TC1219/TC1220

DS21366B-page 6

 2002 Microchip Technology Inc.

4.3

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

will lower the output resistance and larger values of

C2 will reduce output ripple. (Equation 4-1(b) and

Equation 4-3).

Table 4-1 shows various values of C1 and the

corresponding output resistance values @ +25°C. It

assumes a 0.1

shows the output voltage ripple for various values of

current and 0.1

TABLE 4-1:

OUTPUT RESISTANCE VS.

C1 (ESR = 0.1

Ω)

TABLE 4-2:

OUTPUT VOLTAGE RIPPLE

VS. C2 (ESR = 0.1

Ω)

4.4

Input Supply Bypassing

reduce AC impedance and minimize noise effects due

to

the

internal

switching

of

the

device

The

recommended capacitor depends on the configuration

of the TC1219/TC1220.

4.5

Shutdown Input

The TC1219/TC1220 is enabled when SHDN is high,

and disabled when SHDN is low. This input cannot be

allowed to float. (If SHDN is not required, see the

TCM828/829 data sheet.) The SHDN input can be only

flows.

4.6

Voltage Inverter

The most common application for charge pump

devices is the inverter (Figure 4-3). This application

uses two external capacitors: C1 and C2 (plus a power

supply bypass capacitor, if necessary). The output is

Refer

to

Table 4-1

and

Table 4-2

for

capacitor

selection.

FIGURE 4-3:

VOLTAGE INVERTER

TEST CIRCUIT

C1 (

µF)

TC1219

TC1220

1

100

45

3.3

42

25

10

25

19.4

30

19.3

17.5

C2 (

µF)

TC1219

TC1220

1419

145

3.3

128

45

10

44

16

30

16

7

3

2

4

5

1

C3

C1

C2

TC1219

TC1220

C1–

IN

OUT

C1+

GND

Device

C1

C2

C3

TC1219

10

µF

10

µF

10

µF

TC1220

3.3

µF

3.3

µF

3.3

µF

SHDN

6

+

+

+