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)
n 50mA 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.
All registered trademarks and 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
Rev. G
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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 tMIN(ON)
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:
L3 >
( 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:
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:
= 6.04k
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.
28
With these resistors, and including the resistance of the
FBG pin, the battery float voltage is 8.212V.
85% • 2W
considered for determining the on-time and selecting the
1.5MHz operating frequency.
IL(PEAK) = ICHG +
∆IL
2
= 237mA
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:
8.2V
17V = 10mV
10µF
200mA •
∆VIN =
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.
Rev. G
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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•
3V
20V
Design Example 2: Operation with the LTC4125
• 0.02A 2
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
8.2V
• 0.2A 2
20V
⎛
8.2V ⎞⎟
• 0.2A 2 = 0.14mW
+0.5Ω• ⎜⎜ 1–
⎟
20V ⎠
⎝
+0.8Ω•
DR1
VIN
1µF
100k
DSTAT
100k
IN
DTH
47µF
x2
STAT
IN1 IN2
59.0k
10nF
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
PTHM
11.3k
LTX
24µH
NTC
FTH
7.87k
10k
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
Figure 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
Rev. G
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29
LTC4120/LTC4120-4.2
PACKAGE DESCRIPTION
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
Rev. G
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LTC4120/LTC4120-4.2
REVISION HISTORY
REV
DATE
DESCRIPTION
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.
G
11/18
Removed references to PowerByProxi.
PAGE
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
12, 27
Rev. G
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license For
is granted
implication or
otherwise under any patent or patent rights of Analog Devices.
more by
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31
LTC4120/LTC4120-4.2
TYPICAL APPLICATION
C2S
26.7nF
D9
IN
D8
D5
CIN
10µF
D6
OPT
374k
C2P
6.5nF
5µH
FAULT
RUN
CHGSNS
BAT
DHC
FB
102k
Tx CIRCUITRY
LX
2k
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
NTC
PROG
T
RPROG
6.04k
D5, D8, D9: DFLS240L
D6: MMSZ5259BT1G OR DFLZ39 (OPT)
LSW: SLF6028-470MR59
T: NTHS0402N02N1002F
+
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,
