Rainbow Electronics LM93 - Manual (Page 15)

12.0 Functional Description
(Continued)
Value Register V
IN
% ∆ from −12V
77 -11.6758 2.7014
78 -11.6511 2.9072
79 -11.6264 3.1130
80 -11.6018 3.3188
81 -11.5771 3.5245
82 -11.5524 3.7303
83 -11.5277 3.9361
84 -11.5030 4.1418
85 -11.4783 4.3476
86 -11.4536 4.5534
87 -11.4289 4.7591
88 -11.4042 4.9649
89 -11.3795 5.1707
90 -11.3548 5.3765
91 -11.3301 5.5822
92 -11.3054 5.7880
93 -11.2807 5.9938
94 -11.2561 6.1995
95 -11.2314 6.4053
96 -11.2067 6.6111
97 -11.1820 6.8168
98 -11.1573 7.0226
99 -11.1326 7.2284
100 -11.1079 7.4342
101 -11.0832 7.6399
102 -11.0585 7.8457
103 -11.0338 8.0515
104 -11.0091 8.2572
105 -10.9844 8.4630
106 -10.9597 8.6688
107 -10.9351 8.8745
108 -10.9104 9.0803
109 -10.8857 9.2861
110 -10.8610 9.4919
111 -10.8363 9.6976
112 -10.8116 9.9034
113 -10.7869 10.1092
12.7 DYNAMIC Vccp MONITORING USING VID
The AD_IN7 (CPU1 Vccp) and AD_IN8 (CPU2 Vccp) inputs
are dynamically monitored using the P1_VIDx and P2_VIDx
inputs to determine the limits. The dynamic comparisons
operate independently of the static comparisons which use
the statically programmed limits.
According to the VRM/VRD 10 specification when a VID
signal is ramping to a new value, it steps by one LSB at a
time, and one step occurs every 5 µs. In worse case, up to
20 steps may occur at once over 100 µs. The Vccp voltage
from the VRD has to settle to the new value within 50 µs of
the last VID change. The LM93 expects that the VID
changes will not occur more frequently than every 5 µs.
The VID signal can be changed by the processor under
program control, by internal thermal events or by external
control, like force PROCHOT.
The reference voltages selected by each value of the 6 bit
VID can be found in the VRM/VRD 10 spec. Transient VID
values caused by line-to-line skew are ignored by the LM93.
See the VRM/VRD 10 spec for the worst case line-to-line
skew.
The LM93 averages the VID values over a sampling window
to determine the average voltage that the VID input was
indicating during the sampling window. At the completion of a
voltage conversion cycle the LM93 performs limit compari-
sons based on average VID values and not instantaneous
values. The upper limit is determined by adding the upper
limit offset to the average voltage indicated by VID. The
lower limit is determined by subtracting the lower limit offset
from average voltage indicated by VID. If the AD_IN7 (or
AD_IN8) voltage falls outside the upper and lower limits, an
error event is generated. Dynamic and static comparisons
are performed once every 100 ms. The averaging time inter-
val is 1.5 ms.
If at any time during the Vccp sampling window, the VID
code indicates that the VRD should turn off its output, the
dynamic Vccp checking is disabled for that sample.
The comparison accuracy is ± 25 mV, therefore the compari-
son limits must be set to include this error. Since the Vccp
voltage may be in the process of settling to a new value (due
to a VID change), this settling should be taken into account
when setting the upper and lower limit offsets.
The LM93 has a limitation on the upper limit voltage for
dynamic Vccp checking. The upper limit cannot exceed
1.5875V. If the sum of the voltage indicated by VID and the
upper offset voltage exceed 1.5875, the upper limit checking
is disabled.
12.8 V
REF
OUTPUT
V
REF
is a fixed voltage to be used by an external VRD or as
a voltage reference input for the BMC A/D inputs. V
REF
is
2.5V ± 1%. There is internal current limit protection for the
V
REF
output in case it gets shorted to supply or ground
accidentally.
12.9 PROCHOT BACKGROUND INFORMATION
PROCHOT is an output from a processor that indicates that
the processor has reached a predetermined temperature trip
point. At this trip point the processor can be programmed to
lower its internal operating frequency and/or lower its supply
voltage by changing the value of the 6 bit VID that it supplies
to the VRD. The final VID setting and the rate at which it
transitions to the new VID is programmable within the pro-
cessor.
If PROCHOT is 100% throttled, it does not mean that the
CPU is not executing, but it may mean that the CPU is about
to encounter a thermal trip if the processor temperature
continues to rise.
PROCHOT is also an input to some processors so that an
external controller can force a thermal throttle based on
external events.
PROCHOT is no longer asserted by the processor when the
temperature drops below the predefined thermal trip point.
Oscillation around the trip point is avoided by the processor
by requiring that the temperature be above/below the trip
point for a predetermined period of time. A counter inside the
processor is used to track this time and it has to be incre-
LM93
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