PI1004-1 Datasheet, PDF (6/16 Pages) Vicor Corporation – Programmable Point-of-Load Controller with 6-bit VID

Functional Description
The block diagram in Figure 2 shows that the PI1004-1 has
a programmed VID offset function and no OVP function.
Figure 3 shows the PI1004-2 with the OVP function in
place of the VID offset. Unless otherwise stated please
refer to Figure 2 and application diagram Figure 4a for
the following description.
Voltage identification and Reference Out
The REFOUT output pin provides a scaled temperature
stable reference voltage (see temperature curves in figure
15) that is incremented by the VID input state decoding
and DAC (digital to analog converter) function. The 6 bit
DAC provides a minimum increment resolution of 12.5mV.
The VR10.X VID code accuracy shown in Table 1 is
measured at the output of the error amp in the unity gain
buffer configuration.
REFOUT will be determined by VID[5:0] according to the
Intel VR10.X Voltage Identification Table. In a typical CPU
application using AVP (Adaptive Voltage Positioning)
REFIN is tied directly to REFOUT and EAIP is tied to REFOUT
through a resistor for AVP adjustment. VID = x1111 is
treated as a fault and sets the Fault Latch function that
will be explained further in the other sections.
Current Sensing and AVP
Pins ISN and ISP form the input to a differential voltage
sense amplifier that can be used for current sensing and
adaptive voltage positioning (AVP). The amplifier has a
narrow common mode input range for ground reference
voltages.
The AVP amplifier has a fixed gain of 4 to amplify the
voltage across a sense resistor that is representative of the
load current. The output voltage of the amplifier is fed to
a unity gain buffer and impressed across the external RG
resistor converting the voltage to a current that is
reflected as a sink current at the IAVP pin 15.
The PI-1004-1 has a second voltage to current converter to
create the OFFSET function with a fixed reference voltage
of 250mV that is impressed across an external ROFFSET
resistor. This voltage to current conversion reflects a fixed
sink current at the IAVP pin. The sum of these two currents
flows through the external resistor, RAVP when connected
as shown in figure 4a completing the adaptive and offset
functions. The control error amplifier input voltage will be
dependent on the reference determined by the VID input
state, minus any programmed offset voltage, minus the
AVP correction for load setting the slope of the load line.
The IAVP pin is set up to provide a current proportional to
the load current. Various load lines can be selected by
choosing values of the output current shunt resistor, RG
and the resistor between REFOUT and EAIP (RAVP) for the
proper droop. The value of the current shunt should be
chosen for a voltage drop of 135mV or slightly lower at
full load.
Differential Output Voltage Sense
The core control error amplifier has two non-inverting
inputs to accommodate a soft start feature. With the
proper non-faulted conditions the soft-start charging
current of 5uA will be sourced out of the SS pin to an
external capacitor. This feature provides the ability to
control the rate of rise in the output voltage up to the
point of regulation. The fault conditions are defined in the
fault circuitry section and listed in Table 2. If a fault
condition exits the internal sink transistor will hold the SS
pin to the signal ground potential. Recovery from any of
the fault conditions will result in a full soft-start interval.
The lower of the two non-inverting inputs of the error
amplifier will dominate. When all faults are cleared the SS
input provides the dominant ramping input voltage until
it exceeds the EAIP reference. The SS input continues to
ramp to the soft-start clamp voltage while the EAIP
ENABLE
L
H
INPUTS
UVLO
X
H
VID[5:0]
X
X
OUTPUTS
OVP
PWRGD
REFOUT
EAO
SS
L
L
L
L
L
(Limited drive)
L
L
≤ VID
L
L
H
VID Valid
Active
Active
VID
H
L
VID Valid
Active
Active
VID
Active
H
H
L
X11111
Active
Active
VID
L
L
ENABLE Low = Off UVLO High = VCC is low OVP High = Fault PWRGD Low = Fault VID = See VID Table 1
Table 2. I/O Functional States
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PI1004 Data Sheet Rev. 2.5 Page 6 of 16