MPQ2169B

– 6V, DUAL 1.4A/1.4A OR 2A/0.8A SYNC BUCK REGULATOR, AEC-Q100

MPQ2169B Rev. 1.0

MonolithicPower.com

21

12/20/2021

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APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets VOUT. The

feedback resistor (R1) also sets the feedback

(FB)

loop

bandwidth

with

the

internal

compensation. Figure 5 shows the feedback

network.

FB

VOUT

R1

R2

Figure 5: Feedback Network

R1 is used to set the loop bandwidth, where a

lower R1 value means a higher bandwidth.

However, a high bandwidth may cause an

insufficient phase margin, resulting in loop

instability. Therefore, a proper R1 value must

make a tradeoff between the bandwidth and

phase margin. Table 2 lists the recommended

feedback resistor values for common output

voltages.

Table 2: Resistor Selection vs. Output Voltage

Setting

VOUT (V)

R1 (k

Ω)

R2 (k

Ω)

1.2V

100

100

1.5V

100

66.5

1.8V

100

49.9

2.5V

100

31.6

3.3V

100

22.1

If R1 is estimated to be 10

0kΩ, R2 can then be

calculated using Equation (2):

OUT

R1

R2

V

1

0.6V

=

−

(2)

If ceramic capacitors are used as output

capacitors

(CO),

then

the

feedback

loop

bandwidth (fC) should not exceed 1/10 of fSW for

optimal transient performance and good phase

margin. If an electrolytic capacitor is used, fC

should not exceed 1/4 of the ESR zero

frequency (fESR).

fESR can be calculated using Equation (3):

ESR

ESR

O

1

f

2

R

C

=

 



(3)

For example, choose fC = 80kHz with a ceramic

capacitor when CO = 22μF.

Selecting the Inductor

An inductor with a DC current rating at least

25% above the maximum load current is

recommended for most applications. For the

best efficiency, the inductor DC resistance

should be below 2

0mΩ. For most designs, the

inductance can be estimated using Equation (4):

SW

L

IN

OUT

IN

OUT

f

I

V

)

V

-

(V

V

L









=

(4)

Where

∆IL is the inductor ripple current.

Choose

∆IL to be approximately 30% of the

maximum load current. The maximum inductor

peak current (IL(MAX)) can be calculated using

Equation (5):

L

L(MAX)

LOAD

I

II

2



=+

(5)

Selecting the Input Capacitor

The input capacitor reduces the surge current

drawn from the input and the switching noise

from the device. The input capacitor impedance

at fSW should be below the input source

impedance to prevent high-frequency switching

current from passing to the input source.

Ceramic capacitors with X5R or X7R dielectrics

are highly recommended because of their low

ESR and small temperature coefficients. For

most applications, a 22µF capacitor is sufficient.

Selecting the Output Capacitor

The output capacitor (CO) keeps the output

voltage ripple small and ensures a stable

regulation loop. The CO impedance should be

low at fSW. It is recommended to use ceramic

capacitors with X5R or X7R dielectrics. If an

electrolytic

capacitor

is

used,

pay

close

attention to the output ripple voltage, extra

heating,

and

the

selection

of

the

upper

feedback resistor due to the large ESR of

electrolytic capacitors (see the Setting the

Output Voltage section).