Design Note: Temperature Fault Detection and Recovery with a Quad Voltage Supervisor (3/15)

Standard Products
Design Note
Temperature Fault Detection and Recovery
with a Quad Voltage Supervisor
March 2015
www.aeroflex.com/HiRel
Overview
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The Quad Voltage Supervisors are useful in Fault Detection,
Isolation and Recovery (FDIR) schemes where they monitor
for system fault conditions then isolate and reset circuitry to
recover from these faults. One such application uses the
UT04VS33P Quad Voltage Supervisor and an RHD5962 Buffered Thermometer to monitor for temperature faults outside of a user-defined range. The RHD5962 thermometer
monitors the temperature source and generates a voltage
output that tracks linearly with temperature. The Quad
Supervisor uses its voltage comparator channels to define a
min/max tolerance range for the buffered thermometer
and generates error and reset flags whenever the monitored temperature moves outside this defined range.
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The RHD5962 Buffered Thermometer in Figure 1 behaves as
a temperature-controlled voltage reference that linearly
converts the measured temperature to a voltage, VTHERM.
A plot of voltages presented on the VTHERM pin over the
rated operating temperature range of -55°C to +125°C is
shown in Figure 2.
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Figure 1 UT04VS33P Voltage Supervisor with RHD5962 Temperature
Buffer connected for Temperature Fault Monitoring
Monitoring the VTHERM voltage for out- of-range events,
the UT04VS33P Quad Voltage Supervisor generates error
flags and resets to isolate and recover from temperature
faults.
The Quad Supervisor shown in Figure 1 contains four independent voltage comparators that measure the VINx inputs
against an internal reference voltage, VRFTH. The threshold
select inputs, TH0 and TH1, define internal resistor dividers
to adjust the VINx voltage for comparison to VRFTH.
Table 1 Quad Supervisor Input Voltage Threshold Selection
TH1
TH0
VIN1
VIN2
VIN3
VIN4
0
0
3.3
2.5
1.8
1.5
0
1
3.3
1.8
1.5
1.2
1
0
3.3
1.5
1.2
1
1
1
ADJ
ADJ
ADJ
ADJ
Figure 2 RHD5962 Linear temperature conversion
Temperature Fault Monitor Application
Adjustable threshold selection (TH1=TH0=1) requires external resistor dividers to adjust the VINx voltage.
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Figure 1 shows a notional schematic of the RHD5962 Buffered Thermometer and the UT04VS33P Quad Channel VoltAeroflex Microelectronic Solutions - HiRel
age Supervisor used in this application. Figure 3 shows the
lab set-up with the UT04VS33P Evaluation Board and the
RHD5962 Buffered Thermometer mounted to a TO-262
DPAK adapter board.
larly, the nominal threshold for over-voltage events on VIN3
is 1.029V (temperature = 30°C).
In the lab, a Thermonics Precision Temperature Forcing system adjusted the temperature on the RHD5962 Thermometer while an oscilloscope and voltmeter measured the
actual fault voltages. Table 2 summarizes the data. Table 4
shows a reset activated by an under-voltage/ cold fault,
while Table 5 depicts a reset removal when an over-voltage/hot fault returns to ambient range.
Table 2 Measured Voltage for Fault Reset and Removal
Condition
Reset/
Resetb
Calculated
Trigger (V)
Actual
Trigger (V)
Ambient to Cold
Active
0.872
0.876
Cold to Ambient
Removed
0.872
0.895
Ambient to Hot
Active
1.029
1.044
Hot to Ambient
Removed
1.029
1.025
Figure 3 UT04VS33P Voltage Supervisor Evaluation Board with RHD5962
Temperature Buffer mounted on a TO-262 adapter board.
The VTHERM output of the Buffered Thermometer connects
through a voltage divider to both the VIN1 and VIN3 comparator inputs on the Quad Supervisor. The over-voltage
select input, OVSH, is set HIGH to place the Supervisor in
over-voltage/under-voltage (OVSH) mode. In OVSH, the
Supervisor checks for under- voltage faults on channels
VIN1 and VIN2 and over-voltage faults on VIN3 and VIN4.
The combined fault comparison of VIN1 and VIN3 appears
at the VOUT1 output. The combined (that is, ANDed, logically) result of VIN2 and VIN4 appears at the VOUT2 output.
In OVSH mode, VOUT3 and VOUT4 are unused.
Enables EN1 and EN3 are HIGH to enable these two channels for monitoring while EN2 and EN4 are LOW to remove
these comparators from the analysis and eliminate their
effect on the system resets, RESET/RESETb. Threshold
selects TH0 and TH1 are set HIGH to select adjustable
threshold mode. External resistor dividers adjust the
VTHERM monitor voltage for comparison to the internal reference, VRFTH. The first resistor divider, R1 and R2, defines
the under-voltage threshold minimum as
VIN1=VTHERM*[R2/(R1+R2)]. The second resistor divider, R3
and R4, defines the over-voltage threshold maximum as
VIN3=VTHERM*[R4/(R3+R4)]. To define the voltage range in
this application, the resistance potentiometers on the evaluation board were set to measured values of R1=33.1kΩ,
R2=72.9kΩ, R3=44.7kΩ and R4=62.4kΩ. Assuming a nominal reference threshold voltage of 600mV for the
UT04VS33P, this defines a nominal threshold for under-voltage events on VIN1 of 0.872V (temperature = 15°C). Simi-
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Figure 4 Under-voltage / Cold Reset activated by voltage below threshold
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Figure 5 Over-voltage / Hot Reset Removal as voltage returns to ambient
Conclusions
In this application, the UT04VS33P Quad Voltage Supervisor
combines with an RHD5962 Buffered Thermometer to monitor a system for temperature faults. The Thermometer converted a temperature range to a voltage for comparison
with the Quad Supervisor. The Supervisor generated VOUT
and RESET signals for isolation and recovery from the
detected fault. The measured fault voltages varied from the
calculated values due to tolerances throughout the measurement system, the evaluation board components, and
the bandgap voltage and hysteresis of the UT04VS33P
device. The monitored temperature range for this application extends only to approximately -15°C. The Thermometer VTHERM voltage at this temperature is 600mV, which is
the internal reference voltage, VRFTH, generated for the
Supervisors comparators. Inserting a RHD5961 2.0V Precision Voltage Reference for positive voltage comparison
against the RHD5961 instead of VSS referencing would
extend the cold temperature VTHERM range for this application.
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