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TLV3201-Q1: How can I design the TLV3201-Q1 Equivalent Input structure circuit？

CHENG KAI
Prodigy 80 points
Part Number: TLV3201-Q1
Other Parts Discussed in Thread: TLV3201,

Hi，

In Auto driving solution circuit design，we need design a TLV3201 circuit for differential input which from the main connector

under 24V power input car system. Below is my design.

But when I see the TLV3201-Q1 Equivalent Input structure in detasheet figure 26,I think my circuit should change to it.

Would you please help to confirm which TVS should I can use in figure 26 under 24V auto car input system for 4.10 short circuit protection?

  • 0
    Guru 281010 points

    (10.3 V − (3.3 V + 0.5 V)) / 10 mA = 650 Ω

    This TVS would work fine with 1 kΩ series resistors, but it would not hurt to use larger resistors.

  • 0
    TI__Expert 5350 points

    Hi Cheng,

    The suggested input protection structure is meant to protect the comparator inputs by clamping the inputs within the absolute maximum of the of the device:

    When an overvoltage/undervoltage event occurs at the inputs, the external back-to-back diodes serve to clamp the voltage at the inputs to (VEE - VF) < IN < (VCC + VF). These discrete external diodes are usually Schottky diodes with low forward voltage and are capable of continuous conduction. As Clemens stated, the resistors at the inputs are also meant to limit the current going into the device.

    The TVS diode in your design clamps the voltage when the input reaches the clamping voltage VC and would also clamp when it reaches VEE - VF. TVS diodes have fast response times, but they are usually meant for voltage transients only and are not usually meant for continuous conduction.

  • 0 in reply to HO SIU
    Prodigy 80 points

    Thanks a lot for your suggestions,we will design and review it, I will send the deisgn to you and Chemens later.

    Kai

  • 0 in reply to CHENG KAI
    TI__Expert 5350 points

    Hi Cheng,

    Please reopen this post when you have the design ready.

  • 0 in reply to HO SIU
    Prodigy 80 points

    hi Ho siu，

    Below is my circuit design，please have a look. 

    Thanks,

    Kai

  • 0 in reply to CHENG KAI
    TI__Expert 5350 points

    Hi Cheng,

    Thanks for posting your schematic. It looks like you've changed the input resistance to 100kΩ. Keep in mind that the TVS diodes contribute an input capacitance to ground on the input pins of the TLV3201. The large resistance would slow down the charging of the input capacitance, so the inputs would take longer to reach the desired voltage because of the 100kΩ limiting the current. A direct consequence of this would mean that the propagation delay from MCU_CONN_HS1_TXP/MCU_CONN_HS1_TXN to the output of the comparator would become larger.

    Per my last response, your configuration would be sufficient in protecting the inputs from transients like ESD, but it does not have any components capable of continuous conduction like Schottkys or general purpose diodes shown in Figure 26 of the datasheet.

  • 0 in reply to HO SIU
    Prodigy 80 points

    Hi HO Siu,

    Thanks for your suggestions, I will talk with our EMC engineer  and consider how to optimize the design.

    As you said, 100K will make the DIFFER signal propagation lager, but this signal speed is not high from the custom requirement.

    So you think the TVS should be changed to Schottkys for continuous current under short to power/GND test when the US=24V system?

    Kai

  • 0 in reply to CHENG KAI
    TI__Expert 5350 points

    Hi Kai,

    It really depends on what you are trying to protect the input of the comparator from. If you are only expecting transient voltage spikes, the TVS diode is sufficient in protecting the comparator. However, if there are cases where the overvoltage/undervoltage occurs for long periods of time, it would be advantageous to clamp the input using diodes as shown in Figure 26.

  • 0 in reply to HO SIU
    Prodigy 80 points

    hi Ho Siu,

    As these signals from main connector of the AUTO Driving board, we should pass the  ISO 16750-2 SHORT TEST and ESD test, but the US max will be high to 33V in 24V Auto power system.

    Below is test method, our EMC enginner think this TVS will be OK to pass the tests, how do you think, can you recommend any components？

    kai

  • 0 in reply to CHENG KAI
    TI__Expert 5350 points

    Hi Kai,

    I have a couple of questions.

    During the short circuit test, how will the circuit be configured? Will the VCC pin of the comparator be connected to a 3V3 supply referenced to the voltage supply providing USMAX as shown in the schematic?

    I'm also unfamiliar with this test. Is the test performed by driving MCU_CONN_HS1_TXP/MCU_CONN_HS1_TXN to 33V for 60 seconds?

    In order to prevent damage to the comparator, the comparator needs to remain within its absolute maximum conditions:

    MCU_CONN_HS1_TXP/MCU_CONN_HS1_TXN being driven to 33V would cause the worst-case DC current flowing into the input of the comparator to be 0.33mA (due to the 100kΩ current limiting resistor), which would keep the current into the input pins within the 10mA absolute maximum. TLV3201-Q1 has internal input ESD diodes as shown here: Comparator Input Types (ti.com)

     

    The upper ESD diodes would clamp the input voltage to VCC + 0.5V if the VCC pin is not left floating.