LTC3786 LINER [Linear Technology], LTC3786 Datasheet - Page 25

• Manufacturer Part Number: LTC3786
• Description: Multi-Phase Current Mode Step-Up DC/DC Controller
• Manufacturer: LINER [Linear Technology]

Typical Boost Applications Circuit
A basic 2-phase, single output LTC3862-2 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 conduc-
tion 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 LTC3862-2 minimum on-time can be programmed
from 210ns to 375ns using the BLANK pin.
applicaTions inForMaTion
D =
t
ON(MIN)

 
F
V
10nF
O
is the forward voltage of the boost diode. The
V
+ V
=
O
100pF
66.5k
0.1µF
39.2k
1
V
f
+ V
OUT
F

 
– V
V
F
O
12.4k
IN
475k
+ V

 
V
F
= t
O
Figure 18. A Typical 2-Phase, Single Output Boost Converter Application Circuit
– V
+ V
ON
D
SLOPE
BLANK
PHASEMODE
FREQ
SS
ITH
FB
SGND
CLKOUT
SYNC
PLLFLTR
IN(MAX)
MAX
F
• f
LTC3862-2

 
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 first 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
10
10
19µH
19µH
6.8µF 50V
6.8µF 50V
L1
L2
0.005
1W
Q1
HAT2279H
0.005
1W
Q2
HAT2279H
PDS760
PDS760
D1
D2
100µF
100µF
63V
63V
+
+
6.8µF 50V
6.8µF 50V
6.8µF 50V
6.8µF 50V
LTC3862-2
38622 F18
IN
approaches V
V
48V
3A TO 5A
OUT
25
38622f
OUT