Maxim MAX691AEWE Microprocessor supervisory circuit Datasheet

19-0094; Rev 7a; 12/96
Microprocessor Supervisory Circuits
________________________Applications
♦ 200ms Power-OK/Reset Timeout Period
♦ 1µA Standby Current, 30µA Operating Current
♦ On-Board Gating of Chip-Enable Signals,
10ns Max Delay
♦ MaxCap™ or SuperCap™ Compatible
♦ Guaranteed RESET Assertion to VCC = +1V
♦ Voltage Monitor for Power-Fail or Low-Battery
Warning
♦ Power-Fail Accuracy Guaranteed to ±2%
(MAX800L/M)
♦ Available in 16-Pin Narrow SO and Plastic
DIP Packages
______________Ordering Information
Computers
Controllers
PART
TEMP. RANGE
Intelligent Instruments
MAX691ACPE
0°C to +70°C
16 Plastic DIP
Automotive Systems
MAX691ACSE
MAX691ACWE
MAX691AC/D
0°C to +70°C
0°C to +70°C
0°C to +70°C
16 Narrow SO
16 Wide SO
Dice*
Critical µP Power Monitoring
__________Typical Operating Circuit
+8V
____________________________Features
5V
REGULATOR
0.1µF
3
VCC
1N4148
1
5
BATT ON
VOUT
VBATT
CE OUT
2
12
CMOS RAM
MAX691A
9
MAX693A CE IN 13
PFI
MAX800L
MAX800M
GND
WDI
7
NO
CONNECTION
8
A0-A15
I/O
11
µP
10
NMI
OSC SEL
LOW LINE WDO
6
14
*MaxCap
ADDRESS
DECODE
OSC IN
PFO
RESET
SYSTEM STATUS INDICATORS
MAX691AEPE
-40°C to +85°C
16 Plastic DIP
MAX691AESE
-40°C to +85°C
16 Narrow SO
MAX691AEWE
-40°C to +85°C
16 Wide SO
MAX691AEJE
-40°C to +85°C
16 CERDIP
MAX691AMJE
-55°C to +125°C
16 CERDIP
Ordering Information continued on last page.
* Dice are specified at TA = +25 °C, DC parameters only.
__________________Pin Configuration
0.47F*
4
PIN-PACKAGE
15
RESET
TOP VIEW
VBATT 1
16 RESET
VOUT 2
15 RESET
VCC 3
14 WDO
GND 4
BATT ON 5
LOW LINE 6
MAX691A
MAX693A
MAX800L
MAX800M
OSC IN 7
13 CE IN
12 CE OUT
11 WDI
10 PFO
OSC SEL 8
9
PFI
AUDIBLE
ALARM
DIP/SO
SuperCap is a registered trademark of Baknor Industries. MaxCap is a registered trademark of The Carborundum Corp.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
MAX691A/MAX693A/MAX800L/MAX800M
_______________General Description
The MAX691A/MAX693A/MAX800L/MAX800M microprocessor (µP) supervisory circuits are pin-compatible
upgrades to the MAX691, MAX693, and MAX695. They
improve performance with 30µA supply current, 200ms
typ reset active delay on power-up, and 6ns chipenable propagation delay. Features include write protection of CMOS RAM or EEPROM, separate watchdog
outputs, backup-battery switchover, and a RESET output that is valid with VCC down to 1V. The MAX691A/
MAX800L have a 4.65V typical reset-threshold voltage,
and the MAX693A/MAX800M’s reset threshold is 4.4V
typical. The MAX800L/MAX800M guarantee power-fail
accuracies to ±2%.
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
VCC .......................................................................-0.3V to +6V
VBATT...................................................................-0.3V to +6V
All Other Inputs .....................................-0.3V to (VOUT + 0.3V)
Input Current
VCC Peak...........................................................................1.0A
VCC Continuous.............................................................250mA
VBATT Peak ..................................................................250mA
VBATT Continuous ..........................................................25mA
GND, BATT ON .............................................................100mA
All Other Outputs ............................................................25mA
Continuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C) ..........842mW
Narrow SO (derate 8.70mW/°C above +70°C) ...........696mW
Wide SO (derate 9.52mW/°C above +70°C)...............762mW
CERDIP (derate 10.00mW/°C above +70°C) ..............800mW
Operating Temperature Ranges
MAX69_AC_ _/MAX800_C_ _ .............................0°C to +70°C
MAX69_AE_ _/MAX800_E_ _ ...........................-40°C to +85°C
MAX69_AMJE ................................................-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
(MAX691A, MAX800L: VCC = +4.75V to +5.5V, MAX693A, MAX800M: VCC = +4.5V to +5.5V, VBATT = 2.8V, TA = TMIN to TMAX,
unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
Operating Voltage Range,
VCC, VBATT (Note 1)
0
IOUT = 25mA
VOUT Output
TYP
VCC = 4.5V
IOUT = 250mA
VCC-to-VOUT On-Resistance VCC = 4.5V
VOUT in Battery-Backup
Mode
VBATT-to-VOUT
On-Resistance
5.5
V
VCC - 0.02
VCC - 0.2
VCC - 0.05
VCC - 0.3
MAX69_AE,
MAX800_C/E
VCC - 0.2
VCC - 0.35
VCC - 0.17
VCC - 0.3V
MAX69_AC, MAX800_C
0.8
1.2
MAX69_AE, MAX800_E
0.8
1.4
0.8
1.6
MAX69_A/M
VBATT = 4.5V, IOUT = 20mA
VBATT = 2.8V, IOUT = 10mA
VBATT = 2.0V, IOUT = 5mA
VBATT = 4.5V
VBATT = 2.8V
VBATT = 2.0V
VCC > VBATT - 1V
Supply Current in
Battery-Backup Mode
(Excludes IOUT) (Note 2)
VCC < VBATT - 1.2V
VBATT = 2.8V
TA = +25°C
VBATT Standby Current
(Note 3)
VBATT + 0.2V ≤ VCC
TA = +25°C
TA = TMIN + TMIN
Battery Switchover
Threshold
Power-up
Power-down
VBATT - 0.3
VBATT - 0.25
VBATT - 0.15
Ω
V
15
25
30
Ω
30
100
µA
0.04
1
µA
TA = TMIN + TMIN
TA = TMIN + TMIN
V
VCC - 0.40
MAX69_AC/AE,
MAX800_C/E
Supply Current in
Normal Operating Mode
(Excludes IOUT)
2
UNITS
MAX69_AC
MAX69_A/M
IOUT = 210mA
MAX
5
-0.1
-1.0
0.02
0.02
VBATT + 0.3
VBATT - 0.3
_______________________________________________________________________________________
µA
V
Microprocessor Supervisory Circuits
(MAX691A, MAX800L: VCC = +4.75V to +5.5V, MAX693A, MAX800M: VCC = +4.5V to +5.5V, VBATT = 2.8V, TA = TMIN to TMAX,
unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
Battery Switchover
Hysteresis
TYP
MAX
60
1
100
RESET AND WATCHDOG TIMER
MAX691A, MAX800L
4.50
4.65
4.75
MAX693A, MAX800M
4.25
4.40
MAX800L, TA = +25°C, VCC falling
4.55
4.70
MAX800M, TA = +25°C, VCC falling
4.30
4.45
BATT ON Output
Short-Circuit Current
Reset Threshold Voltage
ISINK = 3.2mA
ISINK = 25mA
Sink current
Source current
mV
0.1
0.7
60
15
BATT ON Output
Low Voltage
Reset Threshold Hysteresis
VCC to RESET Delay
Power-down
LOW LINE-to-RESET Delay
Reset Active Timeout Period,
Power-up
Internal Oscillator
140
Reset Active Timeout Period,
Power-up
External Clock (Note 4)
1.0
70
Watchdog Timeout Period,
External Clock (Note 4)
Minimum Watchdog Input
Pulse Width
VIL = 0.8V, VIH = 0.75 x VCC
100
RESET Output Voltage
ISINK = 50µA, VCC = 1V, VBATT = 0V, VCC falling
ISINK = 3.2mA, VCC = 4.25V
ISOURCE = 1.6mA, VCC = 5V
LOW LINE Output Voltage
ISINK = 3.2mA, VCC = 4.25V
ISOURCE = 1µA, VCC = 5V
LOW LINE Output
Short-Circuit Current
Output source current
WDO Output Voltage
ISINK = 3.2mA
ISOURCE = 500µA, VCC = 5V
WDO Output
Short-Circuit Current
Output source current
WDI Threshold Voltage
(Note 6)
WDI Input Current
VIH
VIL
WDI = 0V
WDI = VOUT
4.50
V
mA
µA
V
15
mV
80
µs
800
ns
200
280
1.6
100
4096
1024
ms
Clock
Cycles
2.25
140
sec
ms
Clock
Cycles
ns
0.004
0.1
0.3
0.4
V
7
20
mA
3.5
–
RESET Output Short-Circuit
Output source current
Current
RESET Output Voltage Low
ISINK = 3.2mA
(Note 5)
0.4
1.5
2048
Long period
Short period
Long period
Short period
Watchdog Timeout Period,
Internal Oscillator
UNITS
0.1
0.4
V
0.4
3.5
1
15
100
0.4
3.5
3
10
0.75 x VCC
0.8
-50
-10
20
50
V
µA
V
mA
V
µA
_______________________________________________________________________________________
3
MAX691A/MAX693A/MAX800L/MAX800M
ELECTRICAL CHARACTERISTICS (continued)
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
ELECTRICAL CHARACTERISTICS (continued)
(MAX691A, MAX800L: VCC = +4.75V to +5.5V, MAX693A, MAX800M: VCC = +4.5V to +5.5V, VBATT = 2.8V, TA = TMIN to TMAX,
unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
1.2
1.25
1.3
1.225
1.25
1.275
±0.01
±25
UNITS
POWER-FAIL COMPARATOR
PFI Input Threshold
MAX69_AC/AE/AM, VCC = 5V
MAX800_C/E, VCC = 5V
PFI Leakage Current
PFO Output Voltage
PFO Output Short-Circuit
Current
PFI-to-PFO Delay
ISINK = 3.2mA
ISOURCE = 1µA, VCC = 5V
Output source current
0.4
3.5
1
15
VIN = -20mV, VOD = 15mV
25
VIN = 20mV, VOD = 15mV
60
100
V
nA
V
µA
µs
CHIP-ENABLE GATING
CE IN Leakage Current
Disable mode
±0.005
±1
µA
CE IN-to-CE OUT Resistance
(Note 7)
Enable mode
75
150
Ω
CE OUT Short-Circuit Current
(Reset Active)
–
Disable mode, CE OUT = 0V
0.75
2.0
mA
CE IN-to-CE OUT Propagation
Delay (Note 8)
50Ω source impedance driver, CLOAD = 50pF
6
10
ns
0.1
CE OUT Output Voltage High
(Reset Active)
VCC = 5V, IOUT = -100µA
3.5
VCC = 0V, VBATT = 2.8V, IOUT = 1µA
2.7
RESET-to-CE OUT Delay
Power-down
V
12
µs
INTERNAL OSCILLATOR
OSC IN Leakage Current
OSC SEL = 0V
0.10
±5
µA
OSC IN Input Pull-Up Current
OSC SEL = VOUT or floating, OSC IN = 0V
10
100
µA
OSC SEL Input Pull-Up Current
OSC SEL = 0V
10
100
µA
OSC IN Frequency Range
OSC SEL = 0V
OSC IN External Oscillator
Threshold Voltage
VIH
OSC IN Frequency with
External Capacitor
50
VOUT - 0.3
kHz
VOUT - 0.6
VIL
3.65
OSC SEL = 0V, COSC = 47pF
100
2.00
V
kHz
Note 1: Either VCC or VBATT can go to 0V, if the other is greater than 2.0V.
Note 2: The supply current drawn by the MAX691A/MAX800L/MAX800M from the battery excluding IOUT typically goes to 10µA
when (VBATT - 1V) < VCC < VBATT. In most applications, this is a brief period as VCC falls through this region.
Note 3: “+” = battery-discharging current, “--” = battery-charging current.
Note 4: Although presented as typical values, the number of clock cycles for the reset and watchdog timeout periods are fixed and
do not vary with process or temperature.
Note 5: RESET is an open-drain output and sinks current only.
Note 6: WDI is internally connected to a voltage divider between VOUT and GND. If unconnected, WDI is driven to 1.6V (typ),
disabling the watchdog function.
Note 7: The chip-enable resistance is tested with VCC = +4.75V for the MAX691A/MAX800L and VCC = +4.5V for the
MAX693A/MAX800M. CE IN = CE OUT = VCC / 2.
Note 8: The chip-enable propagation delay is measured from the 50% point at CE IN to the 50% point at CE OUT.
4
_______________________________________________________________________________________
Microprocessor Supervisory Circuits
32
30
28
26
-30
0
30
60
90
120
1.5
1
0.5
150
40
-60
-30
0
30
60
90
120
-60 -30
150
90
120 150 180
VCC = 5V,
VBATT = 0V
1.25
PFI THRESHOLD (V)
1.1
1.0
0.9
0.8
0
30
60
90
120 150
0.75
0.50
VCC = +5V,
VBATT = 0V
NO LOAD ON PFO
0
-60
-30
0
30
60
90
120
-60
150
-30
0
30
60
90
TEMPERATURE (°C)
RESET THRESHOLD
vs. TEMPERATURE
RESET OUTPUT RESISTANCE
vs. TEMPERATURE
RESET DELAY
vs. TEMPERATURE
4.55
4.50
4.45
4.40
MAX693A
MAX800M
4.30
MAX691A TOC-08
500
VCC = 5V, VBATT = 2.8V
SOURCING CURRENT
400
300
200
100
30
60
90
TEMPERATURE (°C)
120
150
220
150
120
150
VCC = 0V TO 5V STEP
VBATT = 2.8V
210
200
190
180
VCC = 0V, VBATT = 2.8V
SINKING CURRENT
0
0
230
RESET DELAY (ms)
MAX691A
MAX800L
RESET OUTPUT RESISTANCE (Ω)
4.70
600
120
MAX691A TOC-09
TEMPERATURE (°C)
MAX691A TOC-07
TEMPERATURE (°C)
VBATT = 2.8V
-30
1.00
0.25
0.7
0.6
-30
MAX691A TOC-06
1.50
MAX691A TOC-05
VCC-to-VOUT ON-RESISTANCE (Ω)
MAX691A TOC-04
1.2
VCC = 0V
5
-60
60
30
PFI THRESHOLD
vs. TEMPERATURE
VBATT = 4.5V
4.35
0
VCC to VOUT ON-RESISTANCE
vs. TEMPERATURE
10
4.60
60
VBATT to VOUT ON-RESISTANCE
vs. TEMPERATURE
VBATT = 2.8V
4.65
80
TEMPERATURE (°C)
15
4.75
100
TEMPERATURE (°C)
VBATT = 2.0V
-60
VCC = 4.75V
VBATT = 2.8V
VCE IN = VCC/2
TEMPERATURE (°C)
20
VBATT-to-VOUT ON-RESISTANCE (Ω)
120
0
-60
RESET THRESHOLD (V)
VCC = 5V
VBATT = 2.8V
NO LOAD
CE ON-RESISTANCE (Ω)
34
2
CHIP-ENABLE ON-RESISTANCE
vs. TEMPERATURE
MAX691A TOC-02
VCC = 5V
VBATT = 2.8V
PFI, CE IN = 0V
BATTERY SUPPLY CURRENT (µA)
MAX691A TOC-01
VCC SUPPLY CURRENT (µA)
36
BATTERY SUPPLY CURRENT
vs. TEMPERATURE
(BATTERY-BACKUP MODE)
MAX691A TOC-03
VCC SUPPLY CURRENT
vs. TEMPERATURE
(NORMAL OPERATING MODE)
170
-60
-30
0
30
60
90
TEMPERATURE (°C)
120
150
-60
-30
0
30
60
90
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX691A/MAX693A/MAX800L/MAX800M
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
8
4
0
1
2
3
4
10
RESET ACTIVE
TIMEOUT PERIOD
1
SHORT WATCHDOG
TIMEOUT PERIOD
10
100
VCC (V)
1000
VBATT to VOUT (mV)
100
SLOPE = 0.8Ω
8
4
1000
0
VCC = 0V
VBATT = 4.5V
10
100
IOUT (mA)
6
1000
150
100
5V
VCC RESET
THRESHOLD
80µs
100
HI
LOW LINE
LO
SLOPE = 8Ω
10
800ns
HI
RESET
LO
HI
12µs
LO
1
10
200
250
300
VCC to LOW LINE
AND CE OUT DELAY
1
1
50
CLOAD (pF)
CE OUT
1
MAX691A TOC-12
12
VBATT to VOUT vs. OUTPUT CURRENT
(BATTERY-BACKUP MODE)
MAX691A TOC-13
VCC = 4.5V
VBATT = 0V
10
16
COSC (pF)
VCC to VOUT vs. OUTPUT CURRENT
(NORMAL OPERATING MODE)
1000
VCC = 5V
CE IN = 0V TO 5V
DRIVER SOURCE
IMPEDANCE = 50Ω
0
0.1
5
20
MAX691A TOC-15
0
LONG WATCHDOG
TIMEOUT PERIOD
PROPAGATION DELAY (ns)
12
VCC = 5V
VBATT = 2.8V
MAX691A TOC-14
IBATT (µA)
16
100
MAX691A TOC-11
VBATT = 2.8V
IOUT = 0A
CHIP-ENABLE PROPAGATION DELAY
vs. CE OUT LOAD CAPACITANCE
WATCHDOG AND RESET TIMEOUT PERIOD
vs. OSC IN TIMING CAPACITOR (COSC)
WATCHDOG AND RESET TIMEOUT PERIOD (sec)
20
MAX691A TOC-10
BATTERY CURRENT
vs. INPUT SUPPLY VOLTAGE
VCC to VOUT (mV)
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
100
IOUT (mA)
_______________________________________________________________________________________
Microprocessor Supervisory Circuits
PIN
NAME
FUNCTION
1
VBATT
2
VOUT
Battery-Backup Input. Connect to external battery or capacitor and charging circuit. If backup battery is not
used, connect to GND.
Output Supply Voltage. When VCC is greater than VBATT and above the reset threshold, VOUT connects to
VCC. When VCC falls below VBATT and is below the reset threshold, VOUT connects to VBATT. Connect a 0.1µF
capacitor from VOUT to GND. Connect VOUT to VCC if no backup battery is used.
Input Supply Voltage, 5V input.
3
VCC
4
GND
5
6
7
8
9
10
11
12
13
14
15
16
Ground. 0V reference for all signals.
Battery On Output. When VOUT switches to VBATT, BATT ON goes high. When VOUT switches to VCC, BATT ON
BATT ON goes low. Connect the base of a PNP through a current-limiting resistor to BATT ON for VOUT current requirements greater than 250mA.
LOW LINE LOW LINE output goes low when VCC falls below the reset threshold. It returns high as soon as VCC rises above
the reset threshold.
External Oscillator Input. When OSC SEL is unconnected or driven high, a 10µA pull-up connects from VOUT to
OSC IN, the internal oscillator sets the reset and watchdog timeout periods, and OSC IN selects between fast
OSC IN
and slow watchdog timeout periods. When OSC SEL is driven low, the reset and watchdog timeout periods may
be set either by a capacitor from OSC IN to ground or by an external clock at OSC IN (Figure 3).
Oscillator Select. When OSC SEL is unconnected or driven high, the internal oscillator sets the reset delay and
OSC SEL watchdog timeout period. When OSC SEL is low, the external oscillator input (OSC IN) is enabled (Table 1).
OSC SEL has a 10µA internal pull-up.
Power-Fail Input. This is the noninverting input to the power-fail comparator. When PFI is less than 1.25V, PFO
PFI
goes low. When PFI is not used, connect PFI to GND or VOUT .
Power-Fail Output. This is the output of the power-fail comparator. PFO goes low when PFI is less than 1.25V.
PFO
This is an uncommitted comparator, and has no effect on any other internal circuitry.
Watchdog Input. WDI is a three-level input. If WDI remains either high or low for longer than the watchdog timeout period, WDO goes low and reset is asserted for the reset timeout period. WDO remains low until the next tranWDI
sition at WDI. Leaving WDI unconnected disables the watchdog function. WDI connects to an internal voltage
divider between VOUT and GND, which sets it to mid-supply when left unconnected.
Chip-Enable Output. CE OUT goes low only when CE IN is low and VCC is above the reset threshold. If CE IN is
CE OUT
low when reset is asserted, CE OUT will stay low for 15µs or until CE IN goes high, whichever occurs first.
CE IN
Chip-Enable Input. The input to chip-enable gating circuit. If CE IN is not used, connect CE IN to GND or VOUT.
Watchdog Output. If WDI remains high or low longer than the watchdog timeout period, WDO goes low and reset
WDO
is asserted for the reset timeout period. WDO returns high on the next transition at WDI. WDO remains high if
WDI is unconnected.
RESET Output goes low whenever VCC falls below the reset threshold. RESET will remain low typically for
RESET
200ms after VCC crosses the reset threshold on power-up.
RESET
RESET is an active-high output. It is open drain, and the inverse of RESET.
_______________Detailed Description
–————–
R E S E T and RESET Outputs
The MAX691A/MAX693A/MAX800L/MAX800M’s RESET
and RESET outputs ensure that the µP (with reset
inputs asserted either high or low) powers up in a
known state, and prevents code-execution errors during power-down or brownout conditions.
The RESET output is active low, and typically sinks
3.2mA at 0.1V saturation
voltage in its active state.
–
When deasserted, RESET sources 1.6mA at typically
VOUT - 0.5V. RESET output is open drain, active high,
and typically sinks 3.2mA with a saturation voltage of
0.1V. When no backup battery is used, RESET output is
guaranteed to be valid down to V CC = 1V, and an
external 10kΩ pull-down resistor on RESET insures
that it will be valid with VCC down to GND (Figure 1).
As VCC goes below 1V, the gate drive to the RESET
output switch reduces accordingly, increasing the
RDS(ON) and the saturation voltage. The 10kΩ pulldown resistor insures the parallel combination of switch
plus resistor is around 10kΩ and the output saturation
voltage is below 0.4V while sinking 40µA. When using
a 10kΩ external pull-down resistor, the high state for
RESET output with VCC = 4.75V will be 4.5V typical.
For battery voltages ≥ 2V connected to VBATT, RESET
and RESET remain valid for VCC from 0V to 5.5V.
_______________________________________________________________________________________
7
MAX691A/MAX693A/MAX800L/MAX800M
______________________________________________________________Pin Description
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
WDI
RESET
MAX691A
MAX693A
15
TO µP RESET
WDO
1k
t2
RESET
t1
t1
t3
t1 = RESET TIMEOUT PERIOD
t2 = NORMAL WATCHDOG TIMEOUT PERIOD
t3 = WATCHDOG TIMEOUT PERIOD IMMEDIATELY AFTER RESET
Figure 1. Adding an external pull-down resistor ensures
–————–
RESET is valid with VCC down to GND.
Figure 2. Watchdog Timeout Period and Reset Active Time
RESET and RESET are asserted when VCC falls below
the reset threshold (4.65V for the MAX691A/MAX800L,
4.4V for the MAX693A/MAX800M) and remain asserted
for 200ms typ after VCC rises above the reset threshold
on power-up (Figure 5). The devices’ batteryswitchover comparator does not affect reset assertion.
However, both reset outputs are asserted in batterybackup mode since V CC must be below the reset
threshold to enter this mode.
Watchdog Output
The Watchdog Output (WDO) remains high if there is a
transition or pulse at WDI during the watchdog timeout
–
period. The watchdog function is disabled and WDO is
a logic high when VCC is below the reset threshold, battery-backup mode is enabled, or WDI is an open circuit.
In watchdog mode, if no transition occurs at WDI during
the watchdog timeout period, RESET and RESET are
asserted for the reset timeout period (200ms typical).
WDO goes low and remains low until the next transition
at WDI (Figure 2). If WDI is held high or low indefinitely,
RESET and RESET will generate 200ms pulses every
1.6sec. WDO has a 2 x TTL output characteristic.
Watchdog Function
The watchdog monitors µP activity via the Watchdog
Input (WDI). If the µP becomes inactive, RESET and
RESET are asserted. To use the watchdog function,
connect WDI to a bus line or µP I/O line. If WDI
remains high or low for longer than the watchdog timeout period (1.6sec nominal), WDO, RESET, and RESET
are asserted (see RESET and RESET Outputs section,
and the Watchdog Output discussion on this page).
Watchdog Input
A change of state (high to low, low to high, or a minimum 100ns pulse) at the WDI during the watchdog
period resets the watchdog timer. The watchdog
default timeout is 1.6sec.
To disable the watchdog function, leave WDI floating.
An internal resistor network (100kΩ equivalent impedance at WDI) biases WDI to approximately 1.6V.
Internal comparators detect this level and disable the
watchdog timer. When VCC is below the reset threshold, the watchdog function is disabled and WDI is disconnected from its internal resistor network, thus
becoming high impedance.
8
Selecting an Alternative
Watchdog and Reset Timeout Period
The OSC SEL and OSC IN inputs control the watchdog
and reset timeout periods. Floating OSC SEL and OSC
IN or tying them both to VOUT selects the nominal 1.6sec
watchdog timeout period and 200ms reset timeout period. Connecting OSC IN to GND and floating or connecting OSC SEL to V OUT selects the 100ms normal
watchdog timeout delay and 1.6sec delay immediately
after reset. The reset timeout delay remains 200ms
(Figure 2). Select alternative timeout periods by connecting OSC SEL to GND and connecting a capacitor
between OSC IN and GND, or by externally driving OSC
IN (Table 1 and Figure 3). OSC IN is internally connected to a ±100nA (typ) current source that charges and
discharges the timing capacitor to create the oscillator
frequency, which sets the reset and watchdog timeout
periods (see Connecting a Timing Capacitor at OSC IN
in the Applications Information section).
_______________________________________________________________________________________
Microprocessor Supervisory Circuits
Watchdog Timeout Period
OSC SEL
OSC IN
Low
External Clock Input
1024 clks
4096 clks
2048 clks
Low
External Capacitor
(600/47pF x C)ms
(2.4/47pF x C)sec
(1200/47pF x C)ms
Normal
Immediately After Reset
Reset Timeout Period
Floating
Low
100ms
1.6sec
200ms
Floating
Floating
1.6sec
1.6sec
200ms
EXTERNAL
OSCILLATOR
EXTERNAL
CLOCK
MAX691A
MAX693A
MAX800L
MAX800M
8
7
8
OSC SEL
7
OSC IN
OSC SEL
OSC IN
50kHz
INTERNAL OSCILLATOR
1.6sec WATCHDOG
N.C.
N.C.
8
7
OSC SEL
OSC IN
INTERNAL OSCILLATOR
100ms WATCHDOG
N.C.
8
7
OSC SEL
OSC IN
Figure 3. Oscillator Circuits
Chip-Enable Signal Gating
The MAX691A/MAX693A/MAX800L/MAX800M provide
internal gating of chip-enable (CE) signals to prevent
erroneous data from being written to CMOS RAM in the
event of a power failure. During normal operation, the
CE gate is enabled and passes all CE transitions. When
reset is asserted, this path becomes disabled, preventing erroneous data from corrupting the CMOS RAM. All
–
these parts use a series transmission gate from CE IN to
CE OUT (Figure 4).
The 10ns max CE propagation delay from CE IN to CE
OUT enables the parts to be used with most µPs.
Chip-Enable Input
The Chip-Enable Input (CE IN) is high impedance (dis–————–
abled mode) while RESET and RESET are asserted.
During a power-down sequence where VCC falls below
–
the reset threshold or a watchdog fault, CE IN assumes
–
a high-impedance state when the voltage at CE IN
goes high or 15µs after reset is asserted, whichever
occurs first (Figure 5).
During a power-up sequence, CE IN remains high
impedance, regardless of CE IN activity, until reset is
deasserted following the reset timeout period.
In the high-impedance mode, the leakage currents into
this terminal are ±1µA max over temperature. In the
–
low-impedance mode, the impedance of CE IN appears
as a 75Ω resistor in series with the load at CE OUT.
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 the Chip–
Enable Output (CE OUT) (see Chip-Enable Propagation
Delay vs. CE OUT Load Capacitance in the Typical
Operating Characteristics). The CE propagation delay
–
is production tested from the 50% point of CE IN to the
–
50% point of CE OUT using a 50Ω driver and 50pF of
load capacitance (Figure 6). For minimum propagation
delay, minimize the capacitive load at CE OUT, and
use a low output-impedance driver.
Chip-Enable Output
In the enabled mode, the impedance of CE OUT is
equivalent to 75Ω in series with the source driving CE
IN. In the disabled mode, the 75Ω transmission gate is
off and CE OUT is actively pulled to VOUT. This source
turns off when the transmission gate is enabled.
–———
——
——–
LOW LINE Output
LOW LINE is the buffered output of the reset threshold
comparator. LOW LINE typically sinks 3.2mA at 0.1V.
For normal operation (VCC above the LOW LINE threshold), LOW LINE is pulled to VOUT.
Power-Fail Comparator
The power-fail comparator is an uncommitted comparator
that has no effect on the other functions of the IC.
Common uses include low-battery indication (Figure 7),
and early power-fail warning (see Typical Operating
Circuit).
Power-Fail Input
Power Fail Input (PFI) is the input to the power-fail comparator. It has a guaranteed input leakage of ±25nA
max over temperature. The typical comparator delay is
25µs from VIL to VOL (power failing), and 60µs from VIH
to VOH (power being restored). If PFI is not used, connect it to ground.
_______________________________________________________________________________________
9
MAX691A/MAX693A/MAX800L/MAX800M
Table 1. Reset Pulse Width and Watchdog Timeout Selections
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
5
BATT ON
4.65V*
VCC
6
3
2
VBATT
CE IN
1
13
12
MAX691A
MAX693A
MAX800L
MAX800M
OSC SEL
WDI
PFI
RESET
GENERATOR
7
15
TIMEBASE FOR
RESET AND
WATCHDOG
8
WATCHDOG
TRANSITION
DETECTOR
11
9
WATCHDOG
TIMER
14
10
1.25V
4 GND
* 4.4V FOR THE MAX693A/MAX800M
Figure 4. MAX691A/MAX693A/MAX800L/MAX800M Block Diagram
5.0V
VCC
RESET
4.0V
THRESHOLD
5.0V
0V
CE IN
5V
0V
CE OUT
15µs
100µs
5V
0V
5V
100µs
RESET
RESET
0V
LOGIC LEVELS SHOWN ARE FROM 0V TO 5V.
Figure 5. Reset and Chip-Enable Timing
10
VOUT
CHIP-ENABLE
OUTPUT
CONTROL
16
OSC IN
LOW LINE
______________________________________________________________________________________
CE OUT
RESET
RESET
WDO
PFO
Microprocessor Supervisory Circuits
VBATT
+5V
VCC
MAX691A
MAX693A
MAX800L
MAX800M
2.8V
2.0V to 5.5V
CE OUT
CE IN
50Ω
OUTPUT
IMPEDANCE
VCC
VBATT
GND
CLOAD
MAX691A
MAX693A
MAX800L PFO
PFI
MAX800M
LOW BATT
GND
Figure 6. CE Propagation Delay Test Circuit
Figure 7. Low-Battery Indicator
Table 2. Input and Output Status in Battery-Backup
Mode
Power-Fail Output
The Power-Fail Output (PFO) goes low when PFI goes
below 1.25V. It typically sinks 3.2mA with a saturation
voltage of 0.1V. With PFI above 1.25V, PFO is actively
pulled to VOUT.
PIN
NAME
1
VBATT
2
VOUT
STATUS
Supply current is 1µA max.
VOUT is connected to VBATT through an
internal PMOS switch.
3
VCC
Battery switchover comparator monitors
VCC for active switchover.
4
GND
GND 0V, 0V reference for all signals.
5
BATT ON
Logic high. The open-circuit output is
equal to VOUT.
6
LOWLINE
Logic low*
7
OSC IN
8
OSC SEL
9
PFI
The power-fail comparator remains
active in the battery-backup mode for
VCC ≥ VBATT - 1.2V typ.
PFO
The power-fail comparator remains
active in the battery-backup mode for
VCC ≥ VBATT - 1.2V typ. Below this voltage, PFO is forced low.
10
OSC IN is ignored.
OSC SEL is ignored.
11
WDI
Watchdog is ignored.
12
CE OUT
13
CE IN
High impedance
14
WDO
Logic high. The open-circuit voltage is
equal to VOUT.
15
RESET
Logic low*
16
RESET
High impedance*
Logic high. The open-circuit voltage is
equal to VOUT.
Battery-Backup Mode
Two conditions are required to switch to battery-backup mode: 1) VCC must be below the reset threshold,
and 2) VCC must be below VBATT. Table 2 lists the status of the inputs and outputs in battery-backup mode.
Battery On Output
The Battery On (BATT ON) output indicates the status
of the internal V CC /battery-switchover comparator,
which controls the internal VCC and VBATT switches.
For VCC greater than VBATT (ignoring the small hysteresis effect), BATT ON typically sinks 3.2mA at 0.1V
saturation voltage. In battery-backup mode, this terminal sources approximately 10µA from VOUT. Use BATT
ON to indicate battery-switchover status or to supply
base drive to an external pass transistor for higher-current applications (see Typical Operating Circuit).
Input Supply Voltage
The Input Supply Voltage (VCC) should be a regulated
5V. VCC connects to VOUT via a parallel diode and a
large PMOS switch. The switch carries the entire current load for currents less than 250mA. The parallel
diode carries any current in excess of 250mA. Both the
switch and the diode have impedances less than 1Ω
each. The maximum continuous current is 250mA, but
power-on transients may reach a maximum of 1A.
* VCC must be below the reset threshold to enter battery-backup
mode.
______________________________________________________________________________________
11
MAX691A/MAX693A/MAX800L/MAX800M
+5V
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
Battery-Backup Input
The Battery-Backup Input (VBATT) is similar to the VCC
input except the PMOS switch and parallel diode are
much smaller. Accordingly, the on-resistances of the
diode and the switch are each approximately 10Ω.
Continuous current should be limited to 25mA and
peak currents (only during power-up) limited to 250mA.
The reverse leakage of this input is less than 1µA over
temperature and supply voltage (Figure 8).
Output Supply Voltage
The Output Supply Voltage (VOUT) pin is internally connected to the substrate of the IC and supplies current
to the external system and internal circuitry. All opencircuit outputs will, for example, assume the VOUT voltage in their high states rather than the VCC voltage. At
the maximum source current of 250mA, VOUT will typically be 200mV below VCC. Decouple this terminal with
a 0.1µF capacitor.
__________Applications Information
The MAX691A/MAX693A/MAX800L/MAX800M are not
short-circuit protected. Shorting VOUT to ground, other
than power-up transients such as charging a decoupling capacitor, destroys the device.
All open-circuit outputs swing between VOUT and GND
rather than VCC and GND.
If long leads connect to the chip inputs, insure that
these leads are free from ringing and other conditions
that would forward bias the chip’s protection diodes.
There are three distinct modes of operation:
1) Normal operating mode with all circuitry powered
up. Typical supply current from VCC is 35µA while
only leakage currents flow from the battery.
2) Battery-backup mode where VCC is typically within
0.7V below VBATT. All circuitry is powered up
and the supply current from the battery is typically
less than 60µA.
3) Battery-backup mode where V CC is less than
VBATT by at least 0.7V. VBATT supply current is
1µA max.
Using SuperCap™ or MaxCap™ with the
MAX691A/MAX693A/MAX800L/MAX800M
VBATT has the same operating voltage range as VCC,
and the battery switchover threshold voltages are typically ±30mV centered at VBATT, allowing use of a
SuperCap and a simple charging circuit as a backup
source (Figure 9).
If VCC is above the reset threshold and VBATT is 0.5V
above VCC, current flows to VOUT and VCC from VBATT
until the voltage at VBATT is less than 0.5V above VCC.
For example, with a SuperCap connected to VBATT and
through a diode to VCC, if VCC quickly changes from 5.4V
to 4.9V, the capacitor discharges through VOUT and VCC
until VBATT reaches 5.1V typ. Leakage current through
the SuperCap charging diode and the internal power
diode eventually discharges the SuperCap to VCC. Also, if
VCC and VBATT start from 0.1V above the reset threshold
and power is lost at VCC, the SuperCap on VBATT discharges through V CC until VBATT reaches the reset
threshold; then the battery-backup mode is initiated and
the current through VCC goes to zero.
+5V
3
VCC
1N4148
VBATT
1
MAX691A
MAX693A
MAX800L
MAX800M
VOUT
0.47F*
0.1µF
VCC
VBATT
VOUT
MAX691A
MAX693A
MAX800L
MAX800M
GND
4
* MaxCap
Figure 8. VCC and VBATT to VOUT Switch
12
Figure 9. SuperCap or MaxCap on VBATT
______________________________________________________________________________________
2
Microprocessor Supervisory Circuits
+5V
CE
CE
VOUT
CE IN
MAX691A/MAX693A/MAX800L/MAX800M
VIN
Rp*
R1
RAM 1
VCC
C1*
PFI
CE OUT
CE
CE
MAX691A
MAX693A
MAX800L
MAX800M
MAX691A
MAX693A
MAX800L
MAX800M
RAM 2
R3
R2
CE
CE
GND
PFO
RAM 3
GND
TO µP
CE
*OPTIONAL
5V
RAM 4
PFO
CE
0V
0V
VL VTRIP VH
VIN
VTRIP = 1.25
*MAXIMUM Rp VALUE DEPENDS ON
THE NUMBER OF RAMS.
MINIMUM Rp VALUE IS 1kΩ.
ACTIVE-HIGH
CE LINES
FROM LOGIC
Figure 10. Alternate CE Gating
VH = 1.25/
R1
VCC
PFO
PFI
Alternate Chip-Enable Gating
Hysteresis adds a noise margin to the power-fail comparator and prevents repeated triggering of PFO when
VIN is near the power-fail comparator trip point. Figure
11 shows how to add hysteresis to the power-fail com-
VL - 1.25 + 5 - 1.25 = 1.25
R1
R3
R2
+5V
If using separate power supplies for VCC and VBATT,
VBATT must be less than 0.3V above VCC when VCC is
above the reset threshold. As described in the previous section, if VBATT exceeds this limit and power is
lost at VCC, current flows continuously from VBATT to
VCC via the VBATT-to-VOUT diode and the VOUT-to-VCC
switch until the circuit is broken (Figure 8).
Adding Hysteresis to the
Power-Fail Comparator
R2 I I R3
R1 + R2 I I R3
Figure 11. Adding Hysteresis to the Power-Fail Comparator
Using Separate Power Supplies
for VBATT and VCC
Using memory devices with both CE and CE inputs
allows the CE loop to be bypassed. To do this, connect CE IN to ground, pull up CE OUT to VOUT, and
–
connect CE OUT to the CE input of each memory
device (Figure 10). The CE input of each part then
connects directly to the chip-select logic, which does
not have to be gated.
R1 + R2
R2
MAX691A
MAX693A
MAX800L
MAX800M
R2
GND
5V
V-
PFO
0V
VTRIP
5 - 1.25 = 1.25 - VTRIP
R1
R2
0V
V-
NOTE: VTRIP IS NEGATIVE
Figure 12. Monitoring a Negative Voltage
______________________________________________________________________________________
13
100
VCC = 5V
TA = +25°C
0.1µF CAPACITOR
FROM VOUT TO GND
80
MAX791-16
Backup-Battery Replacement
MAXIMUM TRANSIENT DURATION (µs)
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
60
40
20
0
10
100
1000
10000
RESET COMPARATOR OVERDRIVE,
(Reset Threshold Voltage - VCC) (mV)
Figure 13. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
parator. Select the ratio of R1 and R2 such that PFI sees
1.25V when VIN falls to the desired trip point (VTRIP).
Resistor R3 adds hysteresis. It will typically be an order
of magnitude greater than 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 to prevent it from
loading down the PFO pin. Capacitor C1 adds noise
rejection.
Monitoring a Negative Voltage
The power-fail comparator can be used to monitor a
negative supply voltage using Figure 12’s circuit. When
the negative supply is valid, PFO is low. When the negative supply voltage drops, PFO goes high. This circuit’s accuracy is affected by the PFI threshold
tolerance, the VCC voltage, and resistors R1 and R2.
14
The backup battery may be disconnected while VCC is
above the reset threshold. No precautions are necessary to avoid spurious reset pulses.
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 13 shows maximum transient duration vs. resetcomparator overdrive, for which reset pulses are not
generated. The graph was produced using negativegoing VCC pulses, starting at 5V and ending below the
reset threshold by the magnitude indicated (reset comparator overdrive). The graph shows the maximum
pulse width a negative-going VCC 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 VCC 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.
Connecting a Timing Capacitor at OSC IN
When OSC SEL is connected to ground, OSC IN disconnects from its internal 10µA (typ) pull-up and is
internally connected to a ±100nA current source.
When a capacitor is connected from OSC IN to ground
(to select alternative reset and watchdog timeout periods), the current source charges and discharges the
timing capacitor to create the oscillator that controls the
reset and watchdog timeout period. To prevent timing
errors or oscillator start-up problems, minimize external
current leakage sources at this pin, and locate the
capacitor as close to OSC IN as possible. The sum of
PC-board leakage plus OSC capacitor leakage must be
small compared to ±100nA.
______________________________________________________________________________________
Microprocessor Supervisory Circuits
MAX691A/MAX693A/MAX800L/MAX800M
Maximum VCC Fall Time
The VCC fall time is limited by the propagation delay of
the battery switchover comparator and should not
exceed 0.03V/µs. A standard rule of thumb for filter
capacitance on most regulators is on the order of 100µF
per amp of current. When the power supply is shut off or
the main battery is disconnected, the associated initial
VCC fall rate is just the inverse or 1A/100µF = 0.01V/µs.
The VCC fall rate decreases with time as VCC falls exponentially, which more than satisfies the maximum fall-time
requirement.
START
SET
WDI
LOW
Watchdog Software Considerations
A way to help the watchdog timer keep a closer watch
on software execution involves setting and resetting the
watchdog 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. Figure
14 shows an example flow diagram where the I/O driving the watchdog input is set high at the beginning of
the program, set low at the beginning of every subroutine or loop, then set high again when the program
returns to the beginning. If the program should “hang”
in any subroutine, the I/O is continually set low and the
watchdog timer is allowed to time out, causing a reset
or interrupt to be issued.
SUBROUTINE
OR PROGRAM LOOP
SET WDI
HIGH
RETURN
END
Figure 14. Watchdog Flow Diagram
______________________________________________________________________________________
15
_Ordering Information (continued)
PART
TEMP. RANGE
MAX693ACPE
0°C to +70°C
16 Plastic DIP
MAX693ACSE
MAX693ACWE
MAX693AC/D
0°C to +70°C
0°C to +70°C
0°C to +70°C
16 Narrow SO
16 Wide SO
Dice*
MAX693AEPE
MAX693AESE
MAX693AEWE
MAX693AEJE
MAX693AMJE
MAX800LCPE
-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
0°C to +70°C
16 Plastic SO
16 Narrow SO
16 Wide SO
16 CERDIP
16 CERDIP
16 Plastic DIP
MAX800LCSE
MAX800LEPE
MAX800LESE
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
16 Narrow SO
16 Plastic DIP
16 Narrow SO
MAX800MCPE
0°C to +70°C
16 Plastic DIP
MAX800MCSE
MAX800MEPE
MAX800MESE
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
16 Narrow SO
16 Plastic DIP
16 Narrow SO
___________________Chip Topography
VOUT
PIN-PACKAGE
* Dice are specified at TA = +25°C, DC parameters only.
VBATT
RESET
RESET
VCC
WDO
CE IN
GND
CE OUT
0.11"
(2.794mm)
BATT ON
LOW LINE
WDI
PFI PFO
OSC IN
OSC SEL
0.07"
(1.778mm)
TRANSISTOR COUNT: 729
SUBSTRATE CONNECTED TO VOUT
________________________________________________________Package Information
SOICN.EPS
MAX691A/MAX693A/MAX800L/MAX800M
Microprocessor Supervisory Circuits
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1996 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.