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LTC1232 Microprocessor Supervisory Circuits
FEATURES

DESCRIPTIO
Guaranteed Reset Assertion at VCC = 1V 8-Pin SO Plastic Package 2.0mA Maximum Supply Current 4.62V/4.37V Precision Voltage Monitor Power OK/Reset Time Delay: 600ms Minimum External Component Count Superior Upgrade for DS1232
The LTC(R)1232 provides power supply monitoring, watchdog timing and external reset for microprocessor systems. A precise internal voltage reference and comparator circuit monitor the power supply line. When an out-of-tolerance condition occurs, the reset outputs are forced to active states. The RST output is guaranteed to remain logic low even with VCC as low as 1V. The LTC1232 has an internal watchdog timer which forces the reset outputs to active states when the Strobe input is not forced low prior to a preset time-out period. The watchdog timing can be set to operate on time-out periods of typically 150ms, 600ms or 1.2 seconds. The LTC1232 performs push-button reset control. The LTC1232 debounces the push-button input and guarantees an active reset pulse width of 250ms minimum.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S

Critical P Power Monitoring Intelligent Instruments Computers and Controllers Automotive Systems
TYPICAL APPLICATIO
RST Output Voltage vs Supply Voltage
5
5V DC
PB RST 5V DC TD
VCC 100k ST
MPU (e.g. 6805) I/O LINE RESET
RST OUTPUT VOLTAGE (V)
4
3
LTC1232 TOL GND RST RST
2
1
LTC1232 * TA01
0
0
1
U
3 4 2 SUPPLY VOLTAGE (V) 5
LTC1232 * TA02
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U
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1
LTC1232
ABSOLUTE
(Note 1, 2 and 3)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW PB RST 1 TD 2 TOL 3 GND 4 8 7 6 5 VCC ST RST RST
Terminal Voltage VCC ....................................................... -0.3V to 7.0V ST and RST .......................................... -0.3V to 7.0V All Other Inputs and Outputs ...... -0.3V to VCC +0.3V Power Dissipation .............................................. 500mW Operating Temperature Range LTC1232C ............................................... 0C to 70C LTC1232I ........................................... -40C to 85C Storage Temperature Range ................. -65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1232CN8
N8 PACKAGE 8-LEAD PDIP TJMAX = 100C, JA = 130C/W TOP VIEW PB RST 1 TD 2 TOL 3 GND 4 8 7 6 5 VCC ST RST RST
ORDER PART NUMBER LTC1232CS8 LTC1232IS8 S8 PART MARKING 1232 1232I
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 100C, JA = 180C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
PRODUCT SELECTIO GUIDE
PINS LTC1232 LTC690 LTC691 LTC694 LTC695 LTC699 LTC1235 8 8 16 8 16 8 16 RESET X X X X X X X WATCHDOG TIMER X X X X X X X X X X X X X X X X X X X X X X BATTERY BACKUP POWER FAIL WARNING RAM WRITE PROTECT PUSH-BUTTON RESET X CONDITIONAL BATTERY BACKUP
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2
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LTC1232
RECO
SYMBOL VCC VIH VIL
over the full operating temperature. VCC = full operating range.
PARAMETER Supply Voltage ST and PB RST Input High Level ST and PB RST Input Low Level
E DED OPERATI G CO DITIO S
CONDITIONS
DC ELECTRICAL CHARACTERISTICS
temperature. VCC = full operating range.
SYMBOL IIL IOH IOL ICC VCCTP VCCTP VHYS VRST PARAMETER Input Leakage Output Current at 2.4V Output Current at 0.4V Supply Current VCC Trip Point VCC Trip Point VCC Trip Point Hysteresis RST Output Voltage at VCC = 1V ISINK = 10A CONDITIONS (Note 3) (Note 5) (Note 5) (Note 4) TOL = GND TOL = VCC
The denotes the specifications which apply over the full operating
MIN

AC CHARACTERISTICS
VCC = full operating range.
SYMBOL tPB tRST tST tRPD tf tRPU tR tTD PARAMETER PB RST = VIL RESET Active Time ST Pulse Width VCC Detect to RST and RST VCC Slew Rate 4.75V-4.25V VCC Detect to RST and RST (Reset Active Time) VCC Slew Rate 4.25V-4.75V ST Pin Detect to RST and RST (Watchdog Time-Out Period) Input Capacitance Output Capacitance
The denotes the specifications which apply over the full operating temperature.
CONDITIONS

tR = 5s
TD = GND TD = Floating TD = VCC
CIN COUT
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to GND. Note 3: The PB RST pin is internally pulled up to VCC with an internal impedance of 10k typical. The TD pin has internal bias current.
Note 4: Measured with outputs open. Note 5: The RST pin is an open drain output.
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The denotes the specifications which apply
MIN

TYP 5
MAX 5.5 VCC +0.3 0.8
UNITS V V V
4.5 2 -0.3
TYP
MAX 1
UNITS A mA mA
-1 -1 2 -13 6 0.5 4.5 4.25 4.62 4.37 40 4
2 4.74 4.49
mA V V mV
200
mV
MIN 40 250 20
TYP
MAX
UNITS ms
610
1000
ms ns
100 300 250 0 60 250 500 150 610 1200 5 5 250 1000 2000 610 1000
ns s ms ns ms ms ms pF pF

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3
LTC1232 TI I G DIAGRA S
Push-Button Reset
PB RST VIL tPB RST RST VIH VIL
LTC1232 * TD01
Strobe Input
tST
tTD
LTC1232 * TD02
BLOCK DIAGRA
VCC TOL
8 6 3 RST
5%, 10% SWITCH
OSC
PB RST
1
LEVEL SENSE AND DEBOUNCE LEVEL SENSE
ST
7
TD
2
TIME-OUT SELECTION
4
W
W
UW
Power Down
VIH tRST
VCC 4.75V 4.25V tF 4.50V tRPD RST RST VOH VOL
LTC1232 * TD03
Power Up
tR VCC 4.50V 4.75V 4.25V tRPU RST RST VOH VOL
LTC1232 * TD04
+
C1
-
1.3V
RESET PULSE GENERATOR
5
RST
WATCHDOG TIMER
LTC1232 * BD01
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LTC1232 TYPICAL PERFOR A CE CHARACTERISTICS
VCC Trip Point vs Temperature
4.63 TOL = GND 4.62 VCC TRIP POINT (V) VCC TRIP POINT (V) 4.61 4.60 4.59 4.58 4.57 -50 -25 4.37
RESET ACTIVE TIME (ms)
50 25 75 0 TEMPERATURE (C)
Time-Out Period vs Temperature
696 WATCHDOG TIME-OUT PERIOD (ms) VCC = 5V TD = NO CONNECTION 672 648 624 600 576 552 -50 -25
RST OUTPUT VOLTAGE (V)
4 5
50 25 75 0 TEMPERATURE (C)
PI FU CTIO S
VCC: 5V Supply Input. The VCC pin should be bypassed with a 0.1F capacitor. GND: Ground Pin. PB RST: Logic Input to be Directly Connected to a PushButton. The PB RST input requires an active low signal which is debounced and timed for a minimum of 40ms. When this condition is satisfied, the reset pulse generator forces the reset outputs to active states. The reset outputs remain in active states for a minimum of 250ms after PB RST is released from logic low level. TOL: Input to Select 5% or 10% Variation on VCC. When TOL is connected to GND, the reset pulse generator forces the reset outputs to active states as VCC falls below 4.75V (4.62V typical). When TOL is connected to VCC, the reset pulse generator forces the reset outputs to active states as VCC falls below 4.5V (4.37V typical). TD: Time-Out Delay. TD is a three-level input to select three different time-out periods. The time-out period is set by the TD input to be 150ms with TD connected to GND, 600ms with TD left floating, and 1.2 seconds with TD connected to VCC.
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UW
100
VCC Trip Point vs Temperature
4.38 TOL = VCC 672 648 624 600 576 696
Reset Active Time vs Temperature
VCC = 5V
4.36 4.35 4.34 4.33 4.32 -50 -25
125
50 25 75 0 TEMPERATURE (C)
100
125
552 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
LTC1232 * TPC01
LTC1232 * TPC02
LTC1232 * TPC03
RST Output Voltage vs Supply Voltage
TA = 25C EXTERNAL PULL-UP = 10A
3
2
1
0
100
125
0
1
3 4 2 SUPPLY VOLTAGE (V)
LTC1232 * TPC05
5
LTC1232 * TPC04
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LTC1232 PI FU CTIO S
RST: Open Drain Logic Output for P Reset Control. The LTC1232 provides three ways to generate P reset. First, when VCC falls below VCC trip point (4.75V with TOL = GND and 4.5V with TOL = VCC), RST goes active low. After VCC returns to 5V, the reset pulse generator forces RST to remain active low for a minimum of 250ms. Second, when the watchdog timer is not serviced prior to a selected time-out period, the reset pulse generator also forces RST to active low for a minimum of 250ms and repeats for every time-out period. Third and the last, when the PB RST pin stays active low for a minimum of 40ms, RST becomes active low. The RST output will remain active low for a minimum of 250ms from the moment the push-button reset input is released from logic low level. RST: RST is an Active High Logic Output. It is the inverse of RST. ST: Logic Input to Reset the Watchdog Timer. Driving ST either high or low longer than the time-out period set by the TD input, forces the reset outputs to active states for a minimum of 250ms. The timer resets itself and begins to time-out again with each high to low transition on the ST input (see Figure 2).
APPLICATIO S I FOR ATIO
Power Monitoring
The LTC1232 uses a bandgap voltage reference and a precision voltage comparator, C1, to monitor the 5V supply input on VCC (see Block Diagram). When VCC falls below the V CC trip point (4.62V typical with TOL = GND and 4.37V typical with TOL VCC), the reset outputs are forced to active states. The VCC trip point accounts for a 5% or 10% variation on VCC, so the reset outputs become active when VCC falls below the VCC trip point. On power-up, the reset signals are held in active states for a minimum of 250ms after the VCC trip point is reached to allow the power supply and microprocessor to stabilize. On power-down, the RST signal remains active low even with VCC as low as 1V. This capability helps hold the microprocessor in stable shutdown condition. Figure 1 shows the timing diagram of the RST signal.
V2 VCC t1 RST
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The precision voltage comparator, C1, typically has 40mV of hysteresis which ensures that glitches at VCC pin do not activate the reset outputs. Response time is typically 10s. To help prevent mitriggering due to transient loads, VCC pin should be bypassed with a 0.1F capacitor with the leads trimmed as short as possible. Push-Button Reset The LTC1232 provides a logic input pin, PB RST, for direct connection to a push-button. This push-button reset input requires an active low signal. Internally, this input signal is debounced and timed for a minimum of 40ms. When this
V2 V1 t1 V1
V1 = VCC TRIP POINT V2 = VCC TRIP POINT + VHYS t1 = RESET ACTIVE TIME
LTC1232 * TA03
Figure 1. Reset Active Time
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LTC1232
APPLICATIO S I FOR ATIO
condition is satisfied, the reset pulse generator forces the reset outputs to active states. The reset signals will remain active for a minimum of 250ms from the moment the push-button reset input is released from logic low level (see Timing Diagram). Watchdog Timer The LTC1232 provides a watchdog timer function to monitor the activity of the microprocessor. If the microprocessor does not stimulate the strobe input, ST, within a selected time-out period, the reset outputs are forced to active states for a minimum of 250ms. The time-out period is selected by the Time-Out Delay input, TD, to be 150ms with TD connected to GND, 600ms with TD left floating, and 1.2 seconds with TD connected to VCC. The 1.2 second time-out period is adequate for many systems to serve the watchdog timer immediately after a reset. Figure 2 shows the timing diagram of watchdog time-out period and reset active time. The watchdog time-out period is restarted as
PACKAGE DESCRIPTIO
N8 Package 8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
.400* (10.160) MAX 8 7 6 5
.300 - .325 (7.620 - 8.255)
.009 - .015 (0.229 - 0.381) +.035 .325 -.015
(
8.255
+0.889 -0.381
)
INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
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NOTE: 1. DIMENSIONS ARE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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VCC = 5V ST t1 RST t1 = RESET ACTIVE TIME t2 = WATCHDOG TIME-OUT PERIOD
LTC1232 * TA04
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t2
t1
t2
t1
Figure 2. Watchdog Time-Out Period and Reset Active Time
soon as the reset outputs are inactive. When a high-to-low transition occurs at the ST pin prior to time-out, the watchdog time is reset and begins to time-out again. To ensure the watchdog time does not time-out, a high-to low transition on the ST pin must occur at or less than the minimum time-out period. If the input to the ST pin remains either high or low, reset pulses will be issued for every time-out period selected by the TD pin. The watchdog timer is disabled when VCC falls below the VCC trip point.
.255 .015* (6.477 0.381)
1
2
3
4 .130 .005 (3.302 0.127)
.045 - .065 (1.143 - 1.651)
.065 (1.651) TYP .125 (3.175) .020 MIN (0.508) MIN .018 .003 (0.457 0.076)
N8 0502
.100 (2.54) BSC
7
LTC1232
PACKAGE DESCRIPTIO
.050 BSC
8 N N .245 MIN .160 .005 .228 - .244 (5.791 - 6.197) 1 2 3 N/2
.030 .005 TYP
RECOMMENDED SOLDER PAD LAYOUT
.010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0- 8 TYP
NOTE: 1. DIMENSIONS IN
INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
RELATED PARTS
PART NUMBER LTC690 LTC694-3.3 LTC699 LTC1326 LTC1326-2.5 LTC1536 LTC1726-2.5 LTC1726-5 LTC1727-2.5/LTC1727-5 LTC1728-1.8/TC1728-3.3 LTC1728-2.5/LTC1728-5 LTC1985-1.8 DESCRIPTION 5V Supply Monitor, Watchdog Timer and Battery Backup 3.3V Supply Monitor, Watchdog Timer and Battery Backup 5V Supply Monitor and Watchdog Timer Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and ADJ Precision Triple Supply Monitor for PCI Applications Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Micropower Triple Supply Monitor for 5V, 3.3V and ADJ Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Push-Pull Reset Output COMMENTS 4.65V Threshold 2.9V Threshold 4.65V Threshold 4.725V, 3.118V, 1V Thresholds (0.75%) 2.363V, 3.118V, 1V Thresholds (0.75%) Meets PCI tFAIL Timing Specifications Adjustable RESET and Watchdog Time-Outs Adjustable RESET and Watchdog Time-Outs Individual Monitor Outputs in MSOP 5-Lead SOT-23 Package 5-Lead SOT-23 Package 5-Lead SOT-23 Package
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
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S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.045 .005
.189 - .197 (4.801 - 5.004) NOTE 3 7 6 5 .150 - .157 (3.810 - 3.988) NOTE 3 N/2 1 2 3 4 .053 - .069 (1.346 - 1.752) .004 - .010 (0.101 - 0.254) .016 - .050 (0.406 - 1.270) .014 - .019 (0.355 - 0.483) TYP .050 (1.270) BSC
SO8 0502
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www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 1992

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