LM4041D: Adjustable version for current sink in PSpice

Joshua Gerdes

Part Number: LM4041D
Other Parts Discussed in Thread: TLV431, TL431LI

In application note SLYC147 there are lots of different examples of what can be done with precision references. One that caught my eye was a current sink circuit using the adjustable LM4041:

Unfortunately I cannot get this to simulate with the proper behavior in PSpice and I cannot determine why. The LM4041 adjustable works fine when configured in a typical application (as shown at right below) whereas the current-sink circuit does not function (shown at left):

I would expect the voltage at R4 to also be 1.244V, but it is not and I cannot seem to figure out why. From everything I've read in the mentioned app note, this should work.

over 4 years ago

0 Joshua Gerdes over 4 years ago

Prodigy 100 points

It seems my images didn't upload. The figure to reference from the app note is on page 31, Figure 3.

0 Marcoo Z over 4 years ago in reply to Joshua Gerdes

TI__Mastermind 19580 points

Hi Joshua,

Are you referencing section 4 on pg 29/30/31? In particular image 3?

0 Joshua Gerdes over 4 years ago in reply to Marcoo Z

Prodigy 100 points

Yes, page 31, Figure 3.

0 Marcoo Z over 4 years ago in reply to Joshua Gerdes

TI__Mastermind 19580 points

That figure only works for "431" products such as the TL431LI or TLV431. This is because the feedback network regulates the cathode to reference pin to ensure that REF = 2.5V.

The LM4041 families are different because they regulate the REF to anode to ensure that the cathode to ref = ~1.2V. So it wont work in this configuration.

I would recommend to use a "431" product to make a current sink.

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LM4041D: Adjustable version for current sink in PSpice