SOT23, Switched-Capacitor

Voltage Inverters with Shutdown

_______________________________________________________________________________________

7

Surface-Mount

Tantalum

PRODUCTION

METHOD

714-969-2491

803-946-0690

PHONE

603-224-1961

603-224-1430

714-960-6492

803-626-3123

FAX

MANUFACTURER

AVX

Matsuo

Sprague

SERIES

TPS series

267 series

593D, 595D series

714-969-2491

803-946-0690

AVX

Matsuo

714-960-6492

803-626-3123

X7R

X7R

Surface-Mount

Ceramic

Table 2. Capacitor Selection for Minimum Output Resistance or Capacitor Size

Table 1. Low-ESR Capacitor Manufacturers

CAPACITORS TO MINIMIZE SIZE

Ω, TYP)

C1 = C2

0.33µF

3.3µF

12kHz

CAPACITORS TO MINIMIZE

OUTPUT RESISTANCE

Ω, TYP)

C1 = C2

125kHz

10µF

1µF

MAX1720

PART

MAX1719/MAX1721

Flying Capacitor (C1)

Increasing the flying capacitor’s value reduces the out-

put resistance. Above a certain point, increasing C1’s

capacitance has a negligible effect because the output

resistance becomes dominated by the internal switch

resistance and capacitor ESR.

Output Capacitor (C2)

Increasing the output capacitor’s value reduces the

output ripple voltage. Decreasing its ESR reduces both

output resistance and ripple. Lower capacitance values

can be used with light loads if higher output ripple can

be tolerated. Use the following equation to calculate the

peak-to-peak ripple:

Input Bypass Capacitor (C3)

Bypass the incoming supply to reduce its AC impedance

and the impact of the MAX1719/MAX1720/MAX1721’s

switching noise. A bypass capacitor with a value equal

to that of C1 is recommended.

Voltage Inverter

The most common application for these devices is a

charge-pump voltage inverter (Figure 1). This applica-

tion requires only two external components—capacitors

C1 and C2—plus a bypass capacitor, if necessary.

Refer to the Capacitor Selection section for suggested

capacitor types.

Cascading Devices

Two devices can be cascaded to produce an even

larger negative voltage (Figure 4). The unloaded output

by the output resistance of the first device multiplied by

the quiescent current of the second. When cascading

more than two devices, the output resistance rises dra-

matically. For applications requiring larger negative

voltages, see the MAX865 and MAX868 data sheets.

The maximum load current and startup current of the

proper startup.

V=

I

2

f

C2

2

I

ESR

RIPPLE

OUT

OSC

OUT

C2

××

+×

×

MAX1719

MAX1720

MAX1721

“n”

MAX1719

MAX1720

MAX1721

“1”

2

1

C2

2

C1

C2

SHDN (MAX1719)

SHDN (MAX1720/

MAX1721)

C1

33

44

6

55

6

1

…

…

Figure 4. Cascading MAX1719s or MAX1720s or MAX1721s

to Increase Output Voltage