LM35
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SNIS159C –AUGUST 1999–REVISED JULY 2013
TYPICAL APPLICATIONS
HEAVY CAPACITIVE LOAD, WIRING, ETC.
2 k
+
LM35
TO A HIGH-IMPEDANCE LOAD
OUT
v
Figure 14. LM35 with Decoupling from Capacitive Load
HEAVY CAPACITIVE LOAD, WIRING, ETC.
+
OUT
LM35
TO A HIGH-IMPEDANCE LOAD
0.01 mF BYPASS
75
OPTONAL
v
1 mF
Figure 15. LM35 with R-C Damper
CAPACITIVE LOADS
Like most micropower circuits, the LM35 has a limited ability to drive heavy capacitive loads. The LM35 alone is
able to drive 50 pf without special precautions. If heavier loads are anticipated, isolating or decoupling the load
with a resistor is easy (see Figure 14). Or you can improve the tolerance of capacitance with a series R-C
damper from output to ground (see Figure 15).
When the LM35 is applied with a 200-W load resistor as shown in Figure 16, Figure 17, or Figure 19, the device
is relatively immune to wiring capacitance because the capacitance forms a bypass from ground to input and not
on the output. However, as with any linear circuit connected to wires in a hostile environment, performance is
affected adversely by intense electromagnetic sources such as relays, radio transmitters, motors with arcing
brushes, and SCR transients, as the wiring acts as a receiving antenna and the internal junctions act as
rectifiers. For best results in such cases, a bypass capacitor from VIN to ground and a series R-C damper, such
as 75 W, in series with 0.2 or 1 μF from output to ground are often useful. These are shown in Figure 24,
Figure 24, and Figure 27.
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