RC4190
PRODUCT SPECIFICATION
+V
s
Another method of automatic shutdown without temperature
limitations is the use of a zener diode in series with the I
C
pin and set resistor. When the battery voltage falls below V
Z
R4
+ 1.2V the circuit will start to shut down. With this connec-
tion and the low battery detector, the application can be
designed to signal a display when the battery voltage has
dropped to the first programmed level, then shut itself off as
the battery reaches the zener threshold.
LBD
8
LBR
1
Q2
C2
ILBD
R5
VREF
1.31V
The set current can also be turned off by forcing the I pin to
C
0.2V or less using an external transistor or mechanical
switch. An example of this is shown in Figure 15.
65-1651
Figure 13. Low Battery Detector
In this circuit an external control voltage is used to determine
the operating state of the RC4190. If the control voltage V
is a logic 1 at the input of the 4025 (CMOS Triple NOR
C
When the battery voltage drops below this threshold Q2 will
turn on and sink over 1500 µA typically. The low battery
detector circuitry may also be used for other, less conven-
tional applications (see Figures 19 and 20).
Gate), the voltage at the I pin will be less than 0.5V forcing
C
the 4190 off (<0.1 µA I ). Both the 2N3904 and 2N2907
CC
will be off insuring long shelf for the battery since less than
1.0 µA is drawn by the circuit.
Automatic Shutdown
The bias control current for the reference is externally set by
a resistor from the I pin to the battery. This current can vary
C
from 1.0 µA to 50 µA without affecting the operation of the
I . Interrupting this current will disable the entire circuit,
C
When V goes to a logic 0, 2.0 µA is forced into the I pin
C
C
through the 2.2 MΩ resistor and the NOR gate, and at the
same time the 2N3904 and 2N2907 turn on, connecting the
battery to the load.
causing the output voltage to go to 0V for step-down appli-
cations, and reducing the supply current to less than 1.0 µA.
As long as V remains low the circuit will regulate the
C
output to 5.0V. This type of circuit is used to back up the
main supply voltage when line interruptions occur, a particu-
larly useful feature when using volatile memory systems.
Automatic shutdown of the RC4190 can be achieved using
the circuit of Figure 14.
9.0V Battery Life Extender
5
+VS
Figure 16 shows a common application: a circuit to extend
the lifetime of a 9.0V battery. The regulator remains in its
quiescent state (drawing only 215 µA) until the battery volt-
age decays below 7.5V, at which time it will start to switch
and regulate the output at 7.0V until the battery falls below
2.2V.
VBAT
R1
R9
4190
6
IC
GND
3
65-2678
If this circuit operates at its typical efficiency of 80%, with
an output current of 10 mA, at 5.0V battery voltage, then the
Figure 14. Automatic Shutdown
A resistor is placed from the I pin to ground, creating a
average input current will be I = (V
IN OUT
x I ) ÷ (V x
BAT
L
C
ef) or (7.0V x 10 mA) ÷ (5.0V x 0.8 mA) = 17.5 mA.
voltage divider. When the voltage at the I pin is less than
C
1.2V, the RC4190 will begin to turn off. This scheme should
only be used in limited temperature range applications since
Bootstrapped Operation (Step-Up)
In step-up applications, power to the RC4190 can be derived
the “turn off” voltage at the I pin has a temperature coeffi-
C
from the output voltage by connecting the +V pin and the
S
cient of -4.0 mV/°C. At 25°C, typically 250 nA is the mini-
top of R1 to the output voltage (Figure 17).
mum current required by the I pin to sustain operation.
C
A 5.0 µA voltage divider works well taking into account the
sustaining current of 250 nA and a threshold voltage of 0.4V
at turn off. As an example, if 3.0V is to be the turn off volt-
age, then R9 = 1.1/4.75 µA and R1 = (3.0 – 1.1) 5.0 µA or
about 240 kΩ and 390 kΩ respectively. The tempco at the
top of the divider will be -4.0 mV (R1 + R9)/R9 or
One requirement for this circuit is that the battery voltage
must be greater than 3.0V when it is energized or else there
will not be enough voltage at pin 5 to start up the I . The big
C
advantage of this circuit is the ability to operate down to a
discharged battery voltage of 1.0V.
-10.5 mV/°C, an acceptable number for many applications.
11
RAYTHEON [ RAYTHEON COMPANY ]
