MIC809-5SBC3 - Micrel Semiconductor, Inc.

July 2005 1 M9999-071305

MIC809-5 Micrel

MIC809-5

Microprocessor Reset Circuit

General Description

The MIC809-5 is a power supply supervisor that provides

under-voltage monitoring and power-on reset generation in

an industry standard 3-pin SOT package and SC-70 pack-

age. The reset output is asserted at power-on and any time

the input voltage drops below the programmed threshold. It

remains asserted for 30ms (min.) after the input subsequently

rises back above the threshold boundary. The MIC809-5 has

an active-low reset output.

The MIC809-5 is inherently immune to brief power supply

transients. Typical supply current is a low 5µA. For those

applications that require a manual reset function, see the

MIC811/812. For those applications that require a longer

reset timeout, see the MIC809/810. (The MIC809-5 is identi-

cal to the industry-standard MIC809 with the exception of a

shorter reset timeout).

Typical Application

VCC

/RESET

µP

/RESET

MIC809-5

VCC

Features

• Under-voltage monitor

• Power-on reset generation (30ms minimum)

• Choice of threshold voltages

• Active-low reset output

• No external components required

• Rejects brief input transients

• Industry standard package and pinout

• 3-pin IttyBitty™ SOT23-3 package and SC-70 package

Applications

• PDAs, hand-held PCs

• Embedded controllers

• Telecommunications systems

• Power supplies

• Wireless/cellular systems

• Networking hardware

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

Ordering Information

Typical Nominal

Application Threshold tRST Operating

Part Number Marking Voltage* Voltage (ms) Temp. Range Package Pb-Free

MIC809-5SU IX 3.3V±5% 2.93 30 –40°C to +85°C SOT23-3 No

MIC809-5SBC3 IX 3.3V±5% 2.93 30 –40°C to +85°C SC70-3 No

MIC809-5SUY IX 3.3V±5% 2.93 30 –40°C to +85°C SOT23-3 Yes

MIC809-5SYC3 IX 3.3V±5% 2.93 30 –40°C to +85°C SC70-3 Yes

*Other voltages available. Contact Micrel for details. Minimum order may apply.

IttyBitty is a trademark of Micrel, Inc.

MIC809-5 Micrel

M9999-071305 2 July 2005

Pin Description

Pin Number Pin Name Pin Function

1 GND Ground return for all IC functions.

2 /RESET Digital Output. Active-low. Asserted whenever VCC falls below the threshold

voltage. It will remain asserted for no less than 30ms and be de-asserted

after VCC returns above the threshold.

3 VCC Analog Input. Power supply input to the IC.

Pin Conﬁguration

1GND

/RESET

VCC3

MIC809-5

3-Lead SOT23

3-Lead SC-70

July 2005 3 M9999-071305

MIC809-5 Micrel

Absolute Maximum Ratings(1)

Terminal Voltage (VCC) .................................–0.3V to +6.0V

Input Current (VCC) ..................................................... 20mA

Output Current (/RESET, RESET) .............................. 20mA

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

Storage Temperature (TS) .......................... –65°C to 150°C

Rate of Rise (VCC) .................................................. 100V/µs

ESD Rating(3) ................................................................ 3kV

Operating Ratings(2)

Ambient Temperature (TA) .......................... –40°C to +85°C

Power Dissipation (TA = +70°C) .............................. 320mW

Electrical Characteristics

For typical values, VCC = 3.3V, TA = 25°C; bold are for –40°C to +85°C; unless otherwise noted

Symbol Parameter Condition Min Typ Max Units

VCC Operating Voltage Range TA = –40°C to 85°C 1 5.5 V

ICC Supply Current VCC < 3.6V 5 10 µA

VTH Reset Voltage Threshold S Voltage Options 2.85 2.93 3.00 V

VHYST Typical hysteresis 5 mV

tRST Reset Timeout Period 30 66 ms

tPROP Propogation delay /RESET < VOL, 100mV Overdrive 14.5 µs

VOH /RESET Output Voltage High ISOURCE = 500µA 0.8×VCC V

VOL /RESET Output Voltage Low VCC = VTH min., ISINK = 1.2mA 0.3 V

VCC > 1V, ISINK = 50µA 0.3 V

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.

Timing Diagram

/RESET

VCC VTH VTH

tRST tRST

Reset Timing Diagram

MIC809-5 Micrel

M9999-071305 4 July 2005

Functional Diagram

Reset

Threshold (V)

VCC (3) RESET (2)

RESET (MIC810)

GND (1)

RESET

GENERATOR

July 2005 5 M9999-071305

MIC809-5 Micrel

Applications Information

Microprocessor Reset

The /RESET pin is asserted whenever VCC falls below the

reset threshold voltage. The /RESET pin remains asserted

for a period of 30ms after VCC has risen above the reset

threshold voltage. The reset function ensures the micropro-

cessor is properly reset and powers up in a known condition

after a power failure. /RESET will remain valid with VCC as

low as 1V.

Transients on VCC

The MIC809-5 is inherently immune to very short “glitches”

on VCC. In the case of very brief transients, VCC may drop

below the reset-voltage threshold without triggering a reset.

As shown in the graph, the MIC809-5 is relatively immune

to transients with typical duration of 20µs. The lines on the

graph of Figure 1 represent the typical allowable transient

duration for a given amount of threshold overdrive that will

not generate a reset. The data was taken by adding nega-

tive-going square-wave pulse to a DC input voltage set at

0.5V above actual measured threshold for the part being

characterized.

0 200 400 600 800 1000

MAX. TRANSIENT DURATION (µs)

RESET COMP. OVERDRIVE, VTH –VCC (mV)

Typical Transient

Response

= 2.932

Figure 1. Comparator Overdrive

vs. Duration

Ensuring Proper Operation at Low VCC

At levels of VCC below 1V, the MIC809-5’s output driver cannot

always turn on sufﬁciently to produce a valid logic-low. In this

situation, other circuits driven by /RESET could be allowed to

ﬂoat, causing undesired operation. (In most cases, however,

it is expected that the circuits driven by the MIC809-5 will be

similarly inoperative at VCC =1V.)

If a given application requires that /RESET be valid below

VCC = 1V, this can be accomplished by adding a pull-down

resistor to the output. A value of 100kΩ is recommended, as

this is usually an acceptable compromise of leakage current

and pull-down current. The resistor’s value is not critical,

however. See Figure 2.

/RESET /RESET INPUT

Microcontroller

Microprocessor

GND

100k

GND

VIN

RPULL-DOWN

VCC

MIC809

Figure 2. Ensuring a Valid

/RESET Signal at Low Voltage

Interfacing to Processors with Bidirectional Reset Pins

Some microprocessors have reset signal pins that are bidi-

rectional, rather than input only. The Motorola 68HC11 fam-

ily is one example. To prevent excessive current ﬂow when

the processor asserts its reset output, a series resistor is

employed between the MIC809-5’s output and the reset pin.

This limits the current that will ﬂow between the MIC809-5

and the reset pin to a theoretical maximum of VCC/RSERIES.

Because this resistor also limits the drive capability of the

supervisor’s output, a buffer may be required to drive ad-

ditional circuitry. See Figure 3.

4.7k

BUFFER

RESET SIGNAL

to OTHER CIRCUITS

VCC

/RESET

GND

VIN

MIC809

RESET I/O

Microcontroller

Microprocessor

GND

VCC

Figure 3. Interfacing to Processors

with Bidirectional Reset Pins

MIC809-5 Micrel

M9999-071305 6 July 2005

Package Information

0.15 (0.006)

0.076 (0.0030)

0.41 (0.016)

0.13 (0.005)

3.05 (0.120)

2.67 (0.105)

8

0

0.445 (0.0175) TYP 3 PLACES

2.50 (0.098)

2.10 (0.083)

1.40 (0.055)

1.19 (0.047)

0.10 (0.004)

0.013 (0.0005)

1.15 (0.045)

0.76 (0.030)

DIMENSIONS:

MM (INCH)

2.36 (0.093)

2.28 (0.090)

3-lead SOT-23 (M3)

3-Lead SC-70 (C3)

MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com

The information furnished by Micrel in this datasheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel

for its use. Micrel reserves the right to change circuitry and speciﬁcations at any time without notiﬁcation to the customer.

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