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PDF MAX6821 Data sheet ( Hoja de datos )
| Número de pieza | MAX6821 | |
| Descripción | Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-1868; Rev 1; 1/01
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
General Description
The MAX6821–MAX6825 are low-voltage microprocessor
(µP) supervisory circuits that combine voltage monitor-
ing, watchdog timer, and manual reset input functions in
a 5-pin SOT23 package. Microprocessor supervisory cir-
cuits significantly improve system reliability and accura-
cy compared to separate ICs or discrete components.
These devices assert a reset signal whenever the moni-
tored voltage drops below its preset threshold, keeping it
asserted for a minimum timeout period after VCC rises
above the threshold. In addition, a watchdog timer moni-
tors against code execution errors. A debounced manual
reset is also available. The MAX6821–MAX6825 monitor
voltages from +1.8V to +5.0V. These outputs are guaran-
teed to be in the correct state for VCC down to +1.0V.
Nine preprogrammed reset threshold voltages are
available (see Threshold Suffix Guide). The MAX6821,
MAX6822, and MAX6823 all have a manual reset input
and a watchdog timer. The MAX6821 has push-pull
RESET, the MAX6822 has open-drain RESET, and the
MAX6823 has push-pull RESET. The MAX6824 has a
watchdog timer and both push-pull RESET and push-
pull RESET. The MAX6825 has a manual reset input
and both push-pull RESET and push-pull RESET. The
Selector Guide explains the functions offered in this
series of parts.
________________________Applications
Set-Top Boxes
Computers and
Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Portable/Battery-
Powered Equipment
Pin Configurations
TOP VIEW
RESET(RESET) 1
5 VCC
GND 2
MR 3
MAX6821
MAX6822
MAX6823
4 WDI
(RESET) MAX6821 ONLY
SOT23-5
Pin Configurations continued at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
Features
o Monitors +1.8V, +2.5V, +3.0V, +3.3V, +5.0V
Supplies
o 140ms (min) Reset Timeout Delay
o 1.6s Watchdog Timeout Period
(MAX6821/MAX6822/MAX6823/MAX6824)
o Manual Reset Input
(MAX6821/MAX6822/MAX6823/MAX6825)
o Three Reset Output Options
Push-Pull RESET
Push-Pull RESET
Open-Drain RESET
o Guaranteed Reset Valid to VCC = +1.0V
o Immune to Short Negative VCC Transients
o No External Components
o Small 5-Pin SOT23 Packages
Ordering Information
PART*
TEMP. RANGE
PIN-PACKAGE
MAX6821_UK-T -40°C to +125°C
5 SOT23-5
MAX6822_UK-T -40°C to +125°C
5 SOT23-5
MAX6823_UK-T -40°C to +125°C
5 SOT23-5
MAX6824_UK-T -40°C to +125°C
5 SOT23-5
MAX6825_UK-T -40°C to +125°C
5 SOT23-5
*Insert the desired suffix letter (from the table below) into the blank
to complete the part number.
Threshold Suffix Guide
SUFFIX
RESET
THRESHOLD (V)
L 4.63
M 4.38
T 3.08
S 2.93
R 2.63
Z 2.32
Y 2.19
W 1.67
V 1.58
Note: Bold indicates standard versions. Samples are typically
available for standard versions only. All parts require a 2.5k
minimum order increment. Contact factory for availability.
Selector Guide appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Pin Description
PIN NUMBERS
PIN
MAX6821 MAX6822 MAX6823 MAX6824 MAX6825 NAME
1 1 1 1 RESET
FUNCTION
Active-Low Open-Drain or Push-Pull Reset Output. RESET
changes from high to low when the VCC input drops below the
selected reset threshold, MR is pulled low, or the watchdog
triggers a reset. RESET remains low for the reset timeout period
after VCC exceeds the device reset threshold, MR goes low to
high, or the watchdog triggers a reset.
Active-High Push-Pull Reset Output. RESET changes from low to
high when the VCC input drops below the selected reset threshold,
1 3 3 RESET MR is pulled low, or the watchdog triggers a reset. RESET remains
high for the reset timeout period after VCC exceeds the device
reset threshold, MR goes low to high, or the watchdog triggers a
reset.
2 2 2 2 2 GND Ground
333
Active-Low Manual Reset Input. Internal 50kΩ pullup to VCC. Pull
4
MR
low to force a reset. Reset remains active as long as MR is low
and for the reset timeout period after MR goes high. Leave
unconnected or connect to VCC if unused.
Watchdog Input. If WDI remains high or low for longer than the
4444
watchdog timeout period, the internal watchdog timer runs out and
a reset is triggered for the reset timeout period. The internal
WDI watchdog timer clears whenever reset is asserted, the manual
reset is asserted, or WDI sees a rising or falling edge. If WDI is
left unconnected or is connected to a three-stated buffer output,
the watchdog feature is disabled.
5 5 5 5 5 VCC Supply Voltage and Input for Reset Threshold Monitor
Detailed Description
RESET/RESET Output
A µP’s reset input starts the µP in a known state. The
MAX6821–MAX6825 µP supervisory circuits assert a
reset to prevent code-execution errors during power-
up, power-down, and brownout conditions. Whenever
VCC falls below the reset threshold, the reset output
asserts low for RESET and high for RESET. Once VCC
exceeds the reset threshold, an internal timer keeps the
reset output asserted for the specified reset timeout
period (tRP); after this interval, reset output returns to its
original state (see Figure 2).
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. On the MAX6821/
MAX6822/MAX6823/MAX6825, a logic low on MR
asserts a reset. Reset remains asserted while MR is
low, and for the timeout period (140ms min) after it
returns high. MR has an internal 50kΩ pullup resistor,
so it can be left open if not used. This input can be dri-
ven with 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 dri-
ven from long cables or the device is used in a noisy
environment, connect a 0.1µF capacitor from MR to
GND to provide additional noise immunity.
Watchdog Input
In the MAX6821–MAX6824, the watchdog circuit moni-
tors the µP’s activity. If the µP does not toggle (low to
high or high to low) the watchdog input (WDI) within the
watchdog timeout period (1.6s nominal), reset asserts
for the reset timoeout period. The internal 1.6s timer
can be cleared by either a reset pulse or by toggling
WDI. The WDI can detect pulses as short as 50ns.
While reset is asserted, the timer remains cleared and
does not count. As soon as reset is released, the timer
starts counting (see Figure 3).
_______________________________________________________________________________________ 5
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet MAX6821.PDF ] | |
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