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PDF MAX811_EUS-T Data sheet ( Hoja de datos )
| Número de pieza | MAX811_EUS-T | |
| Descripción | 4-Pin P Voltage Monitors with Manual Reset Input | |
| Fabricantes | Maxim Integrated | |
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19-0411; Rev 3; 3/99
4-Pin µP Voltage Monitors
with Manual Reset Input
________________General Description
The MAX811/MAX812 are low-power microprocessor
(µP) supervisory circuits used to monitor power sup-
plies in µP and digital systems. They provide excellent
circuit reliability and low cost by eliminating external
components and adjustments when used with 5V-
powered or 3V-powered circuits. The MAX811/MAX812
also provide a debounced manual reset input.
These devices perform a single function: They assert a
reset signal whenever the VCC supply voltage falls
below a preset threshold, keeping it asserted for at
least 140ms after VCC has risen above the reset thresh-
old. The only difference between the two devices is that
the MAX811 has an active-low RESET output (which is
guaranteed to be in the correct state for VCC down to
1V), while the MAX812 has an active-high RESET out-
put. The reset comparator is designed to ignore fast
transients on VCC. Reset thresholds are available for
operation with a variety of supply voltages.
Low supply current makes the MAX811/MAX812 ideal
for use in portable equipment. The devices come in a
4-pin SOT143 package.
________________________Applications
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
___________Typical Operating Circuit
____________________________Features
o Precision Monitoring of 3V, 3.3V, and 5V
Power-Supply Voltages
o 6µA Supply Current
o 140ms Min Power-On Reset Pulse Width;
RESET Output (MAX811), RESET Output (MAX812)
o Guaranteed Over Temperature
o Guaranteed RESET Valid to VCC = 1V (MAX811)
o Power-Supply Transient Immunity
o No External Components
o 4-Pin SOT143 Package
_______________Ordering Information
PART*
TEMP. RANGE PIN-PACKAGE
MAX811_EUS-T -40°C to +85°C 4 SOT143
MAX812_EUS-T -40°C to +85°C 4 SOT143
* This part offers a choice of five different reset threshold
voltages. Select the letter corresponding to the desired
nominal reset threshold voltage, and insert it into the blank
to complete the part number.
RESET THRESHOLD
SUFFIX
VOLTAGE (V)
L 4.63
M 4.38
T 3.08
S 2.93
R 2.63
___________________Pin Configuration
VCC
VCC
MAX811
MAX812
RESET
MR (RESET)
GND
PUSHBUTTON
SWITCH
VCC
µP
RESET
INPUT
GND
( ) ARE FOR MAX812
TOP VIEW
GND 1
MAX811
MAX812
4 VCC
(RESET) RESET 2
3 MR
SOT143
( ) ARE FOR MAX812
NOTE: SEE LAST PAGE FOR MARKING INFORMATION.
________________________________________________________________ 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.
1 page  
4-Pin µP Voltage Monitors
with Manual Reset Input
______________________________________________________________ Pin Description
PIN
MAX811 MAX812
11
NAME
GND
2 — RESET
— 2 RESET
3 3 MR
4 4 VCC
FUNCTION
Ground
Active-Low Reset Output. RESET remains low while VCC is below the reset threshold or while
MR is held low. RESET remains low for the Reset Active Timeout Period (tRP) after the reset
conditions are terminated.
Active-High Reset Output. RESET remains high while VCC is below the reset threshold or while
MR is held low. RESET remains high for Reset Active Timeout Period (tRP) after the reset condi-
tions are terminated.
Manual Reset Input. A logic low on MR asserts reset. Reset remains asserted as long as MR is
low and for 180ms after MR returns high. This active-low input has an internal 20kΩ pull-up
resistor. It can be driven from a TTL or CMOS-logic line, or shorted to ground with a switch.
Leave open if unused.
+5V, +3.3V, or +3V Supply Voltage
_______________ Detailed Description
Reset Output
A microprocessor’s (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.
RESET is guaranteed to be a logic low for VCC > 1V.
Once VCC exceeds the reset threshold, an internal
timer keeps RESET low for the reset timeout period;
after this interval, RESET goes high.
If a brownout condition occurs (VCC dips below the
reset threshold), RESET goes low. Any time VCC goes
below the reset threshold, the internal timer resets to
zero, and RESET goes low. The internal timer starts
after VCC returns above the reset threshold, and RESET
remains low for the reset timeout period.
The manual reset input (MR) can also initiate a reset.
See the Manual Reset Input section.
The MAX812 has an active-high RESET output that is
the inverse of the MAX811’s RESET output.
Manual Reset Input
Many µP-based products require manual reset capabil-
ity, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. A logic low on MR
asserts reset. Reset remains asserted while MR is low,
and for the Reset Active Timeout Period (tRP) after MR
returns high. This input has an internal 20kΩ pull-up
resistor, so it can be left open if it is not used. MR can
be driven with TTL or CMOS-logic levels, or with open-
drain/collector outputs. Connect a normally open
momentary switch from MR to GND to create a manual-
reset function; external debounce circuitry is not
required. If MR is driven from long cables or if the
device is used in a noisy environment, connecting a
0.1µF capacitor from MR to ground provides additional
noise immunity.
Reset Threshold Accuracy
The MAX811/MAX812 are ideal for systems using a 5V
±5% or 3V ±5% power supply with ICs specified for 5V
±10% or 3V ±10%, respectively. They are designed to
meet worst-case specifications over temperature. The
reset is guaranteed to assert after the power supply
falls out of regulation, but before power drops below
the minimum specified operating voltage range for the
system ICs. The thresholds are pre-trimmed and exhibit
tight distribution, reducing the range over which an
undesirable reset may occur.
_______________________________________________________________________________________ 5
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