TLV741P: Does the TLV741P need an external diode for reverse voltage protection?

Hi Shinichi,

Shinichi Inoue said:

Is this comment the same for TLV741P

Yes the comment is a general comment for all of our PMOS LDO's The reverse body diode can allow current to flow, but the transistors internal to our LDO's are not designed to do this and therefore operation with repeated reverse current flowing above 5% it's rated forward voltage has been shown to have negative effects upon the lifespan of the device so we do not recommend customers operate this way.

It is largely to assure that the device continues to operate under the specified datasheet conditions. When reverse currents are forced through the body diode it causes degradation in the performance, and so adding a Schottky diode allows current to flow without harming the device itself.

Regards,

John

Hi Shinichi,

I'm sorry if my explanation was confusing. For P Channel devices the Drain is at a higher potential than the body due to the reverse voltage condition, this PN junction causes the current to flow form the Drain to the body of the PMOS which flow out through to the input rail. In the case of the NMOS the body diode is developed from the Body, which is P doped, to the Drain, which is now N doped. This is a PN junction that forms the resultant body diode as the Source and Body are tied together.

In short the junction is once again formed, just in the opposite direction for the NMOS devices, and as such the 5% recommendation before significant damage may occur is still what we recommend for reverse current.

Link to further explanation and protection ideas for LDO's

Regards,

John

Hi Shinichi,

Our recommendation is to only allow 5% of the rated forward current to ever flow backwards across the pass device of the LDO in order to protect the device from electro migration, excessive die heating, and latch up events.

It is a function of the Body(Bulk) of the FET being tied to the source of the device, which is not inherent to the design of all FET's. The body diode of the FET, like all FET's can provide >5% current. The 5% is a rule of thumb that we tell to customers to assure safe design principles so that the LDO is able to perform across it's lifetime. If a customer foresees greater reverse current being applied, then we recommend reverse current protection features. I'm unaware of FET's that allow 100% rated current in reverse as that is usually damaging due to the non reversible nature of the MOSFET semiconductors, the source and drain cannot be flipped without vastly different behavior and safety of the FET itself.

This is only for our MOSFET devices, our bipolar process devices do not have this limitation due to the PNP and NPN junctions inherently providing more robust reverse current protection.

Regards,

John

Hi Shinichi,

Yes, there is a time component to it, if the reverse is only a femtosecond then no damage will likely occur as the diode was never truly saturated enough to turn on in such an incredibly brief time window.

Unfortunately we do not characterize a time constant for the breakdown of our pass devices. So I cannot give a specific value that is safe for operation. While the thermals are definitely not going to saturate so quickly, the concerns about electro migration and latch up events are still present.

Regards,

John