PRODUCT SPECIFICATION
RC4190
Background Information
Soft Start
During the past several years there have been various switch-
ing regulator ICs introduced by many manufacturers, all of
which attended to the same market, namely controllers for
use in power supplies delivering greater than 10W of DC
power. Raytheon felt there was another area which could use
a switching regulator to even more advance the area of bat-
tery powered equipment. Battery powered systems have
problems peculiar unto themselves: changes in supply volt-
age, space considerations, battery life and usually cost. The
RC4190 was designed with each of these in mind.
+V
S
1M
6
C
T
I
C
RC4190
65-2076
The delay introduced by the RC time constant at start-up
allows the output filter capacitor to charge up, reducing the
instantaneous supply current. A typical value for C is in the
0.1µF range.
The RC4190 was partitioned to work in an eight pin pack-
age, making it smaller than other controllers which go into
14 and 16 pin packages.
Battery powered applications require the load as seen by the
battery to be as small as possible to extend battery life. To
this end, the quiescent current of the RC4190 is 15 to 100
times less than controllers designed for nonbattery applica-
tions. At the same time, the switch transistor can sink 200
mA at 0.4V, comparable to or better than higher powered
controllers. As an example, the 4190 configured in the
step-up mode can supply 5.0V at 40 mA output with an
input of 3.0V.
Bootstrapped Low Voltage Start-Up
Figure 24 shows the bootstrapped application can be "kicked
on" using an extra capacitor and triple pole double throw
switch (3PDT). This connection allows the circuit to start up
using a single Ni-Cad cell of 1.2V to 1.6V. When power is
first applied the 1.2V battery does not provide enough volt-
age to meet the minimum 2.2V supply voltage requirement.
The 22µF capacitor, when switched, temporarily doubles the
battery voltage to bias up the RC4190.
Cost is usually a primary consideration in battery powered
systems. The RC4190, guaranteed to work down to 2.2V, can
save the designer and end user money as well because bat-
tery costs decrease as the number of cells needed goes down.
1N914
D1
L
X
V
= +5V, 10 mA
D2
OUT
100 µH
Motorola
C
22 pF
F
MBR140P
4
R2
5
6
L
22 µF
33K
X
+V
S
7
V
BAT
1.2V
R1
1M
V
TPDT
FB
4190
I
R3
C
V
13K
GND
3
BAT
2
C
X
100 pF
65-2078
Figure 24. Bootstrapped Low Voltage Start-Up
18
RAYTHEON [ RAYTHEON COMPANY ]
