LTC4001-1
2A Synchronous
Buck Li-Ion Charger
FEATURES
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DESCRIPTION
The LTC
®
4001-1 is a 2A Li-Ion battery charger intended for
5V wall adapters. It utilizes a 1.5MHz synchronous buck
converter topology to reduce power dissipation during
charging. Low power dissipation, an internal MOSFET and
sense resistor allow a physically small charger that can be
embedded in a wide range of handheld applications. The
LTC4001-1 includes complete charge termination circuitry,
automatic recharge and a ±1% 4.1V float voltage. Input
short-circuit protection is included so no blocking diode
is required.
This 4.1V version of the standard LTC4001 is intended
for applications which will be operated or stored above
approximately 60°C. Under these conditions, the reduced
float voltage will trade-off initial cell capacity for the benefit
of increased capacity retention over the life of the battery. A
reduced float voltage also minimizes swelling in prismatic
and polymer cells, and avoids open CID (pressure fuse)
in cylindrical cells.
Battery charge current, charge timeout and end-of-charge
indication parameters are set with external components.
Additional features include shorted cell detection, tempera-
ture qualified charging and overvoltage protection. The
LTC4001-1 is available in a low profile (0.75mm) 16-lead
(4mm
×
4mm) QFN package.
Low Power Dissipation
2A Maximum Charge Current
No External MOSFETs, Sense Resistor or
Blocking Diode Required
Remote Sensing at Battery Terminals
Programmable Charge Termination Timer
Preset 4.1V Float Voltage with ±0.5% Accuracy
4.1V Float Voltage Improves Battery Life and High
Temperature Safety Margin
Programmable Charge Current Detection/
Termination
Automatic Recharge
Thermistor Input for Temperature Qualified
Charging
Compatible with Current Limited Wall Adapters
Low Profile 16-Lead (4mm
×
4mm) QFN Package
APPLICATIONS
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Handheld Battery-Powered Devices
Handheld Computers
Charging Docks and Cradles
Digital Cameras
Smart Phones
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
2A Single Cell Li-Ion Battery Charger
1.5μH
SW
V
IN
4.5V TO 5.5V
10μF
PGND
CHRG
NTC
FAULT
EN
PROG IDET TIMER
0.22μF
274Ω
0.1μF
40011 TA01a
Power Loss vs V
BAT
Charging (PWM Mode)
1.25
TOTAL APPLICATION CIRCUIT POWER
DISSIPATION (W)
SENSE
BATSENS
BAT
10μF
V
INSENSE
PV
IN
1.00
+
4.1V
Li-Ion
0.75
LTC4001-1
0.50
0.25
V
IN
= 5V
2A CHARGER
0
3
3.25
3.75
3.5
V
BAT
(V)
4
4.25
40011 TA01b
SS GNDSENS
40011fa
1
LTC4001-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
BATSENS
TIMER
IDET
12 PROG
17
11 NTC
10 FAULT
9
5
SW
6
EN
7
CHRG
8
PV
IN
V
INSENSE
SS
PV
IN
, V
INSENSE
t < 1ms, DC < 1% .................................... –0.3V to 7V
Steady State............................................. –0.3V to 6V
SW, SENSE, BAT, BATSENS, SS, FAULT,
CHRG, EN,
NTC,
PROG, IDET, TIMER Voltage ........................ – 0.3V to 6V
Operating Temperature Range (Note 3) .. –40°C to 85°C
Operating Junction Temperature
(Note 5) ................................................ –40°C to 125°C
Storage Temperature Range.................. –65°C to 125°C
16 15 14 13
BAT 1
SENSE 2
PGND 3
GNDSENS 4
UF PACKAGE
16-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC4001EUF-1#PBF
TAPE AND REEL
LTC4001EUF-1#TRPBF
PART MARKING
40011
PACKAGE DESCRIPTION
16-Lead (4mm × 4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
EN
= 0V, R
PROG
= 549Ω, R
IDET
= 549Ω, unless otherwise
specified.
SYMBOL PARAMETER
V
IN
I
IN
Supply Voltage
CONDITIONS
(Note 2)
PV
IN
Connected to V
INSENSE
, PROG and IDET
Pins Open, Charger On
Shutdown,
EN
= V
IN
V
FLOAT
I
BAT
V
BAT
Regulated Float Voltage
Current Mode Charge Current
Measured from BATSENS to GNDSENS
R
PROG
= 549Ω, V
BAT
= 3.5V
R
PROG
= 1.10k, V
BAT
= 3.5V
Shutdown,
EN
= V
IN
V
BAT
= 2V
V
BAT
Rising
V
BAT
Falling
V
IN
Rising, Measured from V
INSENSE
to GNDSENS
Measured from V
INSENSE
to GNDSENS
V
INSENSE
– V
BATSENS
Rising (Turn-On), V
BATSENSE
= 4V
V
INSENSE
– V
BATSENS
Falling (Turn-Off), V
BATSENSE
= 4V
200
15
●
ELECTRICAL CHARACTERISTICS
MIN
4
TYP
MAX
5.5
2
50
UNITS
V
mA
μA
V
V
A
A
μA
mA
V
V
V
mV
4.059
4.079
1.8
0.9
35
3.05
2.85
2.7
4.1
4.1
2
1
50
3.1
3.0
100
250
30
4.141
4.121
2.2
1.1
±5
65
3.20
3.05
2.82
I
TRIKL
V
TRIKL
V
UVL
ΔV
UVL
V
ASD
Trickle Charge Current
Trickle Charge Threshold
V
IN
Undervoltage Lockout Voltage
V
IN
Undervoltage Lockout
Hysteresis
Automatic Shutdown Threshold
Voltage
300
60
mV
mV
40011fa
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LTC4001-1
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
f
OSC
D
R
PFET
R
NFET
t
TIMER
V
EN
ΔV
EN
V
PROG
V
IDET
I
IDET
I
CHRG
V
CHRG
V
OL
V
OH
Oscillator Frequency
Maximum Duty Factor
R
DS(ON)
of P-Channel MOSFET
R
DS(ON)
of N-Channel MOSFET
Timer Accuracy
Enable Input Threshold Voltage
Enable Input Hysteresis
PROG Pin Voltage
IDET Pin Voltage
IDET Threshold
CHRG
Pin Weak Pull-Down
Current
CHRG
Pin Output Low Voltage
FAULT Pin Output Low Voltage
FAULT Pin Output High Voltage
R
PROG
= 549Ω
R
IDET
= 549Ω
R
IDET
= 549Ω
V
CHRG
= 1V
I
CHRG
= 5mA
1mA Load
1mA Load
V
FLOAT
– V
RECHRG
V
BAT
Falling
4.6
50
4
Percent of Total Charge Time
Percent of Total Charge Time, V
BAT
< 2.8V,
Measured Using BATSENS and GNDSENS Pins
V
BAT
< V
FLOAT
– 100mV, V
BAT
Across BATSENS
and GNDSENS Pins
From NTC to GNDSENS Pin
Rising Threshold
Falling Threshold
From NTC to GNDSENS Pin
Falling Threshold
Rising Threshold
From NTC to GNDSENS Pin
From NTC to GNDSENS Pin
0.015 •
V
INSENSE
6
50
25
12.8
16
100
135
150
15
Measured from PV
IN
to SW
Measured from SW to PGND
C
TIMER
= 0.22μF
V
EN
Rising
0.6
127
121
±10
0.8
100
1.213
1.213
200
30
0.2
250
50
0.4
0.4
1
CONDITIONS
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
EN
= 0V, R
PROG
= 549Ω, R
IDET
= 549Ω, unless otherwise
specified.
MIN
1.3
TYP
1.5
MAX
1.7
100
UNITS
MHz
%
mΩ
mΩ
%
V
mV
V
V
mA
μA
V
V
V
mV
ms
%
%
μA
V
RECHRG
Recharge Battery Threshold
Voltage
t
RB
t
RECHRG
t
TRIKL
I
SS
V
COLD
Recharge Filter Time Constant
Recharge Time
Low-Battery Trickle Charge Time
Soft-Start Ramp Current
NTC Pin Cold Temperature Fault
Threshold
NTC Pin Hot Temperature Fault
Threshold
NTC Disable Threshold (Falling)
NTC Disable Hysteresis
0.74 V
INSENSE
0.72 V
INSENSE
0.29 V
INSENSE
0.30 V
INSENSE
0.02 •
V
INSENSE
0.01 •
V
INSENSE
Note 4:
T
J
is calculated from the ambient temperature T
A
and power dis-
sipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• 37°C/W)
Note 5:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload. Junction temperature will
exceed 125°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
my impair device reliability.
0.025 •
V
INSENSE
V
V
V
V
V
V
V
HOT
V
DIS
ΔV
DIS
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Operation with current limited wall adapters is allowed down to the
undervoltage lockout threshold.
Note 3:
The LTC4001E-1 is guaranteed to meet performance specifica-
tions from 0°C to 85°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
40011fa
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LTC4001-1
TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency vs V
IN
1.00
0.75
PERCENT VARIATION (%)
0.50
0.25
0
–0.25
–0.50
–0.75
–1.00
3
3.5
4
4.5
V
IN
(V)
5
5.5
6
FREQUENCY VARIATION FROM 25°C (%)
V
BAT
= 3.2V
V
SS
= 1V
0.8
(T
A
= 25°C unless otherwise noted)
Dissipation of Figure 8 Circuit
vs I
BAT
1.25
TOTAL APPLICATION CIRCUIT POWER
DISSIPATION (W)
V
IN
= 5V
V
BAT
= 4V
Oscillator Frequency
vs Temperature
V
IN
= 5V
V
BAT
= 3.2V
V
SS
= 1V
0.6
1.00
0.4
0.75
0.2
0.50
0
0.25
–0.2
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
40011 G02
0
500
1000
I
BAT
(mA)
1500
2000
40011 G03
40011 G01
Dissipation of Figure 8 Circuit
vs V
IN
1.4
TOTAL APPLICATION CIRCUIT POWER
DISSIPATION (W)
1.2
1.0
1.0
0.8
0.6
0.4
0.2
0
4.25
I
BAT
= 1A
I
BAT
= 500mA
I
BAT
= 1.5A
V
PROG
(V)
0.8
0.6
0.4
V
BAT
= 4V
I
BAT
= 2A
1.2
PROG Pin Characteristic
(V
PROG
vs I
PROG
)
V
IN
= 5V
2.0
Output Charging Characteristic
Showing Constant Current and
Constant Voltage Operation
I
BAT
(A)
15
20
40011 G05
V
BAT
= 3.2V
V
BAT
= 3.5V
V
BAT
= 3.7V
V
BAT
= 4V
1.5
1.0
0.5
0.2
0
4.5
4.75
V
IN
(V)
40011 G04
5
5.25
5.5
0
5
10
I
PROG
(mA)
0
0
0.5
1
1.5
2.5
V
BAT
(V)
2
3
3.5
4
40011 G06
Trickle Charge Current vs V
BAT
55
FLOAT AND RECHARGE VOLTAGES (V)
4.2
V
FLOAT
and Recharge Battery
Threshold Voltage vs Temperature
V
IN
= 5.5V
50
I
BAT
(mA)
V
IN
= 5V
V
FLOAT
4.1
V
IN
= 4V
V
IN
= 4.5V
45
V
RECHARGE
(V
BAT
FALLING)
4.0
40
0
0.5
1
1.5
V
BAT
(V)
2
2.5
3
40011 G07
3.9
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
40011 G08
40011fa
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LTC4001-1
TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Start (PWM Mode)
400
INPUT
CURRENT (I
IN
)
0.5A/DIV
INDUCTOR
CURRENT (I
L
)
0.5A/DIV
0
SOFT-START
VOLTAGE (V
SS
)
1V/DIV 0
EN
PIN (V
EN
)
5V/DIV 0
V
BAT
= 3.5V
V
IN
= 5V
2ms/DIV
0
IDET (mA)
350
300
250
200
150
100
40011 G09
IDET Threshold vs R
IDET
for
R
PROG
= 549Ω
CHRG
Pin Temperature Fault
Behavior (Detail)
CHRG
1V/DIV
50
0
300 400 500 600 700 800 900 1000 1100 1200
R
IDET
(Ω)
40011 G10
TIME (20μs/DIV)
40011 G11
PIN FUNCTIONS
BAT (Pin 1):
Battery Charger Output Terminal. Connect a
10μF ceramic chip capacitor between BAT and PGND to
keep the ripple voltage small.
SENSE (Pin 2):
Internal Sense Resistor. Connect to ex-
ternal inductor.
PGND (Pin 3):
Power Ground.
GNDSENS (Pin 4):
Ground Sense. Connect this pin to the
negative battery terminal. GNDSENS provides a Kelvin
connection for PGND and must be connected to PGND
schematically.
SW (Pin 5):
Switch Node Connection. This pin connects
to the drains of the internal main and synchronous power
MOSFET switches. Connect to external inductor.
EN
(Pin 6):
Enable Input Pin. Pulling the
EN
pin high
places the LTC4001-1 into a low power state where the
BAT drain current drops to less than 3μA and the supply
current is reduced to less than 50μA. For normal opera-
tion, pull the pin low.
CHRG
(Pin 7):
Open-Drain Charge Status Output. When the
battery is being charged,
CHRG
is pulled low by an internal
N-channel MOSFET. When the charge current drops below
the IDET threshold (set by the R
IDET
programming resistor)
for more than 5milliseconds, the N-channel MOSFET turns
off and a 30μA current source is connected from
CHRG
to
ground. (This signal is latched and is reset by initiating a
new charge cycle.) When the timer runs out or the input
supply is removed, the current source will be disconnected
and the
CHRG
pin is forced to a high impedance state. A
temperature fault causes this pin to blink.
PV
IN
(Pin 8):
Positive Supply Voltage Input. This pin con-
nects to the power devices inside the chip. V
IN
ranges
from 4V to 5.5V for normal operation. Operation down to
the undervoltage lockout threshold is allowed with cur-
rent limited wall adapters. Decouple with a 10μF or larger
surface mounted ceramic capacitor.
V
INSENSE
(Pin 9):
Positive Supply Sense Input. This pin
connects to the inputs of all input comparators (UVL, V
IN
to V
BAT
). It also supplies power to the controller portion
of this chip. When the BATSENS pin rises to within 30mV
of V
INSENSE
, the LTC4001-1 enters sleep mode, dropping
I
IN
to 50μA. Tie this pin directly to the terminal of the PV
IN
decoupling capacitor.
FAULT (Pin 10):
Battery Fault. This pin is a logic high if
a shorted battery is detected or if a temperature fault is
detected. A temperature fault occurs with the temperature
monitor circuit enabled and the thermistor temperature is
either below 0°C or above 50°C (typical).
40011fa
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