KCC's Quizzes AQQ305 about a mutual exponentiation equation
1. Quote of the month: "A train station is where a train stops. A bus station is where a bus stops. I have a work station on my desk, so..." - unknown
2. Quiz AQQ305 about finding a mutual exponential equation
Good luck, and try to be among the
View All
September Monthly Blog Quiz! Read the blog, take the quiz, and you could win a gift card
Quiz: How Well Do You Know Adaptive Power Switching?
Is your I/O module overheating? The AD74416H's Adaptive Power Switching (APS) can cut heat dissipation by up to 40% — but how well do you really understand how it works?
Read the blog first: Cooling
View All
LTC4315
Production
The LTC4315 is a hot-swappable 2-wire bus buffer that provides bidirectional buffering, while maintaining a low offset voltage and high noise margin up...
Datasheet
LTC4315 on Analog.com
Hello.
I have a question about LTC4315.
We are considering using LTC4315 for master and slave connections. Is this possible?
The maximum number of slave boards is about 4, but how many slave boards can be added?
Best regards.
Hi Miky,
Determining the number of cascaded LTC4315 buffers depends on the details of the controller and target device's input & output voltage levels and associated circuitry.
The LTC4315 buffer adds a small voltage offset to its input low voltage and as the number of cascaded buffers increase, the resulting output low voltage keeps increasing. At some point, the resulting output low is higher than the input low threshold for the receiving device and then the communications will not work. Computing this voltage stack up in both directions and picking the smallest number which works will tell you how many cascaded stages will be possible.
Different I2C devices can have different drive strengths which may result in different output low voltages depending on the strength of the pull-up resistors.
If there is series resistance in the bus (we generally discourage adding series R in most I2C applications), then its voltage drop needs to be included.
Note that the voltage offset for the LTC4315 has a variation based on the input voltage and pull up current. When the input voltage is driven to voltages above 200mV, the offset voltage is as described by equation 3 on page 11 of the datasheet. For input voltages below 200mV, the offset voltage is larger and follows the offset voltages on page 3 of the datasheet's electrical characteristics table. The VOS(SAT) values show the saturated offset voltage for two different pull-up currents. VOS shows the offset voltage at the boundary between saturation and equation 3.
When computing the buffer offset voltage for the cascaded combination, you'll want to use the applicable offset voltage based on the particular conditions of the particular buffer. For example:
* if the VOL of the driving device is 50mV & there is a pull up current of 4mA, then the 1st buffer's offset voltage is 280mV (worst case) and then 2nd buffer's offset voltage will depend on Eq 3.
* the VOL of the driving device is 50mV & the pull up current is 500uA, then the 1st buffer's offset voltage is 120mV (worst case) and then the 2nd buffer will still be saturated (VlL=170mV < 200mV) and so its offset voltage will be between 120mV and 280mV depending on the pull up current. In this scenario, the 3rd cascaded buffer will use Eq 3 for its offset voltage since its input voltage is now above 200mV.
Eric
