LT3484-0/LT3484-1/LT3484-2

6

3484012f

DONE (Pin 1): Open NPN Collector Indication Pin. When

target output voltage is reached, NPN turns on, pulling Pin

1 low. This pin needs a pull-up resistor or current source.

CHARGE (Pin 2): Charge Pin. A low (<0.3V) to high (>1V)

transition on this pin puts the part into power delivery

mode. Once the target voltage is reached, the part will stop

charging the output. Toggle this pin to start charging

again. Bringing the pin low (<0.3V) will terminate the

power delivery and put the part in shutdown.

with a good quality ceramic capacitor. Input supply must

be 2.5V or higher.

SW (Pins 4, 5): Switch Pins. These are the collector of the

internal NPN Power switch. Tie these pins together on the

PC Board. Minimize the metal trace area connected to

these pins to minimize EMI. Tie one side of the primary of

the transformer to these pins. 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

.

with a good quality ceramic capacitor. Battery supply must

be 1.7V or higher. The other terminal of the transformer

GND (Pin 7): Ground. Tie directly to local ground plane.

PI FU CTIO S

SW

+

DONE

CHARGE

C1

T1

R2

60k

Q1

ENABLE

CHIP

POWER

PHOTOFLASH

CAPACITOR

40mV

20mV

TO BATTERY

Q2

D1

3484 BD

4, 5

GND

6

1

2

7

+

–

–

+

–

+

–

+

+–

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

3

Figure 1

FU CTIO AL BLOCK DIAGRA