Datasheet

ManualsBrandsAtmel ManualsAVR MicrocontrollersAVR RISC Microcontroller 8bit 8KB SOIJ

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2586N–AVR–04/11

ATtiny25/45/85

Noise Reduction and Idle mode. To make use of this feature, the following procedure should be

used:

• Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must

be selected and the ADC conversion complete interrupt must be enabled.

• Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the

CPU has been halted.

• If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake

up the CPU and execute the ADC Conversion Complete interrupt routine. If another interrupt

wakes up the CPU before the ADC conversion is complete, that interrupt will be executed,

and an ADC Conversion Complete interrupt request will be generated when the ADC

conversion completes. The CPU will remain in active mode until a new sleep command is

executed.

Note that the ADC will not be automatically turned off when entering other sleep modes than Idle

mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before enter-

ing such sleep modes to avoid excessive power consumption.

17.8 Analog Input Circuitry

The analog input circuitry for single ended channels is illustrated in Figure 17-8. An analog

source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-

less of whether that channel is selected as input for the ADC. When the channel is selected, the

source must drive the S/H capacitor through the series resistance (combined resistance in the

input path).

Figure 17-8. Analog Input Circuitry

The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or

less. If such a source is used, the sampling time will be negligible. If a source with higher imped-

ance is used, the sampling time will depend on how long time the source needs to charge the

S/H capacitor, with can vary widely. The user is recommended to only use low impedant sources

with slowly varying signals, since this minimizes the required charge transfer to the S/H

capacitor.

Signal components higher than the Nyquist frequency (f

ADC

/2) should not be present to avoid

distortion from unpredictable signal convolution. The user is advised to remove high frequency

components with a low-pass filter before applying the signals as inputs to the ADC.

ADCn

1..100 kΩ

S/H

= 14 pF