MIC809-5
Micrel
MIC809-5
Microprocessor Reset Circuits
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 pinout. 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. Hysteresis is included to prevent
chattering due to noise, and the MIC809-5 is inherently
immune to brief power supply transients. Typical supply
current is a low 6µA. For those applications that require a
manual reset function, see the MIC811/812. For those appli-
cations that require a longer reset timeout, see the
MIC809/810. (The MIC809-5 is identical to the industry-
standard MIC809 with the exception of a shorter reset timout.)
Features
• Under-voltage monitor
• Power-on reset generation (30ms minimum)
• Choice of threshold voltages (contact Micrel regarding
availability)
• Active-low reset output
• No external components required
• Rejects brief input transients
• Industry standard package and pinout
• 3-pin Itty-Bitty™ SOT23-3 package
Applications
• Monitoring processor, ASIC, or FPGA core and I/O
voltages
• PDAs, hand-held PCs
• Embedded controllers
• Telecommunications systems
• Power supplies
• Wireless / Cellular systems
• Networking hardware
Ordering Information
Part Number
MIC809-5S-U
Marking**
IXxx
Typical
Application
Voltage*
3.3V±5%
Nominal
Threshold
Voltage
2.93
T
RST
(ms)
30
Junction
Temperature
Range
–40°C to +85°C
Package
SOT23-3
*Other voltages available. Contact Micrel for details. Minimum order may apply. **xx indicates the lot code.
Typical Application
V
CC
VCC
VCC
MIC809-5
/RESET
µP
/RESET
Typical Operating Circuit
Itty-Bitty is a trademark of Micrel, Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
December 2001
1
MIC809-5
MIC809-5
Micrel
Pin Configuration
MIC809-5
GND
1
3
/RESET
2
VCC
3-Lead SOT23
Pin Description
Pin Number
1
2
Pin Name
GND
/RESET
Pin Function
Ground return for all IC functions.
Digital Output. Active-low. Asserted whenever V
CC
falls below the threshold
voltage. It will remain asserted for no less than 30ms and be de-asserted
after V
CC
returns above the threshold.
Analog Input. Power supply input to the IC.
3
VCC
MIC809-5
2
December 2001
MIC809-5
Micrel
Absolute Maximum Ratings
(Note 1)
Terminal Voltage (V
CC
) ................................. –0.3V to 6.0V
Lead Temperature (soldering, 10 sec.) ..................... 300°C
Storage Temperature (T
S
) ......................... –65°C to 150°C
Rate of Rise (V
CC
) ................................................. 100V/µs
ESD Rating,
Note 3
Operating Ratings
(Note 2)
Ambient Temperature (T
A
) ......................... –40°C to +85°C
Power Dissipation (T
A
= +70°C) .............................. 320mW
Electrical Characteristics
T
A
= 25°C; V
CC
= 3.3V for MIC809-5S unless otherwise noted. Values in
bold
are for –40°C to +85°C; unless otherwise noted
Symbol
V
CC
I
CC
V
TH
V
HYST
T
RST
T
PROP
V
OH
V
OL
Parameter
Operating Voltage Range
Condition
T
A
= 0°C to 70°C
T
A
= –40°C to 85°C
Supply Current
Reset Voltage Threshold
Typical hysteresis
Reset Timeout Period
Propogation delay
/RESET Output Voltage High
/RESET Output Voltage Low
/RESET < V
OL
, 100mV Overdrive
I
SOURCE
= 500µA
V
CC
= V
TH
min., I
SINK
= 1.2mA
V
CC
> 1.4V, I
SINK
= 50µA, T
A
= 0°C to +70°C
V
CC
> 1.6V, I
SINK
= 50µA, T
A
= –40° to +85°C
Note 1.
Note 2.
Note 3.
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
Min
1.4
1.6
Typ
Max
5.5
5.5
Units
V
V
µA
V
mV
V
CC
< 3.6V
S Voltage Options
2.85
6
2.93
5
30
9.3
0.8·V
CC
10
3.00
66
ms
µs
V
0.3
0.3
0.3
V
V
V
Timing Diagrams
VCC
V
TH
T
RST
RESET
V
TH
T
RST
Reset Timing Diagram
December 2001
3
MIC809-5
MIC809-5
Micrel
Functional Diagram
VCC (3)
V
TH
+
-
RESET
GENERATOR
RESET (2)
GND (1)
MIC809-5 Block Diagram
MIC809-5
4
December 2001
MIC809-5
Micrel
V
CC
Applications Information
Microprocessor Reset
The /RESET pin is asserted whenever V
CC
falls below the
reset threshold voltage. The /RESET pin remains asserted
for a period of 30ms after V
CC
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 V
CC
as low
as 1.4V.
Transients on V
CC
The MIC809-5 is inherently immune to very short “glitches” on
V
CC
. In the case of very brief transients, V
CC
may drop below
the under-voltage threshold without triggering a reset. As
shown in the graph of Figure 1, the narrower the transient, the
deeper the threshold overdrive that will be ignored. The line
on the graph represents the typical allowable transient dura-
tion for a given amount of threshold overdrive that will
not
generate a reset. The data from which Figure 1 is derived was
taken by adding negative-going square-wave pulses to a DC
input voltage set at 0.5V above the actual measured thresh-
old for the part being characterized.
Typical Transient
Response
MAX. TRANSIENT DURATION (µs)
V
CC
V
IN
MIC809
/RESET
GND
R
PULL-DOWN
100k
/RESET INPUT
Microcontroller
or
Microprocessor
GND
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 family
is one example. To prevent excessive current flow when the
processor asserts its reset output, a series resistor is em-
ployed 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 V
CC
/R
SERIES
. Because
this resistor also limits the drive capability of the supervisor’s
output, a buffer may be required to drive additional circuitry.
See Figure 3.
BUFFER
RESET SIGNAL
to OTHER CIRCUITS
V
CC
20
VTH = 2.932
15
10
5
0
200
400
600
RESET COMP. OVERDRIVE, V
TH
–V
CC
(mV)
0
V
IN
MIC809
/RESET
GND
4.7k
V
CC
Figure 1. Comparator Overdrive
vs. Duration
Ensuring Proper Operation at Low V
CC
At levels of V
CC
below 1.4V, 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 V
CC
=1.4V.)
If a given application requires that /RESET be valid below
V
CC
=1.4V, 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 I/O
Microcontroller
or
Microprocessor
GND
Figure 3. Interfacing to Processors
with Bidirectional Reset Pins
December 2001
5
MIC809-5
51单片机
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