ltc3853euj Linear Technology Corporation, ltc3853euj Datasheet - Page 26

• Manufacturer Part Number: ltc3853euj
• Description: Triple Output, Multiphase Synchronous Step-down Controller
• Manufacturer: Linear Technology Corporation

LTC3853
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 IC. Figure 12 illustrates the current waveforms pres-
ent in the various branches of the 3-phase synchronous
regulators operating in the continuous mode. Check the
following in your layout:
1. Are the top N-channel MOSFETs located within 1 cm of
2. Are the signal and power grounds kept separate? The
3. Do the LTC3853 V
26
each other with a common drain connection at C
not attempt to split the input decoupling for the three
channels as it can cause a large resonant loop.
combined IC signal ground pin and the ground return
of C
minals. The V
possible. 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.
the (+) terminals of C
connected between the (+) terminal of C
ground. The feedback resistor connections should not
be along the high current input feeds from the input
capacitor(s).
INTVCC
must return to the combined C
FB
and I
FB
pins’ resistive dividers connect to
OUT
TH
? The resistive divider must be
IN
traces should be as short as
capacitor should have short
OUT
OUT
and signal
(–) ter-
IN
? Do
4. Are the SENSE
5. Is the INTV
6. Keep the switching nodes (SW), top gate nodes (TG),
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 or inductor, whichever
is used for current sensing.
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.
and boost nodes (BOOST) away from sensitive small-
signal nodes, especially from another 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 LTC3853
and occupy minimum PC trace area. If DCR sensing
is used, place the top resistor (Figure 2b, R1) close to
the switching node.
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.
+
and SENSE
CC
decoupling capacitor connected close to
+
and SENSE
CC
and PGND pins can help improve
–
should be as close as possible
CC
and the power ground pins?
–
leads routed together with
3853f
CC