+5V to −5V Regulated Voltage Converter

Another application in which the LM2682 can be used is for

generating a −5V regulated supply from a +5V unregulated

supply. This involves using an op-amp and a reference and

is connected as shown in

Figure 2. The LM358 op-amp was

chosen for its low cost and versatility and the LM4040-5.0

reference was chosen for its low bias current requirement.

Of course other combinations may be used at the designer’s

discretion to fit accuracy, efficiency, and cost requirements.

With this configuration the circuit is well regulated and is still

capable of providing nearly 10 mA of output current. With a 9

mA load the circuit can typically maintain 5% regulation on

the output voltage with the input varying anywhere from 4.5V

to the maximum of 5.5V. With less load the results are even

better. Voltage ripple concerns are reduced in this case since

the ripple at the output of the LM2682 is reduced at the out-

put by the PSRR of the op-amp used.

Paralleling Devices

Any number of devices can be paralleled to reduce the out-

put resistance. As shown in

Figure 3, each device must have

its own pumping capacitors, C1 and C2, but only one shared

output capacitor is required. The effective output resistance

is the output resistance of one device divided by the number

of devices used in parallel. Paralleling devices also gives the

capability of increasing the maximum output current. The

maximum output current now becomes the maximum output

current for one device multiplied by the number of devices

used in parallel. For example, if you parallel two devices you

can get 20 mA of output current and have half the output re-

sistance of one device supplying 10 mA.

DS100997-5

FIGURE 3. Paralleling Devices

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