ANALOG DEVICES LTC 1232 CS8 Datasheet

FEATURES

■

Guaranteed

■

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

Reset Assertion at VCC = 1V

LTC1232

Microprocessor

Supervisory Circuits

U

DESCRIPTIO

The LTC®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 V

as low as 1V.

CC

U

APPLICATIO S

■

Critical µP Power Monitoring

■

Intelligent Instruments

■

Computers and Controllers

■

Automotive Systems

TYPICAL APPLICATIO

5V DC

PB RST

TD

TOL

LTC1232

V

RST

CC

ST

U

5V DC

100k

(e.g. 6805)

I/O LINE

RESET

MPU

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.

RST Output Voltage vs

Supply Voltage

5

4

3

2

GND

RST

LTC1232 • TA01

RST OUTPUT VOLTAGE (V)

1

0

1

0

SUPPLY VOLTAGE (V)

3

4

2

5

LTC1232 • TA02

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1

LTC1232

WWWU

ABSOLUTE AXI U RATI GS

(Note 1, 2 and 3)

Terminal Voltage

V

.......................................................–0.3V to 7.0V

CC

ST and RST .......................................... – 0.3V to 7.0V

All Other Inputs and Outputs ...... – 0.3V to V

Power Dissipation.............................................. 500mW

Operating Temperature Range

LTC1232C ............................................... 0°C to 70°C

LTC1232I ........................................... –40°C to 85°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

+0.3V

CC

UU

W

PACKAGE/ORDER I FOR ATIO

TOP VIEW

PB RST

1

TD

2

TOL

3

GND

4

N8 PACKAGE
8-LEAD PDIP

= 100°C, θJA = 130°C/W

T

JMAX

TOP VIEW

PB RST

1

TD

2

TOL

3

GND

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 100°C, θJA = 180°C/W

JMAX

Consult LTC Marketing for parts specified with wider operating tempera­ture ranges.

V

8

CC

ST

7

RST

6

RST

5

V

8

CC

ST

7

RST

6

RST

5

ORDER

PART NUMBER

LTC1232CN8

ORDER

PART NUMBER

LTC1232CS8
LTC1232IS8

S8 PART MARKING

1232
1232I

U

PRODUCT SELECTIO GUIDE

POWER RAM CONDITIONAL

WATCHDOG BATTERY FAIL WRITE PUSH-BUTTON BATTERY

PINS RESET TIMER BACKUP WARNING PROTECT RESET BACKUP

LTC1232 8 X X X

LTC690 8 X X X X

LTC691 16 X XXXX

LTC694 8 X X X X

LTC695 16 X XXXX

LTC699 8 X X

LTC1235 16 X XXXXX X

2

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LTC1232

WW

RECO E DED OPERATI G CO DITIO S

over the full operating temperature. V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

V

IH

V

IL

Supply Voltage ● 4.5 5 5.5 V

ST and PB RST Input High Level ● 2V

ST and PB RST Input Low Level ● – 0.3 0.8 V

DC ELECTRICAL CHARACTERISTICS

temperature. V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

IL

I

OH

I

OL

I

CC

V

CCTP

V

CCTP

V

HYS

V

RST

= full operating range.

CC

Input Leakage (Note 3) ● –1 1 µA

Output Current at 2.4V (Note 5) ● –1 –13 mA

Output Current at 0.4V (Note 5) ● 26 mA

Supply Current (Note 4) ● 0.5 2 mA

VCC Trip Point TOL = GND ● 4.5 4.62 4.74 V

VCC Trip Point TOL = V

VCC Trip Point Hysteresis 40 mV

RST Output Voltage at VCC = 1V I

= full operating range.

CC

= 10µA 4 200 mV

SINK

The ● denotes the specifications which apply over the full operating

CC

UU UU

The ● denotes the specifications which apply

+0.3 V

CC

● 4.25 4.37 4.49 V

AC CHARACTERISTICS

The ● denotes the specifications which apply over the full operating temperature.

VCC = full operating range.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

t

PB

t

RST

t

ST

t

RPD

t

f

t

RPU

t

R

t

TD

C

IN

C

OUT

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.

PB RST = V

RESET Active Time ● 250 610 1000 ms

ST Pulse Width ● 20 ns

VCC Detect to RST and RST ● 100 ns

VCC Slew Rate 4.75V–4.25V ● 300 µs

VCC Detect to RST and RST tR = 5µs ● 250 610 1000 ms
(Reset Active Time)

VCC Slew Rate 4.25V–4.75V ● 0ns

ST Pin Detect to RST and RST TD = GND ● 60 150 250 ms
(Watchdog Time-Out Period) TD = Floating

Input Capacitance 5pF

Output Capacitance 5 pF

IL

TD = V

CC

Note 4: Measured with outputs open.
Note 5: The RST pin is an open drain output.

● 40 ms

● 250 610 1000 ms

● 500 1200 2000 ms

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3

LTC1232

UWW

TI I G DIAGRA S

Push-Button Reset Power Down

PB RST

RST

RST

t

ST

V

IL

t

PB

V
V

Strobe Input Power Up

t

TD

t

4.50V

4.75V

4.25V

F

t

RPD

V

OH

V

OL

LTC1232 • TD03

t

R

t

RPU

V

OH

V

OL

LTC1232 • TD04

V

IH

V

RST

RST

V

RST

RST

CC

CC

t

RST

IH
IL

LTC1232 • TD01

LTC1232 • TD02

4.75V

4.25V

4.50V

BLOCK DIAGRA

8

V

CC

TOL

3

5%, 10%

SWITCH

OSC

PB RST

1

7

ST

LEVEL SENSE

AND

DEBOUNCE

LEVEL SENSE

W

1.3V

6

RST

+

C1

–

WATCHDOG

TIMER

RESET PULSE

GENERATOR

5

RST

4

2

TD

TIME-OUT

SELECTION

LTC1232 • BD01

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UW

LTC1232 • TPC03

TEMPERATURE (˚C)

–50

RESET ACTIVE TIME (ms)

648

672

696

25 75

624

600

–25 0

50 100 125

576

552

VCC = 5V

TYPICAL PERFOR A CE CHARACTERISTICS

LTC1232

VCC Trip Point vs Temperature

4.63
TOL = GND

4.62

4.61

4.60

TRIP POINT (V)

CC

4.59

V

4.58

4.57

–50

–25 0

25 75

TEMPERATURE (˚C)

Time-Out Period vs Temperature

696

VCC = 5V
TD = NO CONNECTION

672

648

624

600

576

WATCHDOG TIME-OUT PERIOD (ms)

552

–50

–25 0

50 100 125

LTC1232 • TPC01

50 100 125

25 75

TEMPERATURE (˚C)

TRIP POINT (V)

CC

V

LTC1232 • TPC04

VCC Trip Point vs Temperature

4.38
TOL = V

CC

4.37

4.36

4.35

4.34

4.33

4.32

–50

–25 0

TEMPERATURE (˚C)

50 100 125

25 75

Reset Active Time vs Temperature

LTC1232 • TPC02

RST Output Voltage vs Supply Voltage

5

TA = 25°C
EXTERNAL PULL-UP = 10µA

4

3

2

RST OUTPUT VOLTAGE (V)

1

0

1

0

SUPPLY VOLTAGE (V)

3

2

4

LTC1232 • TPC05

5

U

PI FU CTIO S

VCC: 5V Supply Input. The V
with a 0.1µF capacitor.

GND: Ground Pin.

PB RST: Logic Input to be Directly Connected to a Push-

Button. 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.

UU

pin should be bypassed

CC

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
V

falls below 4.5V (4.37V typical).

CC

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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5

LTC1232

U

UU

PI FU CTIO S

RST: Open Drain Logic Output for µP Reset Control.
The LTC1232 provides three ways to generate µP reset.
First, when VCC falls below VCC trip point (4.75V with
TOL = GND and 4.5V with TOL = V

), RST goes active low.

CC

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

WUUU

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 VCC 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 V
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.

falls below the VCC trip

CC

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).

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 10µs.
To help prevent mitriggering due to transient loads, V

CC

pin should be bypassed with a 0.1µF 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

6

V2 V2

V

CC

t

1

RST

Figure 1. Reset Active Time

V1 V1

t

1

V1 = VCC TRIP POINT
V2 = VCC TRIP POINT + V
t1 = RESET ACTIVE TIME

LTC1232 • TA03

HYS

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WUUU

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

LTC1232

= 5V

V

CC

ST

t

2

1

RST

t

1

t

t1 = RESET ACTIVE TIME
t2 = WATCHDOG TIME-OUT PERIOD

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.

t

2

t

1

LTC1232 • TA04

PACKAGE DESCRIPTIO

.300 – .325

(7.620 – 8.255)

.009 – .015

(0.229 – 0.381)

+.035

.325

–.015
+0.889

8.255

()

–0.381

NOTE:

1. DIMENSIONS ARE

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)

U

INCHES

MILLIMETERS

N8 Package

8-Lead PDIP (Narrow .300 Inch)

(Reference LTC DWG # 05-08-1510)

.400*

(10.160)

MAX

87 6

.255 ± .015*

(6.477 ± 0.381)

12

.045 – .065

(1.143 – 1.651)

.065

(1.651)

TYP

.100

(2.54)

BSC

3

5

4

.130 ± .005

(3.302 ± 0.127)

.125

(3.175)

MIN

.018 ± .003

(0.457 ± 0.076)

.020

(0.508)

MIN

N8 0502

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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.

7

LTC1232

PACKAGE DESCRIPTIO

.050 BSC

N

.245
MIN

1 2 3 N/2

.030 ±.005

TYP

RECOMMENDED SOLDER PAD LAYOUT

U

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610)

.189 – .197

.045 ±.005

.160

±.005

.228 – .244

(5.791 – 6.197)

(4.801 – 5.004)

8

N

1

NOTE 3

7

2

6

3

5

N/2

4

.150 – .157

(3.810 – 3.988)

NOTE 3

.010 – .020

(0.254 – 0.508)

.008 – .010

(0.203 – 0.254)

NOTE:

1. DIMENSIONS IN

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)

× 45°

.016 – .050

(0.406 – 1.270)

INCHES

(MILLIMETERS)

0°– 8° TYP

.053 – .069

(1.346 – 1.752)

.014 – .019

(0.355 – 0.483)

TYP

.004 – .010

(0.101 – 0.254)

.050

(1.270)

BSC

SO8 0502

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Timing Specifications

FAIL

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear.com

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LW/TP 1002 1K REV A • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 1992