AT90S/LS2333 and AT90S/LS4433
52
Analog to Digital Converter
Feature list:
• 10-bit Resolution
• ± 2 LSB Absolute Accuracy
• 0.5 LSB Integral Non-Linearity
• 65 - 260 µs Conversion Time
• Up to 15 kSPS
• 6 Multiplexed Input Channels
• Rail-to-Rail Input Range
• Free Run or Single Conversion Mode
• Interrupt on ADC conversion complete.
• Sleep Mode Noise Canceler
The AT90S2333/4433 features a 10-bit successive approximation ADC. The ADC is connected to a 6-channel Analog Mul-
tiplexer which allows each pin of Port C to be used as an input for the ADC. The ADC contains a Sample and Hold Amplifier
which ensures that the input voltage to the ADC is held at a constant level during conversion. A block diagram of the ADC
is shown in Figure 44.
The ADC has two separate analog supply voltage pins, AVCC and AGND. AGND must be connected to GND, and the volt-
age on AVCC must not differ more than ± 0.3 V from V
CC
. See the paragraph ADC Noise Canceling Techniques on how to
connect these pins.
An external reference voltage must be applied to the AREF pin. This voltage must be in the range AGND - AVCC.
Figure 44. Analog to Digital Converter Block Schematic
Operation
The ADC can operate in two modes - Single Conversion and Free Run Mode. In Single Conversion Mode, each conversion
will have to be initiated by the user. In Free Run Mode the ADC is constantly sampling and updating the ADC Data Regis-
ter. The ADFR bit in ADCSR selects between the two available modes.
The ADMUX register selects which one of the six analog input channels to be used as input to the ADC.
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
9
0
ADC MULTIPLEXER
SELECT (ADMUX)
ADC CTRL & STATUS
REGISTER (ADCSR)
ADC DATA REGISTER
(ADCH/ADCL)
MUX2
ADIE
ADIE
ADFR
ADSC
ADEN
ADIF
ADIF
MUX1
MUX0
ADPS0
ADPS1
ADPS2
6-
CHANNEL
MUX
CONVERSION LOGIC
10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
Analog
Inputs
External
Reference
Voltage