SGM8049-1 Datasheet, PDF (8/19 Pages) SG Micro Corp – Rail-to-Rail I/O Operational Amplifiers

SGM8049-1/SGM8049-2
SGM8049-4
1.8V, 2.5µA, 120kHz,
Rail-to-Rail I/O Operational Amplifiers
APPLICATION INFORMATION
The SGM8049-1/2/4 operational amplifiers minimize
power consumption without compromising bandwidth
or noise. Typical values of power supply rejection ratio
(PSRR), common mode rejection ratio (CMRR), and
open-loop gain (A_OL) are 100dB or better.
When designing for ultra low power applications,
choose system components carefully. To minimize
current consumption, select large value resistors. Any
resistors will react with stray capacitance in the circuit
and the input capacitance of the operational amplifiers.
These parasitic RC combinations can affect the stability
of the overall system. A feedback capacitor may be
required to assure stability and limit overshoot or gain
peaking.
Good layout practice mandates the use of a 0.1μF
bypass capacitor placed closely across the supply pins.
Operating Voltage
SGM8049-1/2/4 operational amplifiers are fully specified
and tested from +1.8V to +5.5V or ±0.9V to ±2.75V.
Input Common Mode Voltage Range
The input common mode voltage range of the
SGM8049-1/2/4 is from (-V_S) - 0.1V to (+V_S) + 0.1V. This
rail-to-rail input is achieved using a complementary
input stage. CMRR is specified from the negative rail to
1.2V below the positive rail. Between (-V_S) - 0.1V to
(+V_S) + 0.1V, the amplifier operates with higher offset
voltage because of the transition region of the input
stage.
Protecting Inputs from Over-Voltage
Normally, input currents are 1pA. However, a large
voltage input (greater than 500mV beyond the supply
rails) can cause excessive current to flow in or out of
the input pins. Therefore, as well as keeping the input
voltage below the maximum rating, it is also important
to limit the input current to less than 10mA. This limiting
is easily accomplished with an input voltage resistor, as
shown in Figure 2.
IOVERLOAD
10mA MAX
VIN
2kΩ
VS
-
SGM8049-1
+
VOUT
Figure 2. Input Current Protection for Voltages Exceeding
the Supply Voltage
Noise
Although micro-power amplifiers frequently have high
wideband noise, the SGM8049-1/2/4 offer excellent
noise performance. Resistors should be chosen
carefully because the SGM8049-1/2/4 have only
3.5μV_PP of 0.1Hz to 10Hz noise, and 75nV/ Hz of
wideband noise; otherwise, they can become the
dominant source of noise.
Capacitive Load and Stability
Follower configurations with load capacitance in excess
of 30pF can produce extra overshoot and ringing in the
output signal. Increasing the gain enhances the ability
of the amplifier to drive greater capacitive loads. 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 3. This
resistor significantly reduces ringing while maintaining
direct current (DC) performance for purely capacitive
loads. However, if there is a resistive load in parallel
with the capacitive load, a voltage divider is created,
introducing a DC 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.
VS
-
RS
SGM8049-1
VOUT
10Ω to 20Ω
VIN
+
RL
CL
Figure 3. Series Resistor in Unity-Gain Buffer Configuration
Improves Capacitive Load Drive
SG Micro Corp
www.sg-micro.com
NOVEMBER 2015
8