LTC3568_15 Datasheet, PDF (15/18 Pages) Linear Technology – 1.8A, 4MHz, Synchronous Step-Down DC/DC Converter

LTC3568
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.
Typical Applications
V_IN
2.5V TO
5.5V
C1
22µF
PGND
RS1
BM ^1M
FC
PS _RS2
1M
R3
13k
SV_IN
PV_{IN PGOOD}
LTC3568 SW
SYNC/MODE
I_TH
V_FB
SHDN/R_T
SGND PGND
C3
1000pF
R5
100k
PGOOD
L1
2µH
R2 887K
3.3V
2.5V 1.8V
C4 22pF
R4
R1A R1B R1C
324k 280k 412k 698k
SGND
SGND
GND
SGND
V_OUT
1.8V/2.5V/3.3V
AT 1.8A
C2
22µF
x2
3568 F07a
PGND
NOTE: IN DROPOUT, THE OUTPUT TRACKS THE INPUT VOLTAGE
C1, C2: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A915AY-2ROM (D53LC SERIES)
Figure 7. General Purpose Buck Regulator Using Ceramic Capacitors
Efficiency vs Load Current
100
Burst Mode
OPERATION
95
90
85
80
PULSE SKIP _{FORCED CONTINUOUS}
75
V_IN = 3.3V
V_OUT = 2.5V
CIRCUIT OF FIGURE 7
70
1
10
100
1000
10000
LOAD CURRENT (mA)
3568 F07b
3568fa
15