OPA2381 Datasheet, PDF (8/19 Pages) Burr-Brown (TI) – Precision, Low Power, 18MHz Transimpedance Amplifier

OPA381
OPA2381
SBOS313B − AUGUST 2004 − REVISED NOVEMBER 2004
APPLICATIONS INFORMATION
BASIC OPERATION
The OPA381 is a high-precision transimpedance
amplifier with very low 1/f noise. Due to its unique
architecture, the OPA381 has excellent long-term input
voltage offset stability.
The OPA381 performance results from an internal
auto-zero amplifier combined with a high-speed
amplifier. The OPA381 has been designed with circuitry
to improve overload recovery and settling time over that
achieved by a traditional composite approach. It has
been specifically designed and characterized to
accommodate circuit options to allow 0V output
operation (see Figure 3).
The OPA381 is used in inverting configurations, with the
noninverting input used as a fixed biasing point.
Figure 1 shows the OPA381 in a typical configuration.
Power-supply pins should be bypassed with 1µF
ceramic or tantalum capacitors. Electrolytic capacitors
are not recommended.
C_F
R_F
+5V
1µF
λ
OPA 381
V_OUT(1)
(0.5V to 4.4V)
V_BIAS = 0.5V
NOTE: (1) V_OUT = 0.5V in dark conditions.
Figure 1. OPA381 Typical Configuration
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OPERATING VOLTAGE
OPA381 series op amps are fully specified from 2.7V to
5.5V over a temperature range of −40°C to +125°C.
Parameters that vary significantly with operating
voltages or temperature are shown in the Typical
Characteristics.
INTERNAL OFFSET CORRECTION
The OPA381 series op amps use an auto-zero topology
with a time-continuous 18MHz op amp in the signal
path. This amplifier is zero-corrected every 100µs using
a proprietary technique. Upon power-up, the amplifier
requires approximately 400µs to achieve specified V_OS
accuracy, which includes one full auto-zero cycle of
approximately 100µs and the start-up time for the bias
circuitry. Prior to this time, the amplifier will function
properly but with unspecified offset voltage.
This design has virtually no aliasing and low noise. Zero
correction occurs at a 10kHz rate, but there is virtually
no fundamental noise energy present at that frequency
due to internal filtering. For all practical purposes, any
glitches have energy at 20MHz or higher and are easily
filtered, if necessary. Most applications are not sensitive
to such high-frequency noise, and no filtering is
required.
INPUT VOLTAGE
The input common-mode voltage range of the OPA381
series extends from V− to (V+) –1.8V. With input signals
above this common-mode range, the amplifier will no
longer provide a valid output value, but it will not latch
or invert.
INPUT OVERVOLTAGE PROTECTION
Device inputs are protected by ESD diodes that will
conduct if the input voltages exceed the power supplies
by more than approximately 500mV. Momentary
voltages greater than 500mV beyond the power supply
can be tolerated if the current is limited to 10mA. The
OPA381 family features no phase inversion when the
inputs extend beyond supplies if the input is current
limited.
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