LTC1553LCSW#TRMPBF Linear Technology, LTC1553LCSW#TRMPBF Datasheet - Page 14

• Manufacturer Part Number: LTC1553LCSW#TRMPBF
• Manufacturer: Linear Technology

Specifications of LTC1553LCSW#TRMPBF

• Lead Free Status / RoHS Status: Compliant

Note: Please refer to the manufacturer’s data sheet for testing conditions
and detail information.
LTC1553L
APPLICATIONS
Table 5. Recommended MOSFETs for LTC1553L Applications
PARTS
Siliconix SUD50N03-10
TO-252
Siliconix Si4410DY
SO-8
Motorola MTD20N03HDL
D PAK
SGS-Thomson STD20N03L
D PAK
Motorola MTB75N03HDL
DD PAK
IRF IRL3103S
DD PAK
IRF IRLZ44
TO-220
Fuji 2SK1388
TO-220
14
Inductor Selection
The inductor is often the largest component in the LTC1553L
design and should be chosen carefully. Inductor value and
type should be chosen based on output slew rate require-
ments, output ripple requirements and expected peak
current. Inductor value is primarily controlled by the
required current slew rate. The maximum rate of rise of
current in the inductor is set by its value, the input-to-
output voltage differential and the maximum duty cycle of
the LTC1553L. In a typical 5V input, 2.8V output applica-
tion, the maximum current slew rate will be:
where L is the inductor value in H. With proper frequency
compensation, the combination of the inductor and output
capacitor will determine the transient recovery time. In
general, a smaller value inductor will improve transient
response at the expense of increased output ripple voltage
and inductor core saturation rating. A 2 H inductor would
have a 0.9A/ s rise time in this application, resulting in a
5.5 s delay in responding to a 5A load current step. During
DC
MAX
V
IN
L
V
OUT
U
INFORMATION
U
1 83
L
AT 25 C (m )
R
DS(ON)
7.5
19
20
35
23
14
28
37
W
A
s
U
RATED CURRENT (A)
10 at 100 C
16 at 100 C
14 at 100 C
59 at 100 C
40 at 100 C
36 at 100 C
15 at 25 C
10 at 25 C
20 at 25 C
20 at 25 C
75 at 25 C
56 at 25 C
50 at 25 C
35 at 25 C
8 at 75 C
this 5.5 s, the difference between the inductor current and
the output current must be made up by the output capaci-
tor, causing a temporary voltage droop at the output. To
minimize this effect, the inductor value should usually be
in the 1 H to 5 H range for most typical 5V input LTC1553L
circuits. To optimize performance, different combinations
of input and output voltages and expected loads may
require different inductor values.
Once the required value is known, the inductor core type
can be chosen based on peak current and efficiency
requirements. Peak current in the inductor will be equal to
the maximum output load current plus half of the peak-to-
peak inductor ripple current. Ripple current is set by the
inductor value, the input and output voltage and the
operating frequency. The ripple current is approximately
equal to:
f
L
OSC
O
I
= Inductor value
RIPPLE
= LTC1553L oscillator frequency = 300kHz
TYPICAL INPUT
CAPACITANCE
C
V
ISS
IN
3200
2700
2300
4025
1600
3300
1750
880
f
OSC
(pF)
V
OUT
L
O
V
V
IN
OUT
JC
1.67
2.08
1.8
2.5
1.0
1.8
1.0
( C/W)
—
T
JMAX
175
150
150
175
150
175
175
150
( C)