LTC3728_15 Datasheet, PDF (30/36 Pages) Linear Technology – Dual, 550kHz, 2-Phase Synchronous Step-Down Switching Regulator

LTC3728
APPLICATIONS INFORMATION
SW1
D1
L1
R_{SENSE1 VOUT1}
+
C_OUT1
V_IN
R_IN
+
C_IN
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
3728 F11
Figure 11. Branch Current Waveforms
signal ground. The R2 and R4 connections should not
be along the high current input feeds from the input
capacitor(s).
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 connections 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 im-
mediately next to the INTV_CC and PGND pins can help
improve noise performance substantially.
30
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
feedback pins. All of these nodes have very large and
fast moving signals and therefore should be kept on
the output side of the LTC3728 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.
3728fg