LT3592

20

3592fc

APPLICATIONS INFORMATION

Figure 12. Switching Transient When Going from 50mA to 500mA Current and Back in Voltage Mode

their maximum voltage capability. If a capacitor with a

lower voltage rating is found to not be stable in a design,

it will often result in a smaller solution to choose a larger

capacitor value of the same voltage rating than to choose

one of the same capacitance and higher voltage rating. For

example, a 10μF, 10V ceramic capacitor might be smaller

than a 4.7μF, 16V part, if a 4.7μF, 10V capacitor is found

to not be adequate in a given application. The LT3592HV

can tolerate sustained output voltages of up to 25V. For

output voltages above 12V, use an external Schottky diode

for the boost circuit with the anode tied to CAP and the

cathode tied to BOOST (as shown in Figure 13).

Transient Performance with Voltage Control Loop

The voltage control loop transient characteristics are similar

to, but not identical to the current control loop. Figure 12

shows the transient for a 12V input application running at

900kHz with a 6.8μH inductor and a 4.7μF ceramic output

capacitor. The LT3592 is in BRIGHT (500mA) mode but

the current load is switched from 50mA to 450mA and

back, so the current control loop is not active for either

current level and the output voltage is regulated through

the resistive voltage divider to the FB pin.

Other Linear Technology Publications

Application Notes AN19, AN35, and AN44 contain more

detailed descriptions and design information for Step-down

regulators and other switching regulators. The LT1376 data

sheet has an extensive discussion of output ripple, loop

compensation, and stability testing. Design Note DN100

shows how to generate a bipolar output supply using a

Step-down regulator.

10μs/DIV

10V/DIV

3592 F12

1V/DIV

200mA/DIV

Figure 13. Boost Circuit with External Schottky Diode for Output Voltages Above 12V

CAP

BOOST

GND

SW

DA

BATT

LT3592

D2

C3

3592 F13