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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
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 A, 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
* RESET and RESET signals * Independent comparator with 1.25 V threshold for power failure or
low battery warning
APPLICATIONS
* Manual reset input * 50 A 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
* Battery powered devices * Critical microprocessor monitoring * Controllers * Portable instruments
MICROPROCESSOR VCC RESET VCC
RESET
RESET INPUT
MAX708
R1 1% PFI R2 1% PUSH-BUTTON SWITCH PFO INTERRUPT
MR GND GND
SL01640
Figure 1. Simplified system diagram.
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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 NAME SO8 DESCRIPTION plastic small outline package; 8 leads (see dimensional drawing) TEMPERATURE RANGE -45 C to +85 C
NOTE: The device has 3 voltage output options, indicated by the `x' on the `Type number'. Part number MAX708RD MAX708SD MAX708TD Threshold Voltage (Typical) 2.63 V 2.93 V 3.08 V
Marking code
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. Part MAX708RD MAX708SD MAX708TD Marking ANEx ANDx ANCx
PIN CONFIGURATION
TOP VIEW MR VCC GND PFI 1 2 8 7 RESET RESET NC PFO
PIN DESCRIPTION
PIN 1 SYMBOL MR DESCRIPTION Manual reset input (Active-LOW). Triggers a reset pulse when pulled below 0.6 V. Connect to VCC or leave floating if not used. Supply voltage input. Ground. 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. 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. No connection. 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. 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.
SO8
3 4 6 5
2 3 4
VCC GND PFI
SL01639
Figure 2. Pin configuration. 5 PFO
6 7
NC RESET
8
RESET
MAXIMUM RATINGS
SYMBOL VCC Vn PARAMETER Supply voltage Other input pin voltage Input current at VCC or GND Output current, all outputs Rate of rise at VCC Tamb Tstg P Ambient temperature Storage temperature Power dissipation, SO8 package Tamb = 70 C; Note 2 Note 1 CONDITIONS MIN. -0.3 -0.3 - - - -40 -65 - MAX. 6.0 VCC + 0.3 20 20 100 +85 +160 470 UNIT V V mA mA V/s C C mW
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.
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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 VCC ISUP VRST PARAMETER Operating voltage range Supply current Reset threshold (Note 1) VCC < 3.6 V VCC < 5.5 V MAX708R MAX708S MAX708T Reset threshold hysteresis tRST Reset delay time (Note 1) MAX708R; VCC = 3.0 V MAX708S, MAX708T; VCC = 3.3 V MAX708R, MAX708S, MAX708T; VCC = 5.0 V VOH HIGH-level output voltage RESET VRST(max) < VCC < 3.6V; ISOURCE = 500 A 4.5 V < VCC < 5.5 V; ISOURCE = 800 A RESET VRST(max) < VCC < 3.6V; ISOURCE = 500 A 4.5 V < VCC < 5.5 V; ISOURCE = 800 A PFO VRST(max) < VCC < 3.6V; ISOURCE = 500 A 4.5 V < VCC < 5.5 V; ISOURCE = 800 A VOL LOW-level output voltage RESET VRST(max) < VCC < 3.6 V; ISINK = 1.2 mA 4.5 V < VCC < 5.5 V; ISINK = 3.2 mA VCC = 1.2 V; ISINK = 100 A RESET VRST(max) < VCC < 3.6 V; ISINK = 500 A 4.5 V < VCC < 5.5 V; ISINK = 1.2 mA PFO VRST(max) < VCC < 3.6 V; ISINK = 1.2 mA 4.5 V < VCC < 5.5 V; ISINK = 3.2 mA MR pull-up current tMR VIL VIH tMD MR pulse width MR LOW-level input threshold MR HIGH-level input threshold MR to reset out delay (Note 1) PFI input threshold PFI input current NOTE: 1. Applies to RESET and RESET. VRST(max) < VCC < 3.6 V; MR = 0 V 4.5 V < VCC < 5.5 V; MR = 0 V VRST(max) < VCC < 3.6 V 4.5 V < VCC < 5.5 V VRST(max) < VCC < 3.6 V 4.5 V < VCC < 5.5 V VRST(max) < VCC < 3.6 V 4.5 V < VCC < 5.5 V VRST(max) < VCC < 3.6 V 4.5 V < VCC < 5.5 V PFI falling; MAX708R: VCC = 3.0 V; MAX708S/T: VCC = 3.3 V CONDITIONS MIN. 1.2 - - 2.55 2.85 3.00 - 140 140 - VCC x 0.8 VCC - 1.5 VCC x 0.8 VCC - 1.5 VCC x 0.8 VCC - 1.5 - - - - - - - 25 100 500 150 - - VCC x 0.7 2.0 - - 1.2 -25 TYP. - 50 65 2.63 2.93 3.08 20 200 200 200 - - - - - - - - - - - - - 70 250 - - - - - - - - 1.25 0.01 MAX. 5.5 300 500 2.70 3.00 3.15 - 280 280 - - - - - - - 0.3 0.4 0.3 0.3 0.4 0.3 0.4 250 600 - - 0.6 0.8 - - 750 250 1.3 +25 UNIT V A A V V V mV ms ms ms V V V V V V V V V V V V V A A ns ns V V V V ns ns V nA
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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 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 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. 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 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 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 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. 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 VRST - 20 mV
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.
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Philips Semiconductors
Product data
3 V microprocessor supervisor circuit with power fail comparator and manual reset
MAX708R/S/T
TECHNICAL DISCUSSION General discussion
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 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.
RESET and RESET outputs
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.
Manual Reset
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.
VCC
MAX708R/S/T
Power-fail comparator
8 RESET
MR
1 RESET GENERATOR 7 RESET
VCC
2
VRST GND 3 6 NC
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).
PFI
4 +1.25 V POWER-FAIL COMPARATOR
5
PFO
SL01813
Figure 4. MAX708R/S/T internal block diagram.
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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
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.
Adding hysteresis to the power-fail comparator
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.
VIN
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. 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 (R1 ) R2) R2
VCC2
R1 PFI VCC
R2
C1
R3
MAX708R/S/T
PFO GND
Table 1. Power-fail detection circuit of 3.7 V and 10.9 V
R1 1% 5V unregulated power supply 12 V unregulated power supply 1 M R2 1% 510 k VT 3.7 V
PFO
TO MICROPROCESSOR
SL01814
Figure 5. Adding hysteresis to the power-fail comparator.
1 M
130 k
10.9 V
VCC2
0V 0V
VL
VT
VH
VIN
V T + 1.25 V
(R1 ) R2) R2
The hysteresis of VH and VL voltages are calculated by: V H + 1.25 V 1 ) (R3 ) R2) R1 (R2 R3) 1.25 * V CC R3
V L + 1.25 V ) R1 Thus, V HYS + V H * V L +
1.25 ) R2
R1
V CC2 R3
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Philips Semiconductors
Product data
3 V microprocessor supervisor circuit with power fail comparator and manual reset
MAX708R/S/T
Monitoring a negative voltage
The power-fail comparator can be used to monitor a negative voltage using the circuit shown in Figure 6. 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
Ensuring a valid reset down to VCC = 0 V
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 k 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.
VCC
R1 PFI VCC
R2
MAX708R/S/T
PFO GND TO P INTERRUPT
VCC
VCC
RESET
RESET 100 k MICROPROCESSOR
MAX708R/S/T
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 Solving for VT: V T + 1.25 * R2 R1 V CC * 1.25 + 1.25 * V T R2
Figure 7. RESET valid to VCC = Ground circuit.
Interfacing to a microprocessor with bi-directional reset pins
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. 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 k 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.
VCC
PFO +3 V to +3.3 V
0V VT 0V VIN VCC 4.7 k RESET RESET MOTOROLA 68HCXX VCC
MAX708R/S/T
GND
GND
SL01817
Figure 8. Interfacing to a microprocessor with bi-directional Reset I/O
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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
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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 0.068
4.95 4.80 0.189 0.195 0.51 0.33 0.013 0.020 4.95 4.80 1.27 0.38 0.050 0.015
0.076 0.003
SO8
2003 Aug 08
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Philips Semiconductors
Product data
3 V microprocessor supervisor circuit with power fail comparator and manual reset
MAX708R/S/T
REVISION HISTORY
Rev _3 Date 20030808 Description Product data (9397 750 11882); ECN 853-2354 30185 of 04 August 2003; supersedes data of 13 Feb 2003 (9397 750 10514).
* Ordering information on page 3: add `Marking code' table.
_2 _1 20030213 20020620 Product data (9397 750 10514); ECN 853-2354 29010 of 02 October 2002; supersedes data of 20 Jun 2002 (9397 750 10023). Product data (9397 750 10023); ECN 853-2354 28505 of 20 June 2002.
Modifications:
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Philips Semiconductors
Product data
3 V microprocessor supervisor circuit with power fail comparator and manual reset
MAX708R/S/T
Data sheet status
Level
I
Data sheet status [1]
Objective data
Product status [2] [3]
Development
Definitions
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. 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. 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).
II
Preliminary data
Qualification
III
Product data
Production
[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.
Contact information
For additional information please visit http://www.semiconductors.philips.com. Fax: +31 40 27 24825
(c) Koninklijke Philips Electronics N.V. 2003 All rights reserved. Printed in U.S.A. Date of release: 08-03
For sales offices addresses send e-mail to: sales.addresses@www.semiconductors.philips.com.
Document order number:
9397 750 11882
Philips Semiconductors
2003 Aug 08 12

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