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19-1122; Rev 1; 12/99
4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay
General Description
The MAX821/MAX822 microprocessor (P) supervisory circuits monitor power supplies in P and digital systems. They provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 5V-powered or 3V-powered circuits. The MAX821/MAX822 also provide a power-on reset timeout delay that is pin selectable to 1ms (max), 20ms (min), or 100ms (min). These devices perform a single function: they assert a reset signal whenever the V CC supply voltage falls below a preset threshold, and they keep reset asserted for the pin-selected reset timeout delay after VCC has risen above the reset threshold. The only difference between the two devices is that the MAX821 has an active-low RESET output (which is guaranteed to be in the correct state for V CC down to 1V), while the MAX822 has an active-high RESET output. The reset comparator is designed to ignore fast transients on VCC. Reset thresholds suitable for operation with a variety of supply voltages are available. Low supply current makes the MAX821/MAX822 ideal for use in portable equipment. These devices come in a 4-pin SOT143 package.
Features
o Pin-Selectable, Precision Power-On Reset Delay: 1ms (max), 20ms (min), or 100ms (min) o Precision Monitoring of +3V to +5V Power-Supply Voltages o 2.5A Supply Current o Guaranteed Over Temperature (-40C to +125C) o Guaranteed RESET Valid to VCC = 1V (MAX821) o Power-Supply Transient Immunity o No External Components o SOT143 Package
MAX821/MAX822
Ordering Information
PART MAX821LUS-T NOMINAL VTH (V) TOP MARK* 4.63 AZ_ _ MAX821MUS-T 4.38 BA_ _ MAX821PUS-T 4.00 BM_ _ MAX821TUS-T 3.08 BB_ _ MAX821SUS-T 2.93 BC_ _ MAX821UUS-T 2.78 BL_ _ MAX821RUS-T 2.63 BD_ _ MAX822LUS-T 4.63 BF_ _ MAX822MUS-T 4.38 BG_ _ MAX822TUS-T 3.08 BH_ _ MAX822SUS-T 2.93 BJ_ _ MAX822RUS-T 2.63 BK_ _ * The first two letters in the package top mark identify the part, while the remaining two letters are the lot-tracking code. Note: These parts are offered in the SOT143-4 package, in the extended temperature range (-40C to +85C).
________________________Applications
Bar-Code Scanners Computers Controllers Intelligent Instruments Critical P and C Power Monitoring Portable/Battery-Powered Equipment
__________Typical Operating Circuit
Pin Configuration
VCC VCC
TOP VIEW P
RESET INPUT (RESET) RESET 2 GND 1 4 VCC
MAX821 MAX822
20ms 100ms 1ms RESET (RESET) GND
MAX821 MAX822
SRT
3
SRT
GND
SOT143
( ) ARE FOR MAX822 ( ) ARE FOR MAX822
________________________________________________________________ Maxim Integrated Products
1
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4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay MAX821/MAX822
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND) VCC ......................................................................-0.3V to 6.0V All Other Inputs.......................................-0.3V to (VCC + 0.3V) Input Current, VCC, SRT......................................................20mA Output Current, RESET or RESET .......................................20mA Continuous Power Dissipation (TA = +70C) SOT143-4 (derate 4mW/C above +70C)...................320mW Operating Temperature Range .........................-40C to +125C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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 = full range, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER VCC Range SYMBOL CONDITIONS TA = 0C to +70C TA = -40C to +85C MAX82_L/M/P, VCC = 5.5V, IOUT = 0 MAX82_R/S/T/U, VCC = 5.5V, IOUT = 0 MAX82_L MAX82_M MAX82_P Reset Threshold (Note 1) VTH MAX82_T MAX82_S MAX82_U MAX82_R Reset Threshold Tempco VCC to Reset Delay (Note 1) Reset Active Timeout Period tRP VCC falling at 1mV/s SRT = GND SRT = VCC SRT = unconnected SRT Input Current (Note 2) VIL SRT Input Threshold VIH VOPEN 2 SRT = GND RESET = low for MAX821, SRT = VCC RESET = high for MAX822 SRT = unconnected RESET = low for MAX821, RESET = high for MAX822 0.5 20 100 -100 100 -1 0.9VCC 0.5VCC 1 0.07VCC V A TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C TA = +25C TA = -40C to +125C 4.56 4.50 4.31 4.25 3.97 3.91 3.04 3.00 2.89 2.85 2.74 2.70 2.59 2.55 30 50 0.8 32 160 1 40 200 ms 2.63 2.78 2.93 3.08 4.00 4.38 4.63 1.8 MIN 1.0 1.2 2.5 TYP MAX 5.5 5.5 7.0 12 5.5 9 4.70 4.75 4.45 4.50 4.04 4.09 3.11 3.15 2.96 3.00 2.81 2.85 2.66 2.70 ppm/C s V A UNITS V
Supply Current
ICC
_______________________________________________________________________________________
4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay
ELECTRICAL CHARACTERISTICS (continued)
(VCC = full range, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SRT Input Capacitance (Note 3) (see Setting the Reset Timeout Delay section) SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX821/MAX822
Internal
20
pF
MAX821L/M/P only, ISINK = 3.2mA, VCC = VTH(MIN) MAX821R/S/T/U only, ISINK = 1.2mA, VCC = VTH(MIN) TA = 0C to +70C, VCC 1V TA = -40C to +85C, VCC 1.2V VCC -1.5 0.8VCC
0.4 0.3 0.3 V 0.3
VOL RESET Output Voltage (MAX821)
ISINK = 50A
VOH
MAX821L/M/P only, ISOURCE = 800A, VCC VTH(MAX) MAX821R/S/T/U only, ISOURCE = 500A, VCC VTH(MAX) MAX822L/M only, ISINK = 3.2mA, VCC = VTH(MAX) MAX822R/S/T only, ISINK = 1.2mA, VCC = VTH(MAX) ISOURCE = 150A, 1.4V VCC VTH(MIN)
0.4 0.3 0.8VCC V
RESET Output Voltage (MAX822)
VOL
VOH
Note 1: RESET output for MAX821; RESET output for MAX822. Note 2: During reset active timeout period only. Note 3: Guaranteed by design.
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX 821/822 TOC-04
RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX 821/822 TOC-05
RESET TIMEOUT PERIOD vs. TEMPERATURE
SRT = UNCONNECTED RESET TIMEOUT PERIOD (ms) 175 170 165 160 155 150
MAX 821/822 TOC-06
1.0 SRT = GND RESET TIMEOUT PERIOD (ms) 0.9
36 SRT = VCC RESET TIMEOUT PERIOD (ms) 35 34 33 32 31 30
180
0.8
0.7
0.6 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
_______________________________________________________________________________________
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4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay MAX821/MAX822
____________________________Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX82_R/S/T POWER-DOWN RESET DELAY vs. TEMPERATURE
MAX 821/822 TOC-02
MAX82_L/M POWER-DOWN RESET DELAY vs. TEMPERATURE
POWER-DOWN RESET DELAY (s) VCC FALLING AT 1mV/s 50 40 30 20 10 0
MAX 821/822 TOC-03
45 POWER-DOWN RESET DELAY (s) 40 35 30 25 20 15 10 5 0 -40 -20 0 20 40 60 80 VCC FALLING AT 10mV/s VCC FALLING AT 1mV/s
60
VCC FALLING AT 10mV/s
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
NORMALIZED SUPPLY CURRENT vs. TEMPERATURE
MAX 821/822 TOC-01
NORMALIZED RESET THRESHOLD vs. TEMPERATURE
NORMALIZED RESET THRESHOLD (V)
MAX 821/822 TOC-07
1.10 NORMALIZED SUPPLY CURRENT (A)
1.003 1.002 1.001 1.000 0.999 0.998 0.997
1.05
1.00
0.95
0.90 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
______________________________________________________________Pin Description
PIN MAX821 MAX822 1 NAME GND RESET Ground Active-Low Reset Output. RESET is low while VCC is below the reset threshold. It remains low for the reset timeout period after the reset condition is terminated. The reset timeout period is determined by the SRT input. Active-High Reset Output. RESET is high while VCC is below the reset threshold. It remains high for the reset timeout period after the reset condition is terminated. The reset timeout period is determined by the SRT input. Set Reset Timeout Input. Connect to GND for 1ms (max) delay; connect to VCC for 20ms (min) delay; leave unconnected for 100ms (min) delay. Supply Voltage FUNCTION
1
2
-
-
3 4 4
2
RESET
3 4
SRT VCC
_______________________________________________________________________________________
4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay
_______________Detailed Description
MAXIMUM TRANSIENT DURATION (s)
MAX821/MAX822
A microprocessor's (P's) reset input starts the P in a known state. These P supervisory circuits assert reset to prevent code-execution errors during power-up, power-down, or brownout conditions. They also provide a reset timeout delay that is pin programmable to 1ms (max), 20ms (min), or 100ms (min). This feature allows flexibility in designing bar-code scanners, hand-held devices, and other applications that require quick or nonstandard power-up times. The MAX821's RESET output is guaranteed to be a logic low for VCC > 1V. Once VCC exceeds the reset threshold, an internal timer keeps RESET low for the reset timeout period, as determined by the Set Reset Timeout (SRT) input. See the Setting the Reset Timeout Delay section. If a brownout condition occurs (VCC dips below the reset threshold), RESET goes low. Any time VCC goes below the reset threshold, the internal timer resets to zero, and RESET goes low. The internal timer begins counting after VCC returns above the reset threshold, and RESET remains low for the reset timeout period. The MAX822 has an active-high RESET output that is the inverse of the MAX821's RESET output.
TA = +25C 250 200 150 100 50 0 1 10 100
1000
RESET COMPARATOR OVERDRIVE, VTH-VCC (mV)
Figure 1. Maximum Transient Duration Without Causing a Reset Pulse vs. Comparator Overdrive
__________Applications Information
Negative-Going VCC Transients While designed to issue a reset to the microprocessor (P) during power-up, power-down, and brownout conditions, the MAX821/MAX822 are relatively immune to short-duration, negative-going VCC transients (glitches). Figure 1 shows the maximum transient duration vs. reset comparator overdrive for which the MAX821/MAX822 typically do not generate a reset pulse. This graph was generated using a negative-going pulse applied to VCC, starting 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 to be issued. As the magnitude of the transient increases (goes farther below the reset threshold), the maximum allowable pulse width decreases. Typically, for the MAX821/MAX822, a VCC transient that goes 100mV below the reset threshold and lasts 12s or less will not cause a reset pulse to be issued. A 0.1F capacitor mounted as close as possible to VCC can provide additional transient immunity, if desired.
Setting the Reset Timeout Delay
Use the three-level Set Reset Timeout (SRT) input to set the reset timeout delay. Connect SRT to GND for a 1ms (max) delay; connect it to VCC for a 20ms (min) delay; or leave it unconnected for a 100ms (min) delay. If you choose to drive the SRT pin with an external signal, make sure the signal source can charge/discharge the capacitance on SRT quickly enough (<500s) to avert an unintended reset timeout delay. To ensure proper operation when selecting the 100ms timeout (SRT = unconnected), minimize capacitive loading on the SRT pin (< 200pF). Excessive capacitive loading can select an unintended faster timeout mode.
Reset Threshold Accuracy
The MAX821/MAX822 are designed to meet their worstcase specifications over their entire operating temperature range. Choose a reset threshold guaranteed to assert at a voltage below the power supply's regulation range and above the minimum specified operating voltage range for the system's ICs.
_______________________________________________________________________________________
MAX821/822 FIG-01
Reset Output
300
5
4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay MAX821/MAX822
When VCC falls below 1V, the MAX821 RESET output no longer sinks current--it becomes an open circuit. Therefore, high-impedance CMOS logic inputs connected to the RESET output can drift to undetermined voltages. This presents no problem in most applications, since most P and other circuitry is inoperative with VCC below 1V. However, in applications where the RESET output must be valid down to 0V, adding a pulldown resistor to the RESET pin will cause any stray leakage currents to flow to ground, holding RESET low (Figure 2a). R1's value is not critical; 100k is large enough not to load RESET, and small enough to pull RESET to ground. A 100k pull-up resistor to VCC is also recommended for the MAX822 if RESET is required to remain valid for VCC < 1V (Figure 2b).
Ensuring a Valid RESET Output Down to VCC = 0V
VCC
VCC
VCC
VCC R1
MAX821
RESET R1 GND
MAX822
RESET
GND
a)
b)
Figure 2. RESET/RESET Valid to VCC = Ground Circuit
Interfacing to Ps with Bidirectional Reset Pins
Ps with bidirectional reset pins (such as the Motorola 68HC11 series) can contend with the MAX821 reset output. For example, if the MAX821 RESET output is asserted high and the P wants to pull it low, indeterminate logic levels may result. To correct such cases, connect a 4.7k resistor between the MAX821 RESET output and the P reset I/O (Figure 3). Buffer the reset output to other system components.
VCC
BUFFER
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
VCC P RESET
MAX821
RESET
4.7k
___________________Chip Information
TRANSISTOR COUNT: 492
GND
GND
Figure 3. Interfacing to Ps with Bidirectional Reset I/O
6
_______________________________________________________________________________________
4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay MAX821/MAX822
________________________________________________________Package Information
SOT1434.EPS
_______________________________________________________________________________________
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4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay MAX821/MAX822
NOTES
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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