
AD581
REV. B
–4–
Figure 7. Spectral Noise Density and Total rms Noise
vs. Frequency
Figure 8. Quiescent Current vs. Temperature
PRECISION HIGH CURRENT SUPPLY
The AD581 can be easily connected with power pnp or power
Darlington pnp devices to provide much greater output current
capability. The circuit shown in Figure 9 delivers a precision
10 volt output with up to 4 amperes supplied to the load. The
0.1
F capacitor is required only if the load has a significant
capacitive component. If the load is purely resistive, improved
high frequency supply rejection results from removing the
capacitor.
Figure 9. High Current Precision Supply
the initial tolerance is
±10 mV, the temperature error band is
±15 mV, thus the unit is guaranteed to be 10.000 volts ±25 mV
from –55
°C to +125°C).
OUTPUT CURRENT CHARACTERISTICS
The AD581 has the capability to either source or sink current
and provide good load regulation in either direction, although it
has better characteristics in the source mode (positive current
into the load). The circuit is protected for shorts to either posi-
tive supply or ground. The output voltage vs. output current
characteristics of the device are shown in Figure 5. Source cur-
rent is displayed as negative current in the figure; sink current is
positive. Note that the short circuit current (i.e., zero volts out-
put) is about 28 mA; when shorted to +15 volts, the sink cur-
rent goes to about 20 mA.
Figure 5. AD581 Output Voltage vs. Sink and Source Current
DYNAMIC PERFORMANCE
Many low power instrument manufacturers are becoming in-
creasingly concerned with the turn-on characteristics of the
components being used in their systems. Fast turn-on compo-
nents often enable the end user to keep power off when not
needed, and yet respond quickly when the power is turned on
for operation. Figure 6 displays the turn-on characteristic of
the AD581. This characteristic is generated from cold-start
operation and represents the true turn-on waveform after an
extended period with the supplies off. The figure shows both the
coarse and fine transient characteristics of the device; the total
settling time to within
±10 millivolt is about 180 s, and there is
no long thermal tail appearing after the point.
Figure 6. Output Settling Characteristic