MAX806SESA-T [MAXIM]
Power Supply Management Circuit, Fixed, 1 Channel, CMOS, PDSO8, 0.150 INCH, PLASTIC, SO-8;
| 型号： | MAX806SESA-T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Power Supply Management Circuit, Fixed, 1 Channel, CMOS, PDSO8, 0.150 INCH, PLASTIC, SO-8 微处理器 监控 |
| 文件： | 总12页 (文件大小：99K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-4333; Rev 3; 9/93
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
692/MAX805L
__________________Ge ne ra l De s c ription
___________________________Fe a t u re s
The MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
reduce the complexity and number of components
required for power-supply monitoring and battery-control
functions in microprocessor (µP) systems. They signifi-
cantly improve system reliability and accuracy compared
to separate ICs or discrete components.
♦ Precision Supply-Voltage Monitor:
4.65V for MAX690A/MAX802L/MAX805L
4.40V for MAX692A/MAX802M
♦ Reset Time Delay – 200ms
♦ Watchdog Timer – 1.6sec Timeout
♦ Battery-Backup Power Switching
♦ 200µA Quiescent Supply Current
These parts provide four functions:
1) A reset output during power-up, power-down, and
brownout conditions.
♦ 50nA Quiescent Supply Current in Battery-
Backup Mode
2) Battery-backup switching for CMOS RAM, CMOS
µP, or other low-power logic.
♦ Voltage Monitor for Power-Fail or Low-Battery
Warning
3) A reset pulse if the optional watchdog timer has not
been toggled within 1.6sec.
♦ Power-Fail Accuracy Guaranteed to ±2%
4) A 1.25V threshold detector for power-fail warning or
low-battery detection, or to monitor a power supply
other than +5V.
(MAX802L/M)
♦ Guaranteed RESET Assertion to VCC = 1V
♦ 8-Pin SO and DIP Packages
The parts differ in their reset-voltage threshold levels
and reset outputs. The MAX690A/MAX802L/MAX805L
generate a reset pulse when the supply voltage drops
below 4.65V, and the MAX692A/MAX802M generate a
reset below 4.40V. The MAX802L/MAX802M guaran-
tee power-fail accuracies to ±2%. The MAX805L is the
same as the MAX690A except that RESET is provided
instead of RESET.
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
MAX690ACPA
MAX690ACSA
MAX690AC/D
MAX690AEPA
MAX690AESA
MAX690AMJA
8
Plastic DIP
0°C to +70°C
8 SO
0°C to +70°C
Dice*
All parts are available in 8-pin DIP and SO packages.
The MAX690A/MAX802L are pin compatible with the
MAX690 and MAX694. The MAX692A/MAX802M are
pin compatible with the MAX692.
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8
8
8
Plastic DIP
SO
CERDIP**
_______________________Ap p lic a t io n s
Ordering Information continued on last page.
* Dice are specified at TA = +25°C
**Contact factory for availability and processing to MIL-STD-883.
Battery-Powered Computers and Controllers
Intelligent Instruments
Automotive Systems
Critical µP Power Monitoring
_________________P in Co n fig u ra t io n s
__________Typ ic a l Op e ra t in g Circ u it
TOP VIEW
UNREGULATED DC REGULATED +5V
V
CC
V
OUT
1
2
3
4
O.1µF
8
7
6
5
VBATT
V
CC
RESET
R
1
RESET
PFO
MAX690A
MAX692A
MAX802L
MAX802M
MAX805L
V
CC
RESET (RESET)
WDI
µP
NMI
GND
PFI
PFI
WDI
I/O LINE
GND
3.6V
LITHIUM
BATTERY
R
2
PFO
V
BATT
V
OUT
GND
DIP/SO
V
CC
CMOS
RAM
MAX690A
MAX802L
(
) ARE FOR MAX805L ONLY.
GND
________________________________________________________________ Maxim Integrated Products
1
Ca ll t o ll fre e 1 -8 0 0 -9 9 8 -8 8 0 0 fo r fre e s a m p le s o r lit e ra t u re .
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
Rate of Rise, VCC, VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100V/µs
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V
VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V
All Other Inputs (Note 1) . . . . . . . . . . . . . . . . -0.3V to (VCC + 0.3V)
Input Current
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200mA
VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA
GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA
Output Current
Continuous Power Dissipation
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:
MAX69_AC_ _, MAX80_ _ C_ _ . . . . . . . . . . . . . . . . . . 0°C to +70°C
MAX69_AE_ _, MAX80_ _ E_ _ . . . . . . . . . . . . . . . . -40°C to +85°C
MAX69_AMJA, MAX805LMJA. . . . . . . . . . . . . . . . -55°C to +125°C
Storage Temperature Range . . . . . . . . . . . . . . . . . . -65°C to +160°C
Lead Temperature (soldering, 10sec) . . . . . . . . . . . . . . . . . . +300°C
VOUT . . . . . . . . . . . . . . . . . . . Short-Circuit Protected for up to 10sec
All Other Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA
Note 1: The input voltage limits on PFI and WDI may be exceeded if the current into these pins is limited to less than 10mA.
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 MAX690A/MAX802L/MAX805L, VCC = 4.5V to 5.5V for MAX692A/MAX802M, VBATT = 2.8V,
TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MAX69_AC, MAX802_C
MAX805LC
MIN
1.0
1.1
1.2
TYP
MAX
5.5
UNITS
Operating Voltage Range,
VCC, VBATT (Note 2)
5.5
V
MAX69_AE/M, MAX80_ _E
MAX69_AC, MAX802_C
5.5
200
200
0.05
350
Supply Current (Excluding IOUT
)
ISUPPLY
µA
µA
µA
MAX69_AE/M, MAX802_E, MAX805LE/M
500
1.0
TA = +25°C
VCC = 0V,
ISUPPLY in Battery-Backup Mode
(Excluding IOUT
)
VBATT = 2.8V
TA = TMIN to TMAX
TA = +25°C
5.0
-0.1
-1.0
0.02
0.02
5.5V > VCC
>
V
BATT Standby Current (Note 3)
VBATT +0.2V
TA = TMIN to TMAX
IOUT = 5mA
VCC - 0.05 VCC - 0.025
VOUT Output
V
V
IOUT = 50mA
VCC - 0.5 VCC - 0.25
VOUT in Battery-Backup Mode
IOUT = 250µA, VCC < VBATT - 0.2V
VBATT - 0.1 VBATT - 0.02
Power-up
VCC < VRT
20
-20
40
Battery Switch Threshold, VCC
to VBATT
mV
mV
Power-down
Battery Switchover Hysteresis
MAX690A, MAX802L, MAX805L
MAX692A, MAX802M
4.50
4.25
4.55
4.30
4.65
4.40
4.75
4.50
4.70
4.45
VRT
Reset Threshold
V
MAX802L, TA = +25°C, VCC falling
MAX802M, TA = +25°C, VCC falling
Reset Threshold Hysteresis
Reset Pulse Width
40
mV
ms
tRS
140
200
280
ISOURCE = 800µA
ISINK = 3.2mA
VCC - 1.5
0.4
0.3
692/MAX805L
MAX69_AC, MAX802_C, VCC = 1.0V
ISINK = 50µA
V
RESET Output Voltage
MAX69_AE/M, MAX802_E,
VCC = 1.2V, ISINK = 100µA
0.3
2
_______________________________________________________________________________________
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
692/MAX805L
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 4.75V to 5.5V for MAX690A/MAX802L/MAX805L, VCC = 4.5V to 5.5V for MAX692A/MAX802M, VBATT = 2.8V,
TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX805LC, ISOURCE = 4µA, VCC = 1.1V
MAX805LE/M, ISOURCE = 4µA, VCC = 1.2V
MAX805L, ISOURCE = 800µA
0.8
0.9
RESET Output Voltage
V
VCC - 1.5
MAX805L, ISINK = 3.2mA
0.4
tWD
tWP
Watchdog Timeout
WDI Pulse Width
1.00
50
1.60
2.25
sec
ns
VIL = 0.4V, VIH = (0.8) (VCC
)
Logic low
Logic high
0.8
VCC = 5V
WDI Input Threshold (Note 4)
WDI Input Current
V
3.5
WDI = VCC
WDI = 0V
50
-50
150
µA
-150
1.20
MAX69_A, MAX805L, VCC = 5V
MAX802_C/E, VCC = 5V
1.25
1.250
0.01
1.30
1.275
25
PFI Input Threshold
PFI Input Current
PFO Output Voltage
V
nA
V
1.225
-25
ISOURCE = 800µA
ISINK = 3.2mA
VCC - 1.5
0.4
Note 2: Either VCC or VBATT can go to 0V, if the other is greater than 2.0V.
Note 3: "-" = battery-charging current, "+" = battery-discharging current.
Note 4: WDI is guaranteed to be in an intermediate, non-logic level state if WDI is floating and VCC is in the operating voltage range.
WDI is internally biased to 35% of VCC with an input impedance of 50kΩ.
_______________________________________________________________________________________
3
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
MAX690A
OUTPUT VOLTAGE
vs. LOAD CURRENT
OUTPUT VOLTAGE
vs. LOAD CURRENT
RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
+5V
+5V
5.00
4.95
2.80
2.78
V
T
A
= OV
= +25°C
BATT
V
= +5V
= +2.8V
V = 0V
CC
CC
V
V
BATT
= +2.8V
BATT
V
CC
T = +25°C
A
T = +25°C
A
4.90
4.85
2.76
2.74
0V
V
CC
V
CC
2k
SLOPE = 5Ω
SLOPE = 80Ω
RESET
RESET
RESET
330pF
4.80
4.75
2.72
2.70
GND
0V
0
10
20
30
(mA)
40
50
0
0.2
0.4
0.6
(mA)
0.8
1.0
500ms/div
I
I
OUT
OUT
MAX690A
RESET RESPONSE TIME
POWER-FAIL COMPARATOR
RESPONSE TIME
POWER-FAIL COMPARATOR
RESPONSE TIME
+5V
PFI
V
T
A
= +5V
= +25°C
CC
+5V
V
CC
+5V
PFO
+5V
+4V
PFO
30pF
1k
PFI
+3V
T
A
= +25°C
PFO
1k
PFO
+1.25V
+5V
30pF
V
CC
V
CC
+0V
0V
+1.25V
10k
RESET
+1.3V
RESET
GND
RESET
+1.30V
PFI
V
= +5V
CC
= +25°C
30pF
PFI
T
A
+1.2V
+1.20V
0V
2µs/div
400ns/div
400ns/div
MAX805L
RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
MAX805L
RESET RESPONSE TIME
+5V
+5V
+5V
V
CC
V
CC
+4V
V
CC
RESET
GND
330pF
V
CC
0V
0V
10k
0V
V
BATT
RESET
GND
+4V
330
pF
RESET
692/MAX805L
0V
2µs/div
500ms/div
4
_______________________________________________________________________________________
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
692/MAX805L
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
MAX690A/MAX692A
MAX802L/MAX802M
MAX805L
Supply Output for CMOS RAM. When VCC is above the reset threshold,
VOUT connects to VCC through a P-channel MOSFET switch. When VCC
is below the reset threshold, the higher of VCC or VBATT will be
VOUT
1
1
connected to VOUT
.
VCC
2
3
2
3
+5V Supply Input
Ground
GND
Power-Fail Comparator Input. When PFI is less than 1.25V, PFO goes
low. Connect PFI to GND or VCC when not used.
4
5
4
5
PFI
Power-Fail Output. When PFI is less than 1.25V, PFO goes low;
otherwise PFO stays high.
PFO
Watchdog Input. If WDI remains high or low for 1.6sec, the internal
watchdog timer runs out and reset is triggered. If WDI is left floating or
connected to a high-impedance three-state buffer, the watchdog
feature is disabled. The internal watchdog timer clears whenever reset
is asserted, WDI is three-stated, or WDI sees a rising or falling edge.
6
7
–
8
6
WDI
Reset Output. Whenever RESET is triggered, it pulses low for 200ms. It
stays low when VCC is below the reset threshold (4.65V in the
MAX690A/MAX802L and 4.4V in the MAX692A/MAX802M) and remains
low for 200ms after VCC rises above the reset threshold. A watchdog
timeout also triggers RESET.
RESET
RESET
VBATT
Active-High Reset Output is the inverse of RESET. When RESET is
asserted, the RESET output voltage = VCC or VBATT, whichever is
higher.
7
8
Backup-Battery Input. When VCC falls below the reset threshold, VBATT
will be switched to VOUT if VBATT is 20mV greater than VCC. When VCC
rises to 20mV above VBATT, VOUT will be reconnected to VCC. The 40mV
hysteresis prevents repeated switching if VCC falls slowly.
_______________________________________________________________________________________
5
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
+5V
0V
V
BATT
BATTERY-SWITCHOVER
CIRCUITRY
V
OUT
V
CC
V
CC
V
OUT
t
RS
RESET
(RESET)
3.0V
RESET
0V
GENERATOR
+5V
3.5V
1.25V
RESET
0V
+5V
WATCHDOG
TIMER
WDI
(RESET)
3.0V
0V
MAX690A
MAX692A
MAX802L
MAX802M
MAX805L
0.8V
+5V
PFO
PFI
0V
PFO
1.25V
V
BATT
= PFI = 3.0V
I
= 0mA
OUT
GND
(
) ARE FOR MAX805L ONLY.
(
) ARE FOR MAX805L ONLY.
Figure 1. Block Diagram
Figure 2. Timing Diagram
_______________De t a ile d De s c rip t io n
ed, the watchdog timer remains clear. When RESET
comes high, the watchdog resumes timing and must be
serviced within 1.6sec. If WDI is tied high or low, a
RESET pulse is triggered every 1.8sec (tWD plus tRS).
Re s e t Ou t p u t
A microprocessor’s (µP’s) reset input starts the µP in a
known state. When the µP is in an unknown state, it should
be held in reset. The MAX690A/MAX692A/MAX802L/
MAX802M assert reset during power-up and prevent code
execution errors during power-down or brownout condi-
tions.
The MAX805L active-high RESET output is the inverse
of the MAX690A/MAX692A/MAX802L/MAX802M RESET
output, and is guaranteed to be valid with VCC down to
1.1V. Some µPs, such as Intel’s 80C51, require an
active-high reset pulse.
On power-up, once VCC reaches 1V, RESET is guaran-
teed to be a logic low. As VCC rises, RESET remains
low. When VCC exceeds the reset threshold, an internal
timer keeps RESET low for a time equal to the reset
pulse width; after this interval, RESET goes high (Figure
2). If a brownout condition occurs (if VCC dips below
the reset threshold), RESET is triggered. Each time
RESET is triggered, it stays low for the reset pulse width
interval. Any time VCC goes below the reset threshold,
the internal timer restarts the pulse. If a brownout con-
dition interrupts a previously initiated reset pulse, the
reset pulse continues for another 200ms. On power-
down, once VCC goes below the threshold, RESET is
guaranteed to be logic low until VCC droops below 1V.
Wa t c h d o g In p u t
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 open cir-
cuiting the WDI input. As long as reset is asserted or
the WDI inp ut is op e n c irc uite d , the time r re ma ins
c le a re d a nd d oe s not c ount. As s oon a s re s e t is
released or WDI is driven high or low, the timer starts
counting. It can detect pulses as short as 50ns.
P o w e r-Fa il Co m p a ra t o r
692/MAX805L
The PFI input is compared to an internal 1.25V refer-
ence. If PFI is less than 1.25V, PFO goes low. The
power-fail comparator is intended for use as an under-
voltage detector to signal a failing power supply; it
RESET is also triggered by a watchdog timeout. If a
high or low is continuously applied to the WDI pin for
1.6sec, RESET pulses low. As long as RESET is assert-
6
_______________________________________________________________________________________
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
692/MAX805L
V
BATT
V
CC
+5V
SW1
SW2
SW3
SW4
V
OUT
V
CC
TO STATIC RAM
D1 D2
MAX690A
MAX802L
MAX805L
SUBSTRATE
RESET
V
BATT
TO µP
MAX690A MAX802L MAX805L
MAX692A MAX802M
(RESET)
D3
+
0.1F
V
OUT
GND
CONDITION
SW1/SW2 SW3/SW4
V
> Reset Threshold
Open
Open
Closed
Closed
Open
CC
( ) ARE FOR MAX805L ONLY.
V
< Reset Threshold and
> V
BATT
CC
V
CC
V
< Reset Threshold and
< V
BATT
CC
Closed
Figure 4. Using a SuperCap as a Backup Power Source with a
MAX690A/MAX802L/MAX805L and a +5V ±5% Supply
V
CC
RESET THRESHOLD = 4.65V IN MAX690A/MAX802L/MAX805L.
RESET THRESHOLD = 4.4V IN MAX692A/MAX802M
than V
.
CC
Figure 3. Backup-Battery Switchover Block Diagram
When VCC exceeds the reset threshold, it is connected to
the MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
substrate, regardless of the voltage applied to VBATT
need not be dedicated to this function though, as it is
completely separate from the rest of the circuitry. The
external voltage divider drives PFI to sense the unregu-
la te d DC inp ut to the + 5V re g ula tor (s e e Typ ic a l
Operating Circuit). The voltage-divider ratio can be
chosen such that the voltage at PFI falls below 1.25V
just before the +5V regulator drops out. PFO then trig-
gers an interrupt which signals the µP to prepare for
power-down.
(Figure 3). During this time, the diode (D1) between V
BATT
and the substrate will conduct current from VBATT to V if
CC
Table 1. Input and Output Status in Battery-Backup Mode
SIGNAL
STATUS
VCC
Disconnected from VOUT
To c ons e rve b a c kup -b a tte ry p owe r, the p owe r-fa il
detector comparator is turned off and PFO is forced
Connected to VBATT through an internal 80Ω
PMOS switch
VOUT
low when VBATT connects to VOUT
.
Ba c k u p -Ba t t e ry S w it c h o ve r
Connected to VOUT. Current drawn from the
battery is less than 1µA, as long as
VCC < VBATT - 1V.
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 automati-
cally switch RAM to backup power when VCC fails.
VBATT
PFI
Power-fail comparator is disabled.
Logic low
As long as VCC exceeds the reset threshold, VOUT connects
to VCC through a 5Ω PMOS power switch. Once V falls
CC
PFO
below the reset threshold, V or VBATT (whichever is high-
CC
Logic low
er) switches to VOUT. Unlike the MAX690/MAX692, the
RESET
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L don’t
always connect VBATT to VOUT when VBATT is greater than
VCC. VBATT connects to VOUT (through an 80Ω switch) only
when VCC is below the reset threshold and VBATT is greater
RESET
Logic high (MAX805L only)
Watchdog timer is disabled
WDI
_______________________________________________________________________________________
7
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
V
IN
+5V
+5V
R
1
V
CC
V
OUT
V
CC
TO STATIC RAM
MAX692A
MAX802M
MAX690
MAX692A
MAX802L
MAX802M
MAX805L
PFI
RESET
V
BATT
TO µP
R
3
R
2
C1*
+
PFO
100k
0.1F
GND
GND
TO µP
*OPTIONAL
+5V
Figure 5. Using a SuperCap™ as a Backup Power Source with
the MAX692A/MAX802M and a +5V ±10% Supply
PFO
0V
0V
V
L
V
H
VBATT is 0.6V or greater than V
.
CC
V
TRIP
V
IN
When VBATT connects to VOUT, backup mode is activat-
ed and the internal circuitry is powered from the battery
(Table 1). When VCC is just below VBATT, the current
drawn from VBATT is typically 30µA. When VCC drops to
more than 1V below VBATT, the internal switchover com-
parator shuts off and the supply current falls to less
than 1µA.
R
2
V
= 1.25/
TRIP
R
+ R
2
2
R
|| R
3
2
V
= 1.25/
−1.25
IH
R
+ R || R
1
2 3
V
5
−1.25
1.25
L
+
=
R
R
R
2
1
3
__________Ap p lic a t io n s In fo rm a t io n
Figure 6. Adding Hysteresis to the Power-Fail Comparator
Us in g a S u p e rCa p ™ a s a Ba c k u p
P o w e r S o u rc e
SuperCaps are capacitors with extremely high capaci-
tance values, on the order of 0.1F. Figure 4 shows a
SuperCap used as a backup power source. Do not allow
the SuperCap’s voltage to exceed the maximum reset
threshold by more than 0.6V. In Figure 4’s circuit, the
Allo w a b le Ba c k u p P o w e r-S o u rc e
Ba t t e rie s
Lithium batteries work very well as backup batteries due to
very low self-discharge rates and high energy density.
Single lithium batteries with open-circuit voltages of 3.0V to
3.6V are ideal. Any battery with an open-circuit voltage
less than the minimum reset threshold plus 0.3V can be
SuperCap rapidly charges to within a diode drop of V
However, after a long time, the diode leakage current CwCill
pull the SuperCap voltage up to VCC When using a
.
.
SuperCap with the MAX690A/MAX802L/MAX805L, VCC
may not exceed 4.75V + 0.6V = 5.35V.
Table 2. Allowable Backup-Battery Voltages
(see Using a SuperCap as a Backup Power Source
section for use with a SuperCap)
Use the SuperCap circuit of Figure 5 with a MAX692A
o r MAX8 0 2 M a n d a ± 1 0 % s u p p ly. Th is c irc u it
MAXIMUM BACKUP-BATTERY
e ns ure s tha t the Sup e rCa p only c ha rg e s to VCC
-
PART NO.
VOLTAGE (V)
0.5V. At the maximum VCC of 5.5V, the SuperCap
charges up to 5.0V, only 0.5V above the maximum
reset threshold—well within the requisite 0.6V.
692/MAX805L
MAX690A/
4.80
MAX802L/MAX805L
MAX692A/
4.55
MAX802M
™SuperCap is a trademark of Baknor Industries.
8
_______________________________________________________________________________________
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
692/MAX805L
c onne c te d d ire c tly to the VBATT inp ut of the
ICs where battery-backup mode is entered whenever
VBATT gets close to VCC, an unconnected VBATT pin
a c c umula te s le a ka g e c ha rg e a nd trig g e rs
RESET/RESET in error.
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L with
no additional circuitry (see the Typical Operating Circuit).
However, batteries with open-circuit voltages that are
greater cannot be used for backup, as current is sourced
into the substrate through the diode (D1 in Figure 3) when
VCC is close to the reset threshold.
Ad d in g Hys t e re s is t o t h e
P o w e r-Fa il Co m p a ra t o r
Hysteresis adds a noise margin to the power-fail com-
parator and prevents repeated triggering of PFO when
Op e ra t io n
Wit h o u t a Ba c k u p P o w e r S o u rc e
VIN is close to its trip point. Figure 6 shows how to add
If a backup power source is not used, ground VBATT
hysteresis to the power-fail comparator. Select the
ratio of R1 and R2 such that PFI sees 1.25V when V
falls to its trip point (VTRIP). R3 adds the hysteresis. IINt
will typically be an order of magnitude greater than R1
or R2 (about 10 times either R1 or R2). The current
through R1 and R2 should be at least 1µA to ensure
that the 25nA (max) PFI input current does not shift the
trip point. R3 should be larger than 10kΩ so it does not
load down the PFO pin. Capacitor C1 adds additional
noise rejection.
and connect VOUT to VCC
. Since there is no need to
switch over to any backup power source, VOUT does
not need to be switched. A direct connection to VCC
eliminates any voltage drops across the switch which
may push VOUT below VCC
.
Re p la c in g t h e Ba c k u p Ba t t e ry
The backup battery can be removed while VCC remains
valid, without danger of triggering RESET/RESET. As
long as VCC stays above the reset threshold, battery-
backup mode cannot be entered. In other switchover
Mo n it o rin g a Ne g a t ive Vo lt a g e
The power-fail comparator can be used to monitor a
negative supply rail using the circuit of Figure 7. When
the negative rail is good (a negative voltage of large
magnitude), PFO is low. When the negative rail is
degraded (a negative voltage of lesser magnitude),
PFO goes high. This circuit’s accuracy is affected by
the PFI threshold tolerance, the VCC line, and the resis-
tors.
+5V
R
1
V
CC
MAX690A
MAX692A
MAX802L
MAX802M
MAX805L
PFI
PFO
In t e rfa c in g t o µP s w it h
Bid ire c t io n a l Re s e t P in s
R
2
µPs with bidirectional reset pins, such as the Motorola
68HC11
s e rie s ,
c a n
c onte nd
with
the
GND
MAX690A/MAX692A/MAX802L/MAX802M RESET out-
put. If, for example, the RESET output is driven high
and the µP wants to pull it low, indeterminate logic lev-
els may result. To correct this, connect a 4.7kΩ resis-
tor between the RESET output and the µP reset I/O, as
in Figure 8. Buffer the RESET output to other system
components
V-
+5V
PFO
0V
V
V-
TRIP
0V
5
−1.25
1.25 - V
TRIP
=
R
R
1
2
Figure 7. Monitoring a Negative Voltage
_______________________________________________________________________________________
9
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
V
CC
V
CC
MAX690A
MAX692A
MAX802L
MAX802M
4.7k
RESET
RESET
GND
GND
Figure 8. Interfacing to µPs with Bidirectional Reset I/O
692/MAX805L
10 ______________________________________________________________________________________
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
692/MAX805L
________________________µP S u p e rvis o ry Circ u it s
Minimum Nominal
Nominal
Reset
Threshold Width
Reset
Pulse
Watchdog
Timeout Backup-
Period
(sec)
Power-
Fail
Com-
CE
-
Manual- Watch- Low-
Reset dog Line
Output Output Reset
Active- Battery-
Part
Number
Battery Write
High
On
(V)
(ms)
Switch Protect parator Input
Output
MAX690A/692A 4.65/4.40
MAX691A/693A 4.65/4.40
140
1.6
✔
✔
✔
✔
✔
✔
✔
140/adj.
35/adj.
35/adj.
200
1.6/adj.
1.6/adj.
1.6/adj.
-
✔/10ns
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
MAX696
Adj.
MAX697
Adj.
✔
MAX700
4.65/adj.
4.65/4.40
4.65/4.40
2.63
✔
✔
✔
✔
✔
MAX703/704
MAX705/706
MAX706P
MAX706R/S/T
140
-
✔
✔
✔
✔
✔
140
1.6
✔
✔
✔
140
1.6
✔
2.63/2.93/
3.08
140
1.6
MAX707/708
4.65/4.40
140
140
-
-
✔
✔
✔
✔
✔
✔
MAX708R/S/T
2.63/2.93/
3.08
MAX709L/M/
R/S/T
4.65/4.40/
2.63/2.93/3.08
140
-
MAX791
4.65
140
140
1
1
✔
✔/10ns
✔/10ns
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
MAX792L/M/
R/S/T
4.65/4.40/
2.63/2.93/3.08
MAX800L/M
MAX802L/M
MAX805L
4.60/4.40
4.60/4.40
4.65
140
140
140
140
140
1.6/adj.
1.6
✔
✔
✔
✔/10ns
✔/±2%
✔/±2%
✔
✔
✔
✔
1.6
✔
✔
✔
MAX813L
4.65
1.6
✔
✔
✔
✔
✔
MAX820L/M/
R/S/T
4.65/4.40/
2.63/2.93/3.08
1
✔/10ns
✔/±2%
✔
MAX1232
MAX1259
4.37/4.62
-
250
-
0.15/0.60/1.2
-
✔
✔
✔
✔
______________________________________________________________________________________ 11
Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
__Orde ring Inform a tion (c ontinue d)
____________________Chip Topogra phy
PART
TEMP. RANGE
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
-55°C to +125°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°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
-55°C to +125°C
PIN-PACKAGE
V
V
CC
V
OUT
BATT
MAX692ACPA
MAX692ACSA
MAX692AC/D
MAX692AEPA
MAX692AESA
MAX692AMJA
MAX802LCPA
MAX802LCSA
MAX802LEPA
MAX802LESA
MAX802MCPA
MAX802MCSA
MAX802MEPA
MAX802MESA
MAX805LCPA
MAX805LCSA
MAX805LC/D
MAX805LEPA
MAX805LESA
MAX805LMJA
8
Plastic DIP
SO
8
Dice*
Plastic DIP
8
8
8
8
8
8
8
8
8
8
8
8
8
RESET (RESET)
0. 061"
(1. 55mm)
SO
WDI
CERDIP**
Plastic DIP
SO
GND
Plastic DIP
SO
PFI PFO
Plastic DIP
SO
0. 078"
(1. 98mm)
Plastic DIP
SO
( ) ARE FOR MAX805L ONLY.
TRANSISTOR COUNT: 573;
SUBSTRATE MUST BE LEFT UNCONNECTED.
Plastic DIP
SO
Dice*
8
8
8
Plastic DIP
SO
CERDIP**
* Dice are specified at TA = +25°C.
**Contact factory for availability and processing to MIL-STD-883.
692/MAX805L
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
© 1993 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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