THS4541 datasheet(49/64 Pages) TI1

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THS4541-Q1

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SLOS930B – NOVEMBER 2015 – REVISED NOVEMBER 2019

Product Folder Links: THS4541-Q1

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11 Power Supply Recommendations

The THS4541-Q1 is principally intended to operate with a nominal single-supply voltage of +3 V to +5 V. Supply-

voltage tolerances are supported with the specified operating range of 2.7 V (10% low on a 3-V nominal supply)

and 5.4 V (8% high on a 5-V nominal supply). Supply decoupling is required, as described in the Terminology

and Application Assumptions section. Split (or bipolar) supplies can be used with the THS4541-Q1, as long as

the total value across the device remains less than 5.5 V (absolute maximum). The thermal pad on the package

is electrically isolated; connect the thermal pad to any power or ground plane for heat spreading.

Using a negative supply to deliver a true swing to ground output in driving SAR ADCs may be desired. While the

THS4541-Q1 quotes a rail-to-rail output, linear operation requires approximately a 200-mV headroom to the

supply rails. One easy option for extending the linear output swing to ground is to provide the small negative

supply voltage required using the LM7705 fixed –230-mV, negative-supply generator. This low-cost, fixed

negative-supply generator accepts the 3-V to 5-V positive supply input used by the THS4541-Q1 and provides a

–230-mV supply for the negative rail. Using the LM7705 provides an effective solution, as described in the

Extending Rail-to-Rail Output Range for Fully Differential Amplifiers to Include True Zero Volts reference guide.

12 Layout

12.1 Layout Guidelines

Similar to all high-speed devices, best system performance is achieved with a close attention to board layout.

The THS4541-Q1 evaluation module (EVM) shows a good example of high frequency layout techniques as a

reference. This EVM includes numerous extra elements and features for characterization purposes that may not

apply to some applications. General high-speed, signal-path layout suggestions include:

•

Continuous ground planes are preferred for signal routing with matched impedance traces for longer runs;

however, open up both ground and power planes around the capacitive sensitive input and output device

pins. After the signal is sent into a resistor, parasitic capacitance becomes more of a bandlimiting issue and

less of a stability issue.

•

Use good, high-frequency decoupling capacitors (0.1 µF) on the ground plane at the device power pins.

Higher value capacitors (2.2 µF) are required, but may be placed further from the device power pins and

shared among devices. For best high-frequency decoupling, consider X2Y supply-decoupling capacitors that

offer a much higher self-resonance frequency over standard capacitors.

•

When using differential signal routing over any appreciable distance, use microstrip layout techniques with

matched impedance traces.

•

Higher-speed FDAs, such as the THS4541-Q1, include a duplicate of the output pins on the input feedback

side of the package. This duplication is intended to allow the external feedback resistors to be connected with

virtually no trace length on the input side of the package. Use this layout approach with no extra trace length

on this critical feedback path.

•

The input summing junctions are very sensitive to parasitic capacitance. Connect any Rg elements into the

summing junction with minimal trace length to the device pin side of the resistor. The other side of the Rg

elements can have more trace length if needed to the source or to ground.

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