9

Rev. 9-22-00

SP6830/6831 Low Power Voltage Inverters With Shutdown

© Copyright 2000 Sipex Corporation

DESCRIPTION

The SP6830/6831 devices are CMOS Charge

Pump Voltage Converters that can be used to

invert a +1.15V to +5.3V input voltage. These

devices are ideal for designs involving battery-

powered and/or board level voltage conversion

applications.

The typical operating frequency of the SP6830

is 35kHz. The typical operating frequency of

the SP6831 is 120kHz.

The SP6830 has a

typical operating current of 70

µAandtheSP6831

operates at 200

µA. Both devices can output

25mA with a voltage drop of 500mV. The

devices are ideal for LCD panel bias applications,

cellular phones, pagers, PDAs, medical

instruments, and other portable battery-powered

equipment. The SP6830/6831 devices combine

a high efficiency (>95% over most of its load-

current range) with a low quiescent current.

THEORY OF OPERATION

The SP6830/6831 devices should theoretically

produce an inverted input voltage. In real world

applications, there are small voltage drops at the

output that reduce efficiency. The circuit of an

ideal voltage inverter can be found in Figure 18.

The voltage inverters require two external

capacitors to store the charge. A description of

the two phases follows:

Phase 1

In the first phase of the clock cycle, switches S2

and S4 are opened and S1 and S3 closed. This

connects the flying capacitor, C1, from V

ground. C1 charges up to the input voltage

applied at V

Phase 2

In the second phase of the clock cycle, switches

S1 and S3 are opened and S2 and S4 are closed.

This connects the flying capacitor, C1, in parallel

with the output capacitor, C2. The charge stored

in C1 is now transferred to C2. Simultaneously,

the negative side of C2 is connected to V

the positive side is connected to ground. With

the voltage across C2 smaller than the voltage

across C1, the charge flows from C1 to C2 until

the voltage at the V

Charge-Pump Output

The output of the SP6830/6831 devices is not

regulated and therefore is dependent on the

output resistance and the amount of load current.

As the load current increases, losses may slightly

increase at the output and the voltage may become

slightly more positive. The loss at the negative

output, V

V

OUT

times the negative converter's source

resistance, R

V

The actual inverted output voltage at V

equal the inverted voltage difference of V

V

V

Efficiency

Theoretically, the total power loss of a switched

capacitor voltage converter can be summed up as

follows:

where P

internal loss in the IC including any losses in the

MOSFET switches, P

the charge pump capacitors, and P

Figure 18. Circuit for an Ideal Voltage Inverter

C1

C2

S1

S3

S4

S2