LT3582 datasheet(21/28 Pages) LINER

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LT3582/LT3582-5/LT3582-12

3582512f

APPLICATIONS INFORMATION

and diode. Finally, due to the path from VIN to VOUTP,

current will ﬂow through the integrated feedback resistor

whenever voltage is present on VIN.

Inrush Current

When the Boost inductor input voltage (usually VIN) is

stepped from ground to the operating voltage, a high

level of inrush current may ﬂow through the inductor

and Schottky diode into the CAPP capacitor. Conditions

that increase inrush current include a larger more abrupt

voltage step at the inductor input, larger CAPP capacitors

and inductors with low inductances and/or low saturation

currents. For circuits that use output capacitor values

within the recommended range and have input voltages

of less than 5V, inrush current remains low, posing no

hazard to the devices. In cases where there are large

input voltage steps (more than 5V) and/or a large CAPP

capacitor is used, inrush current should be measured to

ensure safe operation.

Thermal Lockout

If the die temperature reaches approximately 147°C, the

part will go into thermal lockout. In this event, the chip

is reset which turns off the power switches and starts to

discharge the RAMP capacitors. The part will be re-enabled

when the die temperature drops by about 3.5°C.

Board Layout Considerations

As with all switching regulators, careful attention must be

paid to the PCB board layout and component placement.

To maximize efﬁciency, switch rise and fall times are made

as short as possible. To prevent electromagnetic interfer-

ence (EMI) problems, proper layout of the high frequency

switching path is essential. The voltage signals of the

SWP and SWN pins have sharp rising and falling edges.

Minimize the length and area of all traces connected to

the SWP/SWN pins and always use a ground plane under

the switching regulator to minimize interplane coupling.

Suggested component placement is shown in Figure 12.

Make sure to include the ground plane cuts as shown in

Figure 12. The switching action of the regulators can cause

large current steps in the ground plane. The cuts reduce

noise by recombining the current steps into a continuous

ﬂow under the chip, thus reducing di/dt related ground

noise in the ground plane.

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