LTC1733
Monolithic Linear
Lithium-Ion Battery Charger with
Thermal Regulation
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FEATURES
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DESCRIPTIO
Complete Linear Charger for 1-Cell Lithium-Ion
Batteries
Thermal Regulation Maximizes Charging Rate
without Risk of Overheating*
No External MOSFET, Sense Resistor or Blocking
Diode Required
Up to 1.5A Charge Current
Preset Charge Voltage with 1% Accuracy
Programmable Charge Current with 7% Accuracy
Programmable Charge Termination Timer
Tiny Thermally Enhanced 10-Pin MSOP Package
Charge Current Monitor Useful for Gas Gauging*
C/10 Charge Current Detection Output
Automatic Recharge
Thermistor Input for Temperature Qualified Charging
AC Present Logic Output
4.1V/4.2V Pin Selectable Output Voltage
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APPLICATIO S
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Cellular Telephones
Handheld Computers
Digital Still Cameras
Charging Docks and Cradles
No external current sense resistor is needed and no
blocking diode is required due to the internal MOSFET
architecture. The charge current and charge time can be
set externally with a single resistor and capacitor, respectively. When the input supply (wall adapter) is removed,
the LTC1733 automatically enters a low current sleep
mode, dropping the battery drain current to less than 5µA.
The LTC1733 also includes NTC temperature sensing,
C/10 detection circuitry, AC present logic, 4.1V/4.2V pin
selectability and low battery charge conditioning (trickle
charging).
The LTC1733 is available in a 10-pin thermally enhanced
MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*Patent Pending
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■
The LTC ®1733 is a standalone constant-current/
constant-voltage linear charger for lithium-ion batteries
with an on-chip power MOSFET. Internal thermal feedback
regulates the charge current to limit die temperature
during high power operation or high ambient temperature
conditions. This feature allows the user to program a high
charge current without risk of damaging the LTC1733 or
the handheld product.
TYPICAL APPLICATIO
Charge Current vs Battery Voltage
Standalone Li-Ion Battery Charger
1200
TA = 0°C
VIN = 5V
CONSTANT
CURRENT
4.7µF
8
2
SEL
VCC
9
BAT
LTC1733
4
7
TIMER
PROG
GND
NTC
5
6
0.1µF
IBAT = 1A
1.5k
1%
4.2V
1-CELL
Li-Ion
BATTERY*
CHARGE CURRENT (mA)
1000
TA = 40°C
800
TA = 25°C
CONSTANT
POWER
600
CONSTANT
VOLTAGE
400
200 TRICKLE
CHARGE
1733TA01
0
*AN OUTPUT CAPACITOR MAY BE REQUIRED
DEPENDING ON BATTERY LEAD LENGTH
2
2.5
VIN = 5V
θJA = 40°C/W
3
4
3.5
BATTERY VOLTAGE (V)
4.5
1733 TA01b
sn1733 1733fs
1
LTC1733
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Supply Voltage (VCC) ........................................ 7V
BAT ............................................................................ 7V
NTC, SEL, TIMER, PROG ................ –0.3V to VCC + 0.3V
CHRG, FAULT, ACPR ................................... –0.3V to 7V
BAT Short-Circuit Duration ........................... Continuous
BAT Current (Note 2) .............................................. 1.6A
PROG Current (Note 2) ........................................ 1.6mA
Junction Temperature ........................................... 125°C
Operating Temperature Range (Note 3) ...–40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
TOP VIEW
CHRG
VCC
FAULT
TIMER
GND
1
2
3
4
5
10
9
8
7
6
ACPR
BAT
SEL
PROG
NTC
LTC1733EMSE
MSE EXPOSED PAD PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 40°C/W (Note 4)
EXPOSED PAD IS GROUND.
(MUST BE SOLDERED TO PCB
FOR MAXIMUM HEAT TRANSFER).
MSE PART MARKING
LTLX
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V
SYMBOL
PARAMETER
CONDITIONS
MIN
VCC
VCC Supply Voltage
ICC
VCC Supply Current
Charger On; Current Mode; RPROG = 30k (Note 5)
Shutdown Mode; VPROG = 3V
●
●
VBAT
VBAT Regulated Output Voltage
SEL = 0V
SEL = VCC
●
●
IBAT
Battery Pin Current
RPROG = 3k; Current Mode
RPROG = 1k; Current Mode
Shutdown Mode; VPROG = 3V
Sleep Mode VCC < VBAT or VCC < (VUV – ∆VUV)
ITRIKL
Trickle Charge Current
VBAT < 2V; RPROG = 3k
VTRIKL
Trickle Charge Trip Threshold
VBAT Rising
∆VTRIKL
Trickle Charge Trip Hysteresis
VUV
VCC Undervoltage Lockout Voltage
∆VUV
VCC Undervoltage Lockout Hysteresis
VMSD
Manual Shutdown Threshold Voltage
VMSD-HYS
VASD
●
VCC Rising
TYP
4.5
MAX
UNITS
6.5
V
1
0.9
3
2
4.059
4.158
4.1
4.2
4.141
4.242
V
V
●
465
1.395
500
1.5
±1
±1
535
1.605
±5
±5
mA
A
µA
µA
●
35
50
65
mA
●
mA
mA
2.48
V
100
mV
4.2
4.5
V
150
mV
2.15
V
Manual Shutdown Hysteresis Voltage
100
mV
Automatic Shutdown Threshold Voltage (VCC - VBAT) Voltage Falling
(VCC - VBAT) Voltage Rising
30
60
mV
mV
PROG Pin Voltage Rising
sn1733 1733fs
2
LTC1733
ELECTRICAL CHARACTERISTICS
TA = 25°C. VCC = 5V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VPROG
PROG Pin Voltage
RPROG = 3k, IPROG = 500µA; Current Mode
ICHRG
CHRG Pin Weak Pulldown Current
VCHRG
CHRG Pin Output Low Voltage
VACPR
ACPR Pin Output Low Voltage
IACPR = 5mA
VFAULT
FAULT Pin Output Low Voltage
IFAULT = 5mA
IC/10
End of Charge Indication Current Level
RPROG = 3k
tTIMER
TIMER Accuracy
CTIMER = 0.1µF
±10
%
VRECHRG
Recharge Battery Voltage Threshold
Battery Voltage Falling, SEL = 0V
Battery Voltage Falling, SEL = 5V
3.9
4.0
V
V
VNTC-HOT
NTC Pin Hot Threshold Voltage
VNTC Falling
2.5
V
VHOT-HYS
NTC Pin Hot Hysteresis Voltage
70
mV
VNTC-COLD
NTC Pin Cold Threshold Voltage
VNTC Rising
4.375
VCOLD-HYS
NTC Pin Cold Hystersis Voltage
VNTC-DIS
NTC Pin Disable Threshold Voltage
VDIS-HYS
NTC Pin Disable Hystersis Voltage
VSEL-IL
SEL Pin Threshold Input Low
VSEL-IH
SEL Pin Threshold Input High
TLIM
Junction Temperature in
Constant-Temperature Mode
105
°C
RON
Power MOSFET “ON” Resistance
375
mΩ
1.5
V
VCHRG = 1V
25
µA
ICHRG = 5mA
0.35
V
0.35
V
0.35
35
50
V
65
V
70
VNTC Rising
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The Absolute Maximum BAT Current Rating of 1.6A is guaranteed
by design and current density calculations. The Absolute Maximum PROG
Current Rating is guaranteed to be 1/1000 of BAT current rating by design.
Note 3: The LTC1733E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
mA
mV
100
mV
10
mV
0.3
V
1
V
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 4: Failure to solder the exposed backside of the package to the PC
board will result in a thermal resistance much higher than 40°C/W.
Note 5: Supply current includes PROG pin current but does not include
any current delivered to the battery through the BAT pin.
sn1733 1733fs
3
LTC1733
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TYPICAL PERFOR A CE CHARACTERISTICS
Battery Regulation Voltage vs
Battery Charge Current
4.24
Battery Regulation Voltage vs
Temperature
VCC = 5V
TA = 25°C
RPROG = 1.5k
4.22 V
SEL = 5V
4.20
VCC = 5V
4.22 IBAT = 10mA
RPROG = 1.5k
4.20
TA = 25°C
4.22 IBAT = 10mA
RPROG = 1.5k
4.20
VSEL = 5V
4.14
VBAT (V)
4.16
4.16
4.14
4.12 VSEL = 0V
4.12
4.14
4.12
VSEL = 0V
4.10
4.10
4.08
4.08
4.08
4.06
–50
0 100 200 300 400 500 600 700 800 900 1000
IBAT (mA)
–25
25
0
50
75
TEMPERATURE(°C)
100
4.06
4.0
125
Charge Current vs Battery Voltage
800
IBAT (mA)
IBAT (mA)
700
600
500
600
500
400
0.4
300
300
200
200
100
100
0.2
0
0 100 200 300 400 500 600 700 800 900 1000
CHARGE CURRENT (mA)
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
VBAT (V)
1733 G04
RPROG = 1.5k
900
1000
800
900
700
THERMAL CONTROL
LOOP IN OPERATION
500
400
300
600
RPROG = 3k
500
400
4.0
600
IBAT (mA)
IBAT (mA)
700
4.5
5.0
5.5
VCC (V)
6.0
6.5
7.0
1733 G07
4.5
5.0
5.5
VCC (V)
6.0
6.5
V = 5V
200 VCC = 3.5V
BAT
100 RPROG = 1.5k
VSEL = 5V
0
–25
25
0
–50
50
TEMPERATURE (°C)
75
7.0
Charge Current vs Temperature
1000
800
4.0
1733 G06
Charge Current vs Temperature
with Thermal Regulation
VBAT = 3.5V
TA = 25°C
VSEL = VCC
VBAT = 4.1V
TA = 25°C
RPROG = 1.5k
VSEL = 5V
1733 G05
Charge Current vs VCC
7.0
900
400
1100
6.5
1000
0.6
0
6.0
Charge Current vs Input Voltage
700
0.8
5.5
1100
VCC = 5V
1000 TA = 25°C
900 RPROG = 1.5k
VSEL = 5V
800
1.0
5.0
1733 G03
1100
VCC = 5V
1.4 TA = 25°C
RPROG = 1.5k
1.2 VSEL = 5V
4.5
1733 G02
PROG Pin Voltage vs Charge
Current
1.6
VSEL = 0V
VCC (V)
1733 G01
IBAT (mA)
4.16
4.10
4.06
VSEL = VCC
4.18
4.18
VBAT (V)
VBAT (V)
4.18
VPROG (V)
Battery Regulation Voltage vs VCC
4.24
4.24
100
1733 G08
535
530
525
520
515
510
505
500
495
490
485
480
475
470
465
–50
VCC = 5V
VBAT = 4V
RPROG = 3k
VSEL = 5V
–25
50
25
0
TEMPERATURE (°C)
75
100
1733 G09
sn1733 1733fs
4
LTC1733
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TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Voltage vs VCC
Constant Current Mode
PROG Pin Voltage vs Temperature
Constant Current Mode
1.515
VCC = 5V
VBAT = 4V
RPROG = 3k
VSEL = 5V
1.510
1.505
110
IBAT (mA)
1.500
1.500
1.495
90
1.490
1.490
80
4.5
5.0
5.5
VCC (V)
6.0
6.5
7.0
1.485
–50
–25
50
25
0
TEMPERATURE (°C)
1733 G10
Trickle Charge Current vs VCC
105
103
8
7
4.0
4.5
5.0
5.5
VCC (V)
6.0
6.5
7.0
1733 G13
105
103
102
102
101
101
100
99
99
98
97
97
96
96
–25
25
0
50
75
TEMPERATURE(°C)
100
100
100
98
95
–50
75
125
1733 G14
TA = 25°C
IBAT = 0mA
VSEL = 5V
CTIMER = 0.1µF
104
tTIMER (%)
tTIMER (%)
9
50
25
0
TEMPERATURE (°C)
Timer Accuracy vs VCC
VCC = 5V
IBAT = 0mA
VSEL = 5V
CTIMER = 0.1µF
104
11
10
–25
1733 G12
Timer Accuracy vs Temperature
TA = 25°C
VBAT = 2V
RPROG = 1.5k
VSEL = 5V
12
70
–50
100
75
1733 G11
13
IBAT (% OF PROGRAMMED CURRENT)
100
1.495
1.485
4.0
VCC = 5V
VBAT = 2V
RPROG = 1.5k
VSEL = 5V
120
1.505
VPROG (V)
VPROG (V)
130
1.515
TA = 25°C
VBAT = 3.5V
RPROG = 3k
VSEL = 5V
1.510
Trickle Charge Current vs
Temperature
95
4.0
4.5
5.0
5.5
VCC (V)
6.0
6.5
7.0
1733 G15
sn1733 1733fs
5
LTC1733
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PI FU CTIO S
CHRG: Open-Drain Charge Status Output. When the
battery is being charged, the CHRG pin is pulled low by an
internal N-channel MOSFET. When the charge current
drops to 10% of the full-scale current, the N-channel
MOSFET latches off and a 25µA current source is connected from the CHRG pin to ground. The C/10 latch can
be cleared by momentarily pulling the PROG pin above the
2.15V shutdown threshold, or by toggling VCC. When the
timer runs out or the input supply is removed, the current
source is disconnected and the CHRG pin is forced to a
high impedance state.
VCC: Positive Input Supply Voltage. When VCC is within
30mV of VBAT or less than the undervoltage lockout
threshold, the LTC1733 enters sleep mode, dropping IBAT
to less than 5µA. VCC can range from 4.5V to 6.5V. Bypass
this pin with at least a 4.7µF ceramic capacitor to ground.
FAULT: Open-Drain Fault Status Output. The FAULT opendrain logic signal indicates that the charger has timed out
under trickle charge conditions (1/4 of total time period) or
the NTC comparator is indicating an out-of-range battery
temperature condition. When VBAT is less that 2.48V,
trickle charging activates whereby the charge current
drops to one tenth of its programmed value and the timer
period is reduced by a factor of four. When one fourth of
the timing period has elapsed, if VBAT is still less than
2.48V, trickle charging stops and the FAULT pin latches to
ground. The fault can be cleared by toggling VCC, momentarily pulling the PROG pin above the 2.15V shutdown
threshold, or pulling the BAT pin above 2.48V. If the NTC
comparator is indicating an out-of-range battery temperature condition, then the FAULT pin will pull to ground until
the temperature returns to the acceptable range.
TIMER: Timer Capacitor. The timer period is set by placing
a capacitor, CTIMER, to ground. The timer period is:
Time (Hours) = (CTIMER • 3 hr)/(0.1µF)
Short the TIMER pin to ground to disable the internal timer
function.
GND: Ground. Connect exposed back package to ground.
NTC: Input to the NTC (Negative Temperature Coefficient)
Thermistor Temperature Monitoring Circuit. With an external 10kΩ NTC thermistor to ground and a 1% resistor
to VCC, this pin can sense the temperature of the battery
pack and stop charging when it is out of range. When the
voltage at this pin drops below (0.5)•(VCC) at hot temperatures or rises above (0.875)•(VCC) at cold, charging is
suspended and the internal timer is frozen. The CHRG pin
output status is not affected in this hold state. The FAULT
pin is pulled to ground, but not latched. When the temperature returns to an acceptable range, charging will resume
and the FAULT pin is released. The NTC feature can be
disabled by grounding the NTC pin.
PROG: Charge Current Program, Shutdown Input and
Charge Current Monitor Pin. The charge current is programmed by connecting a resistor, RPROG to ground.
When in constant-current mode, the LTC1733 servos the
PROG pin voltage to 1.5V. In all modes the voltage on the
PROG pin can be used to measure the charge current as
follows:
ICHG = (VPROG/RPROG) • 1000.
The IC can be forced into shutdown by pulling the PROG
pin above the 2.15V shutdown threshold voltage (note: it
will not be pulled up when allowed to float).
SEL: 4.1V/4.2V Battery Selection Input. Grounding this
pin sets the battery float voltage to 4.1V, while connecting
to VCC sets the voltage to 4.2V.
BAT: Charge Current Output. A bypass capacitor of at least
1µF with a 1Ω series resistor is required to minimize ripple
voltage when the battery is not present. A precision
internal resistor divider sets the final float potential on this
pin. The internal resistor divider is disconnected in sleep
and shutdown modes.
ACPR: Open-Drain Power Supply Status Output. When
VCC is greater than the undervoltage lockout threshold
and at least 30mV above VBAT, the ACPR pin will pull to
ground. Otherwise, the pin is forced to a high impedance
state.
sn1733 1733fs
6
LTC1733
W
W
SI PLIFIED BLOCK DIAGRA
VCC
2
–
105°C
D1
TA
D2
+
TDIE
M2
×1
D3
M1
×1000
+
–
MA
9
30µA
NTC 6
NTC
MP
+
VA
R2
–
CA
+
–
2.485V
–
HOT COLD DISABLE
CHRG 1
BAT
R1
R4
C1
SHDN
STOP
REF
R3
2.15V
+
C/10
8 SEL
R5
25µA
2.5µA
1.5V
LOGIC
ACPR 10
R6
ACPR
0.15V
+
C2
FAULT 3
R7
–
FAULT
CHARGE
COUNTER
C3
OSCILLATOR
–
2.485V
4
+
TO BAT
7
TIMER
PROG
5
GND
1733 F01
RPROG
CTIMER
Figure 1.
sn1733 1733fs
7
LTC1733
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OPERATIO
The LTC1733 is a linear battery charger designed primarily
for charging single cell lithium-ion batteries. Featuring an
internal P-channel power MOSFET, the charger uses a
constant-current/constant-voltage charge algorithm with
programmable current and a programmable timer for
charge termination. Charge current can be programmed
up to 1.5A with a final float voltage accuracy of ±1%. No
blocking diode or sense resistor is required thus dropping
the external component count to three for the basic
charger circuit. The CHRG, ACPR, and FAULT open-drain
status outputs provide information regarding the status of
the LTC1733 at all times. An NTC thermistor input
provides the option of charge qualification using battery
temperature.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 105°C. This feature protects
the LTC1733 from excessive temperature, and allows the
user to push the limits of the power handling capability of
a given circuit board without risk of damaging the LTC1733
or the external components. Another benefit of the LTC1733
thermal limit is that charge current can be set according to
typical, not worst-case, ambient temperatures for a given
application with the assurance that the charger will automatically reduce the current in worst-case conditions.
The charge cycle begins when the voltage at the VCC pin
rises above the UVLO level and a program resistor is
connected from the PROG pin to ground. At the beginning
of the charge cycle, if the battery voltage is below 2.48V,
the charger goes into trickle charge mode to bring the cell
voltage up to a safe level for charging. The charger goes
into the fast charge constant-current mode once the
voltage on the BAT pin rises above 2.48V. In constantcurrent mode, the charge current is set by RPROG.
When the battery approaches the final float voltage, the
charge current begins to decrease as the LTC1733 switches
to constant-voltage mode. When the current drops to 10%
of the full-scale charge current, an internal comparator
latches off the MOSFET at the CHRG pin and connects a
weak current source to ground to indicate a near end-ofcharge (C/10) condition. The C/10 latch can be cleared by
momentarily pulling the PROG pin above the 2.15V
shutdown threshold, or momentarily removing and reapplying VCC.
An external capacitor on the TIMER pin sets the total
charge time. When this time elapses the charge cycle
terminates and the CHRG pin assumes a high impedance
state. To restart the charge cycle, simply remove the input
voltage and reapply it, or force the PROG pin above the
2.15V shutdown threshold (note: simply floating the PROG
pin will not restart the charging cycle.
For lithium-ion and similar batteries that require accurate
final float potential, the internal reference, voltage amplifier and the resistor divider provide regulation with ±1%
(max) accuracy.
When the input voltage is not present, the charger goes
into a sleep mode, dropping battery drain current, IBAT, to
less than 5µA. This greatly reduces the current drain on the
battery and increases the standby time. The charger can be
shut down (ICC = 0.9mA) by forcing the PROG pin above
2.15V.
sn1733 1733fs
8
LTC1733
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APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until VCC
rises above the undervoltage lockout threshold. The UVLO
circuit has a built-in hysteresis of 150mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if VCC
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown until VCC rises 60mV above the battery voltage.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
low (below 2.48V) the charger goes into trickle charge
reducing the charge current to 10% of the full-scale
current. If the low battery voltage persists for one quarter
of the total charge time, the battery is assumed to be
defective, the charge cycle is terminated, the CHRG pin
output assumes a high impedance state, and the FAULT
pin latches low. The fault can be cleared by toggling VCC,
temporarily forcing the PROG pin above 2.15V, or temporarily forcing the BAT pin voltage above 2.48V.
Shutdown
The LTC1733 can be shutdown (ICC = 0.9mA) by pulling
the PROG pin above the 2.15V shutdown threshold voltage. In shutdown the internal linear regulator is turned off,
and the internal timer is reset.
Recharge
The LTC1733 has the ability to recharge a battery
assuming that the battery voltage has been charged above
4.05V (SEL = 5V) or 3.95V (SEL = 0V). Once above these
thresholds, a new charge cycle will begin if the battery
voltage drops below 4V (SEL = 5V) or 3.9V (SEL = 0V) due
to either a load on the battery or self-discharge. The
recharge circuit integrates the BAT pin voltage for a few
milliseconds to prevent a transient from restarting the
charge cycle.
If the battery voltage remains below 2.48V during trickle
charge for 1/4 of the programmed time, the battery may be
defective and the charge cycle will end. In addition, the
recharge comparator is disabled and a new charge cycle
will not begin unless the input voltage is toggled, the PROG
pin is pulled above the 2.15V shutdown threshold, or the
BAT pin is pulled above the 2.48V trickle charge threshold.
Programming Charge Current
The formula for the battery charge current (see Figure 1)
is:
ICHG = (IPROG) • 1000
= (1.5V / RPROG) • 1000 or
RPROG = 1500/ICHG
where RPROG is the total resistance from the PROG pin to
ground. Under trickle charge conditions, this current is
reduced to 10% of the full-scale value.
For example, if 500mA charge current is required,
calculate:
RPROG = 1500/0.5A = 3kΩ
For best stability over temperature and time, 1% metalfilm resistors are recommended.
If the charger is in constant-temperature or constantvoltage mode, the battery current can be monitored by
measuring the PROG pin voltage as follows:
ICHG = (VPROG / RPROG) • 1000
Programming the Timer
The programmable timer is used to terminate the charge
cycle. The timer duration is programmed by an external
capacitor at the TIMER pin. The total charge time is:
Time (Hours) = (3 Hours) • (CTIMER / 0.1µF) or
CTIMER = 0.1µF • Time (Hours)/3 (Hours)
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied and the
program resistor is connected to ground. After a time-out
occurs, the charge current stops, and the CHRG output
assumes a high impedance state to indicate that the
charging has stopped. Connecting the TIMER pin to ground
disables the timer function.
sn1733 1733fs
9
LTC1733
U
W
U U
APPLICATIO S I FOR ATIO
Open-Drain Status Outputs
The LTC1733 has three open-drain status outputs: ACPR,
CHRG and FAULT. The ACPR pin pulls low when an input
voltage greater than the undervoltage lockout threshold is
applied and goes high impedance when power (VIN < VUV)
is removed. CHRG and FAULT work together to indicate
the status of the charge cycle. Table 1 describes the status
of the charge cycle based on the CHRG and FAULT
outputs.
V+
VDD
8
VCC
400k
LTC1733
CHRG
3
µPROCESSOR
2k
OUT
IN
1733 F02
Figure 2. Microprocessor Interface
Table 1.
FAULT
CHRG
Description
High
Low
Charge cycle has started, C/10 has not been
reached and charging is proceeding normally.
Low
Low
Charge cycle has started, C/10 has not been
reached, but the charge current and timer
have been paused due to an NTC out-oftemperature condition.
High
25µA
pulldown
C/10 has been reached and charging is
proceeding normally.
Low
25µA
pulldown
C/10 has been reached but the charge current
and timer have paused due to an
NTC out-of-temperature condition.
High
High
Normal timeout (charging has terminated).
Low
High
If FAULT goes low and CHRG goes high
impedance simultaneously, then the LTC1733
has timed out due to a bad cell (VBAT
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