MIC1232MYTR - Micrel - Datasheet.Company

January 2006 1 MIC1232

MIC2755 Micrel, Inc.

MIC1232

µP Supervisory Circuit

General Description

The MIC1232 is a multifunction circuit which monitors mi-

croprocessor activity, external reset and power supplies in

microprocessor based systems. The circuit functions include

a watchdog time, power supply monitor, microprocessor reset,

and manual pushbutton reset input.

The power supply line is monitored with a comparator and

an internal voltage reference. /RST is forced low when an

out-of-tolerance condition exists and remains asserted for

at least 250ms after VCC rises above the threshold voltage

(4.5V or 4.75V). The /RST pin will remain logic low with VCC

as low as 1.4V.

The Watchdog input (/ST) monitors µP activity and will as-

sert /RST if no µP activity has occurred with in the watchdog

timeout period. The watchdog timeout period is selectable

with nominal period of 150, 600, 1200 milliseconds.

Typical Application

VCC

RST

µP

RESET

VCC

MIC1232

VCC

PBRST

TOL GND

I/O

Features

• Power OK/Reset time delay, 250ms min.

• Watchdog timer, 150ms, 600ms, or 1.2s typical

• Precision supply voltage monitor, select between 5% or

10% of supply voltage

• Available in 8-pin surface mount (SO)

• Debounced External reset input

• Low supply current, <18µA typical

Applications

• Automotive systems

• Intelligent systems

• Critical microprocessor power monitoring

• Battery powered computers

• Controllers

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

Ordering Information

Part Number Temperature Range Package

Standard Pb-Free

MIC1232N MIC1232NY –40ºC to +85ºC 8-Pin PDIP

MIC1232M MIC1232MY –40ºC to +85ºC 8-Pin SOIC

MIC1232 2 January 2006

MIC1232 Micrel, Inc.

Pin Conﬁguration

TOL

GND

VCC

RST

MIC1232

PBRST

8-Pin PDIP Package

8-Pin SOIC Package

Pin Description

Pin Number Pin Name Pin Function

1 /PBRST Pushbutton Reset Input: This input is debounced and can be driven with ex-

ternal logic signals or by means of a mechanical pushbutton to actively force

a reset. All pulses less than 1ms in duration on the /PBRST pin are ignored,

whereas, any pulse with a duration of 20ms or greater is guaranteed to

cause a reset.

2 TD Time Delay input: This input selects the timebase used by the watchdog

timer. When TD = 0V, the watchdog timeout period is set to a normal value

of 150ms, when TD = open, the watchdog timeout period is et to a nominal

value of 600ms and when TD = VCC, the watchdog period is 1.2s nominally.

3 TOL Tolerance Select Input: Selects whether 5% or 10% of VCC is used as the

reset threshold voltage. When TOL = 0V, the 5% tolerance level is selected

and when TOL = VCC, a 10% tolerance level is selected.

4 GND IC ground pin, 0V reference

5 RST RST is asserted high if either VCC goes below the reset threshold, the watch-

dog times out or /PBRST is pulled low for a minimum of 20ms. RST remains

asserted for one reset timeout period after VCC exceeds the reset threshold

or after the watch times out or after /PBRST goes high.

6 /RST /RST is asserted low if either VCC goes below the reset threshold, the watch-

dog times out or /PBRST is pulled low for a minimum of 20ms. /RST remains

asserted for one reset timeout period after VCC exceeds the reset threshold

or after the watch times out or after /PBRST goes high. Open-drain output

7 /ST Input to watchdog timer. If /ST does not see a transition from high to low

within the watchdog timeout period, RST and /RST will be asserted.

8 VCC Primary supply input, +5V

January 2006 3 MIC1232

MIC2755 Micrel, Inc.

Electrical Characteristics

VCC = 4.5V to 5.5V; TA = Operating Temperature Range, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted

Parameter Condition Min Typ Max Units

Supply Voltage Range VCC 4.5 5.5 V

Supply Current ICC, (Note 4) 18 40 µA

/ST and /PBRST Input Levels VIH, (Note 5) 2.0 VCC+0.3 V

VIL –0.3 0.8 V

Input Leakage IIL ±1 µA

Output Souce Current, RST VOH = 2.4V 1.0 10 mA

Output Sink Current, /RST. RST VOL = 0.4V 2.0 10 mA

VCC 5% Trip Point (Reset TOL = GND 4.5 4.62 4.74 V

Threshold Voltage)

VCC 10% Trip Point (Reset TOL = VCC 4.25 4.37 4.49 V

Threshold Voltage)

Input Capacitance, /ST, TOL CIN, (Note 6) 5 pF

Output Capacitance, /RST, RST COUT, (Note 6) 7 pF

AC Electrical Characteristics

VCC = 4.5V to 5.5V; TA = Operating Temperature Range, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted

/PBRST Min. Pulse Width, tPB /PBRST = VIL (Note 7) 20 ms

/PBRST Delay, tPBD 1 4 20 ms

Reset Active Time, tRST 250 610 1000 ms

/ST Pulse Width, tST 20 ms

/ST Timeout Period, tTD TD = 0V 62.5 150 250 ms

TD = Open 250 600 1000 ms

TD = VCC 500 1200 2000 ms

VCC Fall Time, tF 10 µs

VCC Rise Time, tR 0 ns

VCC Detect to /RST Low VCC Falling (Note 8) 50 150 µs

and RST High, tRPD

VCC Detect to /RST Low VCC Falling (Note 9) 250 610 1000 µs

and RST Low, tRPD

Note 1. Exceeding the absolute maximum rating may damage the device.

Note 2. The device is not guaranteed to function outside its operating rating.

Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.

Note 4. ICC is measured with outputs open and inputs within 0.5V of supply rails

Note 5. /PBRST has an internal pull-up resistor to VCC (typ. 40kΩ)

Note 6. Guaranteed by design

Note 7. /PBRST must be held low for a minimum of 20ms to guarantee a reset

Note 8. VCC falling at 1.66mV/µs

Note 9. /RST has an open drain output

Absolute Maximum Ratings (Note 1)

Terminal Voltage

VCC ..........................................................–0.3V to +6.0V

All other inputs ...............................–0.3V to (VCC + 0.3V)

Input Current

VCC ...................................................................... 250mA

GND, all other inputs .............................................. 25mA

Lead Temperature (soldering, 10 sec.) ...................... 300°C

Storage Temperature .................................. –65°C to 150°C

ESD Rating, Note 3

Operating Ratings (Note 2)

Operating Temperature Range

MIC1232M/N ............................................ –40°C to 85°C

MIC1232 4 January 2006

MIC1232 Micrel, Inc.

Timing Diagrams

VCC

RST

tRPU

VCCTP

tRPD

VCCTP

Figure 1. Power-Up/Power-Down Sequence

tTD

tST

Figure 2. Watchdog Input

RST

tRST

tPDLY

PBRST

tPB

Figure 3. Pushbutton Reset

January 2006 5 MIC1232

MIC2755 Micrel, Inc.

Applications Information

Power Monitor

The /RST and RST pins are asserted whenever VCC falls

below the reset threshold voltage as determined by the TOL

pin. A 5% tolerance level (4.62V reset threshold voltage) can

be selected by connecting the TOL pin to ground and a 10%

tolerance can be selected by connecting the TOL pin to VCC.

The reset pins will remain asserted for a period of 250ms

after VCC has risen above the reset threshold voltage. The

reset function ensures the microprocessor is properly reset

and powers up into a known condition after a power failure.

/RST will remain valid with VCC as low as 1.4V.

Watchdog Timer

The microprocessor can be mounted by connecting the /ST

pin (watchdog input) to a bus line or I/O line. If a high-to-low

does not occur on the/ST pin within the watchdog timeout

Block Diagram

REF

WATCHDOG

TIMER

VCC (8)

GND (4)

RST (5)

TD (2)

RST (6)

RESET

GENERATOR

ST (7)

TIMEOUT

SELECT

PBRST (1)

MANUAL RESET

DEBOUNCE

TRIP POINT

SELECT

TOL (3)

period (determined by the TD pin, see Table 1.), the /RST and

the RST will remain asserted for 250ms when this occurs. A

minimum pulse of 75ns or any transition high-to-low on the

/ST pin will reset the watchdog timer. The watchdog timer

will be reset if /ST sees a valid transition within the watchdog

timeout period.

Pushbutton Reset Input

The /PBRST input can be driven with a manual pushbutton

switch or with external logic signals. the input is internally

debounced and requires an active low signal to force the

reset outputs into their active states. The /PBRST input will

recognize any pulse that is 20ms in duration or greater and

will ignore all pulses that are less than 1ms in duration.

MIC1232 6 January 2006

MIC1232 Micrel, Inc.

Package Information

0.260

0.240

0.400

0.370

0.023

0.015

0.110

0.090

0.150

0.120

0.150

0.125

0.035

0.015

0.370

0.300

0.310

0.290

8-Pin PDIP (N)

8-Pin SOIC (M)

MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com

This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.

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reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into

the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a signiﬁcant injury to the user. A Purchaser's

use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify

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