MAX6443 MAXIM [Maxim Integrated Products], MAX6443 Datasheet - Page 8

• Manufacturer Part Number: MAX6443
• Description: ?P Reset Circuits with Long Manual Reset Setup Period
• Manufacturer: MAXIM [Maxim Integrated Products]

µP Reset Circuits with Long Manual Reset
Setup Period
Figure 7. MAX6451/MAX6452 Application Circuit
a microprocessor for general-purpose I/O control. MR2
monitors a switch to detect when a smart card is inserted.
When the switch is closed high (card inserted), RESET
one-shot pulses low for 140ms. MR2 is internally
debounced for 210ms to prevent false resets when the
smart card is removed.
The open-drain RESET output can be used to interface
to a µP with other logic levels. As shown in Figure 8, the
open-drain output can be connected to voltages from 0
to 6V.
Generally, the pullup resistor connected to the RESET
connects to the supply voltage that is being monitored
at the IC’s V
the open-drain output to level-shift from the monitored
supply to reset circuitry powered by some other supply
(Figure 8). Keep in mind that as the supervisor’s V
decreases toward 1V, so does the IC’s ability to sink
current at RESET. RESET is pulled high as V
toward 0. The voltage where this occurs depends on
the pullup resistor value and the voltage to which it is
connected.
8
+3.3V
+1.5V
_______________________________________________________________________________________
IMMEDIATE ONE-SHOT
SMART CARD DETECT:
WHEN MANUAL
RESET CLOSES
CC
V
RSTIN
CC
MAX6451
pin. However, some systems may use
Interfacing to Other Voltages
GND
RESET
MR1
MR2
for Logic Compatibility
CORE SUPPLY
RESET
DIGITAL INPUT
FRONT-PANEL SWITCH
STANDARD µP INPUT
AND 6.72s MANUAL
RESET DELAY
µP
CC
I/O SUPPLY
decays
CC
When V
bilities decline drastically. The high-impedance CMOS-
logic inputs connected to RESET can drift to
undetermined voltages. This presents no problems in
most applications, because most µPs and other circuitry
do not operate with V
In applications in which RESET must be valid down to
0V, add a pulldown resistor between RESET and GND
for the push-pull outputs. The resistor sinks any stray
leakage currents, holding RESET low (Figure 9). The
value of the pulldown resistor is not critical; 100kΩ is
large enough not to load RESET and small enough to
pull RESET to ground. The external pulldown cannot be
used with the open-drain reset outputs.
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, these supervi-
sors are relatively immune to short-duration falling tran-
sients (glitches). The graph Maximum Transient Duration
vs. Reset Threshold Overdrive in the Typical Operating
Characteristics section shows this relationship.
Figure 8. Interfacing to Other Voltage Levels
CC
MAX6444
MAX6446
MAX6448
MAX6450
MAX6452
falls below 1V, RESET current-sinking capa-
GND
V
5V
CC
Ensuring a Valid
RESET
N
V
CC
CC
below 1V.
= 0V (Push-Pull RESET )
100kΩ
Transient Immunity
RESET Down to
RESET
3.3V
µ
P