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LTC4311ISC6-TRPBF Datasheet(PDF) 6 Page - Linear Technology |
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LTC4311ISC6-TRPBF Datasheet(HTML) 6 Page - Linear Technology |
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6 / 12 page  LTC4311 6 4311fa I2C and SMBus Overview The I2C communication protocol employs open-drain pull-down drivers with resistive or current source pull- ups. This protocol allows multiple devices to drive and monitor the bus without bus contention. The simplicity of resistive or fixed current source pull-ups is offset by the slow rise times resulting when bus capacitance is high. Rise times can be improved by using lower pull-up resistor values or higher fixed current source values, but the additional current increases the low state bus voltage, decreasing noise margins. Slow rise times can seriously impact data reliability, enforcing a maximum practical bus speed well below the established I2C or SMBus maximum transmission rate. The LTC4311 overcomes these limitations by providing a boosted pull-up current only during positive bus transitions to quickly slew large bus capacitances. Therefore, rise time is dramatically improved, especially with maximum or out of specification I2C or SMBus loading conditions. The LTC4311 has separate but identical circuitry for each BUS output pin. The circuitry consists of a positive edge slew rate detector and a voltage comparator. The voltage comparator has a supply dependent threshold. At supply voltages below 2.7V the comparator threshold is 0.3VCC, and at higher voltages the comparator threshold is a constant 0.8V. This allows the rise time accelerator to be used in non-compliant systems where the bus thresholds are optimized for low voltage operation, while still meet- ing standard thresholds for compliant I2C and SMBus systems. The slew limited pull-up current is only turned on if the bus line voltage is greater than the supply dependent comparator threshold voltage and the positive slew rate of the bus line is greater than the typical 0.2V/μs threshold of the slew rate detector. The pull-up current remains on until the voltage on the bus line is within 0.4V of VCC or the slew rate drops below 0.2V/μs. The pull-up current is slew limited to maintain signal integrity for busses that have very little capacitive load. In a lightly loaded system a strong pull-up could result in fast edge rates that cause reflections on the bus. These reflections can be detected by devices on the bus as extra clock edges, could result in erroneous data, or cause a stuck bus. An internal slew limit comparator limits the rate the pull-up current can slew the bus lines to 100V/μs. Auto Detect Standby Mode and Shutdown Mode When BUS1 and BUS2 are both high the LTC4311 reduces the standby supply current. Internal comparators detect when the bus pins are within 400mV of VCC, and reduce the supply current to 26μA. When the ENABLE pin is grounded, the LTC4311 enters a low (<5μA) supply cur- rent shutdown mode. Both bus pins are high impedance in shutdown, regardless of the bus pin voltage. OPERATION |
Similar Part No. - LTC4311ISC6-TRPBF |
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Similar Description - LTC4311ISC6-TRPBF |
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