Fairchild DUAL TRACKING VOLTAGE REGULATORS RC4194 - Manual (Page 8)

PRODUCT SPECIFICATION RC4194
8
Figure 9. RC4194 Recommended Compensation
4194
0.001 µ F
Comp+
R
0 Comp-
R
0
R
SET
R
SET
0.01 µ F
0.01 µ F
0.001 µ F
4.7 µ F
*
65-4201
+V
S
–V
S
+V
S
–V
S
+V
OUT
–V
OUT
+V
OUT
–V
OUT
Note:
All Capacitors are Ceramic Disc
Except * = Solid Tantalum
All compensation and bypass caps should have short leads,
solid grounds, and be located as close to the 4194 as possi-
ble. Refer to Figure 9 for recommended compensation cir-
cuitry.
Protection
In systems using monolithic voltage regulators, a number of
conditions can exist which, left uncorrected, will destroy the
regulator. Fortunately, regulators can easily be protected
against these potentially destructive conditions. Monolithic
regulators can be destroyed by any reversal of input or output
voltage polarity, or if the input voltage drops below the out-
put voltage in magnitude. These conditions can be caused by
inductive loads at the inputs or outputs of the regulator.
Other problems are caused by heavy loads at the unregulated
inputs to the regulator, which might cause the input voltage
to drop below the output voltage at turn-off. If any of the
preceding problem conditions are present in your system, it
is recommended that you protect the regulator using diodes.
These diodes should be high speed types capable of handling
large current surges. Figure 10 shows all six of the possible
protection diodes. The diodes at the inputs and outputs pre-
vent voltages at those points from becoming reversed.
Diodes from outputs to inputs prevent the output voltage
from exceeding the input voltage. Chances are that the sys-
tem under consideration will not require all six diodes, but if
in doubt, be sure to include them.
Brownout Protection
The RC4194 is one of the most easily applied and trouble-
free monolithic ICs available. When used within the data
sheet ratings (package power dissipation, maximum output
current, minimum and maximum input voltages) it provides
the most cost-effective source of regulated
±15V for power-
ing linear ICs.
Sometimes occasions arise in which the RC4194 ratings
must be exceeded. One example is the “brownout.” During
a brownout, line voltages may be reduced to as low as 75
VRMS, causing the input voltage to the RC4194 to drop
below the minimum dropout voltage. When this happens,
the negative output voltage can go to positive. The maximum
amount of current available is approximately 5 mA.
In general this is not enough current to damage most ICs
which the RC4194 might be supplying, but it is a potentially
destructive condition. Fortunately, it is easy to protect
against. As shown in the typical application circuit in Figure
11, a diode, D, can be connected to the negative output.
Figure 10. RC4194 Regulator Showing All Protective Diodes
4194
0.001 µ F
Comp+
+V
S
-V
S
R
0
R
SET Comp-
R
0
R
SET
0.01 µ F
0.01 µ F
0.001 F
4.7 µ F *
-V
OUT
+V
OUT +V
OUT
-V
OUT
65-4202
+V
S
-V
S
To
-V
OUT
Note:
All Capacitors are Ceramic Disc
Except * = Solid Tantalum