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MAX810T Schematic ( PDF Datasheet ) - Maxim Integrated

Teilenummer MAX810T
Beschreibung 3-Pin Microprocessor Reset Circuits
Hersteller Maxim Integrated
Logo Maxim Integrated Logo 




Gesamt 8 Seiten
MAX810T Datasheet, Funktion
19-0344; Rev 4; 12/99
3-Pin Microprocessor Reset Circuits
General Description
The MAX803/MAX809/MAX810 are microprocessor (µP)
supervisory circuits used to monitor the power supplies
in µP and digital systems. They provide excellent circuit
reliability and low cost by eliminating external compo-
nents and adjustments when used with +5V, +3.3V,
+3.0V, or +2.5V-powered circuits.
These circuits perform a single function: they assert a
reset signal whenever the VCC supply voltage declines
below a preset threshold, keeping it asserted for at
least 140ms after VCC has risen above the reset thresh-
old. Reset thresholds suitable for operation with a vari-
ety of supply voltages are available.
The MAX803 has an open-drain output stage, while the
MAX809/MAX810 have push-pull outputs. The
MAX803’s open-drain RESET output requires a pull-up
resistor that can be connected to a voltage higher than
VCC. The MAX803/MAX809 have an active-low RESET
output, while the MAX810 has an active-high RESET
output. The reset comparator is designed to ignore fast
transients on VCC, and the outputs are guaranteed to
be in the correct logic state for VCC down to 1V.
Low supply current makes the MAX803/MAX809/
MAX810 ideal for use in portable equipment. The
MAX803 is available in a 3-pin SC70 package, and the
MAX809/MAX810 are available in 3-pin SC70 or SOT23
packages.
Applications
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
Automotive
Typical Operating Circuit
VCC
VCC
MAX803
MAX809
RESET
RPULL-UP*
VCC
µP
RESET
INPUT
GND GND
*MAX803 ONLY
____________________________Features
o Precision Monitoring of +2.5V, +3V, +3.3V, and
+5V Power-Supply Voltages
o Fully Specified Over Temperature
o Available in Three Output Configurations
Open-Drain RESET Output (MAX803)
Push-Pull RESET Output (MAX809)
Push-Pull RESET Output (MAX810)
o 140ms min Power-On Reset Pulse Width
o 12µA Supply Current
o Guaranteed Reset Valid to VCC = +1V
o Power Supply Transient Immunity
o No External Components
o 3-Pin SC70 and SOT23 Packages
Ordering Information
PART
TEMP. RANGE PIN-PACKAGE
MAX803_EXR-T
-40°C to +105°C 3 SC70-3
MAX803_EXR-T10 -40°C to +105°C 3 SC70-3
MAX809_EXR-T
-40°C to +105°C 3 SC70-3
MAX809_EXR-T10 -40°C to +105°C 3 SC70-3
MAX809_EUR-T
-40°C to +105°C 3 SOT23-3
MAX809_EUR-T10 -40°C to +105°C 3 SOT23-3
MAX810_EXR-T
-40°C to +105°C 3 SC70-3
MAX810_EXR-T10 -40°C to +105°C 3 SC70-3
MAX810_EUR-T
-40°C to +105°C 3 SOT23-3
MAX810_EUR-T10 -40°C to +105°C 3 SOT23-3
Note: These parts are offered in 2.5k or 10k reels, and must be
ordered in 2.5k or 10k increments. Order MAX803_EXR-T for
2.5k reels and MAX803_EXR-T10 for 10k reels. Insert the
desired suffix letter from the Selector Guide into the blank to
complete the part number. All versions of these products may
not be available at the time of announcement. Contact factory for
availability.
Pin Configuration
TOP VIEW
GND 1
MAX803
MAX809
MAX810
3 VCC
RESET (RESET) 2
( ) ARE FOR MAX810.
SC70-3/SOT23-3
MAX803 AVAILABLE IN SC70-3 ONLY.
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.






MAX810T Datasheet, Funktion
3-Pin Microprocessor Reset Circuits
VCC
VCC
MAX803
RESET
VCC
µP
MOTOROLA
RESET 68HCXX
INPUT
+3.3V
+5.0V
VCC
MAX803
RESET
RPULLUP
VCC
5V SYSTEM
RESET
INPUT
GND GND
GND GND
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
ground, holding RESET low (Figure 2). R1’s value is not
critical; 100kis large enough not to load RESET and
small enough to pull RESET to ground.
A 100kpull-up resistor to VCC is also recommended
for the MAX810 if RESET is required to remain valid for
VCC < 1V.
Interfacing to µPs with
Bidirectional Reset Pins
Since the RESET output on the MAX803 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
pull-up resistor allows either device to assert reset
(Figure 3).
MAX803 Open-Drain RESET Output
Allows Use with Multiple Supplies
Generally, the pull-up connected to the MAX803 will
connect to the supply voltage that is being monitored at
the IC’s VCC pin. However, some systems may use the
open-drain output to level-shift from the monitored sup-
ply to reset circuitry powered by some other supply
(Figure 4). Note that as the MAX803’s VCC decreases
below 1V, so does the IC’s ability to sink current at
RESET. Also, with any pull-up, RESET will be pulled
high as VCC decays toward 0. The voltage where this
occurs depends on the pull-up resistor value and the
voltage to which it is connected.
Figure 4. MAX803 Open-Drain RESET Output Allows Use with
Multiple Supplies
Benefits of Highly Accurate
Reset Threshold
Most µP supervisor ICs have reset threshold voltages
between 5% and 10% below the value of nominal sup-
ply voltages. This ensures a reset will not occur within
5% of the nominal supply, but will occur when the sup-
ply is 10% below nominal.
When using ICs rated at only the nominal supply ±5%,
this leaves a zone of uncertainty where the supply is
between 5% and 10% low, and where the reset may or
may not be asserted.
The MAX8_ _L/T/Z use highly accurate circuitry to
ensure that reset is asserted close to the 5% limit, and
long before the supply has declined to 10% below
nominal.
___________________Chip Information
TRANSISTOR COUNT: 275 (SOT23)
380 (SC70)
6 _______________________________________________________________________________________

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