LT3468/LT3468-1/LT3468-2

6

346812fa

SW (Pin 1): Switch Pin. This is the collector of the internal

NPN Power switch. Minimize the metal trace area con-

nected to this pin to minimize EMI. Tie one side of the

primary of the transformer to this pin. The target output

voltage is set by the turns ratio of the transformer.

Choose Turns Ratio N by the following equation:

N

=

+ 2

31 5

.

You must tie a Schottky diode from GND to SW, with the

anode at GND for proper operation of the circuit. Please

refer to the applications section for further information.

GND (Pin 2): Ground. Tie directly to local ground plane.

DONE (Pin 3): Open NPN Collector Indication Pin. When

target output voltage is reached, NPN turns on. This pin

needs a pull-up resistor or current source.

CHARGE (Pin 4): Charge Pin. This pin must be brought

high (>1V) to enable the part. A low (<0.3V) to high (>1V)

transition on this pin puts the part into power delivery

mode. Once the target output voltage is reached, the part

will stop charging the output. Toggle this pin to start

charging again. Ground to shut down. You may bring this

pin low during a charge cycle to halt charging at any time.

with a good quality ceramic capacitor. Input supply must

be 2.5V or higher.

PI FU CTIO S

BLOCK DIAGRA

SW

+

DONE

CHARGE

C1

T1

R2

60k

Q1

ENABLE

PHOTOFLASH

CAPACITOR

36mV

20mV

TO BATTERY

D2

Q2

D1

3486 BD

1

GND

5

3

4

2

+

–

–

+

–

+

–

+

+–

ONE-

SHOT

ONE-

SHOT

DRIVER

PRIMARY

SECONDARY

MASTER

LATCH

DCM COMPARATOR

R1

2.5k

S

RQ

1.25V

REFERENCE

Q3

Q1

QQ

SR

A3

A1

A2

CHIP ENABLE

Figure 1