1
LTC699
s
Guaranteed Reset Assertion at V
CC
= 1V
s
1.5mA Maximum Supply Current
s
SO-8 Packaging
s
4.65V Precision Voltage Monitor
s
Power OK/Reset Time Delay: 200ms
s
Minimum External Component Count
s
Performance Specified Over Temperature
s
Superior Upgrade for MAX699
The LTC699 provides power supply monitoring for
microprocessor-based systems. The features include mi-
croprocessor reset and watchdog timing. Precise internal
voltage reference and comparator circuit monitor the
power supply line. When an out-of-tolerance condition
occurs, the RESET output is forced to active low. In
addition, the RESET output is guaranteed to remain logic
low even with V
CC
as low as 1V.
An internal watchdog timer is also available, which forces
the RESET output to active low when the watchdog input
is not toggled prior to the time-out period of 1.6 seconds.
The LTC699 is offered in DIP and surface mount packages.
D
U
ESCRIPTIO
S
FEATURE
Microprocessor
Supervisory Circuit
U
S
A
O
PPLICATI
s
Critical
P Power Monitoring
s
Intelligent Instruments
s
Computers and Controllers
s
Automotive Systems
U
A
O
PPLICATI
TYPICAL
W
I
D AGRA
BLOCK
0.1F
P POWER
I/O LINE
P RESET
P
SYSTEM
0.1F
500k
LTC699 TA1
V
CC
GND
WDI
RESET
MICROPROCESSOR RESET AND WATCHDOG TIMING IN
A SINGLE CHIP FOR MICROPROCESSOR SYSTEMS.
+5V
LTC699
VCC
RESET PULSE
GENERATOR
WDI
1.3V
+
C1
OSC
RESET
LTC699 BD
GND
TRANSITION
DETECTOR
WATCHDOG
TIMER
2
LTC699
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
Terminal Voltage
V
CC
................................................... 0.3V to 6.0V
WDI Input .............................. 0.3V to V
CC
+ 0.3V
RESET Output ...................................... 0.3V to 6V
Power Dissipation ............................................. 500mW
Operating Temperature Range
LTC699C .............................................. 0
C to 70
C
LTC699I ........................................... 40
C to 85
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec.)................ 300
C
1
2
3
4
5
6
7
8
TOP VIEW
WDI
V
CC
V
CC
GND
GND
LTC699
NC
RESET
N8 PACKAGE
8-LEAD PLASTIC DIP
GND
1
2
3
4
5
6
7
8
TOP VIEW
GND
V
CC
V
CC
NC
GND
GND
S8 PACKAGE
8-LEAD PLASTIC SOIC
WDI
RESET
LTC699
LTC699CN8
LTC699IN8
LTC699CS8
LTC699IS8
ORDER PART
NUMBER
(Notes 1 and 2)
W
U
U
PACKAGE/ORDER I FOR ATIO
PARAMETER
CONDITONS
MIN
TYP
MAX
UNITS
Operating Voltage Range
q
3.0
5.5
V
Supply Current
0.6
1.5
mA
q
0.6
2.5
Power Down Reset Assertion
q
4.5
4.65
4.75
V
Power Up Reset De-Assertion
q
4.75
V
Reset Threshold Hysteresis
40
mV
Reset Active Time
160
200
240
ms
q
140
200
280
Watchdog Time-out Period
1.2
1.6
2.0
sec
q
1.0
1.6
2.25
Reset Active Time PSRR
1
ms/V
Watchdog Time-out Period PSRR
8
ms/V
Minimum WDI Input Pulse Width
V
IL
= 0.4, V V
IH
= 3.5V
q
200
ns
RESET output Voltage at V
CC
= 1V (Note 3)
I
SINK
= 10
A, V
CC
= 1V
4
200
mV
RESET output Voltage
I
SINK
= 1.6mA, V
CC
= 4.25V
0.4
V
RESET Output Short Circuit Current
Output Sink Current
25
mA
WDI Input Threshold
Logic Low
0.8
V
Logic High
2.0
WDI Input Current
WDI = V
OUT
q
4
50
A
WDI = 0V
q
50
8
V
CC
= +5V, T
A
= 25
C, unless otherwise noted.
ELECTRICAL C
C
HARA TERISTICS
Note 2: All voltage values are with respect to GND.
Note 3: RESET is active low, open drain output.
The
q
denotes specifications which apply over the operating temperature
range.
Note 1: Absolute maximum ratings are those values beyond which the life
of device may be impaired.
3
LTC699
but not serviced prior to the time-out period, the reset
pulse generator also forces RESET to active low for a mini-
mum of 140ms for every time-out period (see Figure 2).
WDI: Watchdog Input, WDI, is a three level input. Driving
WDI either high or low for longer than the watchdog time-
out period forces RESET low. Floating WDI disables the
Watchdog Timer. The timer resets itself with each transition
of the Watchdog Input (see Figure 2).
V
CC
: +5V supply input. The V
CC
pin should be bypassed
with a 0.1
F capacitor.
GND: Ground pin.
RESET: Open drain output for
P reset control. When V
CC
falls below the reset voltage threshold (4.65V typically),
RESET goes active low. After V
CC
returns to 5V, the reset
pulse generator forces RESET to remain active low for a
minimum of 140ms . When the watchdog timer is enabled
PI FU CTIO S
U
U
U
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 represen-
tation that the interconnection of circuits as described herein will not infringe on existing patent rights.
SUPPLY VOLTAGE (V)
0
RESET OUTPUT VOLTAGE (V)
3
4
5
4
2
1
0
1
2
3
5
LTC699 G01
T
A
= 25C
EXTERNAL PULLUP = 10
A
TEMPERATURE (
C)
50
RESET ACTIVE TIME (ms)
216
224
232
25
75
LTC699 G02
208
200
25
0
50
100
125
192
184
V
CC
= 5V
Reset Voltage Threshold vs
Temperature
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
down, the RESET signal remains active low even with V
CC
as low as 1V. This capability helps hold the microproces-
sor in stable shutdown condition. Figure 1 shows the
timing diagram of the RESET signal.
The precision voltage comparator, C1, typically has 40mV
of hysteresis which ensures that glitches at V
CC
pin do not
activate the RESET output. Response time is typically
10
s. To help prevent mistriggering due to transient loads,
V
CC
pin should be bypassed with a 0.1
F capacitor with the
leads trimmed as short as possible.
Microprocessor Reset
The LTC699 uses a bandgap voltage reference and a
precision voltage comparator C1 to monitor the 5V supply
input V
CC
(see BLOCK DIAGRAM). When V
CC
falls below
the reset voltage threshold, the RESET output is forced to
active low state. The reset voltage threshold accounts for
a 5% variation on V
CC
, so the RESET output becomes
active low when V
CC
falls below 4.65V typical. On power-
up, the RESET signal is held active low for a minimum of
140ms after reset voltage threshold is reached to allow the
power supply and microprocessor to stabilize. On power-
U
S
A
O
PPLICATI
W
U
U
I FOR ATIO
RESET Output Voltage vs
Supply Voltage
Reset Active Time vs
Temperature
TEMPERATURE (
C)
50
RESET VOLTAGE THRESHOLD (V)
4.64
4.65
4.66
25
75
LTC699 G03
4.63
4.62
25
0
50
100
125
4.61
4.60
4
LTC699
U
S
A
O
PPLICATI
W
U
U
I FOR ATIO
Figure 1. Reset Active Time
Watchdog Timer
The LTC699 provides a watchdog timer function to moni-
tor the activity of the microprocessor. If the microproces-
sor does not toggle the Watchdog Input (WDI) within the
time-out period, RESET is forced to active low for a
minimum of 140ms. The watchdog time-out period is
fixed at a 1.0 second minimum on the LTC699, which is
adequate time for most systems to service 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 soon
as RESET is inactive. When either a high-to-low or low-to-
high transition occurs at the WDI 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, either a high-
to-low or low-to-high transition on the WDI pin must
occur at or less than the minimum time-out period. If the
input to the WDI pin remains either high or low, reset
pulses will be issued every 1.6 seconds typically. The
watchdog time can be deactivated by floating the WDI pin.
The timer is also disabled when V
CC
falls below the reset
voltage threshold.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
q
FAX
: (408) 434-0507
q
TELEX
: 499-3977
LINEAR TECHNOLOGY CORPORATION 1992
LT/GP 0192 10K REV 0
T
JMAX
JA
110
C
180
C/W
CONDITIONS: PCB MOUNT ON FR4 MATERIAL,
STILL AIR AT 25
C, COPPER TRACE
T
JMAX
JA
110
C
130
C/W
V
CC
t1
t1 = RESET ACTIVE TIME
V1 = RESET VOLTAGE THRESHOLD
V2 = RESET VOLTAGE THRESHOLD +
RESET THRESHOLD HYSTERESIS
t1
V2
V2
V1
V1
LTC699 F01
RESET
t1 = RESET ACTIVE TIME
t2 = WATCHDOG TIME-OUT PERIOD
V
CC
= 5V
t2
t1
t1
WDI
RESET
LTC699 F02
t2
t1
Figure 2. Watchdog Time-Out Period and Reset Active Time
PACKAGE DESCRIPTIO
U
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead Plastic DIP
S8 Package
8-Lead Plastic SOIC
N8 1191
E
C
e
A
1
2
3
4
8
7
6
5
E
1
D
Q
1
B
1
e
1
S
A
1
L
A
B
SYMBOL
A
A
1
B
B
1
C
D
E
INCHES
0.130 0.006
0.020 MIN
0.018 0.003
0.045 0.065
0.009 0.015
0.400 MAX
0.300 0.320
MILLIMETERS
3.302 0.127
0.508 MIN
0.457 0.076
1.143 1.651
0.229 0.381
10.160 MAX
7.620 8.128
SYMBOL
E
1
e
A
e
1
L
Q
1
S
INCHES
0.250 0.010
0.325 + 0.025
0.015
0.100 0.010
0.125 MIN
0.065 TYP
0.045 0.015
MILLIMETERS
6.350 0.254
8.255 + 0.635
0.381
2.540 0.254
3.175 MIN
1.651 TYP
1.143 0.381
h
45
S8 1191
C
L
A
B
e
1
A
1
1
2
3
4
8
7
6
5
H
D
E
SYMBOL
A
A
1
B
C
D
E
INCHES
0.053 0.069
0.004 0.010
0.014 0.019
0.008 0.010
0.189 0.197
0.150 0.157
MILLIMETERS
1.346 1.753
0.102 0.254
0.356 0.483
0.203 0.254
4.801 5.004
3.810 3.988
SYMBOL
e
H
h
L
INCHES
0.050 TYP
0.228 0.244
0.010 0.020
0.016 0.050
MILLIMETERS
1.270 TYP
5.791 6.198
0.254 0.508
0.406 1.270
0 8 TYP
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