LTC3707 Datasheet, PDF (28/32 Pages) Linear Technology – High Effi ciency, 2-Phase Synchronous Step-Down Switching Regulator

LTC3707
APPLICATIONS INFORMATION
V_IN
R_IN
+
C_IN
SW1
D1
L1
R_{SENSE1 VOUT1}
+
C_OUT1
BOLD LINES INDICATE
HIGH, SWITCHING
CURRENT LINES.
KEEP LINES TO A
MINIMUM LENGTH.
SW2
D2
L2
R_{SENSE2 VOUT2}
+
C_OUT2
R_L1
R_L2
3707 F11
Figure 11. Branch Current Waveforms
4. Are the SENSE ^– and SENSE ⁺ leads routed together with
minimum PC trace spacing? The filter capacitor between
SENSE⁺ and SENSE^– should be as close as possible to
the IC. Ensure accurate current sensing with Kelvin con-
nections at the SENSE resistor.
5. Is the INTV_CC decoupling capacitor connected close to
the IC, between the INTV_CC and the power ground pins?
This capacitor carries the MOSFET drivers current 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
28
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 LTC3707 and occupy minimum 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 feedback resistive divider and
the SGND pin of the IC.
3707fb