 2002 Microchip Technology Inc.

DS21548B-page 5

TC2682/TC2683/TC2684

4.0

APPLICATIONS INFORMATION

4.1

Output Voltage Considerations

The

TC2682/TC2683/TC2684

perform

inverting

voltage conversions but do not provide any type of

regulation. The output voltage will droop in a linear

manner with respect to the output load current. The

value

of

the

equivalent

output

resistance

is

approximately 120

In this particular case, the output is approximately -10V

at very light loads and will droop according to the

equation below:

4.2

Capacitor Selection

In order to maintain the lowest output resistance and

output ripple voltage, it is recommended that low ESR

capacitors be used. Additionally, larger values of C1

and C2 will lower the output resistance and larger

Note:

For proper charge pump operation, C1

must have a voltage rating greater than or

a voltage rating greater than or equal to

Table 4-1 shows various values of C1/C2 and the

@+25°C.

Table 4-2 shows the output voltage ripple for various

and a 0.1

TABLE 4-1:

OUTPUT RESISTANCE

VS. C1/C2 (ESR = 0.1

Ω)

TABLE 4-2:

OUTPUT VOLTAGE RIPPLE

4.3

Input Supply Bypassing

reduce AC impedance and minimize noise effects due

to the switching internal to the device. It is recom-

mended that a large value capacitor (at least equal to

performance.

4.4

Inverting Voltage Doubler

The most common application for the TC2682/TC2683/

TC2684 devices is the inverting voltage doubler

(Figure 4-1). This application uses three external

Note:

A

power

supply

bypass

capacitor

is

recommended.

to loading. Refer to Table 4-1 and Table 4-2 for

capacitor selection guidelines.

FIGURE 4-1:

DUAL VOLTAGE

INVERTER TEST CIRCUIT

4.5

Layout Considerations

As with any switching power supply circuit, good layout

practice is recommended. Mount components as close

together as possible to minimize stray inductance and

capacitance. Also use a large ground plane to minimize

noise leakage into other circuitry.

C1, C2

(

µF)

TC2682

TC2683

TC2684

0.33

633

184

120

1

262

120

102

3.3

120

95

84

(

µF)

TC2682

(mV)

TC2683

(mV)

TC2684

(mV)

0.33

192

60

27

163

21

16

3.3

17

8

7

1

2

N

N

UT

UT

C2682

C2683

C2684

1

2

1

2

ND

evice

1

2

UT

TC2682

3.3

µF

3.3

µF

3.3

µF

3.3

µF

TC2683

1

µF

1

µF

1

µF

1

µF

TC2684

0.33

µF

0.33

µF

0.33

µF

0.33

µF

UT