LTC3642 Datasheet, PDF (16/20 Pages) Linear Technology – High Effi ciency, High Voltage 50mA Synchronous Step-Down Converter

LTC3642
APPLICATIONS INFORMATION
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3642. Check the following in your layout:
1. Large switched currents flow in the power switches
and input capacitor. The loop formed by these compo-
nents should be as small as possible. A ground plane
is recommended to minimize ground impedance.
2. Connect the (+) terminal of the input capacitor, C_IN, as
close as possible to the V_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. The rapid transitions on the switching
node can couple to high impedance nodes, in particular
V_FB, and create increased output ripple.
4. Flood all unused area 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 (V_IN, V_OUT, GND or any other DC rail in your
system).
TYPICAL APPLICATIONS
V_IN
5V TO 45V
C_IN
4.7μF
V_IN
SW
LTC3642
RUN
V_FB
HYST
I_SET
SS
R_SET
GND
L1
220μH
R1
4.2M
R2
800k
C_SS
47nF
3642 F10a
C_IN: TDK C5750X7R2A475MT
C_OUT: AVX 1812D107MAT
L1: TDK SLF7045T-221MR33-PF
V_OUT
C_OUT ^5V
100μF
Figure 10. High Efficiency 5V Regulator
3.3V, 50mA Regulator with Peak Current Soft-Start, Small Size
V_IN
4.5V TO 24V
C_IN
1μF
C_SS
0.1μF
V_IN
SW
LTC3642
RUN
V_FB
I_SET
SS
HYST
GND
L1
47μH
R1
294k
R2
93.1k
3642 TA02a
C_OUT
10μF
V_OUT
3.3V
50mA
C_IN: TDK C3216X7R1E105KT
C_OUT: AVX 08056D106KAT2A
L1: TAIYO YUDEN CBC2518T470K
Efficiency vs Load Current
94
V_IN = 10V
93
R_SET = 750k
R_SET = 500k
92
I_SET OPEN
91
90
89
88
1
10
LOAD CURRENT (mA)
100
3642 F10b
Soft-Start Waveforms
OUTPUT VOLTAGE
1V/DIV
INDUCTOR CURRENT
20mA/DIV
2ms/DIV
3642 TA03b
3642f
16