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).
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
PDAs, hand-held PCs
Embedded controllers
Telecommunications systems
Power supplies
Wireless/cellular systems
Networking hardware
Applications
Ordering Information
Part Number
MIC809-5SU
MIC809-5SBC3
MIC809-5SUY
MIC809-5SYC3
Marking
IX
IX
IX
IX
Typical
Application
Voltage*
3.3V±5%
3.3V±5%
3.3V±5%
3.3V±5%
Nominal
Threshold
Voltage
2.93
2.93
2.93
2.93
t
RST
(ms)
30
30
30
30
Operating
Temp. Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
SOT23-3
SC70-3
SOT23-3
SC70-3
Pb-Free
No
No
Yes
Yes
*Other voltages available. Contact Micrel for details. Minimum order may apply.
Typical Application
V
CC
VCC
VCC
µP
MIC809-5
/RESET
/RESET
IttyBitty 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
July 2005
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M9999-071305
MIC809-5
Micrel
MIC809-5
GND 1
3 VCC
/RESET 2
Pin Configuration
3-Lead SOT23
3-Lead SC-70
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
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July 2005
MIC809-5
Micrel
Absolute Maximum Ratings
(1)
Terminal Voltage (V
CC
) .................................–0.3V to +6.0V
Input Current (V
CC
)..................................................... 20mA
Output Current (/RESET, RESET) .............................. 20mA
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
(3)
................................................................ 3kV
Operating Ratings
(2)
Ambient Temperature (T
A
) .......................... –40°C to +85°C
Power Dissipation (T
A
= +70°C) .............................. 320mW
Electrical Characteristics
For typical values, V
CC
= 3.3V, T
A
= 25°C;
bold
are for –40°C to +85°C; unless otherwise noted
Symbol
V
CC
I
CC
V
TH
Parameter
Condition
Operating Voltage Range
Supply Current
Reset Voltage Threshold
Typical hysteresis
Reset Timeout Period
Propogation delay
/RESET Output Voltage High
/RESET Output Voltage Low
I
SOURCE
= 500µA
/RESET < V
OL
, 100mV Overdrive
30
14.5
0.8×V
CC
0.3
0.3
T
A
= –40°C to 85°C
S Voltage Options
V
CC
< 3.6V
Min
1
5
2.85
2.93
5
66
Typ
Max
5.5
10
3.00
Units
V
µA
V
mV
ms
µs
V
V
V
V
HYST
t
RST
V
OH
V
OL
t
PROP
V
CC
= V
TH
min., I
SINK
= 1.2mA
V
CC
> 1V, I
SINK
= 50µA
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.
Timing Diagram
V
CC
V
TH
t
RST
/RESET
V
TH
t
RST
Reset Timing Diagram
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MIC809-5
Micrel
Functional Diagram
VCC (3)
+
Reset
Threshold (V)
-
RESET
GENERATOR
RESET (2)
RESET (MIC810)
GND (1)
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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 1V.
Transients on V
CC
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.
Typical Transient
Response
V
TH
V
IN
MIC809
/RESET
GND
R
PULL-DOWN
100k
V
CC
/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 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 V
CC
/R
SERIES
.
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.
BUFFER
RESET SIGNAL
to OTHER CIRCUITS
MAX. TRANSIENT DURATION (µs)
25
20
15
10
5
0
= 2.932
V
CC
0
200 400 600 800 1000
RESET COMP. OVERDRIVE, V
TH
–V
CC
(mV)
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 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 V
CC
=1V.)
If a given application requires that /RESET be valid below
V
CC
= 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 I/O
Microcontroller
or
Microprocessor
GND
Figure 3. Interfacing to Processors
with Bidirectional Reset Pins
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M9999-071305
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