LTC3857 Datasheet, PDF (28/38 Pages) Linear Technology – Low IQ, Dual, 2-Phase Synchronous Step-Down Controller

LTC3857
Applications Information
SW1
D1
V_IN
R_IN
C_IN
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
3857 F12
Figure 12. 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
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’ cur-
rent peaks. An additional 1µF ceramic capacitor placed
immediately next to the INTV_CC and PGND pins can help
improve noise performance substantially.
28
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 LTC3857 and occupy minimum
PC trace area.
7. Use a modified star groundtechnique: a low impedance,
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.
3857fa