LTC3835-1 Linear Technology, LTC3835-1 Datasheet - Page 22

• Manufacturer Part Number: LTC3835-1
• Description: Low IQ Synchronous Step-Down Controller
• Manufacturer: Linear Technology

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PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the IC. These items are also illustrated graphically in the
layout diagram of Figure 8. The Figure 9 illustrates the
current waveforms present in the various branches of the
synchronous regulator operating in the continuous mode.
Check the following in your layout:
1. Is the top N-channel MOSFET M1 located within 1cm
2. Are the signal and power grounds kept separate? The
3. Does the LTC3835-1 V
LTC3835-1
APPLICATIONS INFORMATION
22
of C
combined IC signal ground pin and the ground return
of C
minals. The path formed by the top N-channel MOSFET,
Schottky diode and the C
leads and PC trace lengths. The output capacitor (–)
terminals should be connected as close as possible
to the (–) terminals of the input capacitor by placing
the capacitors next to each other and away from the
Schottky loop described above.
(+) terminals of C
nected between the (+) terminal of C
The feedback resistor connections should not be along the
high current input feeds from the input capacitor(s).
IN
INTVCC
?
must return to the combined C
OUT
? The resistive divider must be con-
FB
pin resistive divider connect to the
IN
f
IN
capacitor should have short
Figure 8. LTC3835-1 Recommended Printed Circuit Layout Diagram
TRACK/SS
SENSE
SENSE
V
PLLLPF
PLLIN/MODE
RUN
I
SGND
TH
FB
OUT
LTC3835EGN-1
+
–
and signal ground.
OUT
BOOST
INTV
PGND
SW
V
BG
TG
CC
IN
(–) ter-
D
C
B
B
4. Are the SENSE
5. Is the INTV
6. Keep the switching node (SW), top gate node (TG), and
7. Use a modifi ed “star ground” technique: a low imped-
minimum PC trace spacing? The fi lter capacitor between
SENSE
to the IC. Ensure accurate current sensing with Kelvin
connections at the SENSE resistor.
the IC, between the INTV
This capacitor carries the MOSFET drivers current peaks.
An additional 1μF ceramic capacitor placed immediately
next to the INTV
noise performance substantially.
boost node (BOOST) away from sensitive small-signal
nodes, especially from the opposites channel’s voltage
and current sensing feedback pins. All of these nodes
have very large and fast moving signals and therefore
should be kept on the “output side” of the LTC3835-1
and occupy minimum PC trace area.
ance, large copper area central grounding point on
the same side of the PC board as the input and output
capacitors with tie-ins for the bottom of the INTV
decoupling capacitor, the bottom of the voltage feedback
resistive divider and the SGND pin of the IC.
C
+
INTVCC
+
and SENSE
C
VIN
V
R
CC
M1
IN
IN
decoupling capacitor connected close to
–
and SENSE
CC
CERAMIC
3835-1 F08
+
M2
1μF
and PGND pins can help improve
C
–
IN
should be as close as possible
L1
CC
and the power ground pins?
+
leads routed together with
R
C
D1
OPTIONAL
SENSE
OUT
+
GND
V
OUT
38351fc
CC