SC2434SWTR datasheet(6/19 Pages) SEMTECH

6 / 19 page

 2005 Semtech Corp.

www.semtech.com

PRELIMINARY

POWER MANAGEMENT

SC2434

Theory of Operation

The simplified voltage regulator (VR) based on SC2434

is depicted in Fig. 1. The key timing chart is also shown

in the same picture. The 12V input power passes through

the input filter establishing the input power rail. The cur-

rent sensing resistor located at positive input rail moni-

tors the top FET currents of all the phases. An internal

differential amplifier amplifies the voltage across the

current sensing resistor. The output of the current am-

plifier and an internally generated saw tooth ramp signal

are added together to be the PWM carrier signal. This

signal meets the output of the error amplifier at the pulse

width modulator (PWM). The output of the PWM is then

divided into three phases alternately to be the inputs of

the synchronous drivers.

Feedback and Regulation

The feedback circuitry reads the regulator output volt-

age and compares it with an accurately trimmed bandgap

voltage reference, which is 1.5V with less then 0.8% tol-

erance. The compensation network allows optimization

of the control-loop for system stability and fast transient

responses.

Applications Information

Flexible VID

The VID circuitry reads the 5 bit digital command and

converts it into a current flowing into the inverting input

pin of the error amplifier. The output current of the DAC

produces a voltage offset on the feedback resistor, R

(see Fig. 1), which changes the set point of the converter

output voltage for different VID combinations.

Active Voltage Positioning

By programming the gain of the error amplifier, one can

easily and accurately implement adaptive output voltage

positioning. This is equivalent to programming the VR

output impedance in an active manner. The advantage

of allowing the VR certain output impedance (typically

1~3 mOhm) is that one can use a minimum amount of

high quality output bulk capacitors to meet the voltage

regulation requirement. Hence, the cost and the size of

the VR solution can be significantly reduced.

SC2434

Fig.1 - The simplified voltage regulator based on SC2434.

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