MAX6800_05 Datasheet, PDF (4/7 Pages) Maxim Integrated Products – 3-Pin, Low-Power uP Reset Circuits

3-Pin, Low-Power
µP Reset Circuits
Applications Information
Interfacing to µPs with Bidirectional
Reset Pins
Since the RESET output on the MAX6802 is open-drain,
this device interfaces easily with µPs that have bidirec-
tional reset pins, such as the Motorola 68HC11.
Connecting the µP supervisor’s RESET output directly
to the microcontroller’s (µC’s) RESET pin with a single
pullup resistor allows either device to assert reset
(Figure 1).
Negative-Going V_CC Transients
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, these devices are
relatively immune to short-duration, negative-going V_CC
transients (glitches). The Typical Operating Characteristics
show the Maximum Transient Duration vs. Reset
Comparator Overdrive graph. The graph shows the maxi-
mum pulse width that a negative-going V_CC transient may
typically have without issuing a reset signal. As the ampli-
tude of the transient increases, the maximum allowable
pulse width decreases.
V_CC
V_CC
MAX6802
RESET
GND
V_CC
100kΩ
µP
MOTOROLA
68HCXX
RESET
GND
Figure 1. Interfacing to µPs with Bidirectional Reset Pins
Pin Configuration
V_CC
V_CC
MAX6801
RESET
GND
(a)
100kΩ
MAX6800
RESET
GND
(b)
*ASSUMES HIGH-Z RESET INPUT TO THE µP
Figure 2. Ensuring Reset Valid Down to V_CC = 0
100kΩ*
Typical Operating Circuit
TOP VIEW
GND 1
MAX6800
MAX6801
MAX6802
3 V_CC
V_CC
V_CC
MAX6801
RESET
V_CC
µP
RESET
RESET (RESET) 2
( ) ARE FOR MAX6800
SOT23-3
GND
GND
4 _______________________________________________________________________________________