LTC3616 LINER [Linear Technology], LTC3616 Datasheet - Page 24

• Manufacturer Part Number: LTC3616
• Description: 6A, 4MHz Monolithic Synchronous Step-Down DC/DC Converter
• Manufacturer: LINER [Linear Technology]

LTC3616
PACKAGE DESCRIPTION
Design Example
As a design example, consider using the LTC3616 in an
application with the following specifications:
V
= 200mA, f = 2.6MHz.
Efficiency is important at both high and low load current,
so Burst Mode operation will be utilized.
First, calculate the timing resistor:
Next, calculate the inductor value for about 30% ripple
current at maximum V
Using a standard value of 0.22μH inductor results in a
maximum ripple current of:
C
to satisfy the output voltage ripple requirement and the
bulk capacitance needed for loop stability. For this design,
a 150μF (or 47μF plus 100μF) ceramic capacitor is used
with a X5R or X7R dielectric.
Assuming worst-case conditions of V
be selected for a maximum current rating of:
Decoupling PV
for most applications.
If we set R2 = 196k, the value of R1 can now be determined
by solving the following equation.
A value of 392k will be selected for R1.
24
IN
OUT
R
L =
I
R1 = 196k •
ΔI
RMS
= 2.25V to 5.5V, V
T
L
will be selected based on the ESR that is required
=
⎛
⎝ ⎜
=
2.6MHz • 2A
= 6A •
3.82 • 10
⎛
⎝ ⎜
2.6MHz • 0.22µH
2.6MHz
1.8V
IN
1.8V
3.6V
⎛
⎝ ⎜
1.8V
1.8V
0.6V
11
with four 22μF capacitors is adequate
Hz
•
OUT
⎞
⎠ ⎟
IN
Ω – 16kΩ = 130kΩ
− 1
• 1–
⎛
⎝ ⎜
:
⎛
⎝ ⎜
= 1.8V, I
3.6V
1.8V
⎞
⎠ ⎟
⎞
⎠ ⎟
1.8V
5.5V
• 1–
⎛
⎝ ⎜
– 1
OUT(MAX)
⎞
⎠ ⎟
⎞
⎠ ⎟
IN
1.8V
5.5V
= 0.233µH
= 3A
= 2V
RMS
⎞
⎠ ⎟
= 6A, I
OUT
= 2.12A
, C
IN
OUT(MIN)
should
Finally, define the soft start-up time choosing the proper
value for the capacitor and the resistor connected to
TRACK/SS. If we set minimum t
of 2MΩ, the following equation can be solved with the
maximum SV
The standard value of 22nF guarantees the minimum
soft-start up time of 5ms.
Figure 1 shows the schematic for this design example.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3616:
1. A ground plane is recommended. If a ground plane layer
2. Connect the (+) terminal of the input capacitor(s), C
3. Keep the switching node, SW, away from all sensitive
4. Flood all unused areas on all layers with copper. Flood-
5. Connect the V
is not used, the signal and power grounds should be
segregated with all small-signal components returning
to the SGND pin at one point which is then connected
to the PGND pin close to the LTC3616.
as close as possible to the PV
as close as possible to the exposed pad, PGND. This
capacitor provides the AC current into the internal power
MOSFETs.
small-signal nodes.
ing with copper will reduce the temperature rise of
power components. Connect the copper areas to PGND
(exposed pad) for best performance.
The resistor divider must be connected between V
and SGND.
C
SS
=
2MΩ •In
IN
= 5.5V :
FB
⎛
⎝ ⎜
pin directly to the feedback resistors.
5ms
5.5V – 0.6V
5.5V
IN
SS
⎞
⎠ ⎟
pin, and the (–) terminal
= 21.6nF
= 5ms and a resistor
OUT
3616f
IN
,