ltc3612 Linear Technology Corporation, ltc3612 Datasheet - Page 23

• Manufacturer Part Number: ltc3612
• Description: 3a, 4mhz Monolithic Synchronous Step-down Dc/dc Converter
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
C
Decoupling the 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.
Finally, defi ne 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 2M, 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.
IN
I
R1 = 196k •
C
RMS
should be sized for a maximum current rating of:
SS
=
= 3A •
2M •In
IN
1.8V
3.6V
⎛
⎝ ⎜
= 5.5V :
⎛
⎝ ⎜
1.8V
0.6V
IN
5.5V – 0.6V
5ms
with two 22μF capacitors, is adequate
•
5.5V
− 1
⎛
⎝ ⎜
3.6V
1.8V
⎞
⎠ ⎟
⎞
⎠ ⎟
– 1
SS
= 21.6nF
⎞
⎠ ⎟
= 5ms and a resistor
= 1.5A
RMS
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3612:
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 LTC3612.
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.
FB
pin directly to the feedback resistors.
IN
pin, and the (–) terminal
LTC3612
23
OUT
3612f
IN
,