19-0130; Rev 2; 11/05 Low-Cost Microprocessor Supervisory Circuits with Battery Backup The MAX703/MAX704 microprocessor (P) supervisory circuits reduce the complexity and number of components required for power-supply monitoring and battery control functions in P systems. These devices significantly improve system reliability and accuracy compared to that obtained with separate ICs or discrete components. The MAX703/MAX704 are available in 8-pin DIP and SO packages and provide four functions: 1) An active-low reset during power-up, power-down, and brownout conditions. 2) Battery-backup switching for CMOS RAM, CMOS Ps, or other low-power logic circuitry. 3) A 1.25V threshold detector for power-fail warning, low-battery detection, or for monitoring a power supply other than +5V. 4) An active-low manual reset input. Features Battery-Backup Power Switching Precision Supply-Voltage Monitor 4.65V (MAX703) 4.40V (MAX704) 200ms Reset Pulse Width Debounced TTL/CMOS-Compatible Manual Reset Input 200A Quiescent Current 50nA Quiescent Current in Battery-Backup Mode Voltage Monitor for Power-Fail or Low-Battery Warning 8-Pin DIP and SO Packages Guaranteed RESET Assertion to VCC = 1V Ordering Information PART The MAX703 and MAX704 differ only in their supplyvoltage monitor levels. The MAX703 generates a reset when the supply drops below 4.65V, while the MAX704 generates a reset below 4.40V. TEMP RANGE PIN-PACKAGE MAX703C/D 0C to +70C Dice* MAX703CPA 0C to +70C 8 PDIP MAX703CSA 0C to +70C MAX703EPA -40C to +85C 8 PDIP MAX703ESA -40C to +85C 8 SO Computers MAX703MJA -55C to +125C 8 CERDIP** Controllers MAX704C/D 0C to +70C Dice* MAX704CPA 0C to +70C 8 PDIP Applications Intelligent Instruments Automotive Systems Critical P Power Monitoring Typical Operating Circuit UNREGULATED DC R1 REGULATED +5V VCC RESET PFO PFI R2 MAX704CSA 0C to +70C MAX704EPA -40C to +85C 8 PDIP MAX704ESA -40C to +85C 8 SO MAX704MJA -55C to +125C 8 CERDIP** MICROPROCESSOR RESET Devices in PDIP and SO packages 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. Lead free not available for CERDIP package. Pin Configuration NMI GND 3.6V LITHIUM BATTERY VBATT MR TOP VIEW MAX703 MAX704 GND BUS VOUT VOUT 1 VCC CMOS RAM PUSHBUTTON SWITCH 8 SO *Dice are tested at TA = +25C only. **Contact factory for availability and processing to MIL-STD-883. VCC 0.1F 8 SO GND VCC 2 GND 3 MAX703 MAX704 PFI 4 8 VBATT 7 RESET 6 MR 5 PFO DIP/SO ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX703/MAX704 General Description MAX703/MAX704 Low-Cost Microprocessor Supervisory Circuits with Battery Backup ABSOLUTE MAXIMUM RATINGS Terminal Voltage (with respect to GND) VCC ....................................................................-0.3V to +6.0V VBATT .................................................................-0.3V to +6.0V All Other Inputs (Note 1).........................-0.3V to (VCB + 0.3V) Input Current VCC ...............................................................................200mA VBATT ..............................................................................50mA GND ................................................................................20mA Output Current VOUT ...............................Short-Circuit Protected for Up to 10s All Other Outputs ............................................................20mA Rate-of-Rise VBATT, VCC .................................................100V/s Operating Temperature Range C Suffix................................................................0C to +70C E Suffix .............................................................-40C to +85C M Suffix ..........................................................-55C to +125C Continuous Power Dissipation (TA = +70C) 8-Pin PDIP (derated 9.09mW/C above +70C) ..........727mW 8-Pin SO (derated 5.88mW/C above +70C) .............471mW 8-Pin CERDIP (derated 8.00mW/C above +85C) .....640mW Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10s) .................................+300C Note 1: VCB is the greater of VCC and VBATT. The input voltage limits on PFI and MR may be exceeded if the current into these pins is limited to less than 10mA. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = +4.75V to +5.5V for MAX703, VCC = +4.5V to +5.5V for MAX704, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL Operating Voltage Range VCC, VBATT Supply Current (Excluding IOUT) CONDITIONS (Note 2) ISUPPLY MIN 0 5.5 V 350 MAX70_E/M 200 500 VBATT Standby Current (Note 3) 5.5V > VCC > VBATT + 0.2V TA = +25C 0.05 TA = TMIN to TMAX 1.0 5.0 TA = +25C -0.10 +0.02 TA = TMIN to TMAX -1.00 +0.02 IOUT = 5mA VCC 0.05 VCC 0.025 IOUT = 50mA VCC 0.5 VCC 0.25 VBATT 0.1 VBATT 0.02 VOUT Output VOUT in Battery-Backup Mode IOUT = 250A, VCC < VBATT - 0.2V Battery Switch Threshold (VCC - VBATT) VCC < VRST Power-up 20 Power-down -20 Battery Switchover Hysteresis 4.75 MAX704 4.25 4.40 4.50 tRST 140 200 mV VOH VCC 1.5 40 RESET Output Voltage VOL V mV 280 ISINK = 3.2mA 0.4 MAX70_C, VCC = 1V, VCC falling, VBATT = 0V, ISINK = 50A 0.3 MAX70_E/M, VCC = 1.2V, VCC falling, VBATT = 0V, ISINK = 100A 0.3 _______________________________________________________________________________________ A mV 40 4.65 ISOURCE = 800A A V 4.50 VRST A V MAX703 RESET Threshold Hysteresis 2 UNITS 200 VCC = 0V, VBATT = 2.8V RESET Pulse Width MAX MAX70_C ISUPPLY in Battery-Backup Mode (Excluding IOUT) RESET Threshold TYP ms V Low-Cost Microprocessor Supervisory Circuits with Battery Backup MAX703/MAX704 ELECTRICAL CHARACTERISTICS (continued) (VCC = +4.75V to +5.5V for MAX703, VCC = +4.5V to +5.5V for MAX704, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL MR Input Threshold CONDITIONS VIL Low VIH High MR Pulse Width tMR MR to RESET Delay tMD MIN TYP MAX UNITS 0.8 V 2.0 150 ns 250 ns 250 600 A MR Pullup Current MR = 0V 100 PFI Input Threshold VCC = 5V 1.20 1.25 1.30 V -25 +0.01 +25 nA PFI Input Current VOH PFO Output Voltage VCC 1.5 ISOURCE = 800A V ISINK = 3.2mA VOL Note 2: Either VCC or VBATT can go to 0V if the other is greater than 2.0V. Note 3: "-" = battery-charging current, "+" = battery-discharging current. 0.4 Typical Operating Characteristics (VCC = +5V, VBATT = 2.8V, TA = +25C, unless otherwise noted.) OUTPUT VOLTAGE vs. LOAD CURRENT 4.90 SLOPE = 5 VCC = 0V VBATT = +2.8V TA = +25C 2.78 VOUT (V) VOUT (V) 4.95 4.85 MAX703 toc02 VCC = +5V VBATT = +2.8V TA = +25C MAX703 toc03 2.80 MAX703 toc01 5.00 MAX703 RESET OUTPUT VOLTAGE vs. SUPPLY VOLTAGE OUTPUT VOLTAGE vs. LOAD CURRENT VCC 1V/div 2.76 OV +5V SLOPE = 80 2.74 RESET GND 2.72 4.75 10 20 30 50 40 0 0.2 0.4 0.6 0.8 IOUT (mA) IOUT (mA) MAX703 RESET RESPONSE TIME POWER-FAIL COMPARATOR RESPONSE TIME 500ms/div 1.0 POWER-FAIL COMPARATOR RESPONSE TIME MAX703 toc06 PFI +5V +4V PFI VCC = +5V TA = +25C PFO 1k +3V PFO +5V +5V +5V PFO 1V/div 330pF MAX703 toc05 MAX703 toc04 +5V VCC RESET 0V 2.70 0 2k VCC VCC RESET 4.80 +5V VBATT = 0V TA = +25C PFO 30pF 1k 1.25V 1V/div 30pF RESET VCC 10k VCC RESET GND 0V TA = +25C +1.30V RESET +1.30V VCC = +5V TA = +25C PFI 30pF 0V 2s/div 0V 1.25V 400ns/div PFI +1.20V +1.20V 400ns/div _______________________________________________________________________________________ 3 Low-Cost Microprocessor Supervisory Circuits with Battery Backup MAX703/MAX704 Pin Description PIN NAME FUNCTION 1 VOUT Supply Output for CMOS RAM. When VCC is above the reset threshold, VOUT connects to VCC through a pchannel MOSFET switch. When VCC is below the reset threshold, the higher of VCC or VBATT is connected to VOUT. 2 VCC +5V Supply Input 3 GND Ground 4 PFI Power-Fail Comparator Input. When PFI is less than 1.25V, PFO goes low; otherwise PFO remains high. Connect PFI to GND or VCC when not used. 5 PFO Power-Fail Comparator Output. It goes low and sinks current when PFI is less than 1.25V; otherwise PFO remains high. 6 MR Manual Reset Input. Generates a reset pulse when pulled below 0.8V. This active-low input is TTL/CMOS compatible and can be shorted to ground with a switch. It has an internal 250A pullup current. Leave floating when not used. 7 RESET 8 Backup-Battery Input. When VCC falls below the reset threshold, VBATT is switched to VOUT if VBATT is 20mV VBATT greater than VCC. When VCC rises 20mV above VBATT, VCC is switched to VOUT. The 40mV hysteresis prevents repeated switching if VCC falls slowly. Reset Output. Remains low while VCC is below the reset threshold (4.65V for the MAX703, 4.40V for the MAX704). It remains low for 200ms after VCC rises above the reset threshold (Figure 2) or MR goes from low to high. +5V VCC VBATT BATTERY-SWITCHOVER CIRCUITRY VBATT = 3.0V VRST VOUT 0V VCC +5V VOUT RESET GENERATOR RESET 3.0V 0V +5V 1.25V tRST RESET MR 0V PFI PFO +5V PFO* 1.25V GND MAX703 MAX704 0V *PFO DEPENDS ON PFI EXCEPT IN BATTERY-BACKUP MODE, WHERE PFO IS LOW. Figure 1. Block Diagram 4 Figure 2. Timing Diagram _______________________________________________________________________________________ Low-Cost Microprocessor Supervisory Circuits with Battery Backup RESET Output 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 MAX703/MAX704 assert reset when VCC is low, preventing code-execution errors during power-up, power-down, or brownout conditions. When VBATT is 2V or more, RESET is always valid, irrespective of VCC. On power-up, as VCC rises, RESET remains low. When VCC exceeds the reset threshold, an internal timer holds RESET low for a time equal to the reset pulse width (typically 200ms); after this interval, RESET goes high (Figure 2). If a power-fail or brownout condition occurs (i.e., VCC drops below the reset threshold), RESET is asserted. As long as VCC remains below the reset threshold, the internal timer is continually restarted, causing the RESET output to remain low. Thus, a brownout condition that interrupts a previously initiated reset pulse causes an additional 200ms delay from the end of the last interruption. Power-Fail Comparator The PFI input is compared to an internal reference. If PFI is less than 1.25V, PFO goes low. The power-fail comparator can be used as an undervoltage detector to signal a failing power supply. In the Typical Operating Circuit, an external voltage-divider at PFI is used to monitor the unregulated DC voltage from which the regulated +5V supply is derived. The voltage-divider can be chosen so the voltage at PFI falls below 1.25V just before the +5V regulator drops out. PFO is then used as an interrupt to prepare the P for power-down. applied to VBATT (Figure 3). During this time, diode D1 (between VBATT and the substrate) conducts current from VBATT to VCC if VBATT (VCC + 0.6V). When the battery-backup mode is activated, V BATT connects to VOUT. In this mode, the substrate connects to VBATT and internal circuitry is powered from the battery (Figure 3). Table 1 shows the status of the MAX703/ MAX704 inputs and outputs in battery-backup mode. When VCC is below, but within, 1V of VBATT, the internal switchover comparator draws about 30A. Once VCC Table 1. Input and Output Status in Battery-Backup Mode SIGNAL STATUS VCC Disconnected from VOUT. VOUT Connected to VBATT through an internal 80 p-channel MOSFET switch. VBATT Connected to VOUT. Supply current is < 1A when VCC < (VBATT - 1V). RESET PFI Logic-low. Power-fail comparator is disabled. PFO Logic-low. MR Disabled. VCC VBATT S1 S2 To conserve power, the power-fail comparator is turned off and PFO is forced low when the MAX703/MAX704 enter battery-backup mode. MAX703 MAX704 D1 D2 S4 SUBSTRATE D3 Backup-Battery Switchover In the event of a brownout or power failure, it may be necessary to preserve the contents of RAM. With a backup battery installed at V BATT , the MAX703/ MAX704 automatically switch RAM to backup power when VCC fails. As long as VCC exceeds the reset threshold, VCC connects to VOUT through a 5 p-channel MOSFET power switch. Once V CC falls below the reset threshold, RESET goes low and VCC or VBATT (whichever is higher) switches to VOUT. Note that VBATT switches to VOUT through an 80 switch only if VCC is below the resetthreshold voltage and VBATT is greater than VCC. When VCC exceeds the reset threshold, it is connected to the MAX703/MAX704 substrate, regardless of the voltage S3 VOUT S1/S2 S3/S4 VCC > Reset Threshold Open Closed VCC < Reset Threshold and VCC > VBATT Open Closed VCC < Reset Threshold and VCC < VBATT Closed Open CONDITION Figure 3. Battery-Switchover Block Diagram _______________________________________________________________________________________ 5 MAX703/MAX704 Detailed Description MAX703/MAX704 Low-Cost Microprocessor Supervisory Circuits with Battery Backup drops to more than 1V below V BATT , the internal switchover comparator shuts off and the supply current falls to less than 1A. +5V VOUT VCC TO STATIC RAM Manual Reset The manual reset input (MR) allows RESET to be activated by a pushbutton switch. The switch is effectively debounced by the 140ms minimum reset pulse width. Because it is TTL/CMOS compatible, MR can be driven by an external logic line. MAX704 RESET VBATT TO P GND 100k 0.1F Applications Information Using a SuperCap(R) as a Backup Power Source SuperCaps are capacitors with extremely high capacitance values (on the order of 0.1 Farad). When using SuperCaps, if VCC exceeds the MAX703/MAX704 reset thresholds (4.65V and 4.40V, respectively), VBATT may not exceed VCC by more than 0.6V. Thus, with a 5% tolerance on VCC, VBATT should not exceed VCC (min) + 0.6V = 5.35V. Similarly, with a 10% tolerance on VCC, VBATT should not exceed 5.1V. Figure 4's SuperCap circuit uses the MAX703 with a 5% tolerance voltage supply. In this circuit, the SuperCap rapidly charges to within a diode drop of VCC. However, the diode leakage current with tricklecharge the SuperCap voltage to VCC. If VBATT = 5.25V and the power is suddenly removed and then reapplied with VCC = 4.75V, VBATT - VCC does not exceed the allowable 0.6V difference voltage. Figure 5's circuit uses the MAX704 with a 10% tolerance voltage supply. Note that if V CC = 5.5V and VBATT 5.1V, the power can be suddenly removed and reapplied with VCC = 4.5V, and VBATT - VCC will not exceed the allowable 0.6V voltage difference. +5V VOUT VCC TO STATIC RAM MAX703 RESET VBATT 0.1F TO P GND Figure 5. Using a SuperCap as a Backup Power Source with the MAX704 and a +5V 10% Supply Batteries and Power Supplies as Backup Power Sources Lithium batteries work well as backup batteries because they have very low self-discharge rates and high-energy density. Single lithium batteries with opencircuit voltages of 3.0V to 3.6V are ideal for use with the MAX703/MAX704. Batteries with an open-circuit voltage less than the minimum reset threshold plus 0.3V can be directly connected to the MAX703/MAX704 VBATT input with no additional circuitry (see the Typical Operating Circuit). However, batteries with open-circuit voltages greater than the reset threshold plus 0.3V CANNOT be used as backup batteries, since they source current into the substrate through diode D1 (Figure 3) when VCC is close to the reset threshold. Table 2. Allowable Backup-Battery Voltages PART MAXIMUM BACKUP-BATTERY VOLTAGE (V) MAX703 4.80 MAX704 4.55 Using the MAX703/MAX704 without a Backup Power Source If a backup power source is not used, ground VBATT and connect VCC to VOUT. A direct connection to VCC eliminates any voltage drop across the internal switch, which would otherwise appear at VOUT. Alternatively, use the MAX705-MAX708, which do not have batterybackup capabilities. Figure 4. Using a SuperCap as a Backup Power Source with a MAX703 and a +5V 5% Supply SuperCap is a registered trademark of Bankor Industries. 6 _______________________________________________________________________________________ Low-Cost Microprocessor Supervisory Circuits with Battery Backup When VCC falls below 1V, the MAX703/MAX704 RESET output no longer sinks current; it becomes an open circuit. High-impedance CMOS logic inputs can drift to undetermined voltages if left as open circuits. If a pulldown resistor is added to the RESET pin as shown in Figure 6, any stray charge or leakage currents will flow to ground, holding RESET low. Resistor value R1 is not critical. It should be about 100k, which is large enough not to load RESET and small enough to pull RESET to ground. Replacing the Backup Battery The backup battery can be removed while VCC remains valid without triggering a reset. As long as VCC stays above the reset threshold, battery-backup mode cannot VOUT VCC MAX703 MAX704 be entered. This is an improvement on switchover ICs that initiate a reset when VCC and VBATT are at or near the same voltage level (regardless of the reset threshold voltage). If the voltage on the unconnected VBATT pin floats up toward VCC, this condition alone cannot initiate a reset when using the MAX703/MAX704. Adding Hysteresis to the Power-Fail Comparator 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 7 shows how to add hysteresis to the power-fail comparator. Select the ratio of R1 and R2 so 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 1A to ensure that the 25nA (max) PFI input current does not shift the trip point. R3 should be larger than 10k to prevent it from loading down the PFO pin. Capacitor C1 adds additional noise rejection. Monitoring a Negative Voltage RESET VBATT The power-fail comparator can be used to monitor a negative supply voltage using Figure 8's circuit. When the negative supply is valid, PFO is low. When the negative supply voltage droops, PFO goes high. This circuit's accuracy is affected by the PFI threshold tolerance, the VCC voltage, and resistors R1 and R2. R1 Figure 6. RESET Valid to Ground Circuit VIN +5V +5V R1 R1 VCC VCC PFI R2 PFO PFI C1* MAX703 MAX704 R3 PFO GND MAX703 MAX704 R2 GND *OPTIONAL V- TO P +5V +5V PFO PFO 0V 0V VL R +R VTRIP = 1.25 1 2 R2 R2 | | R3 VH = 1.25 / R1 + R2 | | R3 VTRIP VIN VH VL - 1.25 5 - 1.25 1.25 + = R1 R3 R2 Figure 7. Adding Hysteresis to the Power-Fail Comparator 0V 5 - 1.25 1.25 - VTRIP = R1 R2 VTRIP V- 0V NOTE: VTRIP IS NEGATIVE Figure 8. Monitoring a Negative Voltage _______________________________________________________________________________________ 7 MAX703/MAX704 Ensuring a Valid RESET Output Down to VCC = 0V MAX703/MAX704 Low-Cost Microprocessor Supervisory Circuits with Battery Backup Using the Power-Fail Comparator to Assert Reset In addition to asserting reset at the VCC reset threshold voltage, reset can also be asserted at the PFI input threshold voltage. Connect PFO to MR to initiate a reset pulse when the monitored supply drops below a userspecified threshold or when VCC falls below the reset threshold. For additional noise rejection, place a capacitor between PFI and GND. Table 3. Maxim Microprocessor Supervisory Products NOMINAL MINIMUM WATCHBACKUPCE MANUAL WATCHRESET DOG POWER-FAIL PULSE BATTERY WRITE RESET DOG TIMEOUT COMPARATOR SWITCH PROTECT INPUT INPUT WIDTH PERIOD (ms) (s) PART NOMINAL RESET THRESHOLD (V) MAX690A 4.65 140 1.6 Yes No Yes No No No No No MAX691A 4.65 140/Adj. 1.6/Adj. Yes Yes Yes No Yes Yes Yes Yes MAX692A 4.40 140 1.6 Yes No Yes No No No No No MAX693A 4.40 140/Adj. 1.6/Adj. Yes Yes Yes No Yes Yes Yes Yes MAX696 Adj. 35/Adj. 1.6/Adj. Yes No Yes No Yes Yes Yes Yes MAX697 Adj. 35/Adj. 1.6/Adj. No Yes Yes No Yes Yes Yes No MAX700 4.65/Adj. 200 -- No No No Yes No No Yes No MAX703 4.65 140 -- Yes No Yes Yes No No No No MAX704 4.40 140 -- Yes No Yes Yes No No No No MAX705 4.65 140 1.6 No No Yes Yes Yes No No No MAX706 4.40 140 1.6 No No Yes Yes Yes No No No MAX707 4.65 140 -- No No Yes Yes No No Yes No LOWLINE OUTPUT ACTIVE- BATT HIGH ON RESET OUTPUT MAX708 4.40 140 -- No No Yes Yes No No Yes No MAX791 4.65 140 1.0 Yes Yes Yes Yes Yes Yes Yes Yes MAX1232 4.50/4.75 250 0.15/0.60/ 1.2 No No No Yes No No Yes No MAX1259 -- -- -- Yes No Yes No No No No No 8 _______________________________________________________________________________________ Low-Cost Microprocessor Supervisory Circuits with Battery Backup Package Information For the latest package outline information, go to www.maxim-ic.com/packages. SUBSTRATE MUST BE LEFT UNCONNECTED TRANSISTOR COUNT: 573 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9 (c) 2005 Maxim Integrated Products REDUTA Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX703/MAX704 Chip Topography