THS4551 Datasheet, PDF (54/70 Pages) Texas Instruments – Low-Noise, Precision, 150-MHz, Fully Differential Amplifier

THS4551
SBOS778A – APRIL 2016 – REVISED AUGUST 2016
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11 Power Supply Recommendations
The THS4551 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 THS4551, as long as the
total value across the device remains less than 5.5 V (absolute maximum). The thermal pad on the RGT
package is electrically isolated form the die; connect the thermal pad (RGT package only) to any power or
ground plane for reduced thermal impedance to the junction temperature. This pad must be connected to some
power or ground plane and not floated.
For the best input offset voltage drift, the THS4551 uses a proportional to absolute temperature (PTAT)
quiescent current biasing scheme. This approach gives a positive over temperature variation in supply current.
Figure 95 shows the 5-V supply current over a wide T_J range for a number of tested units. The Electrical
Characteristics tables report the typical and range on this supply current temperature coefficient for both 5-V and
3-V supply operation.
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1
-45 -30 -15
0 15 30 45 60 75 90 105 120 135
Junction Temperature (qC)
D068
Figure 95. Linear Temperature Coefficient for Supply Current
Using a negative supply to deliver a true swing to ground output when driving SAR ADCs can be desired.
Although the THS4551 quotes a rail-to-rail output, linear operation requires approximately 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 can accept the 3-V to 5-V positive supply input used by the THS4551 and provides a
fixed –230-mV supply for the negative power supply. Using the LM7705 provides an effective solution, as
discussed in the Extending Rail-to-Rail Output Range for Fully Differential Amplifiers to Include True Zero Volts
TI design (TIDU187)
54
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