LTC3857-1_15 Datasheet, PDF (28/38 Pages) Linear Technology – Low IQ, Dual, 2-Phase Synchronous Step-Down Controller

LTC3857-1
APPLICATIONS INFORMATION
I_TH1
TRACK/SS1
V_FB1
SENSE1⁺
PGOOD1
TG1
SENSE1^–
SW1
LTC3857-1
BOOST1
BG1
FREQ
f_IN
PLLIN/MODE
V_IN
RUN1
RUN2
SGND
SENSE2^–
PGND
EXTV_CC
INTV_CC
SENSE2⁺
BG2
V_FB2
I_TH2
TRACK/SS2
BOOST2
SW2
TG2
R_PU1
V_PULL-UP
PGOOD1
L1
R_SENSE
C_B1
M1
M2
D1
C_INTVCC
C_B2
R_IN
C_VIN
1μF
CERAMIC
+
V_IN
C_IN
1μF
CERAMIC
M3
M4
C_OUT1
+
+
C_OUT2
D2
R_SENSE
L2
38571 F11
Figure 11. Recommended Printed Circuit Layout Diagram
V_OUT1
GND
V_OUT2
Reduce V_IN from its nominal level to verify operation of
the regulator in dropout. Check the operation of the un-
dervoltage lockout circuit by further lowering V_IN while
monitoring the outputs to verify operation.
Investigate whether any problems exist only at higher out-
put currents or only at higher input voltages. If problems
coincide with high input voltages and low output currents,
look for capacitive coupling between the BOOST, SW, TG,
and possibly BG connections and the sensitive voltage
and current pins. The capacitor placed across the current
sensing pins needs to be placed immediately adjacent to
the pins of the IC. This capacitor helps to minimize the
effects of differential noise injection due to high frequency
capacitive coupling. If problems are encountered with
high current output loading at lower input voltages, look
for inductive coupling between C_IN, Schottky and the top
38571fc
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