LTC3770 Datasheet, PDF (21/24 Pages) Linear Technology – Synchronous Controller with Margining, Tracking and PLL

APPLICATIO S I FOR ATIO
R7
47k
R8
R5
51k
39k
R6
11k
INTV_CC
5V
R_PG
100k
RUN
R_C
20k
CC1
500pF
CC2
100pF
R3
10k
R_ON
75k
R1
R2
R4
30.1k
95.3k
82k
1
LTC3770EG
28
RUN
FCB
2
27
V_ON
3
Z0
26
PGOOD
BOOST
4
25
V_RNG
5
TG
24
V_FB
6
SW
23
I_TH
7
PGND
22
SGND
BG
8
21
MARGIN1 INTV_CC
9
20
MARGIN0
Z1
10
19
I_ON
11
Z2
18
V_REFIN
12
Z_VIN
17
V_REFOUT
13
V_IN
16
MPGM
PLLIN
14
15
TRACK/SS PLLFLTR
C_SS
0.1µF
CV_IN
0.1µF
LTC3770
M1
Si4884
+ _CB
0.22µF
L1
1.8µH
DB
CMDSH-3
D1
B340A
+
CV_CC
10µF
M2
Si4874
V_IN
5V TO 28V
C_IN
10µF
50V
x3
+
C_OUT3
23µF
x5R
x2
V_OUT
2.5V
10A
C_OUT1-2
180µF
4V
x2
L1: SUMIDA CEP125-1R8MC-H
C_OUT: CORNELL DUBILIER ESRE181E04B
C_IN: UNITED CHEMICON THCR60E1H106ZT
3770 F12
Figure 12. Design Example: 2.5V/10A at 450kHz
To set a ±25% margining, select the resistors R3, R4 such
that
V_REFIN = 0.6 ±25% • 0.6
or
1.18 • R3 _{= 25% • 0.6}
R4
R4 ≈ 8R3
Choose R3 to be 10k, R4 to be 82k for this application.
PC Board Layout Checklist
When laying out a PC board follow one of two suggested
approaches. The simple PC board layout requires a dedi-
cated ground plane layer. Also, for higher currents, it is
recommended to use a multilayer board to help with heat
sinking power components.
• The ground plane layer should not have any traces and
it should be as close as possible to the layer with power
MOSFETs.
• Place C_IN, C_OUT, MOSFETs, D1 and inductor all in one
compact area. It may help to have some components on
the bottom side of the board.
• Use an immediate via to connect the components to
ground plane including SGND and PGND of LTC3770.
Use several bigger vias for power components.
• Use compact plane for switch node (SW) to improve
cooling of the MOSFETs and to keep EMI down.
• Use planes for V_IN and V_OUT to maintain good voltage
filtering and to keep power losses low.
• Flood all unused areas on all layers with copper. Flood-
ing with copper will reduce the temperature rise of
power component. You can connect the copper areas to
any DC net (V_IN, V_OUT, GND or to any other DC rail in
your system).
3770f
21