MAXIM MAX792, MAX820 User Manual

MAX792/MAX820

Microprocessor and Nonvolatile

Memory Supervisory Circuits

________________________________________________________________ Maxim Integrated Products 1

19-0147; Rev. 4; 11/05

General Description

The MAX792/MAX820 microprocessor (µP) supervisory circuits provide the most functions for power-supply and watchdog monitoring in systems without battery backup. Built-in features include the following:

•µP reset: Assertion of RESET and

RESET

outputs during

power-up, power-down, and brownout conditions.

RESET

is guaranteed valid for VCCdown to 1V.

•Manual-reset input.

• Two-stage power-fail warning: A separate low-line comparator compares VCCto a preset threshold 120mV above the reset threshold; the low-line and reset thresholds can be programmed externally.

• Watchdog fault output: Assertion of

WDO

if the watchdog input is not toggled within a preset timeout period.

• Pulsed watchdog output: Advance warning of impending

WDO

assertion from watchdog timeout that

causes hardware shutdown.

• Write protection of CMOS RAM, EEPROM, or other memory devices.

The MAX792 and MAX820 are identical, except the MAX820 guarantees higher low-line and reset threshold accuracy (±2%).

Applications

Computers Controllers Intelligent Instruments Critical µP Power Monitoring

Features

♦ Manual-Reset Input

♦ 200ms Power-OK /Reset Time Delay

♦ Independent Watchdog Timer—Preset or Adjustable

♦ On-Board Gating of Chip-Enable Signals

♦ Memory Write-Cycle Completion

♦ 10ns (max) Chip-Enable Gate Propagation Delay

♦ Voltage Monitor for Overvoltage Warning

♦ ±2% Reset and Low-Line Threshold Accuracy

(MAX820, external programming mode)

MAX792

ADDRESS DECODER

RESET IN/INT

LLIN/ REFOUT

OVI

SWT

GND

RESET

LOW LINE

OVO

CE IN

CE OUT

0.1µF

RAM

A0-A15

GND

NMI

RESET

µP

Typical Operating Circuit

PART** TEMP. RANGE PIN-PACKAGE

MAX792_CPE

0°C to +70°C 16 Plastic DIP

MAX792_CSE 0°C to +70°C 16 Narrow SO

MAX792_C/D 0°C to +70°C Dice*

SUFFIX

RESET THRESHOLD (V)

4.62

4.37

3.06

2.91

2.61

T S R

For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.

Ordering Information

Ordering Information continued at end of data sheet.

* Dice are tested at TA= +25°C, DC parameters only. **These parts offer a choice of five different reset threshold voltages.

Select the letter corresponding to the desired nominal reset threshold voltage and insert it into the blank to complete the part number. Devices in PDIP, SO and µMAX packages are available in both leaded and lead-free packaging. Specify lead free by adding the + symbol at the end of the part number when ordering. Lead free not available for CERDIP package.

MAX792/MAX820

Input Voltage (with respect to GND)

VCC.......................................................................-0.3V to +6V

All Other Inputs.......................................-0.3V to (VCC+ 0.3V)

Input Current

GND ................................................................................25mA

All Other Outputs ............................................................25mA

Continuous Power Dissipation (T

= +70°C)

Plastic DIP (derate 10.53mW/°C above +70°C) ..........842mW

Narrow SO (derate 9.52mW/°C above +70°C) ............762mW

CERDIP (derate 10.00mW/°C above +70°C)...............800mW

Operating Temperature Ranges:

MAX792_C__/MAX820_C_ _ ...............................0°C to +70°C

MAX792_E__/MAX820_E_ _.............................-40°C to +85°C

MAX792_MJE__/MAX820_MJE_ _ .................-55°C to +125°C

Storage Temperature Range .............................-65°C to +160°C

Lead Temperature (soldering, 10s) .................................+300°C

2 _______________________________________________________________________________________

Microprocessor and Nonvolatile Memory Supervisory Circuits

PARAMETER

Reset Active Timeout Period

CONDITIONS

MAX820R, TA= +25°C, VCCfalling 2.55 2.66

MIN TYP MAX UNITS

VCCrising

MAX820S, TA= +25°C, VCCfalling 2.85 2.96

RESET Output Voltage

Reset Threshold Voltage— Internal Threshold Mode (V

)

MAX820T, TA= +25°C, VCCfalling 3.00 3.11

140 200 280

MAX792, VCC= 5V or VCC= 3V 1.25 1.30 1.35

Reset Threshold Voltage External Threshold Mode (V

)

MAX820, VCC= 5V or VCC= 3V 1.274 1.30 1.326

RESET IN/INT Mode Threshold (Note 2)

Internal threshold mode 60 mV

RESET IN/INT Leakage Current

±0.01 ±25 nA

Reset Threshold Hysteresis 0.016 x V

Reset Comparator Delay VCCfalling 70 µs

RESET Output Voltage

SINK

= 50µA, VCC= 1V, VCCfalling 0.01 0.3

SOURCE

= 1mA

2.75 V

Supply Current

VCC- 1

SINK

= 1.6mA 0.1 0.4

70 150 µA

SOURCE

= 100µA VCC- 0.5

SOURCE

= 1mA VCC- 1

MAX792L, MAX820L

SOURCE

= 100µA

4.50 4.62 4.75

VCC- 0.5

MAX792M, MAX820M 4.25 4.37 4.50

MAX792R, MAX820R

SINK

= 1.6mA

2.55 2.61 2.70

0.1 0.4

MAX792S, MAX820S 2.85 2.91 3.00

MAX792T, MAX820T 3.00 3.06 3.15

MAX820L, TA= +25°C, VCCfalling 4.55 4.70

MAX820M, TA= +25°C, VCCfalling 4.30 4.45

ELECTRICAL CHARACTERISTICS

(VCC= 2.75V to 5.5V, TA= 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.

ABSOLUTE MAXIMUM RATINGS

RESET COMPARATOR

Operating Voltage Range (Note 1)

MAX792/MAX820

_______________________________________________________________________________________ 3

Microprocessor and Nonvolatile

Memory Supervisory Circuits

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 2.75V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

PARAMETER CONDITIONS

MIN TYP MAX UNITS

µA

LOWLINE Short-Circuit Current

Output source current, VCC= 5.5V 10 50

SWT connected to V

CC, VCC = 5V

1.00 1.60 2.25

SWT connected to V

CC, VCC = 3V

1.00 1.60 2.25

4.7nF capacitor connected from SWT to GND

CC = 3V

Watchdog Timeout Period

4.7nF capacitor connected from SWT to GND

CC = 5V

MAX792/MAX820L/M

100

sec

50 120 210

Low-Line Threshold Voltage (Internal Threshold Mode)—V

MAX792/MAX820R/S/T

CC = 5V

40 100 210

100

MAX792, VCC= 5V OR VCC= 3V

Watchdog Input Pulse Width VIL= 0V, VIH= V

1.25 1.30 1.35

Low-Line Threshold Voltage (External Programming Mode)

CC = 3V

MAX820, VCC= 5V OR VCC= 3V

300

1.274 1.30 1.326

Low-Line Hysteresis (Internal Threshold Mode)

SINK

= 50µA, VCC= 1V, VCCfalling

20 mV

0.01 0.30

SINK

= 1.6mA 0.1 0.4

SOURCE

= 1mA VCC- 1

WDO Output Voltage

SOURCE

= 100µA VCC- 0.5

SOURCE

= 100µA

WDPO to WDO Delay

70 ns

WDPO Duration

0.5 1.7 6.0 ms

SINK

= 50µA, VCC= 1V, VCCfalling 0.01 0.3

SINK

= 1.6mA 0.1 0.4

SOURCE

= 1mA VCC- 1

WDPO Output Voltage

VCC- 0.5

0.75 x V

VCC= 4.25V

0.8

0.9 x V

WDI Threshold Voltage

VCC= 2.55V

0.2

WDI Input Current ±1 µA

LLIN/REFOUT Leakage Current External Programming Mode

±0.01 ±25 nA

Low-Line Comparator Delay VCCfalling 450 µs

SINK

= 3.2mA 0.4

LOWLINE Voltage

SOURCE

= 1µA VCC- 1

LOW-LINE COMPARATOR

WATCHDOG FUNCTION

MAX792/MAX820

4 _______________________________________________________________________________________

Microprocessor and Nonvolatile Memory Supervisory Circuits

Note 1: The minimum operating voltage is 2.75V; however, the MAX792R and MAX820R are guaranteed to operate down to their

preset reset thresholds.

Note 2: Pulling RESET IN/INT below 60mV selects internal threshold mode and connects the internal voltage divider to the reset

and low-line comparators. External programming mode allows an external resistor divider to set the low-line and reset thresholds (see Figure 4).

Note 3: The Chip-Enable Propagation delay is measured from the 50% point at CE IN to the 50% point at CE OUT.

PARAMETER

CONDITIONS

VCC= 5V or VCC= 3V

MIN TYP MAX UNITS

SINK

= 3.2mA

SOURCE

= 1µA

Output source current, VCC= 5.5V

VOD= 100mV, OVI rising

MR Pull-Up Current

0.75 x V

MR = 0V

VCC= 2.5V

= 4.25V

0.8

0.75 x V

CE IN Threshold Voltage

VCC= 2.55V

0.2

CE IN Leakage Current

50Ω source impedance driver, C

LOAD

= 50pF

Disabled mode ±0.005 ±1 µA

VCC= 5V

VCC= 3V

VCC= 5V 75 150

610

CE IN to CE OUT Resistance

OVI Input Threshold

Enabled mode

VCC= 3V 150 300

1.25 1.30 1.35 V

OVI Leakage Current

Ω

±0.01 ±25 nA

VCC= 5V 0.5 2.5

CE OUT Short-Circuit Current

0.4

OVO Output Voltage

Disabled mode, CE

OUT

= 0V

VCC= 3V 0.05 0.2 0.4

VCC- 1

Chip-Enable Propagation Delay (Note 3)

10 50

813

OUT

= -100µA VCC- 1

Chip-Enable Output Voltage High (Reset Active)

OUT

= 10µA VCC- 0.5

Reset Active to CE OUT High

falling 15 µs

MR Minimum Pulse Width

25 µs

MR to RESET Propagation Delay

12 µs

MR Threshold Range

1.1 1.3 1.5 V

VCC= 4.25V to V

= 5.5V

52380

µA

OVO Short-Circuit Current

µA

OVI to OVO Delay

VOD= 100mV, OVI falling 55

µs

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +2.75V to +5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

MANUAL RESET

CHIP-ENABLE GATING

OVERVOLTAGE COMPARATOR

MAX792/MAX820

Microprocessor and Nonvolatile

Memory Supervisory Circuits

_________________________________________________________________________________________________ 5

400

-60

LOW-LINE COMPARATOR

PROPAGATION DELAY vs. TEMPERATURE

100

300

200

MAX792-3a

TEMPERATURE (°C)

PROPAGATION DELAY (µs)

500

600

-30 0 30 60 90 120

150

= 5V

= 3V

FALLING

15mV OVERDRIVE

EXTERNAL PROGRAMMING MODE

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

-60 150

SUPPLY CURRENT vs. TEMPERATURE

MAX792-1

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

100

-30 0 30 60 90 120

= 2V

VCC = 3V

VCC = 4V

VCC = 5V

SWT = VCC ALL OUTPUTS UNLOADED

-60

OVERVOLTAGE COMPARATOR

PROPAGATION DELAY vs. TEMPERATURE

MAX792-2

TEMPERATURE (°C)

PROPAGATION DELAY (µs)

-30 0 30 60 90 120

150

VIH TO V

VIN = 20mV OVERDRIVE = 15mV

-60

RESET COMPARATOR

PROPAGATION DELAY vs. TEMPERATURE

MAX792-3

TEMPERATURE (°C)

PROPAGATION DELAY (µs)

-30 0 30 90 120

150

VCC FALLING 15mV OVERDRIVE EXTERNAL PROGRAMMING MODE

-60

POWER-UP RESET DELAY

vs. TEMPERATURE

100

MAX792-4

TEMPERATURE (°C)

DELAY (ms)

300

200

150

250

-30 0 30 90 120

150

1.0

NOMINAL WATCHDOG TIMEOUT

PERIOD vs. V

MAX792-5

VCC (V)

NOMINAL WATCHDOG TIMEOUT PERIOD (s)

3.0

2.0

1.5

2.5

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