THS4551 Datasheet, PDF (58/70 Pages) Texas Instruments – Low-Noise, Precision, 150-MHz, Fully Differential Amplifier

THS4551
SBOS778A – APRIL 2016 – REVISED AUGUST 2016
13 Device and Documentation Support
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13.1 Device Support
13.1.1 TINA-TI™ Simulation Model Features
The device model is available on the product folder under www.ti.com in a typical application circuit file. The
model includes numerous features intended to speed designer progress over a wide range of application
requirements. The following list shows the performance parameters included in the model:
• For the small-signal response shape with any external circuit:
– Differential open-loop gain and phase
– Parasitic input capacitance
– Open-loop differential output impedance
• For noise simulations:
– Input differential spot voltage noise and a 100-Hz 1/f corner
– Input current noise on each input with a 6-kHz 1/f corner
• For time-domain, step-response simulations:
– Differential slew rate
– I/O headroom models to predict clipping
– Input stage diodes to predict overdrive limiting
• Fine-scale, dc precision terms:
– PSRR
– CMRR
The Typical Characteristics: 3-V to 5-V Supply Range section provides more detail than the macromodels can
provide; some of the unmodeled features include:
• Harmonic distortion
• Temperature drift in dc error terms (V_IO and I_OS)
• Overdrive recovery time
• Turn-on and turn-off times using the power-down feature
Some unique simulation considerations come with the THS4551 TINA model. This device (and model) include
0.6-pF internal feedback capacitors. These capacitors are intended to improve phase margin when using higher
external feedback resistor values. Higher feedback resistors generate an in-band pole in the feedback signal with
the differential input capacitance, and the internal 0.6 pF capacitors add a zero to the feedback response shape
to shape the noise gain flat at the loop-gain crossover.
In order to generate an accurate open-loop gain and phase simulation, these components must be removed
because they are feedback elements, not forward path elements. Figure 99 illustrates a typical A_OL gain and
phase simulation where external –0.6-pF capacitors cancel out the internal capacitors in the model (TINA
supports negative value elements). The inductors inside the loop close the loop for the dc operating point and
open the loop immediately for an ac sweep. The input-coupling capacitors are open at dc, then couple in the
differential input immediately on an ac sweep. The somewhat odd values help reduce numerical chatter in the
simulation. When using the internal feedback traces from the outputs to the inputs on the RGT package, be sure
to add the 3.3-Ω trace impedance to any simulation. This impedance is not included in the core model.
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