LTC2933
10
2933fa
For more information www.linear.com/LTC2933
operaTion
Figure 1. 1% Threshold Accuracy Improves System Reliability
NOMINAL SUPPLY VOLTAGE
SUPPLY TOLERANCE
MINIMUM RELIABLE
SYSTEM VOLTAGE
2933 F01
5V
4.5V
4.4V
4.45V
–10%
–12%
–11%
REGION OF POTENTIAL MALFUNCTION
IDEAL SUPERVISOR
THRESHOLD
The LTC2933 can perform the following operations:
• Accept I
2
C bus programming commands.
• Simultaneously monitor up to six inputs with respect
to programmed fault limits.
• Configure and monitor for OV/UV faults using two
independent comparators per channel.
• Configure two general purpose inputs as manual reset
(MR), undervoltage disable (UVDIS), margin (MARG)
or auxiliary comparator (AUXC) inputs.
• Configure three general purpose inputs/outputs
(GPIO
n
) to output faults, inputs from GPI
n
or from
other GPIO
n
.
• Independently select each general purpose output
polarity and type (open-drain or weak pull-up).
• Independently select each general purpose output
response delay-on-release (with respect to the mo
-
ment its condition is internally cleared).
•
Generate interrupt (ALERT) signals in response to any
voltage faults, as well as the logic state of the inputs.
• Store register contents to EEPROM.
• Store voltage and timing fault history to EEPROM.
• Restore EEPROM contents into the operating memory,
by I
2
C command and at power-up.
• Report voltage fault status and history.
• Software write-protect the operating memory.
Threshold Accuracy
The LTC2933 ±1% threshold accuracy specification
improves the reliability of the system over supervisors
with wider threshold tolerances. A less accurate voltage
supervisor increases the required system voltage margin.
This in turn increases the probability of system malfunction.
Consider a 5V ±10% supply: it may vary between 4.5V and
5.5V and the circuitry powered by it must operate reliably
within this band. An ideal, perfectly accurate supervisor
would generate a reset at exactly 4.5V. The LTC2933
threshold varies ±1% around the nominal threshold volt
-
age, in the medium range, if the selected value is greater
than 3V. The reset threshold band and the power supply
tolerance bands should not overlap, in order to prevent
false
alarms when the power supply actually meets its
specified tolerance band (see Figure 1).
A ±10% threshold is usually set to 11% below the nominal
input voltage, or 4.45V in this example. The threshold is
guaranteed to be within the 4.4V to 4.5V band over tem
-
perature. To prevent malfunction, the powered system
must operate reliably down to
4.4V.
