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TPS73801: Low Power LDO with Transient protection.

Manoj Turpati
Prodigy 230 points
Part Number: TPS73801
Other Parts Discussed in Thread: LP2951

Hello TI,

I would like to convert 11v to 10V at 3% tolerance and 10mA of load current. I would like to use TPS73801 LDO for my application. However i want LDO output pins to be protected from Transients. The TPS73801 pins can withstand +/-20V. Do you have any low power LDO where the output pin can withstand +/-30V during transients.

Thanks & Regards,

Manoj.

  • 0
    TI__Expert 5130 points

    Hi Manoj,

    I'm looking into our options, there is a device I have in mind, but I need to confirm the abs max rating on the OUT pin with my team. Should take ~2 days for confirmation due to time zone differences between me and that team.

    In the interim, are you able to share what the application is, a schematic of the LDO and surrounding components, as well as why a transient is expected on the output? Typically a transient could be expected at the LDO input (ex. for battery-connected applications), but I haven't commonly seen a requirement for transient protection at the LDO output.

    It would be helpful for me to understand if any other features or specs are required for this use case as well. Ex. TPS73801 is rated at 45μVRMS noise -- is this a requirement?

    With this information, I will be able to understand which device(s) in our portfolio might be the best fit for your use case, or otherwise recommend implementing external protection circuitry.

    Regards,

    Kelsey

  • 0 in reply to Kelsey Farr
    Prodigy 230 points

    Hello Kelsey,

    Thanks for your response. I understand your queries, However I cant share my schematic with you due to various reasons. My 10V output line is exposed to transient environment from load side therefore to protect output of LDO I have placed a 13V  bidirectional TVS diode which will clamp to +/-20V or more during transients(ex. lightning) depends on the transient current. So I need to protect the LDO during this condition.  

    I do not have any special requirements other than the ones that i have already specified. It is fairly simple. from 11V inout to 10V output. Maximum input varies between 10.5V to 11.5V. On the output the voltage variation due to line,load regulation etc should be 3% to 5% at full operating temp(-40 +125C) range of the device. Load current max 10mA.

    Best Regards,

    Manoj.

  • 0 in reply to Manoj Turpati
    TI__Expert 5130 points

    Hi Manoj,

    Thanks for the additional details.

    In this case I think what may be more of an issue than the voltage rating of the LDO OUT pin is the potential for reverse current.

    In general, if the voltage on the LDO OUT pin exceeds the voltage on IN, you'll need to add an extra diode in series with the LDO input to prevent reverse current through the LDO. This is true even if there is a clamping diode at the output, if the voltage at which the diode clamps is >VIN+0.3V. For example, if there is a transient on the OUT pin and the TVS diode clamps the voltage spike to 13V while IN is 11.5V, this will still be a condition where VOUT > VIN+0.3V and reverse current will flow through the LDO and damage the device.

    An alternative instead of adding the extra diode would be reducing the clamp voltage to the range 10V to 10.8V (10.8V = minimum expected VIN + 0.3V). The issue with that approach, though, is that the TVS diode's tolerance can vary over temperature such that it would be difficult to guarantee the small 10V to 10.8V range across all conditions.

    LP2951DR is one option TI has which can be adjusted to 10V output and is rated to 29V (or VIN+0.3V) on the output. What is the max transient you'd expect to see without the clamping diode on the LDO output? LP2951 gives you a bit of a higher voltage rating on the OUT pin, which may potentially mean you can either omit the clamping diode or use a diode that has a looser clamping tolerance.

    Regardless, I'd still recommend adding the diode in series with the input of the LDO to prevent reverse current. Another option would be an LDO that has both integrated reverse current protection and a 30V+ rating on OUT pin, but our option there is TPS7B7701-Q1, which also has integrated diagnostic capabilities and seems to be overkill for your requirements otherwise.

    Regards,
    Kelsey

  • 0 in reply to Kelsey Farr
    Prodigy 230 points

    Hello Kelsey,

    Thanks for your valuable inputs. I completely understand about the reverse current scenario. However, I am looking for an LDO where the OUT pin can withstand negative voltages during transients like it is mentioned in TPS73801 datasheet.

    The reason I am looking for a different LDO other than TPS73801 is becuase i would need more than +/-20V perhaps +/-30V and I need only 10mA load current where as TPS73801 is capable of delivering 1A which is too much for my application. The LDOs that you have suggested cannot withstand negative voltages on OUT pin which is a concern for me. All i need is an LDO similar to TPS73801 but can withstand +/-30V instead of +/-20V. I hope I am clear.

    Best Regards,

    Manoj.

  • 0 in reply to Manoj Turpati
    TI__Expert 5130 points

    Hi Manoj,

    Thanks for clarifying; I was only focusing on the positive part of the transient requirement, you're right.

    Unfortunately, however, we don't have LDO in our portfolio that offers a wider abs max rating on the OUT pin. TPS73801 is the best option in this respect, so additional circuitry will have to be used to maintain the transients within ±20V abs max.

    Regards,

    Kelsey

  • 0 in reply to Kelsey Farr
    Prodigy 230 points

    Hello Kelsey,

    Thanks for your inputs. Usually lot of TI LDOs specifies higher voltages on positive side and diode drop on negative voltage typically -0.3V as absolute maximum ratings. So what will happen if i use a unidirectional TVS diode instead of bidirectional TVS on the output ? since it will clamp to higher voltage (lets say +30V) during positive transients and it acts as forward diode for negative transients. will this work for me ? am I missing something ?

    Best Regadrs,

    Manoj.

  • 0 in reply to Manoj Turpati
    TI__Expert 5130 points

    Hi Manoj,

    I looked into this with my team, and a unidirectional diode should be fine for the reasons you mentioned. 

    HERE is an application note TI has available for selecting surge diodes for further info.

    Regards,

    Kelsey