I2C Quick Guide Datasheet by Analog Devices Inc.

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The I2C (inter-IC) bus is a 2-wire, multi-drop, digital communications link for ICs that has become the defacto standard for many embedded applications.
Serial, 8-bit, bidirectional data transfer can occur at speeds up to 3.4Mbps, though 400kHz is usually sufficient. Since only two bus lines are required, a
serial data line (SDA) and serial clock line (SCL), building a system with multiple master or slave devices is relatively simple. The number of I2C devices
that can be connected to a single I2C bus segment is limited only by a maximum bus capacitance (400pF) and address space.
Frequently Asked Questions
Q1) How are I2C, SMBus and PMBus related?
Answer: Originally developed to facilitate battery management systems, SMBus uses I2C hardware but adds second-level software, which ultimately allows
devices to be hot swapped without restarting the system. PMBus extends SMBus by defining a set of device commands specifically designed to manage
power converters, exposing device attributes such as measured voltage, current, temperature and more. In general, I2C, SMBus and PMBus devices can
share a bus without any major issues.
Q2) How do I build a large system and still meet bus capacitance and rise time specifications?
Answer: Linear Technology’s bus buffers resolve common electrical limitations posed by specifications, thereby allowing more devices to be added to the
bus. These devices break up large busses into several smaller I2C compliant (<400pF) pieces, while still providing simultaneous communications to all bus
segments and optionally injecting a boosted pull-up current during positive bus transitions to quickly slew large bus capacitances.
Q3) How do I resolve a stuck bus?
Answer: Other than having a host try to manually fix a bus stuck low, Linear Technology’s bus buffers provide stuck bus protection which recovers a stuck
bus by automatically generating pulses on SCLOUT in an attempt to unstick the bus. Otherwise, a hard reset is required.
Q4) How do I increase the number of I2C addresses available?
Answer: Linear Technology’s address translators and software or hardware controlled I2C multiplexers provide the ability to address one of multiple
identical devices or simply increase fan-out, thus resolving address conflict issues, while also providing Hot Swap capabilities, bus buffering, rise time
acceleration and stuck bus protection.
I2C Standard
I2C Quick Guide
I2C vs SMBus vs PMBus
Specification I2C
SMBus
PMBusHigh Power Low Power
Signaling
Packet Error Checking (Optional) – •
SMBALERT (Optional) – •
Block Size Limit 32 bytes 255 bytes
Timing
Data Rate (Standard Mode) 100kbps
Data Rate (Fast Mode) 400kbps – – 400kbps
Data Rate (Fast Mode Plus) 1Mbps – –
Data Rate (High Speed Mode) 3.4Mbps – –
Clock Speed 0Hz to 3.4MHz 10kHz to 100kHz 10kHz to 400kHz
Bus Timeout 25ms to 35ms
Bus Master Request Delay (Min) – 50µs
SCL Hold Time (Max) – 2ms
Data Hold Time (Min) – 300ns
Electrical
Capacitance Load per Bus Segment (Max) 400pF – 400pF
Rise Time (Max) 1µs at 100kHz, 300ns at 400kHz 1µs 1µs at 100kHz, 300ns at 400kHz
Pull-Up Current at 0.4V (Max) 3mA (Standard Mode and Fast Mode) 4mA 350µA 4mA
Leakage Current per Device (Max) ±10µA ±5µA ±10µA
VIL Input Logic Low Threshold (Max) 0.3VDD or 1.5V 0.8V
VIH Input Logic High Threshold (Min) 0.7VDD or 3V 2.1V
VOL Output Logic Low Threshold (Max) 0.4V
MASTER
SDA
SCL
SLAVE SLAVE
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog Devices, Inc.
All other trademarks are the property of their respective owners.
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Linear Technology provides a comprehensive family of I2C-enabled devices for a variety of applications. From Hot Swap
controllers to bus isolators, these devices provide on-the-fly adjustability, enhance I2C performance or simply enable designers to
easily manage key system parameters.
I2C Checklist
Hot Swap Controller
n
Control inrush current on a live backplane, while monitoring current, voltage, power and energy
n
Record past and present fault conditions and configure latchoff or auto-restart
Power Supply/LED Driver
n
Control power-on/-off or dimming and configure mode of operation, output voltage, sequencing
and slew rate for single- or multi-topology converters
Power System Management Controller
n
Control, monitor, supervise, sequence and margin multiple power supplies
n
Access EEPROM for user configuration, fault logging and telemetry
Power/Energy Monitor
n
Monitor current, voltage, average power, charge and energy, while minimizing software polling
with min/max registers and configurable alerts
Temperature Monitor
n
Measure combinations of voltage, current and internal or external temperature
n
Trigger single or repeated measurements and change formats (Celsius or Kelvin)
Bus Buffer/Multiplexer/Address Translator/Rise Time Accelerator
n
Break up bus capacitance, increase fan-out, level shift busses, decrease rise times and nest
addresses while providing Hot Swap capabilities and stuck bus protection
Bus Isolator
n
Break ground loops and isolate logic level interfaces, while also providing Hot Swap
capabilities or adjustable isolated power to neighboring components
Power over Ethernet Power Sourcing Equipment (PSE)
n
Efficiently source up to 90W of power, while configuring PSE mode of operation and monitoring
per port status, current, MOSFET health and die temperature
Battery Charger/Gas Gauge
n
Adjust charge current, float voltage and charge termination, while monitoring status, charge,
current, voltage or temperature of battery, USB or wall sources
ADC/DAC
n
Write to or read from data converters with no latency, and select input or output data formats
and use of internal or external reference
Silicon Oscillator
n
Enable and program clock frequency with 0.1% resolution, as well as instantaneously change
octaves using DACs with 10-bit monotonicity and less than 1% nonlinearity
i
BARRIER
VOUT2
VOUT1
t
VOUT
VOUT
VIN
125°C
55°C
Up to
60VIN
I2C
Bus
0916B
www.linear.com/i2c n 1-800-4-LINEAR

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