MP8846 – 6A, 8V SYNCHRONOUS STEP-DOWN CONVERTER

MP8846 Rev. 1.0

www.MonolithicPower.com

22

5/19/2015

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APPLICATION INFORMATION

Setting the Output Voltage in the FB Control

Loop

The reference voltage and external resistor

divider can set the output voltage through FB.

feedback loop bandwidth with the internal

compensation capacitor. Choose the value of

1

V

V

R1

R2

REF

OUT

−

=

Note:

to enable the FB control loop.

The

T-type

network

(see

Fig.

9)

is

FIGURE 9. T-Type Network

Table 3 lists the recommended T-type resistor

values for common output voltages.

TABLE 3. Resistor Selection for Common Output

(11)

(V)

R1

(kΩ)

R2

(kΩ)

(kΩ)

(pF)

(pF)

L

(uH)

0.9

Connect FB to VCC

1

1.2

34(1%)

34(1%)

33(1%)

NS

10

1

3.3

34(1%)

7.5(1%)

15(1%)

NS

33

2.7

Note:

11) The recommended parameters are based on a 5V input

voltage and a 22µFx2 output capacitor. A different input voltage,

output capacitor value, and switching frequency may affect the

parameters, please refer to the Typical Applications Circuits

section on page 26.

Loop

In addition to setting the output voltage through

through VOUT by setting V_BOOT=0. In this

case, the output voltage is the set reference

voltage. Please refer to Table 2 on page 20 for

additional details concerning the output voltage

setting.

Output Voltage Dynamic Scale

To dynamic scale the output voltage during

normal operation, refer to Fig. 10 and follow

the steps below:

Step1: Write the GO_Bit (reg01[6]) to “1;”

Step2: Write reg00 to select the feedback loop

by setting V_BOOT(reg00[7]). Set the reference

voltage using the output reference (reg00[0:6])

simultaneously. If the reference adjustment is

within 50mV, GO_BIT will NOT auto re-set to

“0.” If this is the case, manually set GO_BIT to

“0.”

Repeat the two steps above to dynamic scale to

another voltage.

FIGURE 10. Output Voltage Dynamic Scale Flow

Chart

Selecting the Inductor

For most applications, use a 1µH to 10µH

inductor with a DC current rating at least 25%

percent higher than the maximum load current.

For highest efficiency, use an inductor with a

DC resistance less than 15mΩ. For most