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Linear Technology LTC 4125 Manual

5w autoresonant wireless power transmitter
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FeaTures
Monolithic 5W Wireless Power Transmitter
n
AutoResonant
Switching Frequency Adjusts to Res-
TM
n
onant Capacitance and Transmit Coil Inductance*
Transmit Power Automatically Adjusts to Receiver
n
Load*
Input Voltage Range: 3V to 5.5V
n
Integrated 100mΩ Full Bridge Switches
n
Multiple Foreign Object Detection Methods
n
Programmable Average Input Current Limit and
n
Monitor
NTC Input for System/Component Temperature
n
Qualified Power Transfer
Wide Operating Switching Frequency Range:
n
50kHz to 250kHz
Thermally Enhanced 4mm × 5mm QFN 20-Lead Package
n
applicaTions
Hermetically and/or Electrically Insulated Devices
n
Military Sensors and Devices
n
Medical Equipment
n
Industrial Handhelds
n
Typical applicaTion
V
20m
3V TO 5.5V
2.21k
10nF
11.3k
V
IN
100k
59.0k
10nF
5W Wireless Transmitter
IN
1µF
IN
IN1 IN2
STAT
–
IS
IS +
EN
LTC4125
FTH
PTHM
IMON
CTD
CTS
348k
470pF
4.7nF
For more information
5W AutoResonant Wireless
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.
100µF
10k
NTC
V
IN
SW1
L
TX
10k
24µH
C
TX
100nF
SW2
V
IN
100k
C
FB1
FB
0.1µF
GND
5.23k
4125 TA01
www.linear.com/LTC4125
LTC4125
Power Transmitter
L
L
TX
RX
COIL
COIL
TRANSMITTER
RECEIVER
CIRCUIT
+
–
AIR GAP
CIRCUIT
R
L
4125f
1

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Summary of Contents for Linear Technology LTC 4125

  • Page 1 Military Sensors and Devices 4mm × 5mm QFN package. Medical Equipment L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Industrial Handhelds AutoResonant is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
  • Page 2 LTC4125 absoluTe MaxiMuM raTings pin conFiguraTion (Note 1) – TOP VIEW IN, IS , CTD ..........–0.3V to 6V IN1, IN2, IS ......... –0.3V to V + 0.3V DTH, FTH, PTHM, FB ....–0.3V to V + 0.3V 20 19 18 17 NTC, EN, PTH1, PTH2, CTS..
  • Page 3 LTC4125 elecTrical characTerisTics denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T  = 25°C. V   =  V  =  V   =  5V unless otherwise noted (Notes 2, 3). IN1  SYMBOL PARAMETER CONDITIONS UNITS Input Supply Operating Range  = V  = V Input Supply Quiescent Current...
  • Page 4 LTC4125 elecTrical characTerisTics denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T  = 25°C. V   =  V  =  V   =  5V unless otherwise noted (Notes 2, 3). IN1  SYMBOL PARAMETER CONDITIONS UNITS Input Current Limit and Monitoring –...
  • Page 5 LTC4125 Typical perForMance characTerisTics  = 25°C, unless otherwise noted. Supply Quiescent Current at IN, EN Threshold IN1 and IN2 Over Temperature Over Temperature 120.0 1.225 40.0 = 5V SW1 = SW2 = OPEN 1.220 36.0 105.0 1.215 32.0 90.0 1.210 28.0 EN FALLING THRESHOLD 75.0 1.205...
  • Page 6 LTC4125 pin FuncTions IN (Pin 1): Input Supply Voltage: 3V to 5.5V. Supplies during a power search, an internal comparator indicates power to the internal circuitry. A local 1µF bypass capacitor that the input current threshold has been exceeded, and the to GND is recommended on this pin.
  • Page 7 LTC4125 pin FuncTions STAT (Pin 8): Open Drain Status Pin. This pin pulls low the rectified peak voltage generated in the series LC tank when the part is delivering power. When connected to an and GND (see Applications Information). The voltage on LED, this pin provides a visual indicator that the LTC4125 is the FB pin is monitored during the transmit power search delivering power to a valid resonant receiver.

  • Page 8: Functional Block Diagram

    LTC4125 FuncTional block DiagraM 3V TO 5.5V IS + IS – EXT OSC STARTUP IMON TANK – LIMREF LIMREF IMON IMON DRIVER DIE TEMP INT OSC SENSOR NTC1 TOO HOT RESONANT FEEDBACK – NTC2 FREQUENCY TO VOLTAGE LOGIC CONVERTER DTH1 TANK FTH1 DTH2...
  • Page 9 LTC4125 operaTion INTRODUCTION There are various ways of producing a large AC current in an inductor from a DC voltage. The LTC4125 is designed A wireless power system is composed of two parts sepa- to employ one of the simplest and most efficient methods rated by an air gap: transmit circuitry with a transmit coil, using a series LC resonant circuit.
  • Page 10 LTC4125 operaTion AUTORESONANT DRIVE coupling conditions, such a strong magnetic field will be inefficient and may damage the receiver. Given dissipative Consider the series resonant structure in Figure 2. If a elements in the transmit circuitry, transmitting any more square wave voltage source is used instead of a sinusoi- power than necessary will result in reduced efficiency.
  • Page 11 LTC4125 operaTion By adjusting the pulse width of the full bridge driver, the reduced to zero: the temperature threshold as determined LTC4125 can control both coil current and voltage. by the NTC input, the maximum tank voltage threshold, the internal die over temperature threshold, or the fre- 14.0 = 24µH quency threshold (foreign object) and the input current...
  • Page 12 LTC4125 operaTion Exit Conditions Fault Conditions The Optimum Power Search employs many exit conditions A fault condition will cause the Optimum Power Search to ensure that the optimum transmit power is found during to stop transmitting power immediately by keeping the a search across many different operating situations.
  • Page 13 LTC4125 operaTion Input current limit is detected via the IMON pin. If the and Pulse Width PTH1 PTH2 voltage on the IMON pin exceeds 1.20V (V , typ) after ILIM The pulse width of each half of the full bridge driver a valid exit condition is found, transmit power is reduced can be monitored using the PTH1 and PTH2 pins.
  • Page 14 LTC4125 applicaTions inForMaTion 33nF 4.5V DFLZ39 10µF 5.5V 2.21k 47µF 1µF AIR GAP STAT 100k 100k 24.9k 10mm STAT IN1 IN2 24µH BOOST 47µF 10nF 7.87k 59.0k NTCTX 47µH PTHM LTC4120-4.2 100nF 15µH LTC4125 – CHGSNS 10nF 11.3k FAULT IS + CHRG BATSNS PTH1...
  • Page 15 LTC4125 applicaTions inForMaTion ) before thermal rise (from 25°C ambient) in the Table 1. Recommended Transmit Coils RMS-MAX die causes the internal thermal shutdown to stop power QUALITY INDUCTANCE SIZE FACTOR AT delivery in the coil. MANUFACTURER PART NUMBER (µH) (mm) 100kHz In the specific application shown in Figure 7, a 24μH coil...
  • Page 16 LTC4125 applicaTions inForMaTion rating must be able to withstand this voltage. The maximum voltage the capacitor must withstand is given by: TANK 2 •I RMS _ MAX LMAX CMAX LTC4125 ωC ωC where I is the maximum inductor current during LMAX operation in the series LC circuit.
  • Page 17 LTC4125 applicaTions inForMaTion Figure 9 shows this sweep for the circuit shown in Figure 7. The recommended values for R and R are such that Note that the LTC4120 is set to charge a single cell Li-Ion ≈ 100k. A typical recommended starting value battery in the Constant Current mode at 400mA at the for C is 0.1µF.
  • Page 18 LTC4125 applicaTions inForMaTion INPUT CURRENT LIMIT SETTING AND MONITORING is reduced to zero until the next search interval. Input cur- rent limit is also programmable using R and R IMON 3V TO 5.5V 1.20V ILIM • • IMON IMON IS + IS –...
  • Page 19 LTC4125 applicaTions inForMaTion Figure 12 shows the difference in LTC4125 behavior when An internal frequency to voltage converter creates a volt- a conductive foreign object is placed on the transmit coil, age representation of this AutoResonant Drive frequency with or without a frequency limit programmed at the FTH (Block Diagram).
  • Page 20 LTC4125 applicaTions inForMaTion TIMER CAPACITORS—C AND C Referring to Figure 6 and Figure 13, the two timing intervals that use CTS frequency are T1—the wait time after the The capacitor connected to the CTS pin (C ) sets the CTS initial reset at the beginning of the search, and T2—the frequency (f ) which determines the step settling time settling time after each pulse width step.
  • Page 21 LTC4125 applicaTions inForMaTion The value of T3 determines the delay interval time between In some applications users may find that across all operat- each search. A starting value of 470pF for the C capacitor ing conditions, the pulse width never falls below a particular sets this delay time between each search to 3.7s.
  • Page 22 LTC4125 applicaTions inForMaTion coupling condition, this exit point also coincides with a DELTA THRESHOLD (DTH PIN) voltage step at the feedback pin that is larger than all the One of the exit conditions in the Optimum Power Search earlier voltage steps. algorithm is when the increase in the feedback voltage Note that Optimum Power Search only deems this condition ) at any particular step during the sweep is larger than...
  • Page 23 LTC4125 applicaTions inForMaTion Set the V value to 9.4 bits = 367mV, such that at this As a quick rule of thumb, changing the value of R NTC1 desired step the ∆V  > V condition is satisfied. With be smaller relative to R at 25°C will move the tem- NTC2  = 5V, and a recommended R...
  • Page 24 LTC4125 applicaTions inForMaTion BOARD LAYOUT CONSIDERATIONS as inductance in the loop. Although the inductance of the trace between the LTC4125 and the transmit coil does not When using an LTC4125 circuit, care must be taken when matter, the resistance does. Use a trace that is the shortest, handling the board since high voltage is generated in and has maximum available copper thickness and width.
  • Page 25 LTC4125 applicaTions inForMaTion ground plane, shielding whenever necessary, and routing Figure 19 shows an example of a 4-layer board recom- sensitive signals as short as possible and away from noisy mended layout for the LTC4125 application circuit with sections of the board. the high voltage nodes and hot current loop highlighted.

  • Page 26: Typical Applications

    LTC4125 Typical applicaTions LTC4125 Driving a 24μH Transmit Coil at 103kHz, 119kHz Frequency Limit and 41.5°C Transmit Coil Surface Temperature Limit in a Wireless Power System with LT3652HV as a 1A Single Cell LiFePO (3.6V Float) Battery Charger at the Receiver 33nF 4.75V 10µF...
  • Page 27 ON THE TOP AND BOTTOM OF PACKAGE 4125f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- For more information www.linear.com/LTC4125 tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

  • Page 28: Typical Application

    Timer or C/10 Termination, 12-Lead 3mm x 3mm DFN and MSOP. 4125f Linear Technology Corporation LT 1115 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC4125 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC4125  LINEAR TECHNOLOGY CORPORATION 2015 ● ●...
  • Page 29 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Analog Devices Inc. LTC4125EUFD#TRPBF LTC4125IUFD#PBF LTC4125EUFD#PBF LTC4125IUFD#TRPBF...