Datasheet
2003 Nov 28 15
Philips Semiconductors Product specification
Multiple voltage regulators with switch TDA3608Q; TDA3608TH
Application information
NOISE
The noise on the supply line depends on the value of the
supply capacitor and is caused by a current noise (the
output noise of the regulators is translated into a current
noise by means of the output capacitors). Table 1 shows
the noise figure with the corresponding output capacitor C
o
for each regulator. The noise is minimal when a high
frequency capacitor of 220 nF in parallel with an
electrolytic capacitor of 100 µF is connected directly to
pins V
P
and GND.
Table 1 Noise figure; note 1
Note
1. Measured at a bandwidth of 200 kHz.
S
TABILITY
The regulators are made stable with the externally
connected output capacitors. The output capacitors can be
selected using the graphs of Figs 13 and 14. When an
electrolytic capacitor is used, the temperature behaviour of
this output capacitor can cause oscillations at low
temperature. The next two examples show how an output
capacitor value is selected.
Example 1
The regulator 1 is made stable with an electrolytic output
capacitor of 220 µF with ESR = 0.15 Ω. At T
amb
= −30 °C
the capacitor value is decreased to 73 µF and the ESR is
increased to 1.1 Ω. The regulator remains stable at
T
amb
= −30 °C (see Fig.13).
Example 2
The regulator 2 is made stable with an electrolytic
capacitor of 10 µF with ESR = 3 Ω. At T
amb
= −30 °C the
capacitor value is decreased to 3 µF and the ESR is
increased to 23.1 Ω. The regulator will be instable at
T
amb
= −30 °C (see Fig.14).
Solution
Use a tantalum capacitor of 10 µF or a larger electrolytic
capacitor. The use of tantalum capacitors is recommended
to avoid problems with stability at low temperatures.
REGULATOR
NOISE FIGURE (µV)
C
o
=10µFC
o
=47µFC
o
= 100 µF
1 225 150 135
2 225 150 135
3 255 200 180
handbook, halfpage
1
0
110
C (µF)
MBK100
2
3
4
stable region
maximum ESR
minimum ESR
100
R
(Ω)
Fig.13 Curves for selecting value of output
capacitor for regulator 1 and regulator 3.
handbook, halfpage
2
0
0.22
110
C (µF)
MBK099
4
6
8
10
12
stable region
maximum ESR
minimum ESR
100
R
(Ω)
14
Fig.14 Curves for selecting value of output
capacitor for regulator 2.