® SP791 Low Power Microprocessor Supervisory with Battery Switch-Over ■ Precision 4.65V Voltage Monitoring ■ 200ms Power-OK/Reset Time Delay ■ Independent Watchdog Time-Preset or Adjustable ■ 75µA Maximum Operating Supply Current ■ 1.0µA Maximum Battery Backup Current ■ 0.1µA Maximum Battery Standby Current ■ Power Switching 250mA Output in Vcc Mode (0.6Ω) 25mA Output in Battery Mode (5Ω) ■ On-Board Gating of Chip-Enable Signals Memory Write-Cycle Completion 6ns CE Gate Propagation Delay ■ Voltage Monitor for Power-Fail or Low Battery ■ Backup-Battery Monitor ■ RESET Valid to Vcc=1V ■ Pin Compatible Upgrade to MAX791 DESCRIPTION The SP791 is a microprocessor (µP) supervisory circuit that integrates a myriad of components involved in discrete solutions to monitor power-supply and battery-control functions in µP and digital systems. The SP791 offers complete µP monitoring and watchdog functions. The SP791 is ideal for a low-cost battery management solution and is well suited for portable, battery-powered applications with its supply current of 40µA. The 6ns chip-enable propagation delay, the 25mA current output in battery-backup mode, and the 250mA current output in standard operation also makes the SP791 suitable for larger scale, high-performance equipment. SP791 15 RESET 1 VBATT 3 Vcc _ VOUT + + MR 9 4.65V + RESET GENERATION _ 150mV _ _ 10 5 LOWLINE BATT ON + + 2 _ SWT WDI 8 TIMEBASE FOR RESET AND WATCHDOG 11 WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER + _ PFI 7 V OUT CHIP-ENABLE OUTPUT CONTROL 2V + _ 12 1.25V 6 PFO 14 16 4 GND CE OUT 13 WDO WDPO CE IN Figure 1. Block Diagram SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 1 © Copyright 2000 Sipex Corporation ABSOLUTE MAXIMUM RATINGS Input Voltage (with respect to GND) VCC..................................................-0.3V to +6V VBATT.................................. ............-0.3V to +6V All Other Inputs ................-0.3V to (VOUT + 0.3V) Input Current VCC Peak..................................................... 1.0A VCC Continuous .......................................250mA VBATT Peak ..............................................250mA VBATT Continuous.......................................25mA GND, BATT ON .........................................100mA All Other Outputs ........................................25mA Stresses beyond these 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. Operating Temperature Ranges SP791C ..............................0oC to +70oC SP791E ...........................-40oC to +85oC Storage Temperature Range...........-65oC to +160oC Lead Temperature (soldering,10sec)..........+300oC Continuous Power Dissipation (TA = + 70oC) Plastic DIP (derate 10.53mW/oC above +70oC) 842mW Narrow SO (derate 8.70mW/oC above+70oC) 696mW ESD Rating........................................................4KV ELECTRICAL CHARACTERISTICS (Vcc = 4.75V to 5.5V, VBATT = 2.8V, TA = TMIN to TMAX unless otherwise noted, typicals specified at 25oC) PARAMETER MIN Operating Voltage Range VCC, VBATT (Note 1) TYP MAX UNITS 5.5 V 0 VCC - 0.05 VCC - 0.015 VCC- 0.3 VCC - 0.15 VCC- 0.2 VCC - 0.09 VOUT in Normal Operating Mode VCC = 4.5V, IOUT = 25mA V 0.6 1.2 0.9 2.0 VBATT- 0.3 VBATT- 0.25 VBATT- 0.15 VBATT-to-VOUT On Resistance Supply Current in Normal Operating Mode (Excludes IOUT) Supply Current in Battery Backup Mode (Excludes IOUT) (Note 2) VBATT Standby Current (Note 3) VCC = 4.5V, IOUT = 250mA VCC =3.0V; VBATT = 2.8V, IOUT = 100mA VCC-to-VOUT On Resistance VOUT in Battery Backup Mode CONDITIONS Ω VCC=4.5V; VCC=3.0V; VBATT=4.5V, IOUT=20mA V VBATT=2.8V, IOUT=10mA VBATT=2.0V, IOUT=5mA 5 7 10 15 25 30 Ω 40 75 µA VCC > VBATT – 1V 0.001 1 µA VCC < VBATT – 1.2V ; VBATT = 2.8V 0.02 µA VBATT + 0.2V < VCC -0.1 VBATT=4.5V VBATT=2.8V VBATT=2.0V VBATT +0.03 VBATT -0.03 V Power down Battery-Switch over Hysteresis 60 mV Peak to Peak Low-Battery Detector Threshold 2 V Battery-Switchover Threshold SP791DS/08 Power up SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 2 © Copyright 2000 Sipex Corporation ELECTRICAL CHARACTERISTICS (continued) (Vcc = 4.75V to 5.5V, VBATT = 2.8V, TA = TMIN to TMAX unless otherwise noted, typicals specified at 25oC) PARAMETER MIN TYP MAX BATT ON Output Low Voltage 0.1 0.7 0.4 1.5 BATT ON Output Short Circuit Current 60 15 1 100 UNITS V CONDITIONS ISINK = 3.2mA ISINK = 25mA mA µA Sink Current Source Current RESET, LOW-LINE AND WATCHDOG TIMER RESET Threshold Voltage 4.50 4.65 4.75 V RESET Threshold Hysteresis 15 mV LOWLINE-to-RESET Threshold Voltage 150 mV VCC-to-RESET Delay 100 µs Power down VCC-to-LOWLINE Delay 80 µs Power down RESET Active Timeout Period 140 200 280 ms Power up Watchdog Timeout Period 1.0 1.6 2.25 sec SWT connected to VOUT ms 4.7nF capacitor connected from Minimum Watchdog Timeout Period 10 SWT to GND Minimum Watchdog Input Pulse Width 100 ns WDPO Pulse Width 1 WDPO-to-WDO Delay 70 RESET Output Voltage 0.004 0.1 ms ns 0.3 0.4 V ISOURCE = 1.6mA, VCC = 5V 7 LOWLINE Output Voltage 20 mA Output source current 0.4 V ISINK = 3.2mA, VCC = 4.25V 100 µA Output source current 0.4 V ISINK = 3.2mA 10 mA Output source currrent 0.4 V ISINK = 3.2mA 20 mA 3.5 LOWLINE Output Short-Circuit Current ISOURCE = 1µA, VCC = 5V 15 WDO Output Voltage 3.5 WDO Output Short-Circuit Current ISOURCE = 500µA, VCC = 5V 3 WDPO Output Voltage 3.5 WDPO Output Short-Circuit Current SP791DS/08 ISINK=50µA,VCC=1.0V,VCC ➘ ISINK = 3.2 mA, VCC = 4.25V 3.5 RESET Output Short-Circuit Current VIL = 0.8V, VIH = 0.75 X VCC ISOURCE = 1mA 7 Output source current SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 3 © Copyright 2000 Sipex Corporation ELECTRICAL CHARACTERISTICS (continued) (Vcc = 4.75V to 5.5V, VBATT = 2.8V, TA = TMIN to TMAX unless otherwise noted, typicals specified at 25oC) PARAMETER MIN WDI Threshold Voltage (Note 4) WDI Input Current TYP MAX 0.75 X VCC UNITS V 0.8 -50 µA -10 20 50 1.25 1.30 V +0.01 +25 nA 0.4 V 100 mA µA CONDITIONS VIH VIL WDI = 0V WDI = VOUT POWER FAIL COMPARATOR PFI Input Threshold 1.20 PFI Leakage Current PFO Output Voltage 3.5 PFO Short-Circuit Current 1 PFI-to-PFO Delay VCC = 5V ISINK = 3.2mA ISOURCE = 1µA, VCC = 5V 60 15 µs 15 55 Output sink current Output source current VOD = 15mV VOD = 15mV CHIP-ENABLE GATING CE IN Leakage Current CE IN-to-CE OUT Resistance (Note 5) CE OUT Short-Circuit Current (Reset Active) 0.1 CE IN-to-CE OUT Propagation Delay (Note 6) CE OUT Output Voltage High (Reset Active) +0.005 +1 µA Disabled mode 65 150 Ω Enabled mode 0.75 2.0 mA Disabled mode, CE OUT = 0V 6 10 ns 50Ω source impedance driver, CLOAD = 50pF 3.5 2.7 RESET-to-CE OUT Delay V VCC = 5V, IOUT = 100µA VCC = 0V, VBATT = 2.8V, IOUT = 1µA 15 µs 15 µs 7 µs Power down MANUAL RESET INPUT MR Minimum Pulse Width 25 MR-to-RESET Propagation Delay MR Threshold 1.25 MR Pull-Up Current 23 250 V VCC = 5V µA MR = 0V Note 1: Either VCC or VBATT can go to 0V, if the other is greater than 2.0V. Note 5: The chip-enable resistance is tested with VCC = 4.75V :: VCE IN = VCE OUT =VCC/2. Note 2: The supply current drawn by the SP791 from the battery (excluding IOUT) typically goes to 10µA when (VBATT - 1V) < VCC < VBATT. In most applications, this is a brief period as VCC falls through this region. Note 6: The chip-enable propagation delay is measured from the 50% point at CE IN to the 50% point at CE OUT. Note 3: "+" = battery-discharging "-" = battery-charging current. current, Note 4: WDI is internally connected to a voltage divider between VOUT and GND. If unconnected, WDI is driven to 1.6V (typ), disabling the watchdog function. SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 4 © Copyright 2000 Sipex Corporation PINOUT to select another watchdog-timeout period. Watchdog-timeout period = 2.1 x (capacitor value in nF) ms. TOP VIEW VBATT 1 16 WDPO VOUT 2 15 RESET Vcc 3 14 WDO GND 4 13 CE IN BATT ON 5 Pin 9 — MR — Manual-Reset Input. This input can be tied to an external momentary pushbutton switch, or to a logic gate output. RESET remains low as long as MR is held low and for 200ms after MR returns high. Pin 10 — LOWLINE — LOWLINE Output goes low when VCC falls to 150mV above the reset threshold. The output can be used to generate an NMI (nonmaskable interrupt) if the unregulated supply is inaccessible. Pin 11 — WDI — Watchdog Input. WDI is a threelevel input. If WDI remains either high or low for longer than the watchdog timeout period, WDO goes low. WDO remains low until the next transition at WDI. Leaving WDI unconnected disables the watchdog function. WDI connects to an internal voltage divider between VOUT and GND, which sets it to mid-supply when left unconnected. Pin 12 — CE OUT — Chip-Enable Output. CE OUT goes low only when CE IN is low and VCC is above the reset threshold. If CE IN is low when reset is asserted, CE OUT will stay low for 15us or until CE IN goes high, whichever occurs first. Pin 13 — CE IN — Chip-Enable Input. The Input to chip-enable gating circuit. Connect to GND or VOUT if not used. Pin 14 — WDO — Watchdog Output. WDO goes low if WDI remains either high or low longer than the watchdog timeout period. WDO returns high on the next transition at WDI. WDO remains high if WDI is unconnected. WDO is also high when RESET is asserted. Pin 15 — RESET — RESET Output goes low whenever VCC falls below the reset threshold. RESET will remain low for 200ms after VCC crosses the reset threshold on power-up. Pin 16 — WDPO — Watchdog-Pulse Output. Upon the absence of a transition at WDI, WDPO will pulse low for a minimum of 1ms. WDPO precedes WDO by 70ns. Corporation 12 CE OUT PFO 6 11 WDI PFI 7 10 SWT 8 9 LOWLINE MR DIP/SO PIN ASSIGNMENTS Pin 1 — VBATT — Backup-Battery Input. Connect to external battery or capacitor and charging circuit. Pin 2 —VOUT — Output Supply Voltage. VOUT connects to VCC when VCC is greater than VBATT and VCC is above the reset threshold. When VCC falls below VBATT and VCC is below the reset threshold, VOUT connects to VBATT. Connect a 0.1µF capacitor from VOUT to GND. Pin 3 — V CC — Input Supply Voltage — +5V input Pin 4 — GND — Ground reference for all signals Pin 5 — BATT ON — Battery On Output. Goes high when VOUT switches to VBATT. Goes low when VOUT switches to VCC. Connect the base of a PNP through a current-limiting resistor to BATT ON for VOUT current requirements greater than 250mA. Pin 6 — PFO — Power-Fail Output. This is the output of the power-fail comparator. PFO goes low when PFI is less than1.25V. This is an uncommitted comparator, and has no effect on any other internal circuitry. Pin 7 — PFI — Power-Fail Input. This is the noninverting input to the power-fail comparator. When PFI is less than 1.25V, PFO goes low. Connect PFI to GND or VOUT when not used. Pin 8 — SWT — Set Watchdog-Timeout Input. Connect this input to VOUT to select the default 1.6 sec watchdog timeout period. Connect a capacitor between this input and GND SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 5 © Copyright 2000 Sipex Corporation TYPICAL CHARACTERISTICS (25oC, unless otherwise noted) 2.9 VCC=5V VBATT=2.8V 2.4 1.9 1.4 0.9 0.4 0 30 60 90 120 0 30 60 90 120 150 0.7 0.6 0.5 1.252 1.250 1.248 1.246 -30 0 30 60 90 120 150 -60 -30 0 30 60 90 Temperature Deg. C Temperature Deg. C Reset Threshold vs. Temperature Reset Output Resistance vs. Temperature Reset Delay vs. Temperature 0 30 60 90 Temperature Deg. C SP791DS/08 VCC=5V VBATT=0 NO LOAD ON PFO 1.254 Temperature Deg. C 120 150 212 600 VCC=5V,VBATT=2.8V Soucing Current 500 400 300 200 VCC=0V,VBATT=2.8V Sink Current 100 0 -60 Reset Delay (mS) VBATT=0V Power Down -30 30 60 90 120 150 180 PFI Threshold vs. Temperature 0.4 -60 Resistance (ohms) Reset Threshold (V) VCC=5V VBATT=0V 0.8 0 1.256 0.3 0 60 Temperature Deg. C PFI Threshold (V) VBATT=4.5V Resistance (ohms) Resistance (ohms) VBATT=2V VBATT=2.8V -60 -30 70 40 -60 -30 0.9 5 80 VCC to VOUT On Resistance vs. Temperature 15 10 90 Temperature Deg. C VBATT to VOUT ON Resistance vs. Temperature VCC=0V 100 50 -0.1 -60 -40 -20 0 20 40 60 80 100 120 140 150 VCC=4.75V VBATT=2.8V CE IN=VCC/2 110 VCC=0V VBATT=2.8V Temperature Deg. C 4.70 4.69 4.68 4.67 4.66 4.65 4.64 4.63 4.62 4.61 4.60 -60 120 Resistance (ohms) 57 53 49 45 41 37 33 29 25 -60 -30 Chip Enable On Resistance vs. Temperature Battery Supply Current vs. Temperature (Backup Mode) VBATT Current (µA) VCC Current (µA) VCC Supply Current vs. Temperature (Normal Mode) -30 0 30 60 90 120 150 Temperature Deg. C SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 6 120 150 VCC=0V to 5V Step, VBATT=2.8V 210 208 206 204 202 200 -60 -30 0 30 60 90 120 150 Temperature Deg. C © Copyright 2000 Sipex Corporation TYPICAL CHARACTERISTICS (25oC, unless otherwise noted) 100 Watchdog Timeout vs. Timing Capacitor 250 0.1µF Capacitor VOUT to GND 80 Watchdog Tiimeout (mS) Maximum Transient Duration (uS) Maximum Reset Comparator Overdrive Without Causing a Reset Above Line Reset Generated 60 40 Below Line No Reset Generated 20 150 100 50 0 10 100 1000 VCC=5V VBATT=2.8V 200 0 10000 0 10 Voltage Drop(mV) VCC=5V 50Ω Driver 12 8 50 60 70 80 90 100 VCC=4.5V VBATT=0V Slope=0.6Ω 100 10 4 0 1 0 50 100 150 200 250 300 1 10 Cload (pF) 1000 1000 Battery Current vs. VCC Voltage IE+2 VBATT=4.5V VCC=0V Slope=5Ω VBATT Current(µA) Log Scale IE+1 100 10 1 100 IOUT (mA) VBATT to VOUT vs. Output Current Voltage Drop(mV) 40 1000 20 Propagation Delay (NS) 30 VCC to VOUT vs. Output Current Chip-Enable Propagation Delay vs. CE OUT Load Capacitance 16 20 Timing Capacitor (nF) Reset Threshold Voltage - VCC (mV) VBATT=2.8V IE+0 IE-1 IE-2 IE-3 IE-4 IE-5 IE-6 IE-7 IE-8 1 10 100 .0000 IOUT (mA) SP791DS/08 5.000 VCC (0.5V/div) SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 7 © Copyright 2000 Sipex Corporation +5V 0.1µF 0.1µF CMOS RAM Vcc BATT ON VBATT SWT VOUT 0.47F OTHER SYSTEM RESET SOURCES CE OUT MR ADDRESS DECODE CE IN UNREGULATED SUPPLY AO-A15 µP Corporation PFI WDI PFO I/O LOWLINE NMI RESET UNREGULATED SUPPLY FAILURE GND RESET INT WDO Typical Operating Circuit MR MANUAL RESET 25µs MIN MR 7µs TYP * RESET OTHER RESET SOURCES CE IN 0V CE OUT 15µs TYP * * DIODES NOT REQUIRED ON OPEN-DRAIN OUTPUTS Figure 2. Manual-Reset Timing Diagram Figure 3. Diode "OR" connections allow multiple reset sources to connect to MR. FEATURES The SP791 is a microprocessor (µP) supervisory circuit that monitors the power supplied to digital circuits such as microprocessors, microcontrollers, or memory. The SP791 is an ideal solution for portable, battery-powered equipment that require power supply monitoring. The SP791 watchdog functions will continuously oversee the operational status of a system. Implementing the SP791 will reduce the number of components and overall complexity in a design that requires power supply monitoring circuitry. The operational features and benefits of the SP791 are described in more detail below. 2) Manual-Reset input ➡ Manually resets RESET output 3) Power Fail Comparator ➡ Provides for powerfail warning and low-battery detection, or monitors another power supply. 4) Watchdog function ➡ Monitors µP activity where the watchdog output goes to a logic LOW state if the watchdog input is not toggled for a period greater than the timeout period. 5) Internal switch ➡ Switches over from VCC to VBATT if the VCC falls below the reset threshold and below VBATT. MANUAL RESET INPUT Many microprocessor or microcontroller products include manual-reset capability, allowing the operator or test technician to initiate a reset. The Manual Reset Input (MR) can be connected directly to a switch, without an external pull-up resistor. It connects to a 1.25V comparator, and has an internal pull-up to VOUT as shown in Figure 1. The propagation delay from asserting MR to RESET being asserted is 7us typical. Pulsing THEORY OF OPERATION The SP791 is a complete µP supervisor IC and provides the following main functions: 1) µP reset ➡ RESET output is asserted during power fluctuations such as power-up, powerdown, and brown out conditions, and is guaranteed to be in the correct state for VCC down to 1V. SP791DS/08 Corporation SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 8 © Copyright 2000 Sipex Corporation 100ns MIN 1.6sec RESET 15 TO µP RESET WDI 10k WDPO Corporation WDO 70ns Figure 5. WDI, WDO and WDPO Timing Diagram (VCC mode). Figure 4. Adding an external pull-down resistor ensures RESET is valid with VCC down to GND. +5V 1 3 Vcc VOUT VBATT 2 µP POWER 0.1µF 3.6V µP Corporation 15 RESET 11 WDI 10 LOWLINE 9 WDPO MR WDO GND 4 *1µF 16 14 RESET I/O 1/6 74HC04 14 3 2 Vcc Q 5 CLOCK CD4013 D Q 1 SET RESET Vss 7 6 4 NMI INTERRUPT TWO CONSECUTIVE WATCHDOG FAULT INDICATIONS +5V REACTIVATE 4.7kΩ ∗ SETS Q HIGH ON POWER-UP Figure 6. Two consecutive watchdog faults latch the system in reset. 1.6mA at VOUT – 0.5V. When no backup battery is used, RESET output is valid down to VCC = 1V, and an external 10kΩ pull-down resistor on RESET ensures that RESET will be valid with VCC down to GND as shown on Figure 4. As VCC goes below 1V, the gate drive to the RESET output switch reduces accordingly, increasing the rDS(ON) and the saturation voltage. The 10kΩ pull-down resistor ensures the parallel combination of switch and external resistor is 10kΩ and the output saturation voltage is below 0.4V, while sinking 40µA. When using a 10kΩ external pull-down resistor, the high state for the RESET output with Vcc = 4.75V is 4.5V typical. For battery voltages greater than or equal to 2V, RESET remains valid for VCC between 0V and 5.5V. RESET will be asserted during the following conditions: MR low for a minimum of 25µs resets all the internal counters, sets the Watchdog Output (WDO) and Watchdog-Pulse Output (WDPO) high, and sets the Set Watchdog-Timeout (SWT) input to VOUT if it is not already connected to VOUT (for Internal timeouts). It also, disables the Chip-Enable Output (CE OUT) forcing it to a high state. The RESET output remains at a logic low as long as MR is held low, and the reset-timeout period begins after MR returns high, Figure 2. Use this input as either a digital-logic input or a second low-line comparator. Normal TTL/ CMOS levels can be wire-OR connected via pull-down diodes, Figure 3, and open-drain/collector outputs can be wire-ORed directly. RESET OUTPUT The SP791's RESET output ensures that the µP powers up in a known state, and prevents codeexecution errors during power-down or brownout conditions. The RESET output is active low, and typically sinks 3.2mA at 0.1V saturation voltage in its active state. When deasserted, RESET sources SP791DS/08 1) VCC < 4.65V (typ) 2) MR < 1.25V (typ) 3) RESET = logic "0" ; for 200 ms (typ) after Vcc rises above 4.65V or after MR has exceeded 1.25V. The SP791 battery-switchover comparator does not affect RESET assertion. SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 9 © Copyright 2000 Sipex Corporation WATCHDOG FUNCTION The watchdog monitors µP activity via the Watchdog Input (WDI). If the µP becomes inactive over a period of time, WDO and WDPO are asserted. To use the watchdog functon, connect WDI to a bus line or µP I/O line. If WDI remains high or low for longer than the watchdog timeout period (1.6sec nominal), WDPO and WDO are asserted, indicating a software fault or idle condition. ing edge of WDPO precedes WDO by 70ns. Since WDO is high when WDPO goes low, the Q output of the flip-flop remains high as WDO goes low (Figure 6). If the watchdog timer is not reset by a transition at WDI, WDO remains low and WDPO clocks a logic low to the Q output, causing the SP791 to latch in reset. If the watchdog timer is reset by a transition at WDI, WDO goes high and the flip-flop's Q output remains high. Thus, a system shutdown is only caused by two successive watchdog faults. The internal pull-up resistors associated with WDO and WDPO connect to VOUT. Therefore, do not connect these outputs directly to CMOS logic that is powered from VCC since, in the absence of VCC (i.e., battery mode), excessive current will flow from WDO or WDPO through the protection diode(s) of the CMOS-logic inputs to ground. WATCHDOG INPUT A change of logic state (minimum 100ns duration) at WDI during the watchdog period will reset the watchdog timer. The watchdog default timeout is 1.6sec. To select an alternative timeout period, connect an external capacitor from SWT to GND. To disable the watchdog function, leave WDI floating. An internal impedance network (100kΩ equivalent at WDI) biases WDI to approximately 1.6V. Internal comparators detect this level and disable the watchdog timer. When Vcc is below the reset threshold, the watchdog function is disabled and WDI is disconnected from its internal network, thus becoming high impedance. SELECTING AN ALTERNATIVE WATCHDOG TIMEOUT PERIOD SWT input controls the watchdog-timeout period. Connecting SWT to VOUT selects the internal 1.6sec watchdog-timeout period. Select an alternative timeout period by connecting a capacitor between SWT and GND. Do not leave SWT floating, and do not connect it to ground. The following formula determines the watchdog-timeout period: Watchdog Timeout Period = 2.1 x (capacitor value in nF) ms WATCHDOG OUTPUT WDO remains high if there is activity (transition or pulse) at WDI during the watchdogtimeout period. The watchdog function is disabled and WDO is a logic high when VCC is less than the reset threshold, or when WDI is an open circuit. In watchdog mode, if no transition occurs at WDI during the watchdog-timeout period, WDO goes low 70ns after the falling edge of WDPO and remains low until the next transition at WDI as shown on Figure 5. A flipflop can force the system into a hardware shutdown if there are two successive watchdog faults, shown on Figure 6. WDO has a 2 x TTL output characteristic. This formula is valid for capacitance values between 4.7 nF and 100nF (see the Watchdog Timeout vs. Timing Capacitor graph in the Typical Operating Characteristics). CHIP-ENABLE SIGNAL GATING The SP791 provides internal gating of chip-enable (CE) signals to prevent erroneous data from corrupting the CMOS RAM in the event of a power failure. During normal operation, the CE gate is enabled and passes all CE transitions. When reset is asserted, this path becomes disabled, preventing erroneous data from corrupting the CMOS RAM. The SP791 uses a series transmission gate from CE IN to CE OUT. WATCHDOG-PULSE OUTPUT As described in the preceding section, WDPO can be used as the clock input to an external D flip-flop. Upon the absence of a watchdog edge or pulse at WDI at the end of a watchdog-timeout period, WDPO will pulse low for 1ms. The fallSP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 10 © Copyright 2000 Sipex Corporation Vcc RESET THRESHOLD CE IN CE OUT 15µs 100µs 100µs RESET Figure 7. Reset and Chip-Enable Timing Capacitance graph in the Typical Operating Characteristics). The CE propagation delay is defined from the 50% point on CE IN to the 50% point on CE OUT using a 50Ω driver with 50pF load capacitance as in Figure 8. For minimum propagation delay, minimize the capacitive load at CE OUT and use a low output-impedance driver. The 10ns maximum CE propagation from CE IN to CE OUT enables the SP791 to be used with most µPs. CHIP-ENABLE INPUT CE IN is high impedance (disabled mode) while RESET is asserted. During a power-down sequence where VCC falls below 4.65V, CE IN assumes a high impedance state when the voltage at CE IN goes high or 15µs after RESET is asserted, whichever occurs first, (Figure 7). During a power-up sequence, CE IN remains high impedance until RESET is deasserted. CHIP-ENABLE OUTPUT In the enabled mode, the impedance of CE OUT is equivalent to 65Ω in series with the source driving CE IN. In the disabled mode, the 65Ω transmission gate is off and CE OUT is actively pulled to VOUT. This source turns off when the transmission gate is enabled. In the high-impedance mode, the leakage currents into this input are less than 1µA over temperature. In the low-impedance mode, the impedance of CE IN appears as a 65Ω resistor in series with the load at CE OUT. The propagation delay through the CE transmission gate depends on both the source impedance of the drive to CE IN and the capacitive loading on CE OUT (see the ChipEnable Propagation Delay vs. CE OUT Load +5V Vcc Corporation CE IN CE OUT 50Ω Driver 50pF CLOAD GND Figure 8. CE Propagation Delay Test Circuit SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 11 © Copyright 2000 Sipex Corporation FROM REGULATED SUPPLY 3 Vcc 2 V OUT 0.1µF 0.1µF Corporation µP POWER POWER TO CMOS RAM 1 VBATT µP 3.0V 15 RESET NMI I/O LINE RESET 10 LOWLINE GND 4 a.) 3 Vcc VOLTAGE REGULATOR UNREGULATED SUPPLY WDI 11 V OUT 2 0.1µF 0.1µF Corporation VBATT µP POWER POWER TO CMOS RAM 1 µP 3.0V 7 15 PFI RESET 6 PFO GND WDI 11 RESET NMI I/O LINE 4 b.) Figure 9. a) If the unregulated supply is inaccessible, LOWLINE generates the NMI for the µP. b) Use PFO to generate the µP NMI if the unregulated supply is accessible. LOWLINE OUTPUT The low-line comparator monitors VCC with a typical threshold voltage 150mV above the reset threshold and has 15mV of hysteresis. LOWLINE typically sinks 3.2mA at 0.1V. For normal operation (Vcc above the LOWLINE threshold), LOWLINE is pulled to VOUT. If access to the unregulated supply is unavailable, use LOWLINE to provide a nonmaskable interrupt (NMI) to the µP as shown in Figure 9a. POWER-FAIL INPUT The Power-Fail Input (PFI) has a guaranteed input leakage of +/-25nA max over temperature. The typical comparator delay is 15µs from VIL to VOL (power failing), and 55µs from VIH to VOH (power being restored). Connect PFI to ground if not used. POWER-FAIL OUTPUT The Power-Fail Output (PFO) goes low when PFI falls below 1.25V. It sinks 3.2mA with a saturation voltage of 0.1V. With PFI above 1.25V, PFO is actively pulled to VOUT. Connecting PFI through a voltage divider to an unregulated supply allows PFO to generate an NMI as the unregulated power begins to fall (see Figure 9b). POWER-FAIL COMPARATOR The power-fail comparator is an uncommitted comparator that has no effect on the other functions of the SP791. Common uses include monitoring supplies other than 5V (see the Typical Operating Circuit and the Monitoring a Negative Voltage section) and early power-fail detection when the unregulated power is easily accessible as shown in Figure 9b. SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 12 © Copyright 2000 Sipex Corporation INPUT/OUTPUT STATES IN BATTERY-BACKUP MODE PIN NAME 1 VBATT Supply current is 1µA maximum When VCC < VBATT-1.2V 2 VOUT VOUT is connected to VBATT through an Internal PMOS switch. 3 VCC Battery-switchover comparator monitors VCC for active switchover. VCC is disconnected from VOUT 4 GND 5 BATT ON STATUS The power-fail comparator is disabled PFO is forced low. 7 PFI The power-fail comparator is disabled 8 SWT MR LOWLINE 11 WDI 12 CE OUT Corporation Figure 10. VCC and VBATT-to-VOUT Switch INPUT SUPPLY VOLTAGE The Input Supply Voltage (VCC) should be a regulated +5V source. VCC connects to VOUT via a parallel diode and a large PMOS switch (Figure 10). The switch carries the entire current load for currents less than 250mA. The parallel diode carries any current in excess of 250mA. The maximum continuous current is 250mA, but power-on transients may reach a maximum of 1A. SWT is Ignored. MR is ignored. Logic low. WDI is ignored, and goes high impedance. Logic high. The open-circuit output voltage is equal to VOUT. 13 CE IN High Impedance. 14 WDO Logic high. The open-circuit output voltage is equal to VOUT. 15 RESET Logic low. 16 WDPO Logic high. The open-circuit output voltage is equal to VOUT. BACKUP-BATTERY INPUT The Backup-Battery Input (VBATT) is similar to VCC, except the PMOS switch and parallel diode are much smaller. Continuous current should be limited to 25mA and peak currents (only during power-up) limited to 250mA. The reverse leakage of this input is less than 1µA over temperature and supply voltage. Table 1. Input/Output states in Battery-Backup mode To enter the Battery-Backup mode, VCC must be less than the Reset threshold and less than VBATT. BATTERY-BACKUP MODE The SP791 requires two conditions to switch to battery-backup mode: 1) VCC must be below the reset threshold; 2) V CC must be below VBATT. Table 1 lists the status of the inputs and outputs in battery-backup mode. OUTPUT SUPPLY VOLTAGE The Output Supply Voltage (VOUT) supplies all the current to the external system and internal circuitry. All open-circuit outputs will, for example, assume the VOUT voltage in their high states rather than the VCC voltage. At the maximum source current of 250mA, VOUT will typically be 200mV below VCC. VOUT should be decoupled with 0.1µF capacitor. BATTERY ON OUTPUT The Battery On Output (BATT ON) indicates the status of the internal VCC/battery-switchover comparator, which controls the internal V CC and VBATT switches. For VCC greater than VBATT (ignoring the small hysteresis effect), BATT ON is a logic low. For VCC less than VBATT, BATT ON is a logic high. Use BATT ON to indicate battery-switchover status or to supply base drive to an external pass transistor for higher-current applications (see Typical Operating Circuit). SP791DS/08 VOUT 0.1µF Vcc Logic high. The open-circuit output is equal to VOUT. PFO 9 2 GND-0V reference for all signals. 6 10 VBATT SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 13 © Copyright 2000 Sipex Corporation +5V RESET THRESHOLD Vcc 3 Vcc 1N4148 200ms TYP 1 VBATT VOUT 2 RESET ( 0.47F CE IN Corporation CE OUT GND 4 SECOND CE PULSE ABSENT WHEN VBATT < 2V Figure 11. Backup-Battery Monitor Timing Diagram Figure 12. High Capacity Capacitor on VBATT LOW-BATTERY MONITOR The SP791 low-battery voltage function monitors V BATT. Low-battery detection of 2.0V ±0.15V is monitored only during the resettimeout period (200ms) that occurs either after a normal power-up sequence or after the MR reset input has been returned to its high state. If the battery voltage is below 2.0V, the second CE pulse is inhibited after reset timeout. If the battery voltage is above 2.0V, all CE pulses are allowed through the CE gate after the reset timeout period. To use this function, after the 200ms reset delay, write 00 (HEX) to a location using the first CE pulse, and write FF (HEX) to the same location using the second CE pulse following RESET going inactive on power-up. The contents of the memory then indicates a good battery (FF) or a low battery (00), Figure 11. There are three distinct modes of operation: 1) Normal operating mode with all circuitry powered up from VCC. Typical supply current from VCC is 40µA, while only leakage currents flow from the battery. 2) Battery-backup mode where VCC is typically within 0.7V below VBATT. All circuitry is powered up from VBATT, and the supply current is typically less than 40µA. 3) Battery-backup mode where VCC is less than VBATT by at least 0.7V. VBATT supply current is less than 1µA. USING HIGH CAPACITY CAPACITOR WITH THE SP791 VBATT has the same operating voltage range as VCC, and the battery-switchover threshold voltages are typically +30mV centered at VBATT, allowing use of a capacitor and a simple charging circuit as a backup source (see Figure 12). If VCC is above the reset threshold and VBATT is 0.5V above VCC, current flows to VOUT and VCC from VBATT until the voltage at VBATT is less than 0.5V above VCC. TYPICAL APPLICATIONS The SP791 is not short-circuit protected. Shorting VOUT to ground, other than power-up transients such as charging a decoupling capacitor, may destroy the device. All open-circuit outputs swing between VOUT and GND rather than VCC and GND. If long leads connect to the chip inputs, ensure that these lines are free from ringing and other conditions that would forward bias the chip's protection diodes. ™ - REGISTERED TRADEMARK OF BAKNOR INDUSTRIES SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 14 © Copyright 2000 Sipex Corporation VIN Rp* +5V CE CE VOUT CE IN RAM 1 R1 Vcc PFI CE OUT CE CE C1* RAM 2 R3 Corporation R2 CE Corporation PFO RAM 3 GND CE GND CE * OPTIONAL FOR ADDITIONAL NOISE REJECTION TO µP RAM 4 +5V CE PFO OV OV * MAXIMUM Rp VALUE DEPENDS ON THE NUMBER OF RAM DEVICES. MINIMUM Rp VALUE IS 1KΩ VL VTRIPVH ( VTRIP = 1.25 * R1 + R2 R2 ACTIVE-HIGH CE LINES FROM LOGIC VH = 1.25 VIN ) ( R1 R2+ R2II R3II R3) VL - 1.25 + 5 - 1.25 = 1.25 R1 R3 R2 Figure 13. Alternate CE Gating Figure 14. Adding Hysteresis to the Power-Fail Comparator Leakage current through the capacitor charging diode and the SP791 internal power diode eventually discharges the capacitor to VCC. Also, if VCC and VBATT start from 0.5V above the reset threshold and power is lost at VCC, the capacitor on VBATT discharges through VCC until VBATT reaches the reset threshold; the SP791 then switches to battery-backup mode. 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 trip point. Figure 14 shows how to add hysteresis to the power-fail comparator. Select the ratio of R1 to R2 such that PFI sees 1.25V when VIN falls to the desired trip point (VTRIP). Resistor R3 adds hysteresis. It will typically be an order of magnitude greater than R1 or R2. The current through R1 and R2 should be at least 1µA to ensure that the 25nA (max) PFI input current does not shift the trip point. R3 should be larger than 10kΩ to prevent it from loading down the PFO pin. Capacitor C1 adds additional noise rejection. USING SEPARATE POWER SUPPLIES FOR VBATT AND VCC If using separate power supplies for VCC and VBATT, VBATT must be less than 0.3V above VCC when V CC is above the reset threshold. As described in the previous section, if VBATT exceeds this limit and power is lost at VCC, current flows continuously from VBATT to VCC via the VBATT-to-VOUT diode and the VOUT-to-VCC switch until the circuit is broken. ALTERNATIVE CHIP-ENABLE GATING Using memory devices with CE and CE inputs allows the SP791 CE loop to be bypassed. To do this, connect CE IN to ground, pull up CE OUT to VOUT, and connect CE OUT to the CE input of each memory device as shown in Figure 13. The CE input of each part then connects directly to the chip-select logic, which does not have to be gated by the SP791. SP791DS/08 MONITORING A NEGATIVE VOLTAGE The power-fail comparator can be used to monitor a negative supply voltage using the circuit shown in Figure 15. When the negative supply is valid, PFO is low. When the negative supply voltage drops, PFO goes high. This circuit's accuracy is affected by the PFI threshold tolerance, the VCC voltage, and resistors R1 and R2. BACKUP-BATTERY REPLACEMENT The backup battery may be disconnected while VCC is above the reset threshold. No precautions are necessary to avoid spurious reset pulses. SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 15 © Copyright 2000 Sipex Corporation +5V START R1 Vcc PFO PFI SET WDI LOW Corporation R2 SUBROUTINE OR PROGRAM LOOP SET WDI HIGH GND V– +5V PFO 0V V– VTRIP 0V RETURN 5 - 1.25 R1 = 1.25 - VTRIP R2 END NOTE: VTRIP IS NEGATIVE. Figure 15. Monitoring a Negative Voltage Figure 16. Watchdog Flow Diagram NEGATIVE-GOING VCC TRANSIENTS The SP791 is relatively immune to short-duration negative-going VCC transients resulting from power up, power down, and brownout conditions. It is usually undesirable to reset the µP when VCC experiences only small glitches. Typically, a VCC transient that goes 100mV below the reset threshold and lasts for 40µs or less will not cause a reset pulse to be issued. A 100nF bypass capacitor mounted close to the VCC pin provides additional transient immunity. This technique avoids a "stuck" loop where the watchdog timer continues to be reset within the loop, keeping the watchdog from timing out. Figure 16 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 or loop, then set low again when the program returns to the beginning. 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 or interrupt to be issued. CONNECTING A TIMING CAPACITOR TO THE SWT PIN To prevent timing errors minimize external current leakage sources at this pin, and locate the capacitor as close to SWT as possible. The sum of PC board leakage + SWT capacitor leakage must be small compared to ±100 nA. MAXIMUM VCC FALL TIME The VCC fall time is limited by the propagation delay of the battery switchover comparator and should not exceed 0.03V/µs. A standard rule of thumb for filter capacitance on most regulators is on the order of 100µF per amp of current. When the power supply is shut off or the main battery is disconnected, the associated initial VCC fall rate is just the inverse of 1A/100µF = 0.01V/µs. The VCC fall rate decreases with time as VCC falls exponentially, which more than satisfies the maximum fall-time requirement. WATCHDOG SOFTWARE CONSIDERATIONS A way to help the watchdog timer keep a closer watch on software execution involves setting and resetting the watchdog input at different points in the program, rather than "pulsing" the watchdog input high-low-high or low-high-low. SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 16 © Copyright 2000 Sipex Corporation PACKAGE: PLASTIC DUAL–IN–LINE (NARROW) E1 E D1 = 0.005" min. (0.127 min.) A1 = 0.015" min. (0.381min.) D A = 0.210" max. (5.334 max). C A2 L B1 B e = 0.100 BSC (2.540 BSC) Ø eA = 0.300 BSC (7.620 BSC) ALTERNATE END PINS (BOTH ENDS) DIMENSIONS (Inches) Minimum/Maximum (mm) SP791DS/08 8–PIN 14–PIN 16–PIN 18–PIN 20–PIN 22–PIN A2 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) 0.115/0.195 (2.921/4.953) B 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) 0.014/0.022 (0.356/0.559) B1 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) 0.045/0.070 (1.143/1.778) C 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) 0.008/0.014 (0.203/0.356) D 0.355/0.400 0.735/0.775 0.780/0.800 0.880/0.920 0.980/1.060 1.145/1.155 (9.017/10.160) (18.669/19.685) (19.812/20.320) (22.352/23.368) (24.892/26.924) (29.083/29.337) E 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) 0.300/0.325 (7.620/8.255) E1 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) 0.240/0.280 (6.096/7.112) L 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) 0.115/0.150 (2.921/3.810) Ø 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) 0°/ 15° (0°/15°) SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 17 © Copyright 2000 Sipex Corporation PACKAGE: PLASTIC SMALL OUTLINE (SOIC) (NARROW) E H h x 45° D A Ø e B DIMENSIONS (Inches) Minimum/Maximum (mm) SP791DS/08 A1 L 8–PIN 14–PIN 16–PIN A 0.053/0.069 (1.346/1.748) 0.053/0.069 (1.346/1.748) 0.053/0.069 (1.346/1.748) A1 0.004/0.010 (0.102/0.249 0.004/0.010 (0.102/0.249) 0.004/0.010 (0.102/0.249) B 0.014/0.019 (0.35/0.49) 0.013/0.020 (0.330/0.508) 0.013/0.020 (0.330/0.508) D 0.189/0.197 (4.80/5.00) 0.337/0.344 0.386/0.394 (8.552/8.748) (9.802/10.000) E 0.150/0.157 (3.802/3.988) 0.150/0.157 (3.802/3.988) 0.150/0.157 (3.802/3.988) e 0.050 BSC (1.270 BSC) 0.050 BSC (1.270 BSC) 0.050 BSC (1.270 BSC) H 0.228/0.244 (5.801/6.198) 0.228/0.244 (5.801/6.198) 0.228/0.244 (5.801/6.198) h 0.010/0.020 (0.254/0.498) 0.010/0.020 (0.254/0.498) 0.010/0.020 (0.254/0.498) L 0.016/0.050 (0.406/1.270) 0.016/0.050 (0.406/1.270) 0.016/0.050 (0.406/1.270) Ø 0°/8° (0°/8°) 0°/8° (0°/8°) 0°/8° (0°/8°) SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 18 © Copyright 2000 Sipex Corporation ORDERING INFORMATION Model Temperature Range Package SP791CP ................................................................................... 0˚C to +70˚C .............................................................................. 16-pin, Plastic DIP SP791CN ................................................................................... 0˚C to +70˚C .......................................................................... 16-pin, Narrow SOIC SP791EP .................................................................................... -40˚C to +85˚C .......................................................................... 16–pin, Plastic Dip SP791EN ................................................................................... -40˚C to +85˚C ..................................................................... 16–pin, Narrow SOIC Please consult the factory for pricing and availability on a Tape-On-Reel option. Corporation SIGNAL PROCESSING EXCELLENCE Sipex Corporation Headquarters and Sales Office 22 Linnell Circle Billerica, MA 01821 TEL: (978) 667-8700 FAX: (978) 670-9001 e-mail: [email protected] Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described hereing; neither does it convey any license under its patent rights nor the rights of others. SP791DS/08 SP791 Low Power Microprocessor Supervisory with Battery Switch-Over 19 © Copyright 2000 Sipex Corporation