OPA376-Q1_15 Datasheet, PDF (11/20 Pages) Texas Instruments – Low-Noise, Low Quiescent Current, Precision Operational Amplifier e-trim™ Series

OPA376-Q1
OPA2376-Q1, OPA4376-Q1
www.ti.com
SBOS549 – APRIL 2011
INPUT AND ESD PROTECTION
The OPA376-Q1 family incorporates internal
electrostatic discharge (ESD) protection circuits on all
pins. In the case of input and output pins, this
protection primarily consists of current steering
diodes connected between the input and
power-supply pins. These ESD protection diodes also
provide in-circuit, input overdrive protection, as long
as the current is limited to 10mA as stated in the
Absolute Maximum Ratings. Figure 24 shows how a
series input resistor may be added to the driven input
to limit the input current. The added resistor
contributes thermal noise at the amplifier input and its
value should be kept to a minimum in noise-sensitive
applications.
load, a voltage divider is created, introducing a gain
error at the output and slightly reducing the output
swing. The error introduced is proportional to the ratio
R_S/R_L, and is generally negligible at low output
current levels.
V+
R_S
OPA376
V_OUT
V_IN
10W to
20W
R_L
C_L
Figure 25. Improving Capacitive Load Drive
I_OVERLOAD
10mA max
V_IN
5kW
V+
OPA376
V_OUT
Figure 24. Input Current Protection
CAPACITIVE LOAD AND STABILITY
The OPA376-Q1 series of amplifiers may be used in
applications where driving a capacitive load is
required. As with all op amps, there may be specific
instances where the OPAx376 can become unstable,
leading to oscillation. The particular op amp circuit
configuration, layout, gain, and output loading are
some of the factors to consider when establishing
whether an amplifier will be stable in operation. An op
amp in the unity-gain (+1V/V) buffer configuration and
driving a capacitive load exhibits a greater tendency
to be unstable than an amplifier operated at a higher
noise gain. The capacitive load, in conjunction with
the op amp output resistance, creates a pole within
the feedback loop that degrades the phase margin.
The degradation of the phase margin increases as
the capacitive loading increases.
The OPAx376 in a unity-gain configuration can
directly drive up to 250pF pure capacitive load.
Increasing the gain enhances the ability of the
amplifier to drive greater capacitive loads; see the
typical characteristic plot, Small-Signal Overshoot vs
Capacitive Load. In unity-gain configurations,
capacitive load drive can be improved by inserting a
small (10Ω to 20Ω) resistor, R_S, in series with the
output, as shown in Figure 25. This resistor
significantly reduces ringing while maintaining dc
performance for purely capacitive loads. However, if
there is a resistive load in parallel with the capacitive
ACTIVE FILTERING
The OPA376-Q1 series is well-suited for filter
applications requiring a wide bandwidth, fast slew
rate, low-noise, single-supply operational amplifier.
Figure 26 shows a 50kHz, 2nd-order, low-pass filter.
The components have been selected to provide a
maximally-flat Butterworth response. Beyond the
cutoff frequency, roll-off is –40dB/dec. The
Butterworth response is ideal for applications
requiring predictable gain characteristics such as the
anti-aliasing filter used ahead of an analog-to-digital
converter (ADC).
R₃
5.49kW
C₂
150pF
R₁
5.49kW
R₂
12.4kW
C₁
V_IN
1nF
V+
OPA376
V_OUT
(V+)/2
Figure 26. Second-Order Butterworth 50kHz
Low-Pass Filter
PHOTOSENSITIVITY
Although the OPA2376YZD package has a protective
backside coating that reduces the amount of light
exposure on the die, unless fully shielded, ambient
light can reach the active region of the device. Input
Copyright © 2011, Texas Instruments Incorporated
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Product Folder Link(s): OPA376-Q1 OPA2376-Q1 OPA4376-Q1