MP8869WGL datasheet(33/41 Pages) MPS

33 / 41 page

MP8869W

– 3V - 18V, 12A, SYNCHRONOUS STEP-DOWN CONVERTER

MP8869W Rev. 1.02

www.MonolithicPower.com

1/18/2018

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

APPLICATION INFORMATION

Setting the Output Voltage in a FB Control

Loop

The MP8869W can be controlled by the FB loop

or I2C loop. The FB loop is the default loop during

power-up or EN on. In this case, the output

voltage can be set by the external resistor

dividers. The FB loop reference voltage is a fixed

value (0.6V) and cannot be programmed by the

I2C.

The FB loop network is shown in Figure 11.

VOUT

Figure 11: FB Loop Network

Choose R1 and R2 with Equation (4):





OUT

(4)

Table 6 lists the recommended feedback

resistors value for common output voltages.

Table 6: Resistor Selection for Common Output

Voltages (8)

VOUT (V)

R1 (kΩ)

R2 (kΩ)

Rt(

kΩ)

L(μH)

1.0

80.6

120

1.5

1.2

80.6

1.5

80.6

53.6

1.5

1.8

80.6

40.2

1.5

2.5

80.6

25.5

2.2

3.3

80.6

17.8

2.2

80.6

3.3

NOTE:

The recommended parameters are based on a 12V input

voltage and 22µFx4 output capacitor. Different input voltage

and output capacitor values may affect the selection of R1 and

. For other components’ parameters, please refer to the

Typical Application Circuits on page 34.

Setting the Output Voltage in an I2C control

Loop

After the part powers up and EN turns on, the FB

loop can be programmed to the I2C loop sensing

(VOUT) by setting V_BOOT = 0. In this case, the

output voltage can be set by the I2C from 0.6V to

1.55V. Please refer to Table 3 for more details

about output voltage setting.

Output Voltage Dynamic Scale

The output voltage dynamic scaling can be done

only in the I2C control loop. Refer to Figure 12

and follow the steps below.

1) Write GO_BIT (Reg01[6]) to 1.

2) Write Reg00 to select the feedback loop by

setting V_BOOT (Reg00[7]) and setting the

reference voltage by Output Reference

(Reg00[6:0])

simultaneously.

When

the

command is finished, GO_BIT auto-resets to

0 to prevent false operation of the VOUT

scaling.

Repeat the above two steps if the output voltage

needs to be changed to a different voltage.

Voltage scaling

start

Write Reg01[6]

“GO_BIT”=1

Write Reg00 (Set

“V_BOOT”=0 &

“Vref”code)

Voltage scaling is done

Figure 12: Loop Switch and Output Voltage

Dynamic Scale Flow Chart

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