MAXIM MAX791 User Manual

MAX791

Microprocessor Supervisory Circuit

________________________________________________________________ Maxim Integrated Products 1

19-0075; Rev. 7; 11/05

General Description

The MAX791 microprocessor (µP) supervisory circuit reduces the complexity and number of components needed to monitor power-supply and battery-control functions in µP systems. The 50µA supply current makes the MAX791 ideal for use in portable equipment, while the 6ns chip-enable propagation delay and 250mA output capability (25mA in battery-backup mode) make it suitable for larger, higher-performance equipment.

The MAX791 comes in 16-pin DIP, TSSOP, and narrow SO packages and provides the following functions:

•µP reset. –R—E—S—E—T–output is asserted during power-up, power-down, and brownout conditions, and is guaranteed to be in the correct state for V

down to 1V,

even with no battery in the circuit.

• Manual-reset input.

•A 1.25V threshold detector provides for power-fail warning and low-battery detection, or monitors a power supply other than +5V.

• Two-stage power-fail warning. A separate low-line comparator compares V

to a threshold 150mV

above the reset threshold.

• Backup-battery switchover for CMOS RAM, real-time clocks, µPs, or other low-power logic.

• Software monitoring of backup-battery voltage.

•A watchdog-fault output is asserted if the watchdog input has not been toggled within either a preset or an adjustable timeout period.

• Write protection of CMOS RAM or EEPROM.

• Pulsed watchdog output to give advance warning of impending–W—D—O–assertion caused by watchdog timeout.

Applications

Computers Critical µP Power Monitoring Controllers Intelligent Instruments Portable/Battery-

Powered Equipment

Features

♦ Precision 4.65V Voltage Monitoring ♦ 200ms Power-OK/ Reset Time Delay ♦ Independent Watchdog Timer—Preset or Adjustable ♦ 1µA Standby Current ♦ Power Switching

250mA Output in V

Mode

25mA Output in Battery-Backup Mode

♦ On-Board Gating of Chip-Enable Signals

Memory Write-Cycle Completion 6ns CE Gate Propagation Delay

♦ MaxCap



or SuperCapCompatible

♦ Voltage Monitor for Power-Fail or Low-Battery Warning ♦ Backup-Battery Monitor ♦ Guaranteed –R—E—S—E—T–Valid to V

= 1V

Ordering Information

WDPO

RESET

WDO

CE IN

GND

OUT

VBATT

TOP VIEW

MAX791

CE OUT

WDI

LOWLINE

SWT

PFI

PFO

BATT ON

DIP/SO/TSSOP

CMOS RAM

MAX791

RESET

LOWLINE

WDI

CE IN

CE OUT

+5V

OTHER SYSTEM

RESET SOURCES

+12V

OUT

VBATT

MaxCap

A0–A15

+12V SUPPLY

FAILURE

BATTONSWT

ADDRESS

DECODE

0.1µF

0.47F*

PFI

PFO

GND

I/O

µP

NMI

INT

RESET

WDO

Pin Configuration

Typical Operating Circuit

PART TEMP RANGE PIN-PACKAGE

MAX791CPE 0°C to +70°C 16 Plastic DIP

MAX791CSE 0°C to +70°C 16 Narrow SO

MAX791C/D 0°C to +70°C Dice*

MAX791EPE -40°C to +85°C 16 Plastic DIP

MAX791ESE -40°C to +85°C 16 Narrow SO

MAX791EJE -40°C to +85°C 16 CERDIP

MAX791MJE -55°C to +125°C 16 CERDIP

MaxCap is a registered trademark of Cesiwid Inc. SuperCap is a registered trademark of Baknor Industries.

* Dice are specified at T

= +25°C.

Devices in PDIP, SO and TSSOP 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.

MAX791CUE 0°C to +70°C 16 TSSOP

MAX791EUE -40°C to +85°C 16 TSSOP

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.

MAX791

Microprocessor Supervisory Circuit

2 _______________________________________________________________________________________

Input Voltage (with respect to GND)

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

VBATT..................................................................-0.3V to + 6V

All Other Inputs.....................................-0.3V to (V

OUT

+ 0.3V)

Input Current

VCCPeak ..........................................................................1.0A

VCCContinuous ............................................................250mA

VBATT Peak ..................................................................250mA

VBATT Continuous ..........................................................25mA

GND, BATT ON .............................................................100mA

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

Continuous Power Dissipation (T

= +70°C)

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

Narrow SO (derate 8.70mW/°C above +70°C) ............696mW

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

TSSOP (derate 6.70mW/°C above +70°C) ..................533mW

Operating Temperature Ranges

MAX791C_ _ ......................................................O°C to +70°C

MAX791E_ _ ....................................................-40°C to +85°C

MAX791MJE ..................................................-55°C to +125°C

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

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

ELECTRICAL CHARACTERISTICS

(VCC= 4.75V to 5.5V, VBATT = 2.8V, 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

PARAMETER CONDITIONS

Supply Current in Battery-Backup Mode (excludes I

OUT

) (Note 2)

MIN TYP MAX UNITS

VBATT = 4.5V, I

OUT

= 20mA VBATT - 0.3

Operating Voltage Range VCC, VBATT (Note 1)

0 5.5 V

VCC- 0.3 VCC- 0.2

VCC- 0.05 VCC- 0.02

VBATT-to-V

OUT

On-Resistance

VBATT = 2.0V

µA

17 30

Ω

Battery-Switchover Threshold

Power down VBATT - 0.03

OUT

in Normal

Operating Mode

VCC= 3V, VBATT = 2.8V, I

OUT

= 100mA VCC- 0.2 VCC- 0.12

VCC= 4.5V

0.8 1.6

0.8 1.2

VCC= 4.5V

VCC- 0.40

VBATT = 2.8V, I

OUT

= 10mA VBATT - 0.25

0.04 1

Supply Current in Normal Operating Mode (excludes I

OUT

)

VCC> VBATT - 1V 50 150 µA

VCC-to-V

OUT

On-Resistance

VCC= 3V 1.2 2.0

Ω

VBATT = 4.5V 815

VBATT = 2.8V

Power up

13 25

VBATT + 0.03

OUT

in Battery-Backup Mode

VBATT = 2.0V, I

OUT

= 5mA VBATT - 0.15

Battery-Switchover Hysteresis 60 mV

Low-Battery Detector Threshold 2 V

OUT

= 250mA

OUT

= 25mA

MAX791C/E

MAX791M

MAX791C/E

MAX791M

VCC< VBATT - 1.2V, VBATT = 2.8V

TA= +25°C

TA= T

MIN

to T

MAX

VBATT Standby Current (Note 3)

TA= T

MIN

to T

MAX

TA= +25°C

-1.0 0.02

µAVBATT + 0.2V ≤ V

-0.1 0.02

MAX791

Microprocessor Supervisory Circuit

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 4.75V to 5.5V, VBATT = 2.8V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

0.7 1.5I

SINK

= 25mA

mA720Output source current

–W—D—P—O–

Output

Short-Circuit Current

0.1 0.4I

SINK

= 3.2mA

BATT ON Output Low Voltage

ms104.7nF capacitor connected from SWT to GND

Minimum Watchdog Timeout Period

ms1

–W—D—P—O–

Pulse Width

ns100VIL= 0.8V, VIH= 0.75 x V

Minimum Watchdog Input Pulse Width

µs80Power downVCC-to-–L—O—W

— —L—I—N—E–

Delay

s1.0 1.6 2.25SWT connected to V

OUT

V4.50 4.65 4.75

–R—E—S—E—T–

Threshold Voltage

mV150

–L—O—W— —L—I—N—E–

-to-–R—E—S—E—T

–

Threshold Voltage

µs100Power downVCC-to-–R—E—S—E—T–Delay

mV15

–R—E—S—E—T–

Threshold Hysteresis

Watchdog Timeout Period

ns70

–W—D—P—O–

-to-–W—D—O–Delay

µA

115100Source current

BATT ON Output Short-Circuit Current

mA60Sink current

140 200 280Power up

UNITSMIN TYP MAX

–R—E—S—E—T–

Active Timeout Period

CONDITIONSPARAMETER

0.004 0.3MAX791E/M, I

SINK

= 50µA, VCC= 1.2V, VCCfalling

0.1 0.4I

SINK

= 3.2mA, VCC= 4.25V

3.5I

SOURCE

= 1.6mA, VCC= 5V

–R—E—S—E—T–

Output Voltage

mA720Output source current

–R—E—S—E—T–

Output

Short-Circuit Current

0.4I

SINK

= 3.2mA, VCC= 4.25V

µA15 100Output source current

–L—O—W— —L—I—N—E–

Output

Short-Circuit Current

3.5I

SOURCE

= 1µA, VCC= 5V

–L—O—W— —L—I—N—E–

Output Voltage

0.4I

SINK

= 3.2mA

mA310Output source current

–W—D—O–

Output Short-Circuit Current

3.5I

SOURCE

= 500µA, VCC= 5V

–W—D—O–

Output Voltage

0.4I

SINK

= 3.2mA

3.5I

SOURCE

= 1mA

–W—D—P—O–

Output Voltage

0.004 0.3MAX791C, I

SINK

= 50µA, VCC= 1.0V, VCCfalling

RESET, LOW-LINE, AND WATCHDOG TIMER

MAX791

Microprocessor Supervisory Circuit

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 4.75V to 5.5V, VBATT = 2.8V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

Note 1: Either V

or VBATT can go to 0V, if the other is greater than 2.0V.

Note 2: The supply current drawn by the MAX791 from the battery (excluding I

OUT

) typically goes to 10µA when

(VBATT - 1V) < V

< VBATT. In most applications, this is a brief period as VCCfalls through this region.

Note 3: "+" = battery-discharging current, "-" = battery-charging current. Note 4: WDI is internally connected to a voltage-divider between V

OUT

and GND. If unconnected, WDI is driven to 1.6V (typ),

disabling the watchdog function.

Note 5: The chip-enable resistance is tested with V

= 4.75V V

–C—E–

= V

C—E–OUT

= V

/ 2.

Note 6: The chip-enable propagation delay is measured from the 50% point at –C—E–IN to the 50% point at –C—E–OUT.

61050Ω source impedance driver, C

LOAD

= 50pF

–C—E–

IN-to-C—E–OUT Propagation

Delay (Note 6)

-50 -10WDI = 0V µA

20 50WDI = V

OUT

WDI Input Current

0.75 x V

µA23 250

–M—R–

= 0V

–M—R–

Pull-Up Current

µs7

Ω75 150Enabled mode

–M—R–

-to -–R—E—S—E—T

–

Propagation Delay

–C—E–

IN-to-–C—E–OUT Resistance

(Note 5)

µA±0.005 ±1Disabled mode

–C—E–

IN Leakage Current

µs15Power down

–R—E—S—E—T–

-to-–C—E–OUT Delay

nA±0.01 ±25PFI Leakage Current

V1.25VCC= 5V

–M—R–

Threshold

mA0.1 0.75 2.0

µs

Disabled mode, –C—E–OUT = 0V

25 15

–C—E–

OUT Short-Circuit Current

(Reset Active)

V1.20 1.25 1.30VCC= 5VPFI Input Threshold

0.8V

WDI Threshold Voltage (Note 4)

UNITSMIN TYP MAX

–M—R–

Minimum Pulse Width

CONDITIONSPARAMETER

0.4I

SINK

= 3.2mA

3.5I

SOURCE

= 1µA, VCC= 5V

–P—F—O–

Output Voltage

mA60Output sink current

µA115100Output source current

–P—F—O–

Short-Circuit Current

µs

55VIN= 20mV, VOD= 15mV

PFI-to-–P—F—O–Delay

15VIN= -20mV, VOD= 15mV

3.5VCC= 5V, I

OUT

= -100µA

2.7VCC= 0V, VBATT = 2.8V, I

OUT

= 1µA

–C—E–

OUT Output Voltage High

(Reset Active)

POWER-FAIL COMPARATOR

CHIP-ENABLE GATING

MANUAL RESET INPUT

MAX791

Microprocessor Supervisory Circuit

-60 -30 30 150

VCC SUPPLY CURRENT vs. TEMPERATURE

(NORMAL OPERATING MODE)

MAX791-01

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

0 1209060

VCC = +5V VBATT = 2.8V PFI, CE IN = 0V

4.80

4.30

4.40

4.35

-60 -30 30 150

RESET THRESHOLD vs. TEMPERATURE

MAX791-07

TEMPERATURE (°C)

RESET THRESHOLD (V)

0 1209060

4.45

4.50

4.55

4.60

4.65

4.70

4.75

VBATT = 0V, POWER DOWN

600

100

-60 -30 30 150

RESET OUTPUT RESISTANCE

vs. TEMPERATURE

MAX791-08

TEMPERATURE (°C)

RESET OUTPUT RESISTANCE (Ω)

0 1209060

200

300

400

500

VCC = 0V, VBATT = 2.8V SINKING CURRENT

VCC = +5V, VBATT = 2.8V SOURCING CURRENT

230

170

180

-60 -30 30 150

RESET DELAY

vs. TEMPERATURE

MAX791-09

TEMPERATURE (°C)

RESET DELAY (ms)

01209060

190

200

210

220

VCC = 0V TO 5V STEP VBATT = 2.8V

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

-60 -30 30 150

VBATT-to-V

OUT

ON-RESISTANCE

vs. TEMPERATURE

MAX791-04

TEMPERATURE (°C)

VBATT-to-V

OUT

ON-RESISTANCE (Ω)

0 1209060

VBATT = 2.0V

VBATT = 2.8V

VBATT = 4.5V

VCC = 0V

2.0

-60 -30 30 150

BATTERY-SUPPLY CURRENT vs. TEMPERATURE

(BATTERY-BACKUP MODE)

0.5

MAX791-02

TEMPERATURE (°C)

BATTERY SUPPLY CURRENT (µA)

0 1209060

1.0

1.5

VCC = 0V VBATT = 2.8V NO LOAD

120

-60 -30 30 150 180

CHIP-ENABLE ON-RESISTANCE

vs. TEMPERATURE

MAX791-03

TEMPERATURE (°C)

CE ON-RESISTANCE (Ω)

0 1209060

100

VCC = +4.75V VBATT = 2.8V CE IN = V

1.2

0.6

0.7

-60 -30 30 150

VCC-to-V

OUT

ON-RESISTANCE

vs. TEMPERATURE

MAX791-05

TEMPERATURE (°C)

-to-V

OUT

ON-RESISTANCE (

Ω

)

0 1209060

0.8

0.9

1.0

1.1

VCC = +5V, VBATT = 0V

1.50

0.25

-60 -30 30 150

PFI THRESHOLD

vs. TEMPERATURE

MAX791-05

TEMPERATURE (°C)

PFI THRESHOLD (V)

01209060

0.50

0.75

1.00

1.25

VCC = +5V, VBATT = 0V, NO LOAD ON PFO

_______________________________________________________________________________________ 5

MAX791

Microprocessor Supervisory Circuit

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

1000

1 100 1000

VCC to V

OUT

vs.

OUTPUT CURRENT

100

MAX791-13

OUT

(mA)

- V

OUT

(mV)

VCC = 4.5V VBATT = 0V

SLOPE = 0.8Ω

1000

110100

VBATT to V

OUT

vs.

OUTPUT CURRENT

MAX791-14

OUT

(mA)

VBATT - V

OUT

(mV)

100

VCC = 0V VBATT = 4.5V

SLOPE = 8Ω

04020

WATCHDOG TIMEOUT

vs. TIMING CAPACITOR

MAX791-11

TIMING CAPACITOR (nF)

WATCHDOG TIMEOUT (ms)

3010 70 80 90 1006050

100

150

200

250

VCC = +5V VBATT = 2.8V

0 10050

CHIP-ENABLE PROPAGATION DELAY

vs. CE OUT LOAD CAPACITANCE

MAX791-12

LOAD

(pF)

PROPAGATION DELAY (ns)

200 250 300150

VCC = +5V CE IN = 0V TO 5V DRIVER SOURCE IMPEDANCE = 50Ω

BATTERY CURRENT

vs. INPUT SUPPLY VOLTAGE

MAX791-10

VCC (V)

BATT

(µA)

0432

VBATT = 2.8V, I

OUT

= 0A

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