Maxim MAX704TEPA 3.0v/3.3v microprocessor supervisory circuit Datasheet

19-0243; Rev 1; 9/94
3.0V/3.3V Microprocessor Supervisory Circuits
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MAX805
MAX806
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±75mV
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±2%
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________________________Applications
Battery-Powered Computers and Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Power Monitoring
Portable Equipment
__________________Pin Configuration
____________________________Features
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
–————–
RESET and RESET Outputs
Manual Reset Input
Precision Supply-Voltage Monitor
200ms Reset Time Delay
Watchdog Timer (1.6sec timeout)
Battery-Backup Power Switching—
Battery Can Exceed VCC in Normal Operation
40µA VCC Supply Current
1µA Battery Supply Current
Voltage Monitor for Power-Fail or
Low-Battery Warning
–————–
Guaranteed RESET Assertion to VCC = 1V
8-Pin DIP and SO Packages
______________Ordering Information
PART**
TEMP. RANGE
PIN-PACKAGE
MAX690_CPA
0°C to +70°C
8 Plastic DIP
MAX690_CSA
MAX690_C/D
MAX690_EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX690_ESA
MAX690_MJA
-40°C to +85°C
-55°C to +125°C
8 SO
8 CERDIP
Ordering Information continued on last page.
* Contact factory for dice specifications.
** These parts offer a choice of reset threshold voltage. Select
the letter corresponding to the desired nominal reset threshold
voltage (T = 3.075V, S = 2.925V, R = 2.625V) and insert it into
the blank to complete the part number.
_________Typical Operating Circuits
REGULATED +3.3V OR +3.0V
VCC
UNREGULATED
DC
0.1µF
VCC
RESET
(RESET)
R1
PFO
PFI MAX690T/S/R WDI
TOP VIEW
VOUT
1
VCC
2
GND
3
PFI
4
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
DIP/SO
( ) ARE FOR MAX804T/S/R, MAX805T/S/R
< > ARE FOR MAX704T/S/R, MAX806T/S/R
8
VBATT
7
RESET (RESET)
6
WDI <MR>
5
R2
3.6V
LITHIUM
BATTERY
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
µP
RESET
NMI
I/O LINE GND
BUS
VOUT
VBATT
GND
0.1µF
PFO
0.1µF
VCC
CMOS RAM
GND
( ) ARE FOR MAX804T/S/R, MAX805T/S/R
See last page for MAX704T/S/R, MAX806T/S/R.
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
_______________General Description
These microprocessor (µP) supervisory circuits reduce
the complexity and number of components required for
power-supply monitoring and battery-control functions
in µP systems. They significantly improve system reliability and accuracy compared to separate ICs or
discrete components.
These devices are designed for use in systems powered
by 3.0V or 3.3V supplies. See the selector guide in the
back of this data sheet for similar devices designed for
5V systems. The suffixes denote different reset threshold
voltages: 3.075V (T), 2.925V (S), and 2.625V (R) (see
Reset Threshold section in the Detailed Description). All
these parts are available in 8-pin DIP and SO packages.
Functions offered in this series are as follows:
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V/3.3V Microprocessor Supervisory Circuits
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
VCC.........................................................................-0.3V to 6.0V
VBATT ....................................................................-0.3V to 6.0V
All Other Inputs ...................-0.3V to the higher of VCC or VBATT
Continuous Input Current
VCC ..................................................................................100mA
VBATT ...............................................................................18mA
GND ..................................................................................18mA
Output Current
–————– –——–
R E S E T , P F O ....................................................................18mA
VOUT ................................................................................100mA
Continuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ..............727mW
SO (derate 5.88mW/°C above +70°C) ...........................471mW
CERDIP (derate 8.00mW/°C above +70°C) ...................640mW
Operating Temperature Ranges
MAX690_C_ _/MAX704_C_ _/MAX80_ _C_ _ ........0°C to +70°C
MAX690_E_ _/MAX704_E_ _/MAX80_ _E_ _. .....-40°C to +85°C
MAX690_M_ _/MAX704_M_ _/MAX80_ _M_ _...-55°C to +125°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 = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC = 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC = 2.72V to
5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
Operating Voltage Range,
VCC, VBATT (Note 1)
VCC Supply Current
(excluding IOUT)
VCC Supply Current in BatteryBackup Mode (excluding IOUT)
ISUPPLY
CONDITIONS
MIN
TYP
MAX
MAX690_C, MAX704_C, MAX80_ _C
1.0
5.5
MAX690_E/M, MAX704_E/M, MAX80_ _E/M
1.1
5.5
–—–
M R = VCC
(MAX704_/
MAX806_)
–—–
M R = VCC
(MAX704_/
MAX806_)
MAX690_C/E, MAX704_C/E,
MAX80_ _C/E, VCC < 3.6V
40
50
MAX690_C/E, MAX704_C/E,
MAX80_ _C/E, VCC < 5.5V
50
65
MAX690_M, MAX704_M,
MAX80_ _M, VCC < 3.6V
40
55
MAX690_M, MAX704_M,
MAX80_ _M, VCC < 5.5V
50
70
VCC = 2.0V, VBATT = 2.3V
25
50
MAX690_C/E, MAX704_C/E, MAX80_ _C/E
0.4
1
MAX690_M, MAX704_M, MAX80_ _M
0.4
10
Battery Leakage Current
(Note 3)
MAX690_C/E, MAX704_C/E, MAX80_ _C/E
0.01
0.5
MAX690_M, MAX704_M, MAX80_ _M
0.01
5
2
V
µA
VBATT Supply Current, Any Mode
(excluding IOUT) (Note 2)
VOUT Output Voltage
UNITS
MAX690_C/E, MAX704_C/E, MAX80_ _C/E,
IOUT = 5mA (Note 4)
VCC 0.03
VCC 0.015
MAX690_C/E, MAX704_C/E, MAX80_ _C/E
IOUT = 50mA
VCC 0.3
VCC 0.15
MAX690_M, MAX704_M, MAX80_ _M
IOUT = 5mA (Note 4)
VCC 0.035
VCC 0.015
MAX690_M, MAX704_M, MAX80_ _M
IOUT = 50mA
VCC 0.35
VCC 0.15
IOUT = 250µA, VCC > 2.5V (Note 4)
VCC 0.0015
VCC 0.0006
_______________________________________________________________________________________
µA
µA
µA
V
3.0V/3.3V Microprocessor Supervisory Circuits
(VCC = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC = 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC = 2.72V to
5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25˚C.)
PARAMETER
SYMBOL
CONDITIONS
IOUT = 250µA, VBATT = 2.3V
VOUT in Battery-Backup Mode
MIN
TYP
VBATT
- 0.1
VBATT
- 0.034
VBATT - VCC, VSW > VCC > 1.75V (Note 5)
VSW
Battery Switch Threshold,
VCC Rising (Note 7)
VBATT > VCC (Note 6)
mV
2.50
3.00
3.075
3.15
VCC rising
3.00
3.085
3.17
VCC falling
3.00
3.075
3.12
VCC rising
3.00
3.085
3.14
VCC falling
2.85
2.925
3.00
VCC rising
2.85
2.935
3.02
VCC falling
2.88
2.925
3.00
VCC rising
2.88
2.935
3.02
VCC falling
2.55
2.625
2.70
VCC rising
2.55
2.635
2.72
VCC falling
2.59
2.625
2.70
VCC rising
2.59
2.635
2.72
VCC < 3.6V
140
200
280
VCC
- 0.3
VCC
- 0.05
MAX690S/704S/805S
VRST
MAX802S/804S/806S
MAX690R/704R/805R
MAX802R/804R/806S
tWP
V
V
VCC falling
MAX802T/804T/806T
Reset Timeout Period
25
2.40
This value is identical to the reset threshold,
VCC rising
MAX690T/704T/805T
Reset Threshold (Note 8)
65
2.30
UNITS
V
VBATT
- 0.14
IOUT = 1mA, VBATT = 2.3V
Battery Switch Threshold,
VCC Falling
MAX
V
ms
–——– –————–
P F O , R E S E T Output Voltage
VOH
ISOURCE = 50µA
–——– –————–
P F O , R E S E T Output Short to
GND Current (Note 4)
IOS
VCC = 3.3V, VOH = 0V
180
500
µV
–——– –————–
P F O , R E S E T , RESET
Output Voltage
VOL
ISINK = 1.2mA;
MAX690_/704_/802_/806_, VCC = VRST min;
MAX804_/805_, VCC = VRST max
0.06
0.3
V
0.13
0.3
0.17
0.3
–——– –————–
P F O , R E S E T Output Voltage
RESET Output Leakage Current
(Note 9)
VBATT = 0V, VCC = 1.0V, ISINK = 40µA,
MAX690_C, MAX704_C, MAX80_ _C
VOL
VBATT = 0V, VCC = 1.2V, ISINK = 200µA,
MAX690_E/M, MAX704_E/M, MAX80_ _E/M
VBATT = 0V,
VCC = VRST min;
VRESET = 0V, VCC
V
MAX804_C,
MAX805_C
-1
1
MAX804_E/M,
MAX805_E/M
-10
10
V
µA
_______________________________________________________________________________________
3
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
ELECTRICAL CHARACTERISTICS (continued)
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V/3.3V Microprocessor Supervisory Circuits
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC = 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC = 2.72V to
5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25˚C.)
PARAMETER
PFI Input Threshold
SYMBOL
VPFT
PFI Input Current
PFI Hysteresis, PFI Rising
VPFH
PFI Input Current
CONDITIONS
TYP
MAX
1.212
1.237
1.262
MAX690_/MAX704_/MAX805_
1.187
1.237
1.287
MAX690_C/E, MAX704_C/E, MAX80_ _C/E
-25
2
25
MAX690_M, MAX704_M, MAX80_ _M
-500
2
500
MAX690_C/E, MAX704_C/E,
MAX80_ _C/E
10
20
MAX690_M, MAX704_M, MAX80_ _M
10
25
VCC < 3.6V
VPFI falling
VCC < 3.6V
MAX690_C/E, MAX704_C/E, MAX80_ _C/E
-25
2
25
MAX690_M, MAX704_M, MAX80_ _M
-500
2
500
–—–
M R Input Threshold
VIH
–—–
M R Pulse Width
–—–
M R to Reset Delay
–—–
M R Pull-Up Current
tMR
MAX704_/MAX806_ only
tMD
MAX704_/MAX806_ only
WDI Input Threshold
VIL
VIH
VIL
WDI Input Current
Watchdog Timeout Period
WDI Pulse Width
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
4
MIN
MAX802_C/E, MAX804_C/E,
MAX806_C/E
MAX704_/MAX806_ only
–—–
MAX704_/MAX806_ only, M R = 0V, VCC = 3V
MAX690_/MAX802_/MAX804_/MAX805_ only
100
20
20
nA
mV
nA
V
ns
500
ns
60
350
µA
0.7 x VCC
0.3 x VCC
-1
0.01
1
MAX690_M, MAX802_M,
MAX804_M, MAX805_M
-10
0.01
10
MAX690/MAX802/MAX804/
MAX805 only
1.12
1.60
2.24
MAX690_/MAX802_/MAX804_/MAX805_ only
100
20
VCC < 3.6V
V
60
MAX690_C/E, MAX802_C/E,
MAX804_C/E, MAX805_C/E
0V< VCC < 5.5V
tWD
0.7 x VCC
0.3 x VCC
UNITS
V
µA
sec
ns
–—–
VCC supply current, logic input leakage, watchdog functionality (MAX690_/802_/805_/804_), M R functionality
–————–
(MAX704_/806_), PFI functionality, state of R E S E T (MAX690_/704_/802_/806_), and RESET (MAX804_/805_) tested at
–————–
–——–
VBATT = 3.6V, and VCC = 5.5V. The state of R E S E T or RESET and P F O is tested at VCC = VCC min.
Tested at VBATT = 3.6V, VCC = 3.5V and 0V. The battery current will rise to 10µA over a narrow transition window around
VCC = 1.9V.
Leakage current into the battery is tested under the worst-case conditions at VCC = 5.5V, VBATT = 1.8V and at VCC = 1.5V,
VBATT= 1.0V.
Guaranteed by design.
When VSW > VCC > VBATT, VOUT remains connected to VCC until VCC drops below VBATT. The VCC-to-VBATT comparator
has a small 25mV typical hysteresis to prevent oscillation. For VCC < 1.75V (typ), VOUT switches to VBATT regardless of the
voltage on VBATT.
When VBATT > VCC > VSW, VOUT remains connected to VCC until VCC drops below the battery switch threshold (VSW).
VOUT switches from VBATT to VCC when VCC rises above the reset threshold, independent of VBATT. Switchover back to
–————–
VCC occurs at the exact voltage that causes R E S E T to go high (on the MAX804_/805_, RESET goes low); however
switchover occurs 200ms prior to reset.
The reset threshold tolerance is wider for VCC rising than for VCC falling to accommodate the 10mV typical hysteresis, which
prevents internal oscillation.
The leakage current into or out of the RESET pin is tested with RESET asserted (RESET output high impedance).
_______________________________________________________________________________________
3.0V/3.3V Microprocessor Supervisory Circuits
VBATT-to-VOUT ON-RESISTANCE
vs. TEMPERATURE
VCC = 2.5V
VCC = 3.3V
3
2
VCC = 5V
1
140
VBATT = 3V
100
VBATT = 3.3V
60
VCC = 5V
VCC = 2.5V
20 40 60 80 100 120 140
–60 –40 –20 0
100
VBATT = 3V
1
212
VCC = 5V
208
RESET-COMPARATOR PROPAGATION
DELAY vs. TEMPERATURE
VBATT = 3.0V
204
200
VBATT = 2V
30
VBATT = 3.0V
100mV OVERDRIVE
PROPAGATION DELAY (µs)
VBATT = 5V
216
RESET TIMEOUT PERIOD (ms)
MAX690-806 TOC04
10,000
196
20 40 60 80 100 120 140
22
18
14
10
–60 –40 –20 0
20 40 60 80 100 120 140
–60 –40 –20 0
TEMPERATURE (°C)
PFI THRESHOLD
vs. TEMPERATURE
1.238
VCC = 5V
1.236
VCC = 2.5V
1.234
1.232
VBATT = 3.0V
1.230
1.004
NORMALIZED RESET THRESHOLD (V)
VCC = 3.3V
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
MAX690-806 TOC07
1.240
20 40 60 80 100 120 140
TEMPERATURE (°C)
MAX690-806 TOC08
TEMPERATURE (°C)
PFI THRESHOLD (V)
26
VCC = 3.3V
0.1
–60 –40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
BATTERY SUPPLY CURRENT
vs. TEMPERATURE
1000
35
VCC = 3.3V
VBATT = 3V
PFI = GND
MR/WDI FLOATING
TEMPERATURE (°C)
TEMPERATURE (°C)
VCC = 0V
PFI = GND
40
25
–60 –40 –20 0
20 40 60 80 100 120 140
45
30
VBATT = 5V
MAX690-806 TOC05
–60 –40 –20 0
BATTERY SUPPLY CURRENT (nA)
50
20
0
10
VBATT = 2V
MAX690-806 TOC03
VCC = 0V
MAX690-806 TOC06
4
180
SUPPLY CURRENT (µA)
MAX690-806 TOC01
VCC-to-VOUT ON-RESISTANCE (Ω)
VBATT = 3.0V
VBATT-to-VOUT ON-RESISTANCE (Ω)
5
SUPPLY CURRENT
vs. TEMPERATURE
MAX690-806 TOC02
VCC-to-VOUT ON-RESISTANCE
vs. TEMPERATURE
1.002
1.000
0.998
0.996
VBATT = 3.0V
0.994
–60 –40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
–60 –40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V/3.3V Microprocessor Supervisory Circuits
______________________________________________________________Pin Description
PIN
MAX690 MAX704 MAX804
MAX802 MAX806 MAX805
NAME
FUNCTION
VOUT
Supply Output for CMOS RAM. When VCC is above the reset threshold, VOUT is
connected to VCC through a P-channel MOSFET switch. When VCC falls below VSW and
VBATT, VBATT connects to VOUT. Connect to VCC if no battery is used.
1
1
1
2
2
2
VCC
Main Supply Input
3
3
3
GND
Ground
4
4
4
PFI
5
5
5
–——–
PFO
6
—
6
WDI
—
6
—
–—–
MR
–——–
Power-Fail Input. When PFI is less than VPFT or when VCC falls below VSW, P F O goes
–——–
low; otherwise, P F O remains high. Connect to ground if unused.
–——–
Power-Fail Output. When PFI is less than VPFT, or VCC falls below VSW, P F O goes low;
–——–
otherwise, P F O remains high. Leave open if unused.
Watchdog Input. If WDI remains high or low for 1.6sec, the internal watchdog timer runs out
and reset is triggered. The internal watchdog timer clears while reset is asserted or when
WDI sees a rising or falling edge. The watchdog function cannot be disabled.
–—–
Manual Reset Input. A logic low on M R asserts reset. Reset remains asserted as long as
–—–
–—–
M R is low and for 200ms after M R returns high. This active-low input has an internal
70µA pull-up current. It can be driven from a TTL or CMOS logic line, or shorted to
ground with a switch. Leave open if unused.
7
7
—
—
—
7
Active-Low Reset Output. Pulses low for 200ms when triggered, and stays low whenever
–—–
–————– VCC is below the reset threshold or when M R is a logic low. It remains low for 200ms after
RESET
–—–
either VCC rises above the reset threshold, the watchdog triggers a reset, or M R goes
from low to high.
–————–
RESET Active-High, Open-Drain Reset Output is the inverse of R E S E T .
8
8
8
VBATT
Backup-Battery Input. When VCC falls below VSW and VBATT, VOUT switches from VCC to
VBATT. When VCC rises above the reset threshold, VOUT reconnects to VCC. VBATT may
exceed VCC. Connect to VCC if no battery is used.
_______________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, powerdown, brownout conditions, or a watchdog timeout.
–————–
R E S E T is guaranteed to be a logic low for 0V < VCC <
VRST, provided that VBATT is greater than 1V. Without
–————–
a backup battery, R E S E T is guaranteed valid for VCC
> 1V. Once V CC exceeds the reset threshold, an
–————–
internal timer keeps R E S E T low for the reset timeout
–————–
period; after this interval, R E S E T goes high (Figure 2).
If a brownout condition occurs (VCC dips below the
–————–
–————–
reset threshold), R E S E T goes low. Each time R E S E T
is asserted, it stays low for the reset timeout period.
Any time V CC goes below the reset threshold, the
internal timer restarts.
The watchdog timer can also initiate a reset. See the
Watchdog Input section.
The MAX804_/MAX805_ active-high RESET output is
open drain, and the inverse of the MAX690_/MAX704_/
–————–
MAX802_/MAX806_ R E S E T output.
6
Reset Threshold
The MAX690T/MAX704T/MAX805T are intended for
3.3V systems with a ±5% power-supply tolerance and a
10% system tolerance. Except for watchdog faults,
reset will not assert as long as the power supply
remains above 3.15V (3.3V - 5%). Reset is guaranteed
to assert before the power supply falls below 3.0V.
The MAX690S/MAX704S/MAX805S are designed for
3.3V ±10% power supplies. Except for watchdog
faults, they are guaranteed not to assert reset as long
as the supply remains above 3.0V (3.3V - 10%). Reset
is guaranteed to assert before the power supply falls
below 2.85V (VCC - 14%).
The MAX690R/MAX704R/MAX805R are optimized for
monitoring 3.0V ±10% power supplies. Reset will not
occur until VCC falls below 2.7V (3.0V - 10%), but is
guaranteed to occur before the supply falls below
2.59V (3.0V - 14%).
The MAX802R/S/T, MAX804R/S/T, and MAX806R/S/T
are respectively similar to the MAX690R/S/T,
MAX805R/S/T, and MAX704R/S/T, but with tightened
reset and power-fail threshold tolerances.
_______________________________________________________________________________________
3.0V/3.3V Microprocessor Supervisory Circuits
3.0V OR 3.3V
BATTERY
SWITCHOVER
CIRCUITRY
VCC
VRST
VOUT
VCC
VSW
BATTERY
SWITCHOVER
COMPARATOR
0V
3.0V OR 3.3V
1.237V
RESET
COMPARATOR
VOUT
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
VBATT = 3.6V
VSW
tWP
3.0V OR 3.3V
RESET
1.237V
*
WDI *
RESET
GENERATOR
WATCHDOG
TIMER
RESET
(RESET)
**
(RESET)
MR
PFI
PFO
POWER-FAIL
COMPARATOR
VPFT
* MAX690T/S/R, MAX802T/S/R, MAX804T/S/R, MAX805T/S/R ONLY
** MAX704T/S/R, MAX806T/S/R ONLY
( ) MAX804T/S/R, MAX805T/S/R ONLY
Figure 1. Block Diagram
PFO
VBATT = PFI = 3.6V
IOUT = 0mA
( ) MAX804T/S/R, MAX805T/S/R ONLY, RESET EXTERNALLY PULLED UP TO VCC
Figure 2. Timing Diagram
Watchdog Input
(MAX690_/802_/804_/805_)
The watchdog circuit monitors the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within 1.6sec,
a reset pulse is triggered. The internal 1.6sec timer is
cleared by either a reset pulse or by a transition (low-tohigh or high-to-low) at WDI. If WDI is tied high or low, a
–————–
R E S E T pulse is triggered every 1.8sec (tWD plus tRS).
As long as reset is asserted, the timer remains cleared
and does not count. As soon as reset is deasserted,
the timer starts counting. Unlike the 5V MAX690 family,
the watchdog function cannot be disabled.
Power-Fail Comparator
The PFI input is compared to an internal reference. If
–——–
PFI is less than VPFT, P F O goes low. The power-fail
comparator is intended for use as an undervoltage
detector to signal a failing power supply. However, the
comparator does not need to be dedicated to this
function because it is completely separate from the rest
of the circuitry.
–——–
The power-fail comparator turns off and P F O goes low
when VCC falls below VSW on power-down. The powerfail comparator turns on as V CC crosses V SW on
power-up. If the comparator is not used, connect PFI to
–——–
–——–
ground and leave
–—– P F O unconnected. P F O may be
connected to M R on the MAX704_/MAX806_ so that a
low voltage on PFI will generate a reset (Figure 5b).
_______________________________________________________________________________________
7
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
VBATT
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V/3.3V Microprocessor Supervisory Circuits
Backup-Battery Switchover
In the event of a brownout or power failure, it may be
necessary to preserve the contents of RAM. With a
backup battery installed at VBATT, the devices automatically switch RAM to backup power when V CC
falls.
This family of µP supervisors (designed for 3.3V and 3V
systems) doesn’t always connect VBATT to VOUT when
VBATT is greater than VCC. VBATT connects to VOUT
(through a 140Ω switch) when VCC is below VSW and
VBATT is greater than V CC, or when VCC falls below
1.75V (typ) regardless of the VBATT voltage. This is
done to allow the backup battery (e.g., a 3.6V lithium
cell) to have a higher voltage than VCC.
Switchover at VSW (2.40V) ensures that battery-backup
mode is entered before VOUT gets too close to the 2.0V
minimum required to reliably retain data in CMOS RAM.
Switchover at higher VCC voltages would decrease
backup-battery life. When VCC recovers, switchover is
deferred until V CC rises above the reset threshold
(VRST) to ensure a stable supply. VOUT is connected to
VCC through a 3Ω PMOS power switch.
Manual Reset
–—–
A logic–—
low
– on M R asserts reset. Reset remains
–—–asserted
while M R is low, and for tWP (200ms) after MR returns
high. This input has an internal 70µA
–—– pull-up current, so
it can be left open if it is not used. M R can be driven with
TTL or CMOS logic levels, or with open-drain/collector
outputs.
–—– Connect a normally open momentary switch
from M R to GND to create a manual-reset function;
external debounce circuitry is not required.
Table 1. Input and Output Status in
Battery-Backup Mode
PIN NAME
VOUT
VCC
Disconnected from VOUT
PFI
The power-fail comparator is disabled when
VCC < VSW
–——–
PFO
8
STATUS
Connected to VBATT through an internal
140Ω switch
Logic low when VCC < VSW or PFI < VPFT
WDI
–—–
MR
–————–
RESET
The watchdog timer is disabled
RESET
High impedance
VBATT
Connected to VOUT
Disabled
Low logic
__________Applications Information
These µP supervisory circuits are not short-circuit
protected. Shorting VOUT to ground—excluding powerup transients such as charging a decoupling
capacitor—destroys the device. Decouple both VCC
and VBATT pins to ground by placing 0.1µF capacitors
as close to the device as possible.
Using a SuperCap
as a Backup Power Source
SuperCaps™ are capacitors with extremely high
capacitance values (e.g., order of 0.47F) for their size.
Figure 3 shows two ways to use a SuperCap as a
backup power source. The SuperCap may be
connected through a diode to the 3V input (Figure 3a)
or, if a 5V supply is also available, the SuperCap may
be charged up to the 5V supply (Figure 3b) allowing a
longer backup period. Since VBATT can exceed VCC
while VCC is above the reset threshold, there are no
special precautions when using these µP supervisors
with a SuperCap.
Operation without a Backup
Power Source
These µP supervisors were designed for batterybacked applications. If a backup battery is not used,
connect both VBATT and V OUT to V CC , or use a
different µP supervisor such as the MAX706T/S/R or
MAX708T/S/R.
Replacing the Backup Battery
The backup power source can be removed while VCC
remains valid, if VBATT is decoupled with a 0.1µF
capacitor to ground, without danger of triggering
–————–
RESET/ R E S E T . As long as V CC stays above V SW ,
battery-backup mode cannot be entered.
Adding Hysteresis
to the Power-Fail Comparator
The power-fail comparator has a typical input
hysteresis of 10mV. This is sufficient for most applications where a power-supply line is being monitored
through an external voltage divider (see the section
Monitoring an Additional Power Supply).
If additional noise margin is desired, connect a resistor
–——–
between P F O and PFI as shown in Figure 4a. Select
the ratio of R1 and R2 such that PFI sees 1.237V (VPFT)
when V IN falls to its trip point (VTRIP ). R3 adds the
hysteresis and will typically be more than 10 times the
value of R1 or R2. The hysteresis window extends both
above (VH) and below (VL) the original trip point (VTRIP).
™ SuperCap is a trademark of Baknor Industries.
_______________________________________________________________________________________
3.0V/3.3V Microprocessor Supervisory Circuits
+5V
VCC
1N4148
VBATT
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
VOUT
3.0V OR
3.3V
TO STATIC
RAM
RESET
(RESET)
TO µP
VBATT
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
VOUT
RESET
(RESET)
TO STATIC
RAM
TO µP
0.47F
0.47F
GND
GND
a
VCC
1N4148
( ) ARE FOR MAX804T/S/R, MAX805T/S/R ONLY
b
( ) ARE FOR MAX804T/S/R, MAX805T/S/R ONLY
Figure 3. Using a SuperCap as a Backup Power Source
Connecting an ordinary signal diode in series with R3,
as shown in Figure 4b, causes the lower trip point (VL)
to coincide with the trip point without hysteresis (VTRIP),
so the entire hysteresis window occurs above VTRIP.
This method provides additional noise margin without
compromising the accuracy of the power-fail threshold
when the monitored voltage is falling. It is useful for
accurately detecting when a voltage falls past a
threshold.
The current through R1 and R2 should be at least 1µA to
ensure that the 25nA (max over extended temperature
range) PFI input current does not shift the trip point. R3
should be larger than 10kΩ so it does not load down the
–——–
P F O pin. Capacitor C1 adds additional noise rejection.
Monitoring an Additional Power Supply
These µP supervisors can monitor either positive or
negative supplies using a resistor voltage divider to
–——–
PFI. P F O can be used to generate–—
an
– interrupt to the
–——–
µP (Figure 5). Connecting P F O to M R on the MAX704
and MAX806 causes reset to assert when the
monitored supply goes out of tolerance.
Reset remains
–—–
–——–
asserted as long as P F O holds MR low, and for 200ms
–——–
after P F O goes high.
Interfacing to µPs
with Bidirectional Reset Pins
µPs with bidirectional reset pins, such as the Motorola
68HC11 series, can contend with the MAX690_/
–————–
MAX704_/MAX802_/MAX806_ R E S E T output. If, for
–————–
example, the R E S E T output is driven high and the µP
wants to pull it low, indeterminate logic levels may
result. To correct this, connect a 4.7kΩ resistor
–————–
between the R E S E T output and the µP reset I/O, as in
–————–
Figure 6. Buffer the R E S E T output to other system
components.
Negative-Going VCC Transients
While issuing resets to the µP during power-up, powerdown, and brownout conditions, these supervisors are
relatively immune to short-duration negative-going VCC
transients (glitches). It is usually undesirable to reset
the µP when VCC experiences only small glitches.
Figure 7 shows maximum transient duration vs. resetcomparator overdrive, for which reset pulses are not
generated. The graph was produced using negativegoing VCC pulses, starting at 3.3V and ending below
the reset threshold by the magnitude indicated (reset
comparator overdrive). The graph shows the maximum
pulse width a negative-going V CC transient may
typically have without causing a reset pulse to be
issued. As the amplitude of the transient increases
(i.e., goes farther below the reset threshold), the
maximum allowable pulse width decreases. Typically,
a V CC transient that goes 100mV below the reset
threshold and lasts for 40µs or less will not cause a
reset pulse to be issued.
A 100nF bypass capacitor mounted close to the VCC
pin provides additional transient immunity.
_______________________________________________________________________________________
9
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V OR 3.3V
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V/3.3V Microprocessor Supervisory Circuits
VIN
VIN
R1
VCC
R1
PFI
R2
R3
C1*
PFO
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
VCC
R2
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
PFO
GND
R3
C1*
GND
*OPTIONAL
TO µP
PFI
*OPTIONAL
TO µP
PFO
PFO
0V
VL
0V
VTRIP = VPFT
VTRIP
( R R+ R )
1
VTRIP = VPFT
2
(
VTRIP
0V
2
( R1
)
1
1
+
R2 R3
1
1
1
1
VCC
+
+
–
R3
R1 R2 R3
VH = (VPFT + VPFH) (R1)
VL = R1 VPFT
0V
VIN
VH
+
WHERE VPFT = 1.237V
VPFH = 10mV
Figure 4. a) Adding Additional Hysteresis to the Power-Fail Comparator
( R1
+
1
1
1
+
R2 R3
VIN
VCC
R2
2
2
CC - VD)
R3
3.0V OR 3.3V
VCC
R1
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
) – (V
b) Shifting the Additional Hysteresis above VPFT
3.0V OR 3.3V
PFI
1
WHERE VPFT = 1.237V
VPFH = 10mV
VD = DIODE FORWARD VOLTAGE DROP
VL = VTRIP
b
R1
(R R+ R )
VH = R1 (VPFT + VPFH)
)
a
VIN
VH
PFO
PFI
R2
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R
PFO
MR
*
GND
GND
VVCC
VCC
PFO
PFO
VL
VTRIP = R2 (VPFT + VPFH)
VL = R2 (VPFT)
a
(
1
1
( R1 + R2 ) –
1
1
+
R 1 R2
)
VCC
–
R1
VTRIP
VCC
R1
V-
VTRIP
0V
VTRIP = VPFT
WHERE VPFT = 1.237V
VPFH = 10mV
(
R1 + R2
R2
VH = (VPFT + VPFH)
NOTE: VTRIP IS NEGATIVE
(
VH
)
R1 + R2
R2
* MAX704T/S/R,
MAX806T/S/R ONLY
)
b
Figure 5. Using the Power-Fail Comparator to Monitor an Additional Power Supply
10
VIN
______________________________________________________________________________________
3.0V/3.3V Microprocessor Supervisory Circuits
_Typical Operating Circuits (cont.)
3.0V OR 3.3V
VOUT
VCC
VCC
VCC
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX806T/S/R
µP
4.7k
0.1µF
RESET
RESET
3.6V
0.1µF
MAX704T/S/R
MAX806T/S/R
RESET
MR
GND
GND
RAM
VBATT
0.1µF
µP
PFI
GND
Figure 6. Interfacing to µPs with Bidirectional Reset I/O
DS690-806 fig7
MAXIMUM TRANSIENT DURATION (µs)
100
80
VCC = 3.3V
TA = +25°C
60
40
20
0
10
100
1000
RESET COMPARATOR OVERDRIVE (VRST - VCC) (mV)
Figure 7. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
______________________________________________________________________________________
11
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R
3.0V/3.3V Microprocessor Supervisory Circuits
_Ordering Information (continued)
PART**
TEMP. RANGE
___________________Chip Topography
V OUT
PIN-PACKAGE
MAX704_CPA
0°C to +70°C
8 Plastic DIP
MAX704_CSA
MAX704_C/D
MAX704_EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX704_ESA
MAX704_MJA
MAX802_CPA
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 SO
8 CERDIP
8 Plastic DIP
MAX802_CSA
MAX802_C/D
MAX802_EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX802_ESA
MAX802_MJA
MAX804_CPA
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 SO
8 CERDIP
8 Plastic DIP
MAX804_CSA
MAX804_C/D
MAX804_EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX804_ESA
MAX804_MJA
MAX805_CPA
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 SO
8 CERDIP
8 Plastic DIP
MAX805_CSA
MAX805_C/D
MAX805_EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX805_ESA
MAX805_MJA
MAX806_CPA
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 SO
8 CERDIP
8 Plastic DIP
MAX806_CSA
MAX806_C/D
MAX806_EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX806_ESA
MAX806_MJA
-40°C to +85°C
-55°C to +125°C
8 SO
8 CERDIP
VBATT
V CC
0.110"
(2.794mm)
GND
RESET
(RESET)
WDI
[MR]
PFI PFO
0.080"
(2.032mm)
( ) ARE FOR MAX804T/S/R, MAX805T/S/R.
[ ] ARE FOR MAX704T/S/R, MAX806T/S/R.
TRANSISTOR COUNT: 802;
SUBSTRATE IS CONNECTED TO THE HIGHER OF
V CC OR VBATT, AND MUST BE FLOATED IN ANY
HYBRID DESIGN.
* Contact factory for dice specifications.
** These parts offer a choice of reset threshold voltage. Select
the letter corresponding to the desired nominal reset threshold
voltage (T = 3.075V, S = 2.925V, R = 2.625V) and insert it into
the blank to complete the part number.
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.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.