OPA330_1 Datasheet, PDF (9/30 Pages) Texas Instruments – 50mV VOS, 0.25mV/°C, 35mA CMOS OPERATIONAL AMPLIFIERS Zerø-Drift Series

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OPA330
OPA2330
OPA4330
SBOS432D – AUGUST 2008 – REVISED JUNE 2010
APPLICATIONS INFORMATION
The OPA330, OPA2330, and OPA4330 are unity-gain
stable, precision operational amplifiers free from
unexpected output and phase reversal. The use of
proprietary Zerø-Drift circuitry gives the benefit of low
input offset voltage over time and temperature, as
well as lowering the 1/f noise component. As a result
of the high PSRR, these devices work well in
applications that run directly from battery power
without regulation. The OPA330 family is optimized
for low-voltage, single-supply operation. These
miniature, high-precision, low quiescent current
amplifiers offer high-impedance inputs that have a
common-mode range 100mV beyond the supplies
and a rail-to-rail output that swings within 100mV of
the supplies under normal test conditions. The
OPA330 series are precision amplifiers for
cost-sensitive applications.
OPERATING VOLTAGE
The OPA330 series op amps can be used with single
or dual supplies from an operating range of V_S =
+1.8V (±0.9V) up to +5.5V (±2.75V). Supply voltages
greater than +7V can permanently damage the
device. See the Absolute Maximum Ratings table.
Key parameters that vary over the supply voltage or
temperature range are shown in the Typical
Characteristics section of this data sheet.
INPUT VOLTAGE
The OPA330, OPA2330, and OPA4330 input
common-mode voltage range extends 0.1V beyond
the supply rails. The OPA330 is designed to cover
the full range without the troublesome transition
region found in some other rail-to-rail amplifiers.
Typically, input bias current is about 200pA; however,
input voltages exceeding the power supplies can
cause excessive current to flow into or out of the
input pins. Momentary voltages greater than the
power supply can be tolerated if the input current is
limited to 10mA. This limitation is easily accomplished
with an input resistor, as shown in Figure 18.
Current-limiting resistor
required if input voltage
exceeds supply rails by
³ 0.3V.
I_OVERLOAD
10mA max
V_IN
5kW
+5V
OPA330
V_OUT
Figure 18. Input Current Protection
INPUT DIFFERENTIAL VOLTAGE
The typical input bias current of the OPA330 during
normal operation is approximately 200pA. In
over-driven conditions, the bias current can increase
significantly (see Figure 17).The most common cause
of an over-driven condition occurs when the op amp
is outside of the linear range of operation. When the
output of the op amp is driven to one of the supply
rails the feedback loop requirements cannot be
satisfied and a differential input voltage develops
across the input pins. This differential input voltage
results in activation of parasitic diodes inside the front
end input chopping switches that combine with 10kΩ
electromagnetic interference (EMI) filter resistors to
create the equivalent circuit shown in Figure 19.
Notice that the input bias current remains within
specification within the linear region.
10kW
Clamp
+In
CORE
-In
10kW
Figure 19. Equivalent Input Circuit
INTERNAL OFFSET CORRECTION
The OPA330, OPA2330, and OPA4330 op amps use
an auto-calibration technique with a time-continuous
125kHz op amp in the signal path. This amplifier is
zero-corrected every 8ms using a proprietary
technique. Upon power-up, the amplifier requires
approximately 100ms to achieve specified V_OS
accuracy. This design has no aliasing or flicker noise.
EMI SUSCEPTIBILITY AND INPUT FILTERING
Operational amplifiers vary in their susceptibility to
EMI. If conducted EMI enters the operational
amplifier, the dc offset observed at the amplifier
output may shift from its nominal value while the EMI
is present. This shift is a result of signal rectification
associated with the internal semiconductor junctions.
While all operational amplifier pin functions can be
affected by EMI, the input pins are likely to be the
most susceptible. The OPA330 operational amplifier
family incorporates an internal input low-pass filter
that reduces the amplifier response to EMI. Both
common-mode and differential mode filtering are
provided by the input filter. The filter is designed for a
cutoff frequency of approximately 8MHz (–3dB), with
a roll-off of 20dB per decade.
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