MP8869 datasheet(30/37 Pages) MPS

30 / 37 page

MP8869

– 17V, 12A, SYNCHRONOUS STEP-DOWN CONVERTER

MP8869 Rev.1.0

www.MonolithicPower.com

6/8/2016

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

APPLICATION INFORMATION

Setting the Output Voltage in a FB Control

Loop

The MP8869 can be controlled by the FB loop

or I

2C 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

fixed

value

(0.6V)

and

cannot

programmed by the I

2C.

The FB loop network is shown in Figure 10.

VOUT

Figure 10: 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)

(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 R2

. For other components’ parameters, please refer to

the Typical Application Circuits on page 34.

Setting the Output Voltage in an I

2C Control

Loop

After the part powers up and EN turns on, the

FB loop can be programmed to the I

2C loop

sensing (VOUT) by setting V_BOOT = 0. In this

case, the output voltage can be set by the I

from 0.6V to 1.87V. Refer to Table 3 for more

details about the output voltage setting.

Output Voltage Dynamic Scale

The output voltage dynamic scaling can be

done only in the I

2C control loop. Refer to

Figure 11 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 11: Loop Switch and Output Voltage

Dynamic Scale Flow Chart

MP8869 Datasheet(PDF) 30 Page - Monolithic Power Systems

MP8869 Datasheet(HTML) 30 Page - Monolithic Power Systems

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Datasheet Download

Link URL