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TPS7A4501A - Question on Current and need Schematic

Dan LaChance
Expert 1770 points
Other Parts Discussed in Thread: TPS7A4501M

Hello TI,

My customer has the following issue:

They are using  the TPS7A4501M adjusted to provide 3.3Vdc.  We do a zener diode test on VR9 (6.2V) where we apply an external voltage from Vin through a 100 ohm resistor to verify the zener regulation at 10, 50, 100 and 150 mA. 

 During our zener test we unexpectantly saw a 10mA current from Vin with an input voltage of 1.49Vdc at TP3 (Vin = 2.5Vdc).  The load current is estimated at 0.73mA (V(TP73) = 1.48V, R(load) =  2022 ohms). 

 After troubleshooting and reviewing the data sheet it shows that TPS7A4533 as having ground currents beginning at an input voltage of 1.5Vdc.   

 Does Figure 11 apply to our use of the 4501 set to a 3.3Vdc output?  Or should we be scaling Figure 10 from 1.21V to 3.3Vdc at a 1mA output current? 

 What is difference between quiescent current and ground current? 

 Can you supply us with a schematic to help us understand these currents? 

 The I(GND) at Vin = 2.5V doesn’t seem to map to the graph values.    eg  I(GND) at I(load) = 1mA @ 2.5V in = 1.6mA max. where we get 10mA for this condition. 

Thanks,

Dan

  • 0
    Expert 1770 points

    Hello TI,

    Several days have passed and I don't even have an acknowledgement that this has been received.

    Have you received this?
    Are you going to answer?

    Dan

  • 0 in reply to Dan LaChance
    TI__Prodigy 265 points
    Sorry for the Delay Dan.
    Your post was tagged as belonging to the Lighting Power Products group, but this part is actually from the Drivers and Load Switches Group. I've re-tagged the post and notified the moderator for the correct forum. You should get a response soon.
  • 0
    TI__Genius 15760 points

    Hi Dan,

    Our apologies for the delay in response.

    As to the figure which applies, I would use Figure 11, TPS7A4533 Ground Current vs Input Voltage.  Figure 10 would not apply since the output is set to 1.21V, and the ground current will typically be higher when the VIN voltage is lower than the VOUT voltage.  Taking a look at the 10mA load curve in Figure 11, a ground current of 10mA is expected for VIN = 2.5V.  The 1mA ground pin current in the electrical table does not apply here since VIN is not greater than VOUT by 1V.

    To answer your other question, ground current is the current which the device consumes when the device is enabled (SHDN is high) and is dissipated from VIN to GND.  Quiescent current, on the other hand, is the current leakage into the VIN pin when the device is disabled (SHDN is low).

    Please let me know if you have any additional questions.

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Expert 1770 points
    Hi Alek,

    Thanks. I think this answers about 90% of my questions. Can you confirm the internal config of the TPS7A4533: Is the 3.3V set with internal resistors and therefore matches what we have done on the board?

    Thanks,
    Dan
  • 0 in reply to Dan LaChance
    TI__Genius 15760 points

    Hi Dan,

    You are correct, the TPS7A4533 is the same as the TPS7A4501 except with internal configuration resistors.

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Dan LaChance
    TI__Guru 71526 points
    Hi Dan,
    All questions answered?
    ~Leonard