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Back feeding TLV62130

Mike Ciholas
Prodigy 140 points
Other Parts Discussed in Thread: TLV62130, TLV62130A

What is the behavior of the TLV62130 under the following conditions:

a) the output is already under bias, at the programmed voltage, when it is provided input voltage.

b) the output is or goes above the programmed voltage.

c) the output is at some voltage and the input is zero.

The use case is feeding a 5V rail that may also be supplied by another source.  I could not find discussion of this in the datasheet.

Thanks.

  • 0
    TI__Guru*** 148040 points

    You've hit on several topics, so let me address them one by one.

    For any buck converter, if a voltage is present on the output, this voltage will appear on the input minus the diode drop of the high side FET's body diode.  This is true of every buck converter that I have seen.

    Therefore, anything connected to the input supply will be powered through the output.  Sometimes, customers add a diode in series with the input to prevent this.  The reverse current is ok for the TLV62130 as long as the reverse current through the body diode does not exceed the 3A rating of the IC and the junction temperature limit is not exceeded.  The latter is usually the main limit as the voltage drop of a body diode is typically quite high (~1V).

    Your first scenario is known as starting into a 'pre-biased output' which DCS-Control supports.  I believe this is also mentioned in the D/S.

    For DCS-Control, if the output goes above the setpoint, power save mode is entered.  This is perfectly fine as long as the abs max rating of the output is not exceeded.

    The one problem you may have with applying a voltage on the output of a buck converter is the so-called 'suicide mode'.  In the case where the buck converter is operating in forced PWM mode (not an option for the 62130) and the applied voltage is above the setpoint, by definition the buck converter will try and sink the output voltage by boosting it to the input side of itself.  (If you look at the buck converter in this configuration, it becomes a boost converter circuit.)  In most cases, there is not enough power being drawn on the input and so the input voltage keeps boosting higher until the input rating of the device is exceeded.  Not having this condition is one reason to use a DCS-Control device in your application.

    Finally, anytime you are applying a voltage to the output, it is important to be aware of ESD and ringing from how the voltage is applied.  For instance, if the output voltage is pinned out to a user-accessible test connector, then this should be ESD protected.  As well, if this test connector is connected with a long wire, a TVS or snubber circuit may be required due to the cable-induced ringing that may occur when applying the 5V.

  • 0 in reply to Chris Glaser
    Prodigy 140 points

    I guess I should make my questions more specific.

    Given a TLV62130A setup for 5V output, with floating input, the output voltage is forced by another source.  What is the graph of current draw by the TLV62130A versus forcing voltage look like?  Is it microamps, milliamps, more?  Does anything happen when you cross over 5V?  Does the state of the EN pin change this current draw profile?

  • 0 in reply to Mike Ciholas
    TI__Guru*** 148040 points

    Yes, this is more specific.  You are asking about the current consumption of the device.

    Given my first reply, there will be an input voltage on the device.  With a 5V output, this voltage will be above the UVLO level.  So, if the EN pin is high, the device will be on and if low off.

    If it's on, you have one of two possibilities.  Either the output voltage applied is above or below the setpoint.  If above, power save mode is entered and the current drawn will be the Iq.  If below, 100% mode is entered and the current draw will be some hundreds of uA.  

    I encourage you to order the EVM and evaluate the device under your conditions.