LTC699
Microprocessor
Supervisory Circuit
FEATURES
s
s
s
s
s
s
s
s
DESCRIPTIO
Guaranteed
Reset Assertion at V
CC
= 1V
1.5mA Maximum Supply Current
SO-8 Packaging
4.65V Precision Voltage Monitor
Power OK/Reset Time Delay: 200ms
Minimum External Component Count
Performance Specified Over Temperature
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.
APPLICATI
s
s
s
s
S
Critical
µP
Power Monitoring
Intelligent Instruments
Computers and Controllers
Automotive Systems
TYPICAL APPLICATI
+5V
BLOCK DIAGRA
VCC
500k
V
CC
RESET
LTC699
WDI
GND
µP POWER
µP RESET
+
RESET PULSE
GENERATOR
µP
SYSTEM
I/O LINE
1.3V
C1
–
OSC
0.1µF
0.1µF
WDI
TRANSITION
DETECTOR
LTC699 TA1
MICROPROCESSOR RESET AND WATCHDOG TIMING IN
A SINGLE CHIP FOR MICROPROCESSOR SYSTEMS.
W
U
RESET
GND
WATCHDOG
TIMER
LTC699 BD
UO
UO
1
LTC699
ABSOLUTE
(Notes 1 and 2)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
CC
V
CC
1
2
LTC699
8 GND
7 RESET
6 WDI
5
NC
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
ORDER PART
NUMBER
LTC699CN8
LTC699IN8
GND 3
GND 4
N8 PACKAGE
8-LEAD PLASTIC DIP
TOP VIEW
V
CC
V
CC
GND
GND
1
2
LTC699
3
4
6
5
8
7
GND
RESET
WDI
NC
LTC699CS8
LTC699IS8
S8 PACKAGE
8-LEAD PLASTIC SOIC
ELECTRICAL CHARACTERISTICS
V
CC
= +5V, T
A
= 25°C, unless otherwise noted.
PARAMETER
Operating Voltage Range
Supply Current
Power Down Reset Assertion
Power Up Reset De-Assertion
Reset Threshold Hysteresis
Reset Active Time
Watchdog Time-out Period
q
CONDITONS
q
q
q
q
MIN
3.0
TYP
0.6
0.6
4.65
40
200
200
1.6
1.6
1
8
4
25
4.5
MAX
5.5
1.5
2.5
4.75
4.75
240
280
2.0
2.25
UNITS
V
mA
V
V
mV
ms
sec
ms/V
ms/V
ns
mV
V
mA
V
µA
q
160
140
1.2
1.0
Reset Active Time PSRR
Watchdog Time-out Period PSRR
Minimum WDI Input Pulse Width
RESET output Voltage at V
CC
= 1V (Note 3)
RESET output Voltage
RESET Output Short Circuit Current
WDI Input Threshold
WDI Input Current
V
IL
= 0.4, V V
IH
= 3.5V
I
SINK
= 10µA, V
CC
= 1V
I
SINK
= 1.6mA, V
CC
= 4.25V
Output Sink Current
Logic Low
Logic High
WDI = V
OUT
WDI = 0V
q
200
200
0.4
0.8
2.0
q
q
–50
4
–8
50
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.
Note 2:
All voltage values are with respect to GND.
Note 3:
RESET is active low, open drain output.
2
U
W
U
U
W W
W
LTC699
PI FU CTIO S
V
CC
:
+5V supply input. The V
CC
pin should be bypassed
with a 0.1µF capacitor.
GND:
Ground pin.
RESET:
Open drain output for
µP
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
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).
TYPICAL PERFOR A CE CHARACTERISTICS
RESET Output Voltage vs
Supply Voltage
5
T
A
= 25°C
EXTERNAL PULLUP = 10µA
RESET OUTPUT VOLTAGE (V)
RESET ACTIVE TIME (ms)
4
3
224
216
208
200
192
184
–50 –25
RESET VOLTAGE THRESHOLD (V)
2
1
0
0
1
3
4
2
SUPPLY VOLTAGE (V)
APPLICATI
S I FOR ATIO
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-
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.
U
W
U W
U
U
UO
U
U
Reset Active Time vs
Temperature
232
V
CC
= 5V
4.65
4.64
4.63
4.62
4.61
4.66
Reset Voltage Threshold vs
Temperature
5
LTC699 G01
0
50 75
25
TEMPERATURE (
°
C)
100 125
LTC699 G02
4.60
–50 –25
50
25
75
0
TEMPERATURE (
°
C)
100
125
LTC699 G03
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
10µs. To help prevent mistriggering due to transient loads,
V
CC
pin should be bypassed with a 0.1µF capacitor with the
leads trimmed as short as possible.
3
LTC699
APPLICATI
S I FOR ATIO
V2
V
CC
RESET
t1
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
V
CC
= 5V
WDI
t2
RESET
t1
Figure 2. Watchdog Time-Out Period and Reset Active Time
PACKAGE DESCRIPTIO
N8 Package
8-Lead Plastic DIP
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic SOIC
D
D
E
B
1
A
Q
1
8
7
6
C
S
e
1
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
L
A
1
1
e
A
SYMBOL
A
A
1
B
B
1
C
D
E
B
2
3
MILLIMETERS
SYMBOL INCHES
0.250 ± 0.010 6.350 ± 0.254
E
1
0.325 + 0.025 8.255 + 0.635
e
A
–0.381
–0.015
0.100 ± 0.010 2.540 ± 0.254
e
1
3.175 MIN
L
0.125 MIN
1.651 TYP
Q
1
0.065 TYP
S
0.045 ± 0.015 1.143 ± 0.381
T
JMAX
110°C
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
q
FAX
: (408) 434-0507
q
TELEX
: 499-3977
U
V1
V2
V1 = RESET VOLTAGE THRESHOLD
V2 = RESET VOLTAGE THRESHOLD +
RESET THRESHOLD HYSTERESIS
V1
t1
t1 = RESET ACTIVE TIME
LTC699 F01
U
W
U
UO
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.
t2
t1
t1 = RESET ACTIVE TIME
t2 = WATCHDOG TIME-OUT PERIOD
t1
LTC699 F02
8
7
6
5
5
h
×
45°
C
A
B
L
SYMBOL
A
A
1
B
C
D
E
e
1
A
1
H
E
E
1
α
4
N8 1191
θ
JA
130°C/W
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
α
MILLIMETERS
INCHES
1.270 TYP
0.050 TYP
0.228 – 0.244 5.791 – 6.198
0.010 – 0.020 0.254 – 0.508
0.016 – 0.050 0.406 – 1.270
0° – 8° TYP
1
2
3
4
S8 1191
T
JMAX
110°C
θ
JA
180°C/W
CONDITIONS: PCB MOUNT ON FR4 MATERIAL,
STILL AIR AT 25°C, COPPER TRACE
LT/GP 0192 10K REV 0
©
LINEAR TECHNOLOGY CORPORATION 1992
嵌入式系统
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