ISL28110 Datasheet, PDF (15/19 Pages) Intersil Corporation – Precision Low Noise JFET Operational Amplifiers

ISL28110, ISL28210
rails but damage to the internal ESD protection diodes
can result unless these input currents are limited.
Maximizing Dynamic Signal Range
The amplifiers maximum undistorted output swing is a
figure of merit for precision, low distortion applications.
Audio amplifiers are a good example of amplifiers that
require low noise and low signal distortion over a wide
output dynamic range. When these applications operate
from batteries, raising the amplifier supply voltage to
overcome poor output voltage swing has the penalty of
increased power consumption and shorter battery life.
Amplifiers whose input and output stages can swing
closest to the power supply rails while providing low
noise and undistorted performance, will provide
maximum useful dynamic signal range and longer
battery life.
Rail-to-rail input and output (RRIO) amplifiers have the
highest dynamic signal range but their added complexity
degrades input noise and amplifier distortion. Many
contain two input pairs, one pair operating to each supply
rail. The trade-offs for these are increased input noise
and distortion caused by non-linear input bias current
and capacitance when amplifying high impedance
sources. Their rail-to-rail output stages swing to within a
few millivolts of the rail, but output impedances are high
so that their output swing decreases and distortion
increases rapidly with increasing load current. At heavy
load currents the maximum output voltage swing of RRO
op amps can be lower than a good emitter follower
output stage.
The ISL28110 and ISL28210 low noise input stage and
high performance output stage are optimized for low
THD+N into moderate loads over the full -40°C to
+125°C temperature range. Figures 17 and 18 show the
1kHz THD+N unity gain performance vs output voltage
swing at load resistances of 2kΩ and 600Ω. Figure 41
shows the unity-gain THD+N performance driving
600Ω from ±5V supplies.
1
V_S = ±5V
R_L = 600Ω
0.1 _{AV = 1}
+125°C
+85°C
0.01
+25°C
Power Dissipation
It is possible to exceed the +150°C maximum junction
temperatures under certain load and power supply
conditions. It is therefore important to calculate the
maximum junction temperature (T_JMAX) for all
applications to determine if power supply voltages, load
conditions, or package type need to be modified to
remain in the safe operating area. These parameters are
related using Equation 1:
T_JMAX = T_MAX + θ_JAxPD_MAXTOTAL
(EQ. 1)
where:
• P_DMAXTOTAL is the sum of the maximum power
dissipation of each amplifier in the package (PD_MAX)
• PD_MAX for each amplifier can be calculated using
Equation 2:
PD_MAX
=
V_S × I_qMAX + (V_S
-
V_OU
TM
A
X
)
×
V_{-----O----U----T----M-----A----X--}
R_L
(EQ. 2)
where:
• T_MAX = Maximum ambient temperature
• θ_JA = Thermal resistance of the package
• PD_MAX = Maximum power dissipation of 1 amplifier
• V_S = Total supply voltage
• I_qMAX = Maximum quiescent supply current of 1
amplifier
• V_OUTMAX = Maximum output voltage swing of the
application
• R_L = Load resistance
0.001
0°C
-40°C
0.0001
0 1 2 3 4 5 6 7 8 9 10
V_P-P (V)
FIGURE 41. UNITY-GAIN THD+N vs OUTPUT VOLTAGE
vs TEMPERATURE AT V_S = ±5V FOR 600Ω
LOAD
15
FN6639.0
September 13, 2010