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MAX6314US47D3-T中文资料

General Description

The MAX6314 low-power CMOS microprocessor (μP)supervisory circuit is designed to monitor power supplies in μP and digital systems. The MAX6314’s RESET output is bidirectional, allowing it to be directly connected to μPs with bidirectional reset inputs, such as the 68HC11. It provides excellent circuit reliability and low cost by eliminating external components and adjustments. The MAX6314 also provides a debounced manual reset input.

This device performs a single function: it asserts a reset signal whenever the V CC supply voltage falls below a preset threshold or whenever manual reset is asserted. Reset remains asserted for an internally pro-grammed interval (reset timeout period) after V CC has risen above the reset threshold or manual reset is deasserted.

The MAX6314 comes with factory-trimmed reset threshold voltages in 100mV increments from 2.5V to 5V. Preset timeout periods of 1ms, 20ms, 140ms,and 1120ms (minimum) are also available. The device comes in a SOT143 package.

For a μP supervisor with an open-drain reset pin, see the MAX6315 data sheet.

________________________Applications

Computers Controllers

Intelligent Instruments

Critical μP and μC Power Monitoring Portable/Battery-Powered Equipment

Features

o Small SOT143 Package

o RESET Output Simplifies Interface to Bidirectional Reset I/Os o Precision Factory-Set V CC Reset Thresholds:100mV Increments from 2.5V to 5V o ±1.8% Reset Threshold Accuracy at T A = +25°C o ±2.5% Reset Threshold Accuracy Over Temp.o Four Reset Timeout Periods Available: 1ms, 20ms, 140ms, or 1120ms (minimum) o Immune to Short V CC Transients o 5μA Supply Current

o Pin-Compatible with MAX811

MAX6314*

68HC11/Bidirectional-Compatible

μP Reset Circuit

________________________________________________________________Maxim Integrated Products

1

MAX6314US47D3-T中文资料

Pin Configuration

MAX6314US47D3-T中文资料

Typical Operating Circuit

19-1090; Rev 1; 1/99

Ordering and Marking Information appears at end of data sheet.

* Patents Pending

For free samples & the latest literature: http://www.docsj.com/doc/8ae4aa23cfc789eb172dc8e8.html, or phone 1-800-998-8800.For small orders, phone 1-800-835-8769.

M A X 6314

MAX6314US47D3-T中文资料

68HC11/Bidirectional-Compatible μP Reset Circuit 2

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ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V CC = +2.5V to +5.5V, T A = -40°C to +85°C, unless otherwise noted. Typical values are at T A = +25°C.)

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.

Note 1:The MAX6314 monitors V CC through an internal, factory-trimmed voltage divider that programs the nominal reset threshold.

Factory-trimmed reset thresholds are available in 100mV increments from 2.5V to 5V (see Ordering and Marking Information ).

Note 2:This is the minimum time RESET must be held low by an external pull-down source to set the active pull-up flip-flop.Note 3:Measured from RESET V OL to (0.8 x V CC ), R LOAD = ∞.V CC ........................................................................-0.3V to +6.0V All Other Pins..............................................-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 Dissipation (T A = +70°C)

SOT143 (derate 4mW/°C above +70°C).......................320mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range.............................-65°C to +160°C Lead Temperature (soldering, 10sec).............................+300°C

MAX6314

68HC11/Bidirectional-Compatible

μP Reset Circuit

_______________________________________________________________________________________3

__________________________________________Typical Operating Characteristics

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

4.7k ? PULL-UP 2V/div

MAX6314 PULL-UP 2V/div

INPUT 5V/div

200ns/div PULL-UP CHARACTERISTICS

MAX6314-01

100pF

4.7k ?

+5V

74HC05

74HC05

V CC

GND

MR 100pF

+5V

RESET

MAX6314

6

-50-303090

SUPPLY CURRENT vs. TEMPERATURE

215

MAX6314US47D3-T中文资料

TEMPERATURE (°C)

S U P P L Y C U R R E N T (μA )

-101050347060

1

3

5

SUPPLY CURRENT vs. SUPPLY VOLTAGE

2

15

MAX6314US47D3-T中文资料

SUPPLY VOLTAGE (V)

S U P P L Y C U R R E N T (μA )

2

3

44

500-50

-30

10

90

POWER-DOWN RESET DELAY

vs. TEMPERATURE

10

40

MAX6314US47D3-T中文资料

TEMPERATURE (°C)

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

-10

20

30

30

50

70

1.04

0.96

-50

-30

10

90

NORMALIZED RESET TIMEOUT PERIOD vs. TEMPERATURE (V CC RISING)

0.970.981.021.001.03M A X 6314-05

TEMPERATURE (°C)

N O R M A L I Z E D R E S E T T I M E O U T P E R I O D -10

0.991.0130

50

70

1.0060.994

-50

-30

10

90

NORMALIZED RESET THRESHOLD vs. TEMPERATURE (V CC FALLING)

0.9960.9981.0041.000M A X 6314-06

TEMPERATURE (°C)

N O R M A L I Z E D R E S E T T H R E S H O L D

-10

1.00230

50

70

1000

10

100

1000

MAXIMUM TRANSIENT DURATION vs. RESET COMPARATOR OVERDRIVE

20

MAX6314US47D3-T中文资料

RESET COMP. OVERDRIVE, V TH - V CC (mV)

M A X I M U M T R A N S I E N T D U R A T I O N (μs )

40

60

80

MAX6314US47D3-T中文资料

6000

-50

-30

10

90

RESET PULL-UP TIME vs. TEMPERATURE

100

200

500

300TEMPERATURE (°C)

R E S E T P U L L -U P -T I M E (n s )

-10

40030

50

70

Figure 1. Functional Diagram M A X 6314

MAX6314US47D3-T中文资料

68HC11/Bidirectional-Compatible μP Reset Circuit 4

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______________________________________________________________Pin Description

Supply Voltage and Reset Threshold Monitor Input

V CC

4

Manual Reset Input. A logic low on MR asserts reset. Reset remains asserted as long as MR is low, and for the reset timeout period (t RP ) after the reset conditions are terminated. Connect to V CC if not used.MR 3PIN Active-Low Complementary Output. In addition to the normal N-channel pull-down, RESET has a P-channel pull-up transistor in parallel with a 4.7k ?resistor to facilitate connection to μPs with bidirectional resets. See the Reset Output section.

RESET

2

Ground

GND 1FUNCTION

NAME

MAX6314

68HC11/Bidirectional-Compatible

μP Reset Circuit

_______________________________________________________________________________________5

_______________Detailed Description

The MAX6314 has a reset output consisting of a 4.7k ?pull-up resistor in parallel with a P-channel transistor and an N-channel pull down (Figure 1), allowing this IC to directly interface with microprocessors (μPs) that have bidirectional reset pins (see the Reset Output section).

Reset Output

A μP’s reset input starts the μP in a known state. The MAX6314 asserts reset to prevent code-execution errors during power-up, power-down, or brownout conditions. RESET is guaranteed to be a logic low for V CC > 1V (see the Electrical Characteristics ). Once V CC exceeds the reset threshold, the internal timer keeps reset asserted for the reset timeout period (t RP );after this interval RESET goes high. If a brownout condi-tion occurs (monitored voltage dips below its pro-grammed reset threshold), RESET goes low. Any time V CC dips below the reset threshold, the internal timer resets to zero and RESET goes low. The internal timer starts when V CC returns above the reset threshold, and RESET remains low for the reset timeout period.The MAX6314’s RESET output is designed to interface with μPs that have bidirectional reset pins, such as the Motorola 68HC11. Like an open-drain output, the MAX6314 allows the μP or other devices to pull RESET low and assert a reset condition. However, unlike a standard open-drain output, it includes the commonly specified 4.7k ?pull-up resistor with a P-channel active pull-up in parallel.

This configuration allows the MAX6314 to solve a prob-lem associated with μPs that have bidirectional reset pins in systems where several devices connect to RESET . These μPs can often determine if a reset was asserted by an external device (i.e., the supervisor IC)or by the μP itself (due to a watchdog fault, clock error,or other source), and then jump to a vector appropriate for the source of the reset. However, if the μP does assert reset, it does not retain the information, but must determine the cause after the reset has occurred.

The following procedure describes how this is done with the Motorola 68HC11. In all cases of reset, the μP pulls RESET low for about four E-clock cycles. It then releases RESET , waits for two E-clock cycles, then checks RESET ’s state. If RESET is still low, the μP con-cludes that the source of the reset was external and,when RESET eventually reaches the high state, jumps to the normal reset vector. In this case, stored state information is erased and processing begins from

scratch. If, on the other hand, RESET is high after the two E-clock cycle delay, the processor knows that it caused the reset itself and can jump to a different vec-tor and use stored state information to determine what caused the reset.

The problem occurs with faster μPs; two E-clock cycles is only 500ns at 4MHz. When there are several devices on the reset line, the input capacitance and stray capacitance can prevent RESET from reaching the logic-high state (0.8 x V CC ) in the allowed time if only a passive pull-up resistor is used. In this case, all resets will be interpreted as external. The μP is guaranteed to sink only 1.6mA, so the rise time cannot be much reduced by decreasing the recommended 4.7k ?pull-up resistance.

The MAX6314 solves this problem by including a pull-up transistor in parallel with the recommended 4.7k ?resistor (Figure 1). The pull-up resistor holds the output high until RESET is forced low by the μP reset I/O, or by the MAX6314 itself. Once RESET goes below 0.5V, a comparator sets the transition edge flip-flop, indicating that the next transition for RESET will be low to high. As soon as RESET is released, the 4.7k ?resistor pulls RESET up toward V CC . When RESET rises above 0.5V,the active P-channel pull-up turns on for the 2μs duration of the one-shot. The parallel combination of the 4.7k ?pull-up and the P-channel transistor on-resistance quickly charges stray capacitance on the reset line, allowing RESET to transition low to high with-in the required two E-clock period, even with several devices on the reset line (Figure 2). Once the one-shot times out, the P-channel transistor turns off. This process occurs regardless of whether the reset was caused by V CC dipping below the reset threshold, MR being asserted, or the μP or other device asserting RESET . Because the MAX6314 includes the standard 4.7k ?pull-up resistor, no external pull-up resistor is required. To minimize current consumption, the internal pull-up resistor is disconnected whenever the MAX6314asserts RESET .

Manual Reset Input

Many μP-based products require manual reset capabil-ity, allowing the operator, a test technician, or external logic circuitry to initiate a reset. A logic low on MR asserts reset. Reset remains asserted while MR is low,and for the reset active timeout period after MR returns high. To minimize current consumption, the internal 4.7k ?pull-up resistor on RESET is disconnected whenever RESET is asserted.

M A X 6314

MAX6314US47D3-T中文资料

MAX6314US47D3-T中文资料

68HC11/Bidirectional-Compatible μP Reset Circuit 6_______________________________________________________________________________________

MR has an internal 63k ?pull-up resistor, so it can be left open if not used. Connect a normally open momen-tary switch from MR to GND to create a manual reset function; external debounce circuitry is not required. If MR is driven from long cables or if the device is used in a noisy environment, connecting a 0.1μF capacitor from MR to ground provides additional noise immunity.

__________Applications Information

Negative-Going V CC Transients

In addition to issuing a reset to the μP during power-up,power-down, and brownout conditions, these devices are relatively immune to short-duration negative-going transients (glitches). The Typical Operating Character-istics show the Maximum Transient Duration vs. Reset Threshold Overdrive, for which reset pulses are not generated. The graph was produced using negative-going pulses, starting at V RST max and ending below the programmed reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width that a negative-going V CC transient may typically have without causing a reset pulse to be issued. As the amplitude of the transient increases (i.e., goes farther below the reset threshold),the maximum allowable pulse width decreases. A 0.1μF bypass capacitor mounted close to V CC provides addi-tional transient immunity.

Ensuring a Valid RESET Output

Down to V CC = 0V

When V CC falls below 1V, RESET no longer sinks current—it becomes an open circuit. Therefore, high-impedance CMOS-logic inputs connected to RESET can drift to undetermined voltages. This presents no problem in most applications, since most μP and other circuitry is inoperative with V CC below 1V. However, in applications where RESET must be valid down to V CC = 0V, adding a pull-down resistor to RESET will cause any stray leakage currents to flow to ground,holding RESET low (Figure 3). R1’s value is not critical;100k ?is large enough not to load RESET and small enough to pull RESET to ground.

Figure 2. MAX6314 Supports Additional Devices on the Reset Bus

Figure 3. RESET Valid to V CC = Ground Circuit

MAX6314

68HC11/Bidirectional-Compatible

μP Reset Circuit

_______________________________________________________________________________________7

Figure 4. RESET Timing Diagram

MAX6314US47D3-T中文资料

?The MAX6314 is available in a SOT143 package, -40°C to +85°C temperature range.

??The first two letters in the package top mark identify the part, while the remaining two letters are the lot tracking code.

???Sample stocks generally held on the bolded products; also, the bolded products have 2,500 piece minimum-order quantities.

Non-bolded products have 10,000 piece minimum-order quantities. Contact factory for details.Note:All devices available in tape-and-reel only. Contact factory for availability.

__________________________________________Ordering and Marking Information

MAX6314US47D3-T中文资料

MAX6314US47D3-T中文资料

M A X 6314

MAX6314US47D3-T中文资料

MAX6314US47D3-T中文资料

68HC11/Bidirectional-Compatible μP Reset Circuit 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?1999 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.

_____________________________Ordering and Marking Information (continued)

?The MAX6314 is available in a SOT143 package, -40°C to +85°C temperature range.

??The first two letters in the package top mark identify the part, while the remaining two letters are the lot tracking code.

???Sample stocks generally held on the bolded products; also, the bolded products have 2,500 piece minimum-order quantities.

Non-bolded products have 10,000 piece minimum-order quantities. Contact factory for details.Note:All devices available in tape-and-reel only. Contact factory for availability.

Chip Information

TRANSISTOR COUNT: 519