MAX801NESA [MAXIM]
Interface IC ; 接口IC\n
| 型号： | MAX801NESA |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Interface IC
|
| 文件： | 总12页 (文件大小：93K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1086; Rev 0; 6/96
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
1,AX08LM/N
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
The MAX801/MAX808 microprocessor (µP) supervisory
circuits monitor and control the activities of +5V µPs by
providing backup-battery switchover, low-line indica-
tion, and µP reset. Additional features include a watch-
dog for the MAX801 and CMOS RAM write protection
for the MAX808.
♦ Precision Voltage Monitoring, ±1.5% Reset
Accuracy
♦ 200ms Power-OK/Reset Time Delay
♦ RESET Output (MAX808)
RESET and RESET Outputs (MAX801)
♦ Watchdog Timer (MAX801)
The MAX801/MAX808 offer a choice of reset-threshold
voltage (denoted by suffix letter): 4.675V (L), 4.575V
(N), and 4.425V (M). These devices are available in
8-pin DIP and SO packages.
♦ On-Board Gating of Chip-Enable Signals (MAX808):
Memory Write-Cycle Completion
3ns CE Gate Propagation Delay
♦ 1µA Standby Current
♦ Power Switching:
________________________Ap p lic a t io n s
Computers
250mA in V
Mode
CC
20mA in Battery-Backup Mode
Controllers
♦ MaxCap™/SuperCap™ Compatible
Intelligent Instruments
♦ RESET Guaranteed Valid to V
= 1V
CC
♦ Low-Line Threshold 52mV Above Reset
Threshold
Critical µP Power Monitoring
Portable/Battery-Powered Equipment
Embedded Systems
MaxCap is a trademark of The Carborundum Corp.
SuperCap is a trademark of Baknor Industries.
______________Ord e rin g In fo rm a t io n
Pin Configurations appear at end of data sheet.
PART*
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
8 SO
MAX801_CPA
MAX801_CSA
MAX801_EPA
MAX801_ESA
MAX801_MJA
MAX808_CPA
MAX808_CSA
MAX808_EPA
MAX808_ESA
MAX808_MJA
0°C to +70°C
__________Typ ic a l Op e ra t in g Circ u it
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 Plastic DIP
8 SO
+5V
8 CERDIP**
8 Plastic DIP
8 SO
0.1µF
0.1µF
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 Plastic DIP
8 SO
OUT
V
CC
POWER FOR
µP
CMOS RAM POWER
8 CERDIP**
NMI
BATT
LOWLINE
RESET
* These parts offer a choice of reset threshold voltage. From the
table below, select the suffix corresponding to the desired
threshold and insert it into the blank to complete the part number.
**Contact factory for availability and processing to MIL-STD-883.
0.1µF
RESET
µP SYSTEM
MAX808
RESET THRESHOLD (V)
SUFFIX
FROM I/O SYSTEM OR
ADDRESS DECODER
CE IN
MIN
4.60
4.50
4.35
TYP
4.675
4.575
4.425
MAX
4.75
4.65
4.50
CE OUT
TO CMOS RAM
L
N
M
GND
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
ABSOLUTE MAXIMUM RATINGS
Input Voltage (with respect to GND)
OUT Continuous............................................................500mA
All Other Outputs ............................................................50mA
V
.......................................................................-0.3V to +6V
CC
V
BATT
....................................................................-0.3V to +6V
Continuous Power Dissipation (T = +70°C)
A
All Other Pins ........................................-0.3V to (V
Input Current
+ 0.3V)
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
OUT
V
V
CC
Peak ..........................................................................1.0A
Continuous ............................................................500mA
CC
I
Peak.....................................................................250mA
Continuous ............................................................50mA
MAX801_C_A/MAX808_C_A...............................0°C to +70°C
MAX801_E_A/MAX808_E_A ............................-40°C to +85°C
MAX801_MJA/MAX808_MJA.........................-55°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
BATT
I
BATT
GND ................................................................................50mA
All Other Inputs ...............................................................50mA
Output Current
OUT Peak..........................................................................1.0A
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 = 4.6V to 5.5V for the MAX80_L, V = 4.5V to 5.5V for the MAX80_N, V = 4.35V to 5.5V for the MAX80_M; V = 2.8V;
BATT
CC
CC
CC
T
A
= T
to T
. Typical values are at V = 5V and T = +25°C, unless otherwise noted.)
MIN
MAX
CC
A
PARAMETER
Operating Voltage Range
, BATT (Note 1)
SYMBOL
CONDITIONS
MIN
TYP
MAX
5.5
UNITS
0
X
V
V
CC
I
= 25mA
V
CC
- 0.02
OUT
V
= 4.5V
I
= 250mA, MAX80_C/E
= 250mA, MAX80_M
V
- 0.38
V
CC
- 0.25
- 0.12
V
Mode
in Normal Operating
CC
OUT
CC
OUT
V
I
V
CC
- 0.45
- 0.25
OUT
V
CC
= 3V, V
= 2.8V, I
= 100mA
V
CC
V
CC
BATT
OUT
1,AX08LM/N
MAX80_C/E
MAX80_M
= 100mA
OUT
1.0
1.5
V
= 4.5V,
= 250mA
CC
V
to OUT
CC
I
OUT
1.8
2.5
Ω
V
On-Resistance
V
CC
= 3V, I
= 0V
1.2
- 0.16
V
= 4.5V, I
= 2.8V, I
= 2.0V, I
= 4.5V, I
= 2.8V, I
= 2.0V, I
= 20mA
V
BATT
BATT
OUT
OUT
OUT
OUT
OUT
OUT
V
in Battery-Backup
OUT
V
CC
V
= 10mA
= 5mA
V
- 0.25
- 0.20
V
BATT
- 0.12
- 0.08
BATT
BATT
Mode
V
V
BATT
V
BATT
BATT
V
= 20mA
= 10mA
= 5mA
8
BATT
BATT to OUT
On-Resistance
V
CC
= 0V
V
12
16
25
40
Ω
BATT
V
BATT
Supply Current in Normal
Operating Mode
MAX801
MAX808
68
110
90
µA
µA
48
(excludes I
)
OUT
T
= +25°C
0.4
1
A
Supply Current in Battery-
Backup Mode (excludes
V
V
BATT
= 0V,
CC
MAX80_C/E
MAX80_M
5
T
= 2.8V
= T
A
to T
MIN
I
) (Note 2)
OUT
MAX
50
0.1
1.0
T
A
= +25°C
-0.1
-1.0
BATT Standby Current
(Note 3)
V
≤ V
+ 0.2V
= 2.8V
BATT
µA
V
CC
T
A
= T to T
MIN MAX
Power-up
Power-down
V
+ 0.05
BATT
Battery-Switchover
Threshold
V
BATT
V
BATT
Battery-Switchover
Hysteresis
50
mV
2
_______________________________________________________________________________________
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
1,AX08LM/N
ELECTRICAL CHARACTERISTICS (continued)
(V = 4.6V to 5.5V for the MAX80_L, V = 4.5V to 5.5V for the MAX80_N, V = 4.35V to 5.5V for the MAX80_M; V = 2.8V;
BATT
CC
CC
CC
T
A
= T
to T
. Typical values are at V = 5V and T = +25°C, unless otherwise noted.)
MIN
MAX
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
RESET AND LOW-LINE
MAX80_L
MAX80_N
MAX80_M
4.600
4.500
4.350
4.675
4.575
4.425
13
4.750
V
rising
CC
Reset Threshold
V
4.650
4.500
V
RST
and falling
Reset-Threshold Hysteresis
mV
mV
LOWLINE to RESET
Threshold Voltage
V
V
CC
falling
30
52
70
LR
MAX80_L
MAX80_N
MAX80_M
4.73
4.63
4.48
17
4.81
4.71
4.56
LOWLINE Threshold,
V
V
LL
V
CC
Rising
t
V
CC
falling at 1mV/µs
µs
µs
V
CC
to RESET Delay
RD
t
V
CC
falling at 1mV/µs
17
V
CC
to LOWLINE Delay
LL
RESET Active Timeout
Period
t
V
rising
140
200
280
0.3
ms
RP
CC
I
= 50µA,
= 0V,
falling
SINK
V
= 1.0V, MAX80_C
CC
V
BATT
V
CC
= 1.2V, MAX80_E/M
0.3
0.4
V
CC
V
RESET Output Voltage
I
= 3.2mA, V = 4.25V
CC
0.1
SINK
I
= 0.1mA
V
CC
- 1.5
V
CC
- 0.1
SOURCE
Output sink current, V = 4.25V
CC
40
RESET Output
Short-Circuit Current
I
mA
V
SC
Output source current
1.6
I
= 3.2mA
0.4
0.4
SINK
RESET Output Voltage
(MAX801)
I
= 5mA, V = 4.25V
V
CC
- 1.5
- 1.5
SOURCE
CC
Output sink current
Output source current, V = 4.25V
55
15
RESET Output Short-
Circuit Current (MAX801)
I
SC
mA
V
CC
I
= 3.2mA, V = 4.25V
CC
SINK
LOWLINE Output Voltage
I
= 5mA, V = 4.25V
V
CC
SOURCE
CC
Output sink current, V = 4.25V
CC
40
20
LOWLINE Output
Short-Circuit Current
I
SC
mA
Output source current
WATCHDOG TIMER (MAX801)
Watchdog Timeout Period
t
1.12
100
0.75 x V
1.6
2.24
sec
ns
WD
Minimum Watchdog Input
Pulse Width
V
= 0.8V, V = 0.75V x V
IH CC
IL
V
IH
CC
WDI Threshold Voltage
(Note 4)
V
V
0.8
50
IL
RESET deasserted, WDI = 0V
RESET deasserted, WDI = V
-50
-10
16
WDI Input Current
µA
CC
_______________________________________________________________________________________
3
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
ELECTRICAL CHARACTERISTICS (continued)
(V = 4.6V to 5.5V for the MAX80_L, V = 4.5V to 5.5V for the MAX80_N, V = 4.35V to 5.5V for the MAX80_M; V = 2.8V;
BATT
CC
CC
CC
T
A
= T
to T
. Typical values are at V = 5V and T = +25°C, unless otherwise noted.)
MIN
MAX
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
CHIP-ENABLE GATING (MAX808)
V
= 4.25V
±0.00002
75
±1
µA
CE IN Leakage Current
CC
CE IN to CE OUT
Resistance (Note 5)
Enabled mode, V = V (max)
150
Ω
CC
RST
CE OUT Short-Circuit
Current (RESET Active)
15
3
mA
ns
V
= 4.25V, CE OUT = 0V
CC
V
= 5V, C
= 50pF,
LOAD
CE IN to CE OUT
Propagation Delay (Note 6)
CC
8
50Ω source-impedance driver
V
= 4.25V, I = 2mA
3.5
CC
OUT
CE OUT Output Voltage
High (RESET Active)
V
V
CC
= 0V, I
= 10µA
V
- 0.1
V
BATT
OUT
BATT
RESET to CE OUT Delay
(Note 7)
18
µs
V
CC
falling, CE IN = 0V
Note 1: Either V or V
can go to 0V if the other is greater than 2V.
CC
BATT
Note 2: The supply current drawn by the MAX80_ from the battery (excluding I
) typically goes to 15µA when (V
- 0.1V) <
OUT
BATT
V
CC
< V
. In most applications, this is a brief period as V falls through this region (see Typical Operating
BATT CC
Characteristics).
Note 3: “+” = battery-discharging current, “-” = battery-charging current.
Note 4: WDI is internally connected to a voltage divider between V and GND. If unconnected, WDI is typically driven to 1.8V,
CC
disabling the watchdog function.
1,AX08LM/N
Note 5: The chip-enable resistance is tested with V
= V / 2 and I
= 1mA.
CE IN
CE IN
CC
Note 6: The chip-enable propagation delay is measured from the 50% point at CE IN to the 50% point at CE OUT.
Note 7: If CE IN goes high, CE OUT goes high immediately and stays high until reset is deasserted and CE IN is low.
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(V = 5V, V
= 2.8V, no load, T = +25°C, unless otherwise noted.)
A
CC
BATT
MAX808
BATTERY SUPPLY CURRENT vs.
TEMPERATURE (BATTERY-BACKUP MODE)
V
CC
SUPPLY CURRENT vs. TEMPERATURE
(NORMAL OPERATING MODE)
CHIP-ENABLE PROPAGATION DELAY
vs. TEMPERATURE
3.0
2.5
2.0
1.5
1.0
0.5
0
75
6
5
4
3
2
1
0
70
65
MAX801
60
55
50
45
40
MAX808
-15
-60 -40 -20
0
20 40 60 80 100 120 140
-55 -35
5
25 45 65 85 105 125
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
4
_______________________________________________________________________________________
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
1,AX08LM/N
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(V = 5V, V
= 2.8V, no load, T = +25°C, unless otherwise noted.)
BATT A
CC
MAX808
V
CC
to OUT ON-RESISTANCE
vs. TEMPERATURE
BATT to OUT ON-RESISTANCE
vs. TEMPERATURE
CHIP-ENABLE PROPAGATION DELAY
vs. CE OUT LOAD CAPACITANCE
1.6
1.5
1.4
1.3
1.2
30
8
6
4
V
= 0V
= 10mA
CC
I
= 250mA
OUT
50Ω DRIVER
I
OUT
25
20
15
10
5
V
= 2.0V
BATT
1.1
1.0
V
BATT
= 2.8V
= 4.5V
2
0
0.9
0.8
0.7
V
BATT
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
0
50
(pF)
100
TEMPERATURE (°C)
TEMPERATURE (°C)
C
LOAD
RESET THRESHOLD
vs. TEMPERATURE
RESET TIMEOUT PERIOD
vs. TEMPERATURE (V RISING)
LOWLINE to RESET THRESHOLD
vs. TEMPERATURE (V FALLING)
CC
CC
4.70
4.65
4.60
4.55
4.50
4.45
4.40
280
260
80
70
60
50
MAX80_L
240
220
200
180
160
140
MAX80_N
40
30
20
10
0
MAX80_M
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
LOWLINE COMPARATOR PROPAGATION
RESET COMPARATOR PROPAGATION
LOWLINE THRESHOLD
DELAY vs. TEMPERATURE (V FALLING)
CC
DELAY vs. TEMPERATURE (V FALLING)
CC
vs. TEMPERATURE (V RISING)
CC
40
40
4.80
4.75
4.70
4.65
4.60
4.55
4.50
4.45
4.40
V
FALLING AT 1mV/µs
V
CC
FALLING AT 1mV/µs
CC
MAX80_L
MAX80_N
35
30
25
35
30
25
20
15
20
15
MAX80_M
10
10
5
0
5
0
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(V = 5V, V
= 2.8V, no load, T = +25°C, unless otherwise noted.)
BATT A
CC
BATTERY CURRENT
vs. INPUT SUPPLY VOLTAGE
BATT to OUT VOLTAGE vs.
OUTPUT CURRENT
16
1000
100
10
V
CC
= 0V
14
12
10
SLOPE = 12Ω
8
6
4
2
0
2.5
2.6
2.7
2.8
(V)
2.9
3.0
1
10
(mA)
100
V
I
CC
OUT
MAXIMUM TRANSIENT DURATION vs.
RESET THRESHOLD OVERDRIVE
V
to OUT VOLTAGE vs.
CC
OUTPUT CURRENT
1000
1000
100
10
SLOPE = 1.0Ω
RESET OCCURS
100
10
1
1,AX08LM/N
1
1
10
100
1000
1
10
100
1000
RESET THRESHOLD OVERDRIVE (mV)
I
(mA)
OUT
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
MAX801
MAX808
1
1
V
CC
Input Supply Voltage, nominally +5V. Bypass with a 0.1µF capacitor to GND.
Low-Line Comparator Output. This CMOS-logic output goes low when V falls to 52mV
CC
2
2
above the reset threshold. Use LOWLINE to generate an NMI, initiating an orderly shut-
LOWLINE
down routine when V is falling. LOWLINE swings between V and GND.
CC
CC
Active-Low Reset Output. RESET is triggered and stays low when V is below the reset
CC
threshold (or during a watchdog timeout for the MAX801). It remains low 200ms after
V
rises above the reset threshold (or 200ms after the watchdog timeout occurs).
3
4
3
4
RESET
CC
RESET has a strong pull-down but a relatively weak pull-up, and can be wire-OR con-
nected to logic gates. Valid for V ≥ 1V. RESET swings between V and GND.
CC
CC
GND
Ground
6
_______________________________________________________________________________________
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
1,AX08LM/N
_________________________________________________P in De s c rip t io n (c o n t in u e d )
PIN
NAME
FUNCTION
MAX801
MAX808
Active-High Reset Output. RESET is the inverse of RESET. It is a CMOS output that
5
—
RESET
sources and sinks current. RESET swings between V and GND.
CC
Chip-Enable Output. Output to the chip-enable gating circuit. CE OUT is pulled up to
—
5
CE OUT
the higher of V or V
when the chip-enable gate is disabled.
CC
BATT
Watchdog Input. If WDI remains high or low longer than the watchdog timeout period
(typically 1.6sec), RESET will be asserted for 200ms. Leave unconnected to disable the
watchdog function.
6
—
6
WDI
—
Chip-Enable Input
CE IN
Backup-Battery Input. When V falls below the reset threshold and V
, OUT switch-
BATT
CC
es from V to BATT. V
MAX801/MAX808 is powered up, provided BATT is bypassed with a 0.1µF capacitor to
GND. If no battery is used, connect BATT to ground and V to OUT.
may exceed V . The battery can be removed while the
CC
CC
BATT
7
8
7
8
BATT
OUT
CC
Output Supply Voltage to CMOS RAM. When V exceeds the reset threshold or V
,
CC
BATT
OUT connects to V . When V falls below the reset threshold and V , OUT con-
BATT
CC
CC
nects to BATT. Bypass OUT with a 0.1µF capacitor to GND.
V
CC
OUT
BATT
BATTERY-BACKUP
COMPARATOR
MAX801
MAX808
LOWLINE
WDI
RESET
COMPARATOR
MAX801 ONLY
WATCHDOG
TRANSITION
DETECTOR
LOW-LINE
COMPARATOR
RESET (MAX801 ONLY)
RESET
STATE
MACHINE
OSCILLATOR
2.275V
GND
THE HIGHER
MAX808 ONLY
OF V
CC
OR V
BATT
P
P
CE IN
CE OUT
N
Figure 1. Functional Diagram
_______________________________________________________________________________________
7
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
V
V
V
+ V
V
RST LL
RST LR RST
V
CC
V
CC
t
LL
V
V
LOWLINE
LOWLINE
t
RD
t
RP
V
RESET
V
RESET
t
RD
V
V
RESET
(MAX801)
RESET
t
RP
(MAX801)
V
CE OUT
t
RCE
V
BATT
V
(MAX808)
CE OUT
V
BATT
(MAX808)
SHOWN FOR V = 0V to 5V, V
= 2.8V, CE IN = GND
SHOWN FOR V = 5V to 0V, V
= 2.8V, CE IN = GND
CC
BATT
CC
BATT
Figure 2a. Timing Diagram, V Rising
CC
Figure 2b. Timing Diagram, V Falling
CC
The RESET output is active low, and is implemented with
a strong pull-down/relatively weak pull-up structure. It is
_______________De t a ile d De s c rip t io n
The MAX801/MAX808 microprocessor (µP) supervisory
circuits provide power-supply monitoring and backup-
battery switchover in µP systems. The MAX801 also
p rovid e s p rog ra m-e xe c ution wa tc hd og func tions
(Figure 1). Use of BiCMOS technology results in an
improved, 1.5% reset-threshold precision while keeping
s up p ly c urre nts typ ic a lly a t 68µA (48µA for the
MAX808). The MAX801/MAX808 are intended for bat-
te ry-p owe re d a p p lic a tions tha t re q uire hig h re s e t-
thre s hold p re c is ion, a llowing a wid e p owe r-s up p ly
operating range while preventing the system from oper-
ating below its specified voltage range.
1,AX08LM/N
guaranteed to be a logic low for 0V < V < V , pro-
CC
RST
vided V
is greater than 2V. Without a backup bat-
BATT
tery, RESET is guaranteed valid for V ≥ 1V.
CC
The RESET output is the inverse of the RESET output; it
both sources and sinks current and cannot be wire-OR
connected.
Lo w -Lin e Co m p a ra t o r
The low-line comparator monitors V
with a threshold
CC
voltage typically 52mV above the reset threshold, with
13mV of hysteresis. Use LOWLINE to provide a non-
maskable interrupt (NMI) to the µP when power begins
to fall, initiating an orderly software shutdown routine. In
most battery-operated portable systems, reserve ener-
gy in the battery provides ample time to complete the
shutdown routine once the low-line warning is encoun-
tered and before reset asserts. If the system must con-
RESET a n d RES ET Ou t p u t s
The MAX801/MAX808’s RESET output ensures that the
µP powers up in a known state, and prevents code-
e xe c ution e rrors during powe r-down a nd brownout
conditions. It does this by resetting the µP, terminating
tend with a more rapid V fall time (such as when the
CC
program execution when V
dips below the reset
CC
main battery is disconnected, when a DC-DC converter
shuts down, or when a high-side switch is opened dur-
threshold. Each time RESET is asserted, it stays low for
at least the 200ms reset timeout period (set by an inter-
nal timer) to ensure the µP has adequate time to return
to an initial state. The internal timer restarts any time
ing normal operation), use capacitance on the V line
CC
to provide time to execute the shutdown routine (Figure
3). First calculate the worst-case time required for the
system to perform its shutdown routine. Then, with
worst-case shutdown time, worst-case load current,
V
CC
goes below the reset threshold (V ) before the
RST
reset timeout period is completed. The watchdog timer
on the MAX801 c a n a ls o initia te a re s e t (s e e the
MAX801 Watchdog Timer section).
and minimum low-line to reset threshold (V
),
LR(min)
8
_______________________________________________________________________________________
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
1,AX08LM/N
MAX801
4.5V to 5.5V
REGULATOR
TO µP NMI
MAX808
LOWLINE
V
CC
P
V
CC
C
HOLD
CONTROL
CIRCUITRY
OUT
MAX801
MAX808
0.1µF
BATT
GND
C
> I
x t
P
P
HOLD LOAD SHDN
V
LR
Figure 3. Using LOWLINE to Provide a Power-Fail Warning to
the µP
Figure 4. V and BATT to OUT Switch
CC
calculate the amount of capacitance required to allow
the s hutd own routine to c omp le te b e fore re s e t is
asserted:
Table 1. Input and Output Status in
Battery-Backup Mode
C
= (I
x t
SHDN
) / (V
)
HOLD
LOAD
LR(min)
PIN
NAME
STATUS
where t
is the time required for the system to com-
SHDN
MAX801 MAX808
plete the shutdown routine (including the V
to low-
CC
line propagation delay), I
drained from the capacitor, and V is the low-line to
is the current being
LR
LOAD
Battery switchover
comparator monitors V
CC
1
1
V
CC
reset threshold.
for active switchover.
2
3
2
3
Logic low
LOWLINE
RESET
Ou t p u t S u p p ly Vo lt a g e
The output supply (OUT) transfers power from V
or
CC
Logic low
BATT to the µP, RAM, and other external circuitry. At
the maximum source current of 250mA, V will typi-
Ground—0V reference for
all signals
OUT
4
5
4
GND
cally be 220mV below V . Decouple OUT with a 0.1µF
CC
capacitor to ground.
Logic high; the open-circuit
voltage is equal to V
—
RESET
.
CC
Ba t t e ry-Ba c k u p Mo d e
Battery-backup mode preserves the contents of RAM in
the event of a brownout or power failure. With a backup
battery installed at BATT, the MAX801/MAX808 automati-
Logic high. The open-circuit
output voltage is equal to
—
5
CE OUT
V
(MAX808).
BATT
cally switches RAM to backup power when V
falls.
CC
WDI is ignored and goes
high impedance.
6
—
7
—
6
WDI
CE IN
BATT
Two conditions are required for switchover to battery-
backup mode: 1) V must be below the reset threshold;
CC
High impedance (MAX808)
2) V must be below V
. Table 1 lists the status of
BATT
CC
Supply current is 1µA max for
inputs and outputs during battery-backup mode.
7
V
BATT
≤ 2.8V.
BATT is designed to conduct up to 20mA to OUT dur-
ing battery backup. The PMOS switch on-resistance is
approximately 12Ω. Figure 4 shows the two series pass
e le me nts (b e twe e n the BATT inp ut a nd OUT) tha t
OUT is connected to BATT
through two internal PMOS
switches in series.
8
8
OUT
facilitate UL recognition. V
can exceed V during
BATT
CC
normal operation without causing a reset.
_______________________________________________________________________________________
9
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
MAX8 0 1 Wa t c h d o g Tim e r
The watchdog monitors the µP’s activity. If the µP does
not toggle the watchdog input (WDI) within 1.6sec,
reset asserts for the reset timeout period. The internal
1.6sec timer is cleared when reset asserts or when a
V
CC
transition (low-to-high or high-to-low) occurs at WDI
while reset is not asserted. The timer remains cleared
and does not count as long as reset is asserted. It
starts counting as soon as reset is released (Figure 5).
Supply current is typically reduced by 10µA when WDI
is at a valid logic level. To disable the watchdog func-
tion, le a ve WDI unc onne c te d . An inte rna l volta g e
divider sets WDI to about mid-supply, disabling the
watchdog timer/counter.
t
RP
t
RP
t
WD
RESET
WDI
MAX8 0 8 Ch ip -En a b le Ga t in g
The MAX808 provides internal gating of chip-enable
(CE) signals to prevent erroneous data from corrupting
CMOS RAM in the event of a power failure. During nor-
mal operation, the CE gate is enabled and passes all
CE tra ns itions . Whe n re s e t is a s s e rte d , this p a th
becomes disabled, preventing erroneous data from
corrupting the CMOS RAM. The MAX808 uses a series
transmission gate from the chip-enable input (CE IN) to
the chip-enable output (CE OUT) (Figure 1). The 8ns
max chip-enable propagation from CE IN to CE OUT
enables the MAX808 to be used with most µPs.
Figure 5. Watchdog Timing
V
CC
RESET
THRESHOLD
CE IN
CE OUT
The MAX808 also features write-cycle-completion cir-
M
18µs
17µs
18µs
17µs
cuitry. If V
falls below the reset threshold while the
CC
µP is writing to RAM, the MAX808 holds the CE gate
enabled for 18µs to allow the µP to complete the write
instruction. If the write cycle has not completed by the
end of the 18µs period, the CE transmission gate turns
off and CE OUT goes high. If the µP completes the
write instruction during the 18µs period, the CE gate
turns off (high impedance) and CE OUT goes high as
soon as the µP pulls CE IN high. CE OUT remains high,
even if CE IN falls low for any reason (Figure 6).
RESET
Figure 6. Chip-Enable Timing
In high-impedance mode, the leakage currents into this
input are ±1µA max over temperature. In low-imped-
ance mode, the impedance of CE IN appears as a 75Ω
resistor in series with the load at CE OUT.
Chip-Enable Input
CE IN is high impedance (disabled mode) while reset is
asserted. During a power-down sequence when V
CC
The propagation delay through the CE transmission
gate depends on both the source impedance of the
drive to CE IN and the capacitive loading on CE OUT
(see the Chip-Enable Propagation Delay vs. CE OUT
Loa d Ca p a c ita nc e g ra p h in the Typ ic a l Op e ra ting
Characteristics). The CE propagation delay is produc-
tion tested from the 50% point on CE IN to the 50%
point on CE OUT using a 50Ω driver and 50pF of load
c a p a c ita nc e (Fig ure 7). For minimum p rop a g a tion
delay, minimize the capacitive load at CE OUT and use
a low-output-impedance driver.
passes the reset threshold, the CE transmission gate
disables. CE IN becomes high impedance 18µs after
reset asserts, provided CE IN is still low. If the µP com-
pletes the write instruction during the 18µs period, the
CE gate turns off. CE IN becomes high impedance as
soon as the µP pulls CE IN high. CE IN remains high
impedance even if the signal at CE IN falls low (Figure
6). During a power-up sequence, CE IN remains high
impedance (regardless of CE IN activity) until reset is
deasserted following the reset timeout period.
10 ______________________________________________________________________________________
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
1,AX08LM/N
V
(max)
+5V
RST
V
CC
V
1N4148
0.47F
CC
BATT
OUT
MAX808
CE IN
CE OUT
MAX801
MAX808
50pF C
LOAD
50Ω DRIVER
GND
GND
Figure 7. MAX808 CE Gate Test Circuit
Figure 8. Using the MAX801/MAX808 with a SuperCap
Chip-Enable Output
circuit as a backup source (Figure 8). Since V
can
BATT
In enabled mode, CE OUT’s impedance is equivalent to
75Ω in series with the source driving CE IN. In disabled
mode, the 75Ω transmission gate is off and CE OUT is
exceed V while V is above the reset threshold, no
special precautions are needed when using these µP
supervisors with a SuperCap.
CC CC
a c tive ly p ulle d to the hig he r of V
or V
. The
CC
BATT
Ba c k u p -Ba t t e ry Re p la c e m e n t
source turns off when the transmission gate is enabled.
The backup battery can be disconnected while V
is
CC
__________Ap p lic a t io n s In fo rm a t io n
above the reset threshold, provided BATT is bypassed
with a 0.1µF capacitor to ground. No precautions are
necessary to avoid spurious reset pulses.
The MAX801/MAX808 are not short-circuit protected.
Shorting OUT to ground, other than power-up transients
such as charging a decoupling capacitor, may destroy
the device. If long leads connect to the IC’s inputs,
ensure that these lines are free from ringing and other
conditions that would forward bias the IC’s protection
Ne g a t ive -Go in g V
Tra n s ie n t s
CC
While issuing resets to the µP during power-up, power-
down, and brownout conditions, these supervisors are
relatively immune to short-duration, negative-going V
CC
d iod e s . Byp a s s OUT, V , a nd BATT with 0.1µF
CC
transients (glitches). It is usually undesirable to reset
capacitors to GND.
the µP when V experiences only small glitches.
CC
The MAX801/MAX808 operate in two distinct modes:
The Typical Operating Characteristics show a graph of
Ma ximum Tra ns ie nt Dura tion vs . Re s e t Thre s hold
Overdrive, for which reset pulses are not generated.
1) Normal Operating Mode, with all circuitry powered
up. Typical supply current from V
is 68µA (48µA
CC
for the MAX808), while only leakage currents flow
from the battery.
The graph was produced using negative-going V
CC
p uls e s , s ta rting a t 5V a nd e nd ing b e low the re s e t
threshold by the magnitude indicated (reset compara-
tor overdrive). The graph shows the maximum pulse
2) Battery-Backup Mode, where V
is below V
BATT
CC
and V . The supply current from the battery is typ-
RST
width that a negative-going V transient may typically
CC
ically less than 1µA.
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
Us in g S u p e rCa p s ™ o r Ma x Ca p s ™
w it h t h e MAX8 0 1 /MAX8 0 8
pulse width decreases. Typically, a V
transient that
BATT has the same operating voltage range as V , and
CC
CC
goes 40mV below the reset threshold and lasts for 3µs
or less will not cause a reset pulse to be issued. A
the battery-switchover threshold voltage is typically
V
when V is decreasing or V
+ 0.05V when
BATT
CC
BATT
0.1µF bypass capacitor mounted close to the V
pin
V
CC
is inc re a s ing . This hys te re s is a llows us e of a
CC
provides additional transient immunity.
SuperCap (e.g., around 0.47F) and a simple charging
______________________________________________________________________________________ 11
8 -P in µP S u p e rvis o ry Circ u it s
w it h ±1 .5 % Re s e t Ac c u ra c y
Wa t c h d o g S o ft w a re Co n s id e ra t io n s
To help the watchdog timer keep a closer watch on
software execution, you can set and reset the watch-
dog input at different points in the program, rather than
“pulsing” the watchdog input high-low-high or low-high-
low. This technique avoids a “stuck” loop, where the
watchdog timer continues to be reset within the loop,
keeping the watchdog from timing out.
START
SET
WDI
LOW
Figure 9 shows a sample flow diagram where the I/O
driving the watchdog input is set high at the beginning
of the program, low at the beginning of every subrou-
tine or loop, then high again when the program returns
to the beginning. If the program should “hang” in any
subroutine, the I/O would be continually set low and the
watchdog timer would be allowed to time out, causing a
reset or interrupt to be issued.
SUBROUTINE
OR PROGRAM LOOP,
SET WDI
HIGH
RETURN
END
Ma x im u m V
The V fall time is limited by the propagation delay of
the b a tte ry s witc hove r c omp a ra tor a nd s hould not
exceed 0.03V/µs. A standard rule for filter capacitance
on most regulators is around 100µF per Ampere of cur-
rent. When the power supply is shut off or the main bat-
Fa ll Tim e
CC
CC
Figure 9. Watchdog Flow Diagram
tery is disconnected, the associated initial V fall rate
CC
is just the inverse, or 1A/100µF = 0.01V/µs.
___________________Ch ip In fo rm a t io n
_________________P in Co n fig u ra t io n s
1,AX08LM/N
TRANSISTOR COUNT: 922
TOP VIEW
1
2
3
4
8
7
6
5
OUT
V
CC
BATT
WDI
LOWLINE
RESET
GND
MAX801
RESET
DIP/SO
1
2
3
4
8
7
6
5
OUT
V
CC
BATT
CE IN
CE OUT
LOWLINE
RESET
GND
MAX808
DIP/SO
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 __________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 (4 0 8 ) 7 3 7 -7 6 0 0
© 1996 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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