Document
LTC4120/LTC4120-4.2
Wireless Power Receiver and 400mA Buck Battery Charger
Features
n 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
Applications
n Handheld Instruments n Industrial/Military Sensors and Devices n Harsh Environments n Portable Medical Devices n Physically Small Devices n Electrically Isolated Devices
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Description
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. 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. 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. 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
26.7nF
Tx CIRCUITRY
6.5nF
5µH 47µH
IN RUN 10µF
INTVCC FREQ
BOOST LTC4120
SW
DHC CHGSNS
NTC
FAULT
BAT
CHRG
FB
GND PROG FBG
2.2µF 22nF 33µH
1.01M 1.35M
Li-Ion +
4.2V
T
Wireless Rx Voltage/Charge Current vs Spacing
40
35 VIN
30
25
NOT CHARGING
ICHARGE MAX
400 333
267
200
VIN(RX) (V)
CHARGE CURRENT (mA)
20 CHARGING
15
133 67
3.01k
22µF
4120 TA01a
10 0.4 0.6
0.8 1.0 1.2 1.4 SPACING (cm)
0 1.6 1.8
4120 TA01b
4120fd
For more information w.