SC4502 datasheet(12/19 Pages) SEMTECH

12 / 19 page

 2005 Semtech Corp.

POWER MANAGEMENT

SC4502/SC4502H

www.semtech.com

with

L >

Example: Increase the turn on voltage of a V

IN = 3.3V boost

converter from 1.4V to 2.75V.

Using V

H = 2.75V and R4 = 100KΩ in (12),

Ω

= 150K

The resulting UVLO hysteresis is:

The turn off voltage is:

Figure 6. Programmable Hysteretic UVLO Circuit

1.4V

2.06V

0.69V

2.75V

HYS

−

Frequency Compensation

Figure 7 shows the equivalent circuit of a boost converter

using the SC4502/SC4502H. The output filter capacitor

and the load form an output pole at frequency:

OUT

⋅

(13)

where C

2 is the output capacitance and

OUT

the equivalent load resistance.

The zero formed by C

2 and its equivalent series resistance

(ESR) is neglected due to low ESR of the ceramic output

capacitor.

There is also a right half plane (RHP) zero with angular

frequency:

()

OUT

−

⋅

(14)

z2 decreases with increasing duty cycle D and increasing

OUT. Using the 5V to 12V boost regulator (1.4MHz) in

Figure 1(a) as an example,

Ω

≥

0.5A

OUT

Figure 7. Simplified Block Diagram of a Boost Converter

POWER

STAGE

REFERENCE

VOLTAGE

1.242V

COMP

ESR

ROUT

VOUT

VIN

IOUT

Applications Information

SC4502/SC4502H

SHDN

6/8

1.1V

4.6

µA

I HYS

COMPARATOR

SWITCH CLOSED

WHEN Y = “1”

0.69V

150K

4.6

HYS

Ω

•

SC4502 датащи(PDF) 12 Page - Semtech Corporation

SC4502 датащи(HTML) 12 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

датащи скачать

ссылки URL