 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| 19-0412; Rev 0; 6/95 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits _______________General Description The MAX814/MAX815/MAX816 are high-accuracy microprocessor (P) 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 75A 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 below for a review of features. ____________________________Features o 1% Worst-Case Reset Threshold Accuracy o 4.8V, 4.7V, 4.55V, 3.03V, or Adjustable Reset Thresholds o 1% Low-Line Threshold Accuracy (MAX814) 60mV Above Reset Threshold o 200ms Reset Time Delay o Active-Low RESET Output Active-High RESET Output (MAX814/MAX816) o 75A Max Supply Current o Guaranteed RESET Valid to VCC = 1V o Manual Reset Input o 2% Power-Fail Comparator o Independent Watchdog with 1.56sec Timeout (MAX815) o Power-Supply Glitch Immunity o 8-Pin SO and DIP Packages MAX814/MAX815/MAX816 _____________________Selector Table FEATURE RESET Output RESET Output Manual Reset VCC Reset Voltage Power-Fail Monitor Low-Line Detector Watchdog Circuit K, L, N, T K, L, N, T Adjustable MAX814 MAX815 MAX816 _____________Reset Trip Thresholds SUFFIX K L N T MAX814/MAX815 RESET TRIP THRESHOLD MIN (V) MAX (V) 4.75 4.65 4.50 3.00 MAX816 -- Adjustable Ordering Information appears at end of data sheet. 4.85 4.75 4.60 3.06 ________________________Applications Medical Equipment Controllers Intelligent Instruments Critical P Power Monitoring Portable/Battery-Powered Equipment Set-Top Boxes __________________________________________________________Pin Configurations TOP VIEW MR 1 VCC 2 GND 3 PFI 4 8 RESET RESET LOW LINE PFO MR 1 VCC 2 GND 3 PFI 4 8 WDO RESET WDI PFO MR 1 VCC 2 GND 3 PFI 4 8 RESET RESET RESET IN PFO MAX814 7 6 5 MAX815 7 6 5 MAX816 7 6 5 DIP/SO DIP/SO DIP/SO ________________________________________________________________ Maxim Integrated Products 1 Call toll free 1-800-998-8800 for free samples or literature. 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 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 = +25C) Plastic DIP (derate 9.09mW/C above +70C) ............727mW SO (derate 5.88mW/C above +70C) .........................471mW Operating Temperature Ranges Commercial.........................................................0C to +70C Extended ...........................................................-40C to +85C Storage Temperature Range .............................-65C to +125C 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 SYMBOL VCC ISUPPLY CONDITIONS MAX814_C, MAX815_C MAX814_E, MAX815_E MAX814_C, MAX815_C MAX814_E, MAX815_E MAX814K, MAX815K Reset Threshold Reset Threshold Hysteresis Reset Pulse Width RESET Output Voltage VRT VRT tRS VOH VOL VOH RESET, WDO, PFO, LOW LINE Output Voltage Watchdog Timeout Period WDI Pulse Width WDI Input Threshold WDI Input Current MR to WDO High Delay LOW LINE to RESET Differential Threshold LOW LINE Threshold VOL tWD tWP VWDI IWDI tWDO VLL MAX814 ISOURCE = 800A ISINK = 3.2mA MAX814_C/MAX815_C, VCC = 1.0V, ISINK = 50A MAX814_E/MAX815_E, VCC = 1.2V, ISINK = 100A MAX815 MAX815 MAX815, VCC = 5.0V WDI = VCC or WDI = 0V MAX815 (Note 1) MAX814_C, VCC falling MAX814_E, VCC falling MAX814K, VCC rising VLLT MAX814L, VCC rising MAX814N, VCC rising 50 48 Low High 2.4 -1.0 1 70 73 4.93 4.83 4.68 V 1.0 1.12 50 0.8 ISOURCE = 800A ISINK = 3.2mA VCC -1.5 0.4 0.3 0.3 2.00 sec ns V A s mV V 140 VCC -1.5 0.4 MAX814L, MAX815L MAX814N, MAX815N 4.75 4.65 4.50 0 200 250 MIN 1.0 1.2 TYP MAX 5.5 5.5 75 85 4.85 4.75 4.60 mV ms V V UNITS V A 2 _______________________________________________________________________________________ 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits 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 MR Pull-Up Current MR Pulse Width MR Input Threshold MR to RESET Out Delay PFI Input Threshold PFI Input Current LOW LINE, PFO, WDO Assertion Delay SYMBOL IMR tMR V MRLO V MRHI tMD VPFI IPFI (Note 2) Low High (Note 3) VCC = 5.0V 2.45 -15.00 2.50 6.0 200 0.7 x VCC 250 2.55 35.00 MR = 0V CONDITIONS MIN 70 150 1.1 TYP MAX 240 UNITS A ns V ns V nA s MAX814/MAX815/MAX816 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 Supply Current Reset Threshold RESET IN Threshold RESET IN Input Current Reset Threshold Hysteresis Reset Pulse Width SYMBOL VCC ISUPPLY VRT VRT IRT VRT tRS VOH RESET Output Voltage VOL VOH VOL VOH VOL RESET, WDO, PFO, LOW LINE Output Voltage VOH VOL VOL Watchdog Timeout Period tWD VRT(max) _______________________________________________________________________________________ 3 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 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 MAX815T VRT(max) 4 _______________________________________________________________________________________ 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits __________________________________________Typical Operating Characteristics (TA = +25C, unless otherwise noted.) MAX814/MAX815/MAX816 VCC SUPPLY CURRENT vs. TEMPERATURE 3V PARTS (MAX814T/MAX815T, MAX816) MAX814-01 VCC SUPPLY CURRENT vs. TEMPERATURE 5V PARTS (MAX814/MAX815K, L, N) MAX814-02 RESET TIMEOUT PERIOD vs. TEMPERATURE MAX814-03 70 65 VCC SUPPLY CURRENT (A) 60 55 50 45 40 35 30 -60 -40 -20 0 20 40 60 VCC = 2.5V VCC = 3.3V VCC = 5.0V 70 65 VCC SUPPLY CURRENT (A) 60 55 50 45 40 35 30 VCC = 3.3V VCC = 5.0V 200 RESET TIMEOUT PERIOD (ms) 195 VCC = 3.3V 190 185 VCC = 5.0V 180 175 -60 -40 -20 0 20 40 60 80 100 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C) 80 100 TEMPERATURE (C) RESET-COMPARATOR PROPAGATION DELAY vs. TEMPERATURE MAX814-04 PFI THRESHOLD vs. TEMPERATURE 3V PARTS (MAX814T/MAX815T, MAX816) MAX814-05 PFI THRESHOLD vs. TEMPERATURE 5V PARTS (MAX814/MAX815K, L, N) 2.540 2.530 PFI THRESHOLD (V) 2.520 2.510 2.500 2.490 2.480 2.470 2.460 2.450 MAX814-06 40 100mV OVERDRIVE (VRT - VCC) 1.715 1.710 1.705 PFI THRESHOLD (V) 1.700 1.695 1.690 1.685 1.680 1.675 2.550 PROPAGATION DELAY (s) 35 30 25 20 15 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) 1.670 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) LOW-LINE TO RESET THRESHOLD vs. TEMPERATURE (VCC RISING) MAX814-10 LOW-LINE TO RESET THRESHOLD vs. TEMPERATURE (VCC FALLING) MAX814-09 LOW-LINE COMPARATOR PROPAGATION DELAY vs. TEMPERATURE 100mV OVERDRIVE (VLLT - VCC) MAX814-11 LOW-LINE TO RESET THRESHOLD (mV) LOW-LINE TO RESET THRESHOLD (mV) 70 68 66 64 62 60 58 56 54 52 50 -60 -40 -20 0 20 40 60 70 68 66 64 62 60 58 56 54 52 50 -60 -40 -20 0 20 40 60 60 50 40 30 20 10 0 80 100 80 100 PROPAGATION DELAY (s) -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C) TEMPERATURE (C) _______________________________________________________________________________________ 5 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 ____________________________Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) RESET THRESHOLD DEVIATION vs. TEMPERATURE 5V PARTS (MAX814/MAX815K, L, N) MAX814-07 RESET THRESHOLD DEVIATION vs. TEMPERATURE 3V PARTS (MAX814T/MAX815T, MAX816) 2 RESET THRESHOLD DEVIATION (mV) 1 RESET THRESHOLD DEVIATION (mV) 1 0 0 -1 -1 -2 -3 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) -2 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) MAXIMUM TRANSIENT DURATION vs. RESET COMPARATOR OVERDRIVE 3V PARTS (MAX814T/MAX815T, MAX816) MAX814-12 MAXIMUM TRANSIENT DURATION vs. RESET COMPARATOR OVERDRIVE 5V PARTS (MAX814/MAX815K, L, N) MAXIMUM TRANSIENT DURATION (s) MAX814-13 140 MAXIMUM TRANSIENT DURATION (s) 120 100 80 60 40 20 0 10 100 RESET OCCURS ABOVE CURVE 140 120 100 80 60 40 20 0 RESET OCCURS ABOVE CURVE 1000 10 100 1000 RESET COMPARATOR OVERDRIVE (mV), VRT - VCC RESET COMPARATOR OVERDRIVE (mV), VRT - VCC 6 _______________________________________________________________________________________ MAX814-08 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits ______________________________________________________________Pin Description PIN MAX814 1 MAX815 1 MAX816 1 NAME FUNCTION Manual-Reset Input. Triggers a reset when pulled below 1.10V. This activelow input has an internal 150A pull-up current to VCC, and can be driven with CMOS logic or shorted to GND with a switch or transistor. 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. GND PFI Ground 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. Power-Fail Output. When PFI is below its threshold, PFO is low; otherwise it is high. Watchdog CMOS Input. If WDI remains high or low for more than 1.56sec, the watchdog timer times out, and WDO goes low. The timer is reset to zero on each WDI transition. MAX814/MAX815/MAX816 MR 2 2 -- VCC -- 3 4 -- 3 4 2 3 4 5 5 5 PFO -- 6 -- WDI 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. RESET IN 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. -- -- 6 7 7 7 RESET -- 8 8 -- -- 8 WDO 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 (P) supervisory circuits. They have P-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 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 VCC +3.3V +5V +12V SUPPLY VCC VCC P MAX814 MAX814K/L/N PFI PFI MR PFO GND RESET RESET MANUAL RESET INPUT MR RESET GND LOW LINE PFO NMI INTERRUPT RESET RESET Figure 1a. Typical Application for Dual +3.3V and +5V Systems Figure 1b. MAX814 Typical Application VRT VCC +12V SUPPLY VCC P R1 +12V SUPPLY VCC P VCC MAX815 RESET PFI WDI MANUAL RESET INPUT WDO MR PFO GND I/O LINE NMI R2 INTERRUPT MANUAL RESET INPUT MR RESET MAX816 RESET IN PFI RESET PFO RESET GND RESET INTERRUPT ON POWER-UP, RESET IS LOW UNTIL VCC > 2.8V. Figure 2. MAX815 Typical Application Figure 3. MAX816 Typical Application 8 _______________________________________________________________________________________ 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 8 RESET 7 RESET TIMEBASE 2 VCC 60mV 2 6 LOW LINE RESET THRESHOLD 4 PFI 5 PFO POWER- FAIL THRESHOLD 3 GND POWER-FAIL THRESHOLD 3 GND 4 PFI RESET THRESHOLD 5 PFO VCC 1 MR 150A RESET GENERATOR 7 RESET MAX815 6 WDI WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER 8 WDO MAX814 1 MR 150A RESET GENERATOR Figure 4. MAX814 Block Diagram Figure 5. MAX815 Block Diagram Reset Output 2 VCC 8 RESET 7 RESET 150A 1 MR MAX816 RESET GENERATOR 6 RESET IN 1.70V 4 PFI 5 PFO 1.70V A P's reset input starts the P in a known state. Whenever the P 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. 3 GND Figure 6. MAX816 Block Diagram _______________________________________________________________________________________ 9 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 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 that have a tight operating supply range, like the 386/486 Ps, 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 4.75 5.0 5.25 5.5V 4.5 4.75 5.0 5.25 5.5V POWER-SUPPLY RANGE (5.05V 2%) IC OPERATING RANGE RESET LIMITS "K" (4.8V 1%) POWER-SUPPLY RANGE (5V 5%) IC OPERATING RANGE RESET LIMITS "L" (4.7V 1%) 4.85 4.65 VRT > VIC(MIN) DESIGNED TO MEET WORSTCASE DESIGN PARAMETERS. VRT < VPS(MIN) DESIGNED TO ALLOW OPERATION OVER THE FULL POWER-SUPPLY RANGE. Figure 7a. K Suffix Design Range 4.5 4.75 5.0 5.25 5.5V Figure 7b. L Suffix Design Range 3.0 3.3 3.6V POWER-SUPPLY RANGE (5V 5%) IC OPERATING RANGE RESET LIMITS "N" (4.55V 1%) POWER-SUPPLY RANGE (3.33V 0.26%) IC OPERATING RANGE RESET LIMITS "T" (3.03V 1%) 4.60 3.06 VRT > VIC(MIN) DESIGNED TO MEET WORSTCASE DESIGN PARAMETERS. VRT > VIC(MIN) DESIGNED TO MEET WORSTCASE DESIGN PARAMETERS. Figure 7c. N Suffix Design Range Figure 7d. T Suffix Design Range 10 ______________________________________________________________________________________ 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits (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: VRT = VRIT x R1 + R2 R2 Early Power-Fail Warning Critical systems often require early warning to indicate when power is failing. This warning provides time for the P to store vital data and take care of any additional "housekeeping" before the power supply gets too far out of tolerance for the P to operate reliably. MAX814/MAX815/MAX816 ( ) 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 (100k, for example) and calculate R1 based on the desired reset threshold, using the following formula: R1 = R2 x VRT / VRIT - 1 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 P, 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 300A 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 10s/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 P 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 xt CHOLD = LOAD SHDN VLR [( ) ] The MAX816 can achieve 1.2% accuracy with 0.1% resistors. Watchdog Timer (MAX815) The watchdog circuit monitors the P's activity. If the P 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 P. 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. ______________________________________________________________________________________ 11 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 tWP VCC WDI 0V MR VCC WDO 0V VCC 0V tWD tWD tWDO tWD VCC VLL 60mV VRT VLLT VRT tRS tRS RESET RESET VCC MR 0 tMD VCC WDO (MAX815) tMR VCC RESET 0V Figure 8. MAX815 Watchdog Timing 0 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 Low-Voltage Operation 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). Manual Reset Many P-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 pull-up 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 0.1F capacitor to ground to provide additional noise immunity. 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 pull-down 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 100k--large enough not to load RESET, and small enough to pull RESET to ground. ______________________________________________________________________________________ 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 +12V +5V TO P MAX814 MAX815 MAX816 RESET R1 340k 1% VCC RESET 100k 1% MAX814K/L/N MR MAX815K/L/N PFI GND PFO PARAMETER MIN TYP MAX UNIT V +12V Reset 10.57 11.00 11.45 Threshold at +25C Figure 10. RESET Valid to Ground Circuit Figure 11. Monitoring Both +5V and +12V Monitoring Voltages Other than VCC Monitor voltages other than the V CC 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. 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. Watchdog Software Considerations 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. ______________________________________________________________________________________ 13 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 +5V VCC R1 MR 100k VCC 2N3904 VCC BUFFERED RESET TO OTHER SYSTEM COMPONENTS MAX814 MAX815 PFO PFI MAX816 R2 GND V+5V MR 0V +5V PFO 0V VVTRIP RESET 100k TO P MAX814 MAX815 MAX816 RESET GND P 4.7k RESET GND Figure 14. Interfacing to Ps with Bidirectional Reset I/O 0V Negative-Going VCC Transients In addition to issuing a reset to the P 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 30s or less will not cause a reset pulse to be issued. A 0.1F bypass capacitor mounted as close as possible to pin 2 (VCC) provides additional transient immunity. 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 SUBROUTINE Interfacing to Ps with Bidirectional Reset Pins SET LOW WDI YES RETURN NO Ps 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 P wants to pull it low, indeterminate logic levels may result. To correct this, connect a 4.7k resistor between the RESET output and the P 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 P Supervisory Circuits ______________Ordering Information PART* MAX814_CPA MAX814_CSA MAX814_EPA MAX814_ESA MAX815_CPA MAX815_CSA MAX815_EPA MAX815_ESA MAX816CPA MAX816CSA MAX816EPA MAX816ESA TEMP. RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO ___________________Chip Information TRANSISTOR COUNT: 744 MAX814/MAX815/MAX816 * 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. _____________Reset Trip Thresholds MAX814/MAX815 SUFFIX K L N T -- -- RESET TRIP THRESHOLD MIN (V) 4.75 4.65 4.50 3.00 MAX816 Adjustable MAX (V) 4.85 4.75 4.60 3.06 ______________________________________________________________________________________ 15 1% Accuracy, Low-Power, +3V and +5V P Supervisory Circuits MAX814/MAX815/MAX816 ________________________________________________________Package Information E D A3 A A2 E1 DIM A A1 A2 A3 B B1 C D1 E E1 e eA eB L 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 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 L A1 e B D1 0 - 15 C B1 eA eB Plastic DIP PLASTIC DUAL-IN-LINE PACKAGE (0.300 in.) PKG. DIM PINS P P P P P N D D D D D D 8 14 16 18 20 24 DIM D A e B 0.101mm 0.004in. 0-8 A1 C L 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 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 E H Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.) DIM PINS D D D 8 14 16 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 (c) 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. |
Price & Availability of MAX814
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |