Datasheet

C
1
1nF
C
150pF
2
R
3
5.49kW
R
1
5.49kW
R
2
12.4kW
V+
V
OUT
V
IN
OPA376
(V+)/2
5kW
OPA376
10mAmax
V+
V
IN
V
OUT
I
OVERLOAD
10 toW
20W
V+
V
IN
V
OUT
R
S
R
L
C
L
OPA376
OPA376
OPA2376
OPA4376
www.ti.com SBOS406F –JUNE 2007–REVISED MARCH 2013
INPUT AND ESD PROTECTION load, a voltage divider is created, introducing a gain
error at the output and slightly reducing the output
The OPA376 family incorporates internal electrostatic
swing. The error introduced is proportional to the ratio
discharge (ESD) protection circuits on all pins. In the
R
S
/R
L
, and is generally negligible at low output
case of input and output pins, this protection primarily
current levels.
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.
Figure 25. Improving Capacitive Load Drive
ACTIVE FILTERING
The OPA376 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
Figure 24. Input Current Protection
maximally-flat Butterworth response. Beyond the
cutoff frequency, roll-off is –40dB/dec. The
Butterworth response is ideal for applications
CAPACITIVE LOAD AND STABILITY
requiring predictable gain characteristics such as the
The OPA376 series of amplifiers may be used in
anti-aliasing filter used ahead of an analog-to-digital
applications where driving a capacitive load is
converter (ADC).
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,
Figure 26. Second-Order Butterworth 50kHz Low-
capacitive load drive can be improved by inserting a
Pass Filter
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
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Product Folder Links: OPA376 OPA2376 OPA4376