Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - system monitor Reset/power-on reset SOIC 16

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 V

down to 1V.

•Manual-reset input.

• Two-stage power-fail warning: A separate low-line

comparator compares V

to 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

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 T

= +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 lead-

ed and lead-free packaging. Specify lead free by adding the + sym-

bol at the end of the part number when ordering. Lead free not avail-

able for CERDIP package.

Summary of content (16 pages)

PAGE 1
9-0147; Rev. 4; 11/05 Microprocessor and Nonvolatile Memory Supervisory Circuits Features 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 VCC down to 1V. • Manual-reset input.
PAGE 2
MAX792/MAX820 Microprocessor and Nonvolatile Memory Supervisory Circuits ABSOLUTE MAXIMUM RATINGS 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 ............................................................
PAGE 3
Microprocessor and Nonvolatile Memory Supervisory Circuits MAX792/MAX820 ELECTRICAL CHARACTERISTICS (continued) (VCC = 2.75V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS LOW-LINE COMPARATOR Low-Line Threshold Voltage (Internal Threshold Mode)—VTH MAX792/MAX820L/M 50 120 210 MAX792/MAX820R/S/T 40 100 210 Low-Line Threshold Voltage (External Programming Mode) MAX792, VCC = 5V OR VCC = 3V 1.25 1.30 1.35 MAX820, VCC = 5V OR VCC = 3V 1.274 1.
PAGE 4
MAX792/MAX820 Microprocessor and Nonvolatile Memory Supervisory Circuits ELECTRICAL CHARACTERISTICS (continued) (VCC = +2.75V to +5.5V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 1.30 1.35 V ±0.01 ±25 nA OVERVOLTAGE COMPARATOR OVI Input Threshold VCC = 5V or VCC = 3V 1.25 OVI Leakage Current OVO Output Voltage OVO Short-Circuit Current OVI to OVO Delay ISINK = 3.2mA 0.4 ISOURCE = 1µA VCC - 1 Output source current, VCC = 5.
PAGE 5
Microprocessor and Nonvolatile Memory Supervisory Circuits OVERVOLTAGE COMPARATOR PROPAGATION DELAY vs. TEMPERATURE 50 VCC = 3V 40 30 20 50 40 VIH TO VOL VIN = 20mV OVERDRIVE = 15mV VCC = 2V 10 -60 -30 0 30 60 90 120 150 -60 -30 0 30 70 60 50 VCC FALLING 15mV OVERDRIVE EXTERNAL PROGRAMMING MODE 40 30 0 60 90 120 150 -60 -30 0 30 60 90 120 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) LOW-LINE COMPARATOR PROPAGATION DELAY vs. TEMPERATURE POWER-UP RESET DELAY vs.
PAGE 6
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) INTERNAL-MODE RESET THRESHOLD vs. TEMPERATURE (NORMALIZED) REF OUT VOLTAGE vs. TEMPERATURE ON-RESISTANCE (Ω) 1.31 REF OUT (V) 1.000 0.975 1.30 1.29 1.28 1.27 THE RESET THRESHOLD IS SHOWN NORMALIZED TO 1, REPRESENTING ALL AVAILABLE MAX792/MAX820 0.925 0.900 -30 0 30 60 90 1.26 RESET IN / INT = 0V 120 150 -30 0 30 60 90 120 60 VCC = 5V VCE IN = 2.
PAGE 7
Microprocessor and Nonvolatile Memory Supervisory Circuits PIN NAME FUNCTION 1 RESET Active-Low Reset Output goes low whenever VCC falls below the reset threshold in internal threshold programming mode, or RESET IN falls below 1.30V in external threshold programming mode. RESET remains low for 200ms typ after the threshold is exceeded on power-up. 2 RESET Reset is the inverse of RESET. 3 VCC 4 RESET IN/INT Reset-Input/Internal-Mode Select.
PAGE 8
MAX792/MAX820 Microprocessor and Nonvolatile Memory Supervisory Circuits Detailed Description Manual-Reset Input Many µP-based products require manual-reset capability, allowing the operator to initiate a reset. The manual/external-reset input (MR) can connect directly to a switch without an external pull-up resistor or debouncing network. MR internally connects to a 1.30V comparator, and has a high-impedance pull-up to VCC, as shown in Figure 1.
PAGE 9
Microprocessor and Nonvolatile Memory Supervisory Circuits 3 2 VCC RESET IN/ INT * 4 MAX792/MAX820 VCC RESET RESET COMPARATOR RESET GENERATOR 1 RESET VCC LLIN/ REFOUT MR 5 10 VCC VCC LOW-LINE COMPARATOR CHIP-ENABLE OUTPUT CONTROL VCC 9 LOW LINE P MANUAL RESET COMPARATOR 1.
PAGE 10
MAX792/MAX820 Microprocessor and Nonvolatile Memory Supervisory Circuits VIN 25µs MIN MR 3 VCC 12µs TYP RESET 4 RESET IN/INT RESET 2 TO µP RESET 1 TO µP 10 TO µP NMI CE IN OV 5 CE OUT 15µs TYP MAX792 LLIN/REFOUT LOW LINE Figure 2. Manual-Reset Timing Diagram GND 12 MANUAL RESET 9 MR Figure 4a. Connection for Internal Threshold Mode * OTHER RESET SOURCES * . . . VIN MAX792 MAX820 3 R1 RESET IN/INT * DIODES NOT REQUIRED ON OPEN-DRAIN OUTPUTS Figure 3.
PAGE 11
Microprocessor and Nonvolatile Memory Supervisory Circuits RESET TO µP RESET 10k MAX792 MAX820 VCC R3 1 RESET IN/INT RESET 2 TO µP RESET 1 TO µP R1 MAX792 MAX820 R4 LLIN/REFOUT Figure 5. Adding an external pull-down resistor ensures RESET is valid with VCC down to GND. R2 LOW LINE 10 VLOW LINE = 1.3 ( R1R2+ R2 ) VRESET = 1.3 R3 + R4 ( R4 ) TO µP NMI GND VOLTAGE REGULATOR 3 VCC Figure 4c.
PAGE 12
MAX792/MAX820 Microprocessor and Nonvolatile Memory Supervisory Circuits 1.6s MIN 100ns (VCC = 5V) MIN 300ns (VCC = 3V) VCC 3 VCC WDI 0.1µF VCC WDPO µP POWER MAX792 MAX820 70ns RESET WDO WDI WDPO VCC = 5V 9 Figure 7. WDI, WDO, and WDPO Timing Diagram GND 12 +5V default is 1.6s. Select alternative timeout periods by connecting an external capacitor from SWT to GND (see Selecting an Alternative Watchdog Timeout section). When VCC is below the reset threshold, the watchdog function is disabled.
PAGE 13
Microprocessor and Nonvolatile Memory Supervisory Circuits MAX792/MAX820 Chip-Enable Signal Gating The MAX792/MAX820 provide internal gating of chipenable (CE) signals, which prevents erroneous data from corrupting CMOS RAM in the event of an undervoltage condition. The MAX792/MAX820 use a series transmission gate from CE IN to CE OUT (Figure 1). During normal operation (reset not asserted), the CE transmission gate is enabled and passes all CE transitions.
PAGE 14
+5V RP* CE 3 VCC RAM 1 CE IN TO OTHER SYSTEM RESET INPUTS VCC MAX792 MAX820 14 BUFFER CE CE OUT CE 13 3 VCC RAM 2 VCC CE RESET 1 4.7k µP RESET CE GND 12 RAM 3 MAX792 MAX820 CE CE RAM 4 ACTIVE-HIGH CE LINES FROM LOGIC Figure 11. Alternate CE Gating Alternative Chip-Enable Gating Using memory devices with both CE and CE inputs allows the MAX792/MAX820 CE propagation delay to be bypassed.
PAGE 15
Microprocessor and Nonvolatile Memory Supervisory Circuits PART** TEMP.
PAGE 16
INCHES N DIM A A1 B C e E H L H E MAX MIN 0.093 0.104 0.004 0.012 0.014 0.019 0.013 0.009 0.050 0.299 0.291 0.394 0.419 0.016 0.050 SOICW.EPS ________________________________________________________Package Information MILLIMETERS MIN 2.35 0.10 0.35 0.23 MAX 2.65 0.30 0.49 0.32 1.27 7.40 7.60 10.00 10.65 0.40 1.27 VARIATIONS: 1 INCHES TOP VIEW DIM D D D D D D A B e MIN 0.398 0.447 0.496 0.598 0.697 MAX 0.413 0.463 0.512 0.614 0.713 MILLIMETERS MIN 10.10 11.35 12.60 15.20 17.70 MAX 10.