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MAX703/MAX704

Low-Cost Microprocessor Supervisory

Circuits with Battery Backup

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-0130; Rev 2; 11/05

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.

♦

General Description

The MAX703/MAX704 microprocessor (µP) supervisory

circuits reduce the complexity and number of compo-

nents required for power-supply monitoring and battery

control functions in µP systems. These devices signifi-

cantly improve system reliability and accuracy com-

pared to that obtained with separate ICs or discrete

components.

The MAX703/MAX704 are available in 8-pin DIP and SO

packages and provide four functions:

1) An active-low reset during power-up, power-down,

and brownout conditions.

2) Battery-backup switching for CMOS RAM, CMOS

µPs, or other low-power logic circuitry.

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

low-battery detection, or for monitoring a power

supply other than +5V.

4) An active-low manual reset input.

The MAX703 and MAX704 differ only in their supply-

voltage monitor levels. The MAX703 generates a reset

when the supply drops below 4.65V, while the MAX704

generates a reset below 4.4V.

Features

Applications

Dice are tested at T

= +25°C only.

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

Devices in PDIP and SO 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.

PART TEMP RANGE PIN-PACKAGE

MAX703C/D 0°C to +70°C Dice*

MAX703CPA 0°C to +70°C 8 PDIP

MAX703CSA 0°C to +70°C 8 SO

MAX703EPA -40°C to +85°C 8 PDIP

MAX703ESA -40°C to +85°C 8 SO

MAX703MJA -55°C to +125°C 8 CERDIP**

MAX704C/D 0°C to +70°C Dice*

MAX704CPA 0°C to +70°C 8 PDIP

MAX704CSA 0°C to +70°C 8 SO

MAX704EPA -40°C to +85°C 8 PDIP

MAX704ESA -40°C to +85°C 8 SO

MAX704MJA -55°C to +125°C 8 CERDIP**

Battery-Backup Power Switching

Precision Supply-Voltage Monitor

4.65V (MAX703)

4.40V (MAX704)

200ms Reset Pulse Width

Debounced TTL/CMOS-Compatible Manual Reset

Input

200µA Quiescent Current

50nA Quiescent Current in Battery-Backup Mode

Voltage Monitor for Power-Fail or Low-Battery

Warning

8-Pin DIP and SO Packages

Guaranteed RESET Assertion to V

= 1V

Computers

Controllers

Intelligent Instruments

Automotive Systems

Critical µP Power Monitoring

PFOPFI

BATT

RESETV

GND

OUT

DIP/SO

TOP VIEW

MAX703

MAX704

Pin Configuration

MAX703

MAX704

UNREGULATED DC REGULATED +5V

CMOS RAM

MICROPROCESSOR

3.6V

LITHIUM

BATTERY

PFI

PUSHBUTTON

SWITCH

0.1μF

OUT

BATT

NMI

GND

BUS

RESET

PFO

Typical Operating Circuit

Summary of content (9 pages)

PAGE 1
9-0130; Rev 2; 11/05 Low-Cost Microprocessor Supervisory Circuits with Battery Backup The MAX703/MAX704 microprocessor (µP) supervisory circuits reduce the complexity and number of components required for power-supply monitoring and battery control functions in µP systems. These devices significantly improve system reliability and accuracy compared to that obtained with separate ICs or discrete components.
PAGE 2
MAX703/MAX704 Low-Cost Microprocessor Supervisory Circuits with Battery Backup ABSOLUTE MAXIMUM RATINGS Terminal Voltage (with respect to GND) VCC ....................................................................-0.3V to +6.0V VBATT .................................................................-0.3V to +6.0V All Other Inputs (Note 1).........................-0.3V to (VCB + 0.3V) Input Current VCC ...............................................................................200mA VBATT ..............
PAGE 3
Low-Cost Microprocessor Supervisory Circuits with Battery Backup MAX703/MAX704 ELECTRICAL CHARACTERISTICS (continued) (VCC = +4.75V to +5.5V for MAX703, VCC = +4.5V to +5.5V for MAX704, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL MR Input Threshold CONDITIONS VIL Low VIH High MR Pulse Width tMR MR to RESET Delay tMD MIN TYP MAX UNITS 0.8 V 2.0 150 ns 250 ns 250 600 µA MR Pullup Current MR = 0V 100 PFI Input Threshold VCC = 5V 1.20 1.25 1.
PAGE 4
Low-Cost Microprocessor Supervisory Circuits with Battery Backup MAX703/MAX704 Pin Description PIN NAME FUNCTION 1 VOUT Supply Output for CMOS RAM. When VCC is above the reset threshold, VOUT connects to VCC through a pchannel MOSFET switch. When VCC is below the reset threshold, the higher of VCC or VBATT is connected to VOUT. 2 VCC +5V Supply Input 3 GND Ground 4 PFI Power-Fail Comparator Input. When PFI is less than 1.25V, PFO goes low; otherwise PFO remains high.
PAGE 5
Low-Cost Microprocessor Supervisory Circuits with Battery Backup RESET Output A 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 MAX703/MAX704 assert reset when VCC is low, preventing code-execution errors during power-up, power-down, or brownout conditions. When VBATT is 2V or more, RESET is always valid, irrespective of VCC. On power-up, as VCC rises, RESET remains low.
PAGE 6
MAX703/MAX704 Low-Cost Microprocessor Supervisory Circuits with Battery Backup drops to more than 1V below V BATT , the internal switchover comparator shuts off and the supply current falls to less than 1µA. +5V VOUT VCC TO STATIC RAM Manual Reset The manual reset input (MR) allows RESET to be activated by a pushbutton switch. The switch is effectively debounced by the 140ms minimum reset pulse width. Because it is TTL/CMOS compatible, MR can be driven by an external logic line.
PAGE 7
Low-Cost Microprocessor Supervisory Circuits with Battery Backup When VCC falls below 1V, the MAX703/MAX704 RESET output no longer sinks current; it becomes an open circuit. High-impedance CMOS logic inputs can drift to undetermined voltages if left as open circuits. If a pulldown resistor is added to the RESET pin as shown in Figure 6, any stray charge or leakage currents will flow to ground, holding RESET low. Resistor value R1 is not critical.
PAGE 8
MAX703/MAX704 Low-Cost Microprocessor Supervisory Circuits with Battery Backup Using the Power-Fail Comparator to Assert Reset In addition to asserting reset at the VCC reset threshold voltage, reset can also be asserted at the PFI input threshold voltage. Connect PFO to MR to initiate a reset pulse when the monitored supply drops below a userspecified threshold or when VCC falls below the reset threshold. For additional noise rejection, place a capacitor between PFI and GND. Table 3.
PAGE 9
Low-Cost Microprocessor Supervisory Circuits with Battery Backup Package Information For the latest package outline information, go to www.maxim-ic.com/packages. SUBSTRATE MUST BE LEFT UNCONNECTED TRANSISTOR COUNT: 573 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.