Datasheet

LTC3568
15
3568fa
applicaTions inForMaTion
1. Does the capacitor C
IN
connect to the power V
IN
(Pin 6) and power GND (Pin 5) as close as possible?
This capacitor provides the AC current to the internal
power MOSFETs and their drivers.
2. Are the C
OUT
and L1 closely connected? The (–) plate
of C
OUT
returns current to PGND and the (–) plate
of C
IN
.
3. The resistor divider, R1 and R2, must be connected
between the (+) plate of C
OUT
and a ground line ter-
minated near SGND (Pin 3). The feedback signal V
FB
should be routed away from noisy components and
traces, such as the SW line (Pin 4), and its trace should
be minimized.
4.
Keep sensitive components away from the SW pin. The
input capacitor C
IN
, the compensation capacitor C
C
and
C
ITH
and all the resistors R1, R2, R
T
, and R
C
should be
routed away from the SW trace and the inductor L1.
5. A
ground plane is preferred, but if not available, keep
the signal and power grounds segregated with small
signal components returning to the SGND pin at one
point which is then connected to the PGND pin.
6. Flood
all unused areas on all layers with copper. Flood-
ing with copper will reduce the temperature rise of
power components. These copper areas should be
connected to one of the input supplies: PV
IN
, PGND,
SV
IN
or SGND.
SV
IN
LTC3568
PGOOD PGOOD
SW
PV
IN
SYNC/MODE V
FB
I
TH
SHDN/R
T
SGND
L1
2µH
V
IN
2.5V TO
5.5V
V
OUT
1.8V/2.5V/3.3V
AT 1.8A
R5
100k
R4
324k
R1A
280k
R3
13k
RS1
1M
BM
RS2
1M
3568 F07a
C3
1000pF
C4 22pF
R2 887K
C2
22µF
x2
SGND SGND
R1B
412k
R1C
698k
PS
FC
PGND
C1
22µF
PGND
PGNDSGND
NOTE: IN DROPOUT, THE OUTPUT TRACKS THE INPUT VOLTAGE
C1, C2: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A915AY-2ROM (D53LC SERIES)
GND
3.3V 2.5V 1.8V
LOAD CURRENT (mA)
EFFICIENCY (%)
100
95
90
85
80
75
70
1 100 1000 10000
3568 F07b
10
V
IN
= 3.3V
V
OUT
= 2.5V
CIRCUIT OF FIGURE 7
Burst Mode
OPERATION
PULSE SKIP
FORCED CONTINUOUS
Figure 7. General Purpose Buck Regulator Using Ceramic Capacitors
Efficiency vs Load Current
Typical applicaTions