MP2326 Rev. 1.1

www.MonolithicPower.com

17

1/28/2016

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APPLICATION INFORMATION

COMPONENT SELECTION

Setting the Output Voltage

The external resistor divider is used to set the

output voltage. First, choose a value for R2. R2

should be chosen reasonably; a small value for

R2 will lead to considerable quiescent current

loss while too large of a value for R2 makes the

FB noise sensitive. It is recommended to

choose a value within 5kΩ to 100kΩ for R2.

Typically, set the current through R2 to create a

good balance between system stability and no-

load loss. Then R1 is determined as follows:

OUT

REF

REF

VV

R1

R2

V





(11)

The feedback circuit is shown in Fig. 9.

FIGURE 9. Feedback Network

Table 2 lists the recommended resistor values

for common output voltages.

TABLE 2. Resistor Selection for Common Output

Voltages

(9)

R1(kΩ)

R2(kΩ)

1.0

27

40.2

1.2

40.2

40.2

1.5

60.4

40.2

1.8

80.6

40.2

2.5

127

40.2

3.3

182

40.2

5

294

40.2

Notes:

10) The feedback resistors in table 2 are optimized for a 500kHz

switching frequency. The detailed schematics are shown in

the “Typical Application Circuits” section.

Setting the Frequency

Refer to the “Mode Selection” section. Set the

forced PWM mode switching frequency by

connecting a resistor (R6) from VIN to

FREQ/MODE, leaving R7 NS (see Fig.10) . R6

is determined as follows:



6

Delay _ PWM

IN

SW

IN

Vo 10

T

(ns)

V

0.4

F(kHz) V

R6(k )

14.5

















(12)

FIGURE 10. R6 vs. Forced PWM Mode Switching

Frequency

Set the auto PFM/PWM mode switching

frequency by connecting a resistor (R7) from

FREQ/MODE to ground, leaving R6 NS (see

Fig.11). R7 is determined as follows:



6

Delay _ PFM

IN

SW

IN

Vo 10

T

(ns)

V

0.4

F(kHz) V

R7(k )

13

















(13)

FIGURE 11. R7 vs. Auto PFM/PWM Mode

Switching Frequency