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MAX6343MUT+-MAX6343RUT+-MAX6343TUT+T
6-Pin µP Reset Circuit with Power-Fail Comparator
General DescriptionThe MAX6342–MAX6345 family of microprocessor (µP)
supervisory circuits monitors power supplies in digital sys-
tems. These devices significantly improve system reliabili-
ty and accuracy compared to separate ICs or discrete
components.
The MAX6342–MAX6345 provide factory-trimmed VCC
reset threshold voltages from 2.33V to 4.63V and operate
with supply voltages between +1V and +5.5V. A +1.25V
threshold detector allows for a power-fail warning, for
low-battery detection, or for monitoring another power
supply. The MAX6342 contains an MRinput and an
active-low push-pull reset. The MAX6343 and MAX6344
are identical to the MAX6342 except they provide an
active-low, open-drain reset and an active-high, push-
pull reset, respectively. The MAX6345 provides a second
reset output in place of the MRinput to give it an active-
high push-pull reset and an active-low push-pull reset.
All of the devices are packaged in a miniature 6-pin
SOT23.
ApplicationsPortable Computers
Telecom Equipment
Networking Equipment
Portable/Battery-Powered Equipment
Multivoltage Systems
Embedded Control Systems
FeaturesSmall 6-Pin SOT23 PackagePrecision Factory-Set VCCReset Thresholds
Between 2.33V and 4.63VGuaranteed RESETValid to VCC= +1V100ms min Reset Pulse WidthDebounced CMOS-Compatible Manual-Reset
InputVoltage Monitor for Power-Fail or Low-Battery
Warning
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
Selector Guide 1
Selector Guide 219-1568; Rev 1; 3/00
Pin Configurations
Ordering Information
Typical Operating Circuit appears at end of data sheet.
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +1.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= +3V.) (Note 1)
Stresses 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.
VCCto GND..............................................................-0.3V to +6V
RESET, RESET
(MAX6342/MAX6344/MAX6345).........-0.3V to (VCC+ 0.3V)RESET(MAX6343)...................................................-0.3V to +6V
MR, PFI, PFO..............................................-0.3V to (VCC+ 0.3V)
Input Current, VCC..............................................................50mA
Output Current, RESET, RESET..........................................50mA
Continuous Power Dissipation (TA= +70°C)
6-Pin SOT23 (derate 4mW/°C above +70°C).............320mW
Operating Temperature Range.........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature Range (soldering, 10s).....................+300°C
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
ELECTRICAL CHARACTERISTICS (continued)(VCC= +1.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= +3V.) (Note 1)
Typical Operating Characteristics(VPFI= VCC= +5V, TA= +25°C, unless otherwise noted.)
Note 1:Overtemperature limits are guaranteed by design and not production tested.
Note 2:Apply to each part in accordance with threshold voltage, output configuration, and manual reset status selected.
Note 3:Leakage parameters are guaranteed by design and not production tested.
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator13456
MAX6342-04
SUPPLY VOLTAGE (V)
PFO OUTPUT VOLTAGE HIGH
vs. SUPPLY VOLTAGE PFO (V)
MAX6342-05
SUPPLY VOLTAGE (V)
PFO OUTPUT VOLTAGE LOW
vs. SUPPLY VOLTAGE PFO (V)
10µs/div
MAX6342-06
MAX6344/MAX6345
RESET RESPONSE TIME 2µs/div
MAX6342-07
MAX6342/MAX6345
RESET RESPONSE TIME
Typical Operating Characteristics (continued)(VPFI= VCC= +5V, TA= +25°C, unless otherwise noted.)
Pin Description
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
Pin Description (continued)
_______________Detailed Description
Reset OutputA µP’s reset input starts the µP in a known state. These
µP supervisory circuits assert reset to prevent code-
execution errors during power-up, power-down, or
brownout conditions.
RESETand RESET are guaranteed to be asserted at a
valid logic level for VCC> +1V (see Electrical Char-
acteristics). Once RESET asserts, it remains asserted
for at least 100ms (tRP) after VCCrises above its thresh-
old value or after MRreturns high (Figures 1 and 2).
Open-Drain RESET OutputThe MAX6343 has an active-low, open-drain reset out-
put. This output sinks current when RESETis asserted.
Connect a pull-up resistor from RESETto any positive
supply voltage up to +5.5V (Figure 3). Select a resistor
value large enough to register a logic low (see Elec-
trical Characteristics), and small enough to register a
logic high while supplying all input current and leakage
paths connected to the RESETline. A 10kΩpull-up is
sufficient in most applications.
Manual ResetThe MAX6342/MAX6343/MAX6344s’ manual-reset input
(MR) allows reset to be triggered by a pushbutton
switch. The switch is effectively debounced by the 1µs
min reset pulse width. MRis CMOS-logic compatible.
Power-Fail ComparatorThe power-fail comparator is useful for various purpos-
es because the power-fail output (PFO) is independent
Figure 1. MAX6342/MAX6343/MAX6344 Functional DiagramFigure 2. MAX6345 Functional Diagram
MAX6342–MAX6345of the reset output. The inverting input is internally con-
nected to a +1.25V reference.
To build an early-warning circuit for power failure, con-
nect the PFI pin to a voltage divider (see Typical Oper-
ating Circuit). Choose the voltage-divider ratio so that
the voltage at PFI falls below +1.25V just before the
+5V regulator drops out. Use PFOto interrupt the µP to
prepare for an orderly shutdown.
__________Applications Information
Negative-Going VCCTransientsThe MAX6342–MAX6345 supervisors are immune to
short-duration, negative-going VCCtransients (glitches)
that usually do not require the entire system to shut down.
Figure 4 shows typical transient duration vs. reset com-
parator overdrive, for which the MAX6342–MAX6345 do
not generate a reset pulse. The graph was generated
using a negative-going pulse applied to VCC, starting
0.5V above the actual reset threshold and ending below
it by the magnitude indicated (reset comparator over-
drive). The graph indicates the maximum pulse width a
negative-going VCCtransient can have without causing
a reset pulse. As the magnitude of the transient increas-
es (goes further below the reset threshold), the maxi-
mum allowable pulse width decreases.
Typically, a VCCtransient that goes 100mV below the
reset threshold and lasts 12µs or less will not cause a
reset pulse. A 1µF bypass capacitor mounted as close
as possible to the VCCpin provides additional transient
immunity.
Ensuring a Valid Reset Output
Down to VCC= 0The MAX6342–MAX6345 are guaranteed to operate
properly down to VCC= +1V. In applications that require
valid reset levels down to VCC= 0, a pull-down resistor
to active-low outputs (MAX6342/MAX6345) and a pull-up
resistor to active-high outputs (MAX6344/MAX6345)
ensure that the reset line is valid when the reset output is
no longer sinking or sourcing current (Figures 5 and 6).
Note that this method does not work with the open-drain
output of the MAX6343. The resistor value used is not
critical, but it must be large enough not to load the reset
6-Pin µP Reset Circuit with
Power-Fail ComparatorFigure 4. Maximum Transient Duration Magnitude RejectionFigure 3. Open-Drain RESETOutput Allows Use with Multiple
Supplies
Figure 5. Ensuring RESETValid to VCC= 0 on Active-Low
Push-Pull Outputs
Figure 6. Ensuring RESETValid to VCC= 0 on Active-High
Push-Pull Outputs
