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LTC4314 Pin Functions

Category: Hardware
Product Number: LTC4314

Hello everyone,

By using LTC4314 I2C Multiplexer, I aim to transfer data I send i2c to 4 channels with selectable pins. When I examined the document, a few pins came to my mind.

What exactly do the ACC, DISCEN and FAULT pins do? I understand from the document that it is related to the output rise time of the ACC pin, which I fully understand. The FAULT pin can be observed when an error is detected, but what does the DISCEN pin do? I left the FAULT pin in the HIGH state, the ACC pin in the low state, but I did not fully understand what would change if I set the DISCEN pin HIGH and LOW. It is usually left in the HIGH state in the document, but there is no complete information about why it was left.

 In addition, there is no information about whether the ENABLE pins will be in HIGH state during data transfer and then go back to LOW state or whether it should be HIGH-LOW before starting data transfer, even there is no data transmission image. How will the data coming from the input side be transferred to the output side using ENABLE pins?

  • Hello,

       The ACC pin is an input pin used to configure the behavior of the rise time accelerators (RTA).  The RTA is a pull-up current source which provides the benefits of the fast rise times normally associated with a strong (small valued) pull-up resistor without the drawback of a large sinking current for the bus device pulling the bus down.  Table 1 on page 9 of the data sheet lists the different options.  Summarizing, the RTA is disabled if  ACC is pulled high.  If ACC is left floating (high-Z), then the RTA is configured to assist the pull-up resistors on bus with a 3mA current source.  If ACC is pulled low, then the RTA current source will be up to 45mA (depending on the external circuit).

      The DISCEN pin is an input pin used to configure if the stuck bus disconnect feature is active or not.  The LTC4314 will detect a stuck bus and the based on the state of the DISCEN pin either report a fault by asserting the nFault pin (DISCEN low) or report the fault AND perform corrective actions to attempt to clear/unstick the downstream bus (DISCEN high).  The corrective actions include disconnecting the down stream bus and then generating clock pulses on the downstream bus's SCL to hopefully allow the stalled downstream device's state machine to return to an idle state.  See the last paragraph on the datasheet's page 8 for more details.

      The nFAULT pin is an output pin which is pulled low when a stuck bus is detected.  A stuck bus occurs when the enabled SCLOUT and SDAOUT pins do not have a simultaneous high occur within a 45ms window.

      The ENABLE pins are input pins which determine which SCLOUT/SDAOUT ports are connected to the SCLIN/SDAIN pins.  If the ENABLE pin is high, the associated output port is connected.  If the pin is low, then that output port is disconnected.  The controller driving the ENABLE pins will determine the resulting bus configuration.  Also note that the controller should make sure that the changes to the ENABLE pin states only occur when the I2C bus is in the idle state (both SCL & SDA high following a STOP).

    Eric

  • Hello, 

    I couldn't obtain any data from the SCLOUT of the LTC4314 sensor in my tests according to the above.

    ACC  pin LOW

    DISCEN pin LOW

    FAULT pin HIGH - 3.3 pull-up resistor 10k

    VCC - 3.3V 

    VCC2 - 3.3V

    In the tests I made after setting the above pins, I observed that signals I sent to INPUT side did not give any output on the Output side.

    For example, I expect to see data from OUT1 only when EN1-HIGH, but when I monitor pins I don't see any data. In this case, I think I made a mistake somewhere, but I don't quite understand what the problem is. 

  • Hello,

       Based on what you have described so far, it sounds like the part should at least be passing data, so if it is not, there is likely a mistake elsewhere.

       Do you have pull up resistors installed on the SCL/SDA lines on the input and output buses?

    Eric

    ps - I assume it is just a incorrect word choice in your above comment ("... the LTC4314 sensor..."), but to clarify just in case, the LTC4314 isn't a sensor.  It's a multiplexer which connects or disconnects different I2C bus segments and so does NOT generate data or respond to an I2C command other than passing through the data/response generated by an external device.