Advanced Monolithic Systems, Inc.

www.advanced-monolithic.com

Phone (925) 443-0722

Fax (925) 443-0723

AMS682

DETAILED DESCRIPTION

Phase 1

2

now -10V.

-

+

C

3

+

-

C1

C2

SW2

-5V

SW4

SW3

SW1

V

V

OUT

+

-

Figure 2. Charge Pump - Phase 1

Phase 2

Phase 1 begins again.

-

+

C

3

+

-

C1

C2

SW2

-10V

SW4

SW3

SW1

V

V

OUT

+

-

Figure 3. Charge Pump - Phase 2

MAXIMUM OPERATING LIMITS

The AMS682 has on-chip zener diodes that clamp VIN to

approximately 5.8V, and V

-

OUT

to -11.6V. Exceeding the

maximum supply voltage will potentially damage the chip.

With an input voltage of 2V to 5.5V the AMS682 will operate

over the entire operating temperature range.

EFFICIENCY CONSIDERATIONS

Theoretically a charge pump voltage multiplier can approach

100% efficiency under the following conditions:

•

The charge pump switches have virtually no offset and are

extremely low on resistance.

•

Minimal power is consumed by the drive circuitry.

•

The Impedances of the reservoir and pump capacitors are

negligible.

For the AMS682, efficiency is as shown below:

Power Loss

high with respect to their respective output loads.

ripple will be reduced. The efficiency will be improved if both

pump and reservoir capacitors have larger values. ( See

“Capacitor Selection” in Application Section.)

APPLICATIONS

Negative Doubling Converter

The AMS682 is most commonly used as a charge pump voltage

converter which provides a negative output of two times a

positive input voltage (Fig.4)

GND

V

IN

6

4

OUT

5

7

2

3

1

C

1

-

C

2

+

C

1

+

C

2

-

GND

V

IN

V-

OUT

C

3

22

µF

+

+

+

22

µF

22

µF

C

1

C

2

ON/OFF

8

Figure 4. Inverting Voltage Doubler