LTC3727LX-1_15 Datasheet, PDF (25/28 Pages) Linear Technology – High Efficiency, 2-Phase Synchronous Step-Down Switching Regulator

LTC3727LX-1
APPLICATIO S I FOR ATIO
peaks. An additional 1µF ceramic capacitor placed
immediately next to the INTV_CC and PGND pins can help
improve noise performance substantially.
6. Keep the switching nodes (SW1, SW2), top gate nodes
(TG1, TG2), and boost nodes (BOOST1, BOOST2) away
from sensitive small-signal nodes, especially from the
opposites channel’s voltage and current sensing feed-
back pins. All of these nodes have very large and fast
moving signals and therefore should be kept on the
“output side” of the LTC3727LX-1 and occupy mini-
mum PC trace area.
7. Use a modified “star ground” technique: a low imped-
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_CC
decoupling capacitor, the bottom of the voltage feed-
back resistive divider and the SGND pin of the IC.
PC Board Layout Debugging
Start with one controller on at a time. It is helpful to use
a DC-50MHz current probe to monitor the current in the
inductor while testing the circuit. Monitor the output
switching node (SW pin) to synchronize the oscilloscope
to the internal oscillator and probe the actual output
voltage as well. Check for proper performance over the
operating voltage and current range expected in the
application. The frequency of operation should be main-
tained over the input voltage range down to dropout and
until the output load drops below the low current opera-
tion threshold—typically 10% to 20% of the maximum
designed current level in Burst Mode operation.
The duty cycle percentage should be maintained from
cycle to cycle in a well-designed, low noise PCB imple-
mentation. Variation in the duty cycle at a subharmonic
rate can suggest noise pickup at the current or voltage
V_IN
R_IN
+
C_IN
SW1
D1
BOLD LINES INDICATE
HIGH SWITCHING
CURRENT. KEEP LINES
TO A MINIMUM LENGTH
SW2
D2
L1
R_{SENSE1 VOUT1}
+
C_OUT1
L2
R_{SENSE2 VOUT2}
+
C_OUT2
R_L1
R_L2
3727LX1 F11
Figure 11. Branch Current Waveforms
3727lx1fa
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