MP8670 – 6A, 30V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER

MP8670 Rev. 1.3

www.MonolithicPower.com

12

4/4/2011

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

The schematic on the front page shows a typical

MP8670 application. The IC can provide up to

6A output current at a nominal output voltage of

3.3V. For proper thermal performance, the

exposed pad of the device must be soldered

down to the printed circuit board.

Setting the Output Voltage

The external resistor divider is used to set the

output voltage (see the schematic on front

page). The feedback resistor R1 also sets the

feedback loop bandwidth with the internal

compensation capacitor (see Figure 1). Choose

R1 to be around 40.2kΩ for optimal transient

response. R2 is then given by:

1

V

8

.

0

V

1

R

2

R

=

Table 1—Resistor Selection for Common

Output Voltages

R1 (kΩ)

R2 (kΩ)

1.8

40.2 (1%)

32.4 (1%)

2.5

40.2 (1%)

19.1 (1%)

3.3

40.2 (1%)

13 (1%)

5

40.2 (1%)

7.68 (1%)

Selecting the Inductor

A 1µH to 10µH inductor with a DC current rating

of at least 25% percent higher than the

maximum load current is recommended for

most applications. For highest efficiency, the

inductor DC resistance should be less than

15mΩ. For most designs, the inductance value

can be derived from the following equation.

OSC

L

IN

OUT

IN

OUT

f

I

V

)

V

V

(

V

L

×

∆

×

−

×

=

Choose inductor current to be approximately

30% of the maximum load current, 6A. The

maximum inductor peak current is:

2

I

I

I

L

LOAD

)

MAX

(

L

∆

+

=

Under light load conditions below 100mA, larger

inductance is recommended for improved

efficiency.