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• Motherboard Power Regulation for Computers
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The APW6021A 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 synchronous-rectified buck converter
includes an Intel-compatible , TTL 5-input digital-to-
analog converter (DAC)that adjusts the core PWM
output voltage from 1.3V
DC
to 2.05V
DC
in 0.05V steps
and from 2.1V
DC
to 3.5V
DC
in 0.1V increments. the
precision reference and voltage-mode control provide
±1% static regulation. A TTL-compatible signal ap-
plied to the SELECT pin dictates which method of
control is used for the AGP bus power : a low state
results in linear control of the AGP bus to 1.5V , while
a high state transitions the output through a linearly
controlled softstart to 3.3V , followed by full enhance-
ment of the external MOSFET to pass the input
voltage. The other two linear regulators provide fixed
output voltages of 1.5V GTL bus power and 1.8V
power for the North/South Bridge core and/or cache
memory. These levels are user-adjustable by means
of an external resistor divider and pulling the FIX pin
low. All linear controllers can employ either N-Chan-
nel MOSFETs or bipolar NPNs for the pass transistor.
The APW6021A 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)
• 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
• Shutdown Feature Removed When All Inputs
High
• 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 Upper
MOSFET’s r
DS(ON)
• Small Converter Size
• Constant Frequency Operation
• 200kHz Free-Running Oscillator; Program-
mable From 50kHz to Over 1MHz