Datasheet

191
7728G–AVR–06/10
ATtiny87/ATtiny167
17. ADC – Analog to Digital Converter
17.1 Features
• 10-bit Resolution
• 1.0 LSB Integral Non-linearity
• ± 2 LSB Absolute Accuracy
• 13 - 260 µs Conversion Time (Low - High Resolution)
• Up to 15 kSPS at Maximum Resolution
• 11 Multiplexed Single Ended Input Channels
• 8 Differential input pairs with selectable gain
• Temperature sensor input channel
• Voltage from Internal Current Source Driving (ISRC)
• Optional Left Adjustment for ADC Result Readout
• 0 - AVcc ADC Input Voltage Range
• Selectable 1.1V / 2.56V ADC Voltage Reference
• Free Running or Single Conversion Mode
• ADC Start Conversion by Auto Triggering on Interrupt Sources
• Interrupt on ADC Conversion Complete
• Sleep Mode Noise Canceler
• Unipolar / Bipolar Input Mode
• Input Polarity Reversal Mode
17.2 Overview
The ATtiny87/167 features a 10-bit successive approximation ADC. The ADC is connected to
a 11-channel Analog Multiplexer which allows 16 differential voltage input combinations and
11 single-ended voltage inputs constructed from the pins PA7..PA0 or PB7..PB4. The differen-
tial input is equipped with a programmable gain stage, providing amplification steps of 8x or
20x on the differential input voltage before the A/D conversion. The single-ended voltage
inputs refer to 0V (AGND).
The ADC contains a Sample and Hold circuit 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
17-1.
Internal reference voltages of nominally 1.1V or 2.56V are provided On-chip. Alternatively,
AVcc can be used as reference voltage for single ended channels. There are also options to
output the internal 1.1V or 2.56V reference voltages or to input an external voltage reference
and turn-off the internal voltage reference. These options are selected using the REFS[1:0]
bits of the ADMUX control register and using AREFEN and XREFEN bits of the AMISCR con-
trol register.