Note that this circuit (with or without the MAX8212) can be

used to provide 5V from four alkaline cells. The initial volt-

age is approximately 6V, and the output is maintained at

5V even when the battery voltage falls to less than 2V.

Dual-Tracking Regulator

A MAX634 inverting regulator is combined with a

MAX630 in Figure 8 to provide a dual-tracking ±15V

output from a 9V battery. The reference for the -15V

output is derived from the positive output through R3

and R4. Both regulators are set to maximize output

power at low-battery voltage by reducing the oscillator

CMOS Micropower Step-Up

Switching Regulator

______________________________________________________________________________________

11

MAX630

3V

R3

249k

Ω

R4

499k

Ω

540k

Ω

200k

Ω

C1

100pF

47pF

LBD

8

GND

2

4

1

LBR

μH

1N4148

+5V OUT

470

μF

15V

3

5

7

6

Figure 5. 3V to 5V Converter with Low-Battery Frequency Shift

MAX8212

MAX630

10M

Ω

HYST

OUT

2

THRESHOLD

3

GND

5

8

2.4M

Ω

390k

Ω

9V

BATTERY

1.3M

Ω

1M

Ω

1

LBR

2M

Ω

560k

Ω

7

6

47pF

100pF

LBD

8

2

3

GND

4

1M

Ω

5

1.0mH

470

μF

25V

Figure 7. Battery Life Extension Down to 3V In

MAX630

LINE-POWERED

+5V INPUT

1N4001

200k

Ω

100k

Ω

680

Ω

1N5817

3.6V

NICAD

BATTERY

470

μH

1

LBR

8

LBD

GND

4

2

3

280k

Ω

100k

Ω

1N5817

UNINTERRUPTABLE

+5V OUTPUT

470

μF

15V

5

7

6

POWER FAIL

47pF

Figure 6. Uninterruptable +5V Supply