LT3686 LINER [Linear Technology], LT3686 Datasheet - Page 16

• Manufacturer Part Number: LT3686
• Manufacturer: LINER [Linear Technology]

ApplicAtions inForMAtion
LT3686
BAT54) in parallel with the internal diode to reduce V
following equations can be used to calculate and minimize
boost capacitance in μF:
V
forward drop of the catch diode (D1), and frequency is
in MHz.
For lower output voltages the BD pin can be tied to an
external voltage source with adequate local bypassing
(Figure 8b). The above equations still apply for calculating

D
C
is the forward drop of the boost diode, V
BOOST
=
(V
BD
+ V
CATCH
0.065
– V
D
− 2.2) • f
V
V
V
V
8a
8b
8c
DD
IN
IN
IN
V
MAX V
V
MAX V
V
MAX V
BOOST
BOOST
BOOST
CATCH
BOOST
BOOST
BOOST
V
V
V
– V
– V
– V
IN
IN
IN
SW
SW
SW
D
is the
≅ V
≅ V
≅ 2V
LT3686
LT3686
LT3686
. The
≅ V
≅ V
≅ V
GND
GND
GND
BD
BD
BD
IN
IN
IN
OUT
DD
IN
+ V
+ V
Figure 8
BOOST
BOOST
BOOST
OUT
DD
SW
SW
SW
DA
DA
DA
the optimal boost capacitor for the chosen BD voltage.
The absence of BD voltage during startup will increase
minimum voltage to start and reduce efficiency. You must
also be sure that the maximum voltage rating of BOOST
pin is not exceeded. The BD pin can also be tied to V
(Figure 8c) but V
load circuit is automatically disabled.
The minimum operating voltage of an LT3686 applica-
tion is limited by the undervoltage lockout (3.6V) and by
the maximum duty cycle as outlined above. For proper
start-up, the minimum input voltage is also limited by
the boost circuit. If the input voltage is ramped slowly, or
IN
V
V
V
3686 F08
OUT
OUT
OUT
will be limited to 25V and the active
3686fa
IN