MC33163 查看數據表（PDF） - Motorola => Freescale

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MC33163

POWER SWITCHING REGULATORS

Motorola => Freescale 

MC34163 MC33163

Figures 11 and 12 show that the Current Sense

comparator threshold is tightly controlled over temperature

and has a typical input bias current of 1.0 µA. The

propagation delay from the comparator input to the Output

Switch is typically 200 ns. The parasitic inductance

associated with RSC and the circuit layout should be

minimized. This will prevent unwanted voltage spikes that

may falsely trip the Current Limit comparator.

Internal thermal shutdown circuitry is provided to protect

the IC in the event that the maximum junction temperature is

exceeded. When activated, typically at 170°C, the Latch is

forced into the “Set” state, disabling the Output Switch. This

feature is provided to prevent catastrophic failures from

accidental device overheating. It is not intended to be used

as a replacement for proper heatsinking.

Driver and Output Switch

To aid in system design flexibility and conversion

efficiency, the driver current source and collector, and output

switch collector and emitter are pinned out separately. This

allows the designer the option of driving the output switch into

saturation with a selected force gain or driving it near

saturation when connected as a Darlington. The output

switch has a typical current gain of 70 at 2.5 A and is

designed to switch a maximum of 40 V collector to emitter,

with up to 3.4 A peak collector current. The minimum value for

RSC is:

+ + RSC(min)

0.25 V

3.4 A

0.0735 Ω

When configured for step–down or voltage–inverting

applications, as in Figures 20 and 24, the inductor will forward

bias the output rectifier when the switch turns off. Rectifiers

with a high forward voltage drop or long turn–on delay time

should not be used. If the emitter is allowed to go sufficiently

negative, collector current will flow, causing additional device

heating and reduced conversion efficiency.

Figure 9 shows that by clamping the emitter to 0.5 V, the

collector current will be in the range 10 µA over temperature.

A 1N5822 or equivalent Schottky barrier rectifier is

recommended to fulfill these requirements.

A bootstrap input is provided to reduce the output switch

saturation voltage in step–down and voltage–inverting

converter applications. This input is connected through a

series resistor and capacitor to the switch emitter and is used

to raise the internal 2.0 mA bias current source above VCC.

An internal zener limits the bootstrap input voltage to VCC

+7.0 V. The capacitor’s equivalent series resistance must

limit the zener current to less than 100 mA. An additional

series resistor may be required when using tantalum or other

low ESR capacitors. The equation below is used to calculate

a minimum value bootstrap capacitor based on a minimum

zener voltage and an upper limit current source.

+ + + CB(min)

I

∆t

∆V

4.0 mA

ton

4.0 V

0.001 ton

Parametric operation of the MC34163 is guaranteed over

a supply voltage range of 2.5 V to 40 V. When operating

below 3.0 V, the Bootstrap Input should be connected to VCC.

Figure 15 shows that functional operation down to 1.7 V at

room temperature is possible.

Package

The MC34163 is contained in a heatsinkable 16–lead

plastic dual–in–line package in which the die is mounted on a

special heat tab copper alloy lead frame. This tab consists of

the four center ground pins that are specifically designed to

improve thermal conduction from the die to the circuit board.

Figures 16 and 17 show a simple and effective method of

utilizing the printed circuit board medium as a heat dissipater

by soldering these pins to an adequate area of copper foil.

This permits the use of standard layout and mounting

practices while having the ability to halve the junction–to–air

thermal resistance. These examples are for a symmetrical

layout on a single–sided board with two ounce per square

foot of copper.

APPLICATIONS

The following converter applications show the simplicity

and flexibility of this circuit architecture. Three main converter

topologies are demonstrated with actual test data shown

below each of the circuit diagrams.

MOTOROLA ANALOG IC DEVICE DATA

9

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