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TCAN1145-Q1: LWU

Yasushi Fujiwara
Genius 12725 points
Part Number: TCAN1145-Q1
Other Parts Discussed in Thread: TCAN1043, TCAN1043-Q1

Hello Experts,

My customer would like to implement LWU for their product. Customer is considering for TCAN1145-Q1 and he would like to know how to implement LWU, especially the external circuits of around WAKE-pin and VSUP-pin. He would like to wakeup the device by suppling 28.5V to WAKE-pin. Would you tell a guidance to implement LWU?
 
Best Regards,
Fujiwara

  • 0
    TI__Guru 53555 points

    Hi Fujiwara,

    The WAKE pin is a high voltage input terminal which can be used for local wake up (LWU) requests via a voltage transition. The terminal triggers a local wake up (LWU) event on either a low-to-high, or a high-to-low transition since it has a bi-directional input threshold (falling or rising edge). This transition can be created by an external FET or push-button to create a local wake condition. The local wake feature in TCAN114x is similar to that in TCAN1043, though TCAN114x has more configuration options through its SPI interface. An example circuit suitable for either device can be found in Figure 23 on the TCAN1043's datasheet. 
     

    Example resistor values and explanations can also be found in TCAN1043's datasheet. 

    Let me know if you have any questions about this circuit or the information in either device datasheet.

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Genius 12725 points

    Hi Eric-san,

    I have more question.
    1. Low-side switch configuration(Figure 23 in TCAN1043-Q1 datasheet p30) is for falling edge detection, right?
    2. Regarding equation 3 for Rbias (TCAN1143-Q1 datasheet p30), would you please tell about Iih?
    3. TCAN1145-Q1EVM is set Rseries=33Kohm/Rbias=3Kohm. What is Wake-up threshold voltage?

    I would like to set WAKE threshold voltage 28.5V. How can I determine the value of RBIAS?

    Best Regards,
    Fujiwara

  • 0 in reply to Yasushi Fujiwara
    TI__Guru 53555 points

    Hi Fujiwara-san,

    1. Low-side switch configuration(Figure 23 in TCAN1043-Q1 datasheet p30) is for falling edge detection, right?
    The WAKE pin is sensitive to both rising and falling edges, so both configurations depicted will work. In the case of the low-side switch, the initial button push will crease the falling transition which will wake the device. However, if for instance the button was held down while the device went to sleep, releasing the button would create a rising edge which would similarly wake the device. 

    2. Regarding equation 3 for Rbias (TCAN1143-Q1 datasheet p30), would you please tell about Iih?
    I_IH is defined in the electrical characteristics section of the datasheet under the Wake TERMINAL header. This defines the current that will flow out of the WAKE pin when Vsup exceeds the voltage at the wake pin (V_IH). This accounts for the current that leaks into the WAKE pin when calculating the voltage drop across Rbias due to the remaining current flowing through this path.

    3. TCAN1145-Q1EVM is set Rseries=33Kohm/Rbias=3Kohm. What is Wake-up threshold voltage?
    The user's guide for the evaluation module shows that Rseries(R19)=33k and Rbias(R18)=20k to VSUP.
    V_IH is a specified value determined by Vsup. This is defined in the electrical characteristics section as Vsup - 1.9V

    I would like to set WAKE threshold voltage 28.5V. How can I determine the value of RBIAS?
    This threshold will be set based on Vsup, so this may depend on what supply voltage is available for the device. Are you asking what the value of this bias resistor would need to be if the input voltage for this signal (VSUP) is 28.5V?

    In general, if supply voltage Vsup and the WAKE control voltage are the same, equation 3 can be simplified:

    Rbias < ((    Vsup -  V_IH   ) / I_IH) - Rseries
    Rbias < ((Vsup - (Vsup - 1.9)) / I_IH) - Rseries
    Rbias < ((        1.9        ) / I_IH) - Rseries; // for Vsup == V_WAKE input voltage

    Regards,
    Eric Schott