LTC3831-1 Linear Technology, LTC3831-1 Datasheet - Page 18

• Manufacturer Part Number: LTC3831-1
• Description: High Power Synchronous Switching Regulator Controller
• Manufacturer: Linear Technology

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LTC3831-1
APPLICATIO S I FOR ATIO
Traces carrying high current should be as wide as pos-
sible. For example, a PCB fabricated with 2oz copper
requires a minimum trace width of 0.15" to carry 5A .
1. In general, layout should begin with the location of the
power devices. Be sure to orient the power circuitry so that
a clean power flow path is achieved. Conductor widths
should be maximized and lengths minimized. After you are
satisfied with the power path, the control circuitry should
be laid out. It is much easier to find routes for the relatively
small traces in the control circuits than it is to find
circuitous routes for high current paths.
2. The GND and PGND pins should be shorted directly at
the LTC3831-1 . This helps to minimize internal ground dis-
turbances in the LTC3831-1 and prevents differences in
ground potential from disrupting internal circuit operation.
This connection should then tie into the ground plane at
a single point, preferably at a fairly quiet point in the circuit
such as close to the output capacitors . This is not always
practical, however, due to physical constraints. Another
reasonably good point to make this connection is between
the output capacitors and the source connection of the
bottom MOSFET Q2. Do not tie this single point ground in
the trace run between the Q2 source and the input capaci-
tor ground, as this area of the ground plane will be very
noisy.
18
3.3V
C1
68pF
2.2 F
4.7 F
D1
SHDN
R
1k
C
0.01 F
C
22nF
C
0.1 F
D2
V
SS
FREQSET
SHDN
COMP
PV
CC
CC2
LTC3831-1
U
D3
R
–
PV
PGND
I
CC1
GND
U
MAX
TG
I
BG
R
FB
FB
+
0.1 F
Figure 9. DDR Memory Termination with Triple Charge Pump
W
C
C
D1, D2, D3: MBR0520LT1
Q1, Q2: SILICONIX Si9426DY
IN
OUT
: SANYO POSCAP 4TPB220M
10k
: PANASONIC EEFUE0G181R
1k
0.1 F
U
V
1.5V
DDQ
Q1
Q2
B320A
B320A
1.3 H
3. The small-signal resistors and capacitors for frequency
compensation and soft-start should be located very close
to their respective pins and the ground ends connected to
the signal ground pin through a separate trace. Do not
connect these parts to the ground plane!
4. The V
be as close to the LTC3831-1 as possible. The 4.7 F and
2.2 F bypass capacitors shown at V
will help provide optimum regulation performance.
5. The (+) plate of C
possible to the drain of the upper MOSFET, Q1. An addi-
tional 1 F ceramic capacitor between V
is recommended.
6. The V
ing node. Care should be taken to isolate V
capacitive coupling to the inductor switching signal.
7. In a typical SSTL application, if the R
nected to V
the switching regulator, do not connect R
current flow path; it should be connected to the SSTL in-
terface supply output. R
face supply GND.
8. Kelvin sense I
L
O
180 F
C
OUT
+
CC
FB
+
, PV
pin is very sensitive to pickup from the switch-
38311 F09
DDQ
C
220 F
V
(V
0.75V
IN
CC1
TT
10A
OUT
, which is also the main supply voltage for
MAX
)
and PV
and I
IN
should be connected as close as
–
100
CC2
should be connected to the inter-
90
80
70
60
50
40
30
20
10
FB
0
0
at Q1’s drain and source pins.
decoupling capacitors should
Efficiency vs Load Current
1
2
3
LOAD CURRENT (A)
CC
IN
4
, PV
and power ground
+
FB
pin is to be con-
5
+
CC1
along the high
from possible
6
V
DDQ
and PV
V
7
DDQ
= 1.5V
T
A
8
= 1.8V
= 25 C
38311 F10
9
38311f
CC2
10