_______________Detailed Description

The MAX1682/MAX1683 capacitive charge pumps

double the voltage applied to their input. Figure 1

shows a simplified functional diagram of an ideal volt-

age doubler. During the first half-cycle, switches S1

the second half cycle, S1 and S2 open, S3 and S4

connects C1 to the reservoir capacitor C2, allowing

energy to be delivered to the output as necessary. The

switches S1–S4 have resistance and the load drains

charge from C2.

Charge-Pump Output

The MAX1682/MAX1683 have a finite output resistance

of about 20

Ω (Table 2). As the load current increases,

Efficiency Considerations

The power efficiency of a switched-capacitor voltage

converter is affected by three factors: the internal losses

in the converter IC, the resistive losses of the capacitors,

and the conversion losses during charge transfer

between the capacitors. The total power loss is:

The internal losses are associated with the IC’s internal

functions, such as driving the switches, oscillator, etc.

These losses are affected by operating conditions such

as input voltage, temperature, and frequency.

The next two losses are associated with the voltage

converter circuit’s output resistance. Switch losses

occur because of the on-resistance of the MOSFET

switches in the IC. Charge-pump capacitor losses

occur because of their ESR. The relationship between

these losses and the output resistance is as follows:

the effective resistance from an ideal switched-

capacitor circuit (Figures 2a and 2b).

P

P

I

x R

R

f

x C

R

ESR

ESR

PUMP CAPACITOR LOSSES

SWITCH LOSSES

OUT

OUT

OUT

OSC

SWITCHES

C

C

+

=

+

+

+

2

1

2

1

1

2

4

ΣP

P

P

P

LOSS

INTERNAL LOSSES

PUMP CAPACITOR LOSSES

CONVERSION LOSSES

=

+

+

Switched-Capacitor Voltage Doublers

_______________________________________________________________________________________

5

_____________________Pin Description

NAME

FUNCTION

1

GND

Ground

2

OUT

Doubled Output Voltage. Connect C2

between OUT and GND.

PIN

3

C1-

Negative Terminal of the Flying

Capacitor

4

IN

Input Supply

5

C1+

Positive Terminal of the Flying

Capacitor

Figure 2a. Switched-Capacitor Model

V+

C1

f

C2

Figure 1. Simplified Functional Diagram of Ideal Voltage

Doubler

S1

S3

S2

S4

C1

C2

Figure 2b. Equivalent Circuit

1

V+

f

× C1

C2