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MAX705–MAX708/MAX813L

Low-Cost, µP Supervisory Circuits

________________________________________________________________

Maxim Integrated Products

TOP VIEW

WDO

RESET (RESET)

WDI

PFO

PFI

GND

DIP/SO

MAX705

MAX706

MAX813L

RESET

N.C.

PFO

PFI

GND

DIP/SO

MAX707

MAX708

( ) ARE FOR MAX813L ONLY.

Pin Configurations continued at end of data sheet.

_________________Pin Configurations

PFI

PFO

WDO

RESET

UNREGULATED DC

PUSHBUTTON

SWITCH

PFI

I/O LINE

INTERRUPT

MAX705

MAX706

MAX813L

MAX667

+5V DC LINEAR

REGULATOR

RESET

NMI

__________Typical Operating Circuit

Call toll free 1-800-998-8800 for free samples or literature.

19-4334; Rev. 5; 9/95

_______________General Description

The MAX705-MAX708/MAX813L microprocessor (µP)

supervisory circuits reduce the complexity and number

of components required to monitor power-supply and

battery functions in µP systems. These devices signifi-

cantly improve system reliability and accuracy com-

pared to separate ICs or discrete components.

The MAX705/MAX706/MAX813L provide four functions:

1) A reset output during power-up, power-down, and

brownout conditions.

2) An independent watchdog output that goes low if

the watchdog input has not been toggled within 1.6

seconds.

3) A 1.25V threshold detector for power-fail warning,

low-battery detection, or for monitoring a power sup-

ply other than +5V.

4) An active-low manual-reset input.

The MAX707/MAX708 are the same as the MAX705/

MAX706, except an active-high reset is substituted for

the watchdog timer. The MAX813L is the same as the

MAX705, except RESET is provided instead of RESET.

Two supply-voltage monitor levels are available: The

MAX705/MAX707/MAX813L generate a reset pulse when

the supply voltage drops below 4.65V, while the

MAX706/MAX708 generate a reset pulse below 4.40V.

All four parts are available in 8-pin DIP, SO and µMAX

packages.

_______________________Applications

Computers

Controllers

Intelligent Instruments

Automotive Systems

Critical µP Power Monitoring

___________________________Features

µMAX Package: Smallest 8-Pin SO

Guaranteed RESET Valid at V

= 1V

Precision Supply-Voltage Monitor

4.65V in MAX705/MAX707/MAX813L

4.40V in MAX706/MAX708

200ms Reset Pulse Width

Debounced TTL/CMOS-Compatible

Manual-Reset Input

Independent Watchdog Timer—1.6sec Timeout

(MAX705/MAX706)

Active-High Reset Output

(MAX707/MAX708/MAX813L)

Voltage Monitor for Power-Fail or Low-Battery

Warning

______________Ordering Information

PART

TEMP. RANGE

PIN-PACKAGE

MAX705

CPA

8 Plastic DIP

MAX705CSA

0°C to +70°C

8 SO

MAX705C/D

0°C to +70°C

Dice*

Ordering Information continued at end of data sheet.

* Dice are specified at T

= +25°C.

**Contact factory for availability and processing to MIL-STD-883.

0°C to +70°C

MAX705CUA

0°C to +70°C

8 µMAX

MAX705–MAX708/MAX813L

Low-Cost, µP Supervisory Circuits

_______________________________________________________________________________________

Terminal Voltage (with respect to GND)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V

All Other Inputs (Note 1) . . . . . . . . . . . . . . . -0.3V to (V

+ 0.3V)

Input Current

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA

GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA

Output Current (all outputs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA

Continuous Power Dissipation

Plastic DIP (derate 9.09mW/°C above +70°C) . . . . . . . 727mW

SO (derate 5.88mW/°C above +70°C) . . . . . . . . . . . . . . . 471mW

µMAX (derate 4.10mW/°C above +70°C) . . . . . . . . . . . . 330mW

CERDIP (derate 8.00mW/°C above +70°C) . . . . . . . . . . 640mW

Operating Temperature Ranges

MAX70_C__, MAX813LC__ . . . . . . . . . . . . . . . . . . . . 0°C to +70°C

MAX70_E__, MAX813LE__ . . . . . . . . . . . . . . . . . . . -40°C to +85°C

MAX70_MJA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55°C to +125°C

Storage Temperature Range

. . . . . . . . . . . . . . . . -65°C to +160°C

Lead Temperature (soldering, 10sec)

. . . . . . . . . . . . . . . . +300°C

ELECTRICAL CHARACTERISTICS

= 4.75V to 5.5V for MAX705/MAX707/MAX813L, V

= 4.5V to 5.5V for MAX706/MAX708, T

= T

MIN

to T

MAX

, unless otherwise noted.)

Stresses beyond those listed under "Absolute Maximum Ratings

may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Operating Voltage Range

MAX70_C

1.0

5.5

MAX813LC

1.1

5.5

MAX70_E/M, MAX813LE/M

1.2

5.5

Reset Threshold (Note 2)

MAX705, MAX707, MAX813L

4.50

4.65

4.75

MAX706, MAX708

4.25

4.40

4.50

Reset Pulse Width (Note 2)

140

200

280

RESET Output Voltage

SOURCE

= 800µA

- 1.5

ABSOLUTE MAXIMUM RATINGS

Note 1:

The input voltage limits on PFI and MR can be exceeded if the input current is less than 10mA.

Reset Threshold Hysteresis (Note 2)

SINK

= 3.2mA

0.4

0.3

RESET Output Voltage

MAX707, MAX708, I

SOURCE

= 800µA

MAX707, MAX708, I

SINK

= 1.2mA

0.4

0.8

0.9

MAX813L

- 1.5

0.4

Watchdog Timeout Period

MAX705, MAX706, MAX813L

1.00

1.60

2.25

sec

WDI Pulse Width

= 0.4V, V

= (V

) (0.8)

WDI Input Threshold

0.8

3.5

MAX70_C, V

= 1V, I

SINK

= 50µA

MAX70_E/M, V

= 1.2V, I

SINK

= 100µA

MAX813LC, I

SOURCE

= 4µA, V

= 1.1V

MAX813LE/M, I

SOURCE

= 4µA, V

= 1.2V

SOURCE

= 800µA

SINK

= 3.2mA

Low

High

WDI Input Current

MAX705, MAX706, MAX813L, WDI = V

150

µA

MAX705, MAX706, MAX813L, WDI = 0V

-150

-50

WDO Output Voltage

- 1.5

0.4

MAX705, MAX706, MAX813L,

= 5V

MAX705, MAX706, MAX813L,

SOURCE

= 800µA

MAX705, MAX706, MAX813L,

SINK

= 1.2mA

- 1.5

MAX707C, MAX708C

350

MAX707E/M, MAX708E/M

500

Supply Current

SUPPLY

MAX705C, MAX706C, MAX813LC

150

350

µA

MAX705E/M, MAX706E/M, MAX813LE/M

150

500

MAX705–MAX708/MAX813L

Low-Cost, µP Supervisory Circuits

_______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

= 4.75V to 5.5V for MAX705/MAX707/MAX813L, V

= 4.5V to 5.5V for MAX706/MAX708, T

= T

MIN

to T

MAX

, unless otherwise noted.)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

0.8

2.0

MR Pull-Up Current

MR = 0V

100

250

600

µA

MR Pulse Width

150

Low

High

MR Input Threshold

MR to Reset Out Delay (Note 2)

250

PFI Input Threshold

= 5V

1.20

1.25

1.30

PFI Input Current

-25.00

0.01

25.00

PFO Output Voltage

SOURCE

= 800µA

- 1.5

SINK

= 3.2mA

0.4

Note 2:

Applies to both RESET in the MAX705-MAX708 and RESET in the MAX707/MAX708/MAX813L.

MAX705–MAX708/MAX813L

Low-Cost, µP Supervisory Circuits

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__________________________________________Typical Operating Characteristics

MAX707/MAX708/MAX813L

RESET OUTPUT VOLTAGE

vs. SUPPLY VOLTAGE

500ms/div

RESET

+5V

1V/div

+5V

1V/div

= +25°C

GND

RESET

330pF

10k

MAX813L

RESET RESPONSE TIME

s/div

+5V

+4V

GND

RESET

330pF

10k

MAX705/MAX707

RESET OUTPUT VOLTAGE

vs. SUPPLY VOLTAGE

500ms/div

RESET

+5V

1V/div

+5V

1V/div

GND

RESET

330pF

= +25°C

MAX705/MAX707

RESET RESPONSE TIME

s/div

+5V

RESET

+5V

+4V

1V/div

= +25°C

GND

RESET

10k

RESET

30pF

POWER-FAIL COMPARATOR

DE-ASSERTION RESPONSE TIME

400ns/div

PFI

+1.20V

PFO

+3V

+1.30V

= +5V

= +25°C

+5V

PFO

30pF

+1.25V

PFI

POWER-FAIL COMPARATOR

ASSERTION RESPONSE TIME

400ns/div

PFI

+1.30V

PFO

+5V

+1.20V

1V/div

50mV/div

+5V

PFO

30pF

+1.25V

PFI

= +5V

= +25°C

MAX707

RESET, RESET ASSERTION

400ns/div

+5V

RESET

1V/div

= V

= +25°C

+5V

GND

RESET

10k

330pF

RESET

10k

330pF

MAX707

RESET, RESET DE-ASSERTION

400ns/div

+5V

RESET

2V/div

= V

= +25°C

+5V

VCC

GND

RESET

10k

330pF

10k

330pF

MAX705–MAX708/MAX813L

Low-Cost, µP Supervisory Circuits

_______________________________________________________________________________________

______________________________________________________________Pin Description

Watchdog Output pulls low when the internal watch-

dog timer finishes its 1.6sec count and does not go

high again until the watchdog is cleared. WDO also

goes low during low-line conditions. Whenever V

below the reset threshold, WDO stays low; however,

unlike RESET, WDO does not have a minimum pulse

width. As soon as V

rises above the reset thresh-

old, WDO goes high with no delay.

Active-High Reset Output is the inverse of RESET.

Whenever RESET is high, RESET is low, and vice

versa (Figure 2). The MAX813L has a RESET output

only.

Active-Low Reset Output pulses low for 200ms when

triggered, and stays low whenever V

is below the

reset threshold (4.65V in the MAX705 and 4.40V in the

MAX706). It remains low for 200ms after V

rises

above the reset threshold or MR goes from low to high

(Figure 3). A watchdog timeout will not trigger RESET

unless WDO is connected to MR.

Watchdog Input. If WDI remains high or low for

1.6sec, the internal watchdog timer runs out and

WDO goes low (Figure 1). Floating WDI or connect-

ing WDI to a high-impedance three-state buffer dis-

ables the watchdog feature. The internal watchdog

timer clears whenever reset is asserted, WDI is three-

stated, or WDI sees a rising or falling edge.

Power-Fail Output goes low and sinks current when

PFI is less than 1.25V; otherwise PFO stays high.

Power-Fail Voltage Monitor Input. When PFI is less

than 1.25V, PFO goes low. Connect PFI to GND or

when not used.

FUNCTION

MAX705/MAX706

RESET

WDO

RESET

No Connect

N.C.

WDI

PFO

PFI

0V Ground Reference for all signals

GND

+5V Supply Input

NAME

DIP/SO

MAX707/MAX708

PIN

µMAX

MAX813L

Manual-Reset Input triggers a reset pulse when

pulled below 0.8V. This active-low input has an inter-

nal 250µA pull-up current. It can be driven from a TTL

or CMOS logic line as well as shorted to ground with

a switch.

MAX705–MAX708/MAX813L

_______________Detailed Description

Reset Output

A microprocessor’s (µP’s) reset input starts the µP in a

known state. Whenever the µP is in an unknown state, it

should be held in reset. The MAX705-MAX708/MAX813L

assert reset during power-up and prevent code execu-

tion errors during power-down or brownout conditions.

On power-up, once V

reaches 1V, RESET is a guaran-

teed logic low of 0.4V or less. As V

rises, RESET stays

low. When V

rises above the reset threshold, an inter-

nal timer releases RESET after about 200ms. RESET puls-

es low whenever V

dips below the reset threshold, i.e.

brownout condition. If brownout occurs in the middle of

a previously initiated reset pulse, the pulse continues for

at least another 140ms. On power-down, once V

falls

below the reset threshold, RESET stays low and is guar-

anteed to be 0.4V or less until V

drops below 1V.

The MAX707/MAX708/MAX813L active-high RESET output

is simply the complement of the RESET output, and is

guaranteed to be valid with V

down to 1.1V. Some µPs,

such as Intel’s 80C51, require an active-high reset pulse.

Watchdog Timer

The MAX705/MAX706/MAX813L watchdog circuit moni-

tors the µP’s activity. If the µP does not toggle the watch-

dog input (WDI) within 1.6sec and WDI is not three-stat-

ed, WDO goes low. As long as RESET is asserted or the

WDI input is three-stated, the watchdog timer will stay

cleared and will not count. As soon as reset is released

and WDI is driven high or low, the timer will start counting.

Pulses as short as 50ns can be detected.

Typically, WDO will be connected to the non-maskable

interrupt input (NMI) of a µP. When V

drops below

the reset threshold, WDO will go low whether or not the

watchdog timer has timed out yet. Normally this would

trigger an NMI interrupt, but RESET goes low simultane-

ously, and thus overrides the NMI interrupt.

If WDI is left unconnected, WDO can be used as a low-

line output. Since floating WDI disables the internal

timer, WDO goes low only when V

falls below the

reset threshold, thus functioning as a low-line output.

The MAX705/MAX706 have a watchdog timer and a

RESET output. The MAX707/MAX708 have both active-

high and active-low reset outputs. The MAX813L has

both an active-high reset output and a watchdog timer.

Manual Reset

The manual-reset input (MR) allows reset to be trig-

gered by a pushbutton switch. The switch is effectively

debounced by the 140ms minimum reset pulse width.

MR is TTL/CMOS logic compatible, so it can be driven

by an external logic line. MR can be used to force a

watchdog timeout to generate a reset pulse in the

MAX705/MAX706/MAX813L. Simply connect WDO to

MR.

Low-Cost, µP Supervisory Circuits

_______________________________________________________________________________________

WATCHDOG

TRANSITION

DETECTOR

WATCHDOG

TIMER

TIMEBASE FOR

RESET AND

WATCHDOG

RESET

GENERATOR

250

WDO

RESET

(RESET)

PFO

GND

1.25V

4.65V*

* 4.40V FOR MAX7O6.

( ) ARE FOR MAX813L ONLY.

WDI

PFI

MAX705

MAX706

MAX813L

Figure 1. MAX705/MAX706/MAX813L Block Diagram

RESET

GENERATOR

250

RESET

PFO

GND

1.25V

4.65V*

* 4.40V FOR MAX7O6.

PFI

MAX707

MAX708

Figure 2. MAX707/MAX708 Block Diagram

Power-Fail Comparator

The power-fail comparator can be used for various pur-

poses because its output and noninverting input are

not internally connected. The inverting input is internal-

ly connected to a 1.25V reference.

To build an early-warning circuit for power failure, con-

nect the PFI pin to a voltage divider (see

Typical

Operating Circuit). Choose the voltage divider ratio so

that the voltage at PFI falls below 1.25V just before the

+5V regulator drops out. Use PFO to interrupt the µP

so it can prepare for an orderly power-down.

__________Applications Information

Ensuring a Valid RESET

Output Down to V

= 0V

When V

falls below 1V, the MAX705-MAX708 RESET

output no longer sinks current—it becomes an open cir-

cuit. High-impedance CMOS logic inputs can drift to

undetermined voltages if left undriven. If a pull-down

resistor is added to the RESET pin as shown in Figure 5,

any stray charge or leakage currents will be drained to

ground, holding RESET low. Resistor value (R1) is not

critical. It should be about 100k

Ω

, large enough not to

load RESET and small enough to pull RESET to ground.

Monitoring Voltages Other Than the

Unregulated DC Input

Monitor voltages other than the unregulated DC by

connecting a voltage divider to PFI and adjusting the

ratio appropriately. If required, add hysteresis by con-

necting a resistor (with a value approximately 10 times

the sum of the two resistors in the potential divider net-

work) between PFI and PFO. A capacitor between PFI

and GND will reduce the power-fail circuit’s sensitivity

to high-frequency noise on the line being monitored.

RESET can be asserted on other voltages in addition to

the +5V V

line. Connect PFO to MR to initiate a RESET

pulse when PFI drops below 1.25V. Figure 6 shows the

MAX705-MAX708 configured to assert RESET when the

+5V supply falls below the reset threshold, or when the

+12V supply falls below approximately 11V.

Monitoring a Negative Voltage

The power-fail comparator can also monitor a negative

supply rail (Figure 7). When the negative rail is good (a

negative voltage of large magnitude), PFO is low, and

when the negative rail is degraded (a negative voltage

of lesser magnitude), PFO is high. By adding the resis-

tors and transistor as shown, a high PFO triggers reset.

As long as PFO remains high, the MAX705-

MAX708/MAX813L will keep reset asserted (RESET =

low, RESET = high). Note that this circuit’s accuracy

depends on the PFI threshold tolerance, the V

line,

and the resistors.

MAX705–MAX708/MAX813L

Low-Cost, µP Supervisory Circuits

_______________________________________________________________________________________

+5V

WDI

+5V

WDO

+5V

RESET

+5V

(RESET)

( ) ARE FOR MAX813L ONLY.

RESET EXTERNALLY

TRIGGERED BY MR

Figure 3. MAX705/MAX706/MAX813L Watchdog TIming

Figure 4. MAX705/MAX706 RESET, MR, and WDO Timing with

WDI Three-Stated. The MAX707/MAX708/MAX813L RESET

output is the inverse of RESET shown.

+5V

RESET

WDO

+5V

MR EXTERNALLY DRIVEN LOW

+5V

MAX705–MAX708/MAX813L

Interfacing to µPs with

Bidirectional Reset Pins

µPs with bidirectional reset pins, such as the Motorola

68HC11 series, can contend with the MAX705-MAX708

RESET output. If, for example, the RESET output is driven

high and the µP wants to pull it low, indeterminate logic

levels may result. To correct this, connect a 4.7k

Ω

resistor between the RESET output and the µP reset I/O,

as in Figure 8. Buffer the RESET output to other system

components.

Low-Cost, µP Supervisory Circuits

_______________________________________________________________________________________

MAX70_

RESET

+5V

V-

PFI

GND

PFO

100k

2N3904

PFO

+5V

TRIP

V-

Figure 7. Monitoring a Negative Voltage

MAX70_

BUFFERED RESET TO OTHER SYSTEM COMPONENTS

4.7k

GND

RESET

GND

RESET

Figure 8. Interfacing to µPs with Bidirectional Reset I/O

1.25

VTRIP

, VTRIP

−

MAX70_

RESET

Figure 5. RESET Valid to Ground Circuit

MAX70_

RESET

130k

PARAMETER

MIN

TYP

MAX

UNIT

+12V Reset

Threshold at +25°C

10.67 10.87 11.50

+5V

+12V

PFI

GND

PFO

Figure 6. Monitoring Both +5V and +12V