LTC3770_15 Datasheet, PDF (21/24 Pages) Linear Technology – Fast No RSENSE Step-Down Synchronous Controller with Margining, Tracking and PLL

APPLICATIONS INFORMATION
INTV_CC
5V
R_PG
100k
R7
47k
R8
RUN
R5
51k
39k
R6
11k
R_C
20k
CC1
500pF
R3
CC2
10k
100pF
R_ON
75k
R1
R2
R4
30.1k
95.3k
82k
1
LTC3770EG
28
RUN
FCB
2
27
3 ^VON
Z0
26
PGOOD
BOOST
4
25
5 ^VRNG
TG
24
6 ^VFB
SW
23
7 ^ITH
PGND
22
SGND
BG
8
21
MARGIN1
9
INTV_{CC 20}
MARGIN0
Z1
10
19
11 ^ION
Z2
18
12 ^VREFIN
Z_{VIN 17}
13 ^VREFOUT
V_{IN 16}
MPGM
PLLIN
14
15
TRACK/SS PLLFLTR
C_SS
0.1μF
CV_IN
0.1μF
LTC3770
M1
Si4884
V_IN
5V TO 28V
C_IN
10μF
50V
x3
+ _CB
0.22μF
L1
1.8μH
DB
CMDSH-3
D1
B340A
+ _CVCC
4.7μF
M2
Si4874
V_OUT
2.5V
10A
+
C_OUT3
23μF
x5R
x2
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
dedicated 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. Flooding
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).
3770fc
21