3.3V/5V or Adjustable-Output,

Single-Cell DC-DC Converters

8

_______________________________________________________________________________________

Voltage Reference

The precision voltage reference is suitable for driving

external loads, such as an analog-to-digital converter.

The voltage-reference output changes less than ±2%

when sourcing up to 250µA and sinking up to 20µA. If

the reference drives an external load, bypass it with

0.22µF to GND. If the reference is unloaded, bypass it

with at least 0.1µF.

Logic Inputs and Outputs

The 3/5 input is internally diode clamped to GND and

OUT, and should not be connected to signals outside

this range. The SHDN input and LBO output (open-

drain) are not clamped to V+ and can be pulled as high

control inputs (3/5, LBI, or SHDN) floating.

__________________Design Procedure

Output Voltage Selection

For the MAX866, you can select a 3.3V or 5V output volt-

age under logic control, or by tying 3/5 to GND or OUT.

The MAX867’s output voltage is set by two resistors, R1

and R2 (Figure 2b), which form a voltage divider

between the output and FB. Use the following equation

to determine the output voltage:

R1 + R2

R2

To simplify resistor selection:

R1 = R2

C1

47

µF

L1

330

µF

D1

C2

47

µF

R1

R2

LX

OUT

FB

LBO

LBI

REF

SHDN

GND

C3

0.1

µF

5

1

3

8

6

2

4

7

MAX867

L1 = COILCRAFT DO1608-334

D1 = MOTOROLA MBR0520LTI

C1

47

µF

L1

330

µH

D1

C2

47

µF

R1

LX

OUT

3/5

LBO

LBI

REF

SHDN

GND

C3

0.1

µF

5

1

3

8

6

2

4

7

MAX866

L1 = COILCRAFT DO1608-334

OUTPUT

SELECT

D1 = MOTOROLA MBR0520LTI

Figure 2b. Standard Application Circuit—Adjustable Output

Voltage

Figure 2a. Standard Application Circuit—Preset Output

Voltage