THS4521 Datasheet, PDF (30/43 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521
THS4522
THS4524
SBOS458B – DECEMBER 2008 – REVISED MAY 2009.................................................................................................................................................... www.ti.com
ADC Driver Performance:
THS4521 and ADS1278 Combined
Performance
The THS4521 provides excellent performance when
driving high-performance delta-sigma (ΔΣ) and
successive approximation register (SAR) ADCs in
audio and industrial applications using a single 3-V to
5-V power supply. To show achievable performance,
the THS4521 is tested as the drive amplifier for the
ADS1278 24-bit ADC. The ADS1278 offers excellent
ac and dc performance, with four selectable operating
modes from 10 kSPS to 128 kSPS to enable the user
to fine-tune performance and power for specific
application needs. The circuit shown in Figure 71 was
used to test the performance. Data were taken using
the High-Resolution mode (52 kSPS) of the ADS1278
with input frequencies at 1 kHz and 10 kHz and
signal levels 1/2 dB below full-scale (–0.5 dBFS). FFT
plots showing the spectral performance are given in
Figure 72 and Figure 73; tabulated ac analysis results
are shown in Table 4.
1 kW
1.5 nF
5V
V_IN+
V_IN-
1 kW
1 kW
49.9 W
THS4521
49.9 W
V_OCM
0.1 mF
1.5 nF
1 kW
2.2 nF
AINN1
ADS1278 (CH 1)
AINP1 V_COM
x1
1/2
OPA2350
0.1 mF
Figure 71. THS4521 and ADS1278 (Ch 1) Test
Circuit
0
-20
-40
-60
-80
-100
-120
-140
-160
0
1-kHz FFT
G=1
R_F = R_G = 1 kW
C_F = 1.5 nF
V_S = 5 V
Load = 2 x 49.9 W + 2.2 nF
4
8
12
16
20
Frequency (kHz)
Figure 72. 1-kHz FFT
24 26
0
-20
-40
-60
-80
-100
-120
-140
-160
0
10-kHz FFT
G=1
R_F = R_G = 1 kW
C_F = 1.5 nF
V_S = 5 V
Load = 2 x 49.9 W + 2.2 nF
4
8
12
16
20
Frequency (kHz)
Figure 73. 10-kHz FFT
24 26
Tone
(Hz)
1k
10 k
Table 4. AC Analysis
Signal
(dBFS)
–0.50
–0.50
SNR
(dBc)
109.1
101.8
THD
(dBc)
–107.9
–109.8
SINAD
(dBc)
105.5
101.1
SFDR
(dBc)
113.7
109.8
30
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