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MAX7705中文资料

_______________General Description

In applications with microprocessors (μPs) that have a RESET input, the MAX7705 is functionally and socket compatible with the TL7705, but requires no external components.It provides power-supply glitch immunity and a guaranteed power-up reset delay, while typically consuming 1/27th the power from a +5V supply.

The MAX7705 monitors the power supply in μP and digital systems. The RESET output is valid for V CC down to 1V.The device offers excellent circuit reliability and low cost by eliminating external components and adjustments.

A system reset is provided during power-up, power-down, and brownout conditions. When V CC is below the reset threshold, RESET is low and holds the μP in reset.RESET will go high 280ms after V CC rises above the reset threshold. The MAX7705 is available in 8-pin DIP and SO packages.

________________________Applications

Minimum Component Count, Low-Cost Processor Systems

____________________________Features

o No External Components o Low Cost

o Precise Reset Threshold o 280ms Power-On Reset Delay o 8-Pin DIP and SO Packages

______________Ordering Information

MAX7705

μP Power-Supply Monitor

with Reset

________________________________________________________________Maxim Integrated Products 1

__________________Pin Configuration

__________Typical Operating Circuit

Call toll free 1-800-998-8800 for free samples or literature.

19-0151; Rev 0; 6/93

M A X 7705

μP Power-Supply Monitor with Reset 2_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Terminal Voltage (with respect to GND)

V CC ......................................................................-0.3V to 6.0V RESET ....................................................-0.3V to (V CC + 0.3V)Input Current, V CC ..............................................................20mA Output Current, RESET ......................................................20mA Rate-of-Rise, V CC ............................................................100V/μs Continuous Power Disipation (T A = +70°C)

Plastic DIP (derate 9.09mW/°C above +70°C)............727mW SO (derate 5.88mW/°C above +70°C).........................471mW

Operating Temperature Ranges:

MAX7705C_ _.....................................................0°C to +70°C MAX7705E_ _..................................................-40°C to +85°C Storage Temperature Range.............................-65°C to +160°C Lead Temperature (soldering, 10sec).............................+300°C

ELECTRICAL CHARACTERISTICS

(V CC = full range, T A = 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.

MAX7705

μP Power-Supply Monitor

with Reset

_______________________________________________________________________________________3

240-60

100

POWER-DOWN RESET DELAY

vs. TEMPERATURE

420TEMPERATURE (°C)

P O W E R -D O W N R E S E T D E L A Y (μs )

128-20

163000-60

100

POWER-UP RESET DELAY vs. TEMPERATURE

50250TEMPERATURE (°C)

P O W E R -U P R E S E T D E L A Y (m s )

150100-20

200

10020-60

-20

100

SUPPLY CURRENT vs. TEMPERATURE

TEMPERATURE (°C)

S U P P L Y C U R R E N T (μA )

4.640-60

-2060100

RESET THRESHOLD vs. TEMPERATURE

4.650TEMPERATURE (°C)

R E S E T

T H R E S H O L D (V )

204.6604.630

4.6554.6454.6654.635__________________________________________Typical Operating Characteristics

(T A = +25°C, unless otherwise noted.)

______________________________________________________________Pin Description

PIN NAME FUNCTION

1,2,3,6,7

N.C.No Connection. There is no internal connection to these pins.4GND Ground

5RESET Reset Output remains low while V CC is below the reset threshold, and for 280ms after V CC rises above the reset threshold.8

V CC

+5V Supply Voltage

M A X 7705

μP Power-Supply Monitor with Reset

4_______________________________________________________________________________________

__________Applications Information

Replacing the TL7705 with a MAX7705

in an Existing Design The MAX7705 has only three active pins: V CC , GND,and RESET . When using a TL7705 with a μP that has a RESET input, simply plug the MAX7705 into the same socket and omit the RESET pull-up resistor, reset timing capacitor, and reference bypass capacitor (see the Typical Operating Circuit ).

The MAX7705 monitors the V CC voltage and asserts reset whenever V CC falls below the reset threshold.The reset power-up delay is created by an internal fixed oscillator. This delay is 100% tested and guaran-teed over the full temperature range. The RESET out-put both sources and sinks current (see RESET Output Voltage in the Electrical Characteristics ).

Negative-Going V CC Transients

The MAX7705 asserts RESET during power-up,power-down, and brownout conditions. However, it is relatively immune to short-duration negative-going V CC transients (glitches).

Figure 1 shows typical transient duration vs. reset com-parator overdrive for which the MAX7705 does not gen-erate a reset pulse. The graph was generated using a fast-edge, negative-going pulse applied to V CC , starting 1.5V above the actual reset threshold and ending below the reset threshold by the magnitude indicated (reset comparator overdrive). It indicates the typical maxi-mum pulse width a negative-going V CC transient may have without causing a reset pulse to be issued. As the magnitude of the transient increases (goes farther below the reset threshold), the maximum allowable pulse width decreases. Typically, a V CC transient that goes 100mV below the reset threshold and lasts 40μs or less will not cause a reset pulse to be issued.

A 0.1μF bypass capacitor mounted as close as possible to pin 2 (V CC ) provides additional transient immunity.

Ensuring a Valid RESET Output

Down to V CC = 0V

When V CC falls below 1V, the MAX7705 RESET output no longer sinks current; it becomes high impedance.Therefore, high-impedance CMOS logic inputs con-nected to the RESET output can drift to indeterminate voltages. In most applications this presents no prob-lem, as μP and other circuitry is generally inoperative with V CC below 1V. In applications where the RESET output must be valid down to 0V, adding a pull-down resistor to the RESET pin (as shown in Figure 2) will cause any stray leakage currents to flow to ground,holding RESET low. The resistance value of R1 is not critical. It should be about 100k ?, which is large enough not to load RESET and small enough to pull RESET to ground.

Figure 1.Maximum Transient Duration without Causing a Reset Pulse vs. Reset Comparator Overdrive

RESET CC

___________________Chip Topography

TRANSISTOR COUNT = 380;

SUBSTRATE CONNECTED TO V CC .

MAX7705

μP Power-Supply Monitor

with Reset

_______________________________________________________________________________________5

Interfacing to μPs with Bidirectional Reset Inputs

μPs with bidirectional reset pins, such as Motorola’s 68HC11 series, can contend with the MAX7705 reset output. If, for example, the MAX7705 RESET output is asserted high and the μP wants to pull it low, an inde-terminate logic level may result. To correct this, con-nect a 4.7k ?resistor between the MAX7705 RESET output and the μP reset I/O, as in Figure 3. Buffer the RESET signal to other system components.

RESET

GND

0.045" (1.143mm)

0.056" (1.422mm)

M A X 7705

μP Power-Supply Monitor with Reset 6_______________________________________________________________________________________

_______________________________________________________Package Information

MAX7705

μP Power-Supply Monitor

with Reset

_______________________________________________________________________________________7

__________________________________________Package Information (continued)

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.

8___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600?1993 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.

M A X 7705

μP Power-Supply Monitor with Reset Minimum

Nominal Nominal Reset Watchdog

Power-Reset Pulse Timeout Backup-CE -Fail

Manual-Watch-Low-Active-Battery-Part Threshold Width Period Battery Write Com-Reset dog Line High On

Number

(V)(ms)

(sec)Switch Protect

parator

Input Output Output

Reset Output

MAX690A/692A 4.65/4.40140 1.6 MAX691A/693A 4.65/4.40140/adj. 1.6/adj. /10ns

MAX696Adj.35/adj. 1.6/adj.

MAX697Adj.35/adj. 1.6/adj.

MAX700 4.65/adj.200-

MAX703/704 4.65/4.40140- MAX705/706 4.65/4.40140 1.6 MAX706P 2.63140 1.6

MAX706R/S/T 2.63/2.93/140 1.6

3.08MAX707/708

4.65/4.40140- MAX708R/S/T 2.63/2.93/140

3.08

MAX709L/M/ 4.65/4.40/140

-R/S/T 2.63/2.93/3.08MAX791 4.65

140

/10ns

MAX792L/M/ 4.65/4.40/1401 /10ns

R/S/T 2.63/2.93/3.08MAX800L/M 4.60/4.40140 1.6/adj. /10ns

/±2%

MAX802L/M 4.60/4.40140 1.6 /±2%MAX805L 4.65140 1.6

MAX813L 4.65

140

1.6 MAX820L/M/ 4.65/4.40/1401

/10ns

/±2%

R/S/T 2.63/2.93/3.08MAX1232 4.37/4.622500.15/0.60/1.2

MAX1259

μP Supervisory Circuits