Maxim MAX825 EUK 5-pin microprocessor supervisory circuit Datasheet

19-0487; Rev 1; 6/97
5-Pin Microprocessor Supervisory Circuits
________________________Applications
____________________________Features
♦ Precision Monitoring of +3V, +3.3V, and +5V
Power Supplies
♦ Operating Current: 10µA (MAX823L/M)
3µA (MAX825T/S/R)
♦ Fully Specified Over Temperature
♦ 140ms Min Power-On Reset
♦ Guaranteed RESET Valid to VCC = 1V
♦ Power-Supply Transient Immunity
♦ Watchdog Timer with 1.6sec Timeout
(MAX823/MAX824)
♦ Manual-Reset Input (MAX823/MAX825)
♦ No External Components
______________Ordering Information
PART†
Battery-Powered Computers and Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Portable/Battery-Powered Equipment
MAX823_EUK
MAX824_EUK
MAX825_EUK
TEMP. RANGE
PIN-PACKAGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
5 SOT23-5
5 SOT23-5
5 SOT23-5
†Insert the desired suffix letter (from the table below) into the
blank to complete the part number.
_____________________Selector Guide
FUNCTION
Active-Low Reset
RESET
THRESHOLD (V)
✔
L
4.63
✔
M
4.38
—
✔
T
3.08
S
2.93
R
2.63
MAX824
MAX825
✔
✔
✔
Watchdog Input
—
✔
Manual-Reset Input
✔
—
Active-High Reset
SUFFIX
MAX823
✔
Typical Operating Circuit appears at end of data sheet.
Marking Information appears at end of data sheet.
__________________________________________________________Pin Configurations
TOP VIEW
RESET 1
GND 2
5
VCC
MAX823
MR 3
GND 2
4
SOT23-5
RESET 1
WDI
5 VCC
MAX824
RESET 3
GND 2
4 WDI
SOT23-5
RESET 1
5 VCC
MAX825
RESET 3
4
MR
SOT23-5
*Patents Pending
________________________________________________________________ Maxim Integrated Products
1
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MAX823/MAX824/MAX825
_______________General Description
The MAX823/MAX824/MAX825* microprocessor (µP)
supervisory circuits combine reset output, watchdog,
and manual-reset input functions in a 5-pin SOT23-5
package. They significantly improve system reliability
and accuracy compared to separate ICs or discrete
components. The MAX823/MAX824/MAX825 are
specifically designed to ignore fast transients on VCC.
Five preprogrammed reset threshold voltages are
available, designated by the following package
suffixes: L = 4.63V, M = 4.38V, T = 3.08V, S = 2.93V,
and R = 2.63V. All three devices have an active-low
reset output, which is guaranteed to be in the correct
state for VCC down to 1V. The MAX824/MAX825 also
have an active-high reset output. The following Selector
Guide explains the functions offered in this series of
parts.
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits
ABSOLUTE MAXIMUM RATINGS
VCC ........................................................................-0.3V to +6.0V
All Other Pins..............................................-0.3V to (VCC + 0.3V)
Input Current, All Pins Except RESET and RESET..............20mA
Output Current, RESET, RESET ..........................................20mA
Rate of Rise, VCC ............................................................100V/µs
Continuous Power Dissipation (TA = +70°C)
SOT23-5 (derate 7.1mW/°C above +70°C)...................571mW
Operating Temperature Range
MAX82_EUK .....................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(VCC = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V
to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, TA = TMIN to TMAX, unless otherwise noted. Typical values are at
TA = +25°C.) (Note 1)
PARAMETER
Operating Voltage Range
Supply Current
SYMBOL
VCC
ISUPPLY
CONDITIONS
TA = 0°C to +70°C
1.0
TA = -40°C to +85°C
1.2
WDI and MR
unconnected
MR unconnected
MAX82_L
MAX82_M
Reset Threshold
VRST
MAX82_T
MAX82_S
MAX82_R
Reset Threshold Hysteresis
MIN
2
MAX
5.5
MAX823L/M,
MAX824L/M
10
24
MAX823T/S/R,
MAX824T/S/R
5
12
4.5
12
3
8
4.63
4.70
MAX825L/M
MAX825T/S/R
TA = +25°C
4.56
TA = -40°C to +85°C
4.50
TA = +25°C
4.31
TA = -40°C to +85°C
4.25
TA = +25°C
3.04
TA = -40°C to +85°C
3.00
TA = +25°C
2.89
TA = -40°C to +85°C
2.85
TA = +25°C
2.59
TA = -40°C to +85°C
2.55
V
µA
4.45
4.50
3.08
3.11
3.15
2.93
V
2.96
3.00
2.63
2.66
2.70
10
MAX82_T/S/R
5
mV
40
tRP
UNITS
4.75
4.38
MAX82_L/M
Reset Threshold Temperature
Coefficient
Reset Timeout Period
TYP
ppm/°C
MAX82_L/M
140
200
280
MAX82_T/S/R
140
200
280
_______________________________________________________________________________________
ms
5-Pin Microprocessor Supervisory Circuits
(VCC = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V
to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, TA = TMIN to TMAX, unless otherwise noted. Typical values are at
TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
VOH
RESET Output Voltage
VOL
RESET Output Short-Circuit
Current (Note 2)
ISOURCE
VOH
RESET Output Voltage
VOL
VCC to RESET Delay
CONDITIONS
MIN
MAX82_L/M, VCC = VRST max,
ISOURCE = 120µA
VCC - 1.5
MAX82_T/S/R, VCC = VRST max,
ISOURCE = 30µA
0.8VCC
TYP
MAX
MAX82_L/M, VCC = VRST min,
ISINK = 3.2mA
0.4
MAX82_T/S/R, VCC = VRST min,
ISINK = 1.2mA
0.3
TA = 0°C to +70°C, VCC = 1V,
VCC falling, ISINK = 50µA
0.3
TA = -40°C to +85°C, VCC = 1.2V,
VCC falling, VBATT = 0V, ISINK = 100µA
0.3
MAX82_L/M, RESET = 0V, VCC = 5.5V
800
MAX82_T/S/R, RESET = 0V, VCC = 3.6V
400
VCC > 1.8V, ISOURCE = 150µA
UNITS
V
µA
0.8VCC
MAX824L/M, MAX825L/M,
VCC = VRST max, ISINK = 3.2mA
0.4
MAX824T/S/R, MAX825T/S/R,
VCC = VRST max, ISINK = 1.2mA
0.3
VRST - VCC = 100mV
20
V
µs
WATCHDOG INPUT (MAX823/MAX824)
Watchdog Timeout Period
tWD
WDI Pulse Width
tWDI
WDI Input Threshold (Note 3)
VIL
VIH
1.12
VIL = 0.4V, VIH = 0.8VCC
VCC = 5V
WDI = 0V, time average
2.40
0.7VCC
120
-20
sec
ns
0.3VCC
WDI = VCC, time average
WDI Input Current (Note 4)
1.60
50
160
-15
V
µA
MANUAL-RESET INPUT (MAX823/MAX825)
MR Input Threshold
MR Pulse Width
VIL
0.3VCC
VIH
0.7VCC
1.0
MR Noise Immunity (pulse width
with no reset)
ns
500
MR Pull-Up Resistance (internal)
Note 1:
Note 2:
Note 3:
Note 4:
µs
100
MR to Reset Delay
35
V
52
ns
75
kΩ
Over-temperature limits are guaranteed by design and not production tested.
The RESET short-circuit current is the maximum pull-up current when RESET is driven low by a µP bidirectional reset pin.
WDI is internally serviced within the watchdog period if WDI is left unconnected.
The WDI input current is specified as the average input current when the WDI input is driven high or low. The WDI input is
designed to drive a three-stated-output device with a 10µA maximum leakage current and a maximum capacitive load of
200pF. This output device must be able to source and sink at least 200µA when active.
_______________________________________________________________________________________
3
MAX823/MAX824/MAX825
ELECTRICAL CHARACTERISTICS (continued)
__________________________________________Typical Operating Characteristics
(MAX823L, VCC = +5V, TA = +25°C, unless otherwise noted.)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
10.5
10.0
9.5
9.0
8.5
230
VCC FALLING
220
210
200
190
180
170
25
20
15
10
5
160
8.0
150
7.5
-20
0
20
40
60
80
0
-40
100
-20
0
20
40
60
80
100
-20
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
NORMALIZED RESET THRESHOLD
VOLTAGE vs. TEMPERATURE
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.06
1.04
1.02
1.00
0.98
-20
0
20
40
60
TEMPERATURE (°C)
80
100
140
120
100
80
RESET OCCURS
ABOVE CURVE
60
40
0.96
20
0.94
1.0
160
MAX823/4/5-06
1.9
TRANSIENT DURATION (µs)
MAX823/4/5-04
2.0
-40
-40
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD (V)
-40
4
30
MAX823/4/5-02
240
PROPAGATION DELAY (µs)
11.5
11.0
250
MAX823/4/5-05
SUPPLY CURRENT (µA)
12.0
RESET TIMEOUT PERIOD (ms)
MAX823/4/5-01
12.5
RESET COMPARATOR PROPAGATION DELAY
vs. TEMPERATURE
MAX823/4/5-03
VCC SUPPLY CURRENT
vs. TEMPERATURE
WATCHDOG TIMEOUT PERIOD (sec)
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits
0
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
0
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), VRST - VCC
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits
MAX823
PIN
MAX824
MAX825
NAME
FUNCTION
Active-Low Reset Output. Pulses low for 200ms when triggered, and remains
low whenever VCC is below the reset threshold or when MR is a logic low. It
remains low for 200ms after one of the following occurs: VCC rises above the
reset threshold, the watchdog triggers a reset, or MR goes low to high.
1
1
1
RESET
2
2
2
GND
3
—
4
MR
—
3
3
RESET
Ground. 0V reference for all signals.
Manual-Reset Input. A logic low on MR asserts reset. Reset remains asserted as
long as MR is held low and for 200ms after MR returns high. The active-low input
has an internal 52kΩ pull-up resistor. It can be driven from a CMOS-logic line or
shorted to ground with a switch. Leave open or connect to V CC if unused.
Active-High Reset Output. Inverse of RESET.
4
4
—
WDI
Watchdog Input. If WDI remains either high or low for longer than the watchdog timeout period, the internal watchdog timer runs out and a reset is triggered. The internal watchdog timer clears whenever reset is asserted, or
whenever 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
VCC
Supply Voltage
VCC
MAX823
MAX824
MAX825
RESET
GENERATOR
VCC
RESET
RESET
(MAX824/MAX825
ONLY)
1.25V
MR
(MAX823/MAX825
ONLY)
WDI
(MAX823/MAX824
ONLY)
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
GND
Figure 1. Functional Diagram
_______________________________________________________________________________________
5
MAX823/MAX824/MAX825
______________________________________________________________Pin Description
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits
_______________Detailed Description
RESET Output
A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX823/MAX824/MAX825 µP supervisory circuits assert a reset to prevent code-execution
errors during power-up, power-down, and brownout
conditions. RESET is guaranteed to be a logic low for
VCC down to 1V. Once VCC exceeds the reset threshold, an internal timer keeps RESET low for the specified
reset timeout period (tRP); after this interval, RESET
returns high (Figure 2).
If a brownout condition occurs (VCC dips below the
reset threshold), RESET goes low. Each time RESET is
asserted it stays low for the reset timeout period. Any
time VCC goes below the reset threshold the internal
timer restarts. RESET both sources and sinks current.
RESET on the MAX824/MAX825 is the inverse of
RESET.
Watchdog Input (MAX823/MAX824)
In the MAX823/MAX824, the watchdog circuit monitors
the µP’s activity. If the µP does not toggle the watchdog
input (WDI) within tWD (1.6sec), reset asserts. The internal 1.6sec timer is cleared by either a reset pulse or by
toggling WDI, which detects 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 (Figure 3).
Disable the watchdog function by leaving WDI unconnected or by three-stating the driver connected to WDI.
The watchdog input is internally driven low during the
first 7/8 of the watchdog timeout period and high for the
last 1/8 of the watchdog timeout period. When WDI is
left unconnected, this internal driver clears the 1.6sec
timer every 1.4sec. When WDI is three-stated or unconnected, the maximum allowable leakage current is
10µA and the maximum allowable load capacitance is
200pF.
Manual-Reset Input (MAX823/MAX825)
__________Applications Information
Many µP-based products require manual-reset capability, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. On the MAX823/
MAX825, a logic low on MR asserts reset. Reset remains
asserted while MR is low, and for tRP (200ms nominal)
after it returns high. MR has an internal 52kΩ pull-up
resistor, so it can be left open if not used. This input can
be driven 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
driven 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.
The MAX823/MAX824 WDI inputs are internally driven
through a buffer and series resistor from the watchdog
counter (Figure 1). When WDI is left unconnected, the
watchdog timer is serviced within the watchdog timeout
period by a low-high-low pulse from the counter chain.
For minimum watchdog input current (minimum overall
power consumption), leave WDI low for the majority of
the watchdog timeout period, pulsing it low-high-low
once within the first 7/8 of the watchdog timeout period
to reset the watchdog timer. If WDI is externally driven
high for the majority of the timeout period, up to 160µA
can flow into WDI.
VCC
VCC
1V
Watchdog Input Current
VRST
VRST
tRST
1V
RESET*
RESET
tRP
tRD
RESET
tRP
tRD
tRP
tWD
tRP
WDI
GND
*RESET ON THE MAX824/MAX825 IS THE INVERSE OF RESET.
Figure 2. Reset Timing Diagram
6
Figure 3. MAX823/MAX824 Watchdog Timing Relationship
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits
The RESET output maximum pull-up current is 800µA
for L/M versions (400µA for T/S/R versions). This allows
µPs with bidirectional resets, such as the 68HC11, to
force RESET low when the MAX823/MAX824/MAX825
are pulling RESET high (Figure 4).
Negative-Going VCC Transients
These supervisors are relatively immune to shortduration, negative-going VCC transients (glitches), which
usually do not require the entire system to shut down.
Resets are issued to the µP during power-up, powerdown, and brownout conditions.
The Typical Operating Characteristics show a graph of
the MAX823L’s Maximum VCC Transient Duration vs.
Reset Threshold Overdrive, for which reset pulses are
not generated. The graph was produced using negative-going VCC pulses, starting at 5V and ending below
the reset threshold by the magnitude indicated (reset
threshold overdrive). The graph shows the maximum
pulse width that a negative-going VCC transient can
typically have without triggering a reset pulse. As the
amplitude of the transient increases (i.e., goes farther
below the reset threshold), the maximum allowable
pulse width decreases. Typically, a VCC transient that
goes 100mV below the reset threshold and lasts for
15µs or less will not trigger a reset pulse.
An optional 0.1µF bypass capacitor mounted close to
VCC provides additional transient immunity.
Watchdog Software Considerations
(MAX823/MAX824)
One way to help the watchdog timer monitor software
execution more closely is to set and reset the watchdog
input at different points in the program, rather than
pulsing the watchdog input high-low-high or low-highlow. This technique avoids a stuck loop, in which the
watchdog timer would continue to be reset inside the
loop, keeping the watchdog from timing out.
Figure 5 shows an example of a flow diagram where the
I/O driving the watchdog input is set high at the beginning of the program, set low at the beginning of every
subroutine or loop, then set high again when the program returns to the beginning. If the program should
hang in any subroutine, the problem would quickly be
corrected, since the I/O is continually set low and the
watchdog timer is allowed to time out, causing a reset
or interrupt to be issued. As described in the Watchdog
Input Current section, this scheme results in higher time
average WDI input current than does leaving WDI low
for the majority of the timeout period and periodically
pulsing it low-high-low.
START
SET WDI
HIGH
VCC
VCC
MAX823
MAX824
MAX825
RESET
GENERATOR
VCC
ISOURCE MAX = 800µA L, M
400µA T, S, R
RESET
µP
PROGRAM
CODE
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
GND
GND
RETURN
Figure 4. Interfacing to µPs with Bidirectional Resets
Figure 5. Watchdog Flow Diagram
_______________________________________________________________________________________
7
MAX823/MAX824/MAX825
Interfacing to µPs with
Bidirectional Reset Pins
__________Typical Operating Circuit
___________________Chip Information
TRANSISTOR COUNT: 607
VCC
VCC
VCC
RESET
RESET
MAX823
µP
WDI
MANUAL
RESET
______________Package Information
I/O
MR
GND
MARKING INFORMATION (TOP)
XXXX
AAAI = MAX823L
AAAJ = MAX823M
AAAK = MAX823T
AAAL = MAX823S
AAAM = MAX823R
AAAN = MAX824L
AAAO = MAX824M
AAAP = MAX824T
AAAQ = MAX824S
AAAR = MAX824R
AAAS = MAX825L
AAAT = MAX825M
AAAU = MAX825T
AAAV = MAX825S
AAAW = MAX825R
SOT5L.EPS
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-377-7600
© 1997 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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