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TPS22968 sequencing additional questions

Yoshikazu Kawasaki
Expert 3510 points
Other Parts Discussed in Thread: TPS22968, TPS22968-Q1

Hello,

I have a couple of questions related to the sequence of TPS22968.  Those are related to http://e2e.ti.com/support/power_management/switches/f/949/t/376404.

1. I looked at the comments that TPS22968 can't turn on without VBIAS.  Will the outputs VOUT1 and VOUT2 have some voltage at the following conditions?  Note that the sequence of VBIAS, VIN1 or VIN2 isn't stable.  I mean the case of which one comes first and the voltage level isn't sure.

- ON1 < 0.5V, ON2 < 0.5V (low level input)

- VBIAS=0V - 5V

- VIN1=0V - 3.3V, VIN2=0V - 3.3V

2. If the above conditions are no problem for VOUT1 and VOUT2, how can the customer find the information in the datasheet?

3. Under the low level input conditions (ON1 < 0.5V, ON2 < 0.5V), does QOD work with RPD=270ohm when VBIAS>=2.5V even if VIN1=VIN2=0V?

Best regards,

Yoshikazu Kawasaki

  • 0
    TI__Expert 5275 points

    Hi Yoshikazu,

    1. The sequencing of ON, VIN, and VBIAS will not cause damage to the device. In all cases, when ON, VIN, and VBIAS are above there recommended minimum voltages, the output will turn on. If VIN is ramping from 0 to 3.3V and VBIAS and ON are already present, then the output will follow VIN.

    2. In the datasheet each pin has a recommended maximum voltage. There are no interdependencies. (Some other devices say VIN max is VBIAS)

    3. RPD will work as long as VBIAS is present. Even if there is no VIN voltage.

    Best Regards,

    Adam Hoover

    DLS Applications

     

  • 0 in reply to Adam Hoover
    TI__Expert 3510 points
    Hello Adam,Thank you for your quick reply.
    I understand TPS22968(actually TPS22968-Q1 the customer will use) has no dependency on sequence for VBIAS, VIN1, VIN2 ON1 and ON2 and ON1/2 pins are in low level input state, the VOUT1/2 will be 0V, but the customer says it's not described in the datasheet. Would you please tell me where I can find the information in the datasheet? The customer is worried if TI can't guarantee that unless the datasheet states, so they'd like us to add such comments in the datasheet. Do you think it's possible to add comments in the datasheet?
    Best regards,Yoshikazu Kawasaki
  • 0 in reply to Yoshikazu Kawasaki
    TI__Expert 5275 points
    Hi Yoshikazu,
    I am not sure exactly what the question is. Are they trying to ensure VOUT stays at 0V until VIN, VBIAS, and ON are all applied?
    If the question is about the QOD pulling VOUT to GND when disabled, this circuit requires a valid Vbias voltage in order to work.
    Please let me know if the concern is coming from somewhere else.Regards,Adam
  • 0 in reply to Adam Hoover
    TI__Expert 3510 points
    Hello Adam,
    There are 2 questions here, one is VOUT output conditions and the other one is QOD.
    For VOUT output conditions, I'd like to confirm VOUT will have no output at the conditions of ON1 < 0.5V, ON2 < 0.5V (low level input) even if VBIAS and VIN are any voltages. In other words, if VBIAS and/or VIN get some voltage unexpectedly, VOUT will have no output if ONx < 0.5V. Am I correct? If I am, it is customer's expectation, but they don't find such information in the datasheet. Therefore they'd like us to describe such information in the datasheet.
    For QOD question, I'd like to confirm if QOD works as expected. Under the low level input conditions (ON1 < 0.5V, ON2 < 0.5V), does QOD work with RPD=270ohm when VBIAS>=2.5V even if VIN1=VIN2=0V?
    Best regards,Yoshikazu Kawasaki
  • 0 in reply to Yoshikazu Kawasaki
    TI__Expert 5275 points

     

    Hi Yoshikazu,

     

    For the first question, as long as ONx <0.5V, the main MOSFET will not turn on.  This behavior is guaranteed by design.

    Vbias must be present to power the gate drive circuitry. When Vbias voltage is first available, a power on reset (POR) circuit ensures the device starts up in the off state.  The device will not turn on until ON is high. 

     

    For the second question, QOD will work when Vbias is valid and ON is low, even if VIN is not present.  If Vbias is too low, then QOD will not activate and the output will float.

     

    Best Regards,

    Adam Hoover

    DLS Applications