LTC3854 LINER [Linear Technology], LTC3854 Datasheet - Page 11

• Manufacturer Part Number: LTC3854
• Description: Small Footprint, Wide VIN Range Synchronous Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
capacitor is equal to the voltage drop across the inductor
DCR • R2/(R1+R2). R2 may be used to scale the voltage
across the same terminals when the DCR is greater than
the target sense resistance. Check the manufacturer’s
datasheet for specifications regarding the inductor DCR, in
order to properly dimension the external filter components.
The DCR of the inductor can also be measured using a
precision RLC meter.
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant-fre-
quency architectures by preventing subharmonic oscil-
lations at high duty cycles. It is accomplished internally
by adding a compensating ramp to the inductor current
signal. Normally, this results in a reduction of maximum
inductor peak current for high duty cycles. However, the
LTC3854 uses a novel scheme that allows the maximum
inductor peak current to remain unaffected throughout
all duty cycles.
R
FB1
C
SS
R
R
V
FB2
C
C
IN
C
Figure 2. Buck Regulator Using DCR Current Sense
C
C2
RUN/SS
ITH
FB
SENSE
SENSE
LTC3854
–
+
V
IN
BOOST
INTV
GND
SW
BG
TG
CC
D
C
BOOST
VINT
C
B
Inductor Value Calculation
The inductor value has a direct effect on ripple current.
The inductor ripple current ∆I
inductance or frequency and increases with higher V
Accepting larger values of ∆I
inductors, but results in a higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is I
∆I
Option 1: DCR within desired range
Option 2: DCR > desired R
L
L
R1• C1=
R1||R2 • C1 =
R
occurs at the maximum input voltage.
M1
M2
MIN
SENSE
=
∆I
(EQ) = DCR(MAX) •
R1
C
DCR
INDUCTOR
IN
L
L
L
1
• f
SW
DCR
R2
(R2 not used)
DCR
C1
L
• V
3854 F02
OUT
(at 20°C)
L
SENSE
= 0.4 • (I



L
1−
allows the use of low value
C
R1+ R2
L
OUT
V
V
OUT
IN(MAX)
R2
decreases with higher
V
OUT
MAX
LTC3854
). The maximum




3854fa
IN
.