OPA4650 Datasheet, PDF (9/14 Pages) Burr-Brown (TI) – Wideband, Low Power, Quad Voltage Feedback OPERATIONAL AMPLIFIER

impossible to achieve a smooth, stable response. Best results
are obtained by soldering the part onto the board. If socket-
ing for the DIP package is desired, high frequency flush
mount pins (e.g., McKenzie Technology #710C) can give
good results.
The OPA4650 is nominally specified for operation using ±5V
power supplies. A 10% tolerance on the supplies, or an ECL
–5.2V for the negative supply, is within the maximum speci-
fied total supply voltage of 11V. Higher supply voltages can
break down internal junctions possibly leading to catastrophic
failure. Single supply operation is possible as long as com-
mon mode voltage constraints are observed. The common
mode input and output voltage specifications can be inter-
preted as a required headroom to the supply voltage. Observ-
ing this input and output headroom requirement will allow
non-standard or single supply operation. Figure 1 shows one
approach to single-supply operation.
+V_S
+V_S
V_S
2
V_OUT =
V_S
2
+ A_V V_AC
V_AC
1/4
R_OUT
OPA4650
R_F
402Ω
R_G
402Ω
R_L
A_V = 1 +
R_F
R_G
FIGURE 1. Single Supply Operation.
OFFSET VOLTAGE ADJUSTMENT
One simple way to null the initial offset voltage while
retaining the low offset drift of the OPA4650 is shown in
Figure 2. The 20kΩ potentiometer and the 47kΩ series
resistor R_TRIM create a small correction current which is
summed into the inverting node. The 0.1µF capacitor keeps
high-frequency power supply noise from coupling into the
signal path. Although the initial offset will be nulled to zero
with this technique, issues of temperature drift must also be
considered. The additional resistor R₃ is shown matched to
the parallel combination R₁ and R₂ (the R_TRIM path is
assumed to be negligible in this calculation). This will
eliminate the first-order offset drift due to input bias current
leaving only the input offset current (I_OS) drift multiplied by
the feedback resistor R₂.
ESD PROTECTION
ESD damage has been a well recognized source of degrada-
tion for MOSFET type circuits, but any semiconductor
device can be vulnerable to damage. This becomes more of
an issue for very high speed processes like that used for the
+V_s
20kΩ
–V_S
R_TRIM
47kΩ
0.1µF
R₁
R₂
OPA4650
R₃ = R₁ || R₂₍₁₎
V_IN or Ground
Output Trim Range
≅ +V_S
R_{2 to}
R_TRIM
–V_S
R₂
R_TRIM
NOTE: (1) R₃ is optional and can be used to cancel offset errors
due to input bias currents.
FIGURE 2. Offset Voltage Trim.
OPA4650. ESD damage can cause subtle changes in ampli-
fier input characteristics without necessarily destroying the
device. In precision operational amplifiers, this may cause a
noticeable degradation of offset voltage and drift. ESD
handling precautions are strongly recommended when han-
dling the OPA4650.
OUTPUT DRIVE CAPABILITY
The OPA4650 has been optimized to drive 75Ω and 100Ω
resistive loads. The device can drive 1Vp-p into a 75Ω
load. This high output drive capability makes the OPA4650
an ideal choice for a wide range of RF, IF and video
applications. In many cases, additional buffer amplifiers
are unnecessary.
Many demanding high speed applications, such as driving
Analog-to-Digital converters, require op amps with low
wideband output impedance. For example, low output imped-
ance is essential when driving the signal-dependent capaci-
tance at the input of a flash A/D converter. As shown in
Figure 3, the OPA4650 maintains very low closed-loop
output impedance over frequency. Closed-loop output imped-
ance increases with frequency since loop gain is decreasing.
SMALL-SIGNAL OUTPUT IMPEDANCE
vs FREQUENCY
1k
G = +1
100
10
1
0.1
0.01
10k
100k
1M
10M
Frequency (Hz)
100M
FIGURE 3. Small-Signal Output Impedance vs Frequency.
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OPA4650