6 2005 Semtech Corp. www.semtech.com
PRELIMINARYPOWER 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
FB
(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.
