MIC705/706/707/708
µP Supervisory Circuit
General Des cr ipt i on
The MIC705, MIC706, MIC707, and MIC708 are
inexpensive microprocessor supervisory circuits that
monitor power supplies in microprocessor-based systems.
The circuit functions include a watchdog timer,
microprocessor reset, power-failure warning, and a
debounced manual r eset input.
The MIC705 and MIC706 offer a watchdog timer function
while the MIC707 and MIC708 have an active-high reset
output in addition t o t he acti ve-low reset output.
Supply voltage monitor levels of 4.65V and 4.4V are
available. The MIC705 and MIC707 have a nominal reset
threshold level of 4.65V while the MIC706 and MIC708
have a 4.4V nominal reset threshold level. When the
supply voltage drops below the respective reset threshold
level, /RESET is asserted.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Features
• Debounced manual reset input is TTL/CMOS
compatible
• Reset pulse width: 200ms
• Watchdog timer: 1. 6s (MIC705/706)
• 4.65V or 4.40V precision voltage monito r
• Early power-fail war ni ng or low-battery detect
Applications
• Automotive sy st em s
• Intelligent syst ems
• Critical microprocessor power monitoring
• Battery-powered computers
• Computers
• Controllers
Typical Application
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
September 15, 2014 Revision 2.1
Micrel, Inc.
MIC705/706/707/708
Ordering I nfor m ati on
Part Number
Threshold (V)
/RESET
RESET
WDI
Junction Tem perature Ra nge
Package
MIC705MY 4.65 √ √ −40°C to +85°C 8-Pin SOIC
MIC706MY 4.40 √ √ −40°C to +85°C 8-Pin SOIC
MIC707MY 4.65 √ √ −40°C to +85°C 8-Pin SOIC
MIC708MY 4.40 √ √ −40°C to +85°C 8-Pin SOIC
Pin Configuration
MIC705/706
8-Pin SOIC (M)
(Top View)
MIC707/708
8-Pin SOIC (M)
(Top View)
Pin Description
Pin Number
MIC706 Pin Number
MIC708 Pin Name Pin Name
1 1 /MR Manual reset input forces /RESET to assert when pulled below 0.8V. An internal
pull-up current of 250µA on this input forces it high when left floating. This input
can also be driven from TTL or CMOS logic.
2 2 VCC Primar y supply input, +5V.
3 3 GND IC ground pin, 0V reference.
4 4 PFI
Power-Fail Inp ut: Internally-connected to t he power-fail comparator which is
referenced to 1.25V. The power-fail output ( /PFO) remains hi gh if PFI is above
1.25V. PFI s hould be connected to GND or VCC if t he power-fail comparator is not
used.
5 5 /PFO Power-Fail Output: The power-fail comparator is independent of al l other function
on this device.
6 N/A WDI
Watchdog Input. The WDI i nput monitors mic roprocessor ac tivity; an internal
watchdog timer resets itself with each transition on the watchdog input. I f the WDI
pin is held high or low for longer than the watchdog timeout period, /WDO is forced
to active low. The watchdog func tion can be disabl ed by floating the WD I pin.
N/A 6 N/C Not internally connected.
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MIC705/706/707/708
Pin Description (Continued)
Pin Number
MIC706 Pin Number
MIC708 Pin Name Pin Name
7 7 /RESET
/RESET is ass erted if either V CC goes below the res et threshold voltage or by low
signal on the manual reset inp ut (/MR). /RE SET remains asserted for one reset
timeout period (200ms) after VCC exceeds t he reset threshol d v ol tage or after the
manual reset p i n transition from low to high. The watchdog timer will not assert
/RESET unless /WDO is connected to /MR.
8 N/A /WDO
Output for t he watchdog timer . The watchdog timer resets itself with each transi tion
to the watchdog input. If the WDI pin is held high or low for longer than the
watchdog timeout period, /WDO is forced lo w. /WDO will also be forced low if VCC
is below the re s et threshold volt age and will remain low until VCC returns to a valid
level.
N/A 8 RESET RESET is the complim ent of /RESET and is asserted if eit her VCC goes below the
reset thresho l d voltage or by a low signal on the m anual reset input ( /MR). RESET
is suitable for microprocessor systems that us e active high res et.
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MIC705/706/707/708
Absolute Ma xi mu m Ratings(1)
Terminal Voltage
VCC ....................................................... −0.3V to +6.0V
All Other Inputs. ........................... −0.3V to (VCC + 0.3V)
Input Current
VCC, GND ............................................................ 25mA
Output Current (A l l ) ..................................................... 20mA
Lead Temperature (soldering, 10s) ............................ 300°C
Storage Temperature (TS) ......................... −65°C to +150°C
Operating Ratings(2)
Operating Temperature Range ................... –40°C to +85°C
Power Dissipat i on (S OP) ......................................... 400mW
Thermal Resistance
8-Pin SOIC ....................................................... 150°C/W
Electric al Characterist ics(3)
VCC = 4.75V to 5.5V for MIC705/707; VCC = 4.5V to 5.5V for MIC706/708; TA = Operating Temperature Range,
bold values indicate –40°C ≤ TA ≤ +85°C, unless noted.
Parameter
Condition
Min.
Typ.
Max.
Units
Operating Voltage Range 1.4 5.5 V
Supply Current 60 µA
Reset Voltage Threshold MIC705, MIC707 4.50 4.65 4.75 V
MIC706, MIC708 4.25 4.4 4.5
Reset Threshold Hysteresis 40 mV
Reset Pulse W idth (tRS) 140 200 280 ms
/RESET Output Voltage ISOURCE = 800µA VCC − 1.5V V
ISINK = 3.2mA 0.4
RESET Output Voltage ISOURCE = 800µA VCC − 1.5V V
ISINK = 1.2mA 0.4
Watchdog Timeout Period (tWD) 1.0 1.6 2.25 s
WDI Minimum I nput Pulse (tWP) VIL = 0.4V, VIH = 80% of VCC 50 ns
WDI Threshold Voltage VIH, VCC = 5V 3.5 V
VIL, VCC = 5V 0.8
WDI Input Curr ent WDI = 0V −150 −50 µA
WDI = VCC 50 150
WDO Output Volt age ISOURCE = 800µA VCC − 1.5V V
ISINK = 1.2mA 0.4
/MR Pull-Up Current /MR = 0V 100 250 600 µA
Notes:
1. Exceeding the absolute maximum ratings may damage the device.
2. The device is not guaranteed to function outside its operating ratings.
3. Specification for packaged product only
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MIC705/706/707/708
Electric al Charact eristics(3) (Continued)
VCC = 4.75V to 5.5V for MIC705/707; VCC = 4.5V to 5.5V for MIC706/708; TA = Operating Temperature Range,
bold values indicate –40°C ≤ TA ≤ +85°C, unless noted.
Parameter Condition Min. Typ. Max. Units
/MR Pulse Width (tMR) 150 ns
/MR Input Threshold VIL 0.8 V
VIH 2.0
/MR-to-Reset Output Dela y (tMD) 250 ns
PFI Input Threshold VCC = 5V 1.2 1.25 1.3 V
PFI Input Current −25 0.01 +25 nA
/PFO Output Voltage ISINK = 3.2mA 0.4 V
VCC = 5V, ISOURCE = 800µA VCC − 1.5V
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MIC705/706/707/708
Timing Diagram
Figure 1. Timing Diagram for Reset
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MIC705/706/707/708
Block Diagrams
MIC705/MIC706 Block Diag ram
MIC707/MIC708 Block Diagram
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MIC705/706/707/708
Application Information
Microprocessor Reset
The /RESET pin is asserted whenever VCC falls below the
reset threshold voltage or when /MR goes low. The reset
pin remains asserted for a period of 200ms after VCC has
risen above the reset threshold voltage and /MR goes
high. The reset function ensures the microprocessor is
properly reset and powers up into a known condition after
a power failure. /RESET will remain valid with VCC as lo w
as 1.4V.
Power-Fail Warning
An additional comparator which is independent of the
other functions on the MIC706/706/707/708 is provided
for early warning of power failure. An external voltage
divider can be used to compare unregulated DC to an
internal 1.25V reference. The voltage divider ratio on the
input of the power-fail comparator (PFI) can be chosen so
as to trip the power-fail comparator a few milliseconds
before VCC falls below the maximum reset threshold
voltage. The output of the power-fail comparator (/PFO)
can be used to interrupt the microprocessor when used in
this mode and execute shutdown procedures prior to
power loss. Hysteresis can be added to this comparator
with external resistors, as is commonly done with any
comparator.
Figure 2. Power-Fail Comparator
Watchdog Timer
The microprocessor can be monitored by connecting the
WDI pin (watchdog input) to a bus line or an I/O line. If a
transition doesn't occur on the WDI pin within the
watchdog timeout period, then /WDO will go low. A
minimum pulse of 50ns or any transition low-to-high or
high-to-low on the WDI pin will reset the watchdog timer.
The output of the watchdog timer (/WDO) will remain high
if WDI left floating. If VCC falls below the reset threshold
voltage, then /WDO goes low immediately regardless of
WDI.
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MIC705/706/707/708
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
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