for reviving deeply discharged batteries and for postcharge maintenance
Ø
Built-in battery removal and insertion detection
Ø
Sleep mode for low power consumption
Pin Connections
The bq24400 is a programmable,
monolithic IC for fast-charge management of nickel cadmium (NiCd) and
nickel metal-hydride (NiMH) batteries.
The bq24400 provides a number of
charge termination criteria:
l
Peak voltage, PVD (for NiCd and
NiMH)
l
Maximum temperature
l
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-frequency comparator allows the bq24400 to be the
basis for a complete, high-efficiency
power-conversion circuit.
Pin Names
SNS
1
8
MOD
VSS
2
7
VCC
LED
3
6
RC
BAT
4
5
TS
SNS
Current-sense input
VSS
System ground
LED
Charge-status
output
BAT
Battery-voltage
input
8-Pin DIP or Narrow SOIC
or TSSOP
PN-2000.eps
SLUS498 -SEPTEMBER 2001
1
TS
Temperature-sense
input
RC
Timer-program input
VCC
Supply-voltage input
MOD
Modulation-control
output
bq24400
Pin Descriptions
SNS
RC
Current-sense input
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.
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
VCC
Supply-voltage input
LED
Charge-status output
MOD
Modulation-control output
Open-drain output that indicates the charging status by turning on, turning off, or flashing an external LED.
BAT
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.
Battery-voltage input
Functional Description
Battery-voltage sense input. A simple resistive
divider, across the battery terminals, generates
this input.
TS
The bq24400 is a versatile, NiCd, NiMH battery- charge
control device. See Figure 1 for a functional block diagram and Figure 2 for the state diagram.
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.
TS
Voltage
Reference
BAT
OSC
Voltage
Comparator
ADC
∆T/∆t
ALU
Clock
Phase
Generator
Timer
Charge
Control
LED
Voltage
Comparator
MOD
RC
Internal
OSC
SNS
VCC
VSS
BD2000T.eps
Figure 1. Functional Block Diagram
2
bq24400
4.0 V <V CC <6.0 V
Charge
Initialization
V BAT <V SLP
Battery Voltage
(PVD checked at rate
of MTO/64)
Sleep
Mode
V SLP <V BAT <V CC
V BAT <V MCV
V TS >V HTF
Charge
Suspended
V MCV <V BAT <V SLP
Battery Temperature
(checked 1,750 times
per second)
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
Battery
Conditioning
Current
Regulation
V LBAT <V BAT <V MCV and
V HTF <V TS <V LTF
PVD (after hold-off period), or
V TS <V TCO or
Time =MTO
V CC Reset
No
Maintenance
Charge
Top-Off
Selected?
Yes
Time =MTO
or
V TS <V TCO
Top-Off
V BAT >V MCV
V BAT >V MCV
V CC Reset or Battery Replacement
Figure 2. State Diagram
3
Done
UDG-01088
bq24400
Charge Termination
Initiation and Charge Qualification
Maximum Charge Time
The bq24400 initiates a charge cycle when it detects
l
Application of power to VCC
l
Battery replacement
l
Exit from sleep mode
The bq24400 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
3 shows a typical connection.
The following equation shows the relationship between
the RMTO and CMTO values and the maximum charge
time (MTO) for the bq24400:
Immediately following initiation, the IC enters a
charge-qualification mode. The bq24400 charge qualification is based on battery voltage and temperature. If
voltage on pin BAT is less than the internal threshold,
VLBAT , the bq24400 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 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 Charge,” the
trickle pulse-width is user-selectable and is set by the
value of the resistance connected to pin RC.
MTO = RMTO ∗ CMTO ∗ 35,988
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 Tables 2 and 3 for details.)
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.
During this period, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger.
Similarly, the bq24400 suspends fast charge if the battery
temperature is outside the VLTF to VHTF range. (See Table
4.) For safety reasons, however, it disables the pulse trickle,
in the case of a battery over-temperature condition (i.e., VTS
< VHTF). Fast charge begins when the battery temperature
and voltage are valid.
During fast charge, the bq24400 compares the battery
temperature to an internal high-temperature cutoff
threshold, VTCO. As shown in Table 4, high-temperature
termination occurs when voltage at pin TS is less than
this threshold.
NiCd and NiMH Batteries
Peak Voltage
Following qualification, the bq24400 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 BAT remains below VMCV.
The bq24400 uses a peak-voltage detection (PVD) scheme
to terminate fast charge for NiCd and NiMH batteries.
The bq24400 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 3.8 mV (PVD).
As shown in figure 5, a resistor voltage-divider between
the battery pack’s positive terminal and VSS scales the
battery voltage measured at pin BAT.
The resistor values RB1 And RB2 are calculated by the following equation:
Table 1. Charge Algorithm
Battery Chemistry
NiCd or NiMH
Charge Algorithm
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
4
bq24400
2
VCC
VSS
7
bq24400
bq2000T
CMTO
RC
6
RMTO
F2000T RCI.eps
Figure 3. Typical Connection for the RC Input
VCC
2
VSS
7
VCC
bq24400
bq2000T
RT1
5
TS
RT2
N Battery
T Pack
C
F2000TTMC.eps
Figure 4. Temperature Monitoring Configuration
BAT+
2
VSS
RB1
bq24400
bq2000T
4
BAT
RB2
F2000TBVD.eps
Figure 5. Battery Voltage Divider
5
bq24400
Table 2. Summary of NiCd or NiMH Charging Characteristics
Parameter
Value
Maximum cell voltage (VMCV)
2V
Minimum pre-charge qualification voltage (VLBAT)
950mV
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
Table 3. Temperature-Monitoring Conditions
Temperature
Condition
Action
VTS > VLTF
Cold battery—checked at all times
Suspends fast charge or top-off and timer
Allows trickle charge—LED flashes at 1Hz rate
during pre-charge qualification and fast charge
VHTF < VTS < VLTF
Optimal operating range
Allows charging
VTS < VHTF
Suspends fast-charge initiation, does not allow
Hot battery—checked during charge qualifitrickle charge—LED flashes at 1Hz rate during
cation and top-off and trickle-charge
pre-charge qualification
VTS < VTCO
Battery exceeding maximum allowable temTerminates fast charge or top-off
perature—checked at all times
R B1
= N−1
R B2
Table 4. Charge Status Display
where N is the number of cells in series.
Charge Action State
The end-to-end input impedance of this resistive divider
network should be at least 200kW and no more than
1MW.
Initial Hold-Off Period
The values of the external resistor and capacitor connected to pin RC set the initial hold-off period. During
this period, the bq24400 avoids early termination by disabling the ∆T/∆t feature. This period is fixed at the programmed value of the maximum charge time divided by
32.
hold-off period =
LEDStatus
Battery absent
High impedance
Pre-charge qualification
1Hz flash
Trickle charge (before fast charge)
1Hz flash
Fast charging
Low
Top-off or trickle
High impedance
Charge complete
High impedance
Sleep mode
High impedance
Charge suspended (VTS > VLTF)
1Hz flash
maximum time - out
32
Top-Off and Pulse-Trickle Charge
6
bq24400
Charge Current Control
Top-off 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 to pin RC (Figure 3) should be greater than
0.13µF, and the value of the resistor connected to this pin
should be less than 15kΩ. 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.
The bq24400 controls the charge current through the
MOD output pin. The current-control circuit supports a
switching-current regulator with frequencies up to
500kHz. The bq24400 monitors charge current at the
SNS input by the voltage drop across a sense-resistor,
RSNS, in series with the battery pack. See Figure 8 for a
typical current-sensing circuit. RSNS is sized to provide
the desired fast-charge current (IMAX):
Once enabled, the top-off is performed over a period
equal to the maximum charge time at a rate of 1 16 that of
fast charge.
IMAX =
0.05
RSNS
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. Figure 7 shows a typical
multi-chemistry charge circuit.
Following top-off, the bq24400 trickle-charges the battery
by enabling the MOD 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, which is on pin RC.
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%.
During top-off and trickle-charge, the bq24400 monitors
battery voltage and temperature. These functions are
suspended if the battery voltage rises above the
maximum cell voltage (V MCV ) or if the temperature
exceeds the high-temperature fault threshold (VHTF).
160
140
120
Shows Tolerance
Pulsewidth—ms
100
80
60
40
20
4
3
2
1
2
4
6
8
10
50
100
150
200
250
RMTO—kΩ
2000PNvB3.eps
Figure 6. Relationship Between Trickle Pulse-Width and Value of
R
MTO
7
bq24400
DC+
+
C6
47 mF
D3
MMS D914LT
C7
4.7 P F
D6
BZT52-C5V1
C2
0.1 mF
C8
0.33 mF
R12
120 W
R1
100kW
R6
210 kW
R4
12.4 kW
+
C5
10 mF
C4
0.0022 mF
D1
RED
BAT+
D2
ZHCS 1000
D5
MMS D914LT C9
1000 P F
+ C3
10 mF
R2
2 kW
Q2
MMBT3904LT1
VCC
R10
1 kW
L1
47 mH
Q1
FMMT718
D4
S 1A
BQ24401
1
S NS
MOD
8
2
VS S
VCC
7
3
LED
RC
6
4
BAT
TS
5
R13
1.1 kW
Q3
MMBT3904LT1
R11
220 W
R7
105 kW
THERM
C1
0.1 mF
R5
20 kW
R8
6.81 kW
BAT-
R3
0.05 W
Note s :
1. DC input volta ge : 9 V to 16 V
2. Cha rge curre nt: 1 A
3. L1: 3L globa l P /N P KS MD-1005-470K-1A
UDG-01087
Figure 7. Three-Cell NiCd/NiMH 1A Charger
8
bq24400
Temperature Monitoring
Sleep Mode
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:
The bq24400 features a sleep mode for low power consumption. This mode is enabled when the voltage at pin
BAT is above the low-power-mode threshold, VSLP. During sleep mode, the bq24400 shuts down all internal circuits, drives the LED output to high-impedance state,
and drives pin MOD to low. Restoring BAT below the
VMCV threshold initiates the IC and starts a fast-charge
cycle.
l
l
l
High-temperature cutoff voltage: VTCO = 0.225 ∗ VCC
This voltage corresponds to the maximum temperature
(TCO) at which fast charging is allowed. The bq24400
terminates fast charge if the voltage on pin TS falls
below VTCO.
High-temperature fault voltage: VHTF = 0.25 ∗ VCC This
voltage corresponds to the temperature (HTF) at which
fast charging is allowed to begin.
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 pin TS rises above VLTF, the bq24400
suspends fast charge or top-off but does not terminate
charge. When the voltage falls back below VLTF, fast
charge or top-off resumes from the point where
suspended. Trickle-charge is allowed during this
condition.
Rf
RSNS
1 SNS
Cf
2
BAT-
VSS
bq24400
bq2000T
Power Supply ground
bq2000 ground
bq24400
Table 3 summarizes these various conditions.
2000TCS.eps
Charge Status Display
The charge status is indicated by open-drain output LED.
Table 4 summarizes the display output of the bq24400.
Figure 8. Current-Sensing Circuit
9
bq24400
Absolute Maximum Ratings
Symbol
Parameter
Minimum
Maximum
Unit
VCC
VCC relative to VSS
-0.3
+7.0
V
VT
DC voltage applied on any pin, excluding VCC relative to VSS
-0.3
+7.0
V
TOPR
Operating ambient temperature
-20
+70
°C
TSTG
Storage temperature
-40
+125
°C
TSOLDER
Soldering temperature
-
+260
°C
Note:
Notes
10s max.
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 (TA = TOPR; VCC = 5V ±20% unless otherwise specified)
Symbol
Parameter
Temperature cutoff
VTCO
High-temperature fault
VHTF
VLTF
Low-temperature fault
Rating
0.225 * VCC
0.25 * VCC
0.5 * VCC
Tolerance
±5%
±5%
±5%
Unit
Notes
V
Voltage at pin TS
V
Voltage at pin TS
V
Voltage at pin TS
VBAT > VMCV inhibits
V
fast charge
mV
Voltage at pin BAT
mV
VMCV
Maximum cell voltage
2.00
±2.5%
VLBAT
PVD
950
3.8
±5%
±20%
50
±10
mV
Voltage at pin SNS
-50
±10
mV
Voltage at pin SNS
VSLP
Minimum cell voltage
BAT input change for PVD detection
High threshold at SNS, resulting in
MOD-low
Low threshold at SNS, resulting in
MOD-high
Sleep-mode input threshold
VRCH
Recharge threshold
VSNSHI
VSNSLO
VCC - 1
±0.5
V
Applied to pin BAT
VMCV - 0.1
±0.02
V
At pin BAT
10
bq24400
Recommended DC Operating Conditions
(TA = TOPR)
Symbol
Condition
Minimum
Typical
Maximum
Unit
Notes
VCC
Supply voltage
4.0
5.0
6.0
V
ICC
Supply current
-
0.5
1
mA
Exclusive of external loads
ICCS
Sleep current
-
-
5
µA
VBAT = VSLP
VTS
Thermistor input
0.5
-
VCC
V
VTS < 0.5V prohibited
VOH
Output high
VCC - 0.2
-
-
V
MOD, IOH = 20mA
VOL
Output low
-
-
0.2
V
MOD, LED, IOL = 20mA
IOZ
High-impedance leakage
current
-
-
5
µA
LED
Isnk
Sink current
-
-
20
mA
MOD, LED
RMTO
Charge timer resistor
2
-
250
kΩ
CMTO
Charge timer capacitor
0.001
-
1.0
µF
Note:
All voltages relative to VSS except as noted.
Impedance
Symbol
Parameter
Minimum
Typical
Maximum
Unit
RBAT
Battery input impedance
10
-
-
MΩ
RTS
TS input impedance
10
-
-
MΩ
RSNS
SNS input impedance
10
-
-
MΩ
Timing (TA = TOPR; VCC = 5V ±20% unless otherwise specified)
Symbol
Parameter
Minimum
Typical
Maximum
Unit
dMTO
MTO time-base variation
-5
-
+5
%
fTRKL
Pulse-trickle frequency
0.9
1.0
1.1
Hz
11
bq24400
Ordering Information
bq24400
Package Option:
P = 8-pin narrow plastic DIP
D = 8-pin narrow SOIC
PW = 8-pin TSSOP
Device:
bq24400 NiCd/NiMH Fast-Charge IC with ∆T/∆t Detection
8-Pin DIP (P)
0.400 (10,60)
0.355 (9,02)
8
5
0.260 (6,60)
0.240 (6,10)
1
4
0.070 (1,78) MAX
0.325 (8,26)
0.300 (7,62)
0.020 (0,51) MIN
0.015 (0,38)
Gag e Plane
0.200 (5,08) MAX
S e ating Plane
0.010 (0,25) NOM
0.125 (3,18) MIN
0.100 (2,54)
0.021 (0,53)
0.015 (0,38)
0.430 (10,92)
MAX
0 .0 1 0 (0 ,2 5 ) M
4040082/D 05/98
NOTES:
A. All linear dimensions are in inches (millimeters).
B. This drawing is subject to change without notice.
C. Falls within JEDEC MS-001
12
bq24400
8-Pin SOIC Narrow (D)
14 PINS S HOWN
0.050 (1,27)
0.020 (0,51)
0 .0 1 0 (0 ,2 5 ) M
0.014 (0,35)
14
8
0.008 (0,20) NOM
0.244 (6,20)
0.228 (5,80)
0.157 (4,00)
0.150 (3,81)
Gag e Plane
0.010 (0,25)
1
7
05- 85
A
0.044 (1,12)
0.016 (0,40)
S e ating Plane
0.069 (1,75) MAX
0.010 (0,25)
0.004 (0,10)
0.004 (0,10)
PINS **
8
14
16
A MAX
0.197
(5,00)
0.344
(8,75)
0.394
(10,00)
A MIN
0.189
(4,80)
0.337
(8,55)
0.386
(9,80)
DIM
4 0 4 0 0 4 7 / D 1 0 /9 6
NOTES:
A. All linear dimensions are in inches (millimeters).
B. This drawing is subject to change without notice.
C. Body dimensions do not include mold flash or protrusion, not to exceed 0.006 (0,15).
D. Falls within JEDEC MS-012
13
bq24400
8-Pin TSSOP ~ PW Package Suffix
14 PINS S HOWN
0,30
0,65
0,19
14
0 ,1 0 M
8
0,15 NOM
4,50
4,30
6,60
6,20
Gag e Plane
0,25
1
7
05- 85
A
0,75
0,50
S e ating Plane
0,15
0,05
1,20 MAX
PINS **
DIM
0,10
8
14
16
20
24
28
A MAX
3,10
5,10
5,10
6,60
7,90
9,80
A MIN
2,90
4,90
4,90
6,40
7,70
9,60
4040064/F 01/97
NOTES:
A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
C. Body dimensions do not include mold flash or protrusion not to exceed 0,15.
D. Falls within JEDEC MO-153
14
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15