ltc3862gn-1 Linear Technology Corporation, ltc3862gn-1 Datasheet - Page 24

• Manufacturer Part Number: ltc3862gn-1
• Description: Multi-phase Current Mode Step-up Dc/dc Controller
• Manufacturer: Linear Technology Corporation

LTC3862-1
Typical Boost Applications Circuit
A basic 2-phase, single output LTC3862-1 application
circuit is shown in Figure 18. External component selec-
tion 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:
where V
minimum on-time for a given application operating in
CCM is:
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 LTC3862-1 minimum on-time can be programmed
from 210ns to 375ns using the BLANK pin.
APPLICATIONS INFORMATION
24
D =
t
ON(MIN)
F
V
O
is the forward voltage of the boost diode. The
V
+ V
10nF
=
O
1
f
+ V
100pF
66.5k
0.1μF
39.2k
F
V
– V
V
OUT
F
O
IN
+ V
12.4k
475k
V
F
= t
O
Figure 18. A Typical 2-Phase, Single Output Boost Converter Application Circuit
– V
+ V
ON
IN(MAX)
F
D
SLOPE
BLANK
PHASEMODE
FREQ
SS
ITH
FB
SGND
CLKOUT
SYNC
PLLFLTR
• f
MAX
LTC3862-1
SENSE1
SENSE1
SENSE2
SENSE2
INTV
GATE1
GATE2
PGND
RUN
3V8
V
CC
IN
+
–
–
+
24.9k
4.7μF
1nF
1μF
10nF
10nF
150k
8.5V TO 36V
V
IN
Minimum On-Time Limitations
In a single-ended boost converter, two steady-state condi-
tions can result in operation at the minimum on-time of
the controller. The fi rst condition is when the input voltage
is close to the output voltage. When V
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.
6.8μF 50V
PA2050-193
PA2050-193
10Ω
10Ω
19μH
19μH
6.8μF 50V
6.8μF 50V
L1
L2
Q1
HAT2279H
0.005Ω
1W
0.005Ω
1W
Q2
HAT2279H
PDS760
PDS760
D1
D2
100μF
100μF
63V
63V
+
+
6.8μF 50V
6.8μF 50V
6.8μF 50V
6.8μF 50V
38621 F18
IN
approaches V
V
48V
3A TO 5A
OUT
38621f
OUT