LT3420 LINER [Linear Technology], LT3420 Datasheet - Page 6

• Manufacturer Part Number: LT3420
• Description: Photoflash Capacitor Chargers with Automatic Refresh
• Manufacturer: LINER [Linear Technology]

PI FU CTIO S
LT3420/LT3420-1
R
from the R
V
connected to the power supply or battery, which supplies
power to transformer T1. Must be locally bypassed.
R
from the SW pin to the R
following formula:
V
with a 4.7 F or larger ceramic capacitor.
6
BAT
CC
REF
FB
V
N: Transformer Turns Ratio
R
V
R2: Resistor from the R
Choice
R
R
U
OUT
D
(Pin 3): Feedback Resistor Pin. Place a resistor (R1)
SEC
1
(Pin 4): Input Supply Pin. Must be locally bypassed
1
(Pin 1): Reference Resistor Pin. Place a resistor (R2)
: Diode Forward Voltage Drop
(Pin 2): Battery Voltage Input. This pin should be
: Transformer Secondary Resistance
R
R
N
N
: Desired Output Voltage
2
2
2
2
U
REF
(
( . •
1 4
R
pin to GND. 2k is recommended.
SEC
R
)
SEC
U
N V
(
)
OUT
FB
N V
REF
(
pin. Set R1 according to the
OUT
Pin to GND. 2k is a Typical
2
V
D
)
2
V
(LT3420-1)
D
)
(LT3420)
GND (Pin 5): Ground. Tie directly to local ground plane.
SW (Pin 6): 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.
SEC (Pin 7): Transformer Secondary Pin. Tie one end of
the transformer secondary to this pin. Take care to use the
correct phasing of the transformer (Refer to Figures 1
and 2).
DONE (Pin 8): Done Output Pin. Open collector NPN
output. DONE is pulled low whenever the chip is delivering
power to the output and goes high when power delivery
stops.
CHARGE (Pin 9): Charge Pin. Drive CHARGE high (1.5V or
more) to commence charging of the output capacitor.
Drive to 0.2V or less to put the part in shutdown mode.
C
from the C
according to the following formula:
T
C
t
(Pin 10): Refresh Timer Capacitor Pin. Place a capacitor
REFRESH
T
= 2.5 • 10
T
: Desired Refresh Period in Seconds.
pin to GND to set the refresh timer sample rate
–6
• t
REFRESH
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