AMS682 Просмотр технического описания (PDF) - Advanced Monolithic Systems Inc

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AMS682

INVERTING VOLTAGE DOUBLER

Advanced Monolithic Systems Inc 

AMS682

DETAILED DESCRIPTION

EFFICIENCY CONSIDERATIONS

Phase 1

VSS charge storage- before this phase of the clock cycle,

capacitor C1 is already charged to +5V. C1+ is then switched

to ground and the charge in C1- is transferred to C2-.

Since C2+ is at +5V, the voltage potential across capacitor C2

is now -10V.

VIN =+5V

SW1

SW3

VOUT

+

C1 + C2

-

-

SW2

SW4

-+C3

-5V

Figure 2. Charge Pump - Phase 1

Phase 2

VSS transfer- phase two of the clock connects the negative

terminal of C2 to the negative side of reservoir capacitor C3

and the positive terminal of C2 to the ground, transferring the

generated -10V to C3. Simultaneously, the positive side of

capacitor C1 is switched to +5V and the negative side is

connected to ground. C2 is then switched to VCC and GND and

Phase 1 begins again.

VIN =+5V

SW1

SW3

+ C1

-

SW2

+ C2

-

SW4

-10V

VOUT

-+C3

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.

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:

Voltage Efficiency = VOUT / (-2VIN )

VOUT = -2VIN + VDROP

VDROP = (IOUT) (R OUT)

Power Loss

= IOUT (VDROP)

There will be a substantial voltage difference between VOUT and

2VIN if the impedances of the pump capacitors C1 and C2 are

high with respect to their respective output loads.

If the values of the reservoir capacitor C3 are larger the output

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)

+

C1

22µF

+

C2

22µF

1 C1- ON/OFF 8

2 C2+

C1+ 7

3 C2-

VIN 6

4 V-OUT GND 5

+ C3

22µF

VIN

GND

V-OUT

Figure 4. Inverting Voltage Doubler

Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140

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