Microcontroller: Power, DC Characteristics, I2C Interface

Presented by Nipun Batra

February 2, 2013

Analog Sensors - Temperature

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AD22103 temperature sensor by Analog Devices Temperature coefficient of 28 mV/oC Output proportional to T*VS Temperature span: 0 - 100 oC Price - $1.65 Transfer function: VOUT = (VS/3.3) X [0.25 + 0.028 X TA]

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TSL250R light sensor by TAOS (Texas Advanced Optical Solutions, spinoff of TI)

Consists of photodiode and an integrated amplifier Converts light intensity to a voltage Typical responsivity: 137 mV/(uW/cm2) at

wavelength of 635 nm Typical current consumption: 1 mA Maximum output voltage for a supply of 5V ~ 4V

Loose resolution if we connect directly to 5V ADC What is the solution?

Analog Sensors - Light

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AD623: General purpose Op Amp by Analog Devices Requires only a single external resistor to set the gain using:

RG = 100 / (Gain - 1) kOhms In this case Gain = 1.25 -> RG = 4 kOhms

Analog Sensors - Light

Analog Sensor - Accelerometer

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ADXL150 single-axis accelerometer by Analog Devices Use for measuring gentle vibrations to violent physical shocks

such as car-crash On-chip signal conditioning and amplification Output proportional to both the acceleration and supply

voltage: VOUT = VS/2 - (sensitivity * VS/5 * acceleration) Typical value of sensitivity = 38.0

Voltage Regulators

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Converts a range of input DC voltage to a fixed output DC voltage Used to provide a constant supply voltage within a system Removes noise and provides isolation from external supply voltage

Why constant supply voltage?

Many devices operate on fixed voltage Need to know the supply voltage for ADC to decide the sampled value

Primarily 3 types of voltage regulators: Linear regulator: Produce lower voltage than supply voltage Switching regulator: Step-up/step-down or invert the voltage Charge pumps: Step-up/step-down/invert but with limited current

drive capability

Conversion process is not 100% efficient: Current used for regulator itself is called quiescent current

LM78xx Regulators

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Most commonly used voltage regulators Manufactured by several vendors: Fairchild, ST Microelectronics Part number denotes the output voltage

LM7805 - 5 V output LM7812 - 12 V output

Typical output current of 1 A Quiescent current between 5 and 8 mA

Decoupling capacitors (typically in the range 10 uF and 47 uF are used at input and output)

For negative voltages, use LM79xx regulators

MAX603 Regulators

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Max603 for 5V output and Max604 for 3.3V output Output current up to 500 mA Very small quiescent current - 15 uA

2 uA in shutdown mode

Ideal for low power or battery operated systems Operate from input voltage between 2.7V to 11.5V DC Output capacitor to filter the voltage

MAX1615 Regulators

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Micropower Linear Regulators Only supply 30 mA of output current Maximum of 8 uA of Quiscent current

Less than 1 uA of shutdown current

Use this as power source for modules within the embedded system - shutdown the modules when not in use

Operate from input voltage between 4V to 28V DC 5/3 pin determines the output voltage - 1 implies 5V output

Decoupling Capacitors

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Capacitors used to separate (decouple) one part of electrical circuit from another

Connect them to the input supply for each device on board Provides a path to the ground for any noise present in the power

supply Also act as a source of transient current required when the device

must switch its outputs or internal state Some devices have in-built decoupling capacitors to save on-board

space Look into the datasheet to decide when you should put external

decoupling capacitor

Pull up/down Resistors

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Used in logic circuits to ensure that a line is set at expected voltage levels if external devices are disconnected (or if no active devices are connected on the line)

Why use a resistor? What value should be a resistor?

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AVR32: DC Characteristics

Absolute maximum ratings (AVR32)

Found in the Section “Electrical Characteristics” in the datasheet Stresses beyond “Absolute Maximum Ratings” may cause

permanent damage to the device and hence should be avoided

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Common DC Characteristics

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Common DC Characteristics

VDDCORE represents core operating voltage Max value of VIL denotes highest value where the pin is guaranteed

to be read as 0 Min value of VIH denotes lowest value where the pin is guaranteed

to be read as 1 When a pin is output high, it will be the source of current

Some devices may have an upper limit on total aggregate current as well on a group of pins e.g. Sum of all IOH for ports C0-C5, D0-D4, ADC7, RESET should not exceed 150 mA (ATmega)

When a pin is output low, it will sink current Negative value since the current is going in Similar to IOH, some devices have upper limit on aggregate IOL

as well e.g. sum of IOL on ports C0-C5, ADC6, ADC7 should not exceed 100 mA (ATmega)

Value of pull up resistors based upon the current ratings

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Regulator Characteristics

Internal voltage regulator Can supply voltage to other devices on board

With limited current capabilities Decoupling requirements also typically specified ADC voltage input range also specified

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Caution While Interconnecting

Threshold for logic high and logic low vary across devices For an input device to recognize the signal as high or low, the

output device must provide the signal appropriately Interfacing AT25DF641 Flash with ATMEGA328P

Absolute Maximum Ratings

Operating Range

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Caution While Interconnecting

Interfacing AT25DF641 Flash with ATMEGA328P

Common DC Characteristics

Inter-Integrated Circuit (I2C)

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One of the most common ways to interconnect devices within embedded systems

In existence for more than 20 years, invented by Phillips Data rate - 100 kbps (standard mode) 400 kbps (fast mode) Two wire interface: SDA (Serial Data) and SCL (Serial Clock) Bus is bidirectional Devices may be attached/detached without affecting other devices

Inter-Integrated Circuit (I2C)

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Both SDA and SCL are pulled up to a positive supply Bus remains high when not in use

A device using the bus drives the line high/low as appropriate Each device connected to I2C bus has unique address and can act as

either transmitter (master), receiver (slave) or both

Multi-master bus: More than one device may assume the role of master: In case of conflict, only one continues and rest abort

I2C transaction begins with SDA going low followed by SCL: indicates that a packet transmission is commencing

While SCL is low, SDA transitions (high or low) for the first valid data byte (“START” condition)

I2C: Data Transmission

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For each transmitted bit, it becomes valid on SDA while SCL is low The bit is sampled on the rising edge of SCL and must remain valid until

the falling edge of SCL SDA transitions to the next bit before SCL goes high once more

The transaction completes by SCL returning high (inactive) followed by SDA (“STOP” condition)

I2C: Acknowledgement

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Any number of bytes may be transferred in an I2C packet Most significant bit transmitted first If receiver is unable to receive, it aborts by pulling SCL low

Each byte transmitted must be acknowledged by the receiver After transmission of 8th bit, receiver acknowledges by pulling

SDA low Master generates a clock pulse on SCL to transfer/latch the

acknowledgement bit

So how should a master select a slave device?

I2C Packet

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Since each device has unique address, data transmission starts with address bits followed by data

7 bits of address: 16 reserved address – What is the maximum number of devices supported?

Followed by direction bit: 0 implies write cycle, 1 implies read cycle

Also supports extended 10-bit addressing mode Two bytes for addressing 7-bit devices ignore the transaction

I2C: Key Observations

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Only two lines required: SDA, SCL Same line for read/write

Only one operation can be performed at a time Multiple devices can be connected on the same line

A particular device selected based on the address transmitted on the data line

Additional overhead in case of point to point link More than one master device allowed

Acknowledgement mechanism to confirm receipt of data Typical transfer speed of around 100 KHz

xMega: Two Wire Interface (TWI)

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xMega (and in general devices) support TWI that is compatible to I2C

Connecting EEPROM over I2C

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Atmel AT24C32: 32 KB EEPROM Organized as 4096 words of 8 bits each

1 million write cycles Simple functions for interface: EEOpen(); EEWriteByte(unsigned int

address uint8_t data); EEReadByte(unsigned int address)

What are R1, R2 and R3 typically called?

Connecting APDS-9300 Light Sensor

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Used for light sensing in Mobile Computing Wing Can not be used for hostel deployments (projects) since I2C does

not run on long distances Datasheet will be uploaded on the course website Characteristics:

I2C interface for communication Photodiode senses the light (visible and infrared); on-chip ADC

converts it into 16-bit digital value that is transferred over I2C Low Active Power (2.6 mW) with power down mode

APDS-9300: Block Diagram

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Configurable slave address, selected by ADDR SEL

APDS-9300: Timing Diagram

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Sending a control command to APDS

APDS-9300: Timing Diagram

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Receiving light data from APDS-9300

APDS-9300: Register Set

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Provides a set of user configurable registers written/read using I2C

What did you learn today?

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On a small sheet of paper, give me a short (2-3 sentences) description of what you learned today

You can use it to give any broad comments on the class as well