RC4190M datasheet(6/25 Pages) RAYTHEON

6 / 25 page

PRODUCT SPECIFICATION

RC4190

Principles of Operation

Simple Step-Up Converter

The most common application, the step-up regulator, is

derived from a simple step-up (VOUT > VBAT) DC-to-EC

Converter (Figure 6).

Figure 6. Simple Set-Up

When switch S is closed, the battery voltage is applied

across the inductor L. Charging current ﬂows through the

inductor, building up a magnetic ﬁeld, increasing as the

switch is held closed. While the switch is closed, the diode D

is reverse biased (open circuit) and current is supplied to the

load by the capacitor C. Until the switch is opened, the

inductor current will increase linearly to a maximum value

determined by the battery voltage, inductor value, and the

amount of time the switch is held closed (IMAX = VBAT/

L x TON). When the switch is opened, the magnetic ﬁeld

collapses, and the energy stored in the magnetic ﬁeld is

converted into a discharge current which ﬂows through the

inductor in the same direction as the charging current.

Because there is no path for current to ﬂow through the

switch, the current must ﬂow through the switch, the current

must ﬂow through the diode to supply the load and charge

the output capacitor.

(+)

(–)

VOUT

BAT

65-1646

If the switch is opened and closed repeatedly, at a rate much

greater than the time constant of the output RC, then a

constant dc voltage will be produced at the output.

An output voltage higher than the input voltage is possible

because of the high voltage produced by a rapid change of

current in the inductor. When the switch is opened, the

inductor voltage will instantly rise high enough to forward

bias the diode, to VOUT + VD.

In the complete RC4190 regulator, a feedback control sys-

tem adjusts the on time of the switch, controlling the level of

inductor current, so that the average inductor discharge

current equals the load current, thus regulating the output

voltage.

Complete Step-Up Regulator

A complete schematic of the minimum step-up application is

shown in Figure 7. The ideal switch in the DC-to-DC

Converter diagram is replaced by an open collector NPN

transistor Q1. CF functions as the output ﬁlter capacitor, and

D1 and LX replace D and L.

When power is ﬁrst applied, the current in R1 supplies bias

current to pin 6 (IC). This current is stabilized by a unity gain

current source ampliﬁer and then used as bias current for the

1.31V bandgap reference. A very stable bias current gener-

ated by the bandgap is mirrored and used to bias the remain-

der of the chip. At the same time the RC4190 is starting up,

current will ﬂow through the inductor and the diode to

charge the output capacitor to VBAT – VD.

Figure 7. Complete Step-Up Regulator

REF

VFB

GND

VBAT

+VS

ILX

–

OSC

RC4190

LBR

LBD

+1.31V

ILOAD

VOUT = VREF (

+ 1)

(+)

(–)

65-2673A

RC4190M Datasheet(PDF) 6 Page - Raytheon Company

RC4190M Datasheet(HTML) 6 Page - Raytheon Company

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Datasheet Download

Link URL