TC1219ECH datasheet(6/16 Pages) MICROCHIP

6 / 16 page

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

Ω ESRC1 and 2Ω RSWITCH. Table 4-2

shows the output voltage ripple for various values of

C2. The VRIPPLE values assume 10mA output load

current and 0.1

Ω ESRC2.

TABLE 4-1:

OUTPUT RESISTANCE VS.

C1 (ESR = 0.1

Ω)

TABLE 4-2:

OUTPUT VOLTAGE RIPPLE

VS. C2 (ESR = 0.1

Ω)

IOUT 10mA

4.4

Input Supply Bypassing

The VIN input should be capacitively bypassed to

reduce AC impedance and minimize noise effects due

the

internal

switching

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

driven to 0.5V above VIN to avoid significant current

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

equal to -VIN plus any voltage drops due to loading.

Refer

Table 4-1

and

Table 4-2

for

capacitor

selection.

FIGURE 4-3:

VOLTAGE INVERTER

TEST CIRCUIT

C1 (

µF)

TC1219

ROUT(Ω)

TC1220

ROUT(Ω)

100

3.3

19.4

19.3

17.5

C2 (

µF)

TC1219

VRIPPLE (mV)

TC1220

VRIPPLE (mV)

1419

145

3.3

128

VIN

VOUT

TC1219

TC1220

C1–

OUT

C1+

GND

Device

TC1219

µF

TC1220

3.3

µF

3.3

µF

3.3

µF

SHDN

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