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• Motherboard Power Regulation for Computers
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The APW6021 provides the power control and pro-
tection for four output voltages in high-performance,
graphics intensive microprocessor and computer
applications. The IC integrates voltage-mode PWM
controller and three linear controllers, as well as the
monitoring and protection functions into a 28-pin SOIC
package. The PWM controller regulates the micro-
processor core voltage with a synchronous-rectified
buck converter. The linear controllers regulate the
computer system’s AGP 1.5V or 3.3V bus power, the
1.5V GTL bus power, and the 1.8V power for the
North/South Bridge core voltage and/or cache
memory circuits. The APW6021 includes an Intel-
compatible, TTL 5-input digital-to-analog converter
(DAC) that adjusts the core PWM output voltage from
1.3 V
DC
to 2.05 V
DC
in 0.05V steps and from 2.1 V
DC
to
3.5 V
DC
in 0.1V increments. The precision reference
and voltage-mode control provide ±1% static
regulation. The AGP bus power linear controller’s
output (V
OUT2
) is user-selectable, through a TTL-com-
patible signal applied at the SELECT pin, for levels of
1.5V or 3.3V with ±3% accuracy. Based on the sta-
tus of the FIX pin, the other two linear regulators pro-
vide either fixed output voltages of 1.5V± 3% (V
OUT3
)
and 1.8V±3% (V
OUT4
), or user-adjustable by means
of an external resistor divider. All linear controllers
can employ either N-channel MOSFETs or bipolar
NPNs for the pass transistor.
The APW6021 monitors all the output voltages. A
single Power Good signal is issued when the core is
within ±10% of the DAC setting and all other outputs
are above their under-voltage levels. Additional built-
in over-voltage protection for the core output uses
the lower MOSFET to prevent output voltages above
115% of the DAC setting. The PWM controller’s over-
current function monitors the output current by using
the voltage drop across the upper MOSFET’s r
DS(ON)
.
• 4 Regulated Voltages are provided
• Microprocessor Core (1.3V to 3.5V)
• AGP Bus (1.5V or 3.3V)
• Memory (1.8V)
• GTL Bus (1.5V)
• Linear Controllers Drives with both MOSFET
and Bipolar Series Pass Transistors
• Fixed or Externally Resistor-Adjustable Linear
Outputs (FIX Pin)
• Simple Single-Loop Control Design
• Voltage-Mode PWM Control
• Fast PWM Converter Transient Response
• High-Bandwidth Error Amplifier
• Full 0% to 100% Duty Ratio
• Excellent Output Voltage Regulation
• Core PWM Output: ± 1% Over Temperature
• Other Outputs: ± 3% Over Temperature
• TTL-Compatible 5- Bit DAC Microprocessor
Core Output Voltage Selection
• Wide Range - 1.3V
DC
to 3.5 V
DC
• Power-Good Output Voltage Monitor
• Over-Voltage and Over-Current Fault Monitors
• Switching Regulator Does Not Require
Extra Current Sensing Element, Uses
MOSFET’s r
DS(ON)
• Small Converter Size
• Constant Frequency Operation
• 200kHz Free-Running Oscillator; Program-
mable From 50kHz to Over 1MHz