LT1506CR-3.3#TRPBF Linear Technology, LT1506CR-3.3#TRPBF Datasheet - Page 10
![IC SW REG STEP-DOWN 500KHZ 7-DD](/photos/7/33/73397/7-dd-pkg_sml.jpg)
LT1506CR-3.3#TRPBF
Manufacturer Part Number
LT1506CR-3.3#TRPBF
Description
IC SW REG STEP-DOWN 500KHZ 7-DD
Manufacturer
Linear Technology
Type
Step-Down (Buck)r
Datasheet
1.LT1506CS8-3.3PBF.pdf
(24 pages)
Specifications of LT1506CR-3.3#TRPBF
Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
3.3V
Current - Output
4.5A
Frequency - Switching
500kHz
Voltage - Input
4 ~ 15 V
Operating Temperature
0°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (7 leads + tab)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
LT1506
APPLICATIONS
CHOOSING THE INDUCTOR AND OUTPUT CAPACITOR
For most applications the output inductor will fall in the
range of 3 H to 20 H. Lower values are chosen to reduce
physical size of the inductor. Higher values allow more
output current because they reduce peak current seen by
the LT1506 switch, which has a 4.5A limit. Higher values
also reduce output ripple voltage, and reduce core loss.
Graphs in the Typical Performance Characteristics section
show maximum output load current versus inductor size
and input voltage. A second graph shows core loss versus
inductor size for various core materials.
When choosing an inductor you might have to consider
maximum load current, core and copper losses, allowable
component height, output voltage ripple, EMI, fault cur-
rent in the inductor, saturation, and of course, cost. The
following procedure is suggested as a way of handling
these somewhat complicated and conflicting requirements.
1. Choose a value in microhenries from the graphs of
2. Calculate peak inductor current at full load current to
10
maximum load current and core loss. Choosing a small
inductor with lighter loads may result in discontinuous
mode of operation, but the LT1506 is designed to work
well in either mode. Keep in mind that lower core loss
means higher cost, at least for closed core geometries
like toroids. The core loss graphs show absolute loss
for a 3.3V output, so actual percent losses must be
calculated for each situation.
Assume that the average inductor current is equal to
load current and decide whether or not the inductor
must withstand continuous fault conditions. If maxi-
mum load current is 0.5A, for instance, a 0.5A inductor
may not survive a continuous 4.5A overload condition.
Dead shorts will actually be more gentle on the induc-
tor because the LT1506 has foldback current limiting.
ensure that the inductor will not saturate. Peak current
can be significantly higher than output current, espe-
cially with smaller inductors and lighter loads, so don’t
omit this step. Powdered iron cores are forgiving
U
INFORMATION
U
W
U
3. Decide if the design can tolerate an “open” core geom-
4. Start shopping for an inductor (see representative
5. After making an initial choice, consider the secondary
because they saturate softly, whereas ferrite cores
saturate abruptly. Other core materials fall in between
somewhere. The following formula assumes continu-
ous mode of operation, but it errs only slightly on the
high side for discontinuous mode, so it can be used for
all conditions.
V
f = Switching frequency, 500kHz
etry like a rod or barrel, which have high magnetic field
radiation, or whether it needs a closed core like a toroid
to prevent EMI problems. One would not want an open
core next to a magnetic storage media, for instance!
This is a tough decision because the rods or barrels are
temptingly cheap and small and there are no helpful
guidelines to calculate when the magnetic field radia-
tion will be a problem.
surface mount units in Table 2) which meets the
requirements of core shape, peak current (to avoid
saturation), average current (to limit heating), and fault
current (if the inductor gets too hot, wire insulation will
melt and cause turn-to-turn shorts). Keep in mind that
all good things like high efficiency, low profile, and high
temperature operation will increase cost, sometimes
dramatically. Get a quote on the cheapest unit first to
calibrate yourself on price, then ask for what you really
want.
things like output voltage ripple, second sourcing, etc.
Use the experts in the Linear Technology’s applica-
tions department if you feel uncertain about the final
choice. They have experience with a wide range of
inductor types and can tell you about the latest devel-
opments in low profile, surface mounting, etc.
IN
I
PEAK
= Maximum input voltage
I
OUT
V
OUT
2
f L V
V
IN
V
IN
OUT