THS4532_16 Datasheet, PDF (47/58 Pages) Texas Instruments – Ultra Low Power, Rail-to-Rail Output, Fully-Differential Amplifier

www.ti.com
THS4532
SLOS829A – FEBRUARY 2013 – REVISED JULY 2015
Systems Examples (continued)
Using Equation 9 to Equation 11 to sweep the target gain from 1 to A_V(MAX) < 10 V/V gives Table 9, which shows
exact values for R_T, R_G1, and R_G2, where a 50-Ω source must be matched while setting the two feedback
resistors to 2 kΩ. One possible solution for 1% standard values is shown, and the resulting actual input
impedance and gain with % errors to the targets are also shown in Table 9.
Table 9. Rf = 2 kΩ, Matched Input to 50 Ω, Gain of 1 to 10-V/V Single-Ended to Differential⁽¹⁾
Av
Rt,
EXACT
(Ω)
Rt 1%
Rg1,
EXACT
(Ω)
Rg1 1%
Rg2,
EXACT
(Ω)
Rg2 1%
ACTUAL %ERR TO ACTUAL %ERR TO
Z_IN
Rs
GAIN
Av
1
51
51.1
1996.5
2000
2021.8
2000
50.1
0.3
0.998
–0.2
2
51.7
52.3
996.9
1000
1022.5
1020
50.5
1.0
1.994
–0.3
3
52.5
52.3
656.1
649
681.7
681
49.7
–0.5
3.032
1.1
4
53.2
53.6
491.5
487
517.4
523
50.2
0.4
4.035
0.9
5
54
53.6
388
392
413.9
412
49.6
–0.9
4.953
–0.9
6
54.7
54.9
322.7
324
348.9
348
49.9
–0.2
5.978
–0.4
7
55.5
54.9
272.9
274
299.1
301
49.1
–1.7
6.974
–0.4
8
56.3
56.2
238.1
237
264.6
267
49.3
–1.3
8.034
0.4
9
57.1
57.6
211.2
210
237.9
237
49.7
–0.6
9.044
0.5
10
57.9
57.6
187.4
187
214.1
215
48.9
–2.3
10.017
0.2
(1) R_F = 2 kΩ, R_S = 50 Ω.
These equations and design flow apply to any FDA. Using the feedback resistor value as a starting point is
particularly useful for current-feedback-based FDAs such as the LMH6554, where the value of these feedback
resistors determines the frequency response flatness. Similar tables can be built using the equations provided
here for other source impedances, R_F values, and gain ranges.
The TINA model correctly shows this actively-set input impedance in the single-ended to differential
configuration, and is a good tool to validate the gains, input impedances, response shapes, and noise issues.
9.3.4 Differential Input to Single-Ended Output Amplifier
Fully-differential amplifiers like the THS5432 are not recommended for differential to single-ended conversion.
This application is best performed with an instrumentation amplifier or with a standard amplifier configured as a
classic differential amplifier. See application section of the OPA835 data sheet (SLOS713).
10 Power Supply Recommendations
The THS4532 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 2.5 V (10% low on a 3-V nominal supply)
and 5.5 V (8% high on a 5-V nominal supply). Supply decoupling is required, as described in Application and
Implementation. Split (or bipolar) supplies can be used with the THS4532, as long as the total value across the
device remains less than 5.5 V (absolute maximum).
Using a negative supply to deliver a true swing to ground output in driving SAR ADCs may be desired. While the
THS4532 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- to 5-V positive supply input used by the THS4532 and provides a –230-mV
supply for the negative rail. Using the LM7705 provides an effective solution, as shown in the Extending Rail-to-
Rail Output Range for Fully Differential Amplifiers to Include True Zero Volts, TI Designs TIDU187.
Copyright © 2013–2015, Texas Instruments Incorporated
Product Folder Links: THS4532
Submit Documentation Feedback
47