OPA350: TINA - questions in simulating OPA350 work for triangle generator

Peng Zhang

Part Number: OPA350
Other Parts Discussed in Thread: TINA-TI

Tool/software:

Hi all,

When I try to simulate triangle waveform with OPA350. I found that when I set clamped diode, the rate of voltage will decrease. V+ and V- voltage level is set as the same in two experiments, so the rate of voltage should be same. I have no idea of whether it is from a bug. Pls help me figure out what result this phenomenon.

without clamped diode with clamped diode (rate of voltage decrease)

BR,

Peng

8 months ago

0 Marek Lis 8 months ago

TI__Guru 71711 points

Please attach Tina-TI schematic you used for your simulation by clicking pulldown menu below:

INSERT -> Image/video/file -> Upload and pick the file for upload.

0 Peng Zhang 8 months ago in reply to Marek Lis

TI__Prodigy 160 points

三角波.TSC

Hi Marek,

Here is my schematic for this experiment, thanks.

BR,

Peng

0 Marek Lis 8 months ago in reply to Peng Zhang

TI__Guru 71711 points

Without clamped diode, the op amp does not have a DC feedback and is effectively running open-loop so it is not surprising that the rate of output change will be different.

I cannot open your schematic - you must have saved it under different version. Please re-save it with Tina V7 type (see below) and INSERT it again.

0 Peng Zhang 8 months ago in reply to Marek Lis

TI__Prodigy 160 points

Hi Marek,

Here is the V7 typetriangular.TSC

BR,

Peng

0 Ron Michallick 8 months ago in reply to Peng Zhang

TI__Guru**** 170776 points

Hello Peng,

Remember that the passive components are perfect. Try R1, R2 as [10.1k, 9.9k] and [9.9k, 10.1k] as a non perfect test. One should run low and the other high.

Is this triangle wave continuous? Would be OK if it took some time to settle?

0 Marek Lis 8 months ago in reply to Peng Zhang

TI__Guru 71711 points

Peng,

In the case of no DC feedback output collapses on its rail (3.238V) and the entire 165uA current (1.65V/10k( flows thru 1nF feedback cap.

Since Ic=C*dV/dt, you may solve it for rate of change, dV/dt = Ic/C = 165uA/1nF = 165E-6/1E-9 = ~165,000V/sec or 0.165V/us (see below).

However, in the case of diode in the feedback, DC output is driven to mid-supply (1.65V) and only average AM1 current of 121uA flows thru 1nF cap while remaining AM2 average current of 44uA flows thru the diode - see below. This means that dV/dt = 121uA/1nA = 121,000V/sec.

This is the main reason for lower slope.