LMV641: Maximum voltage can the output pin support

Lacey,

LMV641 maximum output voltage swing is within 100mV of either rail, which means 4.9V for Vs=5V.    Since there is an internal reverse-biased ESD protection diode betwen the output and supply pin, shorting the output to any voltage above Vs but below 13.2V (absolute max rated voltage) may require a blocking Schottky diode, SD1, to prevent a large current flow thru internal ESD diode - this is NOT necessary if the supply voltage cannot sink current (e.g. LDO) - see below.

Hi Lis，
Thanks so much for your reply!
So it means when the voltage added in the output pin is smaller than 13.2V, it will not cause some damage in the device, either the output pin. Correct?
Just need to make sure the supply can afford larger sink current.

Lacey
Thanks so much!

No, this is NOT correct.  You must NOT allowed any current to be sunk by Vs under such condition - this is the reason for the blocking diode. 

The part will not be damaged if the voltage on positive supply, VF1, is below 13.2V and there is only quiescent current, IQ, flowing thru the internal ESD diode from the output to negative supply.  However, this is only possible if the supply voltage cannot sink current.  Otherwise, you must add blocking Schottky diode as shown in the schematic above so no current can flow from the output toward positive Vsupply, Vs.

Hi Marek,
Thanks so much for your reply.
So another case is when they add the -10V voltage in output pin, will this also cause the issue as the positive 10V?
Lacey
Thanks a lot!

Lacey,

Shorting the LMV641 output to -10V in a single supply application poses even greater challenge because without any additional protection it would cause a very large distractive current (AM3=~200mA) to flow from the negative supply thru internal ESD diode to the output - see Fig 1 below.  Therefore, in order to prevent a damage, it will be necessary to add a Schottky blocking diode, SD2, in series with the negative supply.  However, this will protect the circuit only for the output being shorted up to ~-8.8V so that Vs_total is less than 13.2V absolute maximu rated voltage - see below Fig 2.

Shorting the output to -10V would damage the part due to excessive total supply voltage, Vs_total (see below Fig 3) and thus would require adding 13V TVS to clamp the max supply voltage to a safe operating range.  However, this in turn would result in a large current flow that the internal ESD diode could not handle and thus will necessitate another, Schottky diode, SD3, and possibly Rout resistor to limit the current (see below blue path) to what TVS and Schottky diodes can handle in terms of max current - see below Fig 4. 

Thus, in this specific customer application, in order to avoid the extra circuitry required to handle several amps of current, the output may only be shorted to a voltage range between -8.8V and +13.2V - in such case only two blocking diodes, SD1 and SD2, will be required.

Hi Marek,
Thanks so much for your detail explanations! It's very helpful for me.
I have one more confusion about the LDO you mention.
So if the supply will not sink or source current, it means if the voltage range is between -8.8V and 13.2V, there also will not have the current thru the internal ESD diode from positive or negative supply voltage to output pin.
So it means I can solve the issue adding a LDO?----Because I am not familiar with the power device, so don't know why the supply will not sink or source the current is the supply if from LDO.

Lacey
Thanks a lot!

Lacey,

Under normal operation a positve supply sources the current while negative supply sinks the current.  

Under the fault condition, when you pull up the output above the positive supply, the current would only flow if the positive supply can sink current while if you pull down the output below negative supply the current would only flow if the negative supply can source the current. 

LDO stands for Low Dropout regulator - it's a type of power supply that can only source the current.  If that is the case, your customer do not need to add blocking Schottky diode, SD1, to prevent the current flow under fault condition where output gets above positve supply (LDO becomes a high impedance). 

Since in customer's application the negative supply is hard-wired to ground, there will always be a current flowing if output is pulled below ground and for that reason you must include blocking Schottky diode, SD2, for this fault condition and additional components if the output is pulled more than 8.8V below ground while Vs=5V.