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General Description

The MAX817/MAX818/MAX819 microprocessor (µP)

supervisory circuits simplify power-supply monitoring,

battery control, and chip-enable gating in µP systems

by reducing the number of components required.

These devices are designed for use in +5V-powered

systems. Low supply current (11µA typical) and small

package size make these devices ideal for portable

applications. The MAX817/MAX818/MAX819 are specif-

ically designed to ignore fast transients on V

. Other

supervisory functions include active-low reset, backup-

battery switchover, watchdog input, battery freshness

seal, and chip-enable gating. The Selector Guide below

lists the specific functions available from each device.

These devices offer two pretrimmed reset threshold volt-

ages for ±5% or ±10% power supplies: 4.65V for the L

versions and 4.40V for the M versions. The MAX817/

MAX818/MAX819 are available in space-saving µMAX

packages, as well as 8-pin DIP/SO.

________________________Applications

Battery-Powered Computers and Controllers

Embedded Controllers

Intelligent Instruments

Critical µP Monitoring

Portable Equipment

____________________________Features

♦ Precision Supply-Voltage Monitor:

4.65V (MAX81_L)

4.40V (MAX81_M)

♦ 11µA Quiescent Supply Current

♦ 200ms Reset Time Delay

♦ Watchdog Timer with 1.6sec Timeout

(MAX817/MAX818)

♦ Battery-Backup Power Switching; Battery Voltage

Can Exceed V

♦ Battery Freshness Seal

♦ On-Board, 3ns Gating of Chip-Enable Signals

(MAX818)

♦ Uncommitted Voltage Monitor for Power-Fail or

Low-Battery Warning (MAX817/MAX819)

♦ Manual Reset Input (MAX819)

MAX817L/M, MAX818L/M, MAX819L/M*

+5V Microprocessor Supervisory Circuits

________________________________________________________________ Maxim Integrated Products 1

WDI

GND

PFO

PFI

BATT

RESET

OUT

MAX817

DIP/SO/µMAX

TOP VIEW

_________________Pin Configurations

19-0486; Rev 3; 12/05

PART

†

MAX817_CPA

MAX817_CSA

MAX817_CUA 0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

8 Plastic DIP

8 SO

8 µMAX

______________Ordering Information

_____________________Selector Guide

Ordering Information continued on last page.

†

These parts offer a choice of reset threshold voltage. From the

table below, select the suffix corresponding to the desired

threshold and insert it into the blank to complete the part number.

Devices 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.

SUFFIX RESET THRESHOLD (V)

L 4.65

M 4.40

FEATURE

MAX817

L/M

Active-Low Reset

✔

Backup-Battery Switchover

✔

MAX818

L/M

✔

MAX819

L/M

✔

Power-Fail Comparator

✔

—

Watchdog Input

✔ ✔

✔

—

Battery Freshness Seal

✔ ✔

Manual Reset Input — —

✔

Chip-Enable Gating —

✔

Pin-Package

8-DIP/SO/

µMAX

8-DIP/SO/

µMAX

—

8-DIP/SO/

µMAX

Low-Power, Pin-

Compatible Upgrades for:

MAX690A/

MAX692A

—

MAX703/

MAX704

Typical Operating Circuit appears at end of data sheet.

Pin Configurations continued at end of data sheet.

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Summary of content (16 pages)

PAGE 1
9-0486; Rev 3; 12/05 +5V Microprocessor Supervisory Circuits The MAX817/MAX818/MAX819 microprocessor (µP) supervisory circuits simplify power-supply monitoring, battery control, and chip-enable gating in µP systems by reducing the number of components required. These devices are designed for use in +5V-powered systems. Low supply current (11µA typical) and small package size make these devices ideal for portable applications.
PAGE 2
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits ABSOLUTE MAXIMUM RATINGS Input Voltage VCC, BATT ..........................................................-0.3V to +6.0V All Other Pins (Note 1).............................-0.3V to (VCC + 0.3V) Input Current VCC Peak ..............................................................................1A VCC Continuous .............................................................250mA BATT Peak ..............................................
PAGE 3
+5V Microprocessor Supervisory Circuits (VCC = +4.75V to +5.5V for MAX81_L, VCC = +4.5V to +5.5V for MAX81_M, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX MAX81_L 4.50 4.65 4.75 MAX81_M 4.25 4.40 4.
PAGE 4
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits ELECTRICAL CHARACTERISTICS (continued) (VCC = +4.75V to +5.5V for MAX81_L, VCC = +4.5V to +5.5V for MAX81_M, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CHIP-ENABLE GATING (MAX818 only) CE IN Leakage Current Disable mode ±0.
PAGE 5
+5V Microprocessor Supervisory Circuits 12 10 8 -20 0 20 40 60 80 VBATT = 5.0V 120 100 80 VBATT = 2.8V 60 VBATT = 2.0V 40 20 100 VCE IN = 4V 80 70 60 VCE IN = 3V 50 40 VCE IN = 2V 30 20 10 0 -40 -20 0 20 40 60 80 -40 100 -20 0 20 40 60 TEMPERATURE (°C) TEMPERATURE (°C) BATT TO OUT ON-RESISTANCE vs. TEMPERATURE VCC TO OUT ON-RESISTANCE vs. TEMPERATURE RESET TIMEOUT PERIOD vs. TEMPERATURE VBATT = 2.0V 200 150 VBATT = 2.8V 100 VBATT = 5.
PAGE 6
____________________________Typical Operating Characteristics (continued) (VCC = +5V, VBATT = 3.0V, TA = +25°C, unless otherwise noted.) 4.5 MAX81_M 4.3 -40 1000 800 RESET OCCURS ABOVE CURVE 600 400 200 0 -20 0 20 40 60 6 5 4 3 2 1 0 1 80 MAX817/18/19-12 MAX817/18/19-11 1200 7 10 100 1000 10,000 0 1 2 4 3 5 6 TEMPERATURE (°C) RESET COMPARATOR OVERDRIVE, VTH-VCC (mV) VCC (V) CE IN TO CE OUT PROPAGATION DELAY vs. TEMPERATURE MAX817/MAX819 PFI THRESHOLD vs.
PAGE 7
+5V Microprocessor Supervisory Circuits PIN NAME FUNCTION MAX817 MAX818 MAX819 1 1 1 OUT Supply Output for CMOS RAM. When VCC rises above the reset threshold or above VBATT, OUT is connected to VCC through an internal P-channel MOSFET switch. When VCC falls below VBATT, BATT connects to OUT. 2 2 2 VCC Input Supply Voltage, +5V input. 3 3 3 GND Ground. 0V reference for all signals. 4 — 4 PFI — 4 — CE IN 5 — 6 — — 5 6 — 5 — — 6 Power-Fail Comparator Input.
PAGE 8
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits BATT OUT BATTERY SWITCHOVER CIRCUITRY VCC MAX817 MAX818 MAX819 RESET GENERATOR RESET 1.25V THIS PIN FOR MAX819 ONLY. MR BATTERY FRESHNESS SEAL CIRCUITRY WATCHDOG TIMER WDI THIS SECTION FOR MAX817/ MAX818 ONLY. THIS SECTION PFI FOR MAX817/ MAX819 ONLY. PFO 1.25V CHIP-ENABLE OUTPUT CONTROL THIS SECTION FOR MAX818 ONLY. CE IN CE OUT GND Figure 1.
PAGE 9
+5V Microprocessor Supervisory Circuits General Timing Characteristics Designed for 5V systems, the MAX817/MAX818/ MAX819 provide a number of microprocessor (µP) supervisory functions (see the Selector Guide on the first page). Figure 2 shows the typical timing relationships of the various outputs during power-up and power-down with typical VCC rise and fall times. RESET Output A µP’s reset input starts the µP in a known state.
PAGE 10
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits On the MAX819, MR must be high or open to enable the battery freshness seal. Once the battery freshness seal is enabled its operation is unaffected by MR. Watchdog Input (MAX817/MAX818) In the MAX817/MAX818, the watchdog circuit monitors the µP’s activity. If the µP does not toggle the watchdog input (WDI) within tWD (1.6sec), reset asserts. The internal 1.
PAGE 11
+5V Microprocessor Supervisory Circuits Chip-Enable Output (MAX818) When the CE transmission gate is enabled, the impedance of CE OUT is equivalent to a 40Ω resistor in series with the source driving CE IN. In the disabled mode, the transmission gate is off and an active pull-up connects CE OUT to OUT (Figure 5). This pull-up turns off when the transmission gate is enabled. +5V Power-Fail Comparator (MAX817/MAX819) The MAX817/MAX819 PFI input is compared to an internal reference.
PAGE 12
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits Backup-Battery Switchover In a brownout or power failure, it may be necessary to preserve the contents of RAM. With a backup battery installed at BATT, the MAX817/MAX818/MAX819 automatically switch RAM to backup power when VCC falls. These devices require two conditions before switching to battery-backup mode: 1) VCC must be below the reset threshold, and 2) V CC must be below V BATT .
PAGE 13
+5V Microprocessor Supervisory Circuits Using a SuperCap™ as a Backup Power Source SuperCaps are capacitors with extremely high capacitance values (on the order of 0.47F) for their size. Since BATT has the same operating voltage range as VCC, and the battery switchover threshold voltages are typically ±30mV centered at VBATT , a SuperCap and simple charging circuit can be used as a backup power source. Figure 11 shows a SuperCap used as a backup source. If VCC is above the reset threshold and VBATT is 0.
PAGE 14
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits desired trip point (VTRIP). Resistor R3 adds hysteresis. It will typically be an order of magnitude greater than R1 or R2. The current through R1 and R2 should be at least 1µA to ensure that the 25nA (max) PFI input leakage current does not shift the trip point. R3 should be larger than 200kΩ to prevent it from loading down the PFO pin. Capacitor C1 adds additional noise rejection.
PAGE 15
+5V Microprocessor Supervisory Circuits To help the watchdog timer monitor software execution more closely, set and reset the watchdog input at different points in the program, rather than “pulsing” the watchdog input high-low-high or low-high-low. This technique avoids a “stuck” loop, in which the watchdog timer would continue to be reset within the loop, keeping the watchdog from timing out.
PAGE 16
MAX817L/M, MAX818L/M, MAX819L/M* +5V Microprocessor Supervisory Circuits Ordering Information (continued) PART† TEMP.