lt3686a Linear Technology Corporation, lt3686a Datasheet - Page 16

• Manufacturer Part Number: lt3686a
• Description: 37v/1.2a Step-down Regulator In 3mm
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT3686A
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. A typical value of 0.22μF can be used for C
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
16
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
CATCH
V
MAX V
V
MAX V
V
MAX V
BOOST
BOOST
BOOST
BOOST
D
is the
BOOST
BOOST
BOOST
V
V
V
. The
– V
– V
– V
IN
IN
IN
SW
SW
SW
Figure 8.
.
LT3686A
LT3686A
LT3686A
≅ V
≅ V
≅ 2V
≅ V
≅ V
≅ V
GND
GND
GND
BD
BD
BD
IN
IN
IN
OUT
DD
IN
+ V
+ V
BOOST
BOOST
BOOST
the optimal boost capacitor for the chosen BD voltage.
The absence of BD voltage during startup will increase
minimum voltage to start and reduce effi ciency. 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 LT3686A 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
OUT
DD
SW
SW
SW
DA
DA
DA
IN
will be limited to 25V and the active
3686A F08
V
V
V
OUT
OUT
OUT
3686af
IN