Datasheet

LT3592
14
3592fc
APPLICATIONS INFORMATION
BOOST Pin Considerations
The capacitor C3 and an internal Schottky diode from
the CAP to the BOOST pin are used to generate a boost
voltage that is higher than the input voltage. An external
fast switching Schottky diode (such as the BAS40) can
be used in parallel with the internal diode to make this
boost circuit even more effective. In most cases, a 0.1µF
capacitor works well for the boost circuit. The BOOST pin
must be at least 2.5V above the SW pin for best effi ciency.
For output voltages above 12V, use a 0.1µF cap and an
external boost diode (such as a BAS40) connected in
parallel with the internal Schottky diode, anode to CAP
and cathode to BOOST. For outputs between 3.3V and
12V, the 0.1µF cap and the internal boost diode will be
effective. For 3V to 3.3V outputs, use a 0.22µF capacitor.
For output between 2.5V and 3V, use a 0.47µF capacitor
and an external Schottky diode connected as shown in
Figure 5a. For lower output voltages, the external boost
diode’s anode can be tied to the input voltage. This con-
nection is not as effi cient as the others because the BOOST
pin current comes from a higher voltage. The user must
also be sure that the maximum voltage rating of the BOOST
pin is not exceeded.
Figure 4. Transient Load Response of the LT3592 with Different Output Capacitors
Figure 5. Two Circuits for Generating the Boost Voltage
V
IN
CAP
BOOST
GND
SW
DA
BATT
LT3592
(5a)
D2
OPTIONAL
C3
3592 F05a
V
IN
CAP
BOOST
GND
SW
BATT
LT3592
(5b)
D2
C3
3592 F05b
DA
100µs/DIV
V
SW
V
OUT
I
LED
100µs/DIV
V
SW
3592 F04
V
OUT
I
LED
C = 4.7µF
C = 10µF