MAX6452 Maxim Integrated Products, MAX6452 Datasheet - Page 6

• Manufacturer Part Number: MAX6452
• Description: (MAX6443 - MAX6452) uP Reset Circuits
• Manufacturer: Maxim Integrated Products

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µP Reset Circuits with Long Manual Reset
Setup Period
Unlike typical manual reset functions associated with
supervisors, each device in the MAX6443–MAX6452
family includes at least one manual reset input, which
must be held logic-low for an extended setup period
(6.72s typ) before the RESET output asserts. When
valid manual reset input conditions/setup periods are
met, the RESET output is one-shot pulse asserted low
for a fixed reset timeout period (140ms min). Existing
front-panel pushbutton switches (i.e., power on/off,
channel up/down, or mode select) can be used to drive
the manual reset inputs. The extended manual reset
setup period prevents nuisance system resets during
normal front-panel usage or resulting from inadvertent
short-term pushbutton closure.
The MAX6443/MAX6444, MAX6447/MAX6448, and
MAX6451/MAX6452 include a single manual reset input
with extended setup period (MR1). The MAX6445/
MAX6446 and MAX6449/MAX6450 include two manual
reset inputs (MR1 and MR2) with extended setup peri-
ods. For dual MR1, MR2 devices, both inputs must be
held low simultaneously for the extended setup period
(6.72s typ) before the reset output is pulse asserted.
The dual extended setup provides greater protection
from nuisance resets. (For example, the user or service
technician is informed to simultaneously push both the
on/off button and the channel-select button for 6.72s to
reset the system.)
The MAX6443–MAX6452 RESET output is pulse asserted
once for the reset timeout period after each valid manual
reset input condition. At least one manual reset input
must be released (go high) and then be driven low for the
extended setup period before RESET asserts again.
Internal timing circuitry debounces low-to-high manual
reset logic transitions, so no external circuitry is required.
Figure 1 illustrates the single manual reset function of the
MAX6443/MAX6444 single-voltage monitors, and Figure
2 represents the dual manual reset function of the
MAX6445/MAX6446 and MAX6449/MAX6450.
The MAX6447/MAX6448 and MAX6451/MAX6452
include both an extended setup period and immediate
setup period manual reset inputs. A low-to-high MR2
rising edge transition immediately pulse asserts the
RESET output for the reset timeout period (140ms min).
If the MAX6447/MAX6448 and MAX6451/MAX6452
MR2 input senses another rising edge before the end
of the 140ms timeout period (Figure 3), the internal
timer clears and begins counting again. If no rising
edges are detected within the 210ms timeout period,
RESET deasserts. The high-to-low transition on MR2
input is internally debounced for 210ms to ensure that
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Manual Reset Input Options
there are no false RESET assertions when MR2 is dri-
ven from high to low (Figure 4). The MR2 input can be
used for system test purposes or smart-card-detect
applications (see the Applications Information section).
The MAX6449–MAX6452 monitor the voltage on RSTIN
using an adjustable reset threshold set with an external
resistor voltage-divider (Figure 5). Use the following for-
mula to calculate the externally monitored voltage
(V
where V
and V
Resistors R1 and R2 can have very high values to mini-
mize current consumption because of low leakage cur-
rents. Set R2 to some conveniently high value (250kΩ,
for example), and calculate R1 based on the desired
reset threshold voltage, using the following formula:
Figure 1. MAX6443/MAX6444 Manual Reset Timing Diagram
Figure 2. MAX6445/MAX6446/MAX6449/MAX64450 Manual
Reset Timing Diagram
MON-TH
MR1
MR1
MR2
RESET
RESET
TH-RSTIN
MON-TH
R1 = R2
V
):
MON-TH
Adjustable Input Voltage (RSTIN)
is the reset input threshold (0.63V).
is the desired reset threshold voltage
✕
= V
(V
MON-TH
TH-RSTIN
MR1 SETUP PERIOD
6.72s
/ V
✕
6.72s
TH-RSTIN
(R1+ R2) / R2
RESET TIMEOUT PERIOD
210ms
- 1) Ω
210ms