MIC33M350 datasheet(18/32 Pages) MICROCHIP

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MIC33M350

DS20006348B-page 18

 2020-2021 Microchip Technology Inc.

4.6

Output Voltage Setting

The MIC33M350 device has two pins, VSEL1 and

VSEL2, which are used for choosing between nine

predefined voltage settings: 0.6V, 0.8V, 0.9V, 1.0V,

1.2V, 1.5V, 1.8V, 2.5V, 3.3V. These pins can be tied to

VIN, GND or left floating. The relationship between

VSEL1/VSEL2 and the output voltage is shown in

Table 4-1.

VOUT should be connected exactly to the desired

Point-of-Load (POL) regulation, avoiding parasitic

resistive drops. It is possible to fine-tune the desired

output voltage by adding a series resistor on the VOUT

pin. This

allows

slightly

higher

output

value

programming, but should not exceed 5% deviation from

the VSEL selected value.

EQUATION 4-1:

4.7

Converter Stability/Output

Capacitor

The

MIC33M350

device

utilizes

internal

compensation network and is designed to provide

stable operation with output capacitors, from 47 µF to

1000 µF. This greatly simplifies the design, where you

can add supplementary output capacitance without

having to worry about stability

4.8

Soft Start

Excess bulk capacitance on the output can cause

excessive input inrush current. The MIC33M350 soft

start feature forces the output voltage to rise gradually,

keeping the inrush current at reasonable levels. This is

particularly important in battery-powered applications.

When the Enable pin goes high, the output voltage

starts to rise. Once the soft start period has finished,

the Power Good comparator is enabled and the Power

Good output goes high.

The output voltage soft start time is determined by the

soft start equation below. The Soft Start Time, tSS can

be calculated by Equation 4-2.

EQUATION 4-2:

4.9

Dropout Operation

As the input voltage approaches the output voltage, the

minimum on-time limits the maximum duty cycle. To

achieve 100% duty cycle, the high-side switch is

latched when the duty cycle reaches around 92% and

stays latched until the output voltage falls 4% below its

regulated value. In dropout, the output voltage is

determined by the input voltage minus the voltage drop

across the high-side MOSFET.

TABLE 4-1:

OUTPUT VOLTAGE SETTINGS

VSEL2

VSEL1

VOUT

GND

0.6V

GND

OPEN

0.8V

GND

VIN

0.9V

OPEN

GND

1.0V

OPEN

1.2V

OPEN

VIN

1.5V

VIN

GND

1.8V

VIN

OPEN

2.5V

VIN

3.3V

RVOUT

8.2 k

 TRIM



Where:

RVOUT =VOUT series resistance needed for a

TRIM% output voltage increase

tSS

VOUT tRAMP



tSS

1.0V

800

s

 V





tss

800

s

0.8 ms

Where:

VOUT =1.0V

tRAMP =800 µs/V

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