Hello everyone,

**Context:**

I’m trying to get the attached model of a MAX44280 OpAmp to run in QSpice. The model is the result

of importing the Spice model provided at MAX44280 Datasheet and Product Info | Analog Devices

**Problem**

When trying to run a transient simulation I get the following warning:

This circuit has one floating node. From inspection, this node is believed to be floating: 98•X1

Warning: Singular matrix. Check node 98•X1

Which then results in a: Fatal error: Timestep too small(1.25e-19) at t=0

**Attempted Solution**

I’ve checked the model and found the following devices to be connected to Node 98:

GD24A 98 98A TABLE { V(98,98A) } ((-3m,-1000)(-2m,-10)(-1m,-1)(0,0)(1,1n))

GD24B 98 98B TABLE { V(98,98B) } ((-1,-1n)(0,0)(1m,1)(2m,10)(3m,1000))

R24A 0 98A 1 TC=0.00,0.00

R24B 0 98B 1 TC=0.00,0.00

G70 0 98 TABLE { V(96,5X) } ((-11.0,-85.6M)(-1.00M,-84.7M)(0,0)(1.00M,84.7M)(11.0,85.6M))

I’ve added the line:

R99 0 98 10G TC=0.00,0.00

to negate the floating node issue: but now the simulation fails with a: Fatal error: Timestep too small(1.25e-19) at t=0

I’ve added

.options gmin=1e-10

.options abstol=1e-10

.options reltol=0.003

.options cshunt=1e-15

But I’m still getting a: Fatal error: Timestep too small(1.73192e-19) at t=3.85533e-07

**Questions**

- What kind of device is GD24A? Per the QSpice help “Gnn” describes a Voltage dependet current source. But I’m not sure, whether D24A is a valid value for nn, which I had assumed to mean a two digit integer, as in the forth line above: G70
- What does the expresion in curly brackets after TABLE mean? The syntax for TABLE, according to the “Expression of Waveform Data” help page only allows for parantheses
- Is the TC expression used in the two resistors equivalent to a TCE or TC1?
- Is 98A a valid value for a node?
**How can I get the model to simulate?**

I’d be thankful for you help,

kind regards,

Mathias

max44280.qsym (6.0 KB)