19-0075; Rev. 7; 11/05
Microprocessor Supervisory Circuit
General Description
The MAX791 microprocessor (µP) supervisory circuit
reduces the complexity and number of components need-
ed to monitor power-supply and battery-control functions
in µP systems. The 50µA supply current makes the
MAX791 ideal for use in portable equipment, while the 6ns
chip-enable propagation delay and 250mA output capa-
bility (25mA in battery-backup mode) make it suitable for
larger, higher-performance equipment.
The MAX791 comes in 16-pin DIP, TSSOP, and narrow SO
packages and provides the following functions:
–——
— —–
• µP reset. RESET output is asserted during power-up,
power-down, and brownout conditions, and is guaran-
teed to be in the correct state for V
CC
down to 1V,
even with no battery in the circuit.
• Manual-reset input.
• A 1.25V threshold detector provides for power-fail
warning and low-battery detection, or monitors a
power supply other than +5V.
• Two-stage power-fail warning. A separate low-line
comparator compares V
CC
to a threshold 150mV
above the reset threshold.
• Backup-battery switchover for CMOS RAM, real-time
clocks, µPs, or other low-power logic.
• Software monitoring of backup-battery voltage.
• A watchdog-fault output is asserted if the watchdog
input has not been toggled within either a preset or
an adjustable timeout period.
• Write protection of CMOS RAM or EEPROM.
• Pulsed watchdog output to give advance warning of
–— –
—
impending WDO assertion caused by watchdog timeout.
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Features
Precision 4.65V Voltage Monitoring
200ms Power-OK / Reset Time Delay
Independent Watchdog Timer—Preset or Adjustable
1µA Standby Current
Power Switching
250mA Output in V
CC
Mode
25mA Output in Battery-Backup Mode
On-Board Gating of Chip-Enable Signals
Memory Write-Cycle Completion
6ns CE Gate Propagation Delay
MaxCap
or SuperCap
Compatible
Voltage Monitor for Power-Fail or Low-Battery Warning
Backup-Battery Monitor
–——
——–
Guaranteed RESET Valid to V
CC
= 1V
MAX791
Ordering Information
PART
MAX791CPE
MAX791CSE
MAX791C/D
MAX791CUE
MAX791EPE
MAX791ESE
MAX791EJE
MAX791EUE
MAX791MJE
TEMP RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
16 TSSOP
16 Plastic DIP
16 Narrow SO
16 CERDIP
16 TSSOP
16 CERDIP
Applications
Computers
Controllers
Portable/Battery-
Powered Equipment
Critical µP Power Monitoring
Intelligent Instruments
* Dice are specified at T
A
= +25°C.
Devices in PDIP, SO and TSSOP packages are available in both
leaded and lead-free packaging. Specify lead free by adding
the + symbol at the end of the part number when ordering.
Lead free not available for CERDIP package.
Typical Operating Circuit
Pin Configuration
+5V
0.1µF
0.1µF
CMOS
RAM
TOP VIEW
VBATT 1
V
OUT
2
V
CC
3
GND 4
BATT ON 5
PFO 6
PFI 7
SWT 8
16 WDPO
15 RESET
14 WDO
0.47F*
OTHER SYSTEM
RESET SOURCES
V
CC
VBATT
BATT
ON
SWT
V
OUT
CE OUT
MR
+12V
PFI
MAX791
+12V SUPPLY
WDI
PFO
GND
LOWLINE
RESET
WDO
CE IN
ADDRESS
DECODE
A0–A15
µP
I/O
NMI
RESET
INT
MAX791
13 CE IN
12 CE OUT
11 WDI
10 LOWLINE
9
MR
*MaxCap
FAILURE
DIP/SO/TSSOP
MaxCap is a registered trademark of Cesiwid Inc. SuperCap is a registered trademark of Baknor Industries.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Microprocessor Supervisory Circuit
MAX791
ABSOLUTE MAXIMUM RATINGS
Input Voltage (with respect to GND)
V
CC
.......................................................................-0.3V to +6V
VBATT..................................................................-0.3V to + 6V
All Other Inputs.....................................-0.3V to (V
OUT
+ 0.3V)
Input Current
V
CC
Peak ..........................................................................1.0A
V
CC
Continuous ............................................................250mA
VBATT Peak ..................................................................250mA
VBATT Continuous ..........................................................25mA
GND, BATT ON .............................................................100mA
All Other Outputs ............................................................25mA
Continuous Power Dissipation (T
A
= +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C) ..........842mW
Narrow SO (derate 8.70mW/°C above +70°C) ............696mW
CERDIP (derate 10.00mW/°C above +70°C) ...............800mW
TSSOP (derate 6.70mW/°C above +70°C) ..................533mW
Operating Temperature Ranges
MAX791C_ _ ......................................................O°C to +70°C
MAX791E_ _ ....................................................-40°C to +85°C
MAX791MJE ..................................................-55°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+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
(V
CC
= 4.75V to 5.5V, VBATT = 2.8V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Operating Voltage Range
V
CC
, VBATT (Note 1)
I
OUT
= 25mA
V
OUT
in Normal
Operating Mode
V
CC
= 4.5V
I
OUT
= 250mA
MAX791C/E
MAX791M
CONDITIONS
MIN
0
V
CC
- 0.05 V
CC
- 0.02
V
CC
- 0.3
V
CC
- 0.2
V
CC
- 0.40
V
CC
- 0.2
V
CC
- 0.12
0.8
0.8
1.2
VBATT - 0.3
VBATT - 0.25
VBATT - 0.15
8
13
17
50
T
A
= +25°C
T
A
= T
MIN
to T
MAX
T
A
= +25°C
T
A
= T
MIN
to T
MAX
-0.1
-1.0
VBATT + 0.03
VBATT - 0.03
60
2
0.04
15
25
30
150
1
5
0.02
0.02
µA
µA
µA
V
mV
V
Ω
V
1.2
1.6
2.0
Ω
TYP
MAX
5.5
UNITS
V
V
V
CC
= 3V, VBATT = 2.8V, I
OUT
= 100mA
V
CC
-to-V
OUT
On-Resistance
V
CC
= 4.5V
V
CC
= 3V
VBATT = 4.5V, I
OUT
= 20mA
V
OUT
in Battery-Backup Mode
VBATT = 2.8V, I
OUT
= 10mA
VBATT = 2.0V, I
OUT
= 5mA
VBATT = 4.5V
VBATT-to-V
OUT
On-Resistance
Supply Current in Normal
Operating Mode (excludes I
OUT
)
Supply Current in Battery-Backup
Mode (excludes I
OUT
) (Note 2)
VBATT Standby Current
(Note 3)
Battery-Switchover Threshold
Battery-Switchover Hysteresis
Low-Battery Detector Threshold
VBATT = 2.8V
VBATT = 2.0V
V
CC
> VBATT - 1V
V
CC
< VBATT - 1.2V,
VBATT = 2.8V
VBATT + 0.2V
≤
V
CC
Power up
Power down
MAX791C/E
MAX791M
2
_______________________________________________________________________________________
Microprocessor Supervisory Circuit
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 4.75V to 5.5V, VBATT = 2.8V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
BATT ON Output
Low Voltage
BATT ON Output
Short-Circuit Current
I
SINK
= 3.2mA
I
SINK
= 25mA
Sink current
Source current
1
4.50
CONDITIONS
MIN
TYP
0.1
0.7
60
15
4.65
15
150
100
80
140
1.0
200
1.6
10
100
1
70
MAX791C, I
SINK
= 50µA, V
CC
= 1.0V, V
CC
falling
–——
— —–
RESET Output Voltage
–——
— —–
RESET Output
Short-Circuit Current
– ——— –
— ——
LOW LINE Output Voltage
– ——— –
— ——
LOW LINE Output
Short-Circuit Current
–— –
—
WDO Output Voltage
–— –
—
WDO Output Short-Circuit Current
–— —
—–
WDPO Output Voltage
–— —
—–
WDPO Output
Short-Circuit Current
MAX791E/M, I
SINK
= 50µA, V
CC
= 1.2V, V
CC
falling
I
SINK
= 3.2mA, V
CC
= 4.25V
I
SOURCE
= 1.6mA, V
CC
= 5V
Output source current
I
SINK
= 3.2mA, V
CC
= 4.25V
I
SOURCE
= 1µA, V
CC
= 5V
Output source current
I
SINK
= 3.2mA
I
SOURCE
= 500µA, V
CC
= 5V
Output source current
I
SINK
= 3.2mA
I
SOURCE
= 1mA
Output source current
3.5
7
20
3.5
3
10
0.4
3.5
15
100
0.4
3.5
7
20
0.4
mA
V
µA
V
mA
V
mA
0.004
0.004
0.1
0.3
0.3
0.4
280
2.25
100
4.75
MAX
0.4
1.5
UNITS
V
mA
µA
V
mV
mV
µs
µs
ms
s
ms
ns
ms
ns
ns
V
MAX791
RESET, LOW-LINE, AND WATCHDOG TIMER
–——
— —–
RESET Threshold Voltage
–——
— —–
RESET Threshold Hysteresis
– ——— –
— ——
–——
— —–
LOW LINE -to-RESET
Threshold Voltage
–——
— —–
V
CC
-to-RESET Delay
Power down
– ——— –
— ——
V
CC
-to-LOW LINE Delay
Power down
–——
— —–
Power up
RESET Active Timeout Period
Watchdog Timeout Period
Minimum Watchdog
Timeout Period
Minimum Watchdog Input
Pulse Width
–— —
—–
WDPO Pulse Width
–— —
—–
–— –
—
WDPO -to-WDO Delay
SWT connected to V
OUT
4.7nF capacitor connected from SWT to GND
V
IL
= 0.8V, V
IH
= 0.75 x V
CC
_______________________________________________________________________________________
3
Microprocessor Supervisory Circuit
MAX791
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 4.75V to 5.5V, VBATT = 2.8V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
WDI Threshold Voltage
(Note 4)
WDI Input Current
POWER-FAIL COMPARATOR
PFI Input Threshold
PFI Leakage Current
–—
—–
PFO Output Voltage
–—
—–
PFO Short-Circuit Current
–—
—–
PFI-to-PFO Delay
CHIP-ENABLE GATING
––
—
CE IN Leakage Current
––
—
––
—
CE IN-to-CE OUT Resistance
(Note 5)
––
—
CE OUT Short-Circuit Current
(Reset Active)
––
—
—
–
CE IN-to-CE OUT Propagation
Delay (Note 6)
––
—
CE OUT Output Voltage High
(Reset Active)
–—— – –
— —– —
RESET CE OUT Delay
-to-
MANUAL RESET INPUT
–—
–
MR Minimum Pulse Width
–——
— —–
–—
–
MR -to -RESET
Propagation Delay
–—
–
MR Threshold
–—
–
MR Pull-Up Current
I
SINK
= 3.2mA
I
SOURCE
= 1µA, V
CC
= 5V
Output sink current
Output source current
V
IN
= -20mV, V
OD
= 15mV
V
IN
= 20mV, V
OD
= 15mV
Disabled mode
Enabled mode
––
—
Disabled mode, CE OUT = 0V
50Ω source impedance driver, C
LOAD
= 50pF
V
CC
= 5V, I
OUT
= -100µA
V
CC
= 0V, VBATT = 2.8V, I
OUT
= 1µA
Power down
3.5
2.7
15
0.1
1
3.5
60
15
15
55
±0.005
75
0.75
6
±1
150
2.0
10
100
V
CC
= 5V
1.20
1.25
±0.01
1.30
±25
0.4
V
nA
V
mA
µA
µs
V
IH
V
IL
WDI = 0V
WDI = V
OUT
-50
-10
20
50
CONDITIONS
MIN
0.75 x V
CC
0.8
TYP
MAX
UNITS
V
µA
µA
Ω
mA
ns
V
µs
25
15
7
µs
µs
V
250
µA
V
CC
= 5V
–—
–
MR = 0V
1.25
23
Note 1:
Either V
CC
or VBATT can go to 0V, if the other is greater than 2.0V.
Note 2:
The supply current drawn by the MAX791 from the battery (excluding I
OUT
) typically goes to 10µA when
(VBATT - 1V) < V
CC
< VBATT. In most applications, this is a brief period as V
CC
falls through this region.
Note 3:
"+" = battery-discharging current, "-" = battery-charging current.
Note 4:
WDI is internally connected to a voltage-divider between V
OUT
and GND. If unconnected, WDI is driven to 1.6V (typ),
disabling the watchdog function.
—
–
—
–
Note 5:
The chip-enable resistance is tested with V
CC
= 4.75V V
– E IN
= V
CE OUT
= V
CC
/ 2.
C
––
—
––
—
Note 6:
The chip-enable propagation delay is measured from the 50% point at CE IN to the 50% point at CE OUT.
4
_______________________________________________________________________________________
Microprocessor Supervisory Circuit
MAX791
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
CHIP-ENABLE ON-RESISTANCE
vs. TEMPERATURE
V
CC
= +4.75V
VBATT = 2.8V
CE IN = V
CC
/2
MAX791-03
V
CC
SUPPLY CURRENT vs. TEMPERATURE
(NORMAL OPERATING MODE)
MAX791-01
BATTERY-SUPPLY CURRENT vs. TEMPERATURE
(BATTERY-BACKUP MODE)
V
CC
= 0V
VBATT = 2.8V
NO LOAD
MAX791-02
58
V
CC
= +5V
VBATT = 2.8V
PFI, CE IN = 0V
2.0
BATTERY SUPPLY CURRENT (µA)
120
V
CC
SUPPLY CURRENT (µA)
54
50
CE ON-RESISTANCE (Ω)
1.5
100
1.0
80
46
42
0.5
60
38
-60
-30
0
30
60
90
120
150
TEMPERATURE (°C)
0
-60
-30
0
30
60
90
120
150
TEMPERATURE (°C)
40
-60
-30
0
30
60
90
120
150 180
TEMPERATURE (°C)
VBATT-to-V
OUT
ON-RESISTANCE
vs. TEMPERATURE
MAX791-04
V
CC
-to-V
OUT
ON-RESISTANCE
vs. TEMPERATURE
V
CC
-to-V
OUT
ON-RESISTANCE (Ω)
MAX791-05
PFI THRESHOLD
vs. TEMPERATURE
MAX791-05
20
VBATT-to-V
OUT
ON-RESISTANCE (Ω)
VBATT = 2.0V
15
VBATT = 2.8V
1.2
1.1
1.50
1.25
PFI THRESHOLD (V)
1.00
0.75
0.50
0.25
0
V
CC
= +5V,
VBATT = 0V,
NO LOAD ON PFO
-60
-30
0
30
60
90
120
1.0
0.9
0.8
0.7
0.6
10
VBATT = 4.5V
5
-60
-30
0
30
60
90
TEMPERATURE (°C)
V
CC
= 0V
120
150
-60
-30
0
30
60
V
CC
= +5V,
VBATT = 0V
90
120
150
150
TEMPERATURE (°C)
TEMPERATURE (°C)
RESET THRESHOLD
vs. TEMPERATURE
MAX791-07
RESET OUTPUT RESISTANCE
vs. TEMPERATURE
MAX791-08
RESET DELAY
vs. TEMPERATURE
V
CC
= 0V TO 5V STEP
VBATT = 2.8V
MAX791-09
4.80
4.75
4.70
RESET THRESHOLD (V)
4.65
4.60
4.55
4.50
4.45
4.40
4.35
4.30
-60
-30
0
30
60
90
120
VBATT = 0V,
POWER DOWN
600
RESET OUTPUT RESISTANCE (Ω)
500
400
300
200
100
0
V
CC
= 0V, VBATT = 2.8V
SINKING CURRENT
V
CC
= +5V, VBATT = 2.8V
SOURCING CURRENT
230
220
RESET DELAY (ms)
210
200
190
180
170
150
-60
-30
0
30
60
90
120
150
-60
-30
0
30
60
90
120
150
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
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