Design Procedure

Output Voltage Selection

Both output voltages can be selected in three different

ways as indicated by Table 1. Each output has two pre-

set voltages that can be set using FBSEL_ and it can

external resistor voltage-divider.

To use a resistor-divider to set the output voltage to

1.2V or higher (Figure 5), connect a resistor from FB_ to

Ω and

30k

A resistor-divider can also be used to set the voltage of

one output from 0.8V to 1.2V. To do this, the other out-

put must be above 1.2V. Figure 6 shows an example of

this where OUT1 is set to 1V. To set the output voltage to

less than 1.2V, connect a resistor from FB1 to OUT1 (R1),

and from FB1 to OUT2 (R2). Select values of R1 and R2

such that current flowing through R1 and R2 is about

100µA and following equation is satisfied:

Each output is capable of continuously sourcing up to

750mA of current as long as the following condition is

met:

Inductor Value

A 3.3µH to 6.8µH inductor with a saturation current of

800mA (min) is recommended for most applications.

For best efficiency, the inductor’s DC resistance should

be less than 100m

Ω, and saturation current should be

greater than 1A. See Table 2 for recommended induc-

tors and manufacturers.

VI

V

I

V

A

OUT

OUT

OUT

OUT

IN

11

2

2

105

×+

×

≤ .

RR

V

V

OUT

OUT

12

12

12

2

1

=

−

−

.

.

RR

V

ab

OUT

__

.

=×

−









12

1

Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-

Down Regulator with POR and RSI/PFO

14

______________________________________________________________________________________

Figure 2. Timing Diagram

RSI

~1V PKMAX

PFO

4.04V

3.94V

µs MIN

POR