TIOL1115EVM: Trying to connect to an Arduino

Hi Louis,

The TIOL1115EVM comes populated with a TIOL115 device by default, but it can support the other versions of the device if you need to swap it out with a TIOL111 or TIOL1113.  They differ only in the LDO voltage and the digital IO High level which corresponds with the 3.3V or 5V version of the device.  The minimum voltage level to register a digital "1" is 2V regardless of the 3.3V or 5V voltage rail.  If your are using a 1.8V signal from the Arduino, you would need to use a level shifter to make sure the voltage was greater than 2V.

The pin assignments for GND, TX, and RX are correct.

The NFAULT pin is the logical OR of three fault conditions, an over-current , under-voltage, and over-temperature condition.  You will need to determine which one of these three conditions exist in your test setup. I would rank the likelihood as an over-temp, then an over-current, and last an under-voltage condition based on your description.

An over-current condition is when there is more than the expected amount of current flowing through the CQ pin (either source or sink depending on the configuration).  The limit is set with the resistor value on the current limit adjust pin ILIM_ADJ.  If the current exceeds the set limit for longer than approximately 200uS, the device will disable the CQ driver to prevent damage from a short circuit condition.  The device will re-enable the driver every 15mS to see if the over-current condition has cleared which is referred to as Auto-Recovery in the datasheet.  Sections 8.3.2 and 8.3.3 of the datasheet discuss this and Figure 4 shows a typical curve for the current limit vs. "RSET" resistor on the ILIM_ADJ pin.  The EVM has a some jumper settings to enable a fixed resistor, a potentiometer that can be tuned for a particular value, or allow the ILIM_ADJ pin to be shorted to GND, or left floating.  You should check the board to see if you have an appropriate configuration to avoid an over-current fault.

If the L+ voltage supply drops below the UVLO threshold, the NFAULT pin will indicate this as a fault. You should check to make sure the L+ voltage is greater than 7V and that the Master can supply enough current to keep this stable. 

The last fault condition is an over-temperature condition and is usually seen when the device temperature is too high as a result of too much current flowing through the LDO and or the CQ pin.  If this occurs, the CQ driver is disabled, but the LDO remains on allowing the device to cool down.  Once it cools down, it will re-enable the driver and if the conditions are unchanged, this heating/cooling cycle may persist and be the source for the NFAULT LED to blink.  I don't know how much current the Arduino board requires, but the TIOL1115 is only capable of sourcing a maximum of 20mA to external loads.  Depending on how much the Arduino board requires, and the number of LEDs being driven, etc. the load may be too large to prevent the TIOL1115 from overheating.  You should check to see if the problem clears when powering the Arduino from an external source and isolating the load on the TIOL1115 LDO to just the components on the EVM such as the LEDs.

The device is a simply a physical layer transceiver and has no dependency on a protocol such as in UART communication.  If the enable (EN) pin is High, it will pass the digital logic level signals from the MCU on the TX pin to the CQ pin.  The RX pin will always pass a digital logic level version of the CQ pin to the MCU which can be used to receive communication from the Master, or to monitor the communication from itself as a form of loop back.  Section 8.4.3 provides the logic tables for the different operational modes.  For UART communication with a Master, you will want the Push-Pull communication mode shown in table 8.  But generally speaking, the EN pin will enable or disable the CQ driver, and the data to be transmitted when the EN pin is high should be applied to the TX pin.  Given the architecture, the TX and CQ levels are inverted such that a "1" on the TX line will result in a Low voltage on the CQ pin, and a "0" on the TX pin will result in a High voltage on the CQ pin.

Regards,

Jonathan