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MAX6445UK23L-T
1.575 V, mP reset circuit with long manual reset setup period
General DescriptionThe MAX6443–MAX6452 low-current microprocessor
reset circuits feature single or dual manual reset inputs
with an extended 6.72s setup period. Because of the
extended setup period, short switch closures (nuisance
resets) are ignored.
On all devices, the reset output asserts when any of the
monitored supply voltages drops below its specified
threshold. The reset output remains asserted for the
reset timeout period (210ms typ) after all monitored
supplies exceed their reset thresholds. The reset output
is one-shot pulse asserted for the reset timeout period
(140ms min) when selected manual reset input(s) are
held low for an extended setup timeout period of 6.72s.
These devices ignore manual reset transitions of less
than 6.72s (typ).
The MAX6443–MAX6448 are single fixed-voltage µP
supervisors. The MAX6443/MAX6444 have a single
extended manual reset input. The MAX6445/MAX6446
have two extended manual reset inputs. The MAX6447/
MAX6448 have one extended and one immediate manual
reset input.
The MAX6449–MAX6452 have one fixed-threshold µP
supervisor and one adjustable-threshold µP supervisor.
The MAX6449/MAX6450 have two delayed manual
reset inputs. The MAX6451/MAX6452 have one delayed
and one immediate manual reset input.
The MAX6443–MAX6452 have an active-low RESET
with push-pull or open-drain output logic options. These
devices, offered in small SOT packages, are fully guar-
anteed over the extended temperature range (-40°C to
+85°C).
ApplicationsSet-Top Boxes
Consumer Electronics
DVD Players
Modems
MP3 Players
Industrial Equipment
Automotive
Medical Devices
FeaturesSingle- or Dual-Supply Voltage MonitorsPrecision Factory-Set Reset Thresholds from
1.6V to 4.6V Adjustable Threshold to Monitor Voltages Down
to 0.63V (MAX6449–MAX6452)Single or Dual Manual Reset Inputs with Extended
6.72s Setup Period Optional Short Setup Time Manual Reset Input
(MAX6447/MAX6448 and MAX6451/MAX6452)Immune to Short Voltage Transients Low 6µA Supply CurrentGuaranteed Valid Reset Down to VCC= 1.0VActive-Low RESET(Push-Pull or Open-Drain)
Outputs140ms (min) Reset Timeout PeriodSmall SOT143 and SOT23 Packages
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
Pin Configurations
Ordering Information19-2656; Rev 1; 1/03
Note:The “_ _ ” is a placeholder for the threshold voltage level
of the devices. A desired threshold level is set by the two-num-
ber suffix found in Table 1. All devices are available in tape-
and-reel only. There is a 2500-piece minimum order increment
for standard versions (Table 2). Sample stock is typically held
on standard versions only. Nonstandard versions require a
minimum order increment of 10,000 pieces. Contact factory for
availability.
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
ABSOLUTE MAXIMUM RATINGSStresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
All Voltages Referenced to GND
VCC..........................................................................-0.3V to +6V
Open-Drain RESET..................................................-0.3V to +6V
Push-Pull RESET........................................-0.3V to (VCC+ 0.3V)MR1, MR2, MR2, RSTIN ..........................................-0.3V to +6V
Input Current, All Pins.......................................................±20mA
Continuous Power Dissipation (TA= +70°C)
4-Pin SOT143-4 (derate 4.0mW/°C above +70°C).....320mW
5-Pin SOT23-5 (derate 7.1mW/°C above +70°C).......571mW
6-Pin SOT23-6 (derate 8.7mW/°C above +70°C).......696mW
Operating Temperature Range..........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
ELECTRICAL CHARACTERISTICS(VCC= 1.0V to 5.5V, TA= -40°C to +85°C, unless otherwise specified. Typical values are at TA= +25°C.) (Note 1)
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
Note 1:Devices production tested at +25°C. Overtemperature limits are guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)(VCC= 1.0V to 5.5V, TA= -40°C to +85°C, unless otherwise specified. Typical values are at TA= +25°C.) (Note 1)
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
Typical Operating Characteristics(VCC= 3.3V, TA = +25°C, unless otherwise noted.)
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
Detailed Description
Reset OutputThe reset output is typically connected to the reset
input of a microprocessor (µP). A µP’s reset input starts
or restarts the µP in a known state. The MAX6443–
MAX6452 µP supervisory circuits provide the reset
logic to prevent code-execution errors during power-
up, power-down and brownout conditions (see the
Typical Operating Circuit).
RESETchanges from high to low whenever the moni-
tored voltages (RSTIN or VCC) drop below the reset
threshold voltages. Once VRSTINand VCCexceed their
respective reset threshold voltages, RESETremains low
for the reset timeout period and then goes high. RESET
is one-shot pulsed whenever selected manual reset
inputs are asserted. RESETstays asserted for the nor-
mal reset timeout period (140ms min).
RESETis guaranteed to be in the proper output logic
state for VCCinputs ≥1V. For applications requiring valid
reset logic when VCCis less than 1V, see the Ensuring a
Valid RESETOutput Down to VCC= 0Vsection.
Pin Description
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
Manual Reset Input OptionsUnlike 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 RESEToutput asserts. When
valid manual reset input conditions/setup periods are
met, the RESEToutput 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 (MR1and MR2) with extended setup peri-
ods. For dual MR1, MR2devices, 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 RESEToutput 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 RESETasserts 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
RESEToutput 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,
RESETdeasserts. The high-to-low transition on MR2
input is internally debounced for 210ms to ensure that
there are no false RESETassertions 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 Informationsection).
Adjustable Input Voltage (RSTIN)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
(VMON-TH):
VMON-TH= VTH-RSTIN✕(R1+ R2) / R2
where VMON-THis the desired reset threshold voltage
and VTH-RSTINis the reset input threshold (0.63V).
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:
R1 = R2 ✕(VMON-TH/ VTH-RSTIN- 1) Ω
MAX6443–MAX6452
µP Reset Circuits with Long Manual Reset
Setup Period
Applications Information
Interrupt Before ResetTo minimize data loss and speed system recovery,
many applications interrupt the processor or reset only
portions of the system before a processor hard reset is
asserted. The extended setup time of the MAX6443–
MAX6452 manual reset inputs allows the same push-
button (connected to both the processor interrupt and
the extended MR1input, as shown in Figure 6) to con-
trol both the interrupt and hard reset functions. If the
pushbutton is closed for less than 6.72s, the processor
is only interrupted. If the system still does not respond
properly, the pushbutton (or two buttons for the dual
manual reset) can be closed for the full extended setup
period to hard reset the processor. If desired, connect
an LED to the RESEToutput to blink off (or on) for the
reset timeout period to signify when the pushbutton is
closed long enough for a hard reset (the same LED
might be used as the front-panel power-on display).
Smart Card Insertion/RemovalThe MAX6447/MAX6448/MAX6451/MAX6452 dual manu-
al resets are useful in applications in which both an
extended and immediate setup periods are needed.
Figure 7 illustrates the insertion and removal of a smart
card. MR1monitors a front-panel pushbutton. When
closed for 6.72s, RESETone-shot pulses low for 140ms
min. Because MR1is internally pulled to VCCthrough a
50kΩresistor, the front-panel switch can be connected to
Figure 3. MAX6447/MAX6448/MAX6451/MAX6452 MR2
Assertion DebouncingTiming Diagram
Figure 4. MAX6447/MAX6448/MAX6451/MAX6452 MR2
Deassertion Debouncing Timing Diagram
Figure 5. Calculating the Monitored Threshold Voltages
