LTC4120/LTC4120-4.2

20

Rev. G

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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.

The RMS voltage at the rectifier output depends on the

load of the LTC4120, i.e., the charge current, as well as the

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 addition

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.

Resonant Transmitter and Receiver

An example DC/AC transmitter is shown in Figure 10.

A 5V ±5% supply to the transmitter efficiently produces a

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

C4

0.01µF

R1

100

C5

0.01µF

0.3µF

5µH

D2

D1

68µH

68µH

4.75V TO 5.25V

TRANSMITTER

RECEIVER

R2

100

D2

M1

M2

D3

D1

D4

D3

C3

L1

C2S2

C2S1

C2P1

C1

10µF

C5

10µF

D4

39V

OPT

C4

2.2µF

C2

47µF

C2P2

DHC

BOOST

SW

CHGSNS

BAT

FB

FBG

4120 F10

IN

GND

U1

LTC4120

+

U1

LT3480

GND

BD

BOOST

SW

PG

VC

RUN/SS

SYNC

RT

FB

C9

0.47µF

C7

0.068µF

C8

330pF

R5

20k

C10

22µF

M4

2N7002L

M3

Si2333DS

5V

CONNECT

R8

150k

L3

4.7µF

D5

DFLS240L

C6

4.7µF

8V TO 38V

GND

R4

40.2k

R3

150k

R7

536k

R10

100k

R6

100k

4120 F11

Figure 10. DC/AC Converter, Transmit/Receive Coils, Tuned Series Resonant Receiver and AC/DC Rectifier

Figure 11. High Voltage Pre-Regulator for Transmitter