MIC45116 datasheet(24/42 Pages) MICROCHIP

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MIC45116

DS20005571B-page 24



2016 - 2022 Microchip Technology Inc.

EQUATION 5-7:

5.3

Output Voltage Setting

Components

The MIC45116 requires two resistors to set the output

voltage as shown in Figure 5-1.

FIGURE 5-1:

Voltage Divider

Configuration.

The output voltage is determined by Equation 5-8:

EQUATION 5-8:

A typical value of RFB1 used on the standard evaluation

board is 10 kΩ. If RFB1 is too large, it may allow noise

to be introduced into the voltage feedback loop. If RFB1

is too small in value, it will decrease the efficiency of the

power supply, especially at light loads. Once RFB1 is

selected, RFB2 can be calculated using Equation 5-9:

EQUATION 5-9:

For fixed RFB1 = 10 kΩ, output voltage can be selected

by RFB2. Table 5-1 provides RFB2 values for some

common output voltages.

5.4

Ripple Injection

The VFB ripple required for proper operation of the

MIC45116 gm amplifier and error comparator is 20 mV

to 100 mV. However, the output voltage ripple is

generally too small to provide enough ripple amplitude

at the FB pin and this issue is more visible in lower

output voltage applications. If the feedback voltage

ripple is so small that the gm amplifier and error

comparator cannot sense it, then the MIC45116 will

lose control and the output voltage is not regulated. In

order to have some amount of VFB ripple, a ripple

injection method is applied for low output voltage ripple

applications.

The applications are divided into three situations

according to the amount of the feedback voltage ripple:

• Enough ripple at the feedback voltage due to the

large ESR of the output capacitors (Figure 5-2).

The converter is stable without any ripple

injection.

FIGURE 5-2:

Enough Ripple at FB.

CIN

IOUT MAX





1 D

–









 SW dV



-------------------------------------------------------------



Where:

Input ripple voltage

fSW

Switching frequency

Power conversion efficiency

M AMP

FB1

FB2

REF

VOUT VREF 1

RFB1

RFB2

------------











Where:

VREF

0.8V

TABLE 5-1:

VOUT PROGRAMMING

RESISTOR LOOK-UP

RFB2

VOUT

OPEN

0.8V

40.2 kΩ

1.0V

20 kΩ

1.2V

11.5 kΩ

1.5V

8.06 kΩ

1.8V

4.75 kΩ

2.5V

3.24 kΩ

3.3V

1.91 kΩ

5.0V

RFB2

VREF RFB1



VOUT VREF

–

---------------------------------

MIC45116

OUT

GND

FB2

FB1

OUT

ESR

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