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_______________General Description
The MAX793/MAX794/MAX795 microprocessor (µP)
supervisory circuits monitor and control the activities of
+3.0V/+3.3V µPs by providing backup-battery switchover,
among other features such as low-line indication, µP
reset, write protection for CMOS RAM, and a watchdog
(see the
Selector Guide below). The backup-battery volt-
age can exceed V
CC
, permitting the use of 3.6V lithium
batteries in systems using 3.0V to 3.3V for V
CC
.
The MAX793/MAX795 offer a choice of reset threshold
voltage range (denoted by suffix letter): 3.00V to 3.15V
(T), 2.85V to 3.00V (S), and 2.55V to 2.70V (R). The
MAX794’s reset threshold is set externally with a resistor
divider. The MAX793/MAX794 are available in 16-pin
DIP and narrow SO packages, and the MAX795 comes
in 8-pin DIP and SO packages. For similar devices
designed for 5V systems, see the
µP Supervisory
Circuits table at the back of this data sheet.
________________________Applications
Battery-Powered Computers and Controllers
Embedded Controllers
Intelligent Controllers
Critical µP Power Monitoring
Portable Equipment
____________________________Features
MAX793/MAX794/MAX795
o
Precision Supply-Voltage Monitor:
Fixed Reset Trip Voltage (MAX793/MAX795)
Adjustable Reset Trip Voltage (MAX794)
o
Guaranteed Reset Assertion to V
CC
= 1V
o
Backup-Battery Power Switching—Battery
Voltage Can Exceed V
CC
o
On-Board Gating of Chip-Enable Signals—7ns
Max Propagation Delay
MAX793/MAX794 Only
o
Battery Freshness Seal
o
Battery OK Output (MAX793)
o
Uncommitted Voltage Monitor for Power-Fail or
Low-Battery Warning
o
Independent Watchdog Timer (1.6sec timeout)
o
Manual Reset Input
______________Ordering Information
Ordering Information continued on last page.
* The MAX793/MAX795 offer a choice of reset threshold voltage.
Select the letter corresponding to the desired reset threshold
voltage range (T = 3.00V to 3.15V, S = 2.85V to 3.00V, R = 2.55V
to 2.70V) and insert it into the blank to complete the part number.
The MAX794’s reset threshold is adjustable.
MAX793/MAX794/MAX795
3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
________________________________________________________________
Maxim Integrated Products
1
MAX793
RESET
LOWLINE
WDI
CE IN
CE OUT
3.0V OR 3.3V
+5V
BATT
A0-A15
MR
+5V SUPPLY
FAILURE
BATT ON
PFI
WDO
OUT
CMOS
RAM
ADDRESS
DECODER
0.1
µ
F
PMOS
0.1
µ
F
V
CC
PFO
GND
I/O
µ
P
NMI
RESET
V
CC
V
CC
0.1
µ
F
3.6V
BATT OK
(OPTIONAL)
Si9433DY
SILICONIX
19-0366; Rev 1; 1/96
PART*
MAX793
_CPE
MAX793_CSE
MAX793_EPE
-40°C to +85°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
16 Plastic DIP
MAX793_ESE
-40°C to +85°C
16 Narrow SO
FEATURE
Active-Low Reset
Active-High Reset
Programmable Reset
Threshold
Low-Line Early Warning
Output
MAX793
MAX794
MAX795
Backup-Battery
Switchover
External Switch Driver
Power-Fail Comparator
Battery OK Output
_____________________Selector Guide
__________Typical Operating Circuit
Watchdog Input
Battery Freshness Seal
Manual Reset Input
Chip-Enable Gating
Pins-Package
16-DIP/SO 16-DIP/SO
8-DIP/SO
Pin Configurations appear at end of data sheet.
µA
MAX793/MAX794/MAX795
3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
CC
= 3.17V to 5.5V for the MAX793T/MAX795T, V
CC
= 3.02V to 5.5V for the MAX793S/MAX795S, V
CC
= 2.72V to 5.5V for the
MAX793R/MAX794/MAX795R, V
BATT
= 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°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.
Terminal Voltage (with respect to GND)
V
CC
........................................................................-0.3V to 6.0V
V
BATT
.....................................................................-0.3V to 6.0V
All Other Inputs ..................-0.3V to the higher of V
CC
or V
BATT
Continuous Input Current
V
CC
.................................................................................200mA
V
BATT
................................................................................50mA
GND ..................................................................................20mA
Output Current
V
OUT
................................................................................200mA
All Other Outputs ..............................................................20mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) .....727mW
8-Pin SO (derate 5.88mW/°C above +70°C)..................471mW
16-Pin Plastic DIP (derate 10.53mW/°C above +70°C) .842mW
16-Pin Narrow SO (derate 9.52mW/°C above +70°C) ...696mW
Operating Temperature Ranges
MAX793_C_ _/MAX794C_ _/MAX795_C_ _ ......... 0°C to +70°C
MAX793_E_ _/MAX794E_ _/MAX795_E_ _ ........-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
MAX79_E
MAX79_C
V
BATT
> V
CC
(Note 6)
I
OUT
= 250µA (Note 4)
I
OUT
= 30mA (Note 4)
V
SW
> V
CC
> 1.75V (Note 5)
I
OUT
= 75mA
V
BATT
= 2.3V
CONDITIONS
Battery Switch Threshold
(V
CC
falling)
V
2.30
2.41
2.52
V
SW
2.55
2.68
2.80
2.69
2.82
2.95
mV
20
65
V
CC
-
V
BATT
V
V
BATT
- 0.14
V
OUT
OUT Output Voltage in
Battery-Backup Mode
V
BATT
- 0.1
V
BATT
- 0.034
V
1.1
5.5
1.0
5.5
Operating Voltage Range,
V
CC
, V
BATT
(Note 1)
V
V
CC
- 0.001
V
CC
- 0.5mV
V
OUT
OUT Output Voltage in
Normal Mode
V
CC
- 0.12
V
CC
- 0.050
V
CC
- 0.3
V
CC
- 0.125
µA
0.5
Battery Leakage Current
(Note 3)
µA
1
BATT Supply Current
(excluding I
OUT
) (Note 2)
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
V
CC
= 0V, V
OUT
= 0V
µA
1
BATT Leakage Current,
Freshness Seal Enabled
I
OUT
= 250µA
I
OUT
= 1mA
MAX793T/MAX795T
MAX793S/MAX795S
This value is identical to the reset threshold,
V
CC
rising for V
BATT
> V
RST
V
CC
-
V
BATT
MAX793R/MAX795R/
MAX794
V
BATT
< V
RST
mV
25
65
Battery Switch Threshold
(V
CC
rising) (Note 7)
MAX793/MAX794,
MR = V
CC
µA
62
80
I
SUPPLY
46
60
V
CC
Supply Current
(excluding I
OUT
, I
CE OUT
)
V
CC
= 2.1V,
V
BATT
= 2.3V
µA
32
45
I
SUPPLY
V
CC
Supply Current in
Battery-Backup Mode
(excluding I
OUT
)
V
CC
< 3.6V
V
CC
< 5.5V
MAX793/MAX794
MAX795
24
35
MAX795
49
70
35
50
V
CC
< 3.6V
V
CC
< 5.5V
MAX793/MAX794/MAX795
3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3.17V to 5.5V for the MAX793T/MAX795T, V
CC
= 3.02V to 5.5V for the MAX793S/MAX795S, V
CC
= 2.72V to 5.5V for the
MAX793R/MAX794/MAX795R, V
BATT
= 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
CONDITIONS
2.85
2.925
3.00
3.00
3.075
3.15
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
V
CC
Falling
3.00
3.085
3.17
2.55
2.625
2.70
V
RST
V
V
RST IN
V
V
CC
Falling
V
CC
Rising
RESET IN Threshold
(MAX794 only)
1.212
1.240
1.262
Reset Threshold (Note 8)
2.55
2.635
2.72
2.85
2.935
3.02
V
LR
mV
MAX793
LOWLINE-to-Reset
Threshold, (V
LOWLINE
-
V
RST
), V
CC
Falling
V
CC
< 3.6V
5
15
25
30
45
60
mV
MAX793S/MAX795S
MAX793T/MAX795T
MAX794
MAX793
3.08
Low-Line Comparator
Hysteresis
3.23
mV
10
10
ms
t
RP
140
200
280
Reset Timeout Period
V
MAX793R/MAX795R
2.78
nA
V
PFI
rising
V
PFI
falling
PFI Input Current
MAX794
V
-25
2
25
V
TH
1.212
1.250
1.287
PFI Input Threshold
1.212
1.240
1.262
V
LL
1.317
LOWLINE Threshold,
V
CC
Rising
V
V
BOK
2.00
2.25
2.50
BATT OK Threshold
(MAX793)
V
OH
V
I
SOURCE
= 300µA, V
CC
= V
RST
max
BATT OK, BATT ON, WDO,
LOWLINE Output Voltage
High
I
SOURCE
=300µA, V
CC
= V
RST
min
0.8V
CC
0.86V
CC
V
V
OH
0.8V
CC
0.86V
CC
RESET Output Voltage High
mV
10
20
PFI Hysteresis, PFI Rising
MAX793T/MAX795T
MAX793S/MAX795S
MAX793R/MAX795R
MAX793T/MAX795T
MAX793S/MAX795S
MAX793R/MAX795R
nA
RESET IN Leakage Current
(MAX794 only)
-25
2
25
MAX794
V
OH
V
I
SOURCE
= 65µA, V
CC
= V
RST
max
PFO Output Voltage High
0.8V
CC
V
OH
V
I
SOURCE
= 100µA, V
CC
= 2.3V, V
BATT
= 3V
BATT ON Output
Voltage High
0.8V
BATT
I
LEAK
µA
V
CC
= V
RST
max
RESET Output Leakage
Current (Note 9)
-1
-1
I
SC
µA
V
CC
= 3.3V, V
PFO
= 0V
PFO Output Short to GND
Current
180
500
V
OL
V
I
SINK
= 1.2mA; RESET, LOWLINE tested
with V
CC
= V
RST
min; RESET, BATTOK,
WDO tested with V
CC
= V
RST
max
PFO, RESET, RESET, WDO,
LOWLINE Output Voltage
Low
0.08
0.2V
CC
INPUT AND OUTPUT LEVELS
V
CC
Rising
1.212
1.250
1.282
MAX793/MAX794/MAX795
3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
4
_______________________________________________________________________________________
CONDITIONS
V
OL
V
V
OL
V
I
SINK
= 3.2mA, V
CC
= V
RST
max
MAX79_E, V
BATT
= V
CC
= 1.2V, I
SINK
= 200µA
BATT ON Output
Voltage Low
MAX79_C, V
BATT
= V
CC
= 1.0V, I
SINK
= 40µA
0.2V
CC
RESET Output Voltage Low
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
V
IL
V
t
MR
ns
MAX793/MAX794 only
V
RST
max < V
CC
< 5.5V
MR Pulse Width
100
50
All Inputs Including PFO
(Note 10)
0.3V
CC
V
IH
0.7V
CC
0.17
0.3
0.13
0.3
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3.17V to 5.5V for the MAX793T/MAX795T, V
CC
= 3.02V to 5.5V for the MAX793S/MAX795S, V
CC
= 2.72V to 5.5V for the
MAX793R/MAX794/MAX795R, V
BATT
= 3.6V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
t
MD
ns
MAX793/MAX794 only, MR = 0V
MAX793/MAX794 only
µA
MR-to-Reset Delay
25
70
250
MR Pull-Up Current
75
250
Ω
ns
V
CC
= V
RST
max, Figure 9
Enable mode, V
CC
= V
RST
max
CE IN-to-CE OUT
Propagation Delay
Disable mode
2
7
CE IN-to-CE OUT
Resistance
V
OH
V
OL
V
V
CC
= V
RST
max, I
OUT
= 1.6mA,
V
CE IN
= 0V
V
CC
= V
RST
max, I
OUT
= -1mA,
V
CE IN
= V
CC
CE OUT Drive from CE IN
0.2V
CC
0.8V
CC
nA
46
I
LEAK
±10
CE IN Leakage Current
Note 1:
V
CC
supply current, logic input leakage, watchdog functionality (MAX793/MAX794), MR functionality (MAX793/MAX794),
PFI functionality (MAX793/MAX794), state of RESET and RESET (MAX793/MAX794) tested at V
BATT
= 3.6V and V
CC
= 5.5V.
The state of RESET is tested at V
CC
= V
CC
min.
Note 2:
Tested at V
BATT
= 3.6V, V
CC
= 3.5V and 0V. The battery current will rise to 10µA over a narrow transition window around
V
CC
= 1.9V.
Note 3:
Leakage current into the battery is tested under the worst-case conditions at V
CC
= 5.5V, V
BATT
= 1.8V and V
CC
= 1.5V,
V
BATT
= 1.0V.
Note 4:
Guaranteed by design.
Note 5:
When V
SW
> V
CC
> V
BATT
, OUT remains connected to V
CC
until V
CC
drops below V
BATT
. The V
CC
-to-V
BATT
comparator
has a small 15mV typical hysteresis to prevent oscillation. For V
CC
< 1.75V (typical), OUT switches to BATT regardless of
V
BATT
.
Note 6:
When V
BATT
> V
CC
> V
SW
, OUT remains connected to V
CC
until V
CC
drops below the battery switch threshold (V
SW
).
Note 7:
OUT switches from BATT to V
CC
when V
CC
rises above the reset threshold, if V
BATT
> V
RST
. In this case, switchover back
to V
CC
occurs at the exact voltage that causes reset to be asserted, however switchover occurs 200ms prior to reset. If
V
BATT
< V
RST
, OUT switches from BATT to V
CC
when V
CC
exceeds V
BATT
.
Note 8:
The reset threshold tolerance is wider for V
CC
rising than for V
CC
falling to accommodate the 10mV typical hysteresis,
which prevents internal oscillation.
Note 9:
The leakage current into or out of the RESET pin is tested with RESET not asserted (RESET output high impedance).
Note 10:
PFO is normally an output, but is used as an input when activating the battery freshness seal.
µs
10
Reset to CE OUT High Delay
t
WD
sec
0V < V
CC
< 5.5V
Watchdog Timeout Period
I
OH
= 500µA, V
CC
< 2.3V
µA
1.00
1.60
2.25
-1
0.01
1
WDI Input Current
V
V
OH
0.8V
BATT
CE OUT Output Voltage
High (reset active)
ns
WDI Pulse Width
1.00
MANUAL RESET INPUT
CHIP-ENABLE GATING
WATCHDOG (MAX793/MAX794 only)
MAX793/MAX794/MAX795
3.0V/3.3V/Adjustable Microprocessor
Supervisory Circuits
_______________________________________________________________________________________
5
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
-40
100
V
CC
-TO-OUT ON-RESISTANCE
vs. TEMPERATURE
MAX793 TOC1
TEMPERATURE (
°
C)
V
CC
-TO-OUT ON-RESISTANCE (
Ω
)
20
-20
0
80
40
60
I
OUT
= 30mA
V
CC
= 3.0V
V
CC
= 3.3V
V
CC
= 5V
160
140
120
100
80
60
40
-40
100
BATT-TO-OUT ON-RESISTANCE
vs. TEMPERATURE
MAX793 TOC2
TEMPERATURE (
°
C)
BATT-TO-OUT ON-RESISTANCE (
Ω
)
20
-20
0
80
40
60
V
BATT
= 3.6V
V
BATT
= 3.0V
V
BATT
= 5V
I
OUT
= 250
µ
A
V
CC
= 0V
70
60
50
40
30
20
10
0
-40
100
V
CC
SUPPLY CURRENT vs. TEMPERATURE
(NORMAL OPERATING MODE)
MAX793 TOC3
TEMPERATURE (
°
C)
V
CC
SUPPLY CURRENT (
µ
A)
20
-20
0
80
40
60
MAX793/4, V
CC
= 3.3V
MAX795, V
CC
= 3.3V
MAX793/4, V
CC
= 5V
V
BATT
= V
CC
= V
OUT
MAX795, V
CC
= 5V
0.10
0.08
0.06
0.04
0.02
0
-40
100
BATTERY SUPPLY CURRENT vs.
TEMPERATURE (BATTERY-BACKUP MODE)
MAX793 TOC4
TEMPERATURE (
°
C)
SUPPLY CURRENT (
µ
A)
20
-20
0
80
40
60
V
CC
= 0V
V
BATT
= 3.6V
100
90
80
70
60
50
40
30
20
10
0
-40
100
MAX793
LOWLINE-TO-RESET THRESHOLD
vs. TEMPERATURE
MAX793 TOC7
TEMPERATURE (
°
C)
LOWLINE-TO-RESET THRESHOLD (mV)
20
-20
0
80</