MIC2182 datasheet(19/40 Pages) MICROCHIP

19 / 40 page



2022 Microchip Technology Inc. and its subsidiaries

DS20006644A-page 19

MIC2182

It is recommended that the user limits the maximum

synchronized frequency to 600 kHz. If a higher

synchronized frequency is required, it may be possible

and will be design dependent.

4.6

Soft-Start

Soft start reduces the power supply input surge current

at startup by controlling the output voltage rise time.

The input surge appears while the output capacitance

is charged up. A slower output rise time will draw a

lower input surge current. Soft start may also be used

for power supply sequencing.

The soft-start voltage is applied directly to the PWM

comparator. A 5 µA internal current source is used to

charge up the soft-start capacitor. The capacitor is

discharged when either the enable voltage drops below

the UVLO threshold (2.5V) or the VDD voltage drops

below the UVLO level (4.1V).

The part switches at a minimum duty cycle when the

soft-start pin voltage is less than 0.4V. This maintains a

charge on the bootstrap capacitor and insures

high-side gate drive voltage. As the soft-start voltage

rises above 0.4V, the duty cycle increases from the

minimum duty cycle to the operating duty cycle. The

oscillator runs at the foldback frequency of 60 kHz until

the output voltage rises above 0.95V. Above 0.95V, the

switching frequency increases to 300 kHz (or the

synced frequency), causing the output voltage to rise a

greater rate. The rise time of the output is dependent

on the soft-start capacitor, output capacitance, output

voltage, and load current. The oscilloscope photo in

Figure 4-11 show the output voltage and the soft-start

pin voltage at startup.

FIGURE 4-11:

Startup Waveforms.

4.7

Minimum Pulse Width

The MIC2182 has a specified minimum pulse width.

This minimum pulse width places a lower limit on the

minimum duty cycle of the buck converter. When the

MIC2182 is operating in forced PWM mode (Pin 2 low)

and when the output current is very low or zero, there

is a limit on the ratio of VOUT/VIN. If this limit is

exceeded, the output voltage will rise above the

regulated voltage level. A minimum load is required to

prevent the output from rising up. This will not occur for

output voltages greater than 3V.

Figure 4-12 should be used as a guide when the

MIC2182 is forced into PWM-only mode. The actual

maximum input voltage will depend on the exact

external components used (MOSFETs, inductors, etc.).

FIGURE 4-12:

Max. Input Voltage in

Forced-PWM Mode.

This restriction does not occur when the MIC2182 is set

to automatic mode (Pin 2 connected to a capacitor)

since the converter operates in skip mode at low output

current.

TIME

0123456

OUTPUT VOLTAGE (V)

MIC2182 датащи(PDF) 19 Page - Microchip Technology

MIC2182 датащи(HTML) 19 Page - Microchip 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 29 30 31 32 33 34 35 36 37 38 39 40

датащи скачать

ссылки URL