Datasheet
LTC3646/LTC3646-1
20
36461fa
For more information www.linear.com/LTC3646
The following list summarizes the three possible connec-
tions for EXTV
CC
:
1. EXTV
CC
grounded. This will cause INTV
CC
to be powered
from the internal 5.0V regulator.
2. EXTV
CC
connected directly to V
OUT
. This is the normal
connection for a 4.5V to 6V regulated output and pro-
vides the highest efficiency.
3.
EXTV
CC
connected to an external supply. If an external
supply is available in the 4.5V to 6V range, it may be
used to power EXTV
CC
. Ensure that EXTV
CC
< V
IN
.
Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3646.
1. Does the capacitor C
PVIN
connect to PVIN and PGND
as close to the pins as possible? These capacitors
provide the AC current to the internal power MOSFETs
and drivers. The (–) plate of C
PVIN
should be closely
connected to PGND and the (–) plate of C
OUT
.
2. The output capacitor, C
OUT
, and inductor L1 should
be closely connected to minimize loss. The (–) plate
of C
OUT
should be closely connected to PGND and the
(–) plate of C
IN
.
3. The resistive divider, R1 and R2, must be connected
between the (+) plate of C
OUT
and a ground line termi-
nated near SGND. The feedback signal, V
FB
, should be
routed away from noisy components and traces such as
the SW line, and its trace length should be minimized.
In addition, RT and the loop compensation components
should be terminated to SGND.
4. Keep sensitive components away from the SW pin. The
R
RT
resistor, the feedback resistors, the compensation
components, and the INTV
CC
bypass capacitor should
all be routed away from the SW trace and the inductor.
5. A ground plane is preferred, but if not available the
signal and power grounds should be segregated with
both connecting to a common, low noise reference
point. The point at which the ground terminals of the
V
IN
and V
OUT
bypass capacitors are connected makes a
good, low noise reference point. The connection to the
PGND pin should be made with a minimal resistance
trace from the reference point.
6. Flood all unused areas on all layers with copper in order
to reduce the temperature rise of power components.
These copper areas should be connected to the exposed
backside connection of the IC.
applicaTions inForMaTion