LM2682M National Semiconductor, LM2682M Datasheet - Page 5

• Manufacturer Part Number: LM2682M
• Description: Switched Capacitor Voltage Doubling Inverter
• Manufacturer: National Semiconductor

Application Information
+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.
(Continued)
FIGURE 3. Paralleling Devices
5
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
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