LTM8023V datasheet(11/20 Pages) LINER

11 / 20 page

LTM8023

8023fb

APPLICATIONS INFORMATION

that paralleled modules start up together, the RUN/SS pins

may be tied together, as well. If the RUN/SS pins are not

tied together, make sure that the same valued soft-start

capacitors are used for each module. An example of two

LTM8023 modules conﬁgured for load sharing is given in

the Typical Applications section.

Burst Mode Operation

To enhance efﬁciency at light loads, the LTM8023 auto-

matically switches to Burst Mode operation which keeps

the output capacitor charged to the proper voltage while

minimizing the input quiescent current. During Burst Mode

operation, the LTM8023 delivers single cycle bursts of

current to the output capacitor followed by sleep periods

where the output power is delivered to the load by the output

capacitor. In addition, VIN and BIAS quiescent currents are

reduced to typically 20μA and 50μA respectively during

the sleep time. As the load current decreases towards a no

load condition, the percentage of time that the LTM8023

operates in sleep mode increases and the average input

current is greatly reduced, resulting in higher efﬁciency.

Burst Mode operation is enabled by tying SYNC to GND. To

disable Burst Mode operation, tie SYNC to a stable voltage

above 0.7V.

Do not leave the SYNC pin ﬂoating.

Minimum Input Voltage

The LTM8023 is a step-down converter, so a minimum

amount of headroom is required to keep the output in

regulation. In addition, the input voltage required to turn

on is higher than that required to run, and depends upon

whether the RUN/SS is used. As shown in Figure 2, it

takes only about 3.5VIN for the LTM8023 to run a 3.3V

output at light load. If RUN/SS is pulled up to VIN, it takes

5.5VIN to start. If the LTM8023 is enabled via the RUN/SS

pin, the minimum voltage to start at light loads is lower,

about 4.5V. A similar curve for 5VOUT operation is also

provided in Figure 2.

Soft-Start

The RUN/SS pin can be used to soft-start the LTM8023,

reducing the maximum input current during start-up.

The RUN/SS pin is driven through an external RC ﬁlter

to create a voltage ramp at this pin. Figure 3 shows the

start-up and shutdown waveforms with the soft-start

circuit. By choosing an appropriate RC time constant,

Figure 2. The LTM8023 Needs More Voltage to Start Than to Run

Figure 3. To Soft-Start the LTM8023, Add a

Resistor and Capacitor to the RUN/SS Pin

LOAD CURRENT (mA)

8023 F02

LOAD CURRENT (mA)

4.0

4.5

5.0

2000

3.5

3.0

500

1000

1500

2000

500

1000

1500

6.0

5.5

TO START

RUN/SS ENABLED

TO RUN

TO START

RUN/SS ENABLED

TO RUN

VOUT = 3.3V

TA = 25°C

f = 650kHz

6.5

7.0

6.0

5.0

5.5

7.5

VOUT = 5V

TA = 25°C

f = 650kHz

8023 F03

1A/DIV

VRUN/SS

2V/DIV

VOUT

2V/DIV

RUN/SS

GND

0.22μF

RUN

15k

2ms/DIV

LTM8023V датащи(PDF) 11 Page - Linear Technology

LTM8023V датащи(HTML) 11 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

датащи скачать

ссылки URL