UCD9090
SLVSA30A –APRIL 2011–REVISED AUGUST 2011
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3. Divide 15.625MHz by 16 to obtain actual closest frequency of 976.563kHz.
4. Use Equation 2 to determine duty cycle resolution to obtain 6.25% duty cycle resolution.
All frequencies below 238Hz will have a duty cycle resolution of 0.0015%.
Programmable Multiphase PWMs
The FPWMs can be aligned with reference to their phase. The phase for each FPWM is configurable from 0° to
360°. This provides flexibility in PWM-based applications such as power-supply controller, digital clock
generation, and others. See an example of four FPWMs programmed to have phases at 0°, 90°, 180° and 270°
(Figure 20).
Figure 20. Multiphase PWMs
MARGINING
Margining is used in product validation testing to verify that the complete system works properly over all
conditions, including minimum and maximum power-supply voltages, load range, ambient temperature range,
and other relevant parameter variations. Margining can be controlled over PMBus using the OPERATION
command or by configuring two GPIO pins as margin-EN and margin-UP/DOWN inputs. The MARGIN_CONFIG
command in the UCD90xxx Sequencer and System Health Controller PMBus Command Reference describes
different available margining options, including ignoring faults while margining and using closed-loop margining to
trim the power-supply output voltage one time at power up.
Open-Loop Margining
Open-loop margining is done by connecting a power-supply feedback node to ground through one resistor and to
the margined power supply output (VOUT) through another resistor. The power-supply regulation loop responds to
the change in feedback node voltage by increasing or decreasing the power-supply output voltage to return the
feedback voltage to the original value. The voltage change is determined by the fixed resistor values and the
voltage at VOUT and ground. Two GPIO pins must be configured as open-drain outputs for connecting resistors
from the feedback node of each power supply to VOUT or ground.
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