Rainbow Electronics MAX16055 - Manual (Page 7)

The MAX16055 is immune to short IN_ transients. Each
of the internal comparators provides a typical hystere-
sis of 0.3% with respect to the reset threshold. This
built-in hysteresis improves the monitor’s immunity to
ambient noise without significantly reducing threshold
accuracy. See the
Typical Operating Characteristics for
a glitch immunity graph labeled Maximum IN_ Transient
Duration vs. Reset Threshold Overdrive.
Reset Output
The MAX16055 RESET output asserts low when any
monitored IN_ voltage drops below the specified reset
threshold. RESET remains low for the reset timeout peri-
od of 140ms (min) after all inputs rise above the
respective thresholds (Figure 2). The RESET output is
open drain with a weak internal pullup to the monitored
IN1 supply (70µA typ). For many applications, no exter-
nal pullup resistor is required to interface with other
logic devices. Apply an external pullup resistor to any
voltage from 0 to 5.5V when interfacing to different
logic-supply voltages (Figure 3). Internal circuitry pre-
vents reverse current flow from the external pullup volt-
age into the RESET output when RESET is not asserted.
RESET asserts low upon power-up. After all IN_ inputs
rise above the respective threshold voltages, RESET
remains low for the reset timeout period (Figure 4)
before going high.
IN1 powers the MAX16055 and is also a monitored volt-
age. When any monitored supply drops below the
threshold voltage, RESET asserts low and remains low
while either IN1 or IN2 is above 1.0V.
Adjustable Thresholds
The MAX16055 includes monitor options with
adjustable reset thresholds. The threshold voltage at
each adjustable IN_ input is typically 0.5V. To monitor a
voltage higher than 0.5V, connect a resistor-divider net-
work to the circuit as shown in Figure 5:
V
INTH
= 0.5V x (R1 + R2)/R2
Therefore:
R1 = R2 ((V
INTH
/0.5V) - 1)
Use high valued resistors (~ 100k
Ω) to minimize current
through the external resistors. Use lower valued resis-
tors for greater accuracy. The MAX16055 includes an
internal voltage clamp (1.5V typ) at each of the
adjustable voltage inputs. An input voltage higher than
1.5V induces a higher input current.
MAX16055
Ultra-Small, Hex Voltage,
Microprocessor Supervisor
_______________________________________________________________________________________ 7
V TH_ + V HYST
RESET
IN_
V TH_
90%
10%
t RP t RD
Figure 2. RESET Output Timing Diagram
MAX16055
µP
RESET
RESET
+3.3V
V CC
10k Ω
GND GND
IN1
+5V
Figure 3. Interfacing with External Logic-Supply Voltage