LTC3633 LINER [Linear Technology], LTC3633 Datasheet - Page 21

• Manufacturer Part Number: LTC3633
• Description: Dual Channel 3A, 15V Monolithic Synchronous Step-Down Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
of power loss in the package with corresponding output
load current. Although making this measurement with this
method does violate absolute maximum voltage ratings
on the PGOOD pin, the applied power is so low that there
should be no signifi cant risk of damaging the device.
Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3633. Check the following in your layout:
1) Do the input capacitors connect to the V
2) The output capacitor, C
3) The resistive divider, (e.g. R1 to R4 in Figure 8) must be
4) Keep sensitive components away from the SW pin.
5) A ground plane is preferred, but if not available, the
pins as close as possible? These capacitors provide
the AC current to the internal power MOSFETs and their
drivers.
closely connected to minimize loss. The (–) plate of
C
the (–) plate of C
connected between the (+) plate of C
line terminated near SGND. The feedback signal V
should be routed away from noisy components and
traces, such as the SW line, and its trace length should
be minimized. In addition, the R
compensation components should be terminated to
SGND.
The R
feedback resistors, and the INTV
should all be routed away from the SW trace and the
inductor L.
signal and power grounds should be segregated with
both connecting to a common, low noise reference point.
The connection to the PGND pin should be made with
a minimal resistance trace from the reference point.
OUT
should be closely connected to both PGND and
T
resistor, the compensation components, the
IN
.
OUT
, and inductor L should be
CC
T
resistor and loop
OUT
bypass capacitor
and a ground
IN
and PGND
FB
6) Flood all unused areas on all layers with copper in order
Refer to Figures 9 and 10 for board layout examples.
Design Example
As a design example, consider using the LTC3633 in an
application with the following specifi cations: V
= 13.2V, V
I
following discussion will use equations from the previous
sections.
Because effi ciency is important at both high and low load
current, Burst Mode operation will be utilized.
First, the correct R
quency must be chosen. Based on the equation discussed
earlier, R
162k. RT can be tied to INTV
accuracy is not critical.
Next, determine the channel 1 inductor value for about
40% ripple current at maximum V
A standard value of 0.68μH should work well here. Solv-
ing the same equation for channel 2 results in a 1μH
inductor.
C
ment. For a V
OUT(MIN)
OUT
to reduce the temperature rise of power components.
These copper areas should be connected to the exposed
backside of the package (PGND).
L1=
C
OUT1
will be selected based on the charge storage require-
2MHz • 1.2A
T
≈
= 10mA, f = 2MHz, V
should be 160k; the closest standard value is
OUT1
3 • ΔI
f
0
1.8V
DROOP
V
DROOP
= 1.8V, V
OUT
T
resistor value for 2MHz switching fre-
of 90mV for a 3A load step:
=
1
(2MHz)(90mV)
OUT2
13.2V
3 • (3A)
1.8V
CC
DROOP
= 3.3V, I
if switching frequency
IN
= 0.64μH
:
~ (5% • V
LTC3633
= 50μF
OUT(MAX)
OUT
21
IN(MAX)
). The
= 3A,
3633f