Output impedance of cheap logic buffer? (for driving FET)

[eem2am]

Hello,

I wish to drive a switch-mode solenoid driver FET from a microcontroller pin.

Switching frequency is 22KHz.
Solenoid current is 200mA


I cannot drive the FET directly from the microcontroller pin, as the microcontroller’s instantaneous output current rating would be exceeded……….
……also I cannot just add a series gate resistor , since then I would not get enough drive current from the microcontroller, therefore I wish to use a cheap driver…..

…as such , I wish to use the following dual buffer in parallel configuration………

74LVC2G34 DATASHEET (= $0.09 per 5000 pieces)
**broken link removed**


The problem is, that the datasheet does not detail what is the output resistance of the buffers.

Do you have any idea what the output impedance might be?


(I have noticed that other similar parts also do not divulge the output impedance, eg NL27WZ17)

 

[Genomerics]

Page 5) of the data sheet gives,



Which suggests a 32mA voltage drop of 0.7V high and 0.55V low so that might indicate 22R high and 17R low at that supply voltage of 4.5V. That resistance will increase for lower supply voltages which will probably be indicated by the other figures on the data sheet. This will be due to the devices having less voltage to enhance them.

 

[eem2am]

Thankyou , on page 4 it says "output clamping current" = 50mA

Does this mean that it is output short-circuit protected?.....i.e. the output current is prevented from going above 50mA by some internal clamping circuit?.

 

[Genomerics]

I did not know until...

Output Clamp Current

So it seems that would refer, as a limiting level, to the amount of current that can be returned to the input supply via clamp diodes on the output should the output be driven above supply or below ground. I might imagine that they will actually be the Body Source diodes of the output PMOS/NMOS output devices which will be why the peak clamp current matches the peak output current.

Those are not being set by some form of 'active' circuit. They are just maximum ratings.

Genome.