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Digital-to-Analog Conversion
Table of Contents
Microchip MCP4921 Features
General Overview
Serial SPI Interface
Overview
Programmable Gain Block (GA)
Voltage Reference Amplifiers (BUF)
Arduino SPI Test Script
Bipolar Operation
References:
1.
8-bit AVR Microcontroller with 4/8/16/32K Bytes In-System Programmable Flash -
ATmega328P, Chapter 23 "Analog-to-Digital Converter",
2.
Microchip Technology Inc. MCP4921/MCP4922, 12-Bit DAC with SPI™ Interface,
Microchip Technology document DS21897B
Introduction
Before we begin watch the following instructional video on Digital Audio - you may be
surprised to discover that much of what you thought you knew about digitization is wrong.
http://www.wired.com/gadgetlab/2013/02/sound-smart-watch-this-excellent-primer-on-dig
ital-audio/
Microchip MCP4921 Features
• 12-Bit Resolution
• ±0.2 LSB DNL (typ)
• ±2 LSB INL (typ)
• Rail-to-Rail Output
• SPI™ Interface with 20 MHz Clock Support
• Fast Settling Time of 4.5 μs
• Selectable Unity or 2x Gain Output
• External VREF Input
• 2.7V to 5.5V Single-Supply Operation
ATMEL document doc8161
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Related Manuals for Microchip Technology MCP4921
Summary of Contents for Microchip Technology MCP4921
- Page 1 8-bit AVR Microcontroller with 4/8/16/32K Bytes In-System Programmable Flash - ATmega328P, Chapter 23 "Analog-to-Digital Converter", ATMEL document doc8161 Microchip Technology Inc. MCP4921/MCP4922, 12-Bit DAC with SPI™ Interface, Microchip Technology document DS21897B Introduction Before we begin watch the following instructional video on Digital Audio - you may be surprised to discover that much of what you thought you knew about digitization is wrong.
- Page 2 General Overview The MCP4921 is a voltage output string DAC. As shown in Figure 1, this DAC includes an input amplifier, rail-to-rail output amplifier, reference buffer, plus shutdown and reset management circuitry. Figure 1 MCP4921 DAC Simplified Block Diagram Serial communication conforms to the SPI protocol Modes 0 and 3 as defined by the ATmega328P datasheet.
- Page 3 (VDD) as possible (within 4 mm). The power source supplying these devices should be as clean as possible. Figure 2 Arduino to MCP4921 DAC Electrical Interface The MCP4921 is designed to interface with the Serial Peripheral Interface (SPI) port of the...
- Page 4 SCK. The communications are unidirectional and, thus, data cannot be read out of the MCP4921. The CS pin must be held low for the duration of a write command. The write command/data consists of 16 bits and is used to configure the DAC’s control and data...
- Page 5 Writing Command/Data Word Register For the MCP4921 you should keep A/B bit 15 at logic zero and SHDN bit 12 at logic 1. Bits 14 (BUF) and 13 (GA), may be customized to your design solution as discussed in the next two Sections.
- Page 6 10-bit integer using the ATmega328 ADC subsystem. This 10-bit value is then sent to the 12-bit MCP4921 DAC. This 10-bit value is left justified with respect to the 12-bit DAC data word. This script does not use the SPI peripheral of the ATmega328. Instead it manually shifts out the bits.
- Page 7 12-Bit DAC with SPI™ Interface, Microchip Technology document DS21897B Bipolar operation is achievable using the MCP4921 by using an external operational amplifier (op amp). This configuration is desirable due to the wide variety and availability of op amps. This allows a general purpose DAC, with its cost and availability advantages, to meet almost any desired output voltage range, power and noise performance.
- Page 8 2. Calculate the resolution needed: 4.1V/1 mV = 4100, Since 2 = 4096, 12-bit resolution is desired. 3. The amplifier gain (R ), multiplied by V , must be equal to the desired minimum output to achieve bipolar operation. Since any gain can be realized by choosing resistor values ), the V source needs to be determined first.
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