AT90LS4433-4AI datasheet(70/126 Pages) ATMEL

70 / 126 page

AT90S/LS4433

1042H–AVR–04/03

Scanning Multiple

Channels

Since change of analog channel always is delayed until a conversion is finished, the

Free Run mode can be used to scan multiple channels without interrupting the con-

verter. Typically, the ADC Conversion Complete interrupt will be used to perform the

channel shift. However, the user should take the following fact into consideration: The

interrupt triggers once the result is ready to be read. In Free Run mode, the next conver-

sion will start immediately when the interrupt triggers. If ADMUX is changed after the

interrupt triggers, the next conversion has already started and the old setting is used.

ADC Noise Canceling

Techniques

Digital circuitry inside and outside the AT90S4433 generates EMI, which might affect

the accuracy of analog measurements. If conversion accuracy is critical, the noise level

can be reduced by applying the following techniques:

The analog part of the AT90S4433 and all analog components in the application

should have a separate analog ground plane on the PCB. This ground plane is

connected to the digital ground plane via a single point on the PCB.

Keep analog signal paths as short as possible. Make sure analog tracks run over

the analog ground plane and keep them well away from high-speed switching

digital tracks.

The AVCC pin on the AT90S4433 should be connected to the digital V

CC supply

voltage via an LC network as shown in Figure 49.

Use the ADC Noise Canceler function to reduce induced noise from the CPU.

If some Port C pins are used as digital outputs, it is essential that these do not

switch while a conversion is in progress.

Figure 49. ADC Power Connections

Note that since AVCC feeds the Port C output drivers, the RC network shown should not

be employed if any Port C serve as outputs.

PC5 (ADC5)

PC4 (ADC4)

PC3 (ADC3)

PC2 (ADC2)

PC1 (ADC1)

PC0 (ADC0)

AGND

AREF

AVCC

PB5

VCC

100 nF

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