Final Electrical Specifications
LTC1726
Triple Supply Monitor and
µP
Supervisor with Adjustable
Reset and Watchdog Timer
January 2000
FEATURES
s
DESCRIPTIO
s
s
s
s
s
s
s
s
Monitors Three Inputs Simultaneously
LTC1726-5: 5V, 3.3V and ADJ
LTC1726-2.5: 2.5V, 3.3V and ADJ
±1.5%
Threshold Accuracy Over Temperature
Low Supply Current: 16µA Typ
Adjustable Reset Timeout
Adjustable Watchdog Timeout
Active Low Open-Drain Reset Output
Power Supply Glitch Immunity
Guaranteed RESET for V
CC3
≥
1V or V
CC25
/V
CC5
≥
1V
MS8 and SO-8 Packages
The LTC
®
1726 is a triple supply monitor and microproces-
sor supervisory circuit with adjustable reset and watchdog
functions intended for systems with multiple supply volt-
ages. The part has a common open-drain reset output with
an adjustable delay. The reset and watchdog time-out
periods are both adjustable using external capacitors.
Tight 1.5% accuracy specifications and glitch immunity
ensure reliable reset operation without false triggering.
The RST output is guaranteed to be in the correct state for
V
CC5
/V
CC25
or V
CC3
down to 1V. The LTC1726 may also be
configured to monitor any one or two V
CC
inputs instead
of three, depending on system requirements.
The low (16µA typical) supply current makes the LTC1726
ideal for power-conscious systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
DESCRIPTIO
s
s
s
s
s
Desktop Computers
Notebook Computers
Intelligent Instruments
Portable Battery-Powered Equipment
Network Servers
TYPICAL APPLICATIO S
A 3.3V, 5V and 1.8V Monitor
1.8V
(V
TRIP
= 1.665V)
3.3V
0.1µF
5V
0.1µF
C
RT
47nF
8
C
WT
47nF
7
WT
GND
t
RT
= 155ms
t
WT
= 1s
4
1726 TA01
A 3.3V, 2.5V and 1.8V Monitor
1.8V
(V
TRIP
= 1.665V)
3.3V
0.1µF
2.5V
0.1µF
RESET
µP
R1
66.5k
1%
2
1
3
6
R2
100k
1%
V
CC5
V
CC3
V
CCA
RT
RST
LTC1726-5
5
WDI
C
RT
47nF
8
C
WT
47nF
7
I/O
t
RT
= 155ms
t
WT
= 1s
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 its circuits as described herein will not infringe on existing patent rights.
U
R1
66.5k
1%
2
1
3
6
R2
100k
1%
RESET
µP
5
WT
GND
4
1726 TA02
U
U
V
CC25
V
CC3
V
CCA
RT
RST
LTC1726-2.5
WDI
I/O
1
LTC1726
ABSOLUTE
AXI U
RATI GS
Terminal Voltage
V
CC3
, V
CC5
/V
CC25
, V
CCA
.........................
RST .......................................................
WDI .......................................................
RT, WT ..................................................
PACKAGE/ORDER I FOR ATIO
ORDER
PART NUMBER
TOP VIEW
V
CC3
V
CC25
/V
CC5
V
CCA
GND
1
2
3
4
8
7
6
5
RT
WT
RST
WDI
LTC1726EMS8-2.5
LTC1726EMS8-5
MS8 PACKAGE
8-LEAD PLASTIC MSOP
MS8 PART MARKING
LTKZ
LTLA
T
JMAX
= 125°C,
θ
JA
= 200°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
RT3
V
RT5
V
RT25
V
RTA
V
CC
I
VCC3
I
VCC5
I
VCC25
I
VCCA
PARAMETER
Reset Threshold V
CC3
Reset Threshold V
CC5
Reset Threshold V
CC25
Reset Threshold V
CCA
V
CC3
or V
CC5
Operating Voltage
V
CC3
Supply Current
V
CC5
Supply Current
V
CC25
Supply Current
V
CCA
Input Current
RT Charge Current Out
WT Charge Current Out
RT Discharge Current Out
WT Discharge Current Out
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specificaitons are at T
A
= 25°C. V
CC3
= 3.3V, V
CC5
= 5V, V
CC25
= 2.5V, V
CCA
= V
CC3
unless
otherwise noted.
CONDITIONS
V
CC3
Input Threshold
V
CC5
Input Threshold (5V Version)
V
CC25
Input Threshold (2.5V Version)
V
CCA
Input Threshold
RST in Correct Logic State
V
CC5
/V
CC25
> V
CC3
V
CC5
/V
CC25
< V
CC3
, V
CC3
= 3.3V
V
CC5
= 5V
V
CC25
< V
CC3
, V
CC25
= 2.5V (Note 4)
V
CCA
= 1V
V
RT
= 0V
V
WT
= 0V
V
RT
= 1.3V
V
WT
= 1.3V
q
q
q
q
q
q
q
q
q
q
q
q
q
q
2
U
U
W
W W
U
W
(Notes 1, 2)
– 0.3V to 7V
– 0.3V to 7V
– 0.3V to 7V
– 0.3V to 7V
Operating Temperature Range (Note 3) .. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................ 300°C
ORDER
PART NUMBER
TOP VIEW
V
CC3
1
V
CC25
/
2
V
CC5
V
CCA
3
GND 4
8
7
6
5
RT
WT
RST
WDI
LTC1726ES8-2.5
LTC1726ES8-5
LTC1726IS8-2.5
LTC1726IS8-5
S8 PART MARKING
172625
726I25
17265
1726I5
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/W
MIN
3.036
4.600
2.300
0.985
1
TYP
3.085
4.675
2.337
1.000
1
16
16
1
MAX
3.135
4.750
2.375
1.015
7
2
30
30
2
15
2.6
2.6
26
26
UNITS
V
V
V
V
V
µA
µA
µA
µA
nA
µA
µA
µA
µA
– 15
1.4
1.4
14
14
0
2
2
20
20
LTC1726
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specificaitons are at T
A
= 25°C. V
CC3
= 3.3V, V
CC5
= 5V, V
CC25
= 2.5V, V
CCA
= V
CC3
unless
otherwise noted.
SYMBOL
t
RT
t
UV
V
OH
V
OL
PARAMETER
Reset Time-Out Period
V
CC
Undervoltage Detect to RST
RST Output Voltage High (Note 5)
RST Output Voltage Low
CONDITIONS
C
RT
= 1500pF
V
CC25
/V
CC5
, V
CC3
or V
CCA
Less Than Reset
Threshold V
RT
by More Than 1%
I
SOURCE
= 1µA
I
SINK
= 2.5mA, V
CC5
/V
CC25
= 0V
I
SINK
= 100µA, V
CC3
= 1V, V
CC5
/V
CC25
= 0V
I
SINK
= 100µA, V
CC3
= 0V, V
CC5
/V
CC25
= 1V
I
SINK
= 100µA, V
CC3
= 1V, V
CC5
/V
CC25
= 1V
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
MIN
3.5
TYP
5
130
MAX
6.5
UNITS
ms
µs
V
V
CC3
– 1
0.15
0.05
0.05
0.05
0.3 • V
CC3
40
23
33
43
±1
V
CC3
±0.025
0.4
0.3
0.3
0.3
0.7 • V
CC3
V
V
V
V
V
V
ns
ms
µA
V
V
IH
V
IL
t
WP
t
WT
WDI Input Threshold High
WDI Input Threshold Low
WDI Pulse Width
Watchdog Time-Out Period
WDI Leakage Current
C
WT
= 1500pF
q
q
LTC1726-5 Only
V
OVR
V
CC5
Reset Override Voltage (Note 6)
Override V
CC5
Ability to Assert RST
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
All voltage values are with respect to GND.
Note 3:
The LTC1726E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 4:
Both V
CC3
and V
CC25
/V
CC5
can act as the supply depending on
which pin has the greatest potential.
Note 5:
The output pin RST has weak internal pull-ups to V
CC3
of typically
6µA. However, external pull-up resistors may be used when faster rise
times are required or for V
OH
voltages greater than V
CC3
.
Note 6:
The V
CC5
reset override voltage is valid for an operating range less
than approximately 4.15V. Above this point the override is turned off and
the V
CC5
pin functions normally.
TYPICAL PERFOR A CE CHARACTERISTICS
V
CC5
Threshold Voltage
vs Temperature
4.750
V
CC5
THRESHOLD VOLTAGE, V
RT5
(V)
3.135
V
CC3
THRESHOLD VOLTAGE, V
RT3
(V)
3.125
3.115
3.105
3.095
3.085
3.075
3.065
3.055
3.045
3.035
– 60 –40 – 20 0 20 40 60
TEMPERATURE (°C)
80
100
4.725
4.700
4.675
4.650
4.625
4.600
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
V
CCA
THRESHOLD VOLTAGE, V
RTA
(V)
U W
80
V
CC3
Threshold Voltage
vs Temperature
1.015
1.010
1.005
1.000
0.995
0.990
V
CCA
Threshold Voltage
vs Temperature
100
0.985
20
40 60
–60 –40 –20 0
TEMPERATURE (°C)
80 100
1726 G03
1726 G01
1726 G02
3
LTC1726
TYPICAL PERFOR A CE CHARACTERISTICS
V
CC25
Threshold Voltage
vs Temperature
2.375
V
CC25
THRESHOLD VOLTAGE, V
RT25
(V)
2.360
I
VCC5
(µA)
15
14
13
I
VCC3
(µA)
2.345
2.330
2.315
2.300
20
40 60
–60 –40 –20 0
TEMPERATURE (°C)
I
VCC25
vs Temperature
(LTC1726-2.5)
V
CC3
= 3.3V
1.4 V
CC25
= 2.5V
1.3
1.2
I
VCC25
(µA)
I
VCC3
(µA)
1.5
TYPICAL TRANSIENT DURATION (µs)
1.1
1.0
0.9
0.8
0.7
0.6
0.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
V
CCA
Input Current
vs Input Voltage
2.0
1.5
INPUT CURRENT (nA)
T
A
= 25°C
WATCHDOG TIME PERIOD, t
WT
(ms)
RESET PULSE WIDTH, t
RT
(ms)
1.0
0.5
0
– 0.5
–1.0
–1.5
– 2.0
0.80 0.85 0.90 0.95 1 1.05 1.10 1.15 1.20
INPUT VOLTAGE (V)
1726 G14
4
U W
I
VCC5
vs Temperature
V
CC5
= 5V
19 V
CC3
= 3.3V
18
17
16
20
1.5
I
VCC3
vs Temperature (LTC1726-5)
V
CC5
= 5V
1.4 V
CC3
= 3.3V
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
80
100
0.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
12
11
80 100
1726 G04
10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
1726 G05
1726 G06
I
VCC3
vs Temperature
(LTC1726-2.5)
20
V
CC3
= 3.3V
19 V
CC25
= 2.5V
18
17
16
15
14
13
12
11
10
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
700
600
500
400
300
200
100
Typical Transient Duration
vs Comparator Overdrive
T
A
= 25°C
RESET OCCURS
ABOVE CURVE
0
1
10
100
0.1
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V
CC
)
1726 G09
1726 G07
1726 G08
Watchdog Time-Out Period
vs Temperature
40
38
36
34
32
30
28
26
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
C
WT
= 1500pF
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
80
100
Reset Pulse Width vs Temperature
C
RT
= 1500pF
4.0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
1726 G10
1726 G11
LTC1726
TYPICAL PERFOR A CE CHARACTERISTICS
Time-Out Period vs Capacitance
10
6
T
A
= 25°C
10
4
t
WT
t
RT
RST OUTPUT VOLTAGE (V)
10
5
t
RT
OR t
WT
(µs)
10
3
10
2
10
0.1
1
PI FU CTIO S
V
CC3
(Pin 1):
3.3V Sense Input. This pin also supplies
power to the part when the voltage on this pin is greater
than the voltage on V
CC25
/V
CC5
. Bypass this pin to ground
with a 0.1µF or larger ceramic capacitor.
V
CC5
(Pin 2):
5V Sense Input (LTC1726-5). This pin also
supplies power to the part when the voltage on this pin is
greater than the voltage on V
CC3
. Bypass this pin to
ground with a 0.1µF or larger ceramic capacitor.
V
CC25
(Pin 2):
2.5V Sense Input (LTC1726-2.5). This pin
also supplies power to the part when the voltage on this
pin is greater than the voltage on V
CC3
. Bypass this pin to
ground with a 0.1µF or larger ceramic capacitor.
V
CCA
(Pin 3):
1V Sense, High Impedance Input. If unused
it can be tied to either V
CC3
, V
CC5
or V
CC25
.
GND (Pin 4):
Ground.
WDI (Pin 5):
Watchdog Input. A logic input whose rising
or falling edge must occur on this pin within the selected
watchdog time-out period or a reset pulse will occur. The
watchdog time-out period is set by the value of the
capacitor that is placed on the WT pin. The rising or falling
edge of this pin clears the voltage on the WT capacitor,
preventing a reset pulse from occurring. If the watchdog
timer is not cleared, a reset pulse will occur. The watch-
dog timer is cleared during a reset and restarts when the
reset is deasserted. When disabling the watchdog func-
tion, this pin should be connected to either V
CC3
or
ground and WT must be grounded.
RST (Pin 6):
Reset Logic Output. Active low, open-drain
logic output with weak pull-up to V
CC3
. Asserted when
one or more of the supplies are below trip thresholds.
After all supplies become valid, the reset remains as-
serted for the period set by the capacitor on the RT pin.
The watchdog timer can also trigger the reset whenever
the watchdog time-out period is exceeded. This pin can
be pulled up greater than V
CC3
when interfacing to 5V
logic.
WT (Pin 7):
Watchdog Time-Out Input. Place a capacitor
between this pin and ground to adjust the watchdog time-
out period. To determine the watchdog time-out period:
t
WT
= 21.8 • C
WT
with t
WT
in
µs
and C
WT
in pF. As an example, a 47nF
capacitor will generate a 1s watchdog time-out period.
The watchdog function can be disabled by connecting
this pin to ground.
U W
RST Output Voltage vs
Supply Voltage (LTC1726-2.5)
V
CC3
= V
CC25
= V
CCA
10k PULL-UP FROM V
CC3
TO RST
3
T
A
= 25°C
2
1
10
10
2
C
RT
OR C
WT
(pF)
10
3
10
4
1726 G12
0
0
1
2
V
CC3
(V)
1726 F13
3
U
U
U
5
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