LTC4300A-2CMS8#PBF

Overview

The LTC4300A-2CMS8#PBF is a hot swappable 2-wire bus buffer manufactured by Analog Devices Inc. It operates within a supply voltage range of 2.7V to 5.5V on both the backplane (VCC) and card (VCC2) sides, supporting level shifting between these independent supplies. The device provides bidirectional buffering for SDA and SCL lines with a maximum operating frequency of 400kHz. It features a 1V precharge circuitry to minimize bus disturbances during live insertion and includes rise-time accelerator currents to maintain signal integrity with weaker pull-up resistors. The component is housed in an 8-lead plastic MSOP package and supports I2C, I2C Fast Mode, and SMBus standards.

Feature Summary

• Provides bidirectional buffering while isolating backplane and card capacitances during live board insertion
• Enables level translation between disparate 2.7V to 5.5V supply voltages on VCC and VCC2 pins
• Incorporates 1V precharge circuitry to minimize voltage differentials and bus disturbances upon connection
• Features rise-time accelerators that allow the use of weaker DC pull-up currents while meeting system requirements

Applications

• Bidirectional buffer for SDA and SCL lines in CompactPCI systems
• Servers requiring hot-swappable I/O card insertion into live backplanes
• Desktop computers utilizing capacitance buffering or bus extension
• Systems requiring 5V to 3.3V level translation with power supply redundancy

Procurement Notes

Verify the specific suffix CMS8 corresponds to the commercial temperature range of 0°C to 70°C and the MSOP-8 package configuration. Confirm that the #PBF designation indicates lead-free finish compliance. Ensure the ordering information matches the manufacturer's current documentation to avoid discrepancies in pinout or electrical characteristics compared to tape-and-reel variants.

Selection Notes

Select the LTC4300A-2 variant specifically when the design requires independent supply voltages for the backplane and card sides, enabling level shifting capabilities not present in the LTC4300A-1. This model replaces the ENABLE pin with a dedicated VCC2 supply and uses an ACC input for accelerator control. Verify that the application involves 2-wire bus protocols such as I2C or SMBus where hot swapping and capacitance isolation are critical design constraints.

Part Context

This component belongs to the LTC4300A series of hot swappable 2-wire bus buffers designed for I/O card insertion into live backplanes without data corruption. The series includes variants like the LTC4300A-1 which utilizes an ENABLE pin for low-current shutdown, whereas the LTC4300A-2 focuses on level shifting between independent supply rails. The family is widely used in server and desktop computer architectures requiring robust interface protection.

Replacement Considerations

LTC4300A-1CMS8#PBF: Replaces the VCC2 level-shifting capability with an ENABLE pin for chip disable functionality; suitable if independent card-side supply is not required.

FAQ

How does the LTC4300A-2 handle level shifting between different supply voltages?

The LTC4300A-2 utilizes separate VCC and VCC2 supply pins, allowing the backplane and card sides to operate at independent voltages ranging from 2.7V to 5.5V. There are no constraints on which supply voltage must be higher, enabling seamless translation between levels such as 5V and 3.3V.

What is the function of the ACC pin on the LTC4300A-2?

The ACC pin serves as a digital CMOS input that enables or disables the rise-time accelerator currents on all four SDA and SCL pins. Driving ACC to the VCC2 voltage enables the accelerators, while driving it to ground turns them off, allowing users to manage boost currents based on system loading conditions.

How does the device protect against bus disturbances during live insertion?

The LTC4300A-2 incorporates a 1V precharge circuitry that forces the SDA and SCL pins to 1V through nominal 100k resistors before connection. This minimizes the worst-case voltage differential seen by the pins at the moment of contact, thereby reducing electrical disturbances on the live backplane busses.