THS4271_16 Datasheet, PDF (23/50 Pages) Texas Instruments – LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FEEDBACK AMPLIFIER

www.ti.com
Table 3. Power-Down Threshold Voltage Levels
(REF > MIDRAIL)
SUPPLY
VOLTAGE
(V)
±5
5
REFERENCE
PIN VOLTAGE
(V)
Floating or 5
2.5
1
Floating or 5
4
3.5
ENABLE
LEVEL
(V)
≥4
≥ 1.5
≥0
≥ 3.3
≥3
≥ 2.5
DISABLE
LEVEL
(V)
≤ 3.3
≤ 0.8
≤ -0.7
≤ 3.3
≤ 2.3
≤ 1.8
In Table 3, the threshold levels are derived by the
following equations:
REF - 1 V for enable
REF - 1.7 V for disable
Note that in order to maintain these threshold levels,
the reference pin can be any voltage between (V_S+/2)
+ 1 V to V_S+.
The recommended mode of operation is to tie the
reference pin to midrail, thus setting the threshold
levels to midrail +1 V and midrail +1.8 V.
NO. OF CHANNELS
Single (8-pin)
PACKAGES
THS4275D, THS4275DGN, and
THS4275DRB
Power-Supply Decoupling Techniques and
Recommendations
Power-supply decoupling is a critical aspect of any
high-performance amplifier design process. Careful
decoupling provides higher quality ac performance
(most notably improved distortion performance). The
following guidelines ensure the highest level of
performance.
1. Place decoupling capacitors as close to the
power-supply inputs as possible, with the goal of
minimizing the inductance of the path from
ground to the power supply.
2. Placement priority should put the smallest valued
capacitors closest to the device.
3. Use of solid power and ground planes is
recommended to reduce the inductance along
power-supply return current paths, with the
exception of the areas underneath the input and
output pins.
4. Recommended values for power-supply
decoupling include a bulk decoupling capacitor
(6.8 μF to 22 μF), a mid-range decoupling
capacitor (0.1 μF) and a high frequency
decoupling capacitor (1000 pF) for each supply.
THS4271
THS4275
SLOS397F – JULY 2002 – REVISED OCTOBER 2009
A 100-pF capacitor can be used across the
supplies as well for extremely high-frequency
return currents, but often is not required.
APPLICATION CIRCUITS
Driving an Analog-to-Digital Converter With the
THS4271
The THS4271 can be used to drive high-performance
analog-to-digital converters. Two example circuits are
presented below.
The first circuit uses a wideband transformer to
convert a single-ended input signal into a differential
signal. The differential signal is then amplified and
filtered by two THS4271 amplifiers. This circuit
provides low intermodulation distortion, suppressed
even-order distortion, 14 dB of voltage gain, a 50-Ω
input impedance, and a single-pole filter at 100 MHz.
For applications without signal content at dc, this
method of driving ADCs can be very useful. Where dc
information content is required, the THS4500 family
of fully differential amplifiers may be applicable.
V_CM
50 Ω (1:4 Ω)
Source 1:2
100 Ω
5V
+
THS4271
_
-5 V
249 Ω
24.9 Ω
100 Ω
22 pF
22 pF
249 Ω
ADS5422
14-Bit, 62 Msps
24.9 Ω
V_CM
_
THS4271
+
Figure 78. A Linear, Low-Noise, High-Gain
ADC Preamplifier
The second circuit depicts single-ended ADC drive.
While not recommended for optimum performance
using converters with differential inputs, satisfactory
performance can sometimes be achieved with
single-ended input drive. An example circuit is shown
here for reference.
Copyright © 2002–2009, Texas Instruments Incorporated
Product Folder Link(s): THS4271 THS4275
Submit Documentation Feedback
23