LTC4001EUF-1-PBF [Linear]
2A Synchronous Buck Li-Ion Charger; 2A同步降压型锂离子电池充电器
| 型号： | LTC4001EUF-1-PBF |
| 厂家： | 
Linear |
| 描述： | 2A Synchronous Buck Li-Ion Charger |
| 文件： | 总20页 (文件大小：234K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC4001-1
2A Synchronous
Buck Li-Ion Charger
FEATURES
DESCRIPTION
TheLTC®4001-1isa2ALi-Ionbatterychargerintendedfor
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
LTC4001-1includescompletechargeterminationcircuitry,
automatic recharge and a 1ꢀ 4.1V ꢁoat voltage. Input
short-circuit protection is included so no blocking diode
is required.
n
Low Power Dissipation
n
2A Maximum Charge Current
n
No External MOSFETs, Sense Resistor or
Blocking Diode Required
n
Remote Sensing at Battery Terminals
n
Programmable Charge Termination Timer
n
Preset 4.1V Float Voltage with 0.5ꢀ Accuracy
n
4.1V Float Voltage Improves Battery Life and High
Temperature Safety Margin
n
Programmable Charge Current Detection/
Termination
Automatic Recharge
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
ꢁoatvoltagewilltrade-offinitialcellcapacityforthebenefit
ofincreasedcapacityretentionoverthelifeofthebattery.A
reduced ꢁoat voltage also minimizes swelling in prismatic
and polymer cells, and avoids open CID (pressure fuse)
in cylindrical cells.
n
n
Thermistor Input for Temperature Qualified
Charging
n
Compatible with Current Limited Wall Adapters
n
Low Profile 16-Lead (4mm × 4mm) QFN Package
APPLICATIONS
n
Handheld Battery-Powered Devices
Battery charge current, charge timeout and end-of-charge
indication parameters are set with external components.
Additionalfeaturesincludeshortedcelldetection,tempera-
ture qualified charging and overvoltage protection. The
LTC4001-1 is available in a low profile (0.75mm) 16-lead
(4mm × 4mm) QFN package.
n
Handheld Computers
n
Charging Docks and Cradles
Digital Cameras
Smart Phones
n
n
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
Power Loss vs VBAT
Charging (PWM Mode)
2A Single Cell Li-Ion Battery Charger
1.5μH
1.25
1.00
0.75
0.50
0.25
SW
SENSE
V
BATSENS
BAT
INSENSE
PV
V
IN
4.5V TO 5.5V
IN
+
4.1V
Li-Ion
10μF
10μF
PGND
LTC4001-1
CHRG
NTC
FAULT
EN
V
= 5V
IN
2A CHARGER
0
PROG IDET TIMER
SS GNDSENS
3
3.25
3.5
V
3.75
(V)
4
4.25
0.22μF
0.1μF
BAT
40011 TA01b
274Ω
40011 TA01a
40011fa
1
LTC4001-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
PV , V
IN INSENSE
t < 1ms, DC < 1ꢀ .................................... –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
16 15 14 13
BAT
SENSE
1
2
3
4
12 PROG
11 NTC
17
PGND
FAULT
10
9
GNDSENS
V
INSENSE
5
6
7
8
(Note 5) ................................................ –40°C to 125°C
Storage Temperature Range.................. –65°C to 125°C
UF PACKAGE
16-LEAD (4mm × 4mm) PLASTIC QFN
= 125°C, θ = 37°C/W
T
JMAX
JA
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
16-Lead (4mm × 4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
LTC4001EUF-1#PBF
LTC4001EUF-1#TRPBF
40011
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
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VEN = 0V, RPROG = 549Ω, RIDET = 549Ω, unless otherwise
specified.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
5.5
2
UNITS
V
V
Supply Voltage
(Note 2)
4
IN
I
PV Connected to V , PROG and IDET
INSENSE
mA
IN
IN
Pins Open, Charger On
Shutdown, EN = V
50
μA
IN
V
V
Regulated Float Voltage
BAT
Measured from BATSENS to GNDSENS
●
4.059
4.079
4.1
4.1
4.141
4.121
V
V
FLOAT
I
Current Mode Charge Current
R
R
= 549Ω, V = 3.5V
1.8
0.9
2
1
2.2
1.1
5
A
A
μA
BAT
PROG
PROG
BAT
= 1.10k, V = 3.5V
BAT
Shutdown, EN = V
IN
I
Trickle Charge Current
V
BAT
= 2V
35
50
65
mA
TRIKL
V
TRIKL
Trickle Charge Threshold
V
BAT
V
BAT
Rising
Falling
3.05
2.85
3.1
3.0
3.20
3.05
V
V
V
V
V
Undervoltage Lockout Voltage
Undervoltage Lockout
V
Rising, Measured from V to GNDSENS
INSENSE
2.7
2.82
V
UVL
IN
IN
IN
ΔV
Measured from V
to GNDSENS
100
mV
UVL
INSENSE
Hysteresis
V
ASD
Automatic Shutdown Threshold
Voltage
V
V
– V
– V
Rising (Turn-On), V
Falling (Turn-Off), V
= 4V
= 4V
200
15
250
30
300
60
mV
mV
INSENSE
INSENSE
BATSENS
BATSENS
BATSENSE
BATSENSE
40011fa
2
LTC4001-1
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VEN = 0V, RPROG = 549Ω, RIDET = 549Ω, unless otherwise
specified.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
1.7
UNITS
MHz
ꢀ
f
Oscillator Frequency
Maximum Duty Factor
1.3
1.5
OSC
D
R
R
100
R
R
of P-Channel MOSFET
of N-Channel MOSFET
Measured from PV to SW
127
121
10
mΩ
mΩ
ꢀ
PFET
NFET
DS(ON)
DS(ON)
IN
Measured from SW to PGND
t
Timer Accuracy
C
V
= 0.22μF
TIMER
TIMER
V
Enable Input Threshold Voltage
Enable Input Hysteresis
PROG Pin Voltage
Rising
0.6
0.8
1
V
EN
EN
ΔV
100
1.213
1.213
200
30
mV
V
EN
PROG
IDET
V
V
R
R
R
= 549Ω
PROG
IDET Pin Voltage
= 549Ω
= 549Ω
= 1V
V
IDET
IDET
I
I
IDET Threshold
150
15
250
50
mA
μA
IDET
CHRG Pin Weak Pull-Down
Current
V
CHRG
CHRG
V
V
V
V
CHRG Pin Output Low Voltage
FAULT Pin Output Low Voltage
FAULT Pin Output High Voltage
I
= 5mA
0.2
0.4
0.4
V
V
CHRG
CHRG
1mA Load
1mA Load
OL
4.6
50
V
OH
Recharge Battery Threshold
Voltage
V
– V V Falling
RECHRG BAT
100
135
16
mV
RECHRG
FLOAT
t
t
t
Recharge Filter Time Constant
Recharge Time
4
ms
ꢀ
RB
Percent of Total Charge Time
50
25
RECHRG
TRIKL
Low-Battery Trickle Charge Time
Percent of Total Charge Time, V < 2.8V,
Measured Using BATSENS and GNDSENS Pins
ꢀ
BAT
I
Soft-Start Ramp Current
V
< V
– 100mV, V Across BATSENS
6
12.8
μA
SS
BAT
FLOAT
BAT
and GNDSENS Pins
V
V
V
NTC Pin Cold Temperature Fault
Threshold
From NTC to GNDSENS Pin
Rising Threshold
COLD
HOT
DIS
0.74 V
V
V
INSENSE
INSENSE
Falling Threshold
0.72 V
NTC Pin Hot Temperature Fault
Threshold
From NTC to GNDSENS Pin
Falling Threshold
Rising Threshold
0.29 V
0.30 V
V
V
INSENSE
INSENSE
NTC Disable Threshold (Falling)
NTC Disable Hysteresis
From NTC to GNDSENS Pin
0.015 •
INSENSE
0.02 •
INSENSE
0.025 •
V
INSENSE
V
V
V
V
ΔV
From NTC to GNDSENS Pin
0.01 •
INSENSE
V
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.
Note 4: T is calculated from the ambient temperature T and power dis-
J A
sipation P according to the following formula:
D
T = T + (P • 37°C/W)
J
A
D
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.
40011fa
3
LTC4001-1
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
Oscillator Frequency
vs Temperature
Dissipation of Figure 8 Circuit
vs IBAT
Oscillator Frequency vs VIN
0.8
0.6
0.4
1.25
1.00
0.75
0.50
0.25
0
1.00
0.75
0.50
0.25
V
V
V
= 5V
BAT
= 1V
V
V
= 3.2V
V
V
= 5V
IN
= 4V
BAT
IN
BAT
SS
= 3.2V
= 1V
SS
0
0.2
0
–0.25
–0.50
–0.75
–1.00
–0.2
3.5
4
5
3
5.5
6
4.5
(V)
–50 –30 –10 10 30 50 70 90 110 130 150
1000
1500
2000
500
V
TEMPERATURE (°C)
I
(mA)
IN
BAT
40011 G01
40011 G02
40011 G03
Output Charging Characteristic
Showing Constant Current and
Constant Voltage Operation
Dissipation of Figure 8 Circuit
vs VIN
PROG Pin Characteristic
(VPROG vs IPROG
)
1.4
1.2
2.0
1.5
1.0
0.5
V = 5V
IN
V
= 4V
BAT
I
= 2A
1.2
1.0
0.8
0.6
0.4
0.2
0
BAT
V
= 3.2V
V
= 4V
BAT
1.0
0.8
0.6
0.4
0.2
0
BAT
V
V
= 3.5V
= 3.7V
BAT
BAT
I
= 1.5A
BAT
I
= 1A
BAT
I
= 500mA
BAT
0
5
10
(mA)
20
0
15
4.5
4.75
5
5.5
4.25
5.25
0
0.5
1
1.5
2
2.5
(V)
3
3.5
4
I
V
V
(V)
PROG
BAT
IN
40011 G05
40011 G04
40011 G06
VFLOAT and Recharge Battery
Threshold Voltage vs Temperature
Trickle Charge Current vs VBAT
55
50
45
40
4.2
V
= 5.5V
IN
V
FLOAT
V
= 5V
IN
4.1
4.0
3.9
V
= 4V
V
BAT
IN
RECHARGE
FALLING)
(V
V
= 4.5V
IN
–50 –30 –10 10 30 50 70 90 110 130 150
0
0.5
1
1.5
(V)
2
2.5
3
V
TEMPERATURE (°C)
BAT
40011 G08
40011 G07
40011fa
4
LTC4001-1
TYPICAL PERFORMANCE CHARACTERISTICS
IDET Threshold vs RIDET for
CHRG Pin Temperature Fault
Behavior (Detail)
Soft-Start (PWM Mode)
R
PROG = 549Ω
400
350
300
250
200
150
100
50
INPUT
CURRENT (I
)
IN
0.5A/DIV
0
0
INDUCTOR
CHRG
1V/DIV
CURRENT (I )
L
0.5A/DIV
SOFT-START
VOLTAGE (V
)
SS
1V/DIV
0
0
EN PIN (V
)
EN
5V/DIV
40011 G11
40011 G09
V
V
= 3.5V
2ms/DIV
TIME (20μs/DIV)
BAT
IN
= 5V
0
700 800
300 400 500 600
900 100011001200
R
IDET
(Ω)
40011 G10
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.
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
supplyisremoved,thecurrentsourcewillbedisconnected
and the CHRG pin is forced to a high impedance state. A
temperature fault causes this pin to blink.
SENSE (Pin 2): Internal Sense Resistor. Connect to ex-
ternal inductor.
PGND (Pin 3): Power Ground.
PV (Pin 8): Positive Supply Voltage Input. This pin con-
IN
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.
nects to the power devices inside the chip. V ranges
IN
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.
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.
V
(Pin 9): Positive Supply Sense Input. This pin
INSENSE
connects to the inputs of all input comparators (UVL, V
IN
to V ). It also supplies power to the controller portion
BAT
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.
of this chip. When the BATSENS pin rises to within 30mV
of V
, the LTC4001-1 enters sleep mode, dropping
INSENSE
I to 50μA. Tie this pin directly to the terminal of the PV
IN
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).
CHRG(Pin7):Open-DrainChargeStatusOutput.Whenthe
batteryisbeingcharged, CHRGispulledlowbyaninternal
N-channelMOSFET. Whenthechargecurrentdropsbelow
theIDETthreshold(setbytheR
programmingresistor)
IDET
formorethan5milliseconds,theN-channelMOSFETturns
40011fa
5
LTC4001-1
PIN FUNCTIONS
NTC (Pin 11): Input to the NTC (Negative Temperature
Coefficient) Thermistor Temperature Monitoring Circuit.
Under normal operation, tie a thermistor from the NTC pin
to the GNDSENS pin and a resistor of equal value from
SS(Pin14):Soft-Start/Compensation.Providessoft-start
function and compensation for the ꢁoat voltage control
loop and compensation for the charge current control
loop. Tie a soft-start/compensation capacitor between
this pin and GNDSENS.
NTC to V . When the voltage on this pin is above 0.74V
IN
IN
(Cold, 0°C) or below 0.29V (Hot, 50°C), charging is
IN
TIMER (Pin 15): Timer Capacitor. The timer period is set
by placing a capacitor, CTIMER, to GNDSENS. Set CTIMER
to:
disabled and the CHRG pin blinks. When the voltage on
NTC comes back between 0.74V and 0.29V , the timer
IN
IN
continues where it left off and charging resumes. There is
approximately 3°C of temperature hysteresis associated
with each of the input comparators. If the NTC function
is not used connect the NTC pin to GNDSENS. This will
disable all of the NTC functions. NTC should never be
C
TIMER
= Time (Hrs) • 0.0733 (μF)
where time is the desired charging time.
Connect this pin to IDET to disable the timer. Connect this
pin to GNDSENS to end battery charging when I drops
BAT
pulled above V .
IN
below the IDET charge rate threshold.
PROG (Pin 12): Charge Current Program. The R
PROG
BATSENS(Pin16):BatterySenseInput.Aninternalresistor
divider sets the final ꢁoat voltage at this pin. The resistor
divider is disconnected in sleep mode or when
resistor connects from this pin to GNDSENS, setting the
current:
1.110k
IBAT(AMPS)
RPROG
=
EN = H to reduce the battery drain current. Connect this
pin to the positive battery terminal.
where I is the high rate battery charging current.
BAT
Exposed Pad (Pin 17): Ground. This pin must be soldered
to the PCB ground (PGND) for electrical contact and rated
thermal performance.
IDET(Pin13):ChargeRateDetectionThreshold.Connect-
ingaresistor,R
toGNDSENSprogramsthechargerate
IDET
detection threshold. If R
= R
, CHRG provides an
IDET
PROG
I
/10 indication. For other thresholds see the Applica-
BAT
tions Information section.
40011fa
6
LTC4001-1
BLOCK DIAGRAM
Y
T T E R
L O W B A
S H U T D O W N
O V E R C U R R E N T
T R I C K L E O N
W P M O N
40011fa
7
LTC4001-1
OPERATION
Anegativetemperaturecoefficient(NTC)thermistorlocated
close to the battery pack can be used to monitor battery
temperatureandsuspendchargingwhenbatterytempera-
tureisoutsidethe0°Cto50°Cwindow.Atemperaturefault
drives the FAULT pin high and makes the CHRG pin blink.
The LTC4001-1 is a constant current, constant voltage
Li-Ion battery charger based on a synchronous buck
architecture. Low power dissipation makes continuous
high rate (2A) battery charging practical. The battery DC
charge current is programmed by a resistor R
DAC output current) at the PROG pin. The final battery
ꢁoat voltage is internally set to 4.1V.
(or a
PROG
When the input voltage (V ) is present, the charger can
IN
be shut down by pulling the EN pin up.
Charging begins when the V voltage rises above the
IN
IDET Blanking
UVLO level (approximately 2.75V), V is 250mV greater
IN
TheIDETcomparatorprovidesanend-of-chargeindication
by sensing when battery charge current is less than the
IDETthreshold.Topreventafalseend-of-chargeindication
fromoccurringduringsoft-start,thiscomparatorisblanked
until the battery voltage approaches the ꢁoat voltage.
than the battery voltage and EN is low. At the beginning
of the charge cycle, if the battery voltage is less than the
trickle charge threshold, 3V, the charger goes into trickle
charge mode and delivers approximately 50mA to the bat-
tery using a linear charger. If the battery voltage stays low
for more than one quarter of the charge time, the battery
is considered faulty, the charge cycle is terminated and
the FAULT pin produces a logic high output.
Automatic Battery Recharge
After the charge cycle is completed and if both the battery
and the input power supply (wall adapter) are still con-
nected, a new charge cycle will begin if the battery voltage
drops below 4V due to self-discharge or external loading.
This will keep the battery near maximum capacity at all
times without manually restarting the charge cycle.
When the battery voltage exceeds the trickle charge
threshold, the low rate linear charger is turned off and the
high rate PWM charger ramps up (based on the SS pin
capacitance) reaching its full-scale constant current (set
via the PROG pin). When the battery approaches the ꢁoat
voltage, the charge current will start to decrease. When
the charge current drops below the charge rate detec-
tion threshold (set via the IDET pin) for more than 5ms,
an internal comparator turns off the internal pull-down
N-channel MOSFET at the CHRG pin, and connects a weak
current source (30μA typical) to ground to indicate a near
end-of-charge condition.
In some applications such as battery charging in GPRS
cellphones,largeloadcurrenttransientsmaycausebattery
voltagetomomentarilydropbelowtherechargethreshold.
Topreventthesetransientsfrominitiatingarechargecycle
whenitisnotneeded, theoutputoftherechargecompara-
tor is digitally qualified. Only if the battery voltage stays
below the recharge threshold for at least 4ms will battery
recharging occur. (GPRS qualification is available even if
timeout is disabled.)
Total charge time is set by an external capacitor connected
to the timer pin. After timeout occurs, the charge cycle is
terminatedandtheCHRGpinisforcedtoahighimpedance
state. To restart the charge cycle, remove and reapply the
input voltage, or momentarily shut the charger down via
the EN pin. Also, a new charge cycle will begin if the bat-
tery voltage drops below the recharge threshold voltage
(100mV below the ꢁoat voltage). A recharge cycle lasts
only one-half of the normal charge time.
Undervoltage Lockout and Automatic Shutdown
Internal undervoltage lockout circuits monitor V and
IN
keep the charger circuits shut down until V rises above
IN
the undervoltage lockout threshold (3V). The UVLO has
a built-in hysteresis of 100mV. Furthermore, to protect
against reverse current, the charger also shuts down if
V
V
is less than V . If automatic shutdown is tripped,
IN
IN
BAT
must increase to more than 250mV above V
to
BAT
allow charging.
40011fa
8
LTC4001-1
OPERATION
Overvoltage, Chip Overtemperature and Short-Circuit
Current Protection
exceeds approximately 160°C. Battery charging will be
enabled again when temperature drops to approximately
150°C.
TheLTC4001-1includesovervoltage,chipovertemperature
and several varieties of short-circuit protection.
Short-circuit protection is provided in several different
ways. First, a hard short on the battery terminals will
cause the charge to enter trickle charge mode, limiting
charge current to the trickle charge current (typically
50mA). Second, PWM charging is prevented if the high
rate charge current is programmed far above the 2A
maximum recommended charge current (via the PROG
pin).Third,anovercurrentcomparatormonitorsthepeak
inductor current.
A comparator turns off both chargers (high rate and
trickle) if battery voltage exceeds the ꢁoat voltage by ap-
proximately 5ꢀ. This may occur in situations where the
batteryisaccidentallydisconnectedwhilebatterycharging
is underway.
Acomparatorcontinuouslymonitorson-chiptemperature
andwillshutoffthebatterychargerwhenchiptemperature
40011fa
9
LTC4001-1
APPLICATIONS INFORMATION
Soft-Start and Compensation Capacitor Selection
The IDET threshold (a charge current threshold used to
determine when the battery is nearly fully charged) is
programmed in much the same way as the PROG pin,
except that the IDET threshold is 91.5 times the current
delivered by the IDET pin. This current is usually set with
an external resistor from IDET to ground, but it may also
besetwithacurrentoutputDAC. ThevoltageonthePROG
pin is nominally 1.213V.
The LTC4001-1 has a low current trickle charger and a
PWM-basedhighcurrentcharger.Soft-startisusedwhen-
ever the high rate charger is initially turned on, preventing
high start-up current. Soft-start ramp rate is set by the
internal 12.8μA pull-up current and an external capacitor.
The control range on the SS pin is approximately 0.3V
to 1.6V. With a 0.1μF capacitor, the time to ramp up to
maximum duty cycle is approximately 10ms.
For 200mA IDET current (corresponding to C/10 for a
2AHr battery):
TheexternalcapacitorontheSSpinalsosetsthecompensa-
tionforthecurrentcontrolloopandtheꢁoatvoltagecontrol
loop. A minimum capacitance of 10nF is required.
91.5•1.213V
RIDET
=
ꢀ 554.9ꢁ
0.2A
Charge Current and IDET Programming
1.10kΩ programs approximately 100mA and 274Ω ap-
proximately 400mA.
The LTC4001-1 has two different charge modes. If the
battery is severely depleted (battery voltage less than
2.9V) a 50mA trickle current is initially used. If the battery
voltage is greater than the trickle charge threshold, high
rate charging is used.
For applications where IDET is set to one tenth of the high
rate charge current, and slightly poorer charger current
and IDET threshold accuracy is acceptable, the PROG and
IDET pins may be tied together and a single resistor, R1,
can program both (Figure 1).
This higher charge current is programmable and is ap-
proximately 915 times the current delivered by the PROG
pin. This current is usually set with an external resistor
from PROG to GNDSENS, but it may also be set with a
current output DAC connected to the PROG pin. The volt-
age on the PROG pin is nominally 1.213V.
457.5•1.213
R1=
ICHARGE
and
ICHARGE
IDET =
For 2A charge current:
10
915•1.213V
RPROG
=
ꢀ 554.9ꢁ
2A
LTC4001-1
PROG
IDET
R1
274Ω FOR 2A
GNDSENS
40011 F01
Figure 1. Programming Charge Current and
IDET Threshold with a Single Resistor
40011fa
10
LTC4001-1
APPLICATIONS INFORMATION
The equations for calculating R1 (used in single resistor
programming) differ from the equations for calculating
pin low through the 390k resistor. When charging stops,
the CHRG pin changes to a high impedance state and the
390k resistor will then pull the pin high to indicate charg-
ing has stopped.
R
PROG
and R
(2-resistor programming) and reꢁect
IDET
the fact that the current from both the IDET and PROG
pins must ꢁow through a single resistor R1 when a single
programming resistor is used.
Charge Termination
Batterychargingmaybeterminatedseveraldifferentways,
depending on the connections made to the TIMER pin. For
time-based termination, connect a capacitor between the
CHRG Status Output Pin
When a charge cycle starts, the CHRG pin is pulled to
groundbyaninternalN-channelMOSFETwhichiscapable
of driving an LED. When the charge current drops below
the end-of-charge (IDET) threshold for at least 4ms,
and the battery voltage is close to the ꢁoat voltage, the
N-channel MOSFET turns off and a weak 30μA current
source to ground is connected to the CHRG pin. This
weak pull-down remains until the charge cycle ends. After
charging ends, the pin will become high impedance. By
using two different value resistors, a microprocessor can
detect three states from this pin (charging, end-of-charge
and charging stopped). See Figure 2.
TIMERpinandGNDSENS(C
=Time(Hrs)0.0733μF).
TIMER
Charging may be terminated when charge current drops
below the IDET threshold by tying TIMER to GNDSENS.
Finally,chargeterminationmaybedefeatedbytyingTIMER
to IDET. In this case, an external device can terminate
charging by pulling the EN pin high.
Battery Temperature Detection
When battery temperature is out of range (either too hot
or too cold) charging is temporarily halted and the FAULT
pin is driven high. In addition, if the battery is still charg-
ing at a high rate (greater than the IDET current) when a
temperature fault occurs, the CHRG pin NMOS turns on
and off at approximately 50kHz, alternating between a
high and low duty factor at an approximate rate of 1.5Hz
(Figure3).Thisprovidesalowratevisualindication(1.5Hz)
when driving an LED from the CHRG pin while providing
a fast temperature fault indication (20μs typical) to a mi-
croprocessor by tying the CHRG pin to an interrupt line.
Serrations within this pulse are typically 500ns wide.
To detect the charge mode, force the digital output pin,
OUT, high and measure the voltage on the CHRG pin. The
N-channel MOSFET will pull the pin low even with a 2k
pull-up resistor. Once the charge current drops below
the end-of-charge threshold, the N-channel MOSFET is
turned off and a 30μA current source is connected to the
CHRG pin. The IN pin will then be pulled high by the 2k
resistor connected to OUT. Now force the OUT pin into
a high impedance state, the current source will pull the
V
V
DD
IN
R1
390k
R2
2k
μPROCESSOR
OUT
LTC4001-1
CHRG
IN
40011 F02
40011 F03
20μs
667ms
Figure 2. Microprocessor Interface
Figure 3. CHRG Temperature Fault Waveform
40011fa
11
LTC4001-1
APPLICATIONS INFORMATION
Thebatterytemperatureismeasuredbyplacinganegative
temperature coefficient (NTC) thermistor close to the bat-
tery pack. To use this feature, connect the NTC thermistor,
R
will move the trip points to higher temperatures. To
NOM
calculateR
forashifttolowertemperatureforexample,
NOM
use the following equation:
R
R
, betweentheNTCpinandGNDSENSandtheresistor,
NTC
RCOLD
2.815
RNOM
=
•RNTC at 25°C
, fromtheNTCpintoV
. R
shouldbea1ꢀ
NOM
INSENSE NOM
resistor with a value equal to the value of the chosen NTC
thermistor at 25°C. The LTC4001-1 goes into hold mode
when the resistance, R , of the NTC thermistor drops to
0.41 times the value of R
where R
is the resistance ratio of R at the desired
NTC
COLD
coldtemperaturetrippoint.Ifyouwanttoshiftthetrippoints
to higher temperatures use the following equation:
HOT
NOM
. For instance for R = 10k.
NTC
(The value for a Vishay NTHS0603N02N1002J thermistor
at 25°C) hold occurs at approximately 4.1k, which occurs
at 50°C. The hold mode freezes the timer and stops the
charge cycle until the thermistor indicates a return to a
validtemperature.Asthetemperaturedrops,theresistance
of the NTC thermistor rises. The LTC4001-1 is designed to
go into hold mode when the value of the NTC thermistor
RHOT
0.4086
RNOM
=
•RNTC at 25°C
where R
is the resistance ratio of R
hot temperature trip point.
at the desired
HOT
NTC
Here is an example using a 100k R-T Curve 1 thermistor
from Vishay Dale. The difference between trip points is
44°C, from before, and we want the cold trip point to be
0°C, which would put the hot trip point at 44°C. The R
needed is calculated as follows:
increases to 2.82 times the value of R
. This resistance
NOM
isR
. FortheVishay10kthermistor, thisvalueis28.2k,
COLD
NOM
whichcorrespondstoapproximately0°C.Thehotandcold
comparators each have approximately 3°C of hysteresis
to prevent oscillation about the trip point. Grounding the
NTC pin disables the NTC function.
RCOLD
2.815
3.266
RNOM
=
=
•RNTC at 25°C
•100k =116k
Thermistors
2.815
TheLTC4001-1NTCtrippointsweredesignedtoworkwith
thermistorswhoseresistancetemperaturecharacteristics
follow Vishay Dale’s “R-T Curve 2.” However, any thermis-
The nearest 1ꢀ value for RNOM is 115k. This is the value
used to bias the NTC thermistor to get cold and hot trip
points of approximately 0°C and 44°C respectively. To
extend the delta between the cold and hot trip points a
resistor,R1,canbeaddedinserieswithRNTC(seeFigure 4).
The values of the resistors are calculated as follows:
tor whose ratio of R
(Vishay Dale R-T Curve 2 shows a ratio of R
of 2.815/0.4086 = 6.89).
to R
is about 7 will also work
COLD
HOT
to R
HOT
COLD
Power conscious designs may want to use thermistors
whoseroomtemperaturevalueisgreaterthan10k. Vishay
Dalehasanumberofvaluesofthermistorfrom10kto100k
that follow the “R-T Curve 1.” Using these as indicated
in the NTC Thermistor section will give temperature trip
pointsofapproximately3°Cand47°C,adeltaof44°C.This
delta in temperature can be moved in either direction by
RCOLD –RHOT
2.815– 0.4086
0.4086
RNOM
=
R1=
• RCOLD –RHOT –R
(
HOT
)
2.815– 0.4086
changingthevalueofR
withrespecttoR .Increasing
NOM
NTC
40011fa
12
LTC4001-1
APPLICATIONS INFORMATION
V
INSENSE
9
LTC4001-1 NTC BLOCK
TOO COLD
0.74 • V
–
+
INSENSE
R
NOM
121k
NTC
11
R1
13.3k
–
+
TOO HOT
0.29 • V
INSENSE
INSENSE
R
NTC
100k
+
–
NTC ENABLE
0.02 • V
GNDSENS
4
40011 F04
Figure 4. Extending the Delta Temperature
capacitor is recommended for both the input and output
capacitors because it provides low ESR and ESL and can
handle the high RMS ripple currents. However, some
high Q capacitors may produce high transients due to
self-resonance under some start-up conditions, such as
connecting the charger input to a hot power source. For
more information, refer to Application Note 88.
where R
COLD
is the value of the bias resistor, R
and
NOM
HOT
R
are the values of R
at the desired temperature
NTC
trip points. Continuing the example from before with a
desired hot trip point of 50°C:
100k • 3.2636 – 0.3602
R
COLD –RHOT
(
)
RNOM
=
=
2.815– 0.4086
2.815– 0.4086
=120.8k, 121k is nearest 1%
EMI considerations usually make it desirable to minimize
ripple current in the battery leads, and beads or inductors
maybeaddedtoincreasebatteryimpedanceatthe1.5MHz
switching frequency. Switching ripple current splits be-
tween the battery and the output capacitor depending on
theESRoftheoutputcapacitorandthebatteryimpedance.
If the ESR of the output capacitor is 0.1Ω and the battery
impedance is raised to 2Ω with a bead or inductor, only
5ꢀ of the ripple current will ꢁow in the battery. Similar
techniques may also be applied to minimize EMI from
the input leads.
0.4086
2.815– 0.4086
ꢀ
ꢁ
ꢃ
R1=100k •
• 3.266 – 0.3602 – 0.3602
(
)
ꢂ
ꢅ
ꢄ
=13.3k, 13.3k is nearest 1%
The final solution is as shown if Figure 4 where R
=
NOM
121k, R1 = 13.3k and R
= 100k at 25°C.
NTC
Input and Output Capacitors
The LTC4001-1 uses a synchronous buck regulator to
providehighbatterychargingcurrent. A10μFchipceramic
40011fa
13
LTC4001-1
APPLICATIONS INFORMATION
Inductor Selection
Remote Sensing
A high (1.5MHz) operating frequency was chosen for the
buck switcher in order to minimize the size of the inductor.
However, take care to use inductors with low core losses
at this frequency. A good choice is the IHLP-2525AH-01
from Vishay Dale.
For highest ꢁoat voltage accuracy, tie GNDSENS and
BATSENSdirectlytothebatteryterminals.Inasimilarfash-
ion,tieBATandPGNDdirectlytothebatteryterminals.This
eliminates IR drops in the GNDSENS and BATSENS lines
by preventing charge current from ꢁowing in them.
To calculate the inductor ripple current:
Operation with a Current Limited Wall Adapter
2
VBAT
Walladapterswithorwithoutcurrentlimitingmaybeused
with the LTC4001-1, however, lowest power dissipation
batterychargingoccurswithacurrentlimitedwalladapter.
To use this feature, the wall adapter must limit at a current
smaller than the high rate charge current programmed
into the LTC4001-1. For example, if the LTC4001-1 is
programmed to charge at 2A, the wall adapter current
limit must be less than 2A.
VBAT
–
V
IN
ꢀIL =
L • f
where V is the battery voltage, V is the input voltage,
BAT
IN
L is the inductance and f is the PWM oscillator frequency
(typically 1.5MHz). Maximum inductor ripple current oc-
curs at maximum V and V = V /2.
IN
BAT
IN
Peak inductor current will be:
= I + 0.5 • ΔI
Tounderstandoperationwithacurrentlimitedwalladapter,
assume battery voltage, V , is initially below V , the
I
PK
BAT
TRIKL
BAT
L
tricklechargethreshold(Figure5).Batterychargingbegins
where I is the maximum battery charging current.
BAT
atapproximately50mA,wellbelowthewalladaptercurrent
limit so the voltage into the LTC4001-1 (V ) is the wall
When sizing the inductor make sure that the peak current
will not exceed the saturation current of the inductors.
Also, ΔI should never exceed 0.4(I ) as this may in-
IN
adapter’s rated output voltage (V
). Battery voltage
. The linear charger shuts
ADAPTER
rises eventually reaching V
TRIKL
L
BAT
off, the PWM (high rate) charger turns on and a soft-
start cycle begins. Battery charging current rises during
the soft-start cycle causing a corresponding increase in
wall adapter load current. When the wall adapter reaches
current limit, the wall adapter output voltage collapses
and the LTC4001-1 PWM charger duty cycle ramps up to
100ꢀ (the topside PMOS switch in the LTC4001-1 buck
regulator stays on continuously). As the battery voltage
terfere with proper operation of the output short-circuit
protectioncomparator.1.5μHprovidesreasonableinductor
ripple current in a typical application. With 1.5μH and 2A
charge current:
2.85V2
2.85V –
5.5V
ꢀIL =
= 0.61AP-P
1.5μH•1.5MHz
approaches V
, the ꢁoat voltage error amplifier com-
FLOAT
and
mands the PWM charger to deliver less than I
wall adapter exits current limit and the V jumps back up
. The
LIMIT
I
= 2.31A
IN
PK
40011fa
14
LTC4001-1
APPLICATIONS INFORMATION
PWM
CHARGING
LINEAR CHARGING
WALL ADAPTER IN CURRENT LIMIT
V
ADAPTER
V
BAT
+ V
DROP
V
IN
I
LIMIT
I
BAT
I
TRICKLE
40011 F05
V
V
TRIKL
FLOAT
V
BAT
Figure 5. Charging Characteristic
to V
. Battery charging current continues to drop
The total LTC4001-1 power dissipation during current
limited charging is:
ADAPTER
as the V rises, dropping to zero at V
Because the
BAT
FLOAT.
voltage drop in the LTC4001-1 is very low when charge
current is highest, power dissipation is also very low.
P = (V + V
) • (I + I ) + V • I
DROP LIMIT
D
BAT
DROP
IN
P
where I is the chip quiescent current and I is total cur-
IN
P
Thermal Calculations (PWM and Trickle Charging)
rent ꢁowing through the IDET and PROG programming
pins. Maximum dissipation in this mode occurs with the
TheLTC4001-1operatesasalinearchargerwhencondition-
ing (trickle) charging a battery and operates as a high rate
buck battery charger at all other times. Power dissipation
should be determined for both operating modes.
highest V
that keeps the wall adapter in current limit
BAT
(which is very close to V
), highest quiescent current
FLOAT
I , highest PMOS on resistance R , highest I and
IN
PFET
LIMIT
highest programming current I .
P
For linear charger mode:
AssumetheLTC4001-1isprogrammedfor2Achargingand
200mA IDET and that a 1.5A wall adapter is being used:
P = (V – V ) • I
D
+ V • I
IN IN
IN
BAT
TRIKL
where I is V current consumed by the IC.
I
= 1500mA, R
= 127mΩ, I = 2mA, I = 4mA
IN
IN
LIMIT
and V ≈ V
PFET IN P
= 4.141V
BAT
FLOAT
Worst-case dissipation occurs for V
IN
= 0, maximum
BAT
V , and maximum quiescent and trickle charge current.
then:
For example with 5.5V maximum input voltage and 65mA
worst case trickle charge current, and 2mA worst case
chip quiescent current:
V
= 1500mA • 127mΩ = 190.5mV
DROP
and:
P = (5.5 – 0) • 65mA + 5.5 • 2mA = 368.5mW
P = (4.141V + 0.1905V) • (2mA + 4mA) + 0.1905V
D
D
• 1500mA = 312mW
LTC4001-1 power dissipation is very low if a current
limited wall adapter is used and allowed to enter current
limit. When the wall adapter is in current limit, the voltage
drop across the LTC4001-1 charger is:
Power dissipation in buck battery charger mode may be
estimated from the dissipation curves given in the Typical
Performance Characteristics section of the data sheet.
This will slightly overestimate chip power dissipation
because it assumes all loss, including loss from external
components, occurs within the chip.
V
= I
• R
LIMIT PFET
DROP
where I
is the wall adapter current limit and R
is
LIMIT
PFET
the on resistance of the topside PMOS switch.
40011fa
15
LTC4001-1
APPLICATIONS INFORMATION
Insertthehighestpowerdissipationfigureintothefollowing
equation to determine maximum junction temperature:
upuntilV crossesthetricklechargethreshold.Whenthis
BAT
occurs, the LTC4001-1 switches over from trickle charge
to high rate (PWM) charge mode but initially delivers zero
current (because the soft-start pin is at zero). Battery volt-
age drops as a result of the system load, crossing below
the trickle charge threshold. The charger re-enters trickle
charge mode and the battery voltage ramps up again until
the battery charger re-enters high rate mode.
T = T + (P • 37°C/W)
J
A
D
TheLTC4001-1includeschipovertemperatureprotection.
If junction temperature exceeds 160°C (typical), the chip
will stop battery charging until chip temperature drops
below 150°C.
The soft-start voltage is slightly higher this time around
(than in the previous PWM cycle). Every successive time
that the charger enters high rate (PWM) charge mode,
the soft-start pin is at a slightly higher voltage. Eventually
highratechargemodebeginswithasoft-startvoltagethat
causes the PWM charger to provide more current than the
Using the LTC4001-1 in Applications Without a Battery
The LTC4001-1 is normally used in end products that only
operate with the battery attached (Figure 6). Under these
conditions the battery is available to supply load transient
currents. For indefinite operation with a powered wall
adapter there are only two requirements—that the aver-
age current drawn by the load is less than the high rate
systemloaddemands, andV rapidlyrisesuntiltheꢁoat
BAT
voltage is reached.
chargecurrent,andthatV staysabovethetricklecharge
BAT
For battery-less operation, system load current should be
restrictedtolessthantheworstcasetricklechargecurrent
threshold when the load is initially turned on and during
other load transients. When making this determination
take into account battery impedance. If battery voltage
is less than the trickle charge threshold, the system load
(preferably less than 30mA) when V is less than 3.15V
BAT
(through an undervoltage lockout or other means). Above
V
= 3.15V, system load current less than or equal to the
BAT
may be turned off until V is high enough to meet these
BAT
high rate charge current is allowed. If operation without
a battery is required, additional low-ESR output filtering
improves start-up and other load transients. Battery-less
start-up is also improved if a 10k resistor is placed in
series with the soft-start capacitor.
conditions.
The situation changes dramatically with the battery re-
moved (Figure 7). Since the battery is absent, V begins
BAT
at zero when a powered wall adapter is first connected to
the battery charger. With a maximum load less than the
LTC4001-1tricklechargecurrent,batteryvoltagewillramp
LTC4001-1
SYSTEM
LOAD
WALL
ADAPTER
BATTERY
CHARGER
40011 F06
+
Li-Ion
BATTERY
Figure 6. Typical Application
40011fa
16
LTC4001-1
APPLICATIONS INFORMATION
4
3
2
1
0
0
0
0
2
2
2
4
4
4
6
6
6
8
8
8
10
10
10
12
14
16
16
16
18
18
18
20
20
20
22
22
22
24
TIME (ms)
500
250
0
12
14
24
TIME (ms)
PWM
CHARGE
TRICKLE
CHARGE
12
14
24
TIME (ms)
40011 F07
Figure 7. Battery-Less Start-Up
40011fa
17
LTC4001-1
APPLICATIONS INFORMATION
Layout Considerations
With the exception of the input and output filter ca-
pacitors (which should be connected to PGND) all other
components that return to ground should be connected
to GNDSENS.
Switch rise and fall times are kept under 5ns for maximum
efficiency. To minimize radiation, the SW pin and input
bypass capacitor leads (between PV and PGND) should
IN
be kept as short as possible. A ground plane should be
used under the switching circuitry to prevent interplane
coupling. The Exposed Pad must be connected to the
groundplaneforproperpowerdissipation.Theotherpaths
containonlyDCand/or1.5MHztri-waveripplecurrentand
are less critical.
Recommended Components Manufacturers
Foralistofrecommendcomponentmanufacturers,contact
the Linear Technology application department.
L1
1.5μH
SW
SENSE
V
PV
BATSENS
BAT
INSENSE
V
IN
IN
2AHr
4.1V
Li-Ion
4.5V TO 5.5V
+
C4
10μF
C1
10μF
R1
R2
PGND
10k 1k
D1
LED
LTC4001-1
CHRG
NTC
TO μP
FROM μP
FAULT
EN
R3
PROG IDET
TIMER SS GNDSENS
10k
C2
AT 25°C
0.22μF
R4
549Ω
R5
549Ω
C3
0.1μF
40011 F08
L1: VISHAY DALE IHLP-2525AH-01
R3: NTC VISHAY DALE NTHS0603N02N1002J
Figure 8. 2A Li-Ion Battery Charger with 3Hr Timer, Temperature
Qualification, Soft-Start, Remote Sensing and C/10 Indication
40011fa
18
LTC4001-1
PACKAGE DESCRIPTION
UF Package
16-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1692)
0.72 ±0.05
4.35 ± 0.05
2.90 ± 0.05
2.15 ± 0.05
(4 SIDES)
PACKAGE OUTLINE
0.30 ±0.05
0.65 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.35 × 45° CHAMFER
0.75 ± 0.05
R = 0.115
TYP
4.00 ± 0.10
(4 SIDES)
15
16
0.55 ± 0.20
PIN 1
TOP MARK
(NOTE 6)
1
2
2.15 ± 0.10
(4-SIDES)
(UF16) QFN 10-04
0.200 REF
0.30 ± 0.05
0.65 BSC
0.00 – 0.05
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGC)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
40011fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LTC4001-1
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Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit,
Thermistor Sensor and Indicator Outputs, 24-Lead SSOP Package
4A, High Efficiency, Multi-Chemistry Battery Charger Complete Charger for 2- to 6-Cell Li-Ion Batteries or 4- to 18-Cell Nickel
Batteries, Up to 96ꢀ Efficiency, 20-Lead SSOP Package
40011fa
LT 1207 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
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© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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