MAXIM MAX815_CPA

19-0412; Rev 1; 12/05
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
____________________________Features
The MAX814/MAX815/MAX816 are high-accuracy
microprocessor (µP) supervisory circuits that provide
power-on reset, watchdog, and power-fail functions.
They eliminate manual trimming and improve reliability
in critical applications needing high-accuracy reset
thresholds. The RESET output is guaranteed to be in
the correct state for VCC down to 1V. The reset comparator is designed to ignore fast transients on VCC.
Reset thresholds are available for operation with a variety of 3V and 5V supply voltages.
A 75µA maximum supply current makes the MAX814/
MAX815/MAX816 ideal for use in portable equipment. All
three devices are available in 8-pin DIP and SO packages. See the Selector Table for a review of features.
_____________________Selector Table
RESET Output
FEATURE
MAX814
✔
RESET Output
✔
Manual Reset
✔
✔
✔
Power-Fail Monitor
K, L, N, T
✔
K, L, N, T
✔
Adjustable
✔
Low-Line Detector
✔
VCC Reset Voltage
MAX815
✔
MAX816
✔
♦ ±1% Worst-Case Reset Threshold Accuracy
♦ 4.8V, 4.7V, 4.55V, 3.03V, or Adjustable Reset
Thresholds
♦ ±1% Low-Line Threshold Accuracy (MAX814)
60mV Above Reset Threshold
♦ 200ms Reset Time Delay
♦ Active-Low RESET Output
Active-High RESET Output (MAX814/MAX816)
♦ 75µA Max Supply Current
♦ Guaranteed RESET Valid to VCC = 1V
♦ Manual Reset Input
♦ ±2% Power-Fail Comparator
♦ Independent Watchdog with 1.56sec Timeout
(MAX815)
♦ Power-Supply Glitch Immunity
♦ 8-Pin SO and DIP Packages
✔
______________Ordering Information
PART*
MAX814_CPA
✔
Watchdog Circuit
________________________Applications
Medical Equipment
Controllers
Intelligent Instruments
Critical µP Power Monitoring
Portable/Battery-Powered Equipment
Set-Top Boxes
TEMP RANGE
0°C to +70°C
PIN-PACKAGE
8 PDIP
*The MAX814/MAX815 offer a choice of reset threshold voltages.
From the Reset Trip Threshold table, select the suffix corresponding to the desired threshold and insert it into the blank to
complete the part number.
Devices are available in both leaded and lead-free packaging.
Specify lead free by adding the + symbol at the end of the part
number when ordering.
Ordering Information continued at end of data sheet.
Reset Trip Thresholds table appears at end of data sheet.
__________________________________________________________Pin Configurations
TOP VIEW
MR 1
8
RESET
MR 1
7
RESET
VCC 2
GND 3
6
LOW LINE
PFI 4
5
PFO
VCC 2
MAX814
DIP/SO
8
WDO
MR 1
7
RESET
VCC 2
GND 3
6
WDI
PFI 4
5
PFO
MAX815
DIP/SO
8
RESET
7
RESET
GND 3
6
RESET IN
PFI 4
5
PFO
MAX816
DIP/SO
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX814/MAX815/MAX816
_______________General Description
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect GND)
VCC ....................................................................-0.3V to +6.0V
All Other Pins (Note 1)........................... -0.3V to (VCC + 0.3V)
Terminal Current (PFI, RESET IN, MR)................................10mA
Terminal Current (all other pins) .........................................20mA
Continuous Power Dissipation (TA = +25°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW
SO (derate 5.88mW/°C above +70°C) .........................471mW
Operating Temperature Ranges
Commercial.........................................................0°C to +70°C
Extended ...........................................................-40°C to +85C
Storage Temperature Range .............................-65°C to +125°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, +5V Parts (MAX814/MAX815K, L, N)
(VCC = 4.85V to 5.5V for MAX814K/MAX815K, VCC = 4.75V to 5.5V for MAX814L/MAX815L, VCC = 4.60V to 5.5V for MAX814N/
MAX815N, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
Operating Voltage Range
Supply Current
Reset Threshold
SYMBOL
VCC
ISUPPLY
VRT
CONDITIONS
MIN
RESET Output Voltage
5.5
MAX814_E, MAX815_E
1.2
5.5
MAX814_C, MAX815_C
75
MAX814_E, MAX815_E
85
MAX814K, MAX815K
4.75
4.85
MAX814L, MAX815L
4.65
4.75
MAX814N, MAX815N
4.50
4.60
0
tRS
VOH
VOL
VOH
140
MAX814
ISOURCE = 800µA
200
0.4
0.4
MAX814_C/MAX815_C, VCC = 1.0V, ISINK = 50µA
0.3
Watchdog Timeout Period
tWD
MAX815
WDI Pulse Width
tWP
MAX815
MAX814_E/MAX815_E, VCC = 1.2V, ISINK = 100µA
VWDI
MAX815, VCC = 5.0V
WDI Input Current
IWDI
WDI = VCC or WDI = 0V
MR to WDO High Delay
tWDO
MAX815 (Note 1)
LOW LINE to RESET Differential
Threshold
∆VLL
LOW LINE Threshold
VLLT
2
V
µA
V
ms
V
VCC -1.5
ISINK = 3.2mA
VOL
UNITS
mV
250
VCC -1.5
ISINK = 3.2mA
ISOURCE = 800µA
RESET, WDO, PFO, LOW LINE
Output Voltage
WDI Input Threshold
MAX
1.0
Reset Threshold Hysteresis
Reset Pulse Width
TYP
MAX814_C, MAX815_C
0.3
1.12
2.00
50
s
ns
Low
High
V
0.8
2.4
-1.0
1.0
1
µA
µs
MAX814_C, VCC falling
50
70
MAX814_E, VCC falling
48
73
MAX814K, VCC rising
4.93
MAX814L, VCC rising
4.83
MAX814N, VCC rising
4.68
_______________________________________________________________________________________
V
mV
V
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
MAX814/MAX815/MAX816
ELECTRICAL CHARACTERISTICS, +5V Parts (MAX814/MAX815K, L, N) (continued)
(VCC = 4.85V to 5.5V for MAX814K/MAX815K, VCC = 4.75V to 5.5V for MAX814L/MAX815L, VCC = 4.60V to 5.5V for MAX814N/
MAX815N, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
MR Pull-Up Current
IMR
MR Pulse Width
tMR
MR Input Threshold
CONDITIONS
MR = 0V
TYP
70
MAX
UNITS
240
µA
150
V MRLO
Low
V MRHI
High
MR to RESET Out Delay
tMD
(Note 3)
PFI Input Threshold
VPFI
VCC = 5.0V
PFI Input Current
IPFI
LOW LINE, PFO, WDO
Assertion Delay
MIN
ns
1.1
0.7 x VCC
250
V
ns
2.45
2.50
2.55
V
-15.00
+6.0
+35.00
nA
(Note 2)
200
µs
ELECTRICAL CHARACTERISTICS, +3V Parts (MAX814/MAX815T, MAX816)
(VCC = 3.06V to 5.5V for MAX814T/MAX815T and MAX816, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
Operating Voltage Range
SYMBOL
VCC
Supply Current
ISUPPLY
Reset Threshold
VRT
RESET IN Threshold
VRIT
RESET IN Input Current
IRT
CONDITIONS
MIN
5.5
-40°C to +85°C
1.2
5.5
0°C to +70°C
75
-40°C to +85°C
85
0°C to +70°C
3.00
3.06
-40°C to +85°C
3.00
3.08
MAX816C
1.683
1.700
1.717
MAX816E
1.678
1.700
1.722
-15
+6
+35
MAX816
0
tRS
VOH
RESET Output Voltage
VOL
VOH
VOL
VOH
VOL
RESET, WDO, PFO, LOW LINE
Output Voltage
VOH
VOL
VOL
Watchdog Timeout Period
MAX
1.0
Reset Threshold Hysteresis
Reset Pulse Width
TYP
0°C to +70°C
tWD
140
VRT(max) < VCC < 3.6V;
MAX814T, MAX816
ISOURCE = 500µA
4.5V < VCC < 5.5V;
MAX814T, MAX816
ISOURCE = 800µA
VRT(max) < VCC < 3.6V
4.5V < VCC < 5.5V
250
0.3
V
V
nA
ms
V
0.4
0.8 x VCC
ISINK = 1.2mA
0.3
VCC -1.5
ISINK = 3.2mA
0.4
TA = 0°C to +70°C, VCC = 1.0V, ISINK = 50µA
V
0.3
TA = -40°C to +85°C, VCC = 1.2V, ISINK = 100µA
MAX815T
µA
mV
VCC -1.5
ISINK = 3.2mA
ISOURCE = 800µA
V
0.8 x VCC
ISINK = 1.2mA
ISOURCE = 500µA
200
UNITS
0.3
1.12
2.00
s
_______________________________________________________________________________________
3
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
ELECTRICAL CHARACTERISTICS, +3V Parts (MAX814/MAX815T, MAX816) (continued)
(VCC = 3.06V to 5.5V for MAX814T/MAX815T and MAX816, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
WDI Pulse Width
SYMBOL
tWP
CONDITIONS
MAX815T
VRT(max) < VCC <
3.6V; MAX815T
WDI Input Threshold
VWDI
VCC = 5.0V; MAX815T
100
4.5V < VCC < 5.5V
50
High
High
WDI = VCC or 0V, MAX815T
MR to WDO High Delay
tWDO
MAX815T (Note 1)
LOW LINE to RESET Differential
Threshold
∆VLL
LOW LINE Threshold
VLLT
VCC rising
MR Pullup Current
IMR
MR = 0V
MR Pulse Width
tMR
VPFI
PFI Input Current
IPFI
+1.0
1
70
73
3.163
VRT(max) < VCC< 3.6V
70
240
4.5V < VCC < 5.5V
110
370
VRT(max) < VCC < 3.6V
500
4.5V < VCC < 5.5V
150
1.1
0.7 x VCC
750
4.5V < VCC < 5.5V
250
V
µA
V
ns
1.666
1.700
1.734
V
-15.00
+6.0
+35.00
nA
Note 1: Applies if WDO is externally connected to MR or if MR is externally driven.
Note 2: On power-up, delay from reset trip threshold crossing to valid outputs.
Note 3: Applies to both RESET and RESET.
4
mV
ns
VRT(max) < VCC < 3.6V
VCC = 3.3V, 5V
µA
µs
48
High
V
2.4
-1.0
50
Low
PFI Input Threshold
0.8
VCC falling, MAX814TE
V MRHI
UNITS
0.8
0.7 x VCC
VCC falling, MAX814TC
V MRLO
tMD
MAX
ns
Low
IWDI
MR to RESET Out Delay
(Note 3)
TYP
Low
WDI Input Current
MR Input Threshold
MIN
VRT(max) < VCC < 3.6V
_______________________________________________________________________________________
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
VCC = 3.3V
50
45
VCC = 2.5V
40
35
MAX814-02
60
VCC = 5.0V
55
50
45
VCC = 3.3V
40
195
VCC = 3.3V
190
185
VCC = 5.0V
180
30
0
20
40
60
80 100
175
-60
-40 -20
TEMPERATURE (°C)
20
40
60
80 100
-60
1.715
1.710
20
15
20
40
60
1.700
1.695
1.690
1.685
2.520
2.510
2.500
2.490
2.480
1.680
2.470
1.675
2.460
80 100
80 100
2.530
2.450
1.670
0
60
2.550
PFI THRESHOLD (V)
PFI THRESHOLD (V)
25
40
2.540
1.705
30
20
PFI THRESHOLD vs. TEMPERATURE
5V PARTS (MAX814/MAX815K, L, N)
MAX814-05
100mV OVERDRIVE
(VRT - VCC)
0
TEMPERATURE (°C)
PFI THRESHOLD vs. TEMPERATURE
3V PARTS (MAX814T/MAX815T, MAX816)
MAX814-04
40
-60 -40 -20
-40 -20
TEMPERATURE (°C)
RESET-COMPARATOR PROPAGATION
DELAY vs. TEMPERATURE
35
0
MAX814-06
-40 -20
-60
-40 -20
0
20
40
60
-60
80 100
-40 -20
0
20
40
60
80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
LOW-LINE TO RESET THRESHOLD
vs. TEMPERATURE (VCC RISING)
LOW-LINE TO RESET THRESHOLD
vs. TEMPERATURE (VCC FALLING)
LOW-LINE COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
64
62
60
58
56
54
52
60
MAX814-09
68
100mV OVERDRIVE
(VLLT - VCC)
50
66
PROPAGATION DELAY (µs)
66
70
LOW-LINE TO RESET THRESHOLD (mV)
MAX814-10
70
68
64
62
60
58
56
54
MAX814-11
-60
PROPAGATION DELAY (µs)
200
35
30
LOW-LINE TO RESET THRESHOLD (mV)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
RESET TIMEOUT PERIOD (ms)
VCC SUPPLY CURRENT (µA)
60
55
65
VCC SUPPLY CURRENT (µA)
VCC = 5.0V
65
70
MAX814-01
70
VCC SUPPLY CURRENT vs. TEMPERATURE
5V PARTS (MAX814/MAX815K, L, N)
MAX814-03
VCC SUPPLY CURRENT vs. TEMPERATURE
3V PARTS (MAX814T/MAX815T, MAX816)
40
30
20
10
52
50
0
50
-60
-40 -20
0
20
40
TEMPERATURE (°C)
60
80 100
-60
-40 -20
0
20
40
TEMPERATURE (°C)
60
80 100
-60
-40 -20
0
20
40
60
80 100
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX814/MAX815/MAX816
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
RESET THRESHOLD DEVIATION
vs. TEMPERATURE
5V PARTS (MAX814/MAX815K, L, N)
RESET THRESHOLD DEVIATION
vs. TEMPERATURE
3V PARTS (MAX814T/MAX815T, MAX816)
RESET THRESHOLD DEVIATION (mV)
1
0
-1
-2
MAX814-08
1
MAX814-07
RESET THRESHOLD DEVIATION (mV)
2
0
-1
-2
-3
-60
-40 -20
0
20
40
60
-60
80 100
-40 -20
40
20
60
80 100
MAXIMUM TRANSIENT DURATION
vs. RESET COMPARATOR OVERDRIVE
5V PARTS (MAX814/MAX815K, L, N)
RESET THRESHOLD DEVIATION
vs. TEMPERATURE
3V PARTS (MAX814T/MAX815T, MAX816)
1
0
-1
-2
-3
MAX814-13
140
MAXIMUM TRANSIENT DURATION (µs)
MAX814-07
2
120
100
RESET OCCURS
ABOVE CURVE
80
60
40
20
0
-60
-40 -20
0
20
40
TEMPERATURE (°C)
6
0
TEMPERATURE (°C)
TEMPERATURE (°C)
RESET THRESHOLD DEVIATION (mV)
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
60
80 100
10
100
1000
RESET COMPARATOR OVERDRIVE (mV), VRT - VCC
_______________________________________________________________________________________
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
PIN
MAX814
MAX815
MAX816
1
1
1
2
2
—
NAME
FUNCTION
MR
Manual-Reset Input. Triggers a reset when pulled below 1.10V. This activelow input has an internal 150µA pullup current to VCC, and can be driven
with CMOS logic or shorted to GND with a switch or transistor.
VCC
Positive Power-Supply Input. When VCC is below the reset threshold
voltage*, RESET is low, and remains low for a minimum of 140ms after
it rises above the threshold.
Positive Power-Supply Input. On the MAX816, RESET is controlled by
RESET IN, not VCC.
—
—
2
3
3
3
GND
4
4
4
PFI
Power-Fail Input. The PFI threshold voltage is 1.70V on the MAX816 and on
MAX814/MAX815 parts with the T suffix. It is 2.50V on MAX814/MAX815
parts with K, L, and N suffixes. Connect PFI to GND or VCC when not used.
5
5
5
PFO
Power-Fail Output. When PFI is below its threshold, PFO is low;
otherwise it is high.
—
6
—
WDI
Watchdog CMOS Input. If WDI remains high or low for more than 1.56s, the
watchdog timer times out, and WDO goes low. The timer is reset to
zero on each WDI transition.
6
—
—
Low-Line Output. Normally high, LOW LINE goes low when VCC falls 60mV
LOW LINE above the reset threshold. It returns high as soon as VCC rises above the
low-line threshold.
—
—
6
RESET IN
7
7
7
RESET
—
8
—
WDO
8
—
8
RESET
Ground
Reset Comparator Input. Reference is 1.70V. When RESET IN is below
1.70V, RESET is low, and remains low for a minimum of 140ms after it rises
above the reference.
Reset Output. Normally high, active low. Controlled by MR and reset
comparator.
Watchdog Output. Normally high, WDO goes low whenever the VCC reset
threshold comparator input voltage is low or when the watchdog timer
times out. There is no appreciable delay going either direction when the
VCC threshold comparator toggles.
Reset Output. Active high. The inverse of RESET.
*Reset Threshold Voltage is determined by part number suffix: K = 4.80V, L = 4.70V, N = 4.55V, T = 3.03V.
_______________Detailed Description
The MAX814/MAX815/MAX816 are high-accuracy, lowpower microprocessor (µP) supervisory circuits. They
have µP-reset, watchdog-timer, and power-fail functions. Typical applications illustrating their similarities
and differences are shown in Figures 1, 2, and 3.
Figures 4, 5, and 6 show the block diagrams of these
parts.
_______________________________________________________________________________________
7
MAX814/MAX815/MAX816
______________________________________________________________Pin Description
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
VCC
+3.3V
+5V
+12V SUPPLY
VCC
VCC
µP
MAX814
MAX814K/L/N
RESET
RESET
PFI
PFI
RESET
MR
RESET
NMI
LOW LINE
MANUAL
RESET
INPUT
INTERRUPT
PFO
MR
RESET
PFO
GND
GND
Figure 1a. Typical Application for Dual +3.3V and +5V Systems
Figure 1b. MAX814 Typical Application
VRT
VCC
VCC
+12V SUPPLY
+12V SUPPLY
VCC
VCC
µP
R1
µP
MAX816
MAX815
RESET
RESET
RESET IN
PFI
WDI
MANUAL
RESET
INPUT
WDO
MR
PFO
GND
PFI
I/O LINE
RESET
NMI
R2
INTERRUPT
PFO
MANUAL
RESET
INPUT
RESET
INTERRUPT
RESET
MR
GND
ON POWER-UP, RESET IS LOW UNTIL VCC > 2.8V.
Figure 2. MAX815 Typical Application
8
Figure 3. MAX816 Typical Application
_______________________________________________________________________________________
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
8
RESET
150µA
1
MR
RESET
GENERATOR
7
MAX814/MAX815/MAX816
MAX814
MAX815
6
WDI
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
8
WDO
RESET
TIMEBASE
2
VCC
1
MR
150µA
7
RESET
GENERATOR
RESET
60mV
2
VCC
6
LOW LINE
RESET THRESHOLD
4
PFI
RESET THRESHOLD
4
PFI
5
5
PFO
POWER- FAIL THRESHOLD
PFO
POWER-FAIL THRESHOLD
3 GND
3 GND
Figure 4. MAX814 Block Diagram
Figure 5. MAX815 Block Diagram
Reset Output
2 VCC
MAX816
150µA
1
RESET
GENERATOR
MR
8
RESET
7
RESET
6
RESET IN
1.70V
4
PFI
5
PFO
A µP’s reset input starts the µP in a known state.
Whenever the µP is in an unknown state, it should be
held in reset. The MAX814/MAX815/MAX816 assert reset
during power-up, power-down, or brownout conditions.
On power-up, once VCC reaches 1V, RESET is a guaranteed logic low of 0.4V or less. As VCC rises, RESET
stays low. As VCC rises above the reset threshold, an
internal timer releases RESET after 200ms. RESET also
pulses low whenever VCC dips below the reset threshold (i.e., brownout condition). If brownout occurs in the
middle of a previously initiated reset, the internal timer
is reset and the output remains low for at least another
140ms after the brownout ends. On power-down, once
VCC falls below the reset threshold, RESET stays low
and is guaranteed to be less than 0.3V until VCC drops
below 1V.
The MAX814 and MAX816 also offer active-high RESET
outputs. They are the inverse of the RESET outputs.
1.70V
3 GND
Figure 6. MAX816 Block Diagram
_______________________________________________________________________________________
9
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
Reset Threshold
The MAX814/MAX815 have fixed, factory-set reset
thresholds, signified by the first suffix letter in the part
number (see Figure 7 for more information on reset
ranges). The MAX816 has an adjustable reset threshold.
MAX814/MAX815 K-suffix parts have a minimum reset
threshold set to 4.75V, worst case. They are intended
for 5.0V systems with a ±4% or better power-supply tolerance design that must meet worst-case system parameters over time, temperature, line, and load variations.
Typically, the reset threshold (VRT) is greater than or
equal to the minimum IC operating voltage (VICMIN).
The “K” series 1%-tolerance reset threshold allows a
larger range of power-supply tolerance. System ICs
;;
;;
;;;
4.5
POWER-SUPPLY RANGE
(5.05V ±2%)
IC OPERATING RANGE
RESET LIMITS “K”
(4.8V ±1%)
4.75
5.0
5.25
5.5V
that have a tight operating supply range, like the
386/486 µPs, need a RESET initiated at a minimum
threshold of 4.75V, worst case.
L-suffix parts have a minimum reset threshold set to
4.65V, worst case. They are intended for 5.0V systems
with a ±5% power-supply tolerance. Typically, the reset
threshold is less than or equal to the minimum powersupply voltage, allowing system operation over the
complete power-supply range. A reset is initiated at
4.75V maximum. The 1% “L” version maximizes the
System IC Guard-Band Range.
N-suffix parts have a minimum reset threshold set to
4.50V, worst case. They are intended for 5.0V systems
with a ±10% IC system. Typically, the reset threshold
;;;
;;;;;
;
4.5
RESET LIMITS “L”
(4.7V ±1%)
;;;;;
;;;
;;
;;;;;
5.25
POWER-SUPPLY RANGE
(5V ±5%)
IC OPERATING RANGE
RESET LIMITS “N”
(4.55V ±1%)
4.60
VRT > VIC(MIN)
DESIGNED TO MEET WORSTCASE DESIGN PARAMETERS.
Figure 7c. N Suffix Design Range
10
5.5V
4.65
VRT < VPS(MIN)
DESIGNED TO ALLOW OPERATION
OVER THE FULL POWER-SUPPLY RANGE.
Figure 7a. K Suffix Design Range
5.0
5.25
IC OPERATING RANGE
VRT > VIC(MIN)
DESIGNED TO MEET WORSTCASE DESIGN PARAMETERS.
4.75
5.0
POWER-SUPPLY RANGE
(5V ±5%)
4.85
4.5
4.75
Figure 7b. L Suffix Design Range
5.5V
;;
;;
;;;
3.0
POWER-SUPPLY RANGE
(3.33V ±0.26%)
IC OPERATING RANGE
RESET LIMITS “T”
(3.03V ±1%)
3.3
3.6V
3.06
VRT > VIC(MIN)
DESIGNED TO MEET WORSTCASE DESIGN PARAMETERS.
Figure 7d. T Suffix Design Range
______________________________________________________________________________________
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
VRT =
(
)
VRIT × R1 + R2
R2
where VRT = the desired reset threshold, VRIT is the
RESET IN threshold (1.700V), R1 is the resistor connected between V RT and RESET IN, and R2 is the
resistor connected between RESET IN and GND.
Resistors R1 and R2 can have very high values. The
usual procedure is to set R2 to some conveniently high
value (100kΩ, for example) and calculate R1 based on
the desired reset threshold, using the following formula:
[(
)
]
R1 = R2 × VRT / VRIT − 1
The MAX816 can achieve ±1.2% accuracy with 0.1%
resistors.
Watchdog Timer (MAX815)
The watchdog circuit monitors the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within the
watchdog timeout period (tWP), WDO goes low (Figure
8). WDO also goes low during reset conditions.
Whenever VCC is below the reset threshold, WDO stays
low; however, unlike RESET, WDO does not have a minimum pulse width. As soon as VCC rises above the reset
threshold, WDO goes high with no delay (Figure 9).
Typically, WDO is connected to the non-maskable interrupt (NMI) of a µP. When VCC drops below the reset
threshold, WDO goes low whether or not the watchdog
timer has timed out (Figure 9). This would normally trigger an NMI interrupt, but RESET goes low simultaneously and thus overrides the NMI interrupt.
Connecting WDO to MR enables the watchdog timeout
to generate a reset in the MAX815.
Early Power-Fail Warning
Critical systems often require early warning to indicate
when power is failing. This warning provides time for
the µP to store vital data and take care of any additional
“housekeeping” before the power supply gets too far
out of tolerance for the µP to operate reliably.
Power-Fail Comparator
The power-fail comparator is intended as an undervoltage detector to signal a failing power supply. However,
the comparator does not need to be dedicated to this
function, because it is completely separate from the
rest of the circuitry. To build an early-warning circuit for
power failure, connect the PFI pin to a voltage divider
(see Figures 1, 2, and 3). Choose the voltage divider
ratio, so the voltage at PFI falls below VPFI just before
the monitored voltage drops out. Use PFO to interrupt
the µP, so it can prepare for an orderly power-down.
The power-fail input (PFI) is compared to an internal
reference. If the voltage on PFI is less than the powerfail reference, PFO sinks at least 1.2mA to GND; otherwise it sources at least 300µA from VCC. The reference
is 2.50V in the MAX814/MAX815 with K, L, N suffixes, or
1.70V with the T suffix. It is also 1.70V in the MAX816.
LOW LINE Output (MAX814)
The low-line detector is a separate comparator that
monitors VCC with a typical threshold voltage of 60mV
above the normal reset threshold, with 2mV of hysteresis (Figure 9). If VCC rises faster than 10µs/V, insert a
100pF capacitor from LOW LINE to GND to ensure
proper start-up. For normal operation (VCC above the
reset threshold), LOW LINE is pulled to VCC. Use LOW
LINE to provide an NMI to the µP when power begins to
fall. In most battery-operated portable systems, reserve
energy in the battery provides ample time to complete
the shutdown routine once the low-line warning is
encountered, and before reset asserts. If the system
must also contend with a more rapid VCC fall time—
such as when the main battery is disconnected or a
high-side switch is opened during operation—use
capacitance on the VCC line to provide time to execute
the shutdown routine. First, calculate the worst-case
time required for the system to perform its shutdown
routine. Then use the worst-case shutdown time
(tSHDN), worst-case load current (ILOAD), and minimum
low-line to reset threshold (VLR) to calculate the amount
of capacitance required to allow the shutdown routine
to complete before reset is asserted.
I
×t
CHOLD = LOAD SHDN
VLR
______________________________________________________________________________________
11
MAX814/MAX815/MAX816
(VRT) is greater than or equal to the minimum IC operating voltages (VICMIN). The 1% “L” series allows the use
of a 5V ±5% power supply, and guarantees system
operation over worst-case conditions, maximizing the
Power-Supply Guard-Band Range.
T-suffix parts have a minimum reset threshold set to
3.00V, worst case. They are intended for 3.3V systems
(3.33V ±0.26V) with a 7.8% or better power-supply tolerance. Typically, the reset threshold (VRT) is greater
than or equal to the minimum IC operating voltages
(VICMIN).
The MAX816 has an adjustable reset threshold, set with
an external resistive divider (Figure 3). The voltage on
the RESET IN pin is monitored, not the voltage on VCC.
The RESET IN threshold is 1.700V, and has very high
impedance and 35nA maximum leakage. Calculate the
trip point, VRT, as follows:
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
tWP
tWD
tWD
tWDO
tWD
VCC
∆VLL 60mV
VRT
VLLT
VRT
VCC
WDI
0V
tRS
tRS
MR
RESET
VCC
WDO
0V
RESET
RESET
VCC
VCC
0V
MR
VCC
0
tMD
0V
tMR
VCC
WDO
(MAX815)
0
Figure 8. MAX815 Watchdog Timing
VCC
LOW LINE
(MAX814)
0
where CHOLD is the capacitance (in Farads), ILOAD is
the current being drained from the capacitor (in
Amperes), and VLR is the low-line to reset threshold difference (in Volts).
Figure 9. Timing Diagram
__________Applications Information
Manual Reset
Low-Voltage Operation
Many µP-based products require manual-reset capability, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. A logic low on MR
asserts reset. Reset remains asserted while MR is low,
and for tRS (200ms) after MR returns high. This input
has an internal pullup resistor, so it can be left open if
not used. MR can be driven with TTL/CMOS-logic levels or with open-drain/collector outputs.
Connect a normally open momentary switch from MR to
GND to create a manual-reset function; external
debounce circuitry is not required.
The watchdog circuit can be used to force a reset in
the MAX815 by connecting WDO to MR. If MR is driven
from long cables, or the device is used in a noisy environment, connect a 0.1µF capacitor to ground to provide additional noise immunity.
The LOW LINE, PFO, and WDO outputs will be locked to
logic low when the power supply drops below the lockout threshold (typically 1V below the reset threshold).
12
Ensuring a Valid
RESET Output Down to VCC = 0V
When VCC falls below 1V, the RESET output no longer
sinks current, but becomes an open circuit. Highimpedance CMOS-logic inputs can drift to undetermined voltages if left undriven. If a pulldown resistor is
added to the RESET pin as shown in Figure 10, any
stray charge or leakage currents will be drained to
ground, holding RESET low. Resistor value R1 is not
critical. It should be about 100kΩ—large enough not to
load RESET, and small enough to pull RESET to
ground.
______________________________________________________________________________________
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
+5V
VCC
340kΩ
1%
MAX814
MAX815
MAX816
MAX814K/L/N MR
MAX815K/L/N
100kΩ
1%
RESET
TO µP
RESET
PFI
PFO
GND
R1
PARAMETER
MIN
TYP
MAX
+12V Reset
10.57 11.00 11.45
Threshold at +25°C
UNIT
V
Figure 10. RESET Valid to Ground Circuit
Figure 11. Monitoring Both +5V and +12V
Monitoring Voltages Other than VCC
Monitor voltages other than the VCC by connecting a
voltage divider to PFI and adjusting the ratio appropriately. If required, add hysteresis by connecting a resistor (with a value approximately 10-times the sum of the
two resistors in the potential divider network) between
PFI and PFO. A capacitor between PFI and GND will
reduce the power-fail circuit’s sensitivity to high-frequency noise on the line being monitored. RESET can
be asserted on other voltages in addition to the +5V
VCC line. Connect PFO to MR to initiate a reset when
PFI drops below 2.50V (K, L, N suffix) or 1.70V (T suffix
or MAX816). Figure 11 shows the MAX814K/L/N/
MAX815K/L/N configured to assert RESET when the
+5V supply falls below the reset threshold, or when the
+12V supply falls below approximately 11V.
A way to help the watchdog timer keep closer tabs 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 13
shows an example flow diagram where the I/O driving
the watchdog input is set low at the beginning of the
program, set high at the beginning of every subroutine,
then set low at the end of every subroutine. If the program should hang in any subroutine, the I/O is continually set high and the watchdog timer is allowed to time
out, causing a reset to be issued.
Watchdog Software Considerations
Monitoring a Negative Voltage
The power-fail comparator can also monitor a negative
supply rail (Figure 12). 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 is high. By adding the resistors and transistor as shown, a high PFO triggers reset.
As long as PFO remains high, the MAX814/MAX815/
MAX816 will keep reset asserted (RESET = low, RESET
= high). Note that this circuit’s accuracy depends on the
PFI threshold tolerance, the VCC line, and the resistor.
______________________________________________________________________________________
13
MAX814/MAX815/MAX816
+12V
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
+5V
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
VCC
100kΩ
MR
R1
MAX814
MAX815 PFO
PFI
MAX816
R2
VCC
100kΩ
2N3904
TO µP
RESET
GND
VCC
MAX814
MAX815
MAX816
µP
4.7kΩ
RESET
RESET
GND
V-
GND
+5V
MR
0V
+5V
PFO
Figure 14. Interfacing to µPs with Bidirectional Reset I/O
0V
V-
VTRIP
0V
5 - 2.5
2.5 - VTRIP ,
VTRIP < 0V
=
R1
R2
VPFT = 2.5V (K, L, N); 1.70V (T AND MAX816)
Figure 12. Monitoring a Negative Voltage
BEGIN PROGRAM
SET LOW
WDI
SET HIGH
WDI
Negative-Going VCC Transients
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, the MAX814/
MAX815/MAX816 series is relatively immune to short
duration negative-going VCC transients (glitches). The
Typical Operating Characteristics show a graph of
Maximum Transient Duration vs. Reset Comparator
Overdrive, for which a reset is not generated. The
graph was made using a negative-going pulse applied
to VCC, starting 1.5V above the actual reset threshold
and ending below it by the magnitude indicated (reset
comparator overdrive). The graph indicates the typical
maximum pulse width a negative-going VCC transient
may have without causing a reset pulse. As the magnitude of the transient increases (goes further below the
reset threshold), the maximum allowable pulse width
decreases. Typically, a VCC that goes 100mV below the
reset threshold and lasts 30µs or less will not cause a
reset pulse to be issued.
A 0.1µF bypass capacitor mounted as close as possible
to pin 2 (VCC) provides additional transient immunity.
SUBROUTINE
Interfacing to µPs
with Bidirectional Reset Pins
SET LOW
WDI
YES
RETURN
NO
µPs with bidirectional reset pins, such as the Motorola
68HC11 series, can cause a conflict with the RESET
output. If, for example, the RESET output is driven high
and the µP wants to pull it low, indeterminate logic levels may result. To correct this, connect a 4.7kΩ resistor
between the RESET output and the µP reset I/O, as in
Figure 14. Buffer the RESET output to other system
components.
Figure 13. Flow Chart of WDI Implementation
14
______________________________________________________________________________________
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
PART*
TEMP. RANGE
PIN-PACKAGE
MAX814_CPA
0°C to +70°C
8 Plastic DIP
MAX814_CSA
0°C to +70°C
8 SO
MAX814_EPA
-40°C to +85°C
8 Plastic DIP
MAX814_ESA
-40°C to +85°C
8 SO
MAX815_CPA
0°C to +70°C
8 Plastic DIP
MAX815_CSA
0°C to +70°C
8 SO
MAX815_EPA
-40°C to +85°C
8 Plastic DIP
MAX815_ESA
-40°C to +85°C
8 SO
MAX816CPA
0°C to +70°C
8 Plastic DIP
MAX816CSA
0°C to +70°C
8 SO
MAX816EPA
-40°C to +85°C
8 Plastic DIP
MAX816ESA
-40°C to +85°C
8 SO
___________________Chip Information
TRANSISTOR COUNT: 744
Revision History
Pages changed at Rev 1: 1–4, 12-16.
*The MAX814/MAX815 offer a choice of reset threshold voltage.
From the Reset Trip Threshold table, select the suffix corresponding to the desired threshold and insert it into the blank to
complete the part number.
Devices are available in both leaded and lead-free packaging.
Specify lead free by adding the + symbol at the end of the part
number when ordering.
_____________Reset Trip Thresholds
MAX814/MAX815
SUFFIX
RESET TRIP THRESHOLD
MIN (V)
MAX (V)
K
4.75
4.85
L
4.65
4.75
N
4.50
4.60
T
3.00
3.06
—
—
MAX816
Adjustable
______________________________________________________________________________________
15
MAX814/MAX815/MAX816
______________Ordering Information
MAX814/MAX815/MAX816
±1% Accuracy, Low-Power, +3V and +5V
µP Supervisory Circuits
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
D
E
DIM
E1
A
A1
A2
A3
B
B1
C
D1
E
E1
e
eA
eB
L
A3
A A2
L A1
0° - 15°
C
e
B1
eA
B
eB
D1
Plastic DIP
PLASTIC
DUAL-IN-LINE
PACKAGE
(0.300 in.)
INCHES
MAX
MIN
0.200
–
–
0.015
0.175
0.125
0.080
0.055
0.022
0.016
0.065
0.045
0.012
0.008
0.080
0.005
0.325
0.300
0.310
0.240
–
0.100
–
0.300
0.400
–
0.150
0.115
PKG. DIM PINS
P
P
P
P
P
N
D
D
D
D
D
D
8
14
16
18
20
24
INCHES
MIN
MAX
0.348 0.390
0.735 0.765
0.745 0.765
0.885 0.915
1.015 1.045
1.14 1.265
MILLIMETERS
MIN
MAX
–
5.08
0.38
–
3.18
4.45
1.40
2.03
0.41
0.56
1.14
1.65
0.20
0.30
0.13
2.03
7.62
8.26
6.10
7.87
2.54
–
7.62
–
–
10.16
2.92
3.81
MILLIMETERS
MIN
MAX
8.84
9.91
18.67 19.43
18.92 19.43
22.48 23.24
25.78 26.54
28.96 32.13
21-0043A
DIM
D
0°-8°
A
0.101mm
0.004in.
e
B
A1
E
C
H
L
Narrow SO
SMALL-OUTLINE
PACKAGE
(0.150 in.)
A
A1
B
C
E
e
H
L
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.157
0.150
0.050
0.244
0.228
0.050
0.016
DIM PINS
D
D
D
8
14
16
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
3.80
4.00
1.27
5.80
6.20
0.40
1.27
INCHES
MILLIMETERS
MIN MAX
MIN
MAX
0.189 0.197 4.80
5.00
0.337 0.344 8.55
8.75
0.386 0.394 9.80 10.00
21-0041A
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
© 2005 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.