LTC4120/LTC4120-4.2 - Wireless Power Receiver and 400mA Buck Battery Charger

LTC4120/LTC4120-4.2
Wireless Power Receiver and
400mA Buck Battery Charger
FEATURES
DESCRIPTION
Dynamic Harmonization Control Optimizes
Wireless Charging Over a Wide Coupling Range
n Wide Input Voltage Range (12.5V to 40V)
n Adjustable Float Voltage (3.5V to 11V)
n Fixed 4.2V Float Voltage Option (LTC4120-4.2)
n50mA to 400mA Charge Current Programmed with a
Single Resistor
n±1% Feedback Voltage Accuracy
n Programmable 5% Accurate Charge Current
n No Microprocessor Required
n No Transformer Core
n Thermally Enhanced, Low Profile 16-Lead
(3mm × 3mm × 0.75mm) QFN Package
The LTC®4120 is a constant-current/constant-voltage wireless receiver and battery charger. An external programming resistor sets the charge current up to 400mA. The
LTC4120-4.2 is suitable for charging Li-Ion/Polymer batteries, while the programmable float voltage of the LTC4120
accommodates several battery chemistries. The LTC4120
uses a Dynamic Harmonization Control (DHC) technique that
allows high efficiency contactless charging across an air gap.
n
The LTC4120 regulates its input voltage via the DHC pin.
This technique modulates the resonant frequency of a
receiver tank to automatically adjust the power received
as well as the power transmitted to provide an efficient
solution for wirelessly charging battery-powered devices.
Wireless charging with the LTC4120 provides a method
to power devices in harsh environments without requiring
expensive failure-prone connectors. This allows products
to be charged while locked within sealed enclosures, or
in moving or rotating equipment, or where cleanliness or
sanitation is critical.
APPLICATIONS
n
n
n
n
n
n
Handheld Instruments
Industrial/Military Sensors and Devices
Harsh Environments
Portable Medical Devices
Physically Small Devices
Electrically Isolated Devices
This full featured battery charger includes accurate RUN
pin threshold, low voltage battery preconditioning and bad
battery fault detection, timer termination, auto-recharge,
and NTC temperature qualified charging. The FAULT pin
provides an indication of bad battery or temperature faults.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and AutoResonant is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
Once charging is terminated, the LTC4120 signals end-ofcharge via the CHRG pin, and enters a low current sleep
mode. An auto-restart feature starts a new charging cycle
if the battery voltage drops by 2.2%.
TYPICAL APPLICATION
Wireless Rx Voltage/Charge Current vs Spacing
26.7nF
LTC4120
6.5nF
Tx CIRCUITRY
DHC
SW
22nF
35
33µH
47µH
BAT
FAULT
1.01M
CHRG
FB
GND
PROG
FBG
3.01k
Li-Ion
4.2V
ICHARGE
MAX
+
333
VIN
30
CHGSNS
NTC
5µH
400
40
2.2µF
267
NOT
CHARGING
25
200
133
20
T
CHARGING
15
1.35M
22µF
4120 TA01a
10
0.4
CHARGE CURRENT (mA)
10µF
INTVCC
FREQ
BOOST
VIN(RX) (V)
IN
RUN
67
0.6
0.8
1.0 1.2
1.4
SPACING (cm)
1.6
0
1.8
4120 TA01b
4120ff
For more information www.linear.com/LTC4120
1
LTC4120/LTC4120-4.2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
IN, RUN, CHRG, FAULT, DHC....................... –0.3V to 43V
BOOST.................................... VSW – 0.3V to (VSW + 6V)
SW (DC)......................................... –0.3V to (VIN + 0.3V)
SW (Pulsed <100ns).......................–1.5V to (VIN + 1.5V)
CHGSNS, BAT, FBG, FB................................–0.3V to 12V
FREQ, NTC, PROG, INTVCC........................... –0.3V to 6V
ICHGSNS, IBAT...................................................... ±600mA
IDHC................................................................ 350mARMS
ICHRG , IFAULT, IFBG...................................................±5mA
IFB ..........................................................................±5mA
IINTVCC................................................................... –5mA
Operating Junction Temperature Range
(Note 2)................................................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
LTC4120-4.2
11 FBG
BOOST 2
IN 3
10 FB
SW 4
BAT
5
6
7
8
GND
DHC
FREQ
CHGSNS
9
PROG
12 NTC
11 NC
17
GND
10 BATSNS
SW 4
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 54°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB TO OBTAIN θJA
9
5
6
7
8
CHGSNS
IN 3
INTVCC 1
FREQ
17
GND
16 15 14 13
12 NTC
DHC
BOOST 2
CHRG
RUN
16 15 14 13
INTVCC 1
FAULT
TOP VIEW
PROG
CHRG
FAULT
RUN
TOP VIEW
GND
LTC4120
BAT
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 54°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB TO OBTAIN θJA
ORDER INFORMATION
(http://www.linear.com/product/LTC4120#orderinfo)
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4120EUD#PBF
LTC4120EUD#TRPBF
LGHB
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LTC4120IUD#PBF
LTC4120IUD#TRPBF
LGHB
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LTC4120EUD-4.2#PBF
LTC4120EUD-4.2#TRPBF LGMT
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LTC4120IUD-4.2#PBF
LTC4120IUD-4.2#TRPBF
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LGMT
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
LTC4120 OPTIONS
FLOAT VOLTAGE
LTC4120
Programmable
LTC4120-4.2
4.2V Fixed
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = VRUN = 15V, VCHGSNS = VBAT = 4V, RPROG = 3.01k,
VFB = 2.29V (LTC4120), VBATSNS = 4V (LTC4120-4.2). Current into a pin is positive out of the pin is negative.
SYMBOL
PARAMETER
CONDITIONS
Operating Input Supply Range
MIN
l
Battery Voltage Range
IIN
∆VDUVLO
UVINTVCC
TYP
12.5
40
0
DC Supply Current
Switching, FREQ = GND
MAX
11
3.5
UNITS
V
V
mA
Standby Mode (Note 3)
l
130
220
µA
Sleep Mode (Note 3)
LTC4120: VFB = 2.51V (Note 5),
LTC4120-4.2: VBATSNS = 4.4V
l
60
100
µA
Disabled Mode (Note 3)
l
37
70
µA
Shutdown Mode (Note 3)
l
Differential Undervoltage Lockout
VIN-VBAT Falling, VIN = 5V (LTC4120),
VIN-VBATSNS Falling, VIN = 5V (LTC4120-4.2)
l
Hysteresis
VIN-VBAT Rising, VIN = 5V (LTC4120),
VIN-VBATSNS Rising, VIN = 5V (LTC4120-4.2)
INTVCC Undervoltage Lockout
INTVCC Rising, VIN = INTVCC + 100mV, VBAT = NC
Hysteresis
INTVCC Falling (Note 4)
20
20
40
µA
80
160
mV
115
l
4.00
4.15
mV
4.26
220
V
mV
Battery Charger
IBAT
BAT Standby Current
Standby Mode (LTC4120) (Notes 3, 7, 8)
Standby Mode (LTC4120-4.2) (Notes 3, 7, 8)
l
l
2.5
50
4.5
1000
µA
nA
BAT Shutdown Current
Shutdown Mode (LTC4120) (Notes 3, 7, 8)
Shutdown Mode (LTC4120-4.2) (Notes 3, 7, 8)
l
l
1100
10
2000
1000
nA
nA
BATSNS Standby Current (LTC4120-4.2)
Standby Mode (Notes 3, 7, 8)
l
5.4
10
µA
BATSNS Shutdown Current (LTC4120-4.2)
Shutdown Mode (Notes 3, 7, 8)
l
1100
2000
nA
IFB
Feedback Pin Bias Current (LTC4120)
VFB = 2.5V (Notes 5, 7)
l
25
60
nA
IFBG(LEAK)
Feedback Ground Leakage Current (LTC4120) Shutdown Mode (Notes 3, 7)
l
1
µA
RFBG
Feedback Ground Return Resistance (LTC4120)
l
1000
2000
Ω
VFB(REG)
Feedback Regulation Voltage (LTC4120)
IBATSNS
VFLOAT
(Note 5)
2.393
2.370
2.400
l
2.407
2.418
V
V
4.188
4.148
4.200
l
4.212
4.227
V
V
l
l
383
45
402
50
421
55
Regulated Float Voltage (LTC4120-4.2)
ICHG
Battery Charge Current
RPROG = 3.01k
RPROG = 24.3k
VUVCL
Undervoltage Current Limit
VIN Falling
12.0
mA
mA
V
VRCHG
Battery Recharge Threshold
VFB Falling Relative to VFB_REG (LTC4120) (Note 5)
l
–38
–50
–62
mV
VRCHG_4.2
Battery Recharge Threshold
VBATSNS Falling Relative to VFLOAT (LTC4120-4.2)
l
–70
–92
–114
mV
hPROG
Ratio of BAT Current to PROG Current
VTRKL < VFB < VFB(REG) (LTC4120) (Note 5)
VTRKL_4.2 < VBATSNS < VFLOAT (LTC4120-4.2)
VPROG
PROG Pin Servo Voltage
RSNS
CHGSNS-BAT Sense Resistor
988
l
IBAT = –100mA
1.206
1.227
300
mA/mA
1.248
V
mΩ
4120ff
For more information www.linear.com/LTC4120
3
LTC4120/LTC4120-4.2
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = VRUN = 15V, VCHGSNS = VBAT = 4V, RPROG = 3.01k,
VFB = 2.29V (LTC4120), VBATSNS = 4V (LTC4120-4.2). Current into a pin is positive out of the pin is negative.
SYMBOL
PARAMETER
CONDITIONS
ILOWBAT
Low Battery Linear Charge Current
0V < VFB < VTRKL, VBAT = 2.6V (LTC4120),
VBATSNS < VTRKL_4.2, VBAT = 2.6V (LTC4120-4.2)
VLOWBAT
Low Battery Threshold Voltage
VBAT Rising (LTC4120),
VBATSNS Rising (LTC4120-4.2)
l
MIN
TYP
MAX
6
9
16
2.15
2.21
2.28
Hysteresis
ITRKL
VTRKL
VTRKL_4.2
hC/10
UNITS
mA
V
147
mV
Switch Mode Trickle Charge Current
VLOWBAT < VBAT, VFB < VTRKL (LTC4120) (Note 5),
VLOWBAT < VBATSNS < VTRKL_4.2 (LTC4120-4.2)
ICHG/10
mA
PROG Pin Servo Voltage in Switch Mode
Trickle Charge
VLOWBAT < VBAT, VFB < VTRKL (LTC4120) (Note 5),
VLOWBAT < VBATSNS < VTRKL_4.2 (LTC4120-4.2)
122
mV
Trickle Charge Threshold
VFB Rising (LTC4120) (Note 5)
Hysteresis
VFB Falling (LTC4120) (Note 5)
Trickle Charge Threshold
VBATSNS Rising (LTC4120-4.2)
Hysteresis
VBATSNS Falling (LTC4120-4.2)
End of Charge Indication Current Ratio
(Note 6)
l
1.64
1.68
l
2.86
2.91
1.71
50
V
mV
2.98
88
V
mV
0.1
mA/mA
Safety Timer Termination Period
1.3
2.0
2.8
Hours
Bad Battery Termination Timeout
19
30
42
Minutes
1.0
0.5
1.5
0.75
2.0
1.0
MHz
MHz
Switcher
fOSC
Switching Frequency
FREQ = INTVCC
FREQ = GND
tMIN(ON)
Minimum Controllable On-Time
(Note 9)
Duty Cycle Maximum
(Note 9)
Top Switch RDS(ON)
ISW = –100mA
0.8
Ω
Bottom Switch RDS(ON)
ISW = 100mA
0.5
Ω
IPEAK
Peak Current Limit
Measured Across RSNS with a 15µH Inductor in
Series with RSNS (Note 9)
ISW
Switch Pin Current (Note 8)
VIN = Open-Circuit, VRUN = 0V, VSW = 8.4V (LTC4120) l
l
VIN = Open-Circuit, VRUN = 0V, VSW = 4.2V
(LTC4120-4.2)
l
l
120
ns
94
585
%
750
1250
mA
15
7
30
15
µA
µA
500
mV
0
1
µA
Status Pins FAULT, CHRG
Pin Output Voltage Low
I = 2mA
Pin Leakage Current
V = 43V, Pin High Impedance
Cold Temperature VNTC/VINTVCC Fault
Rising VNTC Threshold
Falling VNTC Threshold
l
73
74
72
75
%INTVCC
%INTVCC
Hot Temperature VNTC/VINTVCC Fault
Falling VNTC Threshold
Rising VNTC Threshold
l
35.5
36.5
37.5
37.5
%INTVCC
%INTVCC
NTC Disable Voltage
Falling VNTC Threshold
Rising VNTC Threshold
l
1
2
3
3
%INTVCC
%INTVCC
NTC Input Leakage Current
VNTC = VINTVCC
50
nA
NTC
4
–50
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = VRUN = 15V, VCHGSNS = VBAT = 4V, RPROG = 3.01k,
VFB = 2.29V (LTC4120), VBATSNS = 4V (LTC4120-4.2). Current into a pin is positive out of the pin is negative.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
2.35
2.45
2.55
UNITS
RUN
VEN
VSD
Enable threshold
VRUN Rising
Hysteresis
VRUN Falling
Run Pin Input Current
VRUN = 40V
Shutdown Threshold (Note 3)
VRUN Falling
l
200
0.01
l
0.4
Hysteresis
V
mV
0.1
1.2
220
µA
V
mV
FREQ
FREQ Pin Input Low
l
FREQ Pin Input High
VINTVCC-VFREQ
FREQ Pin Input Current
0V < VFREQ < VINTVCC
0.4
V
l
0.6
V
±1
µA
Dynamic Harmonization Control
VIN(DHC)
Input Regulation Voltage
DHC Pin Current
VDHC = 1V, VIN < VIN(DHC)
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: The LTC4120 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC4120E is guaranteed to meet performance specifications
for junction temperatures from 0°C to 85°C. Specifications over the
–40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC4120I is guaranteed over the full –40°C to 125°C operating
junction temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance, and other environmental factors.
Note 3: Standby mode occurs when the LTC4120 stops switching due
to an NTC fault condition, or when the charge current has dropped low
enough to enter Burst Mode operation. Disabled mode occurs when VRUN
is between VSD and VEN. Shutdown mode occurs when VRUN is below VSD
or when the differential undervoltage lockout is engaged. SLEEP mode
occurs after a timeout while the battery voltage remains above the VRCHG
or VRCHG_42 threshold.
14
V
330
mARMS
Note 4: The internal supply INTVCC should only be used for the NTC
divider, it should not be used for any other loads.
Note 5: The FB pin is measured with a resistance of 588k in series with
the pin.
Note 6: hC/10 is expressed as a fraction of measured full charge current as
measured at the PROG pin voltage when the CHRG pin de-asserts.
Note 7: In an application circuit with an inductor connected from SW to
CHGSNS, the total battery leakage current when disabled is the sum of
IBAT, IFBG(LEAK) and ISW (LTC4120), or IBATSNS and IBAT and ISW (LTC41204.2).
Note 8: When no supply is present at IN, the SW powers IN through
the body diode of the topside switch. This may cause additional SW pin
current depending on the load present at IN.
Note 9: Guaranteed by design and/or correlation to static test.
4120ff
For more information www.linear.com/LTC4120
5
LTC4120/LTC4120-4.2
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
Typical VFLOAT vs Temperature
LTC4120-4.2
Typical VFB(REG) vs Temperature
2.43
4.25
4 UNITS TESTED
4 UNITS TESTED
4.24
2.42
4.23
HIGH LIMIT
DUT1 VFB(REG) (V)
DUT2 VFB(REG) (V)
DUT3 VFB(REG) (V)
DUT4 VFB(REG) (V)
LOW LIMIT
DUT = DEVICE
UNDER TEST
2.40
2.39
2.38
2.37
4.22
VFLOAT (V)
VFB(REG) (V)
2.41
HIGH LIMIT
DUT1 VFLOAT
DUT2 VFLOAT
DUT3 VFLOAT
DUT4 VFLOAT
LOW LIMIT
4.21
4.20
4.19
4.18
4.17
4.16
2.36
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
4.15
–40 –25 –10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
4120 G01
4120 G20
IN Pin Standby/Sleep Current vs
Temperature
180
IN Pin Disabled/Shutdown Current
vs Temperature
60
2 UNITS TESTED
VIN = 15V
50
IIN (µA)
140
IIN STANDBY FREQ = INTVCC
IIN STANDBY FREQ = INTVCC
IIN STANDBY FREQ = GND
IIN STANDBY FREQ = GND
IIN SLEEP
IIN SLEEP
120
100
80
40
IIN (µA)
160
2 UNITS TESTED
VIN = 15V
IIN DISABLED
IIN DISABLED
30
20
IIN SD
IIN SD
10
60
40
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
0
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
IBAT (µA)
6
5
IBAT SLEEP
IBAT SLEEP
4
3
2
IBAT SHUTDOWN
IBAT SHUTDOWN
398
0
–50 –25
395
–50 –25
100
125
1080
DUT1
DUT2
DUT3
1060
399
396
75
50
25
TEMPERATURE (°C)
1100
400
1
0
1120
401
397
4120 G04
6
402
2 UNITS TESTED
VBAT = 4.2V
RFB2 = 1.01M
RFB1 = 1.35M
RPROG = 3.01k
2 UNITS TESTED
FREQ = GND
FREQ = GND
FREQ = INTVCC
FREQ = INTVCC
50
25
75
0
TEMPERATURE (°C)
100
125
IPEAK (mA)
7
Typical RSNS Current Limit
vs Temperature
Typical Battery Charge Current
vs Temperature
ICHG (mA)
8
125
4120 G03
4120 G02
BAT Pin Sleep/Shutdown Current
vs Temperature
100
1040
1020
1000
980
960
940
3 UNITS TESTED
920
50
75
–50 –25
0
25
TEMPERATURE (°C)
100
125
4120 G06
4120 G05
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
vs Temperature
FREQ = GND
FREQ = GND
0.6
0.4
16
90
14
85
12
300
10
250
8
200
6
150
80
75
VIN = 12.5V
VIN = 14V
VIN = 20V
VIN = 30V
70
65
60
0.2
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
50
125
50
0
100 150 200 250 300 350 400
IBAT (mA)
4120 G07
130
70
EFFICIENCY (%)
110
105
100
95
90
85
100
50
20
40
18
30
16
20
14
10
12
0
125
50
0
100
150
200
Typical Wireless Charging Cycle
400
4.0
80
350
3.5
70
3.0
60
250
IBAT
2.5
200
2.0
150 BAT = 940mAhr
LSW = TDK SLF4075 15µH
100 RFB1 = 732k, RFB2 = 976k
RPROG = 3.01k
50 APPLICATION CCT OF FIGURE 10
SPACING = 14mm
0
2
0
1
TIME (HOURS)
1.5
3
4120 G12
IBAT (mA)
300
10
250
RPROG = 3k
VSW
5V/DIV
RPROG = 6.2k
50
0V
VPROG
500mV/DIV 0V
ILSW
200mA/DIV 0mA
40
30
1.0
20
0.5
10
0
9mm EFFICIENCY
10mm EFFICIENCY
11mm EFFICIENCY
9mm V_RX
10mm V_RX
11mm V_RX
Typical Burst Mode Waveforms,
IBAT = 38mA
90
VBAT, VCHRG (V)
BATTERY CURRENT (mA)
4.5
VCHRG
0
125
4120 G11
Burst Mode Trigger Current
VBAT
100
IBAT (mA)
4120 G10
450
50
22
VIN_RX (V)
tMIN(0N) (ns)
115
50
25
0
75
TEMPERATURE (°C)
100
24
VFLOAT = 8.3V
LSW = SLF6028-470MR59
RPROG = 4.64k
60
120
–22
350
Wireless Power Transfer Efficiency,
VIN_RX vs Battery Current
2 UNITS TESTED
80
–50
400
4120 G09
4120 G08
Typical tMIN(ON) vs Temperature
125
VIN = OPEN-CIRCUIT
VBAT = 4.2V
2 UNITS TESTED
4
IBAT
IBAT
2
VBAT-VIN
VBAT-VIN
0
0
50
75
25
–50 –25
TEMPERATURE (°C)
LSW = 68µH, SLF12555T-680M1R3
FREQ = GND
VBAT = 4.2V
55
2 UNITS TESTED
IBAT (µA)
fOSC (MHz)
0.8
95
VBAT-VIN (mV)
EFFICIENCY (%)
FREQ = INTVCC
FREQ = INTVCC
1.0
BAT Pin Leakage Current/VBAT-VIN
vs Temperature
Buck Efficiency vs Battery Current
1.4
1.2
TA = 25°C, unless otherwise noted.
0
4µs/DIV
10
15
20
25
VIN (V)
30
4120 G14
40
35
4120 G13
4120ff
For more information www.linear.com/LTC4120
7
LTC4120/LTC4120-4.2
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
IN Pin Shutdown Current
vs Input Voltage
IN Pin Standby Current vs VIN
220
80
VBAT = 4.21V
NTC = GND
200
60
IIN STBY FREQ HIGH 130°C
IIN STBY FREQ LOW 130°C
IIN STBY FREQ HIGH 25°C
IIN STBY FREQ LOW 25°C
IIN STBY FREQ HIGH –45°C
IIN STBY FREQ LOW –45°C
160
140
120
50
IIN (µA)
IIN (µA)
180
40
30
20
100
80
VRUN = 0.4V
70
IIN SD TEMP = 125°C
IIN SD TEMP = 35°C
IIN SD TEMP = –40°C
10
0
5
10
15
20 25
VIN (V)
30
35
0
40
0
10
20
4120 G15
IN Pin Switching Current vs Input
Voltage
7
VRUN = 1.6V
90
80
–45°C
IICCQ(SWITCHING) FREQ HIGH
FREQ = INTVCC
50
40
30
4
3
2
IIN SD TEMP = 125°C
IIN SD TEMP = 35°C
IIN SD TEMP = –40°C
10
0
10
20
VIN (V)
30
40
1
0
10
UVCL
25
VIN (V)
4120 G17
30
35
0.20
0.15
0.05
IBAT = 0
20
0.25
0.10
IICCQ(SWITCHING) FREQ LOW
FREQ = GND
15
IBAT TEMP = 125°C
IBAT TEMP = 35°C
IBAT TEMP= –40°C
0.30
ICHARGE (mA)
IIN (mA)
IIN (µA)
60
8
25°C
0.35
5
70
0
130°C
UVCL: ICHARGE vs Input Voltage
0.40
6
20
40
4120 G16
IN Pin Disabled Current
vs Input Voltage
100
30
VIN (V)
40
4120 G18
0
11.90 11.95 12.00 12.05 12.10 12.15 12.20
VIN (V)
4120 G19
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
PIN FUNCTIONS
INTVCC (Pin 1): Internal Regulator Output Pin. This pin is
the output of an internal linear regulator that generates the
internal INTVCC supply from IN. It also supplies power to
the switch gate drivers and the low battery linear charge
current ILOWBAT. Connect a 2.2µF low ESR capacitor from
INTVCC to GND. Do not place any external load on INTVCC
other than the NTC bias network. Overloading this pin can
disrupt internal operation. When the RUN pin is above
VEN, and INTVCC rises above the UVLO threshold, and
IN rises above BAT by ∆VDUVLO and its hysteresis, the
charger is enabled.
BOOST (Pin 2): Boosted Supply Pin. Connect a 22nF boost
capacitor from this pin to the SW pin.
IN (Pin 3): Positive Input Power Supply. Decouple to GND
with a 10µF or larger low ESR capacitor.
SW (Pin 4): Switch Pin. The SW pin delivers power from
IN to BAT via the step-down switching regulator. An inductor should be connected from SW to CHGSNS. See
the Applications Information section for a discussion of
inductor selection.
GND (Pin 5, Exposed Pad Pin 17): Ground Pin. Connect
to exposed pad. The exposed pad must be soldered to PCB
GND to provide a low electrical and thermal impedance
connection to ground.
DHC (Pin 6): Dynamic Harmonization Control Pin. Connect
a Schottky diode from the DHC pin to the IN pin, and a
capacitor from the DHC pin as shown in the Typical Application or the Block Diagram. When VIN is greater than
VIN(DHC), this pin is high impedance. When VIN is below
VIN(DHC) this pin is low impedance allowing the LTC4120
to modulate the resonance of the tuned receiver network.
See Applications Information for more information on the
tuned receiver network.
FREQ (Pin 7): Buck Switching Frequency Select Input Pin.
Connect to INTVCC to select a 1.5MHz switching frequency
or GND to select a 750kHz switching frequency. Do not float.
CHGSNS (Pin 8): Battery Charge Current Sense Pin. An
internal current sense resistor between CHGSNS and BAT
pins monitors battery charge current. An inductor should
be connected from SW to CHGSNS.
BAT (Pin 9): Battery Output Pin. Battery charge current
is delivered from this pin through the internal charge
current sense resistor. In low battery conditions a small
linear charge current, ILOWBAT, is sourced from this pin to
precondition the battery. Decouple the BAT pin with a low
ESR 22µF or greater ceramic capacitor to GND.
BATSNS (Pin 10, LTC4120-4.2 Only): Battery Voltage
Sense Pin. For proper operation, this pin must always be
connected physically close to the positive battery terminal.
FB (Pin 10, LTC4120 Only): Battery Voltage Feedback Pin.
The charge function operates to achieve a final float voltage
of 2.4V at this pin. Battery float voltage is programmed
using a resistive divider from BAT to FB to FBG, and can be
programmed up to 11V. The feedback pin input bias current, IFB, is 25nA. Using a resistive divider with a Thevenin
equivalent resistance of 588k compensates for input bias
current error (see curve of FB Pin Bias Current versus
Temperature in the Typical Performance Characteristics).
FBG (Pin 11, LTC4120 Only): Feedback Ground Pin. This
pin disconnects the external FB divider load from the battery
when it is not needed. When sensing the battery voltage
this pin presents a low resistance, RFBG, to GND. When in
disabled or shutdown modes this pin is high impedance.
NTC (Pin 12): Input to the Negative Temperature Coefficient
Thermistor Monitoring Circuit. The NTC pin connects to
a negative temperature coefficient thermistor which is
typically co-packaged with the battery to determine if the
battery is too hot or too cold to charge. If the battery’s
temperature is out of range, the LTC4120 enters standby
mode and charging is paused until the battery temperature re-enters the valid range. A low drift bias resistor is
required from INTVCC to NTC and a thermistor is required
from NTC to GND. Tie the NTC pin to GND to disable NTC
qualified charging if NTC functionality is not required.
PROG (Pin 13): Charge Current Program and Charge Current
Monitor Pin. Connect a 1% resistor between 3.01k (400mA)
and 24.3k (50mA) from PROG to ground to program the
charge current. While in constant-current mode, this pin
regulates to 1.227V. The voltage at this pin represents the
average battery charge current using the following formula:
IBAT = hPROG •
VPROG
RPROG
4120ff
For more information www.linear.com/LTC4120
9
LTC4120/LTC4120-4.2
PIN FUNCTIONS
where hPROG is typically 988. Keep parasitic capacitance
on the PROG pin to a minimum.
CHRG (Pin 14): Open-Drain Charge Status Output Pin.
Typically pulled up through a resistor to a reference
voltage, the CHRG pin indicates the status of the battery
charger. The pin can be pulled up to voltages as high as
IN when disabled, and can sink currents up to 5mA when
enabled. When the battery is being charged, the CHRG
pin is pulled low. When the termination timer expires or
the charge current drops below 10% of the programmed
value, the CHRG pin is forced to a high impedance state.
FAULT (Pin 15): Open-Drain Fault Status Output Pin. Typically pulled up through a resistor to a reference voltage,
this status pin indicates fault conditions during a charge
cycle. The pin can be pulled up to voltages as high as IN
when disabled, and can sink currents up to 5mA when
enabled. An NTC temperature fault causes this pin to be
pulled low. A bad battery fault also causes this pin to
be pulled low. If no fault conditions exist, the FAULT pin
remains high impedance.
RUN (Pin 16): Run Pin. When RUN is pulled below VEN
and its hysteresis, the device is disabled. In disabled
mode, battery charge current is zero and the CHRG and
FAULT pins assume high impedance states. If the voltage
at RUN is pulled below VSD, the device is in shutdown
mode. When the voltage at the RUN pin rises above VEN,
the INTVCC LDO turns on. When the INTVCC LDO rises
above its UVLO threshold the charger is enabled. The
RUN pin should be tied to a resistive divider from VIN to
program the input voltage at which charging is enabled.
Do not float the RUN pin.
BLOCK DIAGRAM
C2S
3
16
CIN
10µF
RUN
2.45V
+
–
0.9V
+
–
C2P
•
BAT
LR
IN – 80mV
6
IN
7
15
DHC
PWM
BOOST
DUVLO
GND
IN
INTVCC
ENABLE
CNTRL
LOWBAT
INTVCC
1.2V
2
CBST
22nF
4
5
LSW
33µH
BAT
8
9
INTVCC
–
+
FB
588k
V-EA
VFB(REG)
FBG
RFB1
10
RFB2
NTC
NTC
BAT
2.21V
–
+
DZ
+
T
10k
Li-Ion
PROG
HOT
COLD
DISABLE
RNOM
10k
CBAT
22µF
11
ENABLE
INTVCC
12
RSNS
0.3Ω
C-EA
+
–
UVCL
CHGSNS
+
–
IN
ITH
CHRG
CINTVCC
2.2µF
INTVCC
VIN(DHC)
FREQ
FAULT
SW
INTVCC
1
SHUTDOWN
+
–
DHC
INTVCC
LDO
INTVCC
ENABLE
IN
14
ENABLE
LTC4120
IN
13
RPROG
LOWBAT
4120 F01
Figure 1. Block Diagram
10
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
BLOCK DIAGRAM
LTC4120-4.2
BATSNS
IN – 80mV
INTVCC
ITH
+
–
CHGSNS
+
–
RSNS
0.3Ω
C-EA
DUVLO
IN
BATSNS
INTVCC
9
10
CBAT
22µF
INTVCC
+
–
1.2V
BAT
8
–
+
UVCL
588k
+
Li-Ion
VFB(REG)
V-EA
ENABLE
BATSNS
2.21V
–
+
PROG
LOWBAT
13
DZ
RPROG
4120 F02
Figure 2. LTC4120-4.2 BATSNS Connections
TEST CIRCUIT
20V
2k
665Ω
680nF
49.9Ω
IRLML5103TR
VIN(DHC)
IN
NTC
LTC4120
RUN
665Ω
INTVCC
10Ω
2.2µF
10µF
DHC
GND
4120 F03
Figure 3. VIN(DHC) Test Circuit
4120ff
For more information www.linear.com/LTC4120
11
LTC4120/LTC4120-4.2
OPERATION
Wireless Power System Overview
The LTC4120 is one component in a complete wireless
power system. A complete system is composed of transmit circuitry, a transmit coil, a receive coil and receive
circuitry—including the LTC4120. Please refer to the
Applications Information section for more information
on transmit circuitry and coils. In particular, the Resonant
Transmitter and Receiver and the Alternative Transmitter Options sections include information necessary to
complete the design of a wireless power system. Further
information can be found in the Applications Information
section of this document under the heading Resonant
Transmitter and Receiver, as well as in AN138: Wireless
Power Users Guide, as well as the DC1969A: wireless
power transmit and receiver demo kit and manual. The
Gerber layout files for both the Transmitter and Receiver
boards are available at the following link:
http://www.linear.com/product/LTC4120#demoboards
LTC4120 Overview
The LTC4120 is a synchronous step-down (buck) wireless battery charger with dynamic harmonization control
(DHC). DHC is a highly efficient method of regulating the
received input voltage in a resonant coupled power transfer
VDC
5V
L1
The circuit in Figure 4 is a fully functional system using a
basic current-fed resonant converter for the transmitter
and a series resonant converter for the receiver with the
LTC4120. Advanced transmitters by Power-By-Proxi1 may
also be used with the LTC4120. For more information on
transmitter design refer to Application Note 138: Wireless
Power Users Guide.
Wireless Power Transfer
A wireless coupled power transfer system consists of a
transmitter that generates an alternating magnetic field,
and a receiver that collects power from that field. The
ideal transmitter efficiently generates a large alternating
current in the transmitter coil, LX. The push-pull currentfed resonant converter, shown in Figure 4, is an example
1www.PowerByProxi.com
TRANSMITTER
C2S
L2
CX LX
C4
application. The LTC4120 serves as a constant-current/
constant-voltage battery charger with the following built-in
charger functions: programmable charge current, programmable float voltage (LTC4120), battery precondition with
half-hour timeout, precision shutdown/run control, NTC
thermal protection, a 2-hour safety termination timer, and
automatic recharge. The LTC4120 also provides output
pins to indicate state of charge and fault status.
LR
C2P
D9
D8
C5
IN
DHC BOOST
SW
R1
R2
D2
D3
M1
D5, D8, D9: DFLS240L
M2
D1
D4
D6
39V
DFLZ39
CIN
D5
LTC4120
CBST
LSW
CHGSNS
BAT
GND
CBAT
+
Li-Ion
4120 F04
Figure 4. DC-AC Converter, Transmit/Receive Coils, Tuned Series Resonant Receiver and AC-DC Rectifier
12
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
OPERATION
of a basic power transmitter that may be used with the
LTC4120. This transmitter typically operates at a frequency
of approximately 130kHz; though the operating frequency
varies depending on the load at the receiver and the coupling to the receiver coil. For LX = 5µH, and CX = 300nF,
the transmitter frequency is:
fO ≈
1
= 130kHz
2 • π • L X • CX
This transmitter typically generates an AC coil current of
about 2.5ARMS. For more information on this transmitter,
refer to AN138: Wireless Power Users Guide.
The receiver consists of a coil, LR, configured in a resonant
circuit followed by a rectifier and the LTC4120. The receiver
coil presents a load reflected back to the transmitter through
the mutual inductance between LR and LX. The reflected
impedance of the receiver may influence the operating
frequency of the transmitter. Likewise, the power output
by the transmitter depends on the load at the receiver. The
resonant coupled charging system, consisting of both the
transmitter and LTC4120 charger, provides an efficient
method for wireless battery charging as the power output
by the transmitter varies automatically based on the power
used to charge a battery.
power to appear at the receiver by tuning the receiver
resonance closer to the transmitter resonance. If the input
voltage exceeds VIN(DHC), the LTC4120 tunes the receiver
resonance away from the transmitter, which reduces the
power available at the receiver. The amount that the input
power increases or decreases is a function of the coupling,
the tuning capacitor, C2P, the receiver coil, LR, and the
operating frequency.
Figure 5 illustrates the components that implement the
DHC function to automatically tune the resonance of the
receiver. Capacitor C2S and inductor LR serve as a series
resonator. Capacitor C2P and the DHC pin of the LTC4120
form a parallel resonance when the DHC pin is low impedance, and disconnect when the DHC pin is high impedance.
C2P adjusts the receiver resonance to control the amount
of power available at the input of the LTC4120. C2P also
affects power dissipation in the LTC4120 due to the AC
current being shunted by the DHC pin. For this reason it
is not recommended to apply total capacitance in excess
of 30nF at this pin.
Using DHC, the LTC4120 automatically adjusts the power
received depending on load requirements; typically the
load is battery charge current. This technique results in
significant power savings, as the power required by the
Dynamic Harmonization Control
C2S
1:n
Dynamic harmonization control (DHC) is a technique for
regulating the received input power in a wireless power
transfer system. DHC modulates the impedance of the
resonant receiver to regulate the voltage at the input to
the LTC4120. When the input voltage to the LTC4120 is
below the VIN(DHC) set point, the LTC4120 allows more
CX
LX
LR
C2P
D9
D8
CIN
D5
IN
LTC4120
DHC
4120 F05
Figure 5. Resonant Receiver Tank
4120ff
For more information www.linear.com/LTC4120
13
LTC4120/LTC4120-4.2
OPERATION
transmitter automatically adjusts to the requirements
at the receiver. Furthermore, DHC reduces the rectified
voltage seen at the input of the LTC4120 under light load
conditions when the battery is fully charged.
The design of the resonant receiver circuit (LR, C2S and
C2P), the transmitter circuit, and the mutual inductance
between LX and LR determines both the maximum unloaded
voltage at the input to the LTC4120 as well as the maximum
power available at the input to the LTC4120. The value and
tolerances of these components must be selected with care
for stable operation, for this reason it is recommended to
only use components with tight tolerances.
To understand the operating principle behind dynamic
harmonization control (DHC), consider the following simplification. Here, a fixed-frequency transmitter is operating
at a frequency fO = 130kHz. DHC automatically adjusts the
impedance of the receiver tuned network so as to modulate
the resonant frequency of the receiver between fT and fD.
fT ≅
1
2 • π • LR • (C2P + C2S)
1
fD ≅
2 • π • LR • C2S
For the LTC4120, the battery float voltage is programmed
by placing a resistive divider from the battery to FB and
FBG as shown in Figure 6. The programmable battery float
voltage, VFLOAT, is then governed by the following equation:
For the resonant converter shown in Figure 4, the operating
frequency of the transmitter is not fixed, but varies depending on the load impedance. However the basic operating
principle of DHC remains valid. For more information on
the design of the wireless power receiver resonant circuit
refer to the applications section.
VFLOAT = VFB(REG) •
(RFB1 + RFB2 )
RFB2
where VFB(REG) is typically 2.4V.
Due to the input bias current (IFB) of the voltage error amp
(V-EA), care must also be taken to select the Thevenin
equivalent resistance of RFB1||RFB2 close to 588k. Start by
calculating RFB1 to satisfy the following relations:
RFB1 =
VFLOAT • 588k
VFB(REG)
Find the closest 0.1% or 1% resistor to the calculated
value. With RFB1 calculate:
When the input voltage is above VIN(DHC) (typically 14V),
the LTC4120 opens the DHC pin, detuning the receiver
resonance away from the transmitter frequency fO, so that
less power is received. When the input voltage is below
VIN(DHC), the LTC4120 shunts the DHC pin to ground,
tuning the receiver resonance closer to the transmitter
frequency so that more power is available.
14
Programming The Battery Float Voltage
RFB2 =
VFB(REG) • RFB1
VFLOAT – VFB(REG)
– 1000Ω
where 1000Ω represent the typical value of RFBG. This is
the resistance of the FBG pin which serves as the ground
return for the battery float voltage divider.
BAT
LTC4120
IFB
FB
VFLOAT
RFB1
22µF
Li-Ion
4120 F06
FBG
RFB2
ENABLE
Figure 6. Programming the Float Voltage with the LTC4120
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
OPERATION
Once RFB1 and RFB2 are selected, recalculate the value of
VFLOAT obtained with the resistors available. If the error
is too large substitute another standard resistor value for
RFB1 and recalculate RFB2. Repeat until the float voltage
error is acceptable.
Table 1 and Table 2 list recommended standard 0.1% and
1% resistor values for common battery float voltages.
Table 1: Recommended 0.1% Resistors for Common VFLOAT
VFLOAT
3.6V
4.1V
4.2V
7.2V
8.2V
8.4V
RFB1
887k
1.01M
1.01M
1.8M
2.00M
2.05M
RFB2
1780k
1.42M
1.35M
898k
825k
816k
TYPICAL ERROR
–0.13%
0.15%
–0.13%
0.08%
0.14%
0.27%
Table 2: Recommended 1% Resistors for Common VFLOAT
VFLOAT
3.6V
4.1V
4.2V
7.2V
8.2V
8.4V
RFB1
887k
1.02M
1.02M
1.78M
2.00M
2.1M
RFB2
1780k
1.43M
1.37M
887k
825k
845k
TYPICAL ERROR
–0.13%
0.26%
–0.34%
0.16%
0.14%
–0.50%
Programming the Charge Current
The current-error amp (C-EA) measures the current
through an internal 0.3Ω current sense resistor between
the CHGSNS and BAT pins. The C-EA outputs a fraction
of the charge current, 1/hPROG, to the PROG pin. The
voltage-error amp (V-EA) and PWM control circuitry can
limit the PROG pin voltage to control charge current. An
internal clamp (DZ) limits the PROG pin voltage to VPROG,
which in turn limits the charge current to:
ICHG =
where hPROG is typically 988, VPROG is either 1.227V or
122mV during trickle charge, and RPROG is the resistance
of the grounded resistor applied to the PROG pin. The
PROG resistor sets the maximum charge current, or the
current delivered while the charger is operating in constantcurrent (CC) mode.
Analog Charge Current Monitor
The PROG pin provides a voltage signal proportional to
the actual charge current. Care must be exercised in measuring this voltage as any capacitance at the PROG pin
forms a pole that may cause loop instability. If observing
the PROG pin voltage, add a series resistor of at least 2k
and limit stray capacitance at this node to less than 50pF.
In the event that the input voltage cannot support the
demanded charge current, the PROG pin voltage may not
represent the actual charge current. In cases such as this,
the PWM switch frequency drops as the charger enters
drop-out operation where the top switch remains on for
more than one clock cycle as the inductor current attempts
to ramp up to the desired current. If the top switch remains
on in drop-out for 8 clock cycles a dropout detector forces
the bottom switch on for the remainder of the 8th cycle.
In such a case, the PROG pin voltage remains at 1.227V,
but the charge current may not reach the desired level.
Undervoltage Current Limit
The undervoltage current limit (UVCL) feature reduces
charge current as the input voltage drops below VUVCL
(typically 12V). This low gain amplifier typically keeps VIN
within 100mV of VUVCL, but if insufficient power is available the input voltage may drop below this value; and the
charge current will be reduced to zero.
hPROG • VPROG 1212V
=
RPROG
RPROG
ICHG _ TRKL =
hPROG • VPROG _ TRKL 120V
=
RPROG
RPROG
4120ff
For more information www.linear.com/LTC4120
15
LTC4120/LTC4120-4.2
OPERATION
NTC Thermal Battery Protection
The LTC4120 monitors battery temperature using a thermistor during the charging cycle. If the battery temperature
moves outside a safe charging range, the IC suspends
charging and signals a fault condition until the temperature returns to the safe charging range. The safe charging
range is determined by two comparators that monitor the
voltage at the NTC pin. NTC qualified charging is disabled
if the NTC pin is pulled below about 85mV (VDIS).
Thermistor manufacturers usually include either a temperature lookup table identified with a characteristic curve
number, or a formula relating temperature to the resistor
value. Each thermistor is also typically designated by a
thermistor gain value B25/85.
The NTC pin should be connected to a voltage divider
from INTVCC to GND as shown in Figure 7. In the simple
application (RADJ = 0) a 1% resistor, RBIAS, with a value
equal to the resistance of the thermistor at 25°C is
connected from INTVCC to NTC, and a thermistor is connected from NTC to GND. With this setup, the LTC4120
pauses charging when the resistance of the thermistor
increases to 285% of the RBIAS resistor as the temperature drops. For a Vishay Curve 2 thermistor with B25/85
= 3490 and 25°C resistance of 10k, this corresponds to
a temperature of about 0°C. The LTC4120 also pauses
charging if the thermistor resistance decreases to 57.5%
LTC4120
TOO COLD
+
–
TOO HOT
+
–
IGNORE NTC
+
–
BAT
INTVCC
RADJ
OPT
74% INTVCC
36.5% INTVCC
RNTC
T
+
Li-Ion
4120 F07
2% INTVCC
The hot and cold trip points may be adjusted using a different type of thermistor, or a different RBIAS resistor, or by
adding a desensitizing resistor, RADJ, or by a combination
of these measures as shown in Figure 7. For example, by
increasing RBIAS to 12.4k, with the same thermistor as
before, the cold trip point moves down to –5°C, and the
hot trip point moves down to 34°C. If a Vishay Curve 1
thermistor with B25/85 = 3950 and resistance of 100k at
25°C is used, a 1% RBIAS resistor of 118k and a 1% RADJ
resistor of 12.1k results in a cold trip point of 0°C, and a
hot trip point of 39°C.
End-Of-Charge Indication and Safety Timeout
The LTC4120 uses a safety timer to terminate charging.
Whenever the LTC4120 is in constant current mode the
timer is paused, and if FB transitions through the VRCHG
threshold the timer is reset. When the battery voltage
reaches the float voltage, a safety timer begins counting down a 2-hour timeout. If charge current falls below
one-tenth of the programmed maximum charge current
(hC/10), the CHRG status pin rises, but top-off charge
current continues to flow until the timer finishes. After
the timeout, the LTC4120 enters a low power sleep mode.
Automatic Recharge
RBIAS
NTC
of the RBIAS resistor. For the same Vishay Curve 2 thermistor, this corresponds to approximately 40°C. With a
Vishay Curve 2 thermistor, the hot and cold comparators
both have about 2°C of hysteresis to prevent oscillations
about the trip points.
In sleep mode, the IC continues to monitor battery voltage. If the battery falls 2.2% (VRCHG or VRCHG_42) from
the full-charge float voltage, the LTC4120 engages an
automatic recharge cycle. Automatic recharge has a
built-in filter of about 0.5ms to prevent triggering a new
charge cycle if a load transient causes the battery voltage
to drop temporarily.
Figure 7. NTC Connections
16
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
OPERATION
State of Charge and Fault Status Pins
Precision Run/Shutdown Control
The LTC4120 contains two open-drain outputs which
provide charge status and signal fault indications. The
binary-coded CHRG pin pulls low to indicate charging at a
rate higher than C/10. The FAULT pin pulls low to indicate
a bad battery timeout, or to indicate an NTC thermal fault
condition. During NTC faults the CHRG pin remains low,
but when a bad battery timeout occurs the CHRG pin deasserts. When the open-drain outputs are pulled up with
a resistor, Table 3 summarizes the charger state that is
indicated by the pin voltages.
The LTC4120 remains in a low power disabled mode until
the RUN pin is driven above VEN (typically 2.45V). While
the LTC4120 is in disabled mode, current drain from the
battery is reduced to extend battery lifetime, the status pins
are both de-asserted, and the FBG pin is high impedance.
Charging can be stopped at any time by pulling the RUN
pin below 2.25V. The LTC4120 also offers an extremely
low operating current shutdown mode when the RUN pin
is pulled below VSD (typically 0.7V). In this condition less
than 20µA is drawn from the supply at IN.
Table 3. LTC4120 Open-Drain Indicator Outputs with Resistor
Pull-Ups
Differential Undervoltage Lockout
FAULT
CHRG
CHARGER STATE
High
High
Off or Topping Off Charging at a Rate Less Than C/10
High
Low
Charging at Rate Higher Than C/10
Low
High
Bad Battery Fault
Low
Low
NTC Thermal Fault Charging Paused
Low Battery Voltage Operation
The LTC4120 automatically preconditions heavily discharged batteries. If the battery voltage is below VLOWBAT
minus its hysteresis (typically 2.05V—e.g., battery pack
protection has been engaged) a DC current, ILOWBAT, is
applied to the BAT pin from the INTVCC supply. When the
battery voltage rises above VLOWBAT, the switching regulator is enabled and charges the battery at a trickle charge
level of 10% of the full-scale charge current (in addition
to the DC ILOWBAT current). Trickle charging of the battery
continues until the sensed battery voltage (sensed via
the feedback pin for the LTC4120) rises above the trickle
charge threshold, VTRKL. When the battery rises above
the trickle charge threshold, the full-scale charge current
is applied and the DC trickle charge current is turned off.
If the battery remains below the trickle charge threshold
for more than 30 minutes, charging terminates and the
fault status pin is asserted to indicate a bad battery.
After a bad battery fault, the LTC4120 automatically restarts
a new charge cycle once the failed battery is removed and
replaced with another battery. The LTC4120-4.2 monitors
the BATSNS pin voltage to sense LOWBAT and TRKL
conditions.
The LTC4120 monitors the difference between the battery
voltage, VBAT, and the input supply, VIN. If the difference
(VIN-VBAT) falls to VDUVLO, all functions are disabled and
the part is forced into shutdown mode until (VIN-VBAT) rises
above the VDUVLO hysteresis. The LTC4120-4.2 monitors
the BATSNS and IN pin voltages to sense DUVLO condition.
User Selectable Buck Operating Frequency
The LTC4120 uses a constant-frequency synchronous
step-down buck architecture to produce high operating
efficiency. The nominal operating frequency of the buck,
fOSC, is programmed by connecting the FREQ pin to
either INTVCC or to GND to obtain a switching frequency
of 1.5MHz or 750kHz, respectively. The high operating
frequency allows the use of smaller external components.
Selection of the operating frequency is a trade-off between
efficiency, component size, and margin from the minimum
on-time of the switcher. Operation at lower frequency
improves efficiency by reducing internal gate charge and
switching losses, but requires larger inductance values to
maintain low output ripple. Operation at higher frequency
allows the use of smaller components, but may require
sufficient margin from the minimum on-time at the lowest
duty cycle if fixed-frequency switching is required.
4120ff
For more information www.linear.com/LTC4120
17
LTC4120/LTC4120-4.2
OPERATION
PWM Dropout Detector
If the input voltage approaches the battery voltage, the
LTC4120 may require duty cycles approaching 100%. This
mode of operation is known as dropout. In dropout, the
operating frequency may fall well below the programmed
fOSC value. If the top switch remains on for eight clock
cycles, the dropout detector activates and forces the
bottom switch on for the remainder of that clock cycle
or until the inductor current decays to zero. This avoids
a potential source of audible noise when using ceramic
input or output capacitors and prevents the boost supply capacitor for the top gate drive from discharging. In
dropout operation, the actual charge current may not be
able to reach the full-scale programmed value. In such a
scenario the analog charge current monitor function does
not represent actual charge current being delivered.
Burst Mode Operation
At low charge currents, for example during constant-voltage
mode, the LTC4120 automatically enters Burst Mode operation. In Burst Mode operation the switcher is periodically
forced into standby mode in order to improve efficiency.
The LTC4120 automatically enters Burst Mode operation
after it exits constant-current (CC) mode and as the charge
current drops below about 80mA. Burst Mode operation
is triggered at lower currents for larger PROG resistors,
and depends on the input supply voltage. Refer to graph
Burst Mode Trigger Current and graph Typical Burst Mode
Waveform, in the Typical Performance Characteristics, for
more information on Burst Mode operation. Burst Mode
operation has some hysteresis and remains engaged for
battery currents up to about 150mA.
While in Burst Mode operation, the PROG pin voltage to
average charge current relationship is not well defined.
This is due to the PROG pin voltage falling to 0V in
18
between bursts, as shown in G14. If the PROG pin voltage
falls below 120mV for longer than 350µs this causes the
CHRG pin to de-assert, indicating C/10. Burst current ripple
depends on the selected switch inductor, and VIN/VBAT.
BOOST Supply Refresh
The BOOST supply for the top gate drive in the LTC4120
switching regulator is generated by bootstrapping the
BOOST flying capacitor to INTVCC whenever the bottom
switch is turned on. This technique provides a voltage of
INTVCC from the BOOST pin to the SW pin. In the event
that the bottom switch remains off for a prolonged period
of time, e.g., during Burst Mode operation, the BOOST
supply may require a refresh. Similar to the PWM dropout
timer, the LTC4120 counts the number of clock cycles
since the last BOOST refresh. When this count reaches
32, the next PWM cycle begins by turning on the bottom
side switch first. This pulse refreshes the BOOST flying
capacitor to INTVCC and ensures that the topside gate
driver has sufficient voltage to turn on the topside switch
at the beginning of the next cycle.
Operation Without an Input Supply or Wireless Power
When a battery is the only available power source, care
should be taken to eliminate loading of the IN pin. Load
current on IN drains the battery through the body diode
of the top side power switch as VIN falls below VSW. To
prevent this possibility, place a diode between the input
supply and the IN capacitor, CIN. The rectification diode
(D9 in Figure 5 and Figure 11) in the wireless power applications also eliminates this discharge path. Alternately,
a P-channel MOSFET may be placed in series with the BAT
pin provided care is taken to directly sense the positive
battery terminal voltage with FB via the battery resistive
divider. This is illustrated in Figure 15.
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
0.50
LX
LR
1:n
COUPLING COEFFICIENT (k)
IR
IAC
VR
4120 F08
Figure 8. Wireless Power Transfer
Wireless Power Transfer
In a wireless power transfer system, power is transmitted
using alternating magnetic fields. Power is transferred
based on the principle that an AC current in a transmitter coil produces an AC current in a receiver coil that is
placed in the magnetic field generated by the transmitter
coil. The magnetic field coupling is described by the mutual inductance, M. This term does not have a physical
representation but is referred to using the unit-less terms
k and n. Where k is the coupling coefficient:
k=
M
L X • LR
And n is the turns ratio—the number of turns in the receiver
coil divided by the number of turns in the transmitter coil:
n=
nR
L
= R
nX
LX
The turns ratio is proportional to the square root of the ratio
of receiver coil inductance to transmitter coil inductance.
In the wireless power transfer system an AC current, IAC,
applied to the transmit coil LX, produces an AC current in
the receive coil, LR of:
IR(AC) = 2 • π • M • IAC = 2 • π • k • √LX • LR • IAC
The coupling coefficient is a variable that depends on the
orientation and proximity of the transmitter coil relative
to the receiver coil. If the two coils are in a transformer,
then k = 1. If the two coils are completely isolated from
each other then k = 0. In a typical LTC4120-based wireless
power design, k varies from around 0.18 at 10mm spacing, to about 0.37 with the coils at 3mm spacing. This is
illustrated in Figure 9.
With low resistance in the LX and LR coils, the efficiency is
inherently high, even at low coupling ratios. The transmitter
in Figures 4 and 10 generates a sine wave at the resonant
frequency, fO, across the transmitter coil and capacitor
+ NO MISALIGNMENT
0.45
X
0.40 X
+
0.35 X
+X
+X
0.30
X
0.25
X
5mm MISALIGNMENT
X
10mm MISALIGNMENT
+X
X
0.20
+X
+X
X
X
0.15
0.10
0
1
2
3
4
5
6
7
COIL DISTANCE (mm)
8
9
10
4120 F09
Figure 9. Coupling Coefficient k vs Distance
(LX||CX). With a peak-to-peak amplitude that is proportional
to the applied input voltage:
VAC ≅ 2 • π • VDC
This generates a sinusoidal current in the transmit coil
with peak-to-peak amplitude:
IAC =
VAC
V
≅ DC
2 • π • fO • L X fO • L X
The AC voltage induced at the receive coil is a function
of both the applied voltage, the coupling, as well as the
impedance at the receiver. With no load at the receiver,
the open-circuit voltage, VIN(OC), is approximately:
VIN(OC) ≅ k • n • 2 • π • VDC
The receiver (shown in Figures 5 and 10) uses a resonant
tuned circuit followed by a rectifier to convert the induced
AC voltage into a DC voltage to power the LTC4120 and
charge a battery. Power delivered to the LTC4120 depends
on the impedance of the LTC4120 and the impedance of
the tuned circuit at the resonant frequency of the transmitter. The LTC4120 employs a proprietary circuit, called
dynamic harmonization control (DHC) that modulates the
impedance of the receiver depending on the voltage at the
input to the LTC4120. This technique ensures that over a
wide range of coupling coefficients the induced rectified
voltage does not exceed voltage compliance ratings when
the load goes away (e.g, when the battery is fully charged).
DHC efficiently adjusts the receiver impedance depending
on the load without compromising available power.
In the event that the coupling may become too large (e.g.
receiver coil is placed too close to the transmitter coil)
then it is recommended to place a Zener diode across the
4120ff
For more information www.linear.com/LTC4120
19
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
input to the LTC4120 to prevent exceeding the absolute
maximum rating of the LTC4120. Diode D6 (in Figure 4
and Figure 10) illustrates this connection.
tion of a 39V Zener diode (D6 in Figures 4 and 10) at the
input to the LTC4120 will prevent overvoltage conditions
from damaging the LTC4120.
The RMS voltage at the rectifier output depends on the
load of the LTC4120, i.e., the charge current, as well as the
applied AC current, IAC. The applied AC current depends
both on the components of the tuned network as well as
the applied DC voltage. The load at the receiver depends
on the state of charge of the battery. If the coupling and/
or the applied AC current is not well controlled, the addiVCC
4.75V TO 5.25V
LB1
68µH
Resonant Transmitter and Receiver
An example DC/AC transmitter is shown in Figure 10.
A 5V ±5% supply to the transmitter efficiently produces a
circulating AC current in LX, which is coupled to LR. For
higher voltage inputs, a pre-regulator DC/DC converter
can be used to generate 5V (see Figure 11). Power is
transmitted from transmitter to receiver at the resonant
TRANSMITTER
RECEIVER
C2S2
LB2
68µH
D1
LX
CX
0.3µF 5µH
C4
0.01µF
LR C2S1
C2P1
D2
D3
C5
0.01µF
DHC
IN
BOOST
SW
R1
100Ω
R2
100Ω
D2
D3
M1
U1
LTC4120
C2P2
C4
2.2µF
M2
INTVCC
C5
10µF
D4
39V
OPT
C1
10µF
C2
47µF
C3
L1
CHGSNS
BAT
+
FB
D1
D4
GND FBG
4120 F10
Figure 10. DC/AC Converter, Transmit/Receive Coils, Tuned Series Resonant Receiver and AC/DC Rectifier
HVIN
8V TO 38V
GND
C6
4.7µF
VIN
BD
BOOST
R3
150k
C7
0.068µF
R4
40.2k
SW
RUN/SS
U1
LT3480
SYNC
RT
FB
GND
PG
VC
C9
0.47µF
L3
4.7µF
D5
DFLS240L
R5
20k
C8
330pF
C10
22µF
R8
150k
M3
Si2333DS
M4
2N7002L
R10
100k
VCC
5V
CONNECT
TO Tx VCC
R7
536k
R6
100k
4120 F11
Figure 11. High Voltage Pre-Regulator for Transmitter
20
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
frequency, fO; which depends on both component values
as well as the load at the receiver. The tolerance of the
components selected in both the transmitter and receiver
circuits is critical to achieving maximum power transfer.
The voltages across the receiver components may reach
40V, so adequate voltage ratings must also be observed.
Resonant Converter Component Selection
It is recommended to use the components listed in Table 4
and Table 5 for the resonant transmitter and receiver
respectively. Figure 12 illustrates the PCB layout of the
embedded receiver coil. Figures 13 and 14 show the
finished transmitter and receiver. The 25mm ferrite bead
Table 4. Recommended Transmitter and High Voltage Pre-Regulator Components
Transmitter Components
ITEM
DESCRIPTION
MANUFACTURER/PART NUMBER
D2, D3
DIODE, SCHOTTKY, 40V, 2A
ON SEMI NSR10F40NXT5G
D1, D4
DIODE, ZENER, 16V, 350mW, SOT23
DIODES BZX84C16
M1, M2
MOSFET, SMT, N-CHANNEL, 60V, 11mΩ, S08
VISHAY Si4470EY-T1GE3
IND, SMT, 68µH, 0.41A, 0.4Ω, ±20%
TDK VLCF5028T-680MR40-2
LB1, LB2
C4, C5
CAP, CHIP, X7R, 0.01µF, ±10%, 50V, 0402
MURATA GRM155R71H103KA88D
VISHAY CRCW0402100RJNED
R1, R2
RES, CHIP, 100Ω, ±5%, 1/16W, 0402
CAP, CHIP, PPS, 0.15µF, ±2%, 50V
PANASONIC ECHU1H154GX9
CX1, 2
CAP, CHIP, PPS, 0.1µF, ±2%, 50V
PANASONIC ECHU1H104GX9
CAP, CHIP, PPS, 0.033µF, ±2%, 50V
PANASONIC ECHU1H333GX9
CAP, PPS, 0.15µF, ±2.5%, 63VAC, MKS02
WIMA MKS0D031500D00JSSD
CX (Opt)
WIMA MKS0D03100
CAP, PPS, 0.10µF, ±2.5%, 63VAC, MKS02
CAP, PPS, 0.033µF, ±2.5%, 63VAC, MKS02
WIMA MKS0D03033
5.0µH TRANSMIT COIL
TDK WT-505060-8K2-LT
LX
or 6.3µH TRANSMIT COIL
TDK WT-505090-10K2-A11-G
or 6.3µH TRANSMIT COIL
WÜRTH 760308111
or 5.0µH TRANSMIT COIL
INTER-TECHNICAL L41200T02
High Voltage Pre-Regulator Components
U1
LT3480EDD, PMIC 38V, 2A, 2.4MHz Step-Down Switching
LINEAR TECH LT3480EDD
Regulator with 70µA Quiescent Current
M3
MOSFET, SMT, P-CHANNEL, –12V, 32mΩ, SOT23
VISHAY Si2333DS
ON SEMI 2N7002L
M4
MOSFET, SMT, N-CHANNEL, 60V, 7.5Ω, 115mA, SOT23
D5
DIODE, SCHOTTKY, 40V, 2A, POWERDI123
DIODES DFLS240L
L3
IND, SMT, 4.7µH, 1.6A, 0.125Ω, ±20%
COILCRAFT LPS4018-472M
C6
CAP, CHIP, X5R, 4.7µF, ±10%, 50V, 1206
MURATA GRM155R71H4755KA12L
C7
CAP, CHIP, X5R, 4.7µF, ±10%, 50V, 0603
MURATA GRM188R71H683K
C8
CAP, CHIP, COG, 330pF, ±5%, 50V, 0402
TDK C1005COG1H331J
MURATA GRM188R71E474K
C9
CAP, CHIP, X7R, 0.47µF, ±10%, 25V, 0603
C10
CAP, CHIP, X5R, 22µF, ±20%, 6.3V, 0805
TAIYO-YUDEN JMK212BJ226MG
R3, R8
RES, CHIP, 150k, ±5%, 1/16W, 0402
VISHAY CRCW0402150JNED
R4
RES, CHIP, 40.2k, ±1%, 1/16W, 0402
VISHAY CRCW040240K2FKED
R5
RES, CHIP, 20k, ±1%, 1/16W, 0402
VISHAY CRCW040220K0FKED
R6, R10
RES, CHIP, 100k, ±1%, 1/16W, 0402
VISHAY CRCW0402100KFKED
VISHAY CRCW0402536KFKED
R7
RES, CHIP, 536k, ±1%, 1/16W, 0402
1C = 300nF with 5µH L coil, or C = 233nF with 6.3µH L coil.
X
X
X
X
2Pay careful attention to assembly guidelines when using ECHU capacitors, as the capacitance value may shift if the capacitor is over heated while
soldering. Plastic film capacitors such as Panasonic ECHU series or Metallized Polypropylene capacitors such as WIMA MKP as suitable for the
transmitter
4120ff
For more information www.linear.com/LTC4120
21
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
Table 5. Recommended Receiver Components
ITEM
D1, D2, D3
D4 (Opt)
LR
DESCRIPTION
DIODE, SCHOTTKY, 40V, 2A, POWERDI123
DIODE, ZENER, 39V, ±5%, 1W, POWERDI123
IND, EMBEDDED, 47µH, 43 TURNS WITH 25mm FERRITE BEAD
or 47µH RECEIVER COIL
or 47µH RECEIVER COIL
or 48µH RECEIVER COIL
L1
C2P1
C2P2
C2S1
C2S2
C1
C2
C3
C4
U1
IND, SMT, 15µH, 260mΩ, ±20%, 0.86A, 4mm × 4mm
CAP, CHIP, COG, 0.0047µF, ±5%, 50V, 0805
CAP, CHIP, COG, 0.00018µF, ±5%, 50V, 0603
CAP, CHIP, COG, 0.022µF, ±5%, 50V, 0805
CAP, CHIP, COG, 0.0047µF, ±5%, 50V, 0805
CAP, CHIP, X5R, 10µF, ±20%, 16V, 0805
CAP, CHIP, X5R, 47µF, ±10%, 16V, 1210
CAP, CHIP, X7R, 0.01µF, ±20%, 6.3V. 0402
CAP, CHIP, X5R, 10µF, ±20%, 16V, 0805
400mA WIRELESS SYNCHRONOUS BUCK BATTERY CHARGER
MANUFACTURER/PART NUMBER
DIODES DFLS240L
DIODES DFLZ39
EMBEDDED 4-LAYER PCB (see Figure 12)
ADAMS MAGNETICS B67410-A0223-X195
TDK WR282840-37K2-LR3
WÜRTH 760308101303
INTER-TECHNICAL L41200R02
COILCRAFT LPS4018-153ML
MURATA GRM21B5C1H472JA01L
KEMET C0603C182J5GAC7533
MURATA GRM21B5C1H223JA01L
MURATA GRM21B5C1H472JA01L
TDK C2012X5R1C106K
MURATA GRM32ER61C476KE15L
TDK C1608X7R1H103K
TDK C2012X5R1C106K
LINEAR TECH LTC4120
LAYER STRUCTURE
L1 – TOP SIDE
L2
L3
L4 – BOTTOM SIDE
FINISHED THICKNESS TO BE 0.031" ±0.005"
TOTAL OF 4 LAYERS WITH 2oz CU ON THE
OUTER LAYERS AND 2oz CU ON THE INNER
LAYERS
TOP METAL
2nd METAL
3rd METAL
BOTTOM METAL
4120 F12
Figure 12. 4-Layer PCB Layout of Rx Coil
22
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
Figure 13. Tx Layout: Demo Circuit 1968A
in Figure 14 covers the embedded receiver coil described
in Figure 12. Gerber layout files for both the transmitter
and receiver boards are available at the following link:
Figure 14. Rx Layout with Ferrite Shield: Demo Circuit 1967A-B
http://www.linear.com/product/LTC4120#demoboards
Alternative component values can be chosen by following
the design procedure outlined below.
Resonant Transmitter Tuning: LX, CX
The basic transmitter (shown in Figure 4) has a resonant
frequency, fO, that is determined by components LX, and
CX. The selection of LX and CX are coupled so as to obtain
the correct operating frequency. The selection of LX and
LR is also coupled to ideally obtain a turns ratio of 1:3.
Having selected a transmitter inductor, LX, the transmitter
capacitor should be selected to obtain a resonant frequency
of 130kHz. Due to limited selection of standard values,
several standard value capacitors may need to be used
in parallel to obtain the correct value for fO:
fO ≅
Resonant Receiver Tuning: LR, C2S, C2P
The tuned circuit resonance of the receiver, fT, is determined
by the selection of LR and C2S + C2P. Select the capacitors to obtain a resonant frequency 1% to 3% below fO:
fT ≅
2 • π • LR • (C2P + C2S)
As in the case of the transmitter, multiple parallel capacitors
may need to be used to obtain the optimum value. Finally,
select the detuned resonance, fD to be about 5% to 15%
higher than the tuned resonance, keeping the value of
C2P below 30nF to limit power dissipation in the DHC pin:
1
= 130kHz
2 • π • L X • CX
1
fD ≅
1
2 • π • LR • C2S
Alternative Transmitter Options
The transmitter inductor and capacitor, LX and CX, support
a large circulating current. Series resistance in the inductor
is a source of loss and should be kept to a minimum for
optimal efficiency. Likewise the transmitter capacitor(s),
CX, must support large ripple currents and must be selected
with adequate voltage rating and low dissipation factors.
The resonant DC/AC transmitter discussed in the previous
section is a basic and inexpensive to build transmitter.
However, this basic transmitter requires a relatively precise DC input voltage to meet a given set of receive power
requirements. It is unable to prevent power transmission
to foreign metal objects—and can therefore cause these
objects to heat up. Furthermore, the operating frequency
of the basic transmitter can vary with component selection.
4120ff
For more information www.linear.com/LTC4120
23
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
LTC4120 customers can also choose more advanced
transmitter options such as the LTC4125. With additional
features such as: foreign metal detection; optimum power
search and AutoResonant™ operating frequency. For more
information on advanced transmitter options refer to the
Wireless Power Users Guide.
Maximum Battery Power Considerations
Using one of the approved transmitter options with this
wireless power design provides a maximum of 2W at the
input to the LTC4120. It is optimized for supplying 400mA
of charge current to a 4.2V Li-Ion battery. If a higher battery voltage is selected, then a lower charge current must
be used as the maximum power available is limited. The
maximum battery charge current, ICHG(MAX), that may
be programmed for a given float voltage, VFLOAT, can be
calculated based on the charger efficiency, ηEFF, as:
ICHG(MAX) ≤
Input Voltage and Minimum On-Time
The LTC4120 can operate from input voltages up to 40V. The
LTC4120 maintains constant frequency operation under
most operating conditions. Under certain situations with
high input voltage and high switching frequency selected
and a low battery voltage, the LTC4120 may not be able
to maintain constant frequency operation. These factors,
combined with the minimum on-time of the LTC4120,
impose a minimum limit on the duty cycle to maintain
fixed-frequency operation. The on-time of the top switch
is related to the duty cycle (VBAT/VIN) and the switching
frequency, fOSC in Hz:
VBAT
fOSC • VIN
The maximum input voltage allowed to maintain constant
frequency operation is:
VLOWBAT
fOSC • tMIN(ON)
Exceeding the minimum on-time constraint does not affect
charge current or battery float voltage, so it may not be
of critical importance in most cases and high switching
frequencies may be used in the design without any fear of
severe consequences. As the sections on Inductor Selection
and Capacitor Selection show, high switching frequencies
allow the use of smaller board components, thus reducing
the footprint of the applications circuit.
Fixed-frequency operation may also be influenced by
dropout and Burst Mode operation as discussed previously.
Switching Inductor Selection: LSW
The primary criterion for switching inductor value selection
in an LTC4120 charger is the ripple current created in that
inductor. Once the inductance value is determined, the
saturation current rating for that inductor must be equal
to or exceed the maximum peak current in the inductor,
IL(PEAK). The peak value of the inductor current is the sum
of the programmed charge current, ICHG, plus one-half of
the ripple current, ∆IL. The peak inductor current must
also remain below the current limit of the LTC4120, IPEAK:
24
VIN(MAX) =
where VLOWBAT, is the lowest battery voltage where the
switcher is enabled.
ηEFF • 2W
VFLOAT
The charger efficiency, ηEFF, depends on the operating
conditions and may be estimated using the Buck Efficiency
curve in the Typical Performance Characteristics. Do
not select a charge current greater than this limit when
selecting RPROG.
tON =
When operating from a high input voltage with a low battery voltage, the PWM control algorithm may attempt to
enforce a duty cycle which requires an on-time lower than
the LTC4120 minimum, tMIN(ON). This minimum duty cycle
is approximately 18% for 1.5MHz operation or 9% for
750kHz operation. Typical minimum on-time is illustrated
in graph G11 in the Typical Performance Characteristics
section. If the on-time is driven below tMIN(ON), the charge
current and battery voltage remain in regulation, but the
switching duty cycle may not remain fixed, and/or the
switching frequency may decrease to an integer fraction
of its programmed value.
IL(PEAK) = ICHG +
∆IL
< IPEAK
2
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
The current limit of the LTC4120, IPEAK, is at least 585mA
(and at most 1250mA). The typical value of IPEAK is
illustrated in graph RSNS Current Limit vs Temperature,
in the Typical Performance Characteristics.
For a given input and battery voltage, the inductor value
and switching frequency determines the peak-to-peak
ripple current amplitude according to the following formula:
∆IL =
( VIN – VBAT ) • VBAT
fOSC • VIN • LSW
Ripple current is typically set to be within a range of 20%
to 40% of the programmed charge current, ICHG. To obtain
a ripple current in this range, select an inductor value using the nearest standard inductance value available that
obeys the following formula:
LSW ≥
( VIN(MAX) – VFLOAT ) • VFLOAT
fOSC • VIN(MAX) • ( 30% •ICHG )
Then select an inductor with a saturation current rating at
a value greater than IL(PEAK).
Input Capacitor: CIN
The LTC4120 charger is biased directly from the input
supply at the VIN pin. This supply provides large switched
currents, so a high quality, low ESR decoupling capacitor
is recommended to minimize voltage glitches at VIN. Bulk
VIN
VIN
CHRG
BST
10µF
RUN
LTC4120
2.2µF
SW
CHGSNS
BAT
capacitance is a function of the desired input ripple voltage
(∆VIN), and follows the relation:
Input ripple voltages (∆VIN) above 10mV are not recommended. 10µF is typically adequate for most charger
applications, with a voltage rating of 40V.
Reverse Blocking
When a fully charged battery is suddenly applied to the BAT
pin, a large in-rush current charges the CIN capacitor through
the body diode of the LTC4120 topside power switch. While
the amplitude of this current can exceed several Amps, the
LTC4120 will survive provided the battery voltage is below
the maximum value of 11V. To completely eliminate this
current, a blocking P-channel MOSFET can be placed in
series with the BAT pin. When the battery is the only source
of power, this PFET also serves to decrease battery drain
current due to any load placed at VIN. As shown in Figure
15, the PFET body diode serves as the blocking component
since CHRG is high impedance when the battery voltage
is greater than the input voltage. When CHRG pulls low,
i.e. during most of a normal charge cycle, the PFET is on
to reduce power dissipation. This PFET requires a forward
current rating equal to the programmed charge current and
a reverse breakdown voltage equal to the programmed float
voltage. Figure 15 illustrates how to add a blocking PFET
connected with the LTC4120.
4.99k*
22nF LSW
49.9k
4.7µF
INTVCC
CIN(BULK) =
VBAT
VIN
(µF )
∆VIN
ICHG
470k
22µF
SI2343DS
+
Li-Ion
RFB1
PROG
FB
RFB2
RPROG
GND
FBG
4120 F15
*ADD 4.99k WHEN MAX BAT VOLTAGE APPROACHES 85% OF VGS LIMIT FOR Si2343.
Figure 15. Reverse Blocking with a P-Channel MOSFET in Series with the BAT Pin
4120ff
For more information www.linear.com/LTC4120
25
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
BAT Capacitor and Output Ripple: CBAT
The LTC4120 charger output requires bypass capacitance
connected from BAT to GND (CBAT). A 22µF ceramic
capacitor is required for all applications. In systems
where the battery can be disconnected from the charger
output, additional bypass capacitance may be desired.
In this type of application, excessive ripple and/or low
amplitude oscillations can occur without additional output
bulk capacitance. For optimum stability, the additional bulk
capacitance should also have a small amount of ESR. For
these applications, place a 100µF low ESR non-ceramic
capacitor (chip tantalum or organic semiconductor capacitors such as Sanyo OS-CONs or POSCAPs) from BAT to
GND, in parallel with the 22µF ceramic bypass capacitor,
or use large ceramic capacitors with an additional series
ESR resistor of less than 1Ω. This additional bypass
capacitance may also be required in systems where the
battery is connected to the charger with long wires. The
voltage rating of all capacitors applied to CBAT must meet
or exceed the battery float voltage.
INTVCC supply is enabled, and when INTVCC rises above
UVINTVCC the charger is enabled.
Calculating Power Dissipation
The user should ensure that the maximum rated junction
temperature is not exceeded under all operating conditions.
The thermal resistance of the LTC4120 package (θJA) is
54°C/W; provided that the exposed pad is soldered to sufficient PCB copper area. The actual thermal resistance in
the application may depend on forced air cooling or other
heat sinking means, and especially the amount of copper
on the PCB to which the LTC4120 is attached. The actual
power dissipation while charging is approximated by the
following formula:
PD ≅ ( VIN – VBAT ) •ITRKL
+VIN •IIN(SWITCHING)
+RSNS •ICHG2
+RDS(ON)(TOP) •
Boost Supply Capacitor: CBST
VBAT
•I 2
VIN CHG
 V 
+RDS(ON)(BOT) •  1– BAT  •ICHG2
VIN 

The BOOST pin provides a bootstrapped supply rail that
provides power to the top gate drivers. The operating voltage of the BOOST pin is internally generated from INTVCC
whenever the SW pin pulls low. This provides a floating
voltage of INTVCC above SW that is held by a capacitor tied
from BOOST to SW. A low ESR ceramic capacitor of 10nF
to 22nF is sufficient for CBST, with a voltage rating of 6V.
During trickle charge (VBAT < VTRKL) the power dissipation
may be significant as ITRKL is typically 10mA, however
during normal charging the ITRKL term is zero.
INTVCC Supply and Capacitor: CINTVCC
TJ = TA + PD • θJA
Power for the top and bottom gate drivers and most other
internal circuitry is derived from the INTVCC pin. A low
ESR ceramic capacitor of 2.2µF is required on the INTVCC
pin. The INTVCC supply has a relatively low current limit
(about 20mA) that is dialed back when INTVCC is low to
reduce power dissipation. Do not use the INTVCC voltage
to supply power for any external circuitry apart from the
NTCBIAS network. When the RUN pin is above VEN the
where TA is the ambient operating temperature.
26
The junction temperature can be estimated using the following formula:
Significant power is also consumed in the transmitter
electronics. The large AC voltage generated across the LX
and CX tank results in power being dissipated in the DC
resistance of the LX coil and the ESR of the CX capacitor.
The large induced magnetic field in the LX coil may also
induce heating in nearby metallic objects.
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
PCB Layout
To prevent magnetic and electrical field radiation and
high frequency resonant problems, proper layout of the
components connected to the LTC4120 is essential. For
maximum efficiency, the switch node rise and fall times
should be minimized. The following PCB design priority
list will help insure proper topology. Layout the PCB using
the guidelines listed below in this specific order.
1. Keep foreign metallic objects away from the transmitter coil. Metallic objects in proximity to the transmit
coil will suffer from induction heating and will be a
source of power loss. With the exception of a ferrite
shield that can be used to improve the coupling from
transmitter coil to receiver coil when placed behind
the transmitter coil.
Advanced transmitters from PowerByProxi include
features to detect the presence of foreign metallic
objects that mitigates this issue.
2. VIN input capacitor should be placed as close as possible to the IN and GND pins, with the shortest copper
traces possible and a via connection to the GND plane
3. Place the switching inductor as close as possible to the
SW pin. Minimize the surface area of the SW pin node.
Make the trace width the minimum needed to support
the programmed charge current, and ensure that the
spacing to other copper traces be maximized to reduce
capacitance from the SW node to any other node.
4. Place the BAT capacitor adjacent to the BAT pin and
ensure that the ground return feeds to the same copper that connects to the input capacitor ground before
connecting back to system ground.
5. Route analog ground (RUN ground and INTVCC capacitor ground) as a separate trace back to the LTC4120
GND pin before connecting to any other ground.
6. Place the INTVCC capacitor as close as possible to the
INTVCC pin with a via connection to the GND plane.
7. Route the DHC trace with sufficient copper and vias
to support 350mA of RMS current, and ensure that
the spacing from the DHC node to other copper traces
be maximized to reduce capacitance and radiated EMI
from the DHC node to other sensitive nodes.
8. It is important to minimize parasitic capacitance on
the PROG pin. The trace connecting to this pin should
be as short as possible with extra wide spacing from
adjacent copper traces.
9. Minimize capacitive coupling to GND from the FB pin.
10.Maximize the copper area connected to the exposed
pad. Place via connections directly under the exposed
pad to connect a large copper ground plane to the
LTC4120 to improve heat transfer.
Design Examples
The design example illustrated in Figure 17, reviews the
design of the resonant coupled power transfer charger
application. First the design of the wireless power receiver
circuit is described. Then consider the design for the charger
function given the maximum input voltage, a battery float
voltage of 8.2V, and a charge current of 200mA for the
LTC4120. This example also demonstrates how to select
the switching inductance value to avoid discontinuous
conduction; where switching noise increases.
The wireless power receiver is formed by the tuned network LR and C2P, C2S. This tuned network automatically
modulates the resonance of the tank with the DHC pin of
the LTC4120 to optimize power transfer. The resonant
frequency of the tank should match the oscillation frequency of the transmitter. Given the transmitter shown
in Figure 4 this frequency is 130kHz. The tuned receiver
resonant frequency is:
fT =
1
= 127kHz
2 • π • LR • (C2P + C2S)
In this design example, the de-tuned resonant frequency is:
fD =
1
= 142kHz
2 • π • LR • C2S
fD should be set between 5% and 15% higher than fT. A
higher level gives more control range but results in more
power dissipation.
A 47µH coil is selected for LR to obtain a turns ratio of 3:1
from the transmitter coil, LX = 5µH.
For more information www.linear.com/LTC4120
4120ff
27
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
Now C2S can be calculated to be 26.7nF. Two standard
parallel 50V rated capacitors, 22nF and 4.7nF, provide a
value within 1% of the calculated C2S. Now C2P can be
calculated to be 6.5nF which can be obtained with 4.7nF
and 1.8nF capacitors in parallel. All of the capacitors should
be selected with 5% or better tolerance.
The rectifier, D8, D9 and D5 are selected as 50V rated
Schottky diodes.
Now consider the design circuit for the LTC4120 charger
function. First, the external feedback divider, RFB1/RFB2,
is found using standard 1% values:
With an 8.2V float voltage the maximum charge current
available is limited by the maximum power available from
the RCPT at ηEFF = 85% charger efficiency:
85% • 2W
= 207mA
8.2V
RPROG =
hPROG • VPROG
= 6.04k
ICHG
The maximum loaded input voltage is used to select the
operating frequency and influences the value of the switching inductor. The saturation current rating of the switching
inductor is selected based on the worst case conditions
at the maximum open-circuit voltage.
28
VIN(OC) = k • n • π • VIN(TX)
VIN(OC) = 0.37 • 3 • 3.14 • 5V = 34.9V
∆IL =
(34.9V – 8.2V ) • 8.2V
1.5MHz • 56µH • 34.9V
= 75mA
This results in a worst-case peak inductor current of:
While charging a battery, the resonant receiver is loaded
by the charge current, this load reduces the input voltage
from the open-circuit value to a typical voltage in a range
from 12V (at UVCL) up to about 26V. The amplitude of
this voltage depends primarily on the amount of coupling
between the transmitter and the receiver, typically this
voltage is about 17V.
(17V – 8.2V ) • 8.2V
= 48µH
1.5MHz • 17V • ( 30% • 200mA )
56µH is the next standard inductor value that is greater than
this minimum. This inductor value results in a worst-case
ripple current at the input open-circuit voltage, VIN(OC).
VIN(OC) is estimated based on the transmitter design in
Figure 4, at the largest coupling coefficient k = 0.37 as:
A charge current of 200mA is achieved by selecting a
standard 1% RPROG resistor of:
5V
= 476ns > tMIN(ON)
1.5MHz • 17V
Now the switching inductor value is calculated. The inductor value is calculated based on achieving a 30% ripple
current. The ripple current is calculated at the typical input
operating voltage of 17V:
With these resistors, and including the resistance of the
FBG pin, the battery float voltage is 8.212V.
tON =
L3 >
8.2V • 588k
RFB1 =
≅ 2.00M
2.4V
2.00M • 588k
RFB2 =
≅ 825k
2.00M – 588k
ICHG(MAX) ≤
A typical 2-cell Li-Ion battery pack engages pack protection
for VBAT less than 5V, this is the lowest voltage considered
for determining the on-time and selecting the 1.5MHz
operating frequency.
IL(PEAK) = ICHG +
∆IL
= 237mA
2
Select an inductor with a saturation current rating greater
than the worst-case peak inductor current of 237mA.
Select a 50V rated capacitor for CIN = 10µF to achieve an
input voltage ripple of 10mV at the typical operating input
voltage of 17V:
∆VIN =
8.2V
17V = 10mV
10µF
200mA •
And select 6V rated capacitors for CINTVCC = 2.2µF,
CBOOST = 22nF, and CBAT = 22µF. Optionally add diode D6,
a 1W, 39V Zener diode if the coupling from transmitter to
receiver coils is not well enough controlled to ensure that
VIN remains below 39V when the battery is fully charged.
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
APPLICATIONS INFORMATION
Finally the RUN pin divider is selected to turn on the charger once the input voltage reaches 11.2V. With R3 = 374k
and R4 = 102k the RUN pin reaches 2.4V at VIN = 11.2V.
With this RUN pin divider, the LTC4120 is disabled once
VIN falls below 10.5V.
PD = 20V • 5mA + 0.3Ω• 0.2A 2
For this design example, power dissipation during trickle
charge, where the switching charge current is 20mA at VBAT
= 3V and IIN switching = 5mA, is calculated as follows:
This dissipated power results in a junction temperature
rise of 6°C over ambient.
PD = ( 20V – 3V ) • 10mA + 20V • 5mA
+0.3Ω• 0.02A 2 + 0.8Ω•
8.2V
• 0.2A 2
20V
 8.2V 
 • 0.2A 2 = 0.14mW
+0.5Ω•  1–
20V 

+0.8Ω•
Design Example 2: Operation with the LTC4125
3V
• 0.02A 2
20V
The LTC4125 is a 5W AutoResonant wireless power
transmitter that offers several advantages over the simple
transmitter shown in Figure 10, including foreign object
detection, external overtemperature detection, automatic
tuning of switching frequency and transmit power. When
operating the LTC4120 receiver with the LTC4125, the
DHC pin serves to enable an external shunt regulator
that optimizes the input supply voltage to the LTC4120
as shown in Figure 16. For more information on using the
LTC4125 see the LTC4125 data sheet.

3V 
2
+0.5Ω•  1–
 • 0.02A
20V


= 0.27W
This dissipated power results in a junction temperature
rise of:
PD • θJA = 0.27W • 54°C/W = 15°C
During regular charging with VBAT > VTRKL, the power
dissipation reduces to:
IIN
4.5V
TO
5.5V
33nF
20mΩ
DR1
VIN
1µF
100k
DSTAT
100k
IN
DTH
STAT
CTX
100nF
LTC4125
IN
PTH1
100k
100V
FB
EN
IMON
348k
CTD
CTS
470pF
GND
47µF
10nF
L1
15µH
CHGSNS
DFB
DC1
PTH2
QR1
DHC
BOOST
LTC4120-4.2
VIN
0.1µF
M1
RC
1k
SW
SW2
IS+
10nF
24.9k
RUN
LRX
47µH
RNTCTX
IS–
DC
AIR GAP
3mm
TO
10mm
SW1
59.0k
10nF
LTX
24µH
NTC
PTHM
11.3k
10k
IN1 IN2
FTH
7.87k
47µF
x2
DFLZ39
10µF
DR2
2.21k
FAULT
BAT
CHRG
BATSNS
PROG
GND FREQ INTVCC
NTC
CFB1
0.1µF
5.23k
3.01k
10k
2.2µF
RNTCRX
4.7nF
LTX: 760308100110
CTX: C3216C0G2A104J160AC
CFB1: GRM188R72A104KA35D
DC1: CDBQR70
DSTAT: LTST-C193KGKT-5A
DFB: BAS521-7
RNTCTX: NTHS0603N02N1002J
RED INDICATES HIGH VOLTAGE PARTS
+
SINGLE
CELL
Li-Ion
BATTERY
PACK
DR1, DR2, DR3: DFLS240L
DC: BZT52C13
4120 F16
M1: Si7308DN
QR1: PMBT3904M
RNTCRX: NTHS0402N02N1002F
LRX: PCB COIL AND FERRITE: B67410-A0223-X195
OR 760308101303
L1: LPS4018-153ML
Figue 16. LTC4125 Driving a 24μH Transmit Coil at 103kHz, with 1.3A Input Current Threshold, 119kHz Frequency Limit
and 41.5°C Transmit Coil Surface Temperature Limit in a Wireless Power System with LTC4120-4.2 as a 400mA Single
Cell Li-Ion Battery Charger at the Receiver
4120ff
For more information www.linear.com/LTC4120
29
LTC4120/LTC4120-4.2
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC4120#packaging for the most recent package drawings.
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691 Rev Ø)
0.70 ±0.05
3.50 ±0.05
1.45 ±0.05
2.10 ±0.05 (4 SIDES)
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 ±0.05
15
PIN 1
TOP MARK
(NOTE 6)
16
0.40 ±0.10
1
1.45 ± 0.10
(4-SIDES)
2
(UD16) QFN 0904
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)
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
30
0.25 ±0.05
0.50 BSC
4120ff
For more information www.linear.com/LTC4120
LTC4120/LTC4120-4.2
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE
A
12/13
Updated Table 4 component values and brands.
20
B
03/14
Removed word “battery” from float voltage range bullet.
Modified various specification limits and removed some temp dots.
Modified frequency range, resistor values and Note 3.
Amended IIN curves.
Modified text to reflect typical fOSC values.
Updated text for VPROG servo.
Amended equation for fD.
Modified ICHG equation.
Changed description of End-Of-Charge indication.
Modified typical fOSC values.
Modified Resonant Converter Selection.
Added high voltage pre-regulator schematic.
Added Table 4: Recommended Transmitter and High Voltage Pre-Regulator Components.
Added Table 5: Recommended Receiver Components.
Added Figure 11, PCB Layout of Rx Coil.
Added Figure 12, Tx layout: photo of Demo Circuit 1968A.
Added Figure 13, Rx layout: photo of Demo Circuit 1967A-B
Modified text of fOSC and fT.
Modified fT equation.
Modified equation for tON, L3, ∆IL, and IL(PEAK) and changed power dissipation calculations.
1
3
4
7
8
9
14
15
16
17
20
20
20
20
20
20
20
23
28
29
C
05/14
Increased minimum VIN to 12.5V
Added fixed 4.2V float version, throughout document, also added electrical parameters for –4.2
Increased IFB specification to TYP 25nA
Reduced min RECHG threshold to –38mV
Modified VPROG servo voltage spec by +3mV and –3mV
Loosened VTRKL threshold voltage spec by –20mV and +10mV
Increased TYP VTRKL hysteresis spec to 50mV
Changed conditions on ISW specification to IN = Open-Circuit from IN = Float
Revised RSNS current limit typical performance characteristics curve
Added typical VFLOAT performance characteristics curve
Corrected error in IIN(SWITCHING) Current curve (x-axis)
Added Block Diagram of –4.2 BATSNS connections
Changed VIN labels to IN in Figure 4, 5, and 10
Remove SW inductor selection Tables 6, 7, 8, and 9
Changed location of BAT decoupling cap in Figure 15 with reverse blocking diode
Corrected error in L3 equation and substituted correct 56µH inductor
D
01/15
Change CBAT from 10µF to 22µF
Add Würth P/N for RX coil
Add INTER-TECH P/N for TX and RX coils
Remove dos on 68µ bias inductor in basic TX schematic for clarity
E
05/15
Clarified Battery Charge Current vs Temperature curve
Clarified End-of-Charge and Battery Recharge sections
Modified Operation without an Input Supply section
Enhanced Reverse Blocking section
Modified INTVCC Supply and Capacitor section
F
02/16
Removed INTVCC spec. Moved Note 4 to UV_INTVCC spec.
Modified INTVCC pin definition.
Included LTC4125 in Applications Information.
Added 4.99k Note.
Added paragraph and Figure 16 from LTC4125 data sheet.
Renumbered Figure 17. Added to Related Parts Table.
1, 3
1 to 32
3
3
3
4
4
4
5
6
8
11
12, 13, 20
N/A
25
28
1, 9, 10, 11, 14, 25,
26, 29 and 32
22
21, 22
12, 20
6
16
18
25,26
26
3
9
24
25
29
32
4120ff
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 representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LTC4120
31
LTC4120/LTC4120-4.2
TYPICAL APPLICATION
C2S
26.7nF
D9
IN
D8
CIN
10µF
D5
D6
OPT
2k
374k
C2P
6.5nF
5µH
FAULT
RUN
CHGSNS
BAT
DHC
FB
102k
Tx CIRCUITRY
LX
INTVCC
FREQ
BOOST
2k
LTC4120
SW
CHRG
LR
CBST
22nF
RFB1
2.00M
CINTVCC
2.2µF
LSW
56µH
VFLOAT
8.2V
CBAT
22µF
10k
RFB2
825k
FBG
47µH
GND
D5, D8, D9: DFLS240L
D6: MMSZ5259BT1G OR DFLZ39 (OPT)
LSW: SLF6028-470MR59
T: NTHS0402N02N1002F
NTC
PROG
T
RPROG
6.04k
+
Li-Ion
4120 F17
Figure 17. Resonant Coupled Power Transfer Charger Application
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
AN138
Wireless Power Users Guide
LTC3335
Nanopower Buck-Boost with
Intergrated Coulomb Counter
LT3650-8.2/
LT3650-8.4
Monolithic 2A Switch Mode
Standalone 9V ≤ VIN ≤ 32V (40V Absolute Maximum), 1MHz, 2A Programmable Charge Current, Timer
Non-Synchronous 2-Cell Li-Ion or C/10 Termination, Small and Few External Components, 3mm × 3mm DFN-12 Package “-8.2” for 2×
4.1V Float Voltage Batteries, “-8.4” for 2× 4.2V Float Voltage Batteries
Battery Charger
LT3650-4.1/
LT3650-4.2
Monolithic 2A Switch Mode
Standalone 4.75V ≤ VIN ≤ 32V (40V Absolute Maximum), 1MHz, 2A Programmable Charge Current,
Non-Synchronous 1-Cell Li-Ion Timer or C/10 Termination, Small and Few External Components, 3mm × 3mm DFN-12 Package “-4.1”
Battery Charger
for 4.1V Float Voltage Batteries, “-4.2” for 4.2V Float Voltage Batteries
LT3652HV
Power Tracking 2A Battery
Charger
Input Supply Voltage Regulation Loop for Peak Power Tracking in (MPPT) Solar Applications Standalone,
4.95V ≤ VIN ≤ 34V (40V Absolute Maximum), 1MHz, 2A Charge Current, 3.3V ≤ VOUT ≤ 18V. Timer or
C/10 Termination, 3mm × 3mm DFN-12 Package and MSOP-12 Packages
LTC4070
Li-Ion/Polymer Shunt Battery
Charger System
Low Operating Current (450nA), 1% Float Voltage Accuracy Over Full Temperature and Shunt Current
Range, 50mA Maximum Internal Shunt Current (500mA with External PFET), Pin Selectable Float
Voltages: 4.0V, 4.1V, 4.2V. Ultralow Power Pulsed NTC Float Conditioning for Li-Ion/Polymer Protection,
8-Lead (2mm × 3mm) DFN and MSOP
LTC4071
Li-Ion/Polymer Shunt Battery
Charger System with Low
Battery Disconnect
Integrated Pack Protection, <10nA Low Battery Disconnect Protects Battery From Over-Discharge. Low
Operating Current (550nA), 1% Float Voltage Accuracy Over Full Temperature and Shunt Current Range,
50mA Maximum Internal Shunt Current, Pin Selectable Float Voltages: 4.0V, 4.1V, 4.2V. Ultralow Power
Pulsed NTC Float Conditioning for Li-Ion/Polymer Protection, 8-Lead (2mm × 3mm) DFN and MSOP
LTC4065/
LTC4065A
Standalone Li-Ion Battery
Charger in 2mm × 2mm DFN
4.2V ±0.6% Float Voltage, Up to 750mA Charge Current ; “A” Version Has /ACPR Function. 2mm × 2mm
DFN Package
LTC4123
25mA NiMH Wireless
Charger-Receiver
Low Minimum Input Voltage: 2.2V, Temperature Compensated Charge Voltage
LTC4125
5W AutoResonant Wireless
Power Transmitter
Monolithic AutoResonant Full Bridge Driver. Transmit Power Automatically Adjusts to Receiver Load,
Foreign Object Detection, Wide Operating Switching Frequency Range: 50kHz to 250kHz, Input Voltage
Range 3V to 5.5V, 20-Lead 4mm × 5mm QFN Package
32
680nA Input Quiescent Current (Output in Regulation at No Load) 1.8V to 5.5V Input Operating Range,
Up to 50mA of Output Current, Up to 90% Efficiency
4120ff
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC4120
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC4120
LT 0216 REV F • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2013