TC105333ECT datasheet(6/14 Pages) MICROCHIP

Part #	TC105333ECT

Description	PFM/PWM Step-Down DC/DC Controller

PDF	14 Pages

Scroll/Zoom	100%

Manufacturer	MICROCHIP [Microchip Technology]

Direct Link	http://www.microchip.com

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6 / 14 page

TC105

DS21349C-page 6

 2001-2012 Microchip Technology Inc.

4.0

APPLICATIONS

4.1

Circuit Examples

Figure 4-3 shows a TC105 using a PNP switching

transistor (Zetex FZT749) that has an hFE of 180 and

VCESAT of 100 mV at IC = 1A. Other high beta transis-

tors can be used, but the values of RB and CB may

need adjustment if hFE is significantly different from that

of the FZT749.

The circuit of Figure 4-4 utilizes a P-channel MOSFET

switching transistor (Silconix Si9430). This transistor is

a member of the Littlefoot™ family of small outline

MOSFETs.

FIGURE 4-1:

SOFT START CIRCUIT

FIGURE 4-2:

EXTERNAL TRANSISTOR CONNECTION

TC105

SHDN

SHDN/SS

TC105

VIN

CSS

0.033

µF

SHDN/SS

Shutdown Not Used

RSS

470K

Shutdown Used

OFF

(From System

Control Logic)

–

RSS

470K

CSS

0.033

µF

TC105

VIN

VOUT

EXT

TC105

VIN

VOUT

EXT

P-Channel MOSFET

PNP Bipolar Transistor

–

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