TDA3682 datasheet(13/20 Pages) PHILIPS

13 / 20 page

2002 Mar 11

Philips Semiconductors

Product speciﬁcation

Multiple voltage regulator with

power switches

TDA3682

Application information

NOISE

The outputs of regulators 1 to 5 are designed in such a

way that the noise is very low and the stability is very good.

The noise output voltage depends on output capacitor Co.

Table 4 shows the influence of the output capacitor on the

noise figure.

Table 4

Noise ﬁgures

Note

1. Measured at a bandwidth from 20 Hz to 20 kHz.

STABILITY

The regulators are made stable with the externally

connected output capacitors. The stability can be

guaranteed with almost any output capacitor. When only

an electrolytic capacitor is used, the temperature

behaviour of this output capacitor can cause oscillations at

extreme low temperature. The following two examples

show how an output capacitor value is selected.

Oscillation problems can be avoided by adding a 47 nF

capacitor in parallel with the electrolytic capacitor.

Example 1 (regulator 2)

Regulator 2 (BU5V) is stabilized with an electrolytic output

capacitor of 10

µF (ESR = 4 Ω). At Tamb = −30 °C the

capacitor value is decreased to 3

µF and the ESR is

increased to 28

Ω. As can be seen from Fig.8 the regulator

will be instable at Tamb = −30 °C.

Solution: To avoid problems with stability at low

temperatures, the use of tantalum capacitors is

recommended. Use a tantalum capacitor with a value of

µF or an electrolytic capacitor with a higher value.

Example 2 (regulator 1)

Regulator 1 (illumination) is stabilized with an electrolytic

capacitor of 2.2

µF (ESR = 8 Ω). At Tamb = − 30 °C the

capacitor value is decreased to 0.8

µF and the ESR is

increased to 56

Ω. As can be seen from Fig.9 the regulator

will be stable at Tamb = −30 °C.

Even when only a small MKT capacitor of 47 nF is used as

the output capacitor, regulator 1 will remain stable over the

temperature range.

REGULATOR

NOISE FIGURE (

µV)(1)

Co =10 µFCo =47 µFCo = 100 µF

170

130

120

110

100

140

110

100

140

110

100

140

110

100

handbook, halfpage

MGT176

Co (µF)

ESR

(

Ω)

maximum

minimum

stable region

100

0.1

Fig.8

Curve for selecting the value of the output

capacitor for regulator 2.

handbook, halfpage

MGT177

Co (µF)

ESR

(

Ω)

maximum

stable region

100

0.1

0.047

100

Fig.9

Curve for selecting the value of the output

capacitor for regulators 1, 3, 4 and 5.

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