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MIC2755
Micrel, Inc.
MIC1232
P Supervisory Circuit
General Description
The MIC1232 is a multifunction circuit which monitors microprocessor 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 P activity and will assert /RST if no P activity has occurred with in the watchdog timeout period. The watchdog timeout period is selectable with nominal period of 150, 600, 1200 milliseconds.
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, <18A typical
Applications
* * * * * Automotive systems Intelligent systems Critical microprocessor power monitoring Battery powered computers Controllers
Ordering Information
Part Number Standard MIC1232N MIC1232M Pb-Free MIC1232NY MIC1232MY Temperature Range -40C to +85C -40C to +85C Package 8-Pin PDIP 8-Pin SOIC
Typical Application
VCC
VCC
TD
ST
RST
VCC
P
MIC1232
PBRST
I/O
RESET
TOL GND
Micrel, Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
January 2006
1
MIC1232
MIC1232
Micrel, Inc.
Pin Configuration
PBRST
1 2 3 4
8
VCC
ST
TD TOL GND
MIC1232
7 6 5
RST RST
8-Pin PDIP Package 8-Pin SOIC Package
Pin Description
Pin Number 1 Pin Name /PBRST Pin Function Pushbutton Reset Input: This input is debounced and can be driven with external 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. 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.
2
TD
3
TOL
4 5
GND RST
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. IC ground pin, 0V reference
RST is asserted high if either VCC goes below the reset threshold, the watchdog 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. /RST is asserted low if either VCC goes below the reset threshold, the watchdog 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 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. Primary supply input, +5V
6
/RST
7 8
/ST VCC
MIC1232
2
January 2006
MIC2755
Micrel, Inc.
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.) ...................... 300C Storage Temperature .................................. -65C to 150C ESD Rating, Note 3
Operating Ratings (Note 2)
Operating Temperature Range MIC1232M/N ............................................ -40C to 85C
Electrical Characteristics
Parameter VCC = 4.5V to 5.5V; TA = Operating Temperature Range, bold values indicate -40C TA +85C; unless noted Condition Min 4.5 18 2.0 -0.3 1.0 2.0 4.5 4.25 10 10 4.62 4.37 4.74 4.49 5 7 VCC Typ Max 5.5 40 VCC+0.3 0.8 1 Units V A V V A mA mA V V pF pF Supply Voltage Range Supply Current /ST and /PBRST Input Levels Input Leakage Output Souce Current, RST Output Sink Current, /RST. RST VCC 5% Trip Point (Reset Threshold Voltage) VCC 10% Trip Point (Reset Threshold Voltage) Input Capacitance, /ST, TOL Output Capacitance, /RST, RST
VIH, (Note 5) VIL IIL
ICC, (Note 4)
VOH = 2.4V VOL = 0.4V TOL = GND TOL = VCC CIN, (Note 6)
COUT, (Note 6)
AC Electrical Characteristics
/PBRST Min. Pulse Width, tPB /PBRST Delay, tPBD Reset Active Time, tRST TD = 0V TD = Open TD = VCC VCC = 4.5V to 5.5V; TA = Operating Temperature Range, bold values indicate -40C TA +85C; unless noted /PBRST = VIL (Note 7) 20 1 250 20 62.5 250 500 10 0 VCC Falling (Note 8) VCC Falling (Note 9) 250 50 610 150 1000 150 600 1200 250 1000 2000 4 610 20 1000 ms ms ms ms ms ms ms s ns s s
/ST Timeout Period, tTD
/ST Pulse Width, tST
VCC Fall Time, tF
VCC Detect to /RST Low and RST High, tRPD VCC Detect to /RST Low and RST Low, tRPD
Note 1. Note 2. Note 3. Note 4. Note 5. Note 6. Note 7. Note 8. Note 9.
VCC Rise Time, tR
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. ICC is measured with outputs open and inputs within 0.5V of supply rails /PBRST has an internal pull-up resistor to VCC (typ. 40k) Guaranteed by design
/PBRST must be held low for a minimum of 20ms to guarantee a reset VCC falling at 1.66mV/s /RST has an open drain output
January 2006
3
MIC1232
MIC1232
Micrel, Inc.
Timing Diagrams
VCC
VCCTP
VCCTP
RST
tRPD
tRPU
RST
Figure 1. Power-Up/Power-Down Sequence
tST
ST
tTD
Figure 2. Watchdog Input
tPB
tPDLY
PBRST
tRST
RST
RST
Figure 3. Pushbutton Reset
MIC1232
4
January 2006
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 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.
Block Diagram
VCC (8)
TOL (3)
TRIP POINT SELECT
+
REF
-
RESET GENERATOR
RST (6)
PBRST (1)
MANUAL RESET DEBOUNCE
RST (5)
ST (7)
WATCHDOG TIMER
TIMEOUT SELECT
TD (2)
GND (4)
January 2006
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MIC1232
MIC1232
Micrel, Inc.
Package Information
0.400 0.370
0.260 0.240
0.310 0.290
0.035 0.015
0.150 0.125
0.110 0.090
0.150 0.120
0.023 0.015
0.370 0.300
8-Pin PDIP (N)
8-Pin SOIC (M)
MICREL INC.
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
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. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can 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 Micrel for any damages resulting from such use or sale. (c) 2000 Micrel, Inc.
MIC1232
6
January 2006

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