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 efficiency.

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 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

OPTIONAL

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