Datasheet

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General Description

The MAX690 family of supervisory circuits reduces the

complexity and number of components required for

power supply monitoring and battery control functions in

microprocessor systems. These include µP reset and

backup-battery switchover, watchdog timer, CMOS RAM

write protection, and power-failure warning. The MAX690

family significantly improves system reliability and accu-

racy compared to that obtainable with separate ICs or

discrete components.

The MAX690, MAX692, and MAX694 are supplied in

8-pin packages and provide four functions:

● A reset output during power-up, power-down, and

brownout conditions.

● Battery backup switching for CMOS RAM, CMOS

microprocessor or other low power logic.

● A Reset pulse if the optional watchdog timer has not

been toggled within a specified time.

● A 1.3V threshold detector for power fail warning, low

battery detection, or to monitor a power supply other

than +5V.

The MAX691, MAX693, and MAX695 are supplied in 16-pin

packages and perform all MAX690, MAX692, MAX694

functions, plus:

● Write protection of CMOS RAM or EEPROM.

● Adjustable reset and watchdog timeout periods.

● Separate outputs for indicating a watchdog timeout,

backup-battery switchover, and low V

Benets and Features

● Supervisory Function Integration Saves Board Space

while Fully Protecting Microprocessor-Based Systems

• Precision Voltage Monitor

- 4.65V (MAX690, MAX691, MAX694, MAX695)

- 4.40V (MAX692, MAX693)

• Power OK/Reset Time Delay

- 50ms, 200ms, or Adjustable

• Watchdog Timer

- 100ms, 1.6s, or Adjustable

• Battery Backup Power Switching

• Voltage Monitor for Power Fail or Low Battery

Warning

• Minimum External Component Count

● Low Power Consumption in Battery Backup Mode

Extends Battery Life

• 1µA Standby Current

● Onboard Gating of Chip Enable Signals Protects

Against Erroneous Data Written to RAM During Low

Events

Applications

● Computers

● Controllers

● Intelligent Instruments

● Automotive Systems

● Critical µP Power Monitoring

Ordering information appears at end of data sheet.

19-0218; Rev 5; 4/15

MAX690

MAX692

MAX694

BATT

RESET

WDI

PFO

OUT

TOP VIEW

GND

PFI

MAX691

MAX693

MAX695

161

152

143

RESET

WDO

CE IN

BATT

OUT

GND

125

116

CE OUT

WDI

PFO

BATT ON

LOW LINE

OSC IN

98 PFIOSC SEL

MAX690

BATT

PFI

OUT

+5V

PFO

WDI

GND

MAX690 TYPICAL APPLICATION

RESET

POWER TO

CMOS RAM

µP

POWER

µP

SYSTEM

µP NMI

I/O

LINE

µP RESET

MAX690–MAX695 Microprocessor Supervisory Circuits

Pin Congurations

Typical Operating Circuit

Summary of content (18 pages)

PAGE 1
MAX690–MAX695 Microprocessor Supervisory Circuits General Description The MAX690 family of supervisory circuits reduces the complexity and number of components required for power supply monitoring and battery control functions in microprocessor systems. These include µP reset and backup-battery switchover, watchdog timer, CMOS RAM write protection, and power-failure warning.
PAGE 2
MAX690–MAX695 Microprocessor Supervisory Circuits 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 (VOUT + 0.5V) Input Current VCC................................................................................200mA VBATT................................................
PAGE 3
MAX690–MAX695 Microprocessor Supervisory Circuits Electrical Characteristics (continued) VCC = full operating range, VBATT = 2.8V, TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN Battery Switchover Hysteresis BATT ON Output Voltage BATT ON Output Short-Circuit Current TYP MAX 20 ISINK = 3.2mA mV 0.4 BATT ON = VOUT = 4.5V sink current BATT ON = 0V source current UNITS 25 V mA 0.5 1 25 MAX690, MAX691, MAX694, MAX695 4.5 4.65 4.75 MAX692, MAX693 4.25 4.4 4.
PAGE 4
MAX690–MAX695 Microprocessor Supervisory Circuits Electrical Characteristics (continued) VCC = full operating range, VBATT = 2.8V, TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS CHIP ENABLE GATING VIL CE IN Thresholds 0.8 VIH V 3.0 CE IN Pullup Current 3 µA ISINK = 3.2mA CE OUT Output Voltage CE Propagation Delay 0.4 ISOURCE = 3.0mA VOUT - 1.5 ISOURCE = 1µA, VCC = 0V VOUT - 0.
PAGE 5
MAX690–MAX695 Microprocessor Supervisory Circuits Pin Description (continued) PIN MAX690/ MAX692/ MAX694 MAX691/ MAX693/ MAX695 NAME 5 10 PFO — 13 CE IN — 12 CE OUT CE OUT goes low only when CE IN is low and VCC is above the reset threshold (4.65V for MAX691 and MAX695, 4.4V for MAX693). See Figure 6. FUNCTION Output of the Power-Fail Comparator. It goes low when PFI is less than 1.3V. The comparator is turned off and PFO goes low when VCC is below VBATT. CE Gating Circuit Input.
PAGE 6
MAX690–MAX695 Microprocessor Supervisory Circuits Typical Applications power-up RESET pulse lasts 50ms* to allow for this oscillator start-up time. The manual reset switch and the 0.1µF capacitor connected to the reset bus can be omitted if manual reset is not needed. An inverted, active high, RESET output is also supplied. MAX691, MAX693, and MAX695 A typical connection for the MAX691/693/695 is shown in Figure 1. CMOS RAM is powered from VOUT.
PAGE 7
MAX690–MAX695 Microprocessor Supervisory Circuits Watchdog Timer application. Operation is much the same as with the MAX691/MAX693/MAX695 (Figure 1), but in this case, the power- fail input (PFI) monitors the unregulated input to the 7805 regulator. The MAX690/MAX694 RESET output goes low when VCC falls below 4.65V. The RESET output of the MAX692 goes low when VCC drops below 4.4V. The microprocessor drives the WATCHDOG INPUT (WDI) with an I/O line.
PAGE 8
MAX690–MAX695 Microprocessor Supervisory Circuits Detailed Description Battery-Switchover and VOUT The battery switchover circuit compares VCC to the VBATT input, and connects VOUT to whichever is higher. Switchover occurs when VCC is 50mV greater than VBATT as VCC falls, and VCC is 70mV more than VBATT as VCC rises (see Figure 4). The switchover comparator has 20mV of hysteresis to prevent repeated, rapid switching if VCC falls very slowly or remains nearly equal to the battery voltage.
PAGE 9
MAX690–MAX695 Microprocessor Supervisory Circuits VCC +5V VOUT VCC P CHANNEL MOSFET BASE DRIVE 100 mV 3V BATTERY INPUT + BATT ON (MAX691, MAX693, MAX695 ONLY) - 700 mV 0.1F TO CMOS RAM AND REALTIME CLOCK VCC IN + + LOW IQ MODE - SELECT INTERNAL SHUTDOWN SIGNAL WHEN VBATT > VCC + 0.7V Figure 4. Battery-Switchover Block Diagram Reset Output RESET is an active-low output which goes low whenever VCC falls below 4.5V (MAX690/MAX691/MAX694/ MAX695) or 4.25V (MAX692/MAX693).
PAGE 10
MAX690–MAX695 Microprocessor Supervisory Circuits CE IN CE OUT LOW LINE VCC RESET POWER-ON RESET METAL LINK TRIMMED RESISTORS + RESET RESET TIME 1.3V RESET QR WATCHDOG FROM WATCHDOG TIMER 10 kHz CLOCK FROM TIMEBASE SECTION Figure 5. Reset Block Diagram VCC RESET OUTPUT 4.7V 50ms* 4.6V 4.7V 4.6V 50ms* LOW LINE OUTPUT CE IN CE IN VOUT - VBATT *200ms FOR MAX694 AND MAX695 Figure 6. Reset Timing www.maximintegrated.
PAGE 11
MAX690–MAX695 Microprocessor Supervisory Circuits 1.3V Comparator and Power-Fail Warning at the end of reset, whether the reset was caused by lack of activity on WDI or by VCC falling below the reset threshold. If WDI remains either high or low, reset pulses will be issued every 1.6s. The watchdog monitor can be deactivated by floating the watchdog input (WDI). The power-fail input (PFI) is compared to an internal 1.3V reference.
PAGE 12
MAX690–MAX695 Microprocessor Supervisory Circuits EXTERNAL CLOCK 8 EXTERNAL OSCILLATOR 8 OSC SEL OSC SEL MAX691 MAX693 MAX695 0 TO 250kHz 7 MAX691 MAX693 MAX695 7 OSC IN OSC IN COSC INTERNAL OSCILLATOR 1.6s WATCHDOG N.C. N.C. 8 7 INTERNAL OSCILLATOR 100ms WATCHDOG N.C. OSC SEL MAX691 MAX693 MAX695 8 7 OSC IN OSC SEL MAX691 MAX693 MAX695 OSC IN Figure 8. Oscillator Circuits Table 1.
PAGE 13
MAX690–MAX695 Microprocessor Supervisory Circuits Application Hints Adding Hysteresis to the Power Fail Comparator Other Uses of the Power-Fail Detector In Figure 9, the power-fail detector is used to initiate a system reset when VCC falls to 4.85V. Since the threshold of the power-fail detector is not as accurate as the onboard reset-voltage detector, a trimpot must be used to adjust the voltage detection threshold.
PAGE 14
MAX690–MAX695 Microprocessor Supervisory Circuits 7V TO 15V +5V 7805 VCC +5V PFO R1 75kΩ VBATT 10MΩ PFI 10MΩ RL CE OUT VCC LOW BATTERY SIGNAL TO µP I/O PIN PFO MAX690 MAX691 MAX692 MAX693 MAX694 MAX695 GND MAX690 MAX691 MAX692 MAX693 MAX694 MAX695 R4 10kΩ PFI R2 13kΩ CE IN LOW APPLIES LOAD TO BATTERY FROM µP I/O PIN GND R3 300kΩ TO P VH = 9.125V VL = 7.9V HYSTERESIS = 1.23V ( ) R1 (5V -1.3V) R1 V = 1.3V (1 + R2 1.3V (R3 + R4) ) VH = 1.
PAGE 15
MAX690–MAX695 Microprocessor Supervisory Circuits Table 2. Input and Output Status In Battery Backup Mode VBATT, VOUT VBATT is connected to VOUT via internal MOSFET. RESET Logic-low RESET Logic-high. The open circuit output voltage is equal to VOUT. LOW LINE Logic-low BATT ON Logic-high WDI WDI is internally disconnected from its internal pullup and does not source or sink current as long as its input voltage is between GND and VOUT. The input voltage does not affect the source current.
PAGE 16
MAX690–MAX695 Microprocessor Supervisory Circuits Ordering Information PART TEMP RANGE PIN-PACKAGE PART TEMP RANGE PIN-PACKAGE MAX690CPA 0°C to +70°C 8 Lead Plastic DIP MAX693CPE 0°C to +70°C 16 Lead Plastic DIP MAX690C/D 0°C to +70°C Dice* MAX693CWE 0°C to +70°C 16 Lead Wide SO MAX690EPA -40°C to +85°C 8 Lead Plastic DIP MAX693EPE -40°C to +85°C 16 Lead Plastic DIP MAX690EJA -40°C to +85°C 8 Lead CERDIP MAX693EJE -40°C to +85°C 16 Lead CERDIP MAX690MJA -55°C to +125°C 8 Le
PAGE 17
MAX690–MAX695 Microprocessor Supervisory Circuits Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
PAGE 18
MAX690–MAX695 Microprocessor Supervisory Circuits Revision History REVISION NUMBER REVISION DATE 5 4/15 DESCRIPTION Revised Benefits and Features section PAGES CHANGED 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product.