LT3437IFE#TRPBF Linear Technology, LT3437IFE#TRPBF Datasheet - Page 15

• Manufacturer Part Number: LT3437IFE#TRPBF
• Description: IC REG SW HV 500MA 16-TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3437IFE#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.25 ~ 54 V
• Current - Output: 500mA
• Frequency - Switching: 200kHz
• Voltage - Input: 3.3 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
CHOOSING THE INDUCTOR
For most applications the output inductor will fall in the
range of 68µH to 220µH. 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 LT3437 switch, which has a 0.5A limit. Higher
values also reduce output ripple voltage and reduce core
loss.
When choosing an inductor you might have to consider
maximum load current, core and copper losses, allow-
able component height, output voltage ripple, EMI, fault
current in the inductor, saturation and of course cost.
The following procedure is suggested as a way of han-
dling these somewhat complicated and conflicting
requirements.
1. Choose a value in microhenries such that the maximum
2. Calculate peak inductor current at full load current to
load current plus half of the inductor ripple current is
less than the minimum peak switch current (I
Choosing a small inductor with lighter loads may result
in discontinuous mode of operation, but the LT3437 is
designed to work well in either mode.
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 0.25A, for instance, a 0.25A
inductor may not survive a continuous minimum peak
switch current overload condition.
For applications with a duty cycle above 50%, the
inductor value should be chosen to obtain an inductor
ripple current of less than 40% of the peak switch
current.
ensure that the inductor will not saturate. Peak current
can be significantly higher than output current, especially
with smaller inductors and lighter loads, so do not omit
this step. Powdered iron cores are forgiving because they
saturate softly, whereas ferrite cores saturate abruptly.
Other core materials fall somewhere in between. The
following formula assumes continuous mode of opera-
tion, but it errs only slightly on the high side for discon-
tinuous mode, so it can be used for all conditions.
U
U
W
U
PK
).
3. Decide if the design can tolerate an “open” core geom-
4. After making an initial choice, consider the secondary
Table 3. Inductor Selection Criteria
VENDOR/
PART NO.
Coiltronics
UP1B-101
UP1B-151
UP2B-221
Coilcraft
D01605T-473MX
D01605T-104MX
D03308P-154
D03308P-224
Sumida
CDRH4D28-470
CDRH4D28-101
CDRH5D28-101
etry like a rod or barrel, which has high magnetic field
radiation, or whether it needs a closed core like a toroid,
to prevent EMI problems. 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 radiation will be a problem.
things like output voltage ripple, second sourcing, etc.
Use the experts in Linear Technology’s applications
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 developments in
low profile, surface mounting, etc.
V
f = switching frequency, 200kHz
I
PEAK
IN
= maximum input voltage
=
I
OUT
VALUE
+
(
100
150
220
100
150
220
100
100
µ
47
47
V
H)
OUT
2
( )( )( )
(
f L V
V
IN
I
DC(MAX)
(mA)
530
460
380
450
300
600
500
480
290
420
–
V
IN
OUT
)
(Ohms)
0.387
0.520
DCR
1.11
1.61
1.96
0.94
1.02
1.1
2.3
1.6
LT3437
HEIGHT
15
(mm)
5.0
5.0
5.0
1.8
1.8
3.0
3.0
3.0
3.0
3.0
3437fc