The first term is the effective resistance from the

switched-capacitor circuit.

Conversion losses occur during the transfer of charge

between capacitors C1 and C2 when there is a voltage

difference between them. The power loss is:

Increasing Efficiency

Efficiency can be improved by lowering output voltage

ripple and output impedance. Both output voltage rip-

ple and output impedance can be reduced by using

large capacitors with low ESR.

The output voltage ripple can be calculated by noting

that the output current is supplied solely from capacitor

C2 during one-half of the charge-pump cycle.

Slowing the oscillator frequency reduces quiescent cur-

rent. The oscillator frequency can be reduced by con-

necting a capacitor to the OSC pin.

Reducing the oscillator frequency increases the ripple

voltage in the MAX1044/ICL7660. Compensate by

increasing the values of the bucket and reservoir

capacitors. For example, in a negative voltage converter,

the pump frequency is around 4kHz or 5kHz. With the

recommended 10µF bucket and reservoir capacitors,

the circuit consumes about 70µA of quiescent current

while providing 20mA of output current. Setting the

oscillator to 400Hz by connecting a 100pF capacitor to

OSC reduces the quiescent current to about 15µA.

Maintaining 20mA output current capability requires

increasing the bucket and reservoir capacitors to

100µF.

Note that lower capacitor values can be used for lower

output currents. For example, setting the oscillator to

40Hz by connecting a 1000pF capacitor to OSC pro-

vides the highest efficiency possible. Leaving the bucket

and reservoir capacitors at 100µF gives a maximum

a power conversion efficiency of 98%.

General Precautions

1) Connecting any input terminal to voltages greater

than V+ or less than ground may cause latchup. Do

not apply any input sources operating from external

supplies before device power-up.

2) Never exceed maximum supply voltage ratings.

3) Do not connect C1 and C2 with the wrong polarity.

4) Do not short V+ to ground for extended periods with

supply voltages above 5.5V present on other pins.

than GND (pin 3). Adding a diode in parallel with

to LV, will prevent this condition.

________________Application Circuits

Negative Voltage Converter

Figure 8 shows a negative voltage converter, the most

popular application of the MAX1044/ICL7660. Only two

external capacitors are needed. A third power-supply

bypass capacitor is recommended (0.1µF to 10µF)

V

1

2 x f

x C2

2 x ESR

I

RIPPLE

OSC

C2

OUT

≅+









P

1

2

C1 (V

V

1

2

C2 V

2V

V

x f

/ 2

CONV.LOSS

OUT

2

RIPPLE

2

OUT RIPPLE

OSC

)

=+

−







 +







−















2

Switched-Capacitor Voltage Converters

_______________________________________________________________________________________

9

MAX1044

ICL7660

4

3

C1

10µF

0.1µF

2

1

5

6

7

8

C2

10µF

V+

BOOST

LV

Figure 8. Negative Voltage Converter with BOOST and LV

Connections

MAX1044

ICL7660

4

3

2

1

5

6

7

8

C1

C2

V+

Figure 9. Voltage Doubler