INTEGRATED CIRCUITS MAX708R/S/T 3 V microprocessor supervisor circuit with power fail comparator and manual reset Product data Supersedes data of 2003 Feb 13 2003 Aug 08 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T DESCRIPTION The MAX708R/S/T are microprocessor supervisory circuits used to monitor +3 V power supply levels in +3 V to +5 V microprocessor and other logic systems. The R, S, T suffixes have reset thresholds of 2.63 V, 2.93 V and 3.08 V, respectively. They reduce the number of circuit components, and improve reliability and accuracy compared to using separate ICs or discrete components. The MAX708R/S/T features make the MAX708R/S/T ideal for use in portable, battery operated equipment. The low supply current, typically 50 µA, minimizes battery load. Both RESET and RESET are active during power-up, power-down and brownout conditions An active-LOW manual reset input is also available. A 1.25 V threshold detector provides power-fail warning. This independent comparator can be used to monitor a second voltage supply and provide an early warning to the microprocessor that voltage is falling. This allows for an orderly shutdown, transmitting an alert to an operator, or activation of an alternate power source before the device asserts the reset signals. The device is available in the 8-pin SO package. FEATURES APPLICATIONS • RESET and RESET signals • Independent comparator with 1.25 V threshold for power failure or • Battery powered devices • Critical microprocessor monitoring • Controllers • Portable instruments low battery warning • Manual reset input • 50 µA quiescent current • Reset thresholds of 2.63, 2.93, and 3.08 V • Guaranteed RESET assertion to VCC = 1 V SIMPLIFIED SYSTEM DIAGRAM REGULATED DC SUPPLY (VCC) UNREGULATED DC SUPPLY MICROPROCESSOR VCC RESET VCC RESET RESET INPUT MAX708 R1 1% PFO INTERRUPT PFI R2 1% PUSH-BUTTON SWITCH MR GND GND SL01640 Figure 1. Simplified system diagram. 2003 Aug 08 2 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T ORDERING INFORMATION TYPE NUMBER MAX708xD PACKAGE TEMPERATURE RANGE NAME DESCRIPTION SO8 plastic small outline package; 8 leads (see dimensional drawing) NOTE: The device has 3 voltage output options, indicated by the ‘x’ on the ‘Type number’. Part number Threshold Voltage (Typical) MAX708RD 2.63 V MAX708SD MAX708TD Each device is marked with a four letter code. The first three letters designate the product. The fourth, represented by an ‘x’, designates the date tracking code. 2.93 V 3.08 V PIN CONFIGURATION 1 VCC 2 Part Marking MAX708RD ANEx MAX708SD ANDx MAX708TD ANCx PIN DESCRIPTION PIN TOP VIEW MR PFI 3 DESCRIPTION MR Manual reset input (Active-LOW). Triggers a reset pulse when pulled below 0.6 V. Connect to VCC or leave floating if not used. NC 2 VCC Supply voltage input. PFO 3 GND Ground. 4 PFI Power fail comparator input. When PFI is less than 1.25 V, PFO goes LOW, otherwise PFO remains HIGH. Connect to ground if not used. 5 PFO Power fail comparator output (Active-LOW). When voltage at PFI is less than 1.25 V, PFO goes LOW and sinks current. Do not connect if not used. 6 NC No connection. 7 RESET Active-LOW reset output. RESET is LOW if VCC is below the threshold voltage or if MR is held LOW. RESET is maintained for 200 ms after the reset conditions are terminated. 8 RESET Active-HIGH reset output. RESET is HIGH if VCC is below the threshold voltage or if MR is held LOW. RESET is maintained for 200 ms after the reset conditions are terminated. RESET 7 RESET 6 5 4 SYMBOL 1 8 SO8 GND –45 °C to +85 °C Marking code SL01639 Figure 2. Pin configuration. MAXIMUM RATINGS SYMBOL PARAMETER VCC Supply voltage Vn Other input pin voltage CONDITIONS Note 1 MIN. MAX. UNIT –0.3 6.0 V –0.3 VCC + 0.3 V Input current at VCC or GND – 20 mA Output current, all outputs – 20 mA Rate of rise at VCC – 100 V/µs Tamb Ambient temperature –40 +85 °C Tstg Storage temperature –65 +160 °C P Power dissipation, SO8 package – 470 mW Tamb = 70 °C; Note 2 NOTES: 1. Input voltage limits on PFI and MR can be exceeded provided the input current is less than 10 mA. 2. Derate the dissipation 5.88 mW/°C above 70 °C. 2003 Aug 08 3 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T ELECTRICAL CHARACTERISTICS Tamb = –40 °C to +85 °C; VCC = (VRST(max) + 0.7 V) to 5.5 V, unless otherwise specified. SYMBOL PARAMETER VCC Operating voltage range ISUP Supply current VRST Reset threshold (Note 1) CONDITIONS VCC < 3.6 V HIGH-level output voltage VIL VIH MR pulse width MR LOW-level input threshold MR HIGH-level input threshold MR to reset out delay (Note 1) V MAX708S 2.85 2.93 3.00 V MAX708T 3.00 3.08 3.15 V – 20 – mV MAX708R; VCC = 3.0 V 140 200 280 ms MAX708S, MAX708T; VCC = 3.3 V 140 200 280 ms – 200 – ms VRST(max) < VCC < 3.6V; ISOURCE = 500 µA VCC × 0.8 – – V 4.5 V < VCC < 5.5 V; ISOURCE = 800 µA VCC – 1.5 – – V VRST(max) < VCC < 3.6V; ISOURCE = 500 µA VCC × 0.8 – – V 4.5 V < VCC < 5.5 V; ISOURCE = 800 µA VCC – 1.5 – – V VRST(max) < VCC < 3.6V; ISOURCE = 500 µA VCC × 0.8 – – V 4.5 V < VCC < 5.5 V; ISOURCE = 800 µA VCC – 1.5 – – V VRST(max) < VCC < 3.6 V; ISINK = 1.2 mA – – 0.3 V 4.5 V < VCC < 5.5 V; ISINK = 3.2 mA – – 0.4 V VCC = 1.2 V; ISINK = 100 µA – – 0.3 V VRST(max) < VCC < 3.6 V; ISINK = 500 µA – – 0.3 V 4.5 V < VCC < 5.5 V; ISINK = 1.2 mA – – 0.4 V VRST(max) < VCC < 3.6 V; ISINK = 1.2 mA – – 0.3 V 4.5 V < VCC < 5.5 V; ISINK = 3.2 mA – – 0.4 V VRST(max) < VCC < 3.6 V; MR = 0 V 25 70 250 µA 4.5 V < VCC < 5.5 V; MR = 0 V 100 250 600 µA VRST(max) < VCC < 3.6 V 500 – – ns 4.5 V < VCC < 5.5 V 150 – – ns VRST(max) < VCC < 3.6 V – – 0.6 V 4.5 V < VCC < 5.5 V – – 0.8 V VCC × 0.7 – – V 2.0 – – V – – 750 ns RESET RESET VRST(max) < VCC < 3.6 V VRST(max) < VCC < 3.6 V 4.5 V < VCC < 5.5 V PFI input threshold PFI falling; MAX708R: VCC = 3.0 V; MAX708S/T: VCC = 3.3 V PFI input current NOTE: 1. Applies to RESET and RESET. 2003 Aug 08 µA µA 4.5 V < VCC < 5.5 V tMD 300 500 PFO tMR 50 2.70 RESET MR pull-up current V – 65 PFO LOW-level output voltage UNIT 2.63 RESET VOL 5.5 – MAX708R, MAX708S, MAX708T; VCC = 5.0 V VOH MAX. – 2.55 Reset threshold hysteresis Reset delay time (Note 1) TYP. 1.2 MAX708R VCC < 5.5 V tRST MIN. 4 – – 250 ns 1.2 1.25 1.3 V –25 0.01 +25 nA Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T TIMING DIAGRAM On power-up, when VCC reaches 1 V, RESET is guaranteed to be a logic LOW and RESET is guaranteed to be a logic HIGH. Event F: The VCC rises above the reset threshold again and remains above the reset threshold for typically 200 ms. At G, the reset is once again released. Event A: VCC rises to the reset threshold voltage, VRST. At this time, the internal reset delay timer is initiated. RESET and RESET will remain asserted for the reset delay time, tRST of typically 200 ms after the supply voltage rises above the reset threshold, VRST. Event H: The MR is externally pulled LOW for longer than 150 ns (minimum MR pulse width, tMR for VCC = +5 V). Event I: The manual reset is asserted within 250 ns (maximum MR to reset out delay time, tMD for VCC = +5V). Event B: At this time, the resets are released. RESET goes HIGH; while RESET goes LOW. The reset delay time helps to ensure valid reset signals despite erratic changes in supply voltage. Event J: the MR pin returns HIGH. At this point, reset delay timer is initiated and in typically 200 ms, (at Event K), the reset condition is released. Events C–E: At Event C, under brown-out conditions, VCC falls below the reset threshold minus the hysteresis voltage (typically 20 mV), and the reset signal is asserted. As power recovers and VCC rises above the reset threshold (Event D), it once again initiates the reset delay time. At Event E, VCC falls below the reset threshold before the reset delay time has elapsed and reset remains asserted. Event L: On power-down, when VCC falls below VRST – 20 mV, RESET and RESET are guaranteed to be asserted until VCC falls below 1 V. VCC VRST VRST – 20 mV VRST tRST tRST tRST RESET RESET MR tMD tMR TIME A B C D E F G H I J K L SL01812 Figure 3. Timing diagram. 2003 Aug 08 5 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T TECHNICAL DISCUSSION General discussion RESET and RESET outputs The MAX708R/S/T microprocessor supervisor circuits are comprised of both RESET and RESET outputs, a MR manual reset input, and a comparator which may be used for power-failure detection (see Figure 4). The MAX708R/S/T RESET and RESET outputs are push-pull outputs and do not require an external pull-up resistor. The RESET output is active-LOW logic, while the RESET output is active-HIGH logic. The reset threshold voltages are guaranteed within ±3% of the nominal reset threshold. The MAX708R/S/T are designed to monitor +3 V to +3.3 V power supplies in +3 V to +5 V microprocessor and other logic systems. With a threshold voltage range between 5% to 10% of the nominal supply voltage, the MAX708R/S/T will assert an output within predictable range of power supply voltage. 1 VCC 2 GND 3 PFI 4 The manual reset input, MR is active-LOW logic. It allows the RESET and RESET to be asserted by a pushbutton switch. A mechanical pushbutton switch is effectively debounced by the 140 ms minimum reset time delay. MR may be driven from an external logic circuit because it is TTL/CMOS compatible. The minimum MR input pulse is 500 ns for VCC = +3 V and 150 ns for VCC = +5 V. If manual reset will not be used, leave the pin left floating or tie it to VCC. MAX708R/S/T VCC MR Manual Reset Power-fail comparator RESET GENERATOR 8 RESET 7 RESET 6 NC 5 PFO The power-fail comparator has many useful purposes, such as monitoring upstream or secondary power supplies. The Power-Fail Output (PFO) and the non-inverting Power-Fail Input (PFI) are pinned out. The inverting input of the power-fail comparator is internally connected to a 1.25 V reference. The comparator has 10 mV of hysteresis which prevents repeated triggering of the output (PFO). VRST +1.25 V POWER-FAIL COMPARATOR SL01813 Figure 4. MAX708R/S/T internal block diagram. 2003 Aug 08 6 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T APPLICATION INFORMATION Operating with a +3 V or +5 V supply Adding hysteresis to the power-fail comparator When powered from either +3.0 V or +5.0 V, the MAX708R/S/T provides voltage monitoring at the reset threshold. The MAX708R/S/T are ideal for portable applications that are powered from a +3 V battery or an AC-DC wall adapter that generates +5 V. Hysteresis adds noise margin to the power-fail comparator and prevents repeated triggering of PFO when VIN is varying around the comparator trip point. In Figure 5, “Adding hysteresis to the power-fail comparator”, R1 and R2 are the divider resistors that set the desired trip point. R3 is added from the comparator input to the output to increase hysteresis; it is typically an order of magnitude greater than R1 and R2. The current through R1 and R2 should be at least 1 mA to ensure that the 25 nA max PFI input current does significantly shift the trip point. Capacitor C1 provides noise rejection. Power-fail comparator An early warning power-fail circuit uses the power-fail input to monitor the upstream, unregulated DC supply that powers the +3 V/+3.3 V regulator powering the MAX708R/S/T. Figure 1, “Simplified system diagram”, shows the resistor divider network that is connected to PFI. The network resistors R1 and R2 are chosen so that the voltage at PFI will fall below 1.25 V before the regulator voltage drops out. The PFO signal may be used to interrupt the microprocessor so it can perform an orderly shutdown. VIN R1 Any unregulated or regulated supply can be monitored by adjusting the resistive divider for the desired power supply trip voltage. Table 1 shows examples for nominal trip voltages of 3.7 V and 10.9 V. The desired trip voltage, VT is calculated by the following equation: V T 1.25 V VCC2 VCC PFI R2 C1 R3 MAX708R/S/T R2) (R1 R2 PFO GND Table 1. Power-fail detection circuit of 3.7 V and 10.9 V TO MICROPROCESSOR SL01814 R1 1% R2 1% VT 5V unregulated power supply 1 MΩ 510 kΩ 3.7 V 12 V unregulated power supply 1 MΩ Figure 5. Adding hysteresis to the power-fail comparator. PFO 130 kΩ 10.9 V VCC2 0V 0V V T 1.25 V VT VL VH R2) (R1 R2 The hysteresis of VH and VL voltages are calculated by: V H 1.25 V 1 V L 1.25 V R1 R1 V CC2 1.25 R2 Thus, V HYS V H V L 2003 Aug 08 7 (R3 R2) R1 (R2 R3) R3 1.25 V CC R3 VIN Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T Monitoring a negative voltage Ensuring a valid reset down to VCC = 0 V The power-fail comparator can be used to monitor a negative voltage using the circuit shown in Figure 6. When VCC falls below 1 V, the MAX708R/S/T RESET no longer sinks current (i.e., it becomes open circuit). A high impedance CMOS logic input connected to RESET can drift to undetermined voltages. In most applications in which the microprocessor circuitry is inoperative below 1 V this will not present a problem. However, in applications in which RESET must be valid down to 0 V, use a relatively large pull-down resistor from RESET to ground (Figure 7). 100 kΩ is small enough to provide a path for any stray leakage currents to flow to ground (holding RESET LOW), while it is large enough not to load RESET. When the negative supply is operating in tolerance, PFO is LOW. However, when the negative supply drops (goes positive) PFO goes HIGH. +3 V to +3.3 V R1 R2 VCC VCC PFI MAX708R/S/T VCC TO µP INTERRUPT PFO VCC RESET RESET GND MAX708R/S/T 100 kΩ MICROPROCESSOR V– SL01815 GND GND Figure 6. Circuit for monitoring a negative voltage. SL01816 When monitoring a negative supply, the trip voltage, VT is a negative voltage. Use the following ratio to determine the divider resistors: V CC 1.25 R1 1.25 Figure 7. RESET valid to VCC = Ground circuit. V T Interfacing to a microprocessor with bi-directional reset pins R2 Microprocessors with bi-directional reset pins, such as the Motorola 68HC11 series, can be connected to the MAX708R/S/T RESET output. The bi-directional reset of the microprocessor functions both as a driven reset input and as an active reset driver. Solving for VT: V T 1.25 R2 V R1 CC 1.25 To ensure a correct output on the MAX708R/S/T even when the microprocessor reset pin is in the opposite state, connect a 4.7 kΩ resistor between the reset pins as shown in Figure 8. This allows the microprocessor to issue commands to the system regardless of the state of the RESET pin. PFO +3 V to +3.3 V VCC 0V VT 0V VIN VCC VCC 4.7 kΩ RESET MAX708R/S/T GND RESET MOTOROLA 68HCXX GND SL01817 Figure 8. Interfacing to a microprocessor with bi-directional Reset I/O 2003 Aug 08 8 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T PACKING METHOD The MAX708R/S/T are packed in reels, as shown in Figure 9. GUARD BAND TAPE REEL ASSEMBLY TAPE DETAIL COVER TAPE CARRIER TAPE BARCODE LABEL BOX SL01305 Figure 9. Tape and reel packing method. 2003 Aug 08 9 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T SO8: plastic small outline package; 8 leads; body width 3.9 mm pin 1 index B2 1.73 4.95 4.80 0.51 0.33 0.068 0.189 0.195 0.013 0.020 4.95 4.80 SO8 2003 Aug 08 10 1.27 0.38 0.076 0.050 0.015 0.003 Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset REVISION HISTORY Rev Date Description _3 20030808 Product data (9397 750 11882); ECN 853–2354 30185 of 04 August 2003; supersedes data of 13 Feb 2003 (9397 750 10514). Modifications: • Ordering information on page 3: add ‘Marking code’ table. _2 20030213 Product data (9397 750 10514); ECN 853–2354 29010 of 02 October 2002; supersedes data of 20 Jun 2002 (9397 750 10023). _1 20020620 Product data (9397 750 10023); ECN 853–2354 28505 of 20 June 2002. 2003 Aug 08 11 MAX708R/S/T Philips Semiconductors Product data 3 V microprocessor supervisor circuit with power fail comparator and manual reset MAX708R/S/T Data sheet status Level Data sheet status [1] Product status [2] [3] Definitions I Objective data Development This data sheet contains data from the objective specification for product development. Philips Semiconductors reserves the right to change the specification in any manner without notice. II Preliminary data Qualification This data sheet contains data from the preliminary specification. Supplementary data will be published at a later date. Philips Semiconductors reserves the right to change the specification without notice, in order to improve the design and supply the best possible product. III Product data Production This data sheet contains data from the product specification. Philips Semiconductors reserves the right to make changes at any time in order to improve the design, manufacturing and supply. Relevant changes will be communicated via a Customer Product/Process Change Notification (CPCN). [1] Please consult the most recently issued data sheet before initiating or completing a design. [2] The product status of the device(s) described in this data sheet may have changed since this data sheet was published. The latest information is available on the Internet at URL http://www.semiconductors.philips.com. [3] For data sheets describing multiple type numbers, the highest-level product status determines the data sheet status. Definitions Short-form specification — The data in a short-form specification is extracted from a full data sheet with the same type number and title. For detailed information see the relevant data sheet or data handbook. Limiting values definition — Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 60134). Stress above one or more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or at any other conditions above those given in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended periods may affect device reliability. Application information — Applications that are described herein for any of these products are for illustrative purposes only. Philips Semiconductors make no representation or warranty that such applications will be suitable for the specified use without further testing or modification. Disclaimers Life support — These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Philips Semiconductors for any damages resulting from such application. Right to make changes — Philips Semiconductors reserves the right to make changes in the products—including circuits, standard cells, and/or software—described or contained herein in order to improve design and/or performance. When the product is in full production (status ‘Production’), relevant changes will be communicated via a Customer Product/Process Change Notification (CPCN). Philips Semiconductors assumes no responsibility or liability for the use of any of these products, conveys no license or title under any patent, copyright, or mask work right to these products, and makes no representations or warranties that these products are free from patent, copyright, or mask work right infringement, unless otherwise specified. Koninklijke Philips Electronics N.V. 2003 All rights reserved. Printed in U.S.A. Contact information For additional information please visit http://www.semiconductors.philips.com. Fax: +31 40 27 24825 Date of release: 08-03 For sales offices addresses send e-mail to: [email protected]. Document order number: 2003 Aug 08 12 9397 750 11882