Atmel AVR178: Atmel AT90PWM81/161 Schematic Checklist Features • • • • Power supplies Reset circuit Clocks and crystal oscillators ISP/debugWIRE 8-bit Atmel Microcontrollers Application Note 1 Introduction A good hardware design comes from a proper schematic. This application note describes a common checklist that should be used when starting and reviewing the schematics for an Atmel® AT90PWM81/161 design. Rev. 8396B-AVR-01/12 2 Power supplies 2.1 Power supply connections Figure 2-1. Power supply schematic. Table 2-1. Power supply connections. Signal name Recommended pin connection Description VCC 2.7V to 5.5V Decoupling/filtering capacitors 100nF (1)(2) and 10µF (1) Digital supply voltage AVCC 2.7V to 5.5V Decoupling/filtering capacitors 100nF (1)(2) and 10µF (1) (3) Ferrite bead prevents VCC noise from interfering with AVCC Analog supply voltage GND Notes: Ground 1. These values are given only as a typical example. 2. Decoupling capacitor should be placed close to the device for each supply pin pair in the signal group. Low ESR capacitors should be used for better decoupling. 3. Ferrite bead has better filtering performance than the common inductor at high frequency. It can be added between VCC and AVCC to prevent digital noise from entering the analog power. The bead should provide enough impedance (for example, 50Ω at 20MHz and 220Ω at 100MHz) for separating the digital power from the analog power. 2 Atmel AVR178 8396B-AVR-01/12 Atmel AVR178 2.2 External analog reference connections The following schematic checklist is necessary only if the design is using the external analog reference. If the internal reference is used, the circuit is not necessary. Figure 2-2. External analog reference schematic. AREF EXTERNAL REFERENCE + _ 4.7μF Close to device 100nF GND Table 2-2. External analog reference connections. Signal name Recommended pin connection Description AREF 2.56V to AVCC-0.6V Decoupling/filtering capacitors (1)(2) and 4.7µF (1) 100nF External references from AREF pin on PORT E3 GND Notes: Ground 1. These values are given only as a typical example. 2. Decoupling capacitor should be placed close to the device. 3 8396B-AVR-01/12 3 External reset circuit The external reset circuit is connected to the reset pin when the external reset function is used. If internal reset is used, the circuit is not necessary. The reset switch also can be removed if manual reset is not necessary. Figure 3-1. External reset circuit example schematic. Table 3-1. Reset circuit connections. Signal name Recommended pin connection Description RESET Reset low-level threshold voltage VCC = 2.7 – 5.5V: below 0.2 × VCC reset pin Note: This pull-up resistor makes sure that RESET does not go low unintentionally. When PDI programming and debugging are used, the reset line is used as the clock. In this case, the reset pull-up should be 10kΩ or greater or be removed altogether. Any reset capacitors should be removed if PDI programming and debugging are used. Other external reset sources should be disconnected. 4 Atmel AVR178 8396B-AVR-01/12 Atmel AVR178 4 Clocks and crystal oscillators 4.1 External clock source Figure 4-1. External clock source example schematic. Table 4-1. External clock source connections. Signal name Recommended pin connection Description XTAL1 XTAL1 is used as input for an external clock signal Input for inverting oscillator pin 1 XTAL2 Can be left unconnected or used as GPIO 4.2 Crystal oscillator Figure 4-2. Crystal oscillator example schematic. Table 4-2. Crystal oscillator checklist. Signal name XTAL1 XTAL2 Notes: Recommended pin connection Biasing capacitor 15pF (1)(2) Biasing capacitor 15pF (1)(2) Description External crystal between 0.9MHz and 16MHz 1. These values are given only as a typical example. Please refer to the crystal datasheet to determine the capacitor value for the crystal used, or refer to the application note, “AVR042: AVR Hardware Design Considerations.” 2. Decoupling capacitor should be placed close to the device for each supply pin pair in the signal group. 5 8396B-AVR-01/12 5 ISP port 5.1 ISP/debugWIRE Figure 5-1. ISP/DW port interface example schematic. SCK (PB5) MISO(PB6) MISO VCC VCC SCK MOSI RESET GND MOSI(PB4) GND RESET Table 5-1. ISP/DW port interface checklist. NOTE 6 Signal name Description MISO SPI communication SCK SPI clock MOSI SPI communication RESET Device external reset line and used in debugWIRE VCC Digital supply voltage GND Ground Some precautions regarding the reset line should be taken to ensure proper communication via the debugWIRE interface. Pull-up resistors on the reset line must not be smaller than 10kΩ (the pull-up resistor is not required for debugWIRE functionality), and there should be no capacitive load. Other logic connected to the reset line should be removed during debugging. Atmel AVR178 8396B-AVR-01/12 Atmel AVR178 6 Suggested reading 6.1 Device datasheet The device datasheet contains block diagrams of the peripherals and details about implementing firmware for the device. The datasheet is available at: http://www.atmel.com/dyn/resources/prod_documents/doc77340.pdf. 6.2 Evaluation kit schematic The Atmel AVR® STK®521 evaluation kit contains the full schematic for the board; it can be used as a reference design. The schematic is available in User Guide: http://www.atmel.com/dyn/resources/prod_documents/doc8194.pdf. 7 8396B-AVR-01/12 7 Table of contents Features ............................................................................................... 1 1 Introduction ...................................................................................... 1 2 Power supplies................................................................................. 2 2.1 Power supply connections................................................................................... 2 2.2 External analog reference connections............................................................... 3 3 External reset circuit ....................................................................... 4 4 Clocks and crystal oscillators ........................................................ 5 4.1 External clock source .......................................................................................... 5 4.2 Crystal oscillator .................................................................................................. 5 5 ISP port ............................................................................................. 6 5.1 ISP/debugWIRE .................................................................................................. 6 6 Suggested reading........................................................................... 7 6.1 Device datasheet................................................................................................. 7 6.2 Evaluation kit schematic...................................................................................... 7 7 Table of contents ............................................................................. 8 8 Atmel AVR178 8396B-AVR-01/12 Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131 USA Tel: (+1)(408) 441-0311 Fax: (+1)(408) 487-2600 www.atmel.com Atmel Asia Limited Unit 01-5 & 16, 19F BEA Tower, Milennium City 5 418 Kwun Tong Road Kwun Tong, Kowloon HONG KONG Tel: (+852) 2245-6100 Fax: (+852) 2722-1369 Atmel Munich GmbH Business Campus Parkring 4 D-85748 Garching b. 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