LT3484EDCB-0#TRM Linear Technology, LT3484EDCB-0#TRM Datasheet - Page 8

• Manufacturer Part Number: LT3484EDCB-0#TRM
• Description: IC PHOTOFLASH CAP CHARGER 6-DFN
• Manufacturer: Linear Technology

Specifications of LT3484EDCB-0#TRM

• Applications: Photoflash Capacitor Charger
• Current - Supply: 5mA
• Voltage - Supply: 1.7 V ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 6-DFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LT3484EDCB-0

APPLICATIO S I FOR ATIO
LT3484-0/LT3484-1/LT3484-2
Table 1. Recommended Transformer Parameters
PARAMETER
L
L
N
V
I
R
R
8
voltage as it changes the amplitude of the reflected voltage
from the output to the SW pin. Choose N according to the
following equation:
Where: V
in the numerator is used to include the effect of the voltage
drop across the output diode(s).
Thus for a 320V output, N should be 322/31.5 or 10.2. For
a 300V output, choose N equal to 302/31.5 or 9.6.
The next parameter that needs to be set is the primary
inductance, L
formula:
Where: V
the transformer turns ratio. I
(LT3484-1), and 1.0 (LT3484-2).
L
that the LT3484-0/LT3484-1/LT3484-2 has adequate time
to respond to the flyback waveform.
SAT
PRI
LEAK
ISO
PRI
SEC
PRI
N
L
PRI
needs to be equal or larger than this value to ensure
=
V
≥
OUT
OUT
31 5 .
OUT
V
OUT
+ 2
is the desired output voltage. The number 2
PRI
is the desired output voltage. N is
. Choose L
•
N I
200 10
NAME
Primary Inductance
Primary Leakage Inductance
Secondary: Primary Turns Ratio
Secondary to Primary Isolation Voltage
Primary Saturation Current
Primary Winding Resistance
Secondary Winding Resistance
•
U
PK
•
U
PRI
−
9
PK
according to the following
is 1.4 (LT3484-0), 0.7
W
U
All other parameters need to meet or exceed the recom-
mended limits as shown in Table 1. A particularly impor-
tant parameter is the leakage inductance, L
power switch of the LT3484-0/LT3484-1/LT3484-2 turns
off, the leakage inductance on the primary of the trans-
former causes a voltage spike to occur on the SW pin. The
height of this spike must not exceed 40V, even though the
absolute maximum rating of the SW Pin is 50V. The 50V
absolute maximum rating is a DC blocking voltage speci-
fication, which assumes that the current in the power NPN
is zero. Figure 3 shows the SW voltage waveform for the
circuit of Figure 6 (LT3484-0). Note that the absolute
maximum rating of the SW pin is not exceeded. Make sure
to check the SW voltage waveform with V
target output voltage, as this is the worst case condition
for SW voltage. Figure 4 shows the various limits on the
SW voltage during switch turn off.
It is important not to minimize the leakage inductance to
a very low level. Although this would result in a very low
leakage spike on the SW pin, the parasitic capacitance of
the transformer would become large. This will adversely
affect the charge time of the photoflash circuit.
Linear Technology has worked with several leading mag-
netic component manufacturers to produce pre-designed
flyback transformers for use with the LT3484-0/
LT3484-1/LT3484-2. Table 2 shows the details of several
of these transformers.
TYPICAL RANGE
100 to 300
1:8 to 1:12
LT3484-0
>500
<300
>1.6
<40
>5
TYPICAL RANGE
200 to 500
1:8 to 1:12
LT3484-1
>500
<500
>0.8
>10
<80
TYPICAL RANGE
200 to 500
1:8 to 1:12
LT3484-2
>500
<400
>1.0
<60
>7
LEAK
OUT
. When the
near the
3484012f
UNITS
mΩ
µH
nH
Ω
V
A