Datasheet

LTC3862
24
3862fc
For more information www.linear.com/LTC3862
Figure 18. A Typical 2-Phase, Single Output Boost Converter Application Circuit
Typical Boost Applications Circuit
A basic 2-phase, single output LTC3862 application circuit
is shown in Figure 18. External component selection is
driven by the characteristics of the load and the input supply.
Duty Cycle Considerations
For a boost converter operating in a continuous conduction
mode (CCM), the duty cycle of the main switch is:
D
VVV
VV
tf
OFIN
OF
ON
=
+
+






=
–
•
where V
F
is the forward voltage of the boost diode. The
minimum on-time for a given application operating in
CCM is:
t
f
VVV
VV
ON MIN
OFIN MAX
OF
()
()
–
=
+
+






1
For a given input voltage range and output voltage, it is
important to know how close the minimum on-time of the
application comes to the minimum on-time of the control
IC. The LTC3862 minimum on-time can be programmed
from 180ns to 340ns using the BLANK pin.
Minimum On-Time Limitations
In a single-ended boost converter, two steady-state con
-
ditions can result in operation at the minimum on-time of
the controller. The first condition is when the input voltage
is close to the output voltage. When V
IN
approaches V
OUT
the voltage across the inductor approaches zero during
the switch off-time. Under this operating condition the
converter can become unstable and the output can experi
-
ence high ripple voltage oscillation at audible frequencies.
For applications where the input voltage can approach
or exceed the output
voltage, consider using a SEPIC or
buck-boost topology instead of a boost converter.
The second condition that can result in operation at the
minimum on-time of the controller is at light load, in deep
discontinuous mode. As the load current is decreased,
the on-time of the switch decreases, until the minimum
on-time limit of the controller is reached. Any further de
-
crease in the output current will result in pulse skipping,
a typically benign condition where cycles are skipped in
order to maintain output regulation.
applicaTions inForMaTion
SENSE1
+
3V8
SLOPE
BLANK
CLKOUT
SYNC
PLLFLTR
PHASEMODE
D
MAX
10nF
SENSE1
–
SENSE2
–
SENSE2
+
RUN
FREQ
SS
V
IN
66.5k 24.9k
84.5k
10Ω
V
IN
5V TO 36V
D1
PDS760
D2
PDS760
10Ω
L2
19.4µH
PA2020-193
ITH
SGND
V
OUT
12.4k
FB
68.1k
475k
10nF
1µF
1nF
6.8µF 50V
0.006Ω
1W
Q1
HAT2266H
Q2
HAT2266H
0.006Ω
1W
V
OUT
48V
2A TO 5A
3862 F18
100µF
63V
100µF
63V
6.8µF 50V
6.8µF 50V
6.8µF 50V
LTC3862
10nF
100pF
INTV
CC
GATE1
GATE2
PGND
4.7µF
10nF
6.8µF 50V
6.8µF 50V
6.8µF 50V
L1
19.4µH
PA2020-193
+
+