ADM693AN

a FEATURES Superior Upgrade for MAX690–MAX695 Specified Over Temperature Low Power Consumption (5 mW) Precision Voltage Monitor Reset Assertion Down to 1 V V CC Low Switch On-Resistance 1.5 Normal, 20 in Backup High Current Drive (100 mA) Watchdog Timer—100 ms, 1.6 s, or Adjustable 600 nA Standby Current Automatic Battery Backup Power Switching Extremely Fast Gating of Chip Enable Signals (5 ns) Voltage Monitor for Power Fail APPLICATIONS Microprocessor Systems Computers Controllers Intelligent Instruments Automotive Systems GENERAL DESCRIPTION VBATT VBATT VCC Microprocessor Supervisory Circuits ADM690–ADM695 FUNCTIONAL BLOCK DIAGRAMS VOUT 4.65V 1 RESET GENERATOR 2 RESET WATCHDOG INPUT (WDI) POWER FAIL INPUT (PFI) WATCHDOG TRANSITION DETECTOR (1.6s) ADM690 ADM692 ADM694 POWER FAIL OUTPUT (PFO) 1.3V 1 VOLTAGE 2 RESET DETECTOR = 4.65V (ADM690, ADM694) 4.40V (ADM692) PULSE WIDTH = 50ms (ADM690, ADM692) 200ms (ADM694) BATT ON The ADM690–ADM695 family of supervisory circuits offers complete single chip solutions for power supply monitoring and battery control functions in microprocessor systems. These functions include µP reset, backup battery switchover, watchdog timer, CMOS RAM write protection, and power failure warning. The complete family provides a variety of configurations to satisfy most microprocessor system requirements. The ADM690, ADM692 and ADM694 are available in 8-pin DIP packages and provide: 1. Power-on reset output during power-up, power-down and brownout conditions. The RESET output remains operational with VCC as low as 1 V. 2. Battery backup switching for CMOS RAM, CMOS microprocessor or other low power logic. 3. A reset pulse if the optional watchdog timer has not been toggled within a specified time. 4. A 1.3 V threshold detector for power fail warning, low battery detection, or to monitor a power supply other than +5 V. The ADM691, ADM693 and ADM695 are available in 16-pin DIP and small outline packages and provide three additional functions. 1. Write protection of CMOS RAM or EEPROM. 2. Adjustable reset and watchdog timeout periods. 3. Separate watchdog timeout, backup battery switchover, and low VCC status outputs. R EV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. VOUT VCC CE IN ADM691 ADM693 ADM695 CE OUT 4.65V 1 LOW LINE RESET OSC IN OSC SEL RESET & WATCHDOG TIMEBASE RESET GENERATOR RESET WATCHDOG INPUT (WDI) POWER FAIL INPUT (PFI) WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER WATCHDOG OUTPUT (WDO) POWER FAIL OUTPUT (PFO) 1.3V 1VOLTAGE DETECTOR = 4.65V (ADM691, ADM695) 4.40V (ADM693) The ADM690–ADM695 family is fabricated using an advanced epitaxial CMOS process combining low power consumption (5 mW), extremely fast Chip Enable gating (5 ns) and high reliability. RESET assertion is guaranteed with VCC as low as 1 V. In addition, the power switching circuitry is designed for minimal voltage drop thereby permitting increased output current drive of up to 100 mA without the need for an external pass transistor. © Analog Devices, Inc., 1996 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703 ADM690–ADM695–SPECIFICATIONS Parameter BATTERY BACKUP SWITCHING VCC Operating Voltage Range ADM690, ADM691, ADM694, ADM695 ADM692, ADM693 VBATT Operating Voltage Range ADM690, ADM691, ADM694, ADM695 ADM692, ADM693 VOUT Output Voltage VOUT in Battery Backup Mode Supply Current (Excludes IOUT) Supply Current in Battery Backup Mode Battery Standby Current (+ = Discharge, – = Charge) Battery Switchover Threshold VCC – VBATT Battery Switchover Hysteresis BATT ON Output Voltage BATT ON Output Short Circuit Current 0.5 RESET AND WATCHDOG TIMER Reset Voltage Threshold ADM690, ADM691, ADM694, ADM695 ADM692, ADM693 Reset Threshold Hysteresis Reset Timeout Delay ADM690, ADM691, ADM692, ADM693 ADM694, ADM695 Watchdog Timeout Period, Internal Oscillator Watchdog Timeout Period, External Clock Minimum WDI Input Pulse Width RESET Output Voltage @ VCC = +1 V RESET, LOW LINE Output Voltage RESET, WDO Output Voltage Output Short Circuit Source Current Output Short Circuit Sink Current WDI Input Threshold Logic Low Logic High WDI Input Current POWER FAIL DETECTOR PFI Input Threshold PFI Input Current PFO Output Voltage PFO Short Circuit Source Current PFO Short Circuit Sink Current CHIP ENABLE GATING CEIN Threshold 3.0 CEIN Pull-Up Current CEOUT Output Voltage VOUT – 1.5 VOUT – 0.05 CE Propagation Delay 5 3 3.5 1 3 25 Min Typ 4.75 4.5 2.0 2.0 VCC – 0.05 VCC – 0.025 VCC – 0.5 VCC – 0.25 VBATT – 0.05 VBATT – 0.02 1 0.6 –0.1 –1.0 70 50 20 (VCC = Full Operating Range, VBATT = +2.8 V, TA = TMIN to TMAX unless otherwise noted) Max Units Test Conditions/Comments 5.5 5.5 4.25 4.0 V V V V V V V mA µA µA µA mV mV mV V mA µA 1.95 1 +0.02 +0.02 IOUT = 1 mA IOUT ≤ 100 mA IOUT = 250 µA, VCC < VBATT – 0.2 V IOUT = 100 mA VCC = 0 V, VBATT = 2.8 V 5.5 V > VCC > VBATT + 0.2 V TA = +25°C Power Up Power Down ISINK = 3.2 mA BATT ON = VOUT = 4.5 V Sink Current BATT ON = 0 V Source Current 0.3 35 1 25 4.5 4.25 4.65 4.4 40 50 200 1.6 100 4.73 4.48 V V mV ms ms s ms Cycles Cycles ns mV V V V V µA mA V V µA µA V nA V V µA mA V V µA V V V ns OSC SEL = HIGH, VCC = 5 V, TA = +25°C OSC SEL = HIGH, VCC = 5 V, TA = +25°C Long Period, VCC = 5 V, TA = +25°C Short Period, VCC = 5 V, TA = +25°C Long Period Short Period VIL = 0.4, VIH = 3.5 V ISINK = 10 µA, VCC = 1 V ISINK = 1.6 mA, VCC = 4.25 V ISOURCE = 1 µA, VCC = 5 V ISINK = 1.6 mA, VCC = 5 V ISOURCE = 1 µA, VCC = 4.25 V 35 140 1.0 70 3840 768 50 70 280 2.25 140 4097 1025 200 0.4 0.4 25 4 3.5 VCC = 5 V1 0.8 3.5 –50 1.25 –25 3.5 1 20 –15 1.3 ± 0.01 50 WDI = VOUT, TA = +25°C WDI = 0 V, TA = +25°C VCC = +5 V ISINK = 3.2 mA ISOURCE = 1 µA PFI = Low, PFO = 0 V PFI = High, PFO = VOUT VIL VIH ISINK = 3.2 mA ISOURCE = 3.0 mA ISOURCE = 1 µA, VCC = 0 V 1.35 +25 0.4 25 3 25 0.8 0.4 9 –2– REV. A ADM690–ADM695 Parameter OSCILLATOR OSC IN Input Current OSC SEL Input Pull-Up Current OSC IN Frequency Range OSC IN Frequency with External Capacitor Min Typ ±2 5 0 4 250 Max Units µA µA kHz kHz Test Conditions/Comments OSC SEL = 0 V OSC SEL = 0 V, COSC = 47 pF NOTE 1 WDI is a three level input which is internally biased to 38% of V CC and has an input impedance of approximately 125 k Ω. Specifications subject to change without notice. ABSOLUTE MAXIMUM RATINGS* (TA = +25°C unless otherwise noted) ORDERING GUIDE Model Temperature Range Package Option VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V All Other Inputs . . . . . . . . . . . . . . . . . . –0.3 V to VOUT + 0.5 V Input Current VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 mA VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 mA GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA Power Dissipation, N-8 DIP . . . . . . . . . . . . . . . . . . . . 400 mW θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 120°C/W Power Dissipation, Q-8 DIP . . . . . . . . . . . . . . . . . . . . 500 mW θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 125°C/W Power Dissipation, N-16 DIP . . . . . . . . . . . . . . . . . . . 600 mW θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 135°C/W Power Dissipation, Q-16 DIP . . . . . . . . . . . . . . . . . . . 600 mW θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 100°C/W Power Dissipation, R-16 SOIC . . . . . . . . . . . . . . . . . . 600 mW θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 110°C/W Operating Temperature Range Industrial (A Version) . . . . . . . . . . . . . . . . . –40°C to +85°C Extended (S Version) . . . . . . . . . . . . . . . . . –55°C to +125°C Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . . +300°C Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . . +215°C Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C *Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum ratings for extended periods of time may affect device reliability. ADM690AN ADM690AQ ADM690SQ ADM691AN ADM691AR ADM691AQ ADM691SQ ADM692AN ADM692AQ ADM692SQ ADM693AN ADM693AR ADM693AQ ADM693SQ ADM694AN ADM694AQ ADM694SQ ADM695AN ADM695AR ADM695AQ ADM695SQ –40°C to +85°C –40°C to +85°C –55°C to +125°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –55°C to +125°C –40°C to +85°C –40°C to +85°C –55°C to +125°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –55°C to +125°C –40°C to +85°C –40°C to +85°C –55°C to +125°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –55°C to +125°C N-8 Q-8 Q-8 N-16 R-16 Q-16 Q-16 N-8 Q-8 Q-8 N-16 R-16 Q-16 Q-16 N-8 Q-8 Q-8 N-16 R-16 Q-16 Q-16 CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADM690–ADM695 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. WARNING! ESD SENSITIVE DEVICE REV. A –3– ADM690–ADM695 PIN FUNCTION DESCRIPTION Mnemonic Function VCC VBATT VOUT GND RESET Power Supply Input: +5 V Nominal. Backup Battery Input. Connect to Ground if a backup battery is not used. Output Voltage, VCC or VBATT is internally switched to VOUT depending on which is at the highest potential. VOUT can supply up to 100 mA to power CMOS RAM. Connect VOUT to VCC if VOUT and VBATT are not used. 0 V. Ground reference for all signals. Logic Output. RESET goes low if 1. VCC falls below the Reset Threshold 2. VCC falls below VBATT 3. The watchdog timer is not serviced within its timeout period. The reset threshold is typically 4.65 V for the ADM690/ADM691/ADM694/ADM695 and 4.4 V for the ADM692 and ADM693. RESET remains low for 50 ms (ADM690/ADM691/ADM692/ADM693) or 200 ms (ADM694/ADM695) after VCC returns above the threshold. RESET also goes low for 50 (200) ms if the watchdog timer is enabled but not serviced within its timeout period. The RESET pulse width can be adjusted on the ADM691/ADM693/ADM695 as shown in Table I. The RESET output has an internal 3 µA pull up, and can either connect to an open collector Reset bus or directly drive a CMOS gate without an external pull-up resistor. WDI Watchdog Input. WDI is a three level input. If WDI remains either high or low for longer than the watchdog timeout period, RESET pulses low and WDO goes low. The timer resets with each transition on the WDI line. The watchdog timer may be disabled if WDI is left floating or is driven to midsupply. Power Fail Input. PFI is the noninverting input to the Power Fail Comparator when PFI is less than 1.3 V, PFO goes low. Connect PFI to GND or VOUT when not used. Power Fail Output. PFO is the output of the Power Fail Comparator. It goes low when PFI is less than 1.3 V. The comparator is turned off and PFO goes low when VCC is below VBATT. Logic Input. The input to the CE gating circuit. Connect to GND or VOUT if not used. Logic Output. CEOUT is a gated version of the CEIN signal. CEOUT tracks CEIN when VCC is above the reset threshold. If VCC is below the reset threshold, CEOUT is forced high. See Figures 5 and 6. Logic Output. BATT ON goes high when VOUT is internally switched to the VBATT input. It goes low when VOUT is internally switched to VCC. The output typically sinks 35 mA and can directly drive the base of an external PNP transistor to increase the output current above the 100 mA rating of VOUT. Logic Output. LOW LINE goes low when VCC falls below the reset threshold. It returns high as soon as VCC rises above the reset threshold. Logic Output. RESET is an active high output. It is the inverse of RESET. Logic Oscillator Select Input. When OSC SEL is unconnected (floating) or driven high, the internal oscillator sets the reset active time and watchdog timeout period. When OSC SEL is low, the external oscillator input, OSC IN, is enabled. OSC SEL has a 3 µA internal pull up, (see Table I). Oscillator Logic Input. With OSC SEL low, OSC IN can be driven by an external clock signal or an external capacitor can be connected between OSC IN and GND. This sets both the reset active pulse timing and the watchdog timeout period (see Table I and Figure 4). With OSC SEL high or floating, the internal oscillator is enabled and the reset active time is fixed at 50 ms typ. (ADM691/ADM693) or 200 ms typ (ADM695). In this mode the OSC IN pin selects between fast (100 ms) and slow (1.6 s) watchdog timeout periods. In both modes, the timeout period immediately after a reset is 1.6 s typical. Logic Output. The Watchdog Output, WDO, goes low if WDI remains either high or low for longer than the watchdog timeout period. WDO is set high by the next transition at WDI. If WDI is unconnected or at midsupply, the watchdog timer is disabled and WDO remains high. WDO also goes high when LOW LINE goes low. PFI PFO CEIN CEOUT BATT ON LOW LINE RESET OSC SEL OSC IN WDO –4– REV. A ADM690–ADM695 PIN CONFIGURATIONS VBATT 1 VOUT 2 V CC 16 RESET 3 4 GND ADM691 ADM693 ADM695 TOP VIEW (Not to Scale) 15 RESET 14 WDO 13 CE 12 IN OUT VOUT V CC 1 2 3 4 BATT ON 5 LOW LINE 6 OSC IN 7 CE ADM690 ADM692 ADM694 TOP VIEW (Not to Scale) 8 7 6 5 VBATT RESET WDI PFO GND PFI 11 WDI 10 9 PFO PFI OSC SEL 8 PRODUCT SELECTION GUIDE Part Number Nominal Reset Time Nominal VCC Reset Threshold Nominal Watchdog Timeout Period Battery Backup Switching Base Drive Ext PNP Chip Enable Signals ADM690 ADM691 ADM692 ADM693 ADM694 ADM695 50 ms 50 ms or ADJ 50 ms 50 ms or ADJ 200 ms 200 ms or ADJ 4.65 V 4.65 V 4.4 V 4.4 V 4.65 V 4.65 V 1.6 s 100 ms, 1.6 s, ADJ 1.6 s 100 ms, 1.6 s, ADJ 1.6 s 100 ms, 1.6 s, ADJ Yes Yes Yes Yes Yes Yes No Yes No Yes No Yes No Yes No Yes No Yes CIRCUIT INFORMATION Battery Switchover Section The battery switchover circuit compares VCC to the VBATT input, and connects VOUT to whichever is higher. Switchover occurs when VCC is 50 mV higher than VBATT as VCC falls, and when VCC is 70 mV greater than VBATT as VCC rises. This 20 mV of hysteresis prevents repeated rapid switching if VCC falls very slowly or remains nearly equal to the battery voltage. If the continuous output current requirement at VOUT exceeds 100 mA or if a lower VCC–VOUT voltage differential is desired, an external PNP pass transistor may be connected in parallel with the internal transistor. The BATT ON output (ADM691/ ADM693/ADM695) can directly drive the base of the external transistor. A 20 Ω MOSFET switch connects the VBATT input to VOUT during battery backup. This MOSFET has very low input-tooutput differential (dropout voltage) at the low current levels required for battery back up of CMOS RAM or other low power CMOS circuitry. The supply current in battery back up is typically 0.6 µA. The ADM690/ADM691/ADM694/ADM695 operates with battery voltages from 2.0 V to 4.25 V and the ADM692/ADM693 operates with battery voltages from 2.0 V to 4.0 V. High value capacitors, either standard electrolytic or the farad size double layer capacitors, can also be used for short-term memory back up. A small charging current of typically 10 nA (0.1 µA max) flows out of the VBATT terminal. This current is useful for maintaining rechargeable batteries in a fully charged condition. This extends the life of the back up battery by compensating for its self discharge current. Also note that this current poses no problem when lithium batteries are used for back up since the maximum charging current (0.1 µA) is safe for even the smallest lithium cells. If the battery-switchover section is not used, VBATT should be connected to GND and VOUT should be connected to VCC. Figure 1. Battery Switchover Schematic During normal operation with VCC higher than VBATT, VCC is internally switched to VOUT via an internal PMOS transistor switch. This switch has a typical on-resistance of 1.5 Ω and can supply up to 100 mA at the VOUT terminal. VOUT is normally used to drive a RAM memory bank which may require instantaneous currents of greater than 100 mA. If this is the case then a bypass capacitor should be connected to VOUT. The capacitor will provide the peak current transients to the RAM. A capacitance value of 0.1 µF or greater may be used. REV. A –5– ADM690–ADM695 POWER FAIL RESET OUTPUT Watchdog Timer RESET RESET is an active low output which provides a RESET signal to the Microprocessor whenever VCC is at an invalid level. When VCC falls below the reset threshold, the RESET output is forced low. The nominal reset voltage threshold is 4.65 V (ADM690/ ADM691/ADM694/ADM695) or 4.4 V (ADM692/ADM693). VCC V2 V1 V2 V1 RESET t1 t1 LOW LINE The watchdog timer circuit monitors the activity of the microprocessor in order to check that it is not stalled in an indefinite loop. An output line on the processor is used to toggle the Watchdog Input (WDI) line. If this line is not toggled within the selected timeout period, a RESET pulse is generated. The nominal watchdog timeout period is preset at 1.6 seconds on the ADM690/ADM692/ADM694. The ADM691/ADM693/ADM695 may be configured for either a fixed “short” 100 ms or a “long” 1.6 second timeout period or for an adjustable timeout period. If the “short” period is selected, some systems may be unable to service the watchdog timer immediately after a reset, so the ADM691/ADM693/ADM695 automatically selects the “long” timeout period directly after a reset is issued. The watchdog timer is restarted at the end of reset, whether the reset was caused by lack of activity on WDI or by VCC falling below the reset threshold. The normal (short) timeout period becomes effective following the first transition of WDI after RESET has gone inactive. The watchdog timeout period restarts with each transition on the WDI pin. To ensure that the watchdog timer does not time out, either a high-to-low or low-to-high transition on the WDI pin must occur at or less than the minimum timeout period. If WDI remains permanently either high or low, reset pulses will be issued after each “long” timeout period (1.6 s). The watchdog monitor can be deactivated by floating the Watchdog Input (WDI) or by connecting it to midsupply. t1 = RESET TIME. V1 = RESET VOLTAGE THRESHOLD LOW V2 = RESET VOLTAGE THRESHOLD HIGH HYSTERESIS = V2–V1 Figure 2. Power Fail Reset Timing On power-up RESET will remain low for 50 ms (200 ms for ADM694 and ADM695) after VCC rises above the appropriate reset threshold. This allows time for the power supply and microprocessor to stabilize. On power-down, the RESET output remains low with VCC as low as 1 V. This ensures that the microprocessor is held in a stable shutdown condition. This RESET active time is adjustable on the ADM691/ADM693/ ADM695 by using an external oscillator or by connecting an external capacitor to the OSC IN pin. Refer to Table I and Figure 4. The guaranteed minimum and maximum thresholds of the ADM690/ADM691/ADM694/ADM695 are 4.5 V and 4.73 V, while the guaranteed thresholds of the ADM692/ADM693 are 4.25 V and 4.48 V. The ADM690/ADM691/ADM694/ADM695 is, therefore, compatible with 5 V supplies with a +10%, –5% tolerance while the ADM692/ADM693 is compatible with 5 V ± 10% supplies. The reset threshold comparator has approximately 50 mV of hysteresis. The response time of the reset voltage comparator is less than 1 µs. If glitches are present on the VCC line which could cause spurious reset pulses, then VCC should be decoupled close to the device. In addition to RESET the ADM691/ADM693/ADM695 contain an active high RESET output. This is the complement of RESET and is intended for processors requiring an active high RESET signal. WDI WDO t2 RESET t3 t1 t1 t1 t1 = RESET TIME. t2 = NORMAL (SHORT) WATCHDOG TIMEOUT PERIOD. t3 = WATCHDOG TIMEOUT PERIOD IMMEDIATELY FOLLOWING A RESET. Figure 3. Watchdog Timeout Period and Reset Active Time –6– REV. A ADM690–ADM695 Table I. ADM691, ADM693, ADM695 Reset Pulse Width and Watchdog Timeout Selections Watchdog Timeout Period Immediately Normal After Reset Reset Active Period ADM691/ADM693 ADM695 OSC SEL OSC IN Low Low Floating or High Floating or High External Clock Input External Capacitor Low Floating or High 1024 CLKS 260 ms × C/47 pF 100 ms 1.6 s 4096 CLKS 1.04 s × C/47 pF 1.6 s 1.6 s 512 CLKS 130 ms × C/47 pF 50 ms 50 ms 2048 CLKS 520 ms × C/47 pF 200 ms 200 ms NOTE With the OSC SEL pin low, OSC IN can be driven by an external clock signal, or an external capacitor can be connected between OSC IN and GND. The nominal internal oscillator frequency is 10.24 kHz. The nominal oscillator frequency with external capacitor is: F OSC (Hz) = 184,000/C (pF). The watchdog timeout period is fixed at 1.6 seconds, and the reset pulse width is fixed at 50 ms on the ADM690/ADM692. On the ADM694 the watchdog timeout period is also 1.6 seconds but the reset pulse width is fixed at 200 ms. The ADM691/ ADM693/ADM695 allow these times to be adjusted as shown in Table I. Figure 4 shows the various oscillator configurations which can be used to adjust the reset pulse width and watchdog timeout period. The internal oscillator is enabled when OSC SEL is high or floating. In this mode, OSC IN selects between the 1.6 second and 100 ms watchdog timeout periods. With OSC IN connected high or floating, the 1.6 second timeout period is selected; while with it connected low, the 100 ms timeout period is selected. In either case, immediately after a reset, the timeout period is 1.6 seconds. This gives the microprocessor time to reinitialize the system. If OSC IN is low, then the 100 ms watchdog period becomes effective after the first transition of WDI. The software should be written such that the I/O port driving WDI is left in its power-up reset state until the initialization routines are completed and the microprocessor is able to toggle WDI at the minimum watchdog timeout period of 70 ms. Watchdog Output (WDO) 8 OSC SEL ADM691 ADM693 ADM695 7 OSC IN COSC Figure 4b. External Capacitor NC 8 OSC SEL ADM691 ADM693 ADM695 7 NC OSC IN The Watchdog Output WDO (ADM691/ADM693/ADM695) provides a status output which goes low if the watchdog timer “times out” and remains low until set high by the next transition on the Watchdog Input. WDO is also set high when VCC goes below the reset threshold. 8 OSC SEL Figure 4c. Internal Oscillator (1.6 Second Watchdog) NC 8 OSC SEL ADM691 ADM693 ADM695 7 OSC IN CLOCK 0 TO 250kHz 7 OSC IN ADM691 ADM693 ADM695 Figure 4d. Internal Oscillator (100 ms Watchdog) Figure 4a. External Clock Source REV. A –7– ADM690–ADM695 CE Gating and RAM Write Protection (ADM691/ADM693/ ADM695) Power Fail Warning Comparator The ADM691/ADM693/ADM695 products include memory protection circuitry which ensures the integrity of data in memory by preventing write operations when VCC is at an invalid level. There are two additional pins, CEIN and CEOUT, which may be used to control the Chip Enable or Write inputs of CMOS RAM. When VCC is present, CEOUT is a buffered replica of CEIN, with a 5 ns propagation delay. When VCC falls below the reset voltage threshold or VBATT, an internal gate forces CEOUT high, independent of CEIN. CEOUT typically drives the CE, CS, or write input of battery backed up CMOS RAM. This ensures the integrity of the data in memory by preventing write operations when VCC is at an invalid level. Similar protection of EEPROMs can be achieved by using the CEOUT to drive the store or write inputs. If the 5 ns typical propagation delay of CEOUT is excessive, connect CEIN to GND and use the resulting CEOUT to control a high speed external logic gate. ADM69x CE IN CEOUT An additional comparator is provided for early warning of failure in the microprocessor’s power supply. The Power Fail Input (PFI) is compared to an internal +1.3 V reference. The Power Fail Output (PFO) goes low when the voltage at PFI is less than 1.3 V. Typically PFI is driven by an external voltage divider which senses either the unregulated dc input to the system’s 5 V regulator or the regulated 5 V output. The voltage divider ratio can be chosen such that the voltage at PFI falls below 1.3 V several milliseconds before the +5 V power supply falls below the reset threshold. PFO is normally used to interrupt the microprocessor so that data can be stored in RAM and the shut down procedure executed before power is lost INPUT POWER R1 1.3V POWER FAIL INPUT PFO POWER FAIL OUTPUT R2 ADM69x VCC LOW = 0 VCC OK = 1 Figure 7. Power Fail Comparator Table II. Input and Output Status In Battery Backup Mode Figure 5. Chip Enable Gating VCC V2 V1 V2 V1 Signal Status VOUT RESET VOUT is connected to VBATT via an internal PMOS switch. Logic low. Logic high. The open circuit output voltage is equal to VOUT. Logic low. Logic high. The open circuit voltage is equal to VOUT. WDI is ignored. It is internally disconnected from the internal pull-up resistor and does not source or sink current as long as its input voltage is between GND and VOUT. The input voltage does not affect supply current. Logic high. The open circuit voltage is equal to VOUT. The Power Fail Comparator is turned off and has no effect on the Power Fail Output. Logic low. CEIN is ignored. It is internally disconnected from its internal pull-up and does not source or sink current as long as its input voltage is between GND and VOUT. The input voltage does not affect supply current. Logic high. The open circuit voltage is equal to VOUT. OSC IN is ignored. OSC SEL is ignored. REV. A RESET t1 t1 RESET LOW LINE LOW LINE BATT ON WDI CEIN WDO CEOUT PFI t1 = RESET TIME. V1 = RESET VOLTAGE THRESHOLD LOW V2 = RESET VOLTAGE THRESHOLD HIGH HYSTERESIS = V2–V1 PFO CEIN Figure 6. Chip Enable Timing CEOUT OSC IN OSC SEL –8– Typical Performance Curves–ADM690–ADM695 5.00 VCC = 5V TA = +25°C 4.95 2.80 VCC = 0V VBATT = +2.8V TA = +25°C A4 100 90 3.36 V 2.79 VOUT – V VOUT – V 4.90 SLOPE = 1.5Ω 4.85 2.78 SLOPE = 20Ω 2.77 10 0% 1V 4.80 0 20 40 60 80 100 IOUT – mA 1V 500ms 2.76 0 200 400 600 IOUT – µA 800 1000 Figure 8. VOUT vs. IOUT Normal Operation Figure 9. VOUT vs. IOUT Battery Backup Figure 10. Reset Output Voltage vs. Supply Voltage 1.303 53 RESET VOLTAGE THRESHOLD – V VCC = +5V 4.70 VCC = +5V 4.68 POWER-UP 4.66 ADM690 ADM691 ADM694 ADM695 PFI INPUT THRESHOLD – V 1.302 RESET ACTIVE TIME – ms 52 1.301 51 ADM690 ADM691 ADM692 ADM693 1.300 50 4.64 POWER-DOWN 1.299 20 49 40 60 80 100 120 4.62 20 40 60 80 100 TEMPERATURE – °C 120 20 40 60 80 100 TEMPERATURE – °C 120 TEMPERATURE – °C Figure 11. PFI Input Threshold vs. Temperature Figure 12. Reset Active Time vs. Temperature Figure 13. Reset Voltage Threshold vs. Temperature 6 5 4 3 2 1 0 VPFI 1.3V PFO 30pF VCC = 5V TA = +25 °C 6 5 4 3 2 1 0 VPFI 1.3V PFO 30pF VCC = 5V TA = +25 °C 6 5 4 3 2 1 0 VPFI 1.3V PFO 30pF +5V 10k VCC = 5V TA = +25 °C 1.35 1.25 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 TIME – µs 1.35 1.25 0 10 20 30 40 50 60 TIME – µs 70 80 90 1.35 1.25 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 TIME – µs Figure 14. Power Fail Comparator Response Time Figure 15. Power Fail Comparator Response Time Figure 16. Power Fail Comparator Response Time with Pull-Up Resistor REV. A –9– ADM690–ADM695 +APPLICATION INFORMATION Increasing the Drive Current If the continuous output current requirements at VOUT exceed 100 mA or if a lower VCC–VOUT voltage differential is desired, an external PNP pass transistor may be connected in parallel with the internal transistor. The BATT ON output (ADM691/ ADM693/ADM695) can directly drive the base of the external transistor. PNP TRANSISTOR +5V INPUT POWER 0.1µF 0.1µF When PFO is low, resistor R3 sinks current from the summing junction at the PFI pin. When PFO is high, the series combination of R3 and R4 source current into the PFI summing junction. This results in differing trip levels for the comparator. +7V TO +15V INPUT POWER R1 7805 +5V VCC R4 1.3V PFI R2 PFO TO µP NMI ADM69x R3 VCC VBATT BATTERY BATT ON VOUT ADM691 ADM693 ADM695 5V Figure 17. Increasing the Drive Current Using a Rechargeable Battery for Back Up PFO If a capacitor or a rechargeable battery is used for back up then the charging resistor should be connected to VOUT since this eliminates the discharge path that would exist during power down if the resistor is connected to VCC. I = VOUT – V BATT +5V INPUT POWER R 0V 0V VL VIN VH R1 R1 VH = 1.3V 1+ ––– + ––– R3 R2 ( ) ) 0.1µF R 0.1µF R1 (5V – 1.3V) R1 VL = 1.3V 1+ ––– – ––––––––––––– 1.3V (R 3 + R4 ) R2 ( ASSUMING R 4 < < R3 THEN VCC VBATT RECHARGEABLE BATTERY VOUT R1 HYSTERESIS V H – VL = 5V ––– R2 ( ) Figure 19. Adding Hysteresis to the Power Fail Comparator ADM69x Monitoring the Status of the Battery Figure 18. Rechargeable Battery Adding Hysteresis to the Power Fail Comparator For increased noise immunity, hysteresis may be added to the power fail comparator. Since the comparator circuit is noninverting, hysteresis can be added simply by connecting a resistor between the PFO output and the PFI input as shown in Figure 19. The power fail comparator can be used to monitor the status of the backup battery instead of the power supply if desired. This is shown in Figure 20. The PFI input samples the battery voltage and generates an active low PFO signal when the battery voltage drops below a chosen threshold. It may be necessary to apply a test load in order to determine the loaded battery voltage. This can be done under processor control using CEOUT. Since CEOUT is forced high during the battery backup mode, the test load will not be applied to the battery while it is in use, even if the microprocessor is not powered. –10– REV. A ADM690–ADM695 +5V INPUT POWER VBATT BATTERY 10MΩ PFI 20kΩ OPTIONAL TEST LOAD 10MΩ CE OUT VCC PFO LOW BATTERY SIGNAL TO µP I/O PIN CEIN FROM µP I/O PIN APPLIES TEST LOAD TO BATTERY CONTROL INPUT* D1 D2 OSC SEL ADM69x OSC IN ADM69x *LOW = INTERNAL TIMEOUT HIGH = EXTERNAL TIMEOUT Figure 20. Monitoring the Battery Status Alternate Watchdog Input Drive Circuits Figure 21b. Programming the Watchdog Input Replacing the Backup Battery The watchdog feature can be enabled and disabled under program control by driving WDI with a 3-state buffer (Figure 21a). When three-stated, the WDI input will float thereby disabling the watchdog timer. WATCHDOG STROBE WDI When changing the backup battery with system power on, spurious resets can occur when the battery is removed. This occurs because the leakage current flowing out of the VBATT pin will charge up the stray capacitance. If the voltage on VBATT reaches within 50 mV of VCC, a reset pulse is generated. If spurious resets during battery replacement are acceptable, then no action is required. If not, then one of the following solutions should be considered: 1. A capacitor from VBATT to GND. This gives time while the capacitor is charging up to replace the battery. The leakage current will charge up the external capacitor towards the VCC level. The time taken is related to the charging current, the size of external capacitor and the voltage differential between the capacitor and the charging voltage supply. t = CEXT × VDIFF/I The maximum leakage (charging) current is 1 µA over temperature and VDIFF = VCC–VBATT. Therefore, the capacitor size should be chosen such that sufficient time is available to make the battery replacement. CEXT = TREQD (1 µA/(VCC–VBATT)) If a replacement time of 5 seconds is allowed and assuming a VCC of 4.5 V and a VBATT of 3 V CEXT = 3.33 µF VBATT BATTERY CEXT ADM69x CONTROL INPUT Figure 21a. Programming the Watchdog Input This circuit is not entirely foolproof, and it is possible that a software fault could erroneously 3-state the buffer. This would then prevent the ADM69x from detecting that the microprocessor is no longer operating correctly. In most cases a better method is to extend the watchdog period rather than disabling the watchdog. This may be done under program control using the circuit shown in Figure 21b. When the control input is high, the OSC SEL pin is low and the watchdog timeout is set by the external capacitor. A 0.01 µF capacitor sets a watchdog timeout delay of 100 seconds. When the control input is low, the OSC SEL pin is driven high, selecting the internal oscillator. The 100 ms or the 1.6 s period is chosen, depending on which diode in Figure 21b is used. With D1 inserted the internal timeout is set at 100 ms, while with D2 inserted the timeout is set at 1.6 s. ADM69x Figure 22a. Preventing Spurious RESETS During Battery Replacement 2. A resistor from VBATT to GND. This will prevent the voltage on VBATT from rising to within 50 mV of VCC during battery replacement. REV. A –11– ADM690–ADM695 R =(VCC – 50 mV)/1 µA Note that the resistor will discharge the battery slightly. With a VCC supply of 4.5 V, a suitable resistor is 4.3 MΩ. With a 3 V battery this will draw around 700 nA. This will be negligible in most cases. VBATT BATTERY R +5V R1 PFI R2 VCC VOUT µP POWER CMOS RAM POWER ADM690 ADM692 ADM694 RESET PFO GND WDI 0.1µF µP SYSTEM µP RESET µP NMI I/O LINE ADM69x + BATTERY VBATT Figure 22b. Preventing Spurious RESETS During Battery Replacement TYPICAL APPLICATIONS ADM690, ADM692 AND ADM694 Figure 23a. ADM690/ADM692/ADM694 Typical Application Circuit A Figure 23 shows the ADM690/ADM692/ADM694 in a typical power monitoring, battery backup application. VOUT powers the CMOS RAM. Under normal operating conditions with VCC present, VOUT is internally connected to VCC. If a power failure occurs, VCC will decay and VOUT will be switched to VBATT thereby maintaining power for the CMOS RAM. A RESET pulse is also generated when VCC falls below 4.65 V for the ADM690/ADM694 or 4.4 V for the ADM692. RESET will remain low for 50 ms (200 ms for ADM694) after VCC returns to 5 V. The watchdog timer input (WDI) monitors an I/O line from the µP system. This line must be toggled once every 1.6 seconds to verify correct software execution. Failure to toggle the line indicates that the µP system is not correctly executing its program and may be tied up in an endless loop. If this happens, a reset pulse is generated to initialize the processor. If the watchdog timer is not needed, the WDI input should be left floating. The Power Fail Input, PFI, monitors the input power supply via a resistive divider network. The voltage on the PFI input is compared with a precision 1.3 V internal reference. If the input voltage drops below 1.3 V, a power fail output (PFO) signal is generated. This warns of an impending power failure and may be used to interrupt the processor so that the system may be shut down in an orderly fashion. The resistors in the sensing network are ratioed to give the desired power fail threshold voltage VT. VT = (1.3 R1/R2) + 1.3 V R1/R2 = (VT/1.3) – 1 Figure 23b shows a similar application but in this case the PFI input monitors the unregulated input to the 7805 voltage regulator. This gives an earlier warning of an impending power failure. It is useful with processors operating at low speeds or where there are a significant number of housekeeping tasks to be completed before the power is lost. INPUT POWER V > 8V R1 PFI R2 7805 +5V 0.1µF µP POWER VOUT CMOS RAM POWER VCC ADM690 ADM692 ADM694 RESET PFO GND WDI 0.1µF µP SYSTEM µP RESET µP NMI I/O LINE VBATT BATTERY Figure 23b. ADM690/ADM692/ADM694 Typical Application Circuit B ADM691, ADM693, ADM695 A typical connection for the ADM691/ADM693/ADM695 is shown in Figure 24. CMOS RAM is powered from VOUT. When 5 V power is present this is routed to VOUT. If VCC fails then VBATT is routed to VOUT. VOUT can supply up to 100 mA from VCC, but if more current is required, an external PNP transistor can be added. When VCC is higher than VBATT, the BATT ON output goes low, providing up to 25 mA of base drive for the external transistor. A 0.1 µF capacitor is connected to VOUT to supply the transient currents for CMOS RAM. When VCC is lower than VBATT, an internal 20 Ω MOSFET connects the backup battery to VOUT. –12– REV. A ADM690–ADM695 INPUT POWER +5V 0.1µF VCC VBATT BATT ON VOUT CEOUT CE IN 0.1µF CMOS RAM ADDRESS DECODE A0–A15 WDI NC OSC IN OSC SEL PFO RESET RESET 0.1µF RAM Write Protection The ADM691/ADM693/ADM695 CEOUT line drives the Chip Select inputs of the CMOS RAM. CEOUT follows CEIN as long as VCC is above the 4.65 V (4.4 V for ADM693) reset threshold. If VCC falls below the reset threshold, CEOUT goes high, independent of the logic level at CEIN. This prevents the microprocessor from writing erroneous data into RAM during power-up, power-down, brownouts and momentary power interruptions. Watchdog Timer I/O LINE NMI RESET 3V BATTERY R1 PFI GND R2 ADM691 ADM693 ADM695 µP LOW LINE WDO SYSTEM STATUS INDICATORS Figure 24. ADM691/ADM693/ADM695 Typical Application Reset Output The internal voltage detector monitors VCC and generates a RESET output to hold the microprocessor’s Reset line low when VCC is below 4.65 V (4.4 V for ADM693). An internal timer holds RESET low for 50 ms (200 ms for the ADM695) after VCC rises above 4.65 V (4.4 V for ADM693). This prevents repeated toggling of RESET even if the 5 V power drops out and recovers with each power line cycle. The crystal oscillator normally used to generate the clock for microprocessors can take several milliseconds to stabilize. Since most microprocessors need several clock cycles to reset, RESET must be held low until the microprocessor clock oscillator has started. The power-up RESET pulse lasts 50 ms (200 ms for the ADM695) to allow for this oscillator start-up time. If a different reset pulse width is required, then a capacitor should be connected to OSC IN or an external clock may be used. Please refer to Table I and Figure 4. The manual reset switch and the 0.1 µF capacitor connected to the reset line can be omitted if a manual reset is not needed. An inverted, active high, RESET output is also available. Power Fail Detector The microprocessor drives the Watchdog Input (WDI) with an I/O line. When OSC IN and OSC SEL are unconnected, the microprocessor must toggle the WDI pin once every 1.6 seconds to verify proper software execution. If a hardware or software failure occurs such that WDI not toggled, the ADM691/ ADM693 will issue a 50 ms (200 ms for ADM695) RESET pulse after 1.6 seconds. This typically restarts the microprocessor’s power-up routine. A new RESET pulse is issued every 1.6 seconds until WDI is again strobed. If a different watchdog timeout period is required, then a capacitor should be connected to OSC IN or an external clock may be used. Please refer to Table I and Figure 4. The WATCHDOG OUTPUT (WDO) goes low if the watchdog timer is not serviced within its timeout period. Once WDO goes low, it remains low until a transition occurs at WDI. The watchdog timer feature can be disabled by leaving WDI unconnected. The RESET output has an internal 3 µA pull-up, and can either connect to an open collector reset bus or directly drive a CMOS gate without an external pull-up resistor. The +5 V VCC power line is monitored via a resistive potential divider connected to the Power Fail Input (PFI). When the voltage at PFI falls below 1.3 V, the Power Fail Output (PFO) drives the processor’s NMI input low. If for example a Power Fail threshold of 4.8 V is set with resistors R1 and R2, the microprocessor will have the time when VCC falls from 4.8 V to 4.65 V to save data into RAM. An earlier power fail warning can be generated if the unregulated dc input to the 5 V regulator is available for monitoring. This will allow more time for microprocessor housekeeping tasks to be completed before power is lost. REV. A –13– ADM690–ADM695 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Pin Plastic DIP (N-8) 8 PIN 1 1 5 0.280 (7.11) 0.240 (6.10) 4 0.430 (10.92) 0.348 (8.84) 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93) 0.060 (1.52) 0.015 (0.38) 0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93) 0.150 (3.81) MIN SEATING PLANE 0.015 (0.381) 0.008 (0.204) 0.022 (0.558) 0.014 (0.356) 0.100 (2.54) BSC 0.070 (1.77) 0.045 (1.15) 16-Lead Plastic DIP (N-16) 16 PIN 1 1 0.840 (21.33) 0.745 (18.93) 0.210 (5.33) 0.200 (5.05) 0.125 (3.18) 9 0.280 (7.11) 0.240 (6.10) 8 0.325 (8.25) 0.300 (7.62) 0.060 (1.52) 0.015 (0.38) 0.195 (4.95) 0.115 (2.93) 0.150 (3.81) 0.015 (0.381) 0.008 (0.204) 0.022 (0.558) 0.014 (0.356) 0.100 (2.54) BSC 0.070 (1.77) 0.045 (1.15) SEATING PLANE 8-Pin Cerdip (Q-8) 8 PIN 1 1 5 0.310 (7.87) 0.220 (5.59) 4 0.420 (10.67) MAX 0.320 (8.13) 0.290 (7.37) 0.200 (5.08) MAX 0.060 (1.52) 0.015 (0.38) SEATING PLANE 0.022 (0.558) 0.014 (0.356) 0.100 (2.54) BSC 0.070 (1.78) 0.30 (0.76) 0.150 (3.81) MIN 0.015 (0.381) 0.008 (0.204) –14– REV. A ADM690–ADM695 16-Lead Cerdip (Q-16) 16 PIN 1 1 0.840 (21.34) MAX 0.200 (5.08) MAX 9 0.310 (7.87) 0.220 (5.59) 8 0.320 (8.13) 0.290 (7.37) 0.060 (1.52) 0.015 (0.38) SEATING PLANE 0.022 (0.558) 0.014 (0.356) 0.100 (2.54) BSC 0.070 (1.78) 0.30 (0.76) 0.150 (3.81) MIN 0.015 (0.381) 0.008 (0.204) 16-Lead SOIC (R-16) 16 9 0.299 (7.60) 0.419 (10.65) 1 8 0.413 (10.50) 0.012 (0.3) 0.104 (2.65) 0.05 (1.27) REF 0.019 (0.49) 0.030 (0.75) 0.013 (0.32) 0.042 (1.07) REV. A –15– –16– C1782a–2–6/96 PRINTED IN U.S.A.