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TCAN2857-Q1: sleep current of TCAN28575 while two HSS are activated

Martin Blinzler
Prodigy 140 points

Part Number: TCAN2857-Q1

Hello, 

we want to use one HSS output controlled by the internal Timer On 20ms Cycle 2000ms.

A second HSS shall be used to be controlled by the Wake3/DIR input. On 300µs Cycle 50ms.

The VCC1 shall be active.

First question: Is this possible to control two HSS in sleep mode? One with Timer the second one with WAKE3/DIR?

According to Datasheet the sleep current for ISUPslpswodr is at 85°C typical at 60µA (see chapter 6.6 page 10)

image.png

How will the additional pulsed HSS will increase here the current. Acc. to Datasheet for ISUPhssnoload will increase the current typ. to 35µA. Is this only in active phase? So can I strip it down, if we are only active 20ms every 2000ms? --> 35µA x 20/2000 = 0,35µA?

image.png

 

Thank you for your support.

BR,

Martin

  • 0
    TI__Genius 17176 points

    Hi Martin,

    For your first question, the HSSs can only be used for cyclic sensing wake or direct drive in sleep mode, so the first HSS you mentioned will turn off when the device goes to sleep mode. 

    For your second question, the ISUP_HSSNOLOAD spec is measured when the HSS is turned ON with no load connected to it (open load condition). So in PWM mode when the HSS is in the OFF portion of the cycle, I don't believe you would see this current. However, your current wouldn't be zero since you would be using the internal timer which consumes 5-8uA. 

    Regards,

    Matt 

  • 0 in reply to Matt Smith
    Prodigy 140 points

    Hi Matt,

    thank you for your fast reply. So as I understand it correct it is not possible to have cyclic wake on HSS3 and direct drive on HSS4. 

    It is only possible to choose one of these functions but not both on the same time.

    The second point is now clear for me.

    Thank you for your support.

    BR,

    Martin

  • 0 in reply to Martin Blinzler
    TI__Genius 17176 points

    Hi Martin,

    Cyclic sensing wake can only be performed with HSS4. Any HSS can have direct drive, so if you want to use an HSS with direct drive while cyclic sensing wake is enabled, you could use HSS3 for direct drive while HSS4 does the cyclic sensing wake when in sleep mode. 

    Regards,

    Matt

  • 0 in reply to Matt Smith
    Prodigy 140 points

    Hi, 

    That's sounds quite good for me. So I would use the HSS3 with direct drive and would use the timer for cyclic sense to activate a LED ever 2000ms for 20ms. Even If don't want to wake up over the Wake Pins. So i just would not configure any Wake pin. Or if I have to I just connect the HSS4 paralell to the LED. So no change and also no wake up. Am I right?

    Can I then still calculate the sleep current like above mentioned, but have to add the 5-8µA for the internal timer?

    Thank you for your support.

    BR,

    Martin

  • 0 in reply to Martin Blinzler
    TI__Genius 17176 points

    Hi Martin, 

    To make sure we're clear, cyclic sensing wake is different from just using the HSS to drive an LED. If you are using HSS4 for cyclic sensing wake, it needs to be connected to a configured WAKE pin and a stimulus as Figure 8-36 in the datasheet shows. I wanted to clarify that because it seems like you are trying to use HSS4 in sleep mode to drive an LED via the cyclic sensing wake functionality, which is not recommended. To be able to drive an LED with an HSS in sleep mode, direct drive will be the only recommended way to do this with this device. I only mentioned cyclic sensing wake because that is the only other function an HSS can perform while in sleep mode, but it can only be used for that function. 

    Regards,

    Matt