LTC3858_15 Datasheet, PDF (28/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

LTC3858
APPLICATIONS INFORMATION
SS1
LTC3858
I_TH1
PGOOD2
V_FB1
SENSE1⁺
PGOOD1
TG1
SENSE1^–
SW1
FREQ
BOOST1
PHASMD
BG1
CLKOUT
f_IN
PLLIN/MODE
V_IN
RUN1
RUN2
SGND
SENSE2^–
PGND
EXTV_CC
INTV_CC
V_OUT1
SENSE2⁺
BG2
V_FB2
BOOST2
I_TH2
SW2
TG2
SS2
R_PU2
V_PULL-UP
(<6V)
PGOOD2
R_PU1
V_PULL-UP
(<6V)
PGOOD1
L1
R_SENSE
C_B1
M1
M2
D1
C_VIN
R_IN
1μF
CERAMIC
C_OUT1
C_INTVCC
C_B2
V_IN
C_IN
1μF
CERAMIC
M3
M4
L2
C_OUT2
D2
R_SENSE
V_OUT1
GND
V_OUT2
3858 F10
Figure 10. Recommended Printed Circuit Layout Diagram
Reduce V_IN from its nominal level to verify operation
of the regulator in dropout. Check the operation of the
undervoltage 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
3858fc
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