ata6616 ATMEL Corporation, ata6616 Datasheet - Page 278

• Manufacturer Part Number: ata6616
• Description: Microcontroller With Lin Transceiver, 5v Regulator And Watchdog
• Manufacturer: ATMEL Corporation

4.24
278
Decoupling Capacitors
ATA6616/ATA6617 [Preliminary]
The operating frequency (i.e. system clock) of the processor determines in 95% of cases the
value needed for microcontroller decoupling capacitors.
The hypotheses used as first evaluation for decoupling capacitors are:
Figure 4-114. Capacitor Description
According to the operating frequency of the product, the decoupling capacitances are chosen
considering the frequencies to filter,
The relation between frequencies to cut and decoupling characteristics are defined by:
where:
Then, in normalized value range, the decoupling capacitors become:
Table 4-92.
These decoupling capacitors must to be implemented as close as possible to each pair of power
supply pins:
Nevertheless, a bulk capacitor of 10-47 µF is also needed on the power distribution network of
the PCB, near the power source.
For further information, please refer to Application Notes AVR040 “EMC Design Considerations”
and AVR042 “Hardware Design Considerations“on the Atmel web site.
fop
• The operating frequency (
• An SMC capacitor connected to 2 micro-vias on a PCB has the following characteristics:
peaks are located at
=
– 1.5 nH from the connection of the capacitor to the PCB,
– 1.5 nH from the capacitor intrinsic inductance.
– L: the inductance equivalent to the global inductance on the Vcc/GND lines.
– C
– 16-17 for logic sub-system,
– 5-6 for analogical sub-system.
---------------------
2
fop, Operating Frequency
1
1
LC
& C
1
2
Decoupling Capacitors versus Frequency
: decoupling capacitors (C
16 MHz
12 MHz
10 MHz
8 MHz
6 MHz
4 MHz
and
f
op
and 2
f
0.75 nH
op
2
) supplies itself the maximum peak levels of noise. The main
fop
f
f
op
op
=
.
and 2
---------------------
2
1
= 4
1
Capacitor
LC
1.5 nH
2
f
DRAFT
op
C
.
2
).
120 nF
220 nF
560 nF
33 nF
56 nF
82 nF
C
1
0.75 nH
PCB
120 nF
10 nF
15 nF
22 nF
33 nF
56 nF
9132A–AUTO–10/08
C
2