MIC2132 datasheet(25/48 Pages) MICROCHIP

25 / 48 page

 2022 Microchip Technology Inc. and its subsidiaries

DS20006654B-page 25

MIC2132

4.5.5

SOFT START

Soft start reduces the power supply input surge current

at start-up by controlling the output voltage rise time.

The input surge appears while the output capacitor is

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

input surge current.

The MIC2132 features adjustable soft start time. The

soft start time can be adjusted by changing the value of

the capacitor connected from the SS pin to AGND. The

soft start time can be adjusted from 5 ms to 100 ms.

The MIC2132 forces 1.2 µA current from the SS pin.

This constant current flows through the soft start

capacitor connected from the SS pin to AGND in order

to adjust the soft start time.

The soft start capacitor value for the desired VOUT

ramp-up time can be calculated from Equation 4-19.

EQUATION 4-19:

4.5.6

VDD REGULATOR AND EXTVDD

LDO

The MIC2132 has an integrated high-voltage LDO that

provides a 5V regulated output from Input Voltage, VIN,

ranging from 8V to 75V. When VIN < 5.5V, VDD must be

tied to the VIN pins to bypass the internal linear regulator.

The internal LDO powers the control circuitry from the

VDD pin and gate drive current from the PVDD pin.

The MIC2132 also features an auxiliary low-voltage

LDO, which is powered by EXTVDD. When the voltage

on the EXTVDD is at 4.7V (typical) or higher, this

auxiliary LDO is enabled and powers all the internal

circuitry. At the same time, the main high-voltage LDO is

disabled. This increases the efficiency of the system by

reducing the differential voltage across the high-voltage

LDO, hence reducing the power losses in the LDO. In

general, the output of the buck converter is used as the

power supply for the auxiliary LDO by connecting the

EXTVDD pin to the output of the buck converter. The

maximum voltage that can be applied at EXTVDD is

limited to 14V. Figure 4-11 shows the internal 5V LDO

and EXTVDD connection in the MIC2132.

FIGURE 4-11:

MIC2132 EXTVDD.

Given that the EXTVDD is powered from the VOUT of

the buck regulator, the VOUT is noisy if there is a fast

changing load. When VOUT > 5V + VDROPOUT, the

noise could be suppressed by a loop of 12V LDO. How-

ever, when VOUT = 5V, the 12V LDO works in Dropout

mode and there is no loop gain. The LDO acts just like

a resistor. It is not recommended to connect EXTVDD

to VOUT if VOUT < 5V.

4.5.7

POWER GOOD (PG)

The Power Good (PG) pin is an open-drain output,

which indicates logic high when the output is nominally

over 88% of its steady-state voltage. A pull-up resistor

of more than 10 kΩ should be connected from PG to

VDD. During soft start, the PG is held low and is

allowed to be pulled high after VOUT is achieved over

88% of the target level.

4.5.8

SEQUENCING

The MIC2132 has a precision enable function. The EN

pin threshold will either enable/disable switching.

When the EN pin voltage is higher than 1.2V (typical),

the MIC2132 is put into operation. The internal

regulator will power up and start switching. Figure 4-12

shows the EN pin sequencing.

Where:

tSS = Output Voltage Soft Start Ramp-up Time

CSS =

1.2 µA × tSS

VREF

HV LDO

4.7V

VIN

EXTVDD

12V LDO

with

everse

locking

OUT

VDD

OUT

2.2 ohm

2.2 μF

4.7 μF

PVDD

PGND

AGND

MIC2132 REG_ With EXTVDD

HV LDO

OUT

VIN

2 ohm

2.2 μF

4.7 μF

VDD

AGND

PGND

PVDD

MIC2132 REG_Internal 5V

lock

Bypass_B

Bypass

VDD

ypass

MIC2132 Datasheet(PDF) 25 Page - Microchip Technology

MIC2132 Datasheet(HTML) 25 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 41 42 43 44 45 46 47 48

Datasheet Download

Link URL