MAX6854 MAXIM [Maxim Integrated Products], MAX6854 Datasheet - Page 12

• Manufacturer Part Number: MAX6854
• Description: Nanopower uP Supervisory Circuits with Manual Reset and Watchdog Timer
• Manufacturer: MAXIM [Maxim Integrated Products]

In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, the MAX6854/
MAX6855/MAX6856/MAX6858/MAX6860–MAX6869 are
relatively immune to short-duration supply transients, or
glitches. The Maximum V
Threshold Overdrive graph in the Typical Operating
Characteristics shows this relationship.
The area below the curve of the graph is the region in
which these devices typically do not generate a reset
pulse. This graph was generated using a falling pulse
applied to V
threshold, V
threshold overdrive). As the magnitude of the transient
increases, the maximum allowable pulse width
decreases. Typically, a 100mV V
of 40µs or less does not cause a reset.
The open-drain RESET output can be used to interface
to a µP with other logic levels. As shown in
open-drain output can be connected to voltages from 0
to 5.5V.
Generally, the pullup resistor connected to RESET con-
nects to the supply voltage that is being monitored at
the IC’s V
Nanopower µP Supervisory Circuits with
Manual Reset and Watchdog Timer
Figure
12
______________________________________________________________________________________
Interfacing to Other Voltages for Logic
4. Interfacing with Other Voltage Levels
CC
MAX6856
MAX6860
MAX6863
MAX6866
MAX6869
TH
CC
GND
1.8V
V
CC
input. However, some systems use the
, and ending below this threshold (reset-
, starting 100mV above the actual reset
N
RESET
CC
Transient Duration vs. Reset
Transient Immunity
100kΩ
CC
RESET
transient duration
Compatibility
Figure
GND
3.3V
V
µP
CC
4, the
open-drain output to level-shift from the monitored sup-
ply to reset circuitry powered by another supply voltage.
Keep in mind that as the supervisor’s V
so does the IC’s ability to sink current at RESET.
When V
capability declines drastically. The high-impedance
CMOS logic inputs connected to RESET can drift to
undetermined voltages. This presents no problems in
most applications, since most µPs and other circuitry
do not operate with V
In those applications where RESET must be valid down
to 0, add a pulldown resistor between RESET and GND
for the MAX6854/MAX6858/MAX6861/MAX6864/
MAX6867 push-pull outputs. The resistor sinks any stray
leakage currents, holding RESET low
a pulldown resistor that accommodates leakages, such
that RESET is not significantly loaded and is capable of
pulling to GND. The external pulldown cannot be used
with the open-drain reset outputs.
One way to help the watchdog timer monitor software
execution more closely is to set and reset the watchdog
Figure
Ensuring a Valid RESET Down to V
5. Ensuring RESET Valid to V CC = Ground
CC
Watchdog Software Considerations
falls below 1.1V, RESET’s current-sinking
MAX6854
MAX6858
MAX6861
MAX6864
MAX6867
GND
CC
below 1.1V.
RESET
V
CC
(Push-Pull RESET )
V
CC
(Figure
2MΩ
CC
decreases,
5). Choose
CC
= 0V