RC4190M datasheet(18/25 Pages) RAYTHEON

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PRODUCT SPECIFICATION

RC4190

Background Information

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.

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.

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.

Soft Start

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

0.1

µF range.

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 22

µF capacitor, when switched, temporarily doubles the

battery voltage to bias up the RC4190.

65-2076

RC4190

+VS

Figure 24. Bootstrapped Low Voltage Start-Up

65-2078

100

µH

1N914

Motorola

MBR140P

33K

VOUT = +5V, 10 mA

22 pF

13K

4190

GND

µF

TPDT

VBAT

1.2V

100 pF

+VS

VFB

VBAT

RC4190M Datasheet(PDF) 18 Page - Raytheon Company

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