Datasheet

Data Sheet AD420
Rev. I | Page 13 of 16
EXTERNAL BOOST FUNCTION
The external boost transistor reduces the power dissipated in
the AD420 by reducing the current flowing in the on-chip
output transistor (dividing it by the current gain of the external
circuit). A discrete NPN transistor with a breakdown voltage,
BV
CEO
, greater than 32 V can be used as shown in Figure 13.
00494-013
AD420
MJD31C
OR
2N3053
19
BOOST
I
OUT
0.022µF
1kΩ
R
LOAD
18
Figure 13. External Boost Configuration
The external boost capability has been developed for those
users who may wish to use the AD420, in the SOIC package, at
the extremes of the supply voltage, load current, and
temperature range. The PDIP package (because of its lower
thermal resistance) will operate safely over the entire specified
voltage, temperature, and load current ranges without the boost
transistor. The plot in Figure 14 shows the safe operating region
for both package types. The boost transistor can also be used to
reduce the amount of temperature induced drift in the part.
This will minimize the temperature induced drift of the on-chip
voltage reference, which improves drift and linearity.
00494-014
28V
20V
12V
4V
–60 –40 –20 0 20 40 60 80 100
TEMPERATURE (°C)
25V
AD420 OR AD420-32
32V
V
CC
WHEN USING SOIC PACKAGED DEVICES,
AN EXTERNAL BOOST TRANSISTOR IS
REQUIRED FOR OPERATION IN THIS AREA.
Figure 14. Safe Operating Region