TCAN4550: TACN4550 some questions

Hello Sukmin,

Sukmin Hong said:

1. Is there are power up sequence between Vsup and VIO?

    For example, VIO should be after Vsup?

    Or Is it okay if vio comes in before Vsup?

There is not a required power up sequence and Vsup and VIO can come up in either order.  But but will be required for the device to function.  Vsup will supply the internal digital and 5V LDOs needed by the device.  VIO is only used to supply the Crystal/clock circuit on OSC1/2 and also as the reference voltage for the digital IO level translators (3.3V or 5V).

Sukmin Hong said:

2. I will supply VIO from LDO 3.3V, in this case I don't need INH. Right?

If I don't use INH, then Can I left this pin floating? or is it better to connect pull down 100k ohm?

Correct, INH is not required to use.  It's primary function is to control the enable pin of the low-voltage regulator so that it can be disabled when the TCAN4550 (and board) is placed into the low-power sleep mode and then enabled otherwise.  INH is an output pin so if unused, it can be left unconnected and a 100k pull down resistor is not required.  However, if INH is used, a 100k pull down resistor is required to help create a "Low" because the INH is driven to a High level, but simply becomes HI-Z otherwise, and any capacitance on the net will need to be discharge through a resistive path.

Sukmin Hong said:

3. What does the WAKE pin? and nWKRQ pin do? 

I don't understand "local wake up" mean.

Is this some kind of enable pin?  (Wake Pin -> nWKRQ Pin -> Wake up the MCU? _

 
I want to make this device always on.

and in this case

3-1. Can I Just connect Wake PIN to VSUP 24V?

3-2.  nWKRQ Pin can be floating?

The TCAN4550 has 3 main functional modes:

1. Standby Mode - The device is fully powered and all internal circuits are active, but the device has not been configured and is not active in CAN bus communication.
2. Normal Mode - The device is fully powered, configured, and can communicate in CAN bus communication
3. Sleep Mode - The device is in a low power mode and the internal LDOs are disabled.  Only a small monitoring circuit is still active that is sourced from the VSUP supply is enabled that allows for the device to "wake up" from sleep mode when it sees one of the valid wake up events which include a "local wake up" or voltage level transition on the WAKE pin that could come from either a switch or FET circuit, or CAN bus message activity that meets the "Wake Up Pattern (WUP)" of a filtered dominant, recessive, dominant pattern found in most CAN messages.

The WAKE pin is an input pin that can detect a voltage pulse while the device is in Sleep Mode and cause it to "wake up" and transition in to Standby Mode.

The nWKRQ pin is a "wake request" pin that is a low-voltage output pin that typically mirrors the function of INH which operates at the higher VSUP voltage levels.  nWKRQ is also inverted logic from INH, but it can be used as a request to the MCU or device that controls the low-voltage supply regulator to enable the regulator used for the VIO supply.

If you do not intend do use Sleep Mode, then nWKRQ and WAKE pins are not required.  The WAKE pin should be tied off to either VSUP or GND because it is an input pin and we don't want any noise coupling into the unused pin.  nWKRQ pin is an output pin, so if unused it can just be left unconnected.

I will note that the TCAN4550 does have a failsafe feature that starts a 4 minute timer called the Sleep Wake Error (SWE) Timer which requires the device to have had the PWRON bit cleared, and/or configured into Normal Mode within 4 minutes of powering on, waking up from sleep, or being issued a power on reset (POR).  If this timer is allowed to expire the device will transition to Sleep Mode.  If the WAKE pin is unused, then you will need to either use another method to wake the device up such as a WUP on the CAN bus, or a power cycle. Having a testpoint access to this pin during development is helpful.

Sukmin Hong said:

4. Adding the crystal damping resistor value  50ohm will be fine? (I will tune it after) 

Adding a 50 ohm damping resistor between OSC1 and the crystal is a good start.  Please see the TCAN455x Clock Optimization and Design Guidelines application note for additional information. (Link)

The TCAN4550 supports both a crystal and a single-ended clock through the OSC1 an OSC2 pins.  There is a voltage comparator on the OSC2 pin that is looking for a "grounded" pin which would indicate the device should use the single-ended clock mode.  Therefore, it is important to tune the crystal circuit with enough margin to prevent the lowest level of the crystal peak-to-peak oscillation wavefrom from crossing below 150mV which could cause the device to switch from crystal mode to single-ended mode during normal operation.  The series damping resistor is useful in this tuning process.

Regards,

Jonathan

Hi Sukmin,

Sukmin Hong said:

1. nWKRQ is just an output function pin that indicates whether TCAN4550 is in sleep mode or standby mode.

nWKRQ itself does not control the MCU or other devices. 

:So If I'm not going to do any action using nwkrq, I can just left floating. 

Yes I think you correctly understand.  For applications that do want to use Sleep Mode for lower power consumption during idle times, there are two general architectures that are used to wake up the board from the sleep mode state.

The first is by using the INH pin that is connected to the voltage regulator's EN pin which powers the board and MCU when a WAKE up condition is detected.  The MCU then boots as a result of power-up and the system starts operating normally.

The second is when the regulator is not controlled by INH and instead by the MCU or another device such as a PMIC.  In this case, the nWKRQ can be used as an indicator a wake up event has occurred at a lower digital voltage level (mirrors INH functionality).  It can also be configured to work as a dedicated wake up interrupt pin, but this requires both VSUP, VIO, and the clock are functioning so that the digital core can generate the interrupt.

You are also correct, that if you do not intend to use the nWKRQ pin, you can leave it floating.

Sukmin Hong said:

2. As you explained, due to SWE timer, it seems that even if I don't want to use Sleep mode, 

TCAN4550 will be automatically enters Sleep mode if there is no wake up event in 4m after Power up.

: So, In this case, If I just want to TCAN4550 wake up only by WUP, I can just connect "WAKE" Pin to VSUP. Right?

Yes, this is correct.  Local Wake Up (LWU) through the WAKE pin is not required and if unused, the WAKE pin should be tied off to either VSUP or GND to prevent it from transitioning on noise.  There is slightly less leakage current when it is connected to VSUP, but it could also be connected to GND depending on your preference.

Sukmin Hong said:

3. Can WUP be considered as a general Can message?

Thanks very very much. It would be great help.

A general CAN message generally meets the WUP requirements, but the device is just using a small state machine to detect a sequence of dominant, recessive, dominant bits of a specific bit width within a specific amount of time.

A WUP doesn't have to be a CAN message but usually a CAN message that meets the WUP requirements is transmitted by a node to wake up the nodes on the bus. 

Regards,

Jonathan