MAX6829ZEUT-T Maxim Integrated, MAX6829ZEUT-T Datasheet - Page 10

• Manufacturer Part Number: MAX6829ZEUT-T
• Description: Supervisory Circuits
• Manufacturer: Maxim Integrated
• Series: MAX6826, MAX6827, MAX6828, MAX6829, MAX6830, MAX6831r

Specifications of MAX6829ZEUT-T

• Number Of Voltages Monitored: 2
• Monitored Voltage: 0.9 V to 2.5 V, 1.8 V to 5 V
• Undervoltage Threshold: 2.238 V, 0.806 V
• Overvoltage Threshold: 2.388 V, 0.86 V
• Output Type: Active Low, Push-Pull
• Manual Reset: Resettable
• Watchdog: Watchdog
• Battery Backup Switching: No Backup
• Power-up Reset Delay (typ): 320 ms
• Supply Voltage - Max: 5.5 V
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SOT-23
• Chip Enable Signals: No
• Maximum Power Dissipation: 696 mW
• Minimum Operating Temperature: - 40 C
• Power Fail Detection: No
• Supply Current (typ): 10 uA
• Supply Voltage - Min: 1.2 V

directly to the microcontroller’s RESET pin with a single
pullup resistor allows the device to assert a reset
(Figure 6).
These supervisors are relatively immune to short-dura-
tion, negative-going V
usually do not require the entire system to shut down.
Resets are issued to the µP during power-up, power-
down, and brownout conditions. The Typical Operating
Characteristics show a graph of the Maximum V
Transient Duration vs. Reset Threshold Overdrive, for
which reset pulses are not generated. The graph was
produced using negative-going V
the standard monitored voltage and ending below the
reset threshold by the magnitude indicated (reset
threshold overdrive). The graph shows the maximum
pulse width that a negative-going V
typically have without triggering a reset pulse. As the
amplitude of the transient increases (i.e., goes farther
below the reset threshold), the maximum allowable
pulse width decreases. Typically, a V
goes 100mV below the reset threshold and lasts for
20µs or less will not trigger a reset pulse.
The MAX6826–MAX6831 are guaranteed to operate
properly down to V
valid reset levels down to V
to active-low outputs (push/pull only, Figure 7) and a
pullup resistor to active-high outputs (push/pull only) will
ensure that the reset line is valid while the reset output
can no longer sink or source current. This scheme does
not work with the open-drain outputs of the
MAX6828/MAX6831. The resistor value used is not criti-
cal, but it must be small enough not to load the reset
output when V
slew rates greater than 1V/s, a 100kΩ is adequate.
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Figure 7. RESET Valid to V
10
______________________________________________________________________________________
CC
Negative-Going V
is above the reset threshold. For falling
CC
= 1V. In applications that require
MAX6826
MAX6829
CC
CC
Output Down to V
Ensuring a Valid RESET
V
GND
= Ground Circuit
CC
transients (glitches), which
CC
= 0, a pulldown resistor
RESET
CC
CC
pulses, starting at
CC
CC
Transients
transient can
transient that
R1
100kΩ
CC
= 0
CC
One way to help the watchdog timer monitor software
execution more closely is to set and reset the watchdog
input at different points in the program, rather than
pulsing the watchdog input high-low-high or low-high-
low. This technique avoids a stuck loop, in which the
watchdog timer would continue to be reset inside the
loop, keeping the watchdog from timing out.
Figure 8 shows an example of a flow diagram where the
I/O driving the watchdog input is set high at the begin-
ning of the program, set low at the beginning of every
subroutine or loop, then set high again when the pro-
gram returns to the beginning. If the program should
hang in any subroutine, the problem would quickly be
corrected, since the I/O is continually set low and the
watchdog timer is allowed to time out, causing a reset
or interrupt to be issued. As described in the Watchdog
Input Current section, this scheme results in higher time
average WDI input current than does leaving WDI low
for the majority of the timeout period and periodically
pulsing it low-high-low.
Figure 8. Watchdog Flow Diagram
Watchdog Software Considerations
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
PROGRAM
SET WDI
RETURN
START
CODE
HIGH