tda3681a NXP Semiconductors, tda3681a Datasheet - Page 17

• Manufacturer Part Number: tda3681a
• Description: Tda3681a Multiple Voltage Regulator With Switch And Ignition Buffer
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Application information
N
Table 1 Noise figures
Note
1. Measured at a bandwidth of 30 kHz.
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 to a current
noise by the output capacitors). The noise is minimal when
a high frequency capacitor of 220 nF in parallel with an
electrolytic capacitor of 100 F is connected directly to the
supply pins V
S
The regulators are stabilized by the externally connected
output capacitors.
2003 Aug 29
handbook, halfpage
REGULATOR
TABILITY
OISE
Multiple voltage regulator with
switch and ignition buffer
Fig.9
1
2
3
4
ESR
( )
Curve for selecting the value of the output
capacitor for regulators 1, 3 and 4.
20
15
10
5
0
P1
0.1
, V
C
P2
o
and GND.
= 10 F C
170
440
120
85
stable region
1
NOISE FIGURE ( V)
maximum ESR
o
10
= 47 F C
110
240
100
70
C ( F)
MGL912
100
o
(1)
= 100 F
110
190
80
55
17
The output capacitors can be selected by using the graphs
given in Figs 9 and 10. When an electrolytic capacitor is
used, its temperature behaviour can cause oscillations at
a low temperature. The two examples below show how an
output capacitor value is selected.
Example 1
Regulators 1, 3 and 4 are stabilized with an electrolytic
output capacitor of 220 F (ESR = 0.15 ).
At T
73 F and the ESR is increased to 1.1 . The regulator
remains stable at T
Example 2
Regulator 2 is stabilized with a 10 F electrolytic capacitor
(ESR = 3 ). At T
decreased to 3 F and the ESR is increased to 23.1 .
As can be seen from Fig.10, the regulator will be unstable
at T
Solution
To avoid problems with stability at low temperatures, the
use of tantalum capacitors is recommended. Use a
tantalum capacitor of 10 F or a larger electrolytic
capacitor.
handbook, halfpage
Fig.10 Curve for selecting the value of the output
amb
amb
= 30 C.
ESR
= 30 C, the capacitor value is decreased to
( )
capacitor for regulator 2.
14
12
10
8
6
4
2
0
2
0.22
amb
amb
= 30 C, the capacitor value is
= 30 C (see Fig.9).
1
maximum ESR
minimum ESR
stable region
10
Product specification
C ( F)
TDA3681A
MGL913
100