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TCAN1044-Q1: CAN Ic damage

EZE
Prodigy 25 points
Part Number: TCAN1044-Q1
Other Parts Discussed in Thread: ESD2CAN24-Q1

Tool/software:

1. One of our customer is using CAN IC in 2Wheeler speedometer.Speedometer get power from battery. Two type of batteries customer is using. Only issue in type B battery

2. There are two types of batteries :

a) Type A Battery: One is high side cut off i.e Bat +ve lines get cut when fault happens , while Bat- remains there

b) Type B Battery: THis is low side cut off i.e Bat +ve remains when fault happens , while Bat- cut off is there

C) speedometer has 4 pin connector: bat+ , bat- , canh, canl

Speedometer get power from bat+ and bat-

3. Earlire in filed customer used to get CAN got damaged issue

4. Then they connected ESD diodes at CANH & CANL. Now ESD started getting damaged in field

5. THen they increased ESD diode power, so now track getting burst in field

6. ESD are connected near to output board.

7. Plz advise what could be issue? Plz suggest suitable solution

  • 0
    TI__Guru 51746 points

    Hi EZE,

    EZE said:
    Plz advise what could be issue?
    • It seems the speedometer's ground reference is lost, leading to a floating ground condition. I.e., CAN transceiver's reference becomes undefined, leading to voltage spikes / excessive potential differences and possible IC damage.
    • With floating GND, CANH/CANL voltage becomes unbalanced and expose ESD to excessive stress causing failures as the ESD diodes are designed for short transients and not overvoltage stress.
    • The PCB traces may not have been designed to handle the higher surge currents handled by the increased ESD ratings, leading to track burning. Hence, indicating sustained high-energy transients rather than typical ESD pulses.

    EZE said:
    Plz suggest suitable solution
    • I would recommend implementing a proper GND referenced for the Type B battery since BAT- can be cut off in a fault condition. Hence, preventing floating conditions.
      • Add a local high value ceramic GND reference capacitor of 100 uF to 470 uF, 50V - between BAT+ and the CAN transceivers GND. You may also consider adding diode between the BAT- line and chassis GND to provide a discharge path.
    • Use TVS diodes instead of standard ESD diodes as they are not designed for repeated high-energy transients.
      • We typically recommend ESD2CAN24-Q1 for all CAN applications.
    • Add series resistors or ferrite beads to limit inrush current that burns PCB tracks
      • May use 10 to 33 ohms series resistors on CAN and CANL before TVS diodes.
      • May use 600 ohms @ 100 MHz to help filter high-frequency transients, thanks

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 25 points

    Hi Michael

    Thanks for response. Attached is block diagram of system.

    We have three grounds in system:

    A) Bat-

    B) Speedometer digital ground

    C) Chassis ground (it is not present as of now, we are checking with end customer for this)

    Few recommendations which trying to incorporate these factors, plz advise if they are ok, plz advise any comments:

    A) 100uF(electrolytic) , 10uF+100nF(ceramic)

    1. Connect capacitor near to CAN transceiver VDD & GND pins.

    2. Here GND pin is speedometer digital ground

    3. Voltage of 100uF/10uF/100nF to be double than transcreceiver VDD voltage

    4. for 100uF selecting electrolytic rather then ceramix, as ceramic 100uF would be very expensive.  

    B) TVS diode from CANH/CANL:

    1. Scenario where there is no chassis ground available. We will connect ESD2CAN24-Q1 in this case. We will use speedometer gnd in this case. But will place TVS as close as possible near to output connector.

    2. Scenario where there is chassis ground is available. We will connect TVS to chassis ground

    C) We will increase the trace width of speedometer GND. Because when Bat- is disconnected, large transient currents can flow through small PCB traces, causing damage.

    D) Connect a Schottky diode from speedometer GND to battery Bat-. When Bat- is present, the diode is reverse biased and does nothing. When Bat- is lost, the diode allows some current to flow through, preventing complete floating of speedometer GND.

    Not sure when bat- is not present how diode allow current to flow?

    Can you share some circuit plz or app note?

    E) Add a local high value ceramic GND reference capacitor of 100 uF to 470 uF, 50V - between BAT+ and the CAN transceivers GND. 

    Not sure how it helps if Bat- is not present, can you explain? Also since Bat+ is not directly powering speedometer, its via dc dc in between. Can I connect capacitor b/w dc-dc output & gnd of transreceiver?

    F) You may also consider adding diode between the BAT- line and chassis GND to provide a discharge path.

    1. in case chassis ground is present, can you advise polarity of diode?

    2. What if chassis ground not available

    G) Use TVS diodes instead of standard ESD diodes as they are not designed for repeated high-energy transients.

    We typically recommend ESD2CAN24-Q1 for all CAN applications.

    Ok

    H) Add series resistors or ferrite beads to limit inrush current that burns PCB tracks

    May use 10 to 33 ohms series resistors on CAN and CANL before TVS diodes.

    May use 600 ohms @ 100 MHz to help filter high-frequency transients, thanks

    Will use series resitor 27ohm as it would be cheape

    I) Any other suggestions?

    scan.pdf

  • 0 in reply to EZE
    TI__Guru 51746 points

    Hi EZE,

    Sounds really good. 

    A) Decoupling Capacitors for VDD & GND

    If budget allows, 4.7 ceramic in parallel can improve response  

    B) TVS Diodes (CANH/CANL Protection)

    Both cases (chassis ground present or absent) are correctly considered.

    If no chassis ground, connect ESD2CAN24-Q1 TVS to speedometer ground.

    If chassis ground is present, connect TVS to chassis ground, ensuring a stable low-impedance return path.

    Placement: As close as possible to the connector to shunt transients before they enter PCB traces.

    C) Increasing Speedometer GND Trace Width

    Sounds good. If feasible, can also use ground planes instead of traces for better current handling and EMI shielding.

    D) Schottky Diode from Speedometer GND to BAT-

    Schottky Diode Connection: Anode -> Speedometer GND

    Cathode -> BAT-  

    When BAT- is present, the diode is reverse biased (no current flows).

    When BAT- is lost, it conducts transient current, preventing speedometer GND from floating.

    E) Local High-Value Capacitor  Between BAT+ & GND

    If BAT- is disconnected, the capacitor can temporarily hold charge, reducing sudden voltage drops for a short time.

    With DC-DC present, you should place the capacitor on the DC-DC output (Vout to GND of transceiver) instead of BAT+.

    Value Recommendation: 100µF is enough in most cases, but higher may help in extreme transients.

    F) Diode Between BAT- and Chassis Ground

    Can be useful if chassis ground is present.

    1. If chassis ground is present

    Using a Schottky diode (low forward voltage) helps divert transient currents safely to chassis.

    2. If no chassis ground

    The diode has no effect since BAT- is the only reference.

    Ensure the chassis ground is a low-impedance return path; otherwise, it may introduce unwanted noise.

    I) Additional Suggestions

    1. Pull-Down Resistor on BAT- (Optional, for Stability)

    If BAT- disconnects, floating ground may cause erratic behavior.

    Adding a 100k pull-down resistor to chassis ground can prevent complete floating.

    2. Consider Split-Termination for CAN Bus (If Not Already Used)

    Instead of a single 120 ohm termination resistor, use two 60 ohms resistors with a capacitor (~4.7nF) in between to GND.

    Helps reduce emissions and improve signal integrity. May also consider CMC for additional filtering  

    3. Grounding Strategy

    If chassis ground is introduced, ensure proper star grounding to avoid ground loops.

    Measure ground potential differences if connecting multiple grounds, thanks. 

    Best Regards,

    Michael.