LTC3714EG#TRPBF Linear Technology, LTC3714EG#TRPBF Datasheet - Page 9

• Manufacturer Part Number: LTC3714EG#TRPBF
• Description: IC STP-DWN CNTRLR W/OPAMP 28SSOP
• Manufacturer: Linear Technology

Specifications of LTC3714EG#TRPBF

• Applications: Controller, Intel Pentium®
• Voltage - Input: 4 ~ 36 V
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 1.75 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

applicaTions inForMaTion
A general LTC3417A application circuit is shown in
Figure 4. External component selection is driven by the
load requirement, and begins with the selection of the
inductors L1 and L2. Once L1 and L2 are chosen, C
C
Operating Frequency
Selection of the operating frequency is a tradeoff between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves efficiency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency, f
by pulling the FREQ pin to V
by connecting an external resistor from FREQ to ground.
The value of the resistor sets the ramp current that is
used to charge and discharge an internal timing capacitor
within the oscillator and can be calculated by using the
following equation:
for 0.6MHz ≤ f
select the value for R
OUT1
R
T
and C
≈
1.61• 10
160
140
120
100
80
40
60
20
0
OUT2
0
f
O
O
0.5 1.0
Figure 1. Frequency vs R
≤ 4MHz. Alternatively, use Figure 1 to
can be selected.
11
( )
Ω
T
.
FREQUENCY (MHz)
1.5
– 16.586kΩ
O
2.0
, of the LTC3417A is determined
2.5
IN
for 1.5MHz operation or
3.0
3.5
4.0
T
3417 F01
4.5
IN
,
The maximum operating frequency is also constrained
by the minimum on-time and duty cycle. This can be
calculated as:
The minimum frequency is limited by leakage and noise
coupling due to the large resistance of R
Inductor Selection
Although the inductor does not influence the operating
frequency, the inductor value has a direct effect on ripple
current. The inductor ripple current, ∆I
higher inductance and increases with higher V
V
Accepting larger values of ∆I
tances, but results in higher output voltage ripple, greater
core losses and lower output current capability.
A reasonable starting point for setting ripple current is
∆I
current output. The largest ripple, ∆I
mum input voltage. To guarantee that the ripple current
stays below a specified maximum, the inductor value
should be chosen according to the following equation:
The inductor value will also have an effect on Burst Mode
operation. The transition from low current operation begins
when the peak inductor current falls below a level set by the
burst clamp. Lower inductor values result in higher ripple
current which causes this to occur at lower load currents.
This causes a dip in efficiency in the upper range of low
current operation. In Burst Mode operation, lower inductor
values will cause the burst frequency to increase.
OUT
L
L =
∆I
f
O(MAX)
= 0.35I
.
L
=
f
O
V
V
f
OUT
• ∆I
O
OUT
LOAD(MAX)
≈ 6.67
• L
L
⎛
⎜
⎝
⎛
⎜
⎜
⎝
1–
1–
⎛
⎜
⎜
⎝
V
V
V
IN(MAX)
V
IN(MAX)
OUT
, where I
V
V
IN
OUT
OUT
⎞
⎟
⎠
L
⎞
⎟ MHz
⎟
⎠
⎞
⎟
⎟
⎠
allows the use of low induc-
LOAD(MAX)
(
L
LTC3417A
)
, occurs at the maxi-
L
, decreases with
is the maximum
T
.
IN
3417afc
9
or