lt3592emse-trpbf Linear Technology Corporation, lt3592emse-trpbf Datasheet - Page 14

• Manufacturer Part Number: lt3592emse-trpbf
• Description: 500ma Wide Input Voltage Range Step-down Led Driver With 10 1 Dimming
• Manufacturer: Linear Technology Corporation

LT3592
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 BAS70) can be
used in parallel with the internal diode to make this boost
circuit even more effective. In most cases, a 0.1μF capaci-
tor works well for the boost circuit. The BOOST pin must
be at least 2.5V above the SW pin for best effi ciency. For
outputs of 3.3V and above, the 0.1μF cap and the internal
14
BATT
CAP
V
IN
LT3592
BOOST
GND
Figure 4. Transient Load Response of the LT3592 with Different Output Capacitors
SW
DA
(5a)
C3
Figure 5. Two Circuits for Generating the Boost Voltage
3592 F05a
D2
V
V
V
V
I
I
OUT
OUT
LED
LED
SW
SW
C = 4.7μF
C = 10μF
100μs/DIV
100μs/DIV
boost diode will be effective. For 3V to 3.3V outputs, use
a 0.22μF capacitor. For outputs between 2.5V and 3V,
use a 0.47μF capacitor and and external Schottky diode
(such as a BAS70) connected in parallel with the internal
Schottky diode, anode to CAP and cathode to BOOST. For
lower input voltages, the external boost Schottky diode’s
anode can be tied to the input voltage. This connection
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.
BATT
3592 F04
D2
CAP
V
IN
BOOST
LT3592
GND
SW
DA
(5b)
C3
3592 F05b
3592f