LT3592

14

3592fa

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 efficiency. For

outputs of 3.3V and above, the 0.1μF cap and the internal

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 efficient 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

CAP

BOOST

GND

SW

DA

BATT

LT3592

(5a)

D2

C3

3592 F05a

CAP

BOOST

GND

SW

BATT

LT3592

(5b)

D2

C3

3592 F05b

DA

100μs/DIV

100μs/DIV

3592 F04

C = 4.7μF

C = 10μF