OPA684
OPA
684
OPA6
84
SBOS219A – MARCH 2002
Low-Power, Current Feedback
OPERATIONAL AMPLIFIER With Disable
FEATURES
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MINIMAL BANDWIDTH CHANGE VERSUS GAIN
> 120MHz BANDWIDTH TO GAIN > +10
LOW DISTORTION: < –78dBc at 5MHz
HIGH OUTPUT CURRENT: 120mA
SINGLE +5V TO +12V SUPPLY OPERATION
DUAL
±
2.5 TO
±
6.0V SUPPLY OPERATION
LOW SUPPLY CURRENT: 1.7mA
LOW SHUTDOWN CURRENT: 100
µ
A
APPLICATIONS
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LOW-POWER BROADCAST VIDEO DRIVERS
EQUALIZING FILTERS
SAW FILTER HIGH GAIN POST AMPLIFIERS
MULTICHANNEL SUMMING AMPLIFIERS
PROFESSIONAL CAMERAS
ADC INPUT DRIVERS
DESCRIPTION
The OPA684 provides a new level of performance in low-power,
wideband, current-feedback (CFB) amplifiers. This CFB
plus
ampli-
fier is the first to use an internally closed-loop input buffer stage that
enhances performance significantly over earlier low-power CFB
amplifiers. While retaining the benefits of very low power operation,
this new architecture provides many of the benefits of a more ideal
CFB amplifier. The closed-loop input stage buffer gives a very low
and linearized impedance path at the inverting input to sense the
feedback error current. This improved inverting input impedance
retains exceptional bandwidth to much higher gains and improves
harmonic distortion over earlier solutions limited by inverting input
linearity. Beyond simple high-gain applications, the OPA684 CFB
plus
amplifier permits the gain setting element to be set with consider-
able freedom from amplifier bandwidth interaction. This allows
frequency response peaking elements to be added, multiple input
inverting summing circuits to have greater bandwidth, and low-
power line drivers to meet the demanding requirements of studio
cameras and broadcast video.
The output capability of the OPA684 also sets a new mark in
performance for low-power current feedback amplifiers. Delivering
a full
±4Vp-p
swing on
±5V
supplies, the OPA684 also has the
output current to support this swing into a 100Ω load. This minimal
output headroom requirement is complemented by a similar 1.2V
input stage headroom giving exceptional capability for single +5V
operation.
The OPA684’s low 1.7mA supply current is precisely trimmed at
25°C. This trim, along with low shift over temperature and supply
voltage, gives a very robust design over a wide range of operating
conditions. System power may be further reduced by using the
optional disable control pin. Leaving this disable pin open, or holding
it HIGH, gives normal operation. If pulled LOW, the OPA684 supply
current drops to less than 100µA while the I/O pins go to a high
impedance state.
BW (MHz) vs GAIN
V+
3
0
Normalized Gain
+
G=2
G=5
V
O
–3
–6
–9
–12
–15
–18
–21
R
F
= 1kΩ
G = 10
G = 20
G = 50
G = 100
100
200
V–
I
ERR
R
F
Z
(S)
I
ERR
R
G
10
Low-Power
Patent Pending
Amplifier
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright © 2001, Texas Instruments Incorporated
www.ti.com
TI [ TEXAS INSTRUMENTS ]
