OPA137 Datasheet, PDF (7/8 Pages) Burr-Brown (TI) – LOW COST FET-INPUT OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series

APPLICATIONS INFORMATION
OPA137 series op amps are unity-gain stable and suitable
for a wide range of general-purpose applications. Power
supply pins should be bypassed with 10nF ceramic capaci-
tors or larger. All circuitry is completely independent in dual
and quad versions, assuring normal performance when one
amplifier in a package is overdriven or short circuited. Many
key parameters are guaranteed over the specified tempera-
ture range, –40°C to +85°C.
OPERATING VOLTAGE
OPA137 op amps can be operated on power supplies as low
as ±2.25V. Performance remains excellent with power sup-
plies ranging from ±2.25V to ±18V (+4.5V to +36V single
supply). Most parameters vary only slightly throughout this
supply voltage range. Quiescent current and short-circuit
current vs supply voltage are shown in Typical Performance
Curves.
Operation at very low supply voltage (V_S ≤ ±3V) requires
careful attention to ensure that the common-mode voltage
remains within the linear range, V_CM = (V–)+3V to (V+).
Inputs may need to be biased above ground in accordance
with the common-mode voltage range restrictions for linear
operation.
INPUT VOLTAGE
The input common-mode voltage range of OPA137 series
op amps extends from (V–)+3V to the positive rail, V+. For
normal operation, inputs should be limited to this range. The
inputs may go beyond the power supplies without output
phase-reversal. Many FET-input op amps (such as TL061
types) exhibit phase-reversal of the output when the input
common-mode range is exceeded. This can occur in voltage-
follower circuits, causing serious problems in control loop
applications.
Input terminals are diode-clamped to the power supply rails
for ESD protection. If the input voltage can exceed the
negative supply by 500mV, input current should be limited
to 2mA (or less). If the input current is not adequately
limited, you may see unpredicatable behavior in the other
amplifiers in the package. This is easily accomplished with
an input resistor as shown in Figure 1. Many input signals
are inherently current-limited, therefore, a limiting resistor
may not be required.
HIGH-SIDE CURRENT SENSING
Many applications require the sensing of signals near the
positive supply. The common-mode input range of OPA137
op amps includes the positive rail, enabling them to be used
to sense power supply currents as shown in Figure 2.
R₁
0.1Ω
V+
R₂
1kΩ
Load
Zetex
Darlington
ZTX712
OPA137
20pF
V_O =
R₁ R₃
R₂
I_L
R₃
10kΩ
OPA241
V_O
Ground-referred
output
FIGURE 2. High-Side Current Monitor.
INPUT BIAS CURRENT
The input bias current is approximately 5pA at room tem-
perature and increases with temperature as shown in the
typical performance curve “Input Bias Current vs Tempera-
ture.”
Input Bias current also varies with common-mode voltage
and power supply voltage. This variation is dependent on
the voltage between the negative power supply and the
common-mode input voltage. The effect is shown in the
typical performance curve “Input Bias Current vs Common-
Mode Voltage.”
R_F
1MΩ
3.3pF
I_OVERLOAD
2mA max
V_IN
V+
OPA137
Inputs are internally
V–
clamped to V+ and V–
V_OUT
I_D
λ
Photodiode
BPW34
C_D = 75pF
OPA137
V_O = – R_F I_D
I_D is proportional to
light intensity (radiant power)
FIGURE 3. Photodetector Amplifier.
FIGURE 1. Input Current Protection for Voltages Exceed-
ing the Supply Voltage.
7
®
OPA137, 2137, 4137