THS4561 Datasheet, PDF (20/35 Pages) Texas Instruments – Low-Power, High Supply Range, 70-MHz, Fully Differential Amplifier

THS4561
SBOS874 – AUGUST 2017
www.ti.com
9.3 Feature Description
In addition to the core differential I/O voltage feedback gain block, there are two TBD-kΩ resistors internally
across the outputs to sense the average voltage at the outputs. These resistors feed the average voltage back
into a V_CM error amplifier where the voltage is compared to either a default voltage divider across the supplies or
an externally set V_OCM target voltage. When the amplifier is disabled, the default midsupply bias string is disabled
to save power.
To achieve the very-low noise at the low power provided by the THS4561, the input stage transistors are
relatively large, thus resulting in a higher differential input capacitance (2.4 pF in the Functional Block Diagram).
As a default compensation for the 2.4-pF differential input capacitance and the 1.5-kΩ feedback resistors used in
characterization, internal TBD-pF capacitors are placed between the two output and input pins. Adjust any
desired external feedback capacitor value to account for these TBD-pF internal elements. When using the 16-pin
WQFN package and the internal feedback traces to the input side of the package, include the nominal trace
impedance of 3.3 Ω in the design. These elements are not included in the TINA-TI™ model and must be added
externally to a design intending to use the RGT package.
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