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TPS7A3001-EP: Datasheet clarification

Part Number: TPS7A3001-EP
Other Parts Discussed in Thread: TPS7A30, TPS7A49

Hi Team,

Can you please help with the inquiry below?

In the datasheet, the enable pin has a maximum rating of +36V to VIN or +36 / -36 V to GND. In the electrical characteristics, it specify +15V in the max value, with a -1V out. If the TPS7A3001 is supplied with a -33V, it is ok if the enable pin is supplied with a +16V through a 16k resistor?

A customer encountered an issue where the design keeps failing due to oscillations and they can figure out why, the datasheet is indeed unclear on this point. It was working fine with the enable pin tied to -Vin. but if PGODD pin up to +16V to drive the enable pin it is breaking.
 
Here's more information: 
The RONA (15.8k) and RONB (14.3k) form a resistor divider with the -16V GND reference and Vf of LED diode to drive low to 0-0.1V the Enable pin when the output of the the DCDC is not ready. Whenever the PGOOD is released the EN pin on TPS7As goes to +16V through the RONA resistor.
Now, if RONA is shorted with a 0 Ohm, thus driving always +16V to the EN pin it works fine (thus TPS7A30 can work work with +16V of enable voltage while -33V on its input? Which voltage can the enable go up to with reference to the Input voltage? The datasheet is not clear on this).
If I use the 15.8k for RONA, the voltage behaves fine, goes 0V and +16V depending on the DC/DC output state, but the TPS7A limits the voltage and breaks burning, as if its enable pin is tristated.
Also could also confirm that the TPS7A49 is capable of driving up to 200mA and not 150mA? 
Regards,
Marvin
  • Hi Marvin, 

    Thank you for reaching out. 

    It is somewhat hard to read the schematics. Is it possible to share a PDF version? If this is sensitive information then you can share this via private message.

    Also, is it possible to share scope shots showing the behavior as well? 

    This device has a dual polarity enable, so having said that, it can be driven either by a positive voltage or a negative voltage. 

    Now, the abs maximum is -36/36 V for the EN, however, operating at or beyond this limits do no guarantee proper operation of the device, therefore, we highly recommend staying withing the Recommended Operating conditions and/or ranges described on the Electrical Characteristics table. 

    So although the EN can withstand up to 36V, the recommended value is 15V, therefore, we cannot guarantee proper operation at 16V, the device could be enabled with 16V, but again 

    On the negative side, the device can take up to Vin, hence when connecting it directly to Vin, there are no issues: 

    Has it been verified that when RONA is shorted Ven is actually 16V? 

    There seems to be something odd going with the PGOOD of the DCDC + Voltage divider interaction. 

    Again, showing waveforms will also help us understand what is going on, and also indicating if the voltage is being referenced to GND or -16V. 

    As for the TPS7A49, this device is rated for 150mA and its current limit is ~300mA.

    Best, 

    Edgar Acosta

  • Hi Edgar,
    Here is an update.
    The customer changed the design tying the EN directly to the VIN and it works. They found the problem and it was the overshoot on the input side during the shutdown, exceeding the AMRs, thus breaking the IC.
    About the TPS7A49 the positive version, if you compare the datasheet the current limits are both min 220mA, and max 500mA (the limiting range).
    It is written 150mA of regulated output, however it works fine up to 200 mA as exactly as the TPS7A30 accordingly with the almost same current limiting values range  based on the customer tests. This is why they think the 150mA might be an error and the right value could be 200mA. Can you confirm?
    Regards,
    Marvin
  • Hi Marvin, 

    Thank you for the update. 

    For the TPS7A49, I looked at previous documents and it was defined as a 150mA device. I can go ahead and ask the team to triple verify this. I will respond once I get a clear answer. 

    Best, 

    Edgar Acosta

  • Hi Edgar,

    Thanks! I look forward to your response.

    Regards,

    Marvin

  • Hi Marvin, 

    Still looking into this. So far, it seems it might be due to a characterization decision. Since this device is from 2010 timeframe, I have to reach out to the right team members that might have more information. 

    Best, 

    Edgar Acosta

  • Hi Marvin, 

    After doing some more research and talking to other team members. It could be that a decision was made when characterizing the device to leave the spec of 150mA. This could be various reasons, i.e perhaps at 200mA some of the required specs were not being met like dropout or Load regulation. 

    Therefore, the device is capable of supplying 200mA, and by looking at the current limit specs, this is below the specified range. However, some other specs could suffer from operating at 200mA, as explained. 

    Best, 

    Edgar Acosta