LTC3616 datasheet(13/28 Pages) LINER

13 / 28 page

LTC3616

3616f

APPLICATIONS INFORMATION

If the output voltage drops below 50% of its nominal value,

the clamp voltage at ITH pin is lowered causing the maxi-

mum peak inductor current to decrease gradually with the

output voltage. When the output voltage reaches 0V the

clamp voltage at the ITH pin drops to 40% of the clamp

voltage during normal operation. The short-circuit peak

inductor current is determined by the minimum on-time

of the LTC3616, the input voltage and the inductor value.

This foldback behavior helps in limiting the peak inductor

current when the output is shorted to ground. It is disabled

during internal or external soft-start and tracking up/down

operation (see the Applications Information section).

A secondary limit is also imposed on the valley inductor

current. If the inductor current measured through the

bottom MOSFET increases beyond 12A typical, the top

power MOSFET will be held off and switching cycles will

be skipped until the inductor current is reduced.

OPERATION

The basic LTC3616 application circuit is shown in Figure 1.

Operating Frequency

Selection of the operating frequency is a trade-off between

efficiency and component size. High frequency operation

allows the use of smaller inductor and capacitor values.

Operation at lower frequencies improves efficiency by

reducing internal gate charge losses but requires larger

inductance values and/or capacitance to maintain low

output ripple voltage.

The operating frequency of the LTC3616 is determined

by an external resistor that is connected between the

RT/SYNC pin and ground. The value of the resistor sets

RUN

TRACK/SS

RT/SYNC

PGOOD

ITH

SGND

PGND

VIN

2.25V TO 5.5V

SRLIM/DDR

SVIN

LTC3616

PVIN

CIN1

22μF

470pF

CSS

22nF

220nH

392k

196k

3616 F01

MODE

VFB

COUT1

47μF

COUT2

100μF

VOUT

1.8V

15k

130k

RSS

CC1

10pF

(OPT)

Figure 1. 1.8V, 6A Step-Down Regulator

the ramp current that is used to charge and discharge an

internal timing capacitor within the oscillator and can be

calculated by using the following equation:

RT =

3.82 •1011Hz

fOSC Hz

(

)

Ω –16kΩ

Although frequencies as high as 4MHz are possible, the

minimum on-time of the LTC3616 imposes a minimum

limit on the operating duty cycle. The minimum on-time

is typically 60ns; therefore, the minimum duty cycle is

equal to 60ns • fOSC(Hz)•100%.

Tying the RT/SYNC pin to SVIN sets the default internal

operating frequency to 2.25MHz ±20%.

LTC3616 bảng dữ liệu(PDF) 13 Page - Linear Technology

LTC3616 bảng dữ liệu(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

bảng dữ liệu tải về

Link URL