LT3506 LINER [Linear Technology], LT3506 Datasheet - Page 12

• Manufacturer Part Number: LT3506
• Description: Dual Monolithic 1.6A Step-Down Switching Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT3506/LT3506A
shows three ways to arrange the boost circuit. The BOOST
pin must be more than 2.5V above the SW pin for full
efficiency. For outputs of 3.3V and higher the standard
circuit (Figure 3a) is best. For outputs between 2.8V and
3.3V, use a small Schottky diode (such as the BAT-54).
For lower output voltages the boost diode can be tied to
the input (Figure 3b). The circuit in Figure 3a is more ef-
ficient because the BOOST pin current comes from a lower
voltage source. Finally, as shown in Figure 3c, the anode
of the boost diode can be tied to another source that is
at least 3V. For example, if you are generating 3.3V and
1.8V and the 3.3V is on whenever the 1.8V is on, the 1.8V
boost diode can be connected to the 3.3V output. In any
case, you must also be sure that the maximum voltage at

V
INB
> 3V
V
V
IN
IN
V
MAX V
V
MAX V
MINIMUM VALUE FOR V
BOOST
BOOST
U
V
BOOST
V
BOOST
IN
– V
D2
– V
IN
SW
SW
BOOST
LT3506
BOOST
LT3506
≅ V
U
GND
≅ V
GND
≅ V
≅ V
IN
INB
OUT
INB
+ V
+ V
SW
SW
OUT
(3a)
(3c)
IN
INB =
W
3V
C3
C3
Figure 3. Generating the Boost Voltage
D2
U
V
OUT
V
OUT
the BOOST pin is less than the maximum specified in the
Absolute Maximum Ratings section.
The boost circuit can also run directly from a DC voltage
that is higher than the input voltage by more than 3V,
as in Figure 3d. The diode is used to prevent damage to
the LT3506 in case V
The circuit saves several components (both BOOST pins
can be tied to D2). However, efficiency may be lower and
dissipation in the LT3506 may be higher. Also, if V
absent, the LT3506 will still attempt to regulate the output,
but will do so with very low efficiency and high dissipation
because the switch will not be able to saturate, dropping
1.5V to 2V in conduction.
>V
IN
+ 3V
V
V
V
INB
IN
IN
V
MAX V
MAX V
MAX V
MINIMUM VALUE FOR V
BOOST
V
BOOST
V
BOOST
BOOST
D2
D2
IN
– V
IN
SW
BOOST
LT3506
BOOST
LT3506
≅ 2V
– V
≅ V
GND
GND
INB
≅ V
SW
INB
IN
IN
is held low while V
≅ V
SW
SW
(3b)
(3d)
INB
INB =
V
IN
+ 3V
C3
3506 F03
IN
V
V
OUT
OUT
is present.
INB
3506afb
is