LTC4125
5W AutoResonant Wireless
Power Transmitter
FeaTures
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DescripTion
The
LTC
®
4125
is a simple and high performance monolithic
full bridge resonant driver capable of delivering over 5W of
power wirelessly to a properly tuned receiver. The device
controls the current flow in a series connected transmit coil
LC network to create a simple, safe and versatile wireless
power transmitter.
The LTC4125 automatically adjusts its driving frequency
to match the LC network resonant frequency. This
AutoResonant switching allows the device to deliver
maximum power from a low voltage input supply (3V to
5.5V) to a tuned receiver. To optimize system efficiency,
the LTC4125 employs a periodic transmit power search
and adjusts the transmission power based on the receiver
load requirements. The device stops delivering power
during a fault condition, or if a foreign object is detected.
The LTC4125 also includes a programmable maximum
average input current limit and an NTC input as additional
means for foreign object and overload protection. The
LTC4125 is available in a 20-lead low profile (0.75mm)
4mm
×
5mm QFN package.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
AutoResonant is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 9041254.
*The AutoResonant and Auto Load Detect features use patent pending circuits and algorithms.
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Monolithic 5W Wireless Power Transmitter
AutoResonant
TM
Switching Frequency Adjusts to Res-
onant Capacitance and Transmit Coil Inductance*
Transmit Power Automatically Adjusts to Receiver
Load*
Input Voltage Range: 3V to 5.5V
Integrated 100mΩ Full Bridge Switches
Multiple Foreign Object Detection Methods
Programmable Average Input Current Limit and
Monitor
NTC Input for System/Component Temperature
Qualified Power Transfer
Wide Operating Switching Frequency Range:
50kHz to 250kHz
Thermally Enhanced 4mm
×
5mm QFN 20-Lead Package
applicaTions
n
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Hermetically and/or Electrically Insulated Devices
Military Sensors and Devices
Medical Equipment
Industrial Handhelds
Typical applicaTion
3V TO 5.5V
20m
2.21k
V
IN
5W Wireless Transmitter
L
TX
COIL
L
RX
COIL
RECEIVER
CIRCUIT
1µF
IN
STAT
IS
–
IN1 IN2
NTC
SW1
100µF
10k
V
IN
10k
L
TX
24µH
+
–
TRANSMITTER
CIRCUIT
R
L
AIR GAP
11.3k
V
IN
10nF
IS+
EN
100k
FTH
59.0k
PTHM
IMON
10nF
348k
CTD
470pF
CTS
4.7nF
FB
GND
LTC4125
SW2
V
IN
C
TX
100nF
100k
C
FB1
0.1µF
5.23k
4125 TA01
For more information
www.linear.com/LTC4125
1
4125f
LTC4125
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
SW1
SW2
IN1
IN2
16 GND
15
EN
21
GND
14 CTD
13 FB
12 PTHM
11 PTH1
7
DTH
8
STAT
9 10
FTH
PTH2
IN, IS
–
, CTD ............................................. –0.3V to 6V
IN1, IN2, IS
+
................................. –0.3V to V
IN
+ 0.3V
DTH, FTH, PTHM, FB ................... –0.3V to V
IN
+ 0.3V
NTC,
EN,
PTH1, PTH2, CTS.......... –0.3V to V
IN
+ 0.3V
IMON ................ –0.3V to MIN(V
IN
, V
IS
+, V
IS
–) + 0.3V
STAT ........................................... –0.3V to V
IN
+ 0.3V
STAT ......................................................–1mA to 2mA
Operating Junction Temperature Range
(Note 2) ............................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
20 19 18 17
IN 1
CTS 2
IS 3
IS+ 4
IMON 5
NTC 6
–
UFD20 PACKAGE
20-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 21) MUST BE CONNECTED TO GND
orDer inForMaTion
LEAD FREE FINISH
LTC4125EUFD#PBF
LTC4125IUFD#PBF
TAPE AND REEL
LTC4125EUFD#TRPBF
LTC4125IUFD#TRPBF
PART MARKING
4125
4125
PACKAGE DESCRIPTION
20-Lead (4mm × 5mm) Plastic QFN
20-Lead (4mm × 5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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.
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For more information
www.linear.com/LTC4125
LTC4125
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
IN1
= V
IN2
= 5V unless otherwise noted (Notes 2, 3).
SYMBOL PARAMETER
Input Supply Operating Range
Input Supply Quiescent Current
At IN pin
At IN1, IN2 pin
Enable Pin
EN
Leakage Current
EN
Falling Threshold
EN
Hysteresis
Search Delay Oscillator Pins
I
CTS,PU
I
CTS,PD
CTS Pull-Up Current
CTS Pull-Down Current
CTS Pin Frequency
CTS Threshold for AutoResonant Disable
I
CTD,PU
I
CTD,PD
CTD Pull-Up Current
CTD Pull-Down Current
CTD Pin Frequency
Resonant Driver and Pulse Width Modulator
Operating Frequency Range
R
A,B,C,D
Switch On Resistances
Switch Pins Minimum On Time
Minimum PTH Voltage for Switching
PTH Voltage to Pulse Width Gain normalized to
the LC natural frequency (f
n
)
PTH Pull Up Current when Overdriving
PTH Pull Down Current when Overdriving
Auto Load Detection
V
PTH
Step Size during Auto Load Detection
Search
Delay Time between Optimum Point Search
Optimum Point Search Duration
FB Pin Leakage Current
FB Over-Range Rising Threshold
FB Over-Range Threshold Hysteresis
PTHM Pin Leakage Current
PTHM Pin Common Mode Voltage Range
FTH Pin Leakage Current
FTH Voltage to Frequency Gain
DTH Pin Leakage Current
V
DTH
= 0V
l
elecTrical characTerisTics
CONDITIONS
V
IN
= V
IN1
= V
IN2
SW1 and SW2 Open
EN
= 5V
V
EN
= 5V
V
EN
Falling
l
l
MIN
3
TYP
MAX
5.5
UNITS
V
mA
μA
μA
V
mV
µA
µA
1
50
0.2
0.5
1.20
16
2
150
1.2
V
CTS
= 0V
V
CTS
= 2V
C
CTS
= 4.7nF
l
–10
10
1.0
1.8
1.7
2.3
–10
10
10
50
17
24
250
150
150
35
0.24
l
l
2.4
2.8
kHz
V
µA
µA
kHz
kHz
mΩ
ns
mV
V
–1
V
CTD
= 0V
V
CTD
= 2V
C
CTD
= 470pF
MOSFETs A, B, C and D (Block Diagram)
SW1, SW2
SW1 On Time
•
f
n
/ ∆V
PTH1
,
SW2 On Time
•
f
n
/ ∆V
PTH2
V
PTH1
= V
PTH2
= 0V
V
PTH1
= V
PTH2
= 5V
–20
10
–10
20
75
–5
40
μA
μA
mV
s
ms
C
CTD
= 470pF
C
CTS
= 470pF (Figure 13)
V
FB
= 5V
V
FB
Rising
V
PTHM
= 5V
V
FTH
= 0V
l
l
3.7
40
0.2
V
IN
– 0.04
0.2
0
l
0.5
V
IN
40
0.5
–0.5
64
–0.5
1.2
V
IN
+ 0.04
1.2
5
–0.2
–0.2
μA
V
mV
μA
V
μA
kHz/V
μA
l
–1.2
–1.2
For more information
www.linear.com/LTC4125
3
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LTC4125
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
IN1
= V
IN2
= 5V unless otherwise noted (Notes 2, 3).
SYMBOL PARAMETER
Input Current Limit and Monitoring
V
IS
+
,IS
–
Sense Voltage Offset
l
elecTrical characTerisTics
CONDITIONS
MIN
–500
–1.5
–100
TYP
MAX
500
1.5
100
UNITS
µV
mV
nA
μA
nA
V
V
mV
IS
+
Pin Current
IS
–
Pin Current
IMON Pin Leakage Current
V
ITH
V
ILIM
Input Current Comparator Threshold at IMON
during Search
Input Current Limit Comparator Threshold at
IMON during Delay Time
Input Current Limit Comparator Hysteresis
Thermistor Input
NTC Hot Threshold
NTC Thresholds Hysteresis
NTC Open Circuit Voltage
NTC Open Circuit Input Resistance
Open Drain Status Pin
STAT Pin Leakage Current
STAT Pin Output Voltage Low
V
IS
+ = 5V, V
IS
+
,IS
– = –50mV
V
IS
– = V
IS
+ = 5V
V
IS
+
,IS
– = –50mV, V
IMON
= 0V – 5V
V
IMON
Rising
V
IMON
Rising
l
l
15
–100
0.785
1.175
0.800
1.200
40
100
0.815
1.225
V
NTC
Falling, % of V
IN
% of V
IN
% of V
IN
l
33
48
35
5
50
300
37
52
% V
IN
% V
IN
% V
IN
kΩ
l
V
STAT
= 5V
I
STAT
= 1mA
l
–1
1
0.4
μA
V
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 LTC4125 is tested under conditions such that T
J
≈ T
A
. The
LTC4125E is guaranteed to meet specifications from 0°C to 85°C junction
temperature. Specifications over the -40°C to 125°C operating junction
temperature are assured by design, characterization and correlation
with statistical process controls. The LTC4125I is guaranteed over the
full -40°C to 125°C operating junction temperature range. The junction
temperature (T
J
, in °C) is calculated from the ambient temperature (T
A
,
in °C) and power dissipation (P
D
, in Watts) according to the following
formula:
T
J
= T
A
+ (P
D
•
θ
JA
), where
θ
JA
(in °C/W) is the package thermal
impedance.
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. This IC includes over temperature protection
that is intended to protect the device during momentary SW MOSFETs
over current situation. Junction temperature will exceed 125°C when over
temperature protection is active. Continuous operation above the specified
maximum operating junction temperature may impair device reliability.
Note 3:
All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
Note 4:
This IC includes overtemperature protection that is intended
to protect the device. Junction temperature will exceed 125°C when
overtemperature protection is active. Continuous operation above the
specified maximum operating junction temperature will reduce lifetime.
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4125f
For more information
www.linear.com/LTC4125
LTC4125
Typical perForMance characTerisTics
Supply Quiescent Current at IN,
IN1 and IN2 Over Temperature
1.6
V
IN
= V
IN1
= V
IN2
= 5V
1.4 SW1 = SW2 = OPEN
1.2
1.0
I
IN
(mA)
0.8
0.6
0.4
0.2
0.0
–45
–20
5
55
30
80
TEMPERATURE (°C)
105
I
IN
I
IN1
, I
IN2
120.0
105.0
90.0
75.0
60.0
45.0
30.0
15.0
0.0
130
I
IN1
, I
IN2
(µA)
EN
FALLING THRESHOLD (V)
1.225
1.220
1.215
1.210
1.205
1.200
1.195
1.190
1.185
1.180
1.175
–45
–20
5
55
30
80
TEMPERATURE (°C)
105
HYSTERESIS
EN
FALLING THRESHOLD
T
A
= 25°C, unless otherwise noted.
EN
Threshold
Over Temperature
40.0
36.0
32.0
28.0
24.0
20.0
16.0
12.0
8.0
4.0
0.0
130
HYSTERESIS (mV)
4125 G01
4125 G02
C
TS
, C
TD
Pin Frequency and
Search Delay Time Over
Temperature
22.5
C
TD
= C
TS
= 470pF
6.0
200
Switch Resistances Over
Temperature
V
IN
= 5V
19.5
F
CTD
, F
CTS
(kHz)
F
CTD
, F
CTS
16.5
SEARCH DELAY TIME (T3)
13.5
5.0
160
RESISTANCE (m )
T3 – SEARCH DELAY TIME (s)
120
4.0
R
A
, R
D
R
B
, R
C
80
3.0
40
10.5
–45
–20
5
55
30
80
TEMPERATURE (°C)
105
2.0
130
0
–45
–20
5
55
30
80
TEMPERATURE (°C)
105
130
4125 G03
4125 G04
V
IS
+
,IS
– Sense Amplifier Offset
Over Temperature
1.5
1
0.5
V
IMON
(V)
0
–0.5
–1.0
–1.5
–45
V
ISN
= 5V
1.225
1.220
1.215
1.210
1.205
1.200
1.195
1.190
1.185
1.180
–20
5
55
30
80
TEMPERATURE (°C)
105
130
Input Current Threshold and Limit
Over Temperature
0.815
0.812
0.809
0.806
INPUT CURRENT THRESHOLD
INPUT CURRENT LIMIT
0.803
0.800
0.797
0.794
0.791
0.788
–20
5
55
30
80
TEMPERATURE (°C)
105
0.785
130
V
IMON
(V)
V
IS
+
,IS
– (mV)
1.175
–45
4125 G05
4125 G06
For more information
www.linear.com/LTC4125
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