SP828 datasheet(13/16 Pages) SIPEX

13 / 16 page

SP828DS/03

SP828/829 High Efficiency Voltage Inverters

Combining a Doubler and Inverter Circuit

A designer can connect a SP828/829 device in a

combination doubler/inverter circuit as seen in

Figure 24. The doubler uses capacitors C3 and

C4 while the inverter uses C1 and C2. Loading

either output decreases both output voltages to

GND because both the doubler and the inverter

circuits use the charge pump. Designers should

not allow the total current output from the doubler

and the inverter to exceed 40mA.

Implementing Shutdown

If shutdown control of the SP828/829 devices is

necessary, the circuit found in Figure 25 can be

implemented. The 0.1

µF capacitor at IN absorbs

transient input currents. The output resistance of

the devices can be determined by the following

equation:

OUT = 20 + 2 x RBUFFER ,

where R

OUT is the output resistance and RBUFFER

is the output resistance of the buffer driving IN.

BUFFER can be reduced by connecting multiple

buffers in parallel at IN. The polarity of the

SHUTDOWN signal can be changed by using a

noninverting buffer to drive IN.

Connecting in Parallel

A designer can parallel a number of SP828/829

devices to reduce the output resistance for specific

designs. All devices will need their own flying

capacitor, C1, but a single output capacitor will

serve all of the devices connected in parallel by

increasing the capacitance of C2 by a factor of n

where n equals the total number of devices

connected. This connection can be found in

Figure 26.

Cascading Devices

A designer can cascade SP828/829 devices to

produce a larger inverted voltage output. Refer

to Figure 27 for this circuit connection. With two

cascaded devices, the unloaded output voltage is

decreased by the output resistance of the first

device multiplied by the quiescent current of the

second device connected. The total output

resistance is greatly increased when more than

two devices are cascaded.

Layout and Grounding

Designers should make an effort to minimize

noise by paying special attention to the circuit

layout with the SP828/829 devices. External

components should be connected in close

proximity to the device and a ground plane

should be implemented. This will keep electrical

traces short minimizing parasitic inductance and

capacitance.

Figure 25. SP828/829 Device with Shutdown Control

OUT

SP828

SP829

C1+

C1-

GND

+VIN

VOUT

CIN

0.1

µF

Shutdown

Logic

OFF

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