OPA338NA250 Datasheet, PDF (8/25 Pages) Texas Instruments – MicroSIZE, Single-Supply CMOS OPERATIONAL AMPLIFIERS MicroAmplifier
Series

OPA337, OPA2337
OPA338, OPA2338
SBOS077B − JUNE 1997 − REVISED MARCH 2005
APPLICATIONS INFORMATION
The OPA337 and OPA338 series are fabricated on a
state-of-the-art CMOS process. The OPA337 series is
unity-gain stable. The OPA338 series is optimized for
gains greater than or equal to 5. Both are suitable for a
wide range of general-purpose applications. Power-
supply pins should be bypassed with 0.01µF ceramic
capacitors.
OPERATING VOLTAGE
The OPA337 series and OPA338 series can operate from
a +2.5V to +5.5V single supply with excellent
performance. Unlike most op amps which are specified at
only one supply voltage, these op amps are specified for
real-world applications; a single limit applies throughout
the +2.7V to +5.5V supply range. This allows a designer
to have the same assured performance at any supply
voltage within the specified voltage range. Most behavior
remains unchanged throughout the full operating voltage
range. Parameters which vary significantly with operating
voltage are shown in the Typical Characteristic curves.
INPUT VOLTAGE
The input common-mode range extends from (V−) − 0.2V
to (V+) − 1.2V. For normal operation, inputs should be
limited to this range. The absolute maximum input voltage
is 500mV beyond the supplies. Inputs greater than the
input common-mode range but less than maximum input
voltage, while not valid, will not cause any damage to the
op amp. Furthermore, if input current is limited the inputs
may go beyond the power supplies without phase
inversion (as shown in Figure 1) unlike some other op
amps.
OPA337, V_IN = ±3V Greater Than V_S = ±2.5V
V_OUT, G = −1
3V
(not limited by
input common−
mode range)
0V
G = ±1 V_OUT, G = +1
(limited by input
common−mode
−3V
range)
Figure 1. OPA337—No Phase Inversion with
Inputs Greater than the Power-Supply Voltage
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Normally, input currents are 0.2pA. However, large inputs
(greater than 500mV beyond the supply rails) can cause
excessive current to flow in or out of the input pins.
Therefore, as well as keeping the input voltage below the
maximum rating, it is also important to limit the input
current to less than 10mA. This is easily accomplished
with an input resistor as shown in Figure 2.
I_OVERLOAD
10mA max
V_IN
5kΩ
+5V
OPA337
V_OUT
Figure 2. Input Current Protection for Voltages
Exceeding the Supply Voltage
USING THE OPA338 IN LOW GAINS
The OPA338 series is optimized for gains greater than or
equal to 5. It has significantly wider bandwidth (12.5MHz)
and faster slew rate (4.6V/µs) when compared to the
OPA337 series. The OPA338 series can be used in lower
gain configurations at low frequencies while maintaining
its high slew rate with the proper compensation.
Figure 3 shows the OPA338 in a unity-gain buffer
configuration. At dc, the compensation capacitor C₁ is
effectively open resulting in 100% feedback (closed-loop
gain = 1). As frequency increases, C₁ becomes lower
impedance and closed-loop gain increases, eventually
becoming 1 + R₂/R₁ (in this case 5, which is equal to the
minimum gain required for stability).
Improved slew rate (4.6V/µs) versus
OPA337 (1.2V/µs) in unity gain.
R₂
10kΩ
C₁
68pF
V_IN
R₁
2.5kΩ
OPA338
1
C₁ = _2πfCR1
V_OUT
Where f_C is the frequency at which closed−loop
gains less than 5 are not appropriatesee text.
Figure 3. Compensation of the OPA338 for
Unity-Gain Buffer
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