LTC1730-4/LTC1730-4.2
Lithium-Ion Battery
Pulse Charger with
Overcurrent Protection
FEATURES
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DESCRIPTIO
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Complete Pulse Charger for 1-Cell Lithium-Ion
Batteries
Sense Resistor Limits Maximum Current for Safety
1% Float Voltage Accuracy
End-of-Charge (C/10) Detection Output
Programmable Charge Termination Timer
Internal 0.35Ω NMOS Switch
No Blocking Diode Required
SEL Pin to Set Either 4.1V or 4.2V/Cell (LTC1730-4)
Low-Battery Drain (1µA Max) when Input Supply Is
Removed
Battery Temperature Sensing and Charge
Qualification
Automatic Trickle Charge for Low-Battery
Automatic Battery Refresh
The LTC
®
1730 is a complete pulse charger for 1-cell
lithium-ion batteries. When charging a depleted cell, the
internal MOSFET is fully on allowing the current limited
input power source to provide charge current to the
battery, virtually eliminating heat generation in the charger.
As the battery accepts charge and approaches the pro-
grammed voltage, the internal MOSFET begins switching
off and on with the duty cycle gradually decreasing as the
battery approaches a fully charged condition. A program-
mable timer ends the charge cycle. The end-of-charge
condition is indicated at the CHRG pin when the average
charge current falls to
C/10.
Removing the input voltage
puts the LTC1730 into a sleep mode, dropping the battery
current drain to less than 1µA (maximum).
An external sense resistor limits the maximum charge
current as a safety precaution against a user connecting a
wall adapter with the incorrect or no current limit. The
internal MOSFET prevents reverse battery current from
flowing if the input voltage is shorted to ground, eliminat-
ing the need for a blocking diode.
The LTC1730-4 is available in the 16-pin SSOP package
and the LTC1730-4.2 is available in the 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Standalone Lithium-Ion Battery Charger
Handheld Computers
Cellular Telephones
TYPICAL APPLICATIO
1A, Single Cell 4.2V Li-Ion Battery Charger (8-Pin Package)
V
IN
= 4.5V TO 12V
WITH 1A CURRENT LIMIT
R1
1k
R3
4.1k
CHARGE STATUS
3
CHRG
SENSE
6
T
R4
10k
NTC*
C
TIMER
0.1µF
*NTC: DALE NTHS-1206N02
1730 TA01
2
V
CC
LTC1730ES8-4.2
GATE
7
R2
10k
C3
0.047µF
R
SENSE
0.05Ω
D3
0.022µF
1
8
1-CELL
Li-Ion
BATTERY
NTC/SHDN
BAT
TIMER
5
GND
4
U
4.7Ω
C1
1µF
U
U
sn1730 1730fs
1
LTC1730-4/LTC1730-4.2
ABSOLUTE
AXI U RATI GS
Supply Voltage (V
CC
) ............................................ 13.2V
SENSE, GATE, BAT,
TIMER, NTC/SHDN, SEL ............................ – 0.3V to V
CC
CHRG, ACPR, FAULT ..............................– 0.3V to 13.2V
TOP VIEW
GND*
SENSE
V
CC
ACPR
FAULT
CHRG
NC**
GND*
1
2
3
4
5
6
7
8
16 GND*
15 BAT
14 NC**
13 GATE
12 SEL
11 NTC/SHDN
10 TIMER
9
GND*
ORDER PART
NUMBER
LTC1730EGN-4
TOP VIEW
SENSE 1
V
CC
2
8
7
6
5
BAT
GATE
NTC/SHDN
TIMER
GN PART MARKING
17304
GN PACKAGE
16-LEAD PLASTIC SSOP
* FOUR CORNER PINS ARE FUSED TO
INTERNAL DIE ATTACH PADDLE FOR
HEAT SINKING. CONNECT THESE FOUR
PINS TO EXPANDED PC LANDS FOR
PROPER HEAT SINKING.
** NO INTERNAL CONNECTION
T
JMAX
= 125°C,
θ
JA
= 90°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
DC ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
CONDITIONS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 6V unless otherwise noted.
MIN
q
Charger On; Fast Charge Mode
Shutdown: V
NTC/SHDN
= 0V
Sleep Mode; V
BAT
= 4V
LTC1730ES8-4.2 (5V
≤
V
CC
≤
12V)
LTC1730EGN-4 (5V
≤
V
CC
≤
12V), SEL = GND
LTC1730EGN-4 (5V
≤
V
CC
≤
12V), SEL = V
CC
R
SENSE
= 0.1Ω
V
BAT
= 2V
(V
CC
– V
BAT
) Low to High
(V
CC
– V
BAT
) High to Low
V
BAT
= 4V
NTC/SHDN Pin High to Low
V
BAT
Regulated Output Voltage
I
MAX
I
TRICKL
V
TRICKL
V
ASD
R
DS(ON)
V
SHDN
Maximum Charge Overcurrent
Trickle Charge Current
Trickle Charge Trip Threshold
Automatic Shutdown Threshold Voltage
(Sleep Mode)
Internal Switch On-Resistance
Shutdown Threshold Voltage
2
U
W W
W
(Note 1)
Operating Junction
Temperature Range (Note 2) .................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1730ES8-4.2
CHRG 3
GND 4
S8 PART MARKING
173042
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/W
TYP
2
2
MAX
12
5
5
1
4.242
4.141
4.242
1.3
60
2.55
150
UNITS
V
mA
mA
µA
V
V
V
A
mA
V
mV
mV
Ω
mV
sn1730 1730fs
4.5
q
q
q
q
q
q
q
4.158
4.059
4.158
0.7
15
4.2
4.1
4.2
1
35
2.45
0
0.35
50
LTC1730-4/LTC1730-4.2
DC ELECTRICAL CHARACTERISTICS
SYMBOL
I
CHRG
T
TIMER
V
GATE
T
SHDN
∆T
SHDN
∆V
RECHRG
V
NTC_HOT
V
NTC_COLD
V
SEL
V
ACPR
V
FAULT
V
CHRG
PARAMETER
CHRG Pin Pull-Down Current
TIMER Accuracy
GATE Pin Voltage
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
Recharge Battery Voltage Offset from
Full Charged Battery Voltage
NTC/SHDN Pin Threshold Voltage (Hot)
NTC/SHDN Pin Threshold Voltage (Cold)
SEL Pin Threshold
ACPR Pin Output Low Voltage
FAULT Pin Output Low Voltage
CHRG Pin Output Low Voltage
V
BAT(Full Charged)
– V
RECHRG
(Note 3)
High to Low; V
CC
= 4V
Hysteresis
Low to High; V
CC
= 4V
Hysteresis
LTC173ECGN-4
LTC1730EGN-4, I
ACPR
= 5mA
LTC1730EGN-4, I
FAULT
= 3mA
I
CHRG
= 5mA, Charging Mode
q
q
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 6V unless otherwise noted.
CONDITIONS
V
CHRG
= 1V, C/10 Mode
C
TIMER
= 0.1µF
V
BAT
= 3V
V
BAT
= 4V
7.5
10
140
5
150
1.95
3.4
2
50
3.5
45
0.7
0.6
1.2
0.9
2.05
3.6
MIN
10
TYP
40
MAX
70
10
UNITS
µA
%
V
V
°C
°C
mV
V
mV
V
mV
V
V
V
V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1730-4/LTC1730-4.2 are guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
For the LTC1730-4 version, the full charged V
BAT
value is
typically 4.1V.
sn1730 1730fs
3
LTC1730-4/LTC1730-4.2
TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Current vs Input
Supply Voltage
50
45
40
TA = 25°C
2.50
V
TRIKL
(V)
I (mA)
I (mA)
35
30
25
20
5
6
7
9
8
V
CC
(V)
10
Internal Switch On-Resistance vs
Temperature
0.50
V
BAT
= 4V
0.45
0.40
R
DS(ON)
(Ω)
t
TIMER
(%)
100
95
90
I
MAX
(A)
0.35
0.30
0.25
0.20
–50
–25
50
25
75
0
TEMPERATURE (°C)
Battery Recharge Threshold Offset
from V
BAT
vs Temperature
300
V
CC
= 6V
250
0.9
0.8
1.0
∆V
RECHRG
(mV)
200
V
CHRG
(V)
0.7
0.6
0.5
0.4
0.3
–50
150
100
50
0
–50 –25
0
4
U W
11
12
1730 G01
Trickle Charge Threshold Voltage
vs Temperature
50
V
CC
= 6V
Trickle Charge Current vs
Temperature
V
CC
= 6V
45
40
2.48
2.46
35
30
2.44
2.42
25
20
–50
2.40
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
125
–25
50
25
75
0
TEMPERATURE (°C)
100
125
1730 G02
1730 G03
Timer Accuracy vs Temperature
115
110
105
V
CC
= 6V
C
TIMER
= 0.1µF
1.3
1.2
1.1
1.0
0.9
0.8
0.7
Overcurrent vs Temperature
V
CC
= 6V
R
SEN
= 0.1Ω
85
80
–50
100
125
–25
50
25
75
0
TEMPERATURE (°C)
100 125
1730 G06
0.6
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
125
1730 G05
1730 G07
CHRG Pin Output Low Voltage vs
Temperature
25 50
75 100 125 150
TEMPERATURE (°C)
1730 G09
–25
50
25
75
0
TEMPERATURE (°C)
100
125
1730 G08
sn1730 1730fs
LTC1730-4/LTC1730-4.2
PI FU CTIO S
LTC1730ES8-4.2
SENSE (Pin 1):
Maximum Overcurrent Sense Input. A
sense resistor (R
SENSE
) should be connected from V
CC
to
the SENSE pin. When the voltage drop across R
SENSE
exceeds 100mV, the pass transistor immediately turns off
and turns back on after a 400ms time-out period (C
TIMER
= 0.1µF). The on-off cycle will continue, as long as the
overcurrent condition persists or until the timer runs out.
If overcurrent protection is not needed, short SENSE to
V
CC
.
V
CC
(Pin 2):
Positive Input Supply Voltage (4.5V
≤
V
CC
≤
13.2V). Bypass this pin with a 1µF capacitor in series with
a 4.7Ω resistor. An RC network from the V
CC
pin to the
GATE pin is also required. The capacitor controls the slew
rate at the V
CC
pin, while the resistor limits the inrush
current when the input voltage is first applied. When the
pass transistor turns on, V
CC
ramps down in a controlled
manner, with a slope equal to 10µA/C. When the pass
transistor turns off, V
CC
ramps up with a slope of 40µA/C.
CHRG (Pin 3):
Open-Drain Charge Status Output. When a
depleted battery is being charged, the CHRG pin is pulled
to ground by an N-MOSFET capable of driving an LED.
Once the duty cycle at the GATE pin drops below 10%, the
N-MOSFET turns off and a weak 40µA current source to
ground turns on to indicate a near end-of-charge (C/10)
condition. When a time-out occurs or the input supply is
removed, the CHRG pin goes high impedance.
GND (Pin 4):
Electrical Ground Connection and provides
a thermal path from the IC to the PC board copper. Use
large copper pads and traces for maximum heat transfer.
TIMER (Pin 5):
Timer Set Pin. The timer period is set by a
capacitor (C
TIMER
) to ground. The timer period is:
t
TIMER
= (C
TIMER
• 3Hr)/(0.1µF). The minimum ON time,
OFF time and the overcurrent time-out period are all set by
the same timer period.
NTC/SHDN (Pin 6):
Input to the NTC (Negative Tempera-
ture Coefficient) Thermistor Monitoring and Shutdown
Circuitry. With an external 10kΩ NTC thermistor to ground
and a 1% resistor to V
CC
, this pin can sense the tempera-
ture of the battery pack and stop charging when the
temperature is out of range. When the voltage at this pin
drops below 0.5 • V
CC
, or 2V at hot temperature or rises
above 0.875 • V
CC
, or 3.5V at cold (with V
CC
= 4V), the
charge cycle is suspended and the internal timer is frozen.
The CHRG pin output status is not affected in this hold
state.
When this pin is pulled below 50mV, the IC goes into the
shutdown mode. The charging stops (the GATE pin is
pulled to ground) the timer is reset and the CHRG pin goes
into a high impedance state.
GATE (Pin 7):
Gate Drive Output Pin for Internal and
External Pass Transistors. An external N-MOSFET transis-
tor can be connected in parallel with the internal transistor
to reduce the on-resistance for higher charge current. In
this case, an external blocking diode is required to prevent
damage to the battery if V
CC
is shorted to ground. A 10µA
current source pulls this pin up to the charge pump
potential when turned on and a 40µA current source pulls
it down to ground to turn it off. If an overcurrent condition
is detected, the GATE pin is immediately pulled to ground.
A series RC network from the GATE to the V
CC
pin is
required to control the slew rate at the V
CC
pin when the
switch is turned on or off. The slew rate control prevents
excessive current from the capacitor located in the wall
adapter from flowing into the battery when the pass
transistor is turned on. The voltage at this pin is internally
clamped to 12V above the BAT pin.
BAT (Pin 8):
Battery Sense Input Pin. This pin is clamped
to 4.7V if the battery is disconnected while charging. An
internal resistor divider presets the final float voltage to
4.2V.
If the voltage at the BAT pin drops 150mV below final float
voltage after the charge cycle has ended, the timer resets
and a new charge cycle begins.
LTC1730EGN-4
GND (Pins 1, 8, 9, 16):
Refer to LTC1730ES8-4.2
SENSE (Pin 2):
Refer to LTC1730ES8-4.2
V
CC
(Pin 3):
Refer to LTC1730ES8-4.2
ACPR (Pin 4):
Wall Adapter Present Open-Drain Output.
When the input voltage (wall adapter) is applied to the
LTC1730, this pin is pulled to ground by an internal
sn1730 1730fs
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