LTC3603
16
3603fc
For more information www.linear.com/LTC3603
applications inForMation
Choose a standard value of R2 = 475k. The voltage on
the MODE pin will be set to 0.6V by tying the MODE pin
to the FB pin. This will set the burst current equal to ap
-
proximately 1A. Figure 6 shows a complete schematic for
this design example.
How to Reduce SW Ringing
As with any switching regulator, there will be voltage
ringing on the SW node, especially for high input voltages.
The ringing amplitude and duration is dependent on the
switching speed (gate drive), layout (parasitic inductance)
and MOSFET output capacitance. This ringing contributes
to the overall EMI, noise and high frequency ripple. One
way to reduce ringing is to optimize layout. A good layout
minimizes parasitic inductance. Adding an RC snubber
from SW to GND is also an effective way to reduce ringing.
Finally, adding a resistor (10Ω to 100Ω) in series with the
BOOST pin will slow down the MOSFET turn-on slew rate
and dampen ringing, but at the cost of reduced efficiency.
Note that since the IC is buffered from high frequency
transients by PCB and bondwire inductances, the ringing
by itself is normally not a concern for reliability.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC3603. Check the following in your layout:
1. A ground plane is recommended. If a ground plane layer
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 LTC3603.
2. Connect the (+) terminal of the input capacitor(s), C
IN
, as
close as possible to the PV
IN
pin. This capacitor provides
the AC current into the internal power MOSFETs.
3. Keep the switching node, SW, away from all sensitive
small-signal nodes.
4. Flood all unused areas on all layers with copper. Flooding
with copper will reduce the temperature rise of power
components. You can connect the copper areas to any
DC net (PV
IN
, INTV
CC
, V
OUT
, PGND, SGND, or any other
DC rail in your system).
Figure 6. 12V to 3.3V, 2.5A Regulator at 1MHz, Burst Mode Operation
C
IN
22µF
V
IN
12V
V
OUT
3.3V
2.5A
3603 F06
D1
L1
2.2µH
R
OSC
105k
R
ITH
4.32k
R1
105k
R
PG
200k
L1: VISHAY IHLP2525CZER2R2MO1
C
IN
: TAIYO YUDEN TMK325BJ226MM-T
C
OUT
:
TDK
C3225X5ROJ107M
C
VCC
1µF
C
ITH
1nF
C
OUT
100µF
SYNC/MODE
PGOOD
RT
ITH
V
FB
RUN
TRACK/SS
PGND
INTV
CC
PV
IN
PV
IN
BOOST
SW
SW
SW
PGND
PGND
LTC3603
R2
475k
C
BST
0.22µF
PGOOD
C
FB
10pF
