LTC1727/LTC1728
Micropower Precision
Triple Supply Monitors in 8-Lead MSOP
and 5-Lead SOT-23 Packages
DESCRIPTION
FEATURES
Monitors Three Inputs Simultaneously
LTC1727-5: 5V, 3.3V and ADJ
LTC1727-2.5: 2.5V, 3.3V and ADJ
LTC1728-5: 5V, 3.3V and ADJ
LTC1728-2.5: 2.5V, 3.3V and ADJ
LTC1728-1.8: 3V, 1.8V and ADJ
LTC1728-3.3: 3.3V, 1.8V and ADJ
n ±1.5% Threshold Accuracy Over Temperature
n Very Low Supply Current: 10µA Typ
n 200ms Reset Time Delay
n Active Low RESET Output
n Power Supply Glitch Immunity
n Guaranteed RESET for V
CC3 ≥ 1V
or VCC5 /VCC25/VCC18 ≥ 1V
n LTC1727 Includes Monitor Output for Each Supply
n LTC1727: 8-Lead MSOP and SO Packages
n LTC1728: 5-Lead SOT-23 Package
n
APPLICATIONS
n
n
n
n
n
The LTC®1727 is a triple supply monitor intended for
systems with multiple supply voltages. Each supply monitor has its own open-drain output for individual supply
monitoring. A common open-drain reset output remains
low until all three supplies have been in compliance for
200ms. Tight 1.5% accuracy specifications and glitch
immunity ensure reliable reset operation without false
triggering.
The LTC1728 is functionally identical to the LTC1727
without the individual monitor outputs.
The RST output is guaranteed to be in the correct state
for VCC5 /VCC25/VCC18 or VCC3 down to 1V. The LTC1727/
LTC1728 may also be configured to monitor any one or
two VCC inputs instead of three, depending on system
requirements.
Very low (10µA typical) supply current makes the LTC1727/
LTC1728 ideal for power conscious systems.
The LTC1727 is available in an 8-lead MSOP or SO package and the LTC1728 is available in a 5-lead SOT-23
package.
Desktop Computers
Notebook Computers
Intelligent Instruments
Portable Battery-Powered Equipment
Network Servers
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
DC/DC
CONVERTER
3.3V
5V
1.8V
SYSTEM
LOGIC
VCC3
Triple Supply Monitor with Power Good Output
(3.3V, 2.5V and Adjustable)
LTC1727-2.5
RST
LTC1728-5
0.1µF
0.1µF
61.9k
1%
100k
1%
VCC5
VCCA
ADJUSTABLE
SUPPLY
GND
1727/28 TA01
3.3V
VCC3
2.5V
VCC25 COMP25
R1
R2
10k
VCCA
RST
GND
COMPA
10k
POWER
GOOD
COMP3
SYSTEM
RESET
1727/28 TA08
Rev. E
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1
LTC1727/LTC1728
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
VCC3, VCC5 /VCC25/VCC18, VCCA ......................... – 0.3V to 7V
RST.............................................................. – 0.3V to 7V
COMPA, COMP3, COMP25/COMP5
(MS8 and SO-8 Only).............................. – 0.3V to 7V
Operating Temperature Range
LTC1727/LTC1728E (Note 3)................ – 40°C to 85°C
LTC1728H...........................................– 40°C to 125°C
LTC1727I..............................................– 40°C to 85°C
Storage Temperature Range................... – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
VCC3
VCC5/VCC25
VCCA
GND
1
2
3
4
8
7
6
5
COMP3
COMP25/COMP5
RST
COMPA
6
GND 2
5
COMPA
VCCA 3
8
GND 4
7
TJMAX = 125°C, θJA = 200°C/W
RST 1
5 VCC3
VCC5/
4 VCC25/
VCC18
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S8 PACKAGE
8-LEAD PLASTIC SO
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TOP VIEW
COMP3
COMP25/
COMP5
RST
VCC3 1
VCC5/
2
VCC25
VCCA 3
TJMAX = 125°C, θJA = 150°C/W
TJMAX = 125°C, θJA = 250°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC1727EMS8-2.5#PBF LTC1727EMS8-2.5#TRPBF
LTHY
8-Lead Plastic MSOP
–40°C to 85°C
LTC1727EMS8-5#PBF
LTC1727EMS8-5#TRPBF
LTHX
8-Lead Plastic MSOP
–40°C to 85°C
LTC1727ES8-2.5#PBF
LTC1727ES8-2.5#TRPBF
172725
8-Lead Plastic SO
–40°C to 85°C
LTC1727IS8-2.5#PBF
LTC1727IS8-2.5#TRPBF
727I25
8-Lead Plastic SO
–40°C to 85°C
LTC1727ES8-5#PBF
LTC1727ES8-5#TRPBF
17275
8-Lead Plastic SO
–40°C to 85°C
LTC1727IS8-5#PBF
LTC1727IS8-5#TRPBF
1727I5
8-Lead Plastic SO
–40°C to 85°C
LTC1728ES5-1.8#PBF
LTC1728ES5-1.8#TRPBF
LTPH
8-Lead Plastic SOT-23
–40°C to 85°C
LTC1728ES5-2.5#PBF
LTC1728ES5-2.5#TRPBF
LTIA
8-Lead Plastic SOT-23
–40°C to 85°C
LTC1728ES5-3.3#PBF
LTC1728ES5-3.3#TRPBF
LTYP
8-Lead Plastic SOT-23
–40°C to 85°C
LTC1728ES5-5#PBF
LTC1728ES5-5#TRPBF
LTHZ
8-Lead Plastic SOT-23
–40°C to 85°C
LTC1728HS5-5#PBF
LTC1728HS5-5#TRPBF
LTHZ
8-Lead Plastic SOT-23
–40°C to 125°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
Rev. E
2
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LTC1727/LTC1728
ELECTRICAL CHARACTERISTICS
All except LTC1728-1.8/LTC1728-3.3. The l denotes specifications which
apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC3 = 3.3V, VCC5 = 5V,
VCC25 = 2.5V, VCCA = VCC3 unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX UNITS
VRT3
Reset Threshold VCC3
VCC3 Input Threshold
l
3.036
3.086
3.135
V
VRT5
Reset Threshold VCC5
VCC5 Input Threshold (5V Version)
l
4.600
4.675
4.750
V
VRT25
Reset Threshold VCC25
VCC25 Input Threshold (2.5V Version)
l
2.300
2.338
2.375
V
VRTA
Reset Threshold VCCA
VCCA Input Threshold
l
0.985
1.000
1.015
V
VCCOP
VCC3, VCC5 /VCC25 Operating Voltage
RST, COMP3, COMP5, COMP25 in Correct Logic State
l
1
7
V
VCCOPA
VCC3, VCC5 /VCC25 Operating Voltage
Minimum Supply Voltage to Guarantee COMPA
in Correct Logic State
l
2
2.3
V
IVCC3
VCC3 Supply Current
VCC5/VCC25 > VCC3
VCC5/VCC25 < VCC3, VCC3 = 3.3V (Note 4)
l
l
1
10
2
20
µA
µA
IVCC25
VCC25 Supply Current
VCC25 < VCC3, VCC25 = 2.5V (Note 4)
l
1
2
µA
IVCC5
VCC5 Supply Current
VCC5 = 5V, VCC3 < VCC5
l
10
20
µA
IVCCA
VCCA Input Current
VCCA = 1V
–40°C < TA < 125°C
l
l
–15
–20
0
0
15
50
nA
nA
tRST
Reset Pulse Width
RST Low with 10k Pull-Up to VCC3 (Note 5)
–40°C < TA < 125°C
l
l
140
140
200
280
350
ms
ms
tUV
VCC Undervoltage Detect to RST
or COMPX
VCC5, VCC25, VCC3 or VCCA Less Than Reset
Threshold VRT by More Than 1% (Note 5)
VOL
Output Voltage Low, RST, COMPX
ISINK = 2.5mA, VCC3 = 3V, VCC5 /VCC25 = 0V
ISINK = 100µA, VCC3 = 1V, VCC5 /VCC25 = 0V
ISINK = 100µA, VCC3 = 0V, VCC5 /VCC25 = 1V
ISINK = 100µA, VCC3 = 1V, VCC5 /VCC25 = 1V
110
Output Voltage High, RST, COMPX (Note 6) ISOURCE = 1µA
LTC1727-5/LTC1728-5 Only
VOVR
VCC5 Reset Override Voltage (Note 7)
0.15
0.05
0.05
0.05
l
l
l
l
VOH
µs
0.4
0.3
0.3
0.3
l VCC3 – 1
Override VCC5 Ability to Assert RST
V
V
V
V
V
VCC3 ±0.025
V
LTC1728-1.8 The l denotes specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC3 = 3V, VCC18 = 1.8V, VCCA = VCC3 unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT3
Reset Threshold VCC3
VCC3 Input Threshold
l
2.760
2.805
2.850
V
VRT18
Reset Threshold VCC18
VCC18 Input Threshold
l
1.656
1.683
1.710
V
VRTA
Reset Threshold VCCA
VCCA Input Threshold
l
0.985
1.000
1.015
V
VCCOP
VCC3, VCC18 Operating Voltage
RST in Correct Logic State
l
1
7
V
IVCC3
VCC3 Supply Current
VCC18 > VCC3
VCC18 < VCC3, VCC3 = 3V (Note 4)
l
l
2
20
µA
µA
IVCC18
VCC18 Supply Current
VCC18 < VCC3, VCC18 = 1.8V (Note 4)
l
1
2
µA
IVCCA
VCCA Input Current
VCCA = 1V
l
–15
0
15
nA
tRST
Reset Pulse Width
RST Low (Note 5)
l
140
200
280
ms
tUV
VCC Undervoltage Detect to RST
VCC18, VCC3 or VCCA Less Than Reset (Note 5)
Threshold VRT by More Than 1%
VOL
Output Voltage Low, RST
ISINK = 2.5mA, VCC3 = 3V, VCC18 = 0V
ISINK = 100µA, VCC3 = 1V, VCC18 = 0V
ISINK = 100µA, VCC3 = 0V, VCC18 = 1V
ISINK = 100µA, VCC3 = 1V, VCC18 = 1V
l
l
l
l
VOH
Output Voltage High, RST
ISOURCE = 1µA (Note 6)
l
1
10
110
0.15
0.05
0.05
0.05
VCC3 – 1
µs
0.4
0.3
0.3
0.3
V
V
V
V
V
Rev. E
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3
LTC1727/LTC1728
ELECTRICAL CHARACTERISTICS
LTC1728-3.3 The l denotes specifications which apply over the full operating temperature range, otherwise specifications are at
TA = 25°C. VCC3 = 3.3V, VCC18 = 1.8V, VCCA = VCC3 unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT3
Reset Threshold VCC3
VCC3 Input Threshold
l
3.036
3.086
3.135
V
VRT18
Reset Threshold VCC18
VRTA
Reset Threshold VCCA
VCC18 Input Threshold
l
1.656
1.683
1.710
V
VCCA Input Threshold
l
0.985
1.000
1.015
V
VCCOP
VCC3, VCC18 Operating Voltage
RST in Correct Logic State
l
1
7
V
IVCC3
VCC3 Supply Current
VCC18 > VCC3
VCC18 < VCC3, VCC3 = 3.3V (Note 4)
l
l
2
20
µA
µA
IVCC18
VCC18 Supply Current
VCC18 < VCC3, VCC18 = 1.8V (Note 4)
l
1
2
µA
IVCCA
VCCA Input Current
VCCA = 1V
l
–15
0
15
nA
tRST
Reset Pulse Width
RST Low (Note 5)
l
140
200
280
ms
tUV
VCC Undervoltage Detect to RST
VCC18, VCC3 or VCCA Less Than Reset (Note 5)
Threshold VRT by More Than 1%
VOL
Output Voltage Low, RST
ISINK = 2.5mA, VCC3 = 3.3V, VCC18 = 0V
ISINK = 100µA, VCC3 = 1V, VCC18 = 0V
ISINK = 100µA, VCC3 = 0V, VCC18 = 1V
ISINK = 100µA, VCC3 = 1V, VCC18 = 1V
l
l
l
l
VOH
Output Voltage High, RST
ISOURCE = 1µA (Note 6)
l
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All voltage values are with respect to GND.
Note 3: The LTC1727E/LTC1728E are guaranteed to meet specified
performance from 0°C to 70°C and are designed, characterized and
assured to meet the extended temperature limits of –40°C to 85°C
but are not tested at these temperatures.
1
10
110
0.15
0.05
0.05
0.05
VCC3 – 1
µs
0.4
0.3
0.3
0.3
V
V
V
V
V
Note 4: Both VCC3 and VCC5/VCC25/VCC18 can act as the supply depending
on which pin has the greatest potential.
Note 5: Measured from when input passes through the input threshold
(VRTX) until RST or COMPX passes through 1.5V.
Note 6: The output pins RST and COMPX have internal pull-ups to VCC3 of
typically 6µA. However, external pull-up resistors may be used when faster
rise times are required or for VOH voltages greater than VCC3.
Note 7: The VCC5 reset override voltage is valid for an operating range less
than approximately 4.15V. Above this point the override is turned off and
the VCC5 pin functions normally.
Rev. E
4
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LTC1727/LTC1728
TYPICAL PERFORMANCE CHARACTERISTICS
VCCA Input Current
vs Input Voltage
450
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)
TYPICAL TRANSIENT DIRATION (µs)
1.0
1.010
1.005
1.000
0.995
0.990
0.985
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
Reset Pulse Width
vs Temperature
10
9
260
180
40
60
80
100
1.2
VOL = 0.2V
1.1
1.0
0.9
0.8
0.7
0.6
0
0.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
0
1
3
4
2
VCC3 OR VCC5 (V)
5
6
1.5
VCC3 = 3.3V
VCC25 = 2.5V
VCCA = 3.3V
1.4
1.3
15
VCC5 = 5V
VCC3 = 3.3V
VCCA = 3.3V
14
13
12
11
1.1
11
IVCC3 (µA)
1.2
1.0
0.9
VCC5 = 5V
VCC3 = 3.3V
VCCA = 3.3V
10
9
8
0.8
8
7
0.7
7
6
0.6
6
0.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
1727/28 G07
100
IVCC5 vs Temperature
(LTC1727-5/LTC1728-5)
12
9
80
1727/28 G06
1727/28 G05
IVCC3 vs Temperature
(LTC1727-5/LTC1728-5)
10
VCC3 = 3.3V
VCC25 = 2.5V
VCCA = 3.3V
1
IVCC3 vs Temperature (LTC17272.5/LTC1728-2.5/LTC1728-3.3)
IVCC3 (µA)
1.3
IVCC25 (µA)
4
1727/28 G04
13
50
1.4
5
TEMPERATURE (°C)
14
100
1.5
2
160
20
150
IVCC25 vs Temperature
(LTC1727-2.5/LT1728-2.5)
6
3
0
250
200
1727/28 G03
VOL = 0.4V
7
200
RESET OCCURS
ABOVE CURVE
300
0
1
10
100
0.1
RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VCC)
100
TA = 25°C
8
240
ISINK (mA)
RESET PULSE WIDTH, tRST (ms)
280
140
–60 –40 –20
350
RST, COMPX ISINK
vs Supply Voltage
220
TA = 25°C
400
1727/28 G02
1727/28 G01
15
80
IVCC5 (µA)
INPUT CURRENT (nA)
1.5
Typical Transient Duration
vs Comparator Overdrive
1.015
TA = 25°C
VCCA THRESHOLD VOLTAGE, VRTA (V)
2.0
VCCA Threshold Voltage
vs Temperature
80
100
1727/28 G08
80
100
1727/28 G09
Rev. E
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5
LTC1727/LTC1728
TYPICAL PERFORMANCE CHARACTERISTICS
VCC3 Threshold Voltage
vs Temperature
(All But LTC1728-1.8)
3.135
2.3675
3.125
2.3600
2.3525
2.3450
2.3375
2.3300
2.3225
2.3150
2.3075
2.3000
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
4.750
4.725
3.115
3.105
4.700
3.095
3.085
4.675
3.075
4.650
3.065
3.055
4.625
3.045
3.035
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
1727/28 G10
1.4
100
4.600
20
40 60
–60 –40 –20 0
TEMPERATURE (°C)
VCC3 = 3V
14 VCC18 = 1.8V
VCCA = 3V
13
1.2
12
1.1
11
1.0
0.9
10
9
0.8
8
0.7
7
0.6
6
0.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
80
100
1727/28 G14
1727/28 G13
VCC18 Threshold Voltage
vs Temperature
(LTC1728-1.8/LTC1728-3.3)
VCC3 Threshold Voltage
vs Temperature (LTC1728-1.8)
2.845
VCC3 THRESHOLD VOLTAGE, VRT3 (V)
1.710
VCC18 THRESHOLD VOLTAGE, VRT18 (V)
1727/28 G12
15
VCC3 = 3V
VCC18 = 1.8V
VCCA = 3V
1.700
1.690
1.680
1.670
1.660
1.650
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80 100
IVCC3 vs Temperature
(LTC1728-1.8)
IVCC3 (µA)
IVCC18 (µA)
1.3
80
1727/28 G11
IVCC18 vs Temperature
(LTC1728-1.8/LTC1728-3.3)
1.5
VCC5 Threshold Voltage
vs Temperature
(LTC1727-5/LTC1728-5)
VCC5 THESHOLD VOLTAGE, VRT5 (V)
2.3750
VCC3 THRESHOLD VOLTAGE, VRT3 (V)
VCC25 THRESHOLD VOLTAGE, VRT25 (V)
VCC25 Threshold Voltage
vs Temperature
(LTC1727-2.5/LTC1728-2.5)
80
100
2.835
2.825
2.815
2.805
2.795
2.785
2.775
2.765
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
1727/28 G15
80
100
1727/28 G16
Rev. E
6
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LTC1727/LTC1728
PIN FUNCTIONS
(LTC1727/LTC1728)
VCC3 (Pin 1/Pin 5): 3.3V Sense Input and Power Supply
Pin. (3V Sense Input and Power Supply Pin for LTC17281.8.) This pin provides power to the part when the voltage
on VCC3 is greater than the voltage on VCC5/VCC25/VCC18.
Bypass to ground with a ≥ 0.1µF ceramic capacitor.
VCC5 (Pin 2/Pin 4): 5V Sense Input and Power Supply Pin.
This pin is used on the LTC1727-5/LTC1728-5 to provide
power to the part when the voltage on VCC5 is greater
than the voltage on VCC3. Bypass to ground with a ≥0.1µF
ceramic capacitor.
VCC25 (Pin 2/Pin 4): 2.5V Sense Input and Power Supply
Pin. This pin is used on the LTC1727-2.5/LTC1728-2.5 to
provide power to the part when the voltage on VCC25 is
greater than the voltage on VCC3. Bypass to ground with
a ≥0.1µF ceramic capacitor.
VCC18 (Pin 2/Pin 4): 1.8V Sense Input and Power Supply
Pin. This pin is used on the LTC1728-1.8/LTC1728‑3.3 to
provide power to the part when the voltage on VCC18 is
greater than the voltage on VCC3. Bypass to ground with
a ≥0.1µF ceramic capacitor.
VCCA (Pin 3/Pin 3): 1V Sense, High Impedance Input. If unused, it can be tied to either VCC3 or VCC5 /VCC25/VCC18.
GND (Pin 4/Pin 2): Ground.
COMPA (Pin 5): VCCA Comparator Output for the LTC1727.
Active high, open-drain logic output with weak pull-up to
VCC3. Asserted when VCCA is above VRTA. Deasserted when
VCCA is below VRTA or if both the VCC3 and VCC5 supply
pins are too low to power the internal bandgap reference
(typically < 2.0V). Can be pulled greater than VCC3 using
an external pull-up.
RST (Pin 6/Pin 1): Reset Logic Output. Active low, opendrain logic output with weak pull-up to VCC3. Can be pulled
up greater than VCC3 when interfacing to 5V logic. Asserted
when one or all of the supplies are below trip thresholds
and held for 200ms after all supplies become valid.
COMP5 (Pin 7): VCC5 Comparator Output for the
LTC1727-5. Active high, open-drain logic output with weak
pull-up to VCC3. Asserted when VCC5 is above VRT5. Can
be pulled greater than VCC3 using an external pull-up.
COMP25 (Pin 7): VCC25 Comparator Output for the
LTC1727-2.5. Active high, open-drain logic output with
weak pull-up to VCC3. Asserted when VCC25 is above
VRT25. Can be pulled greater than VCC3 using an external
pull-up.
COMP3 (Pin 8): VCC3 Comparator Output for the LTC1727.
Active high, open-drain logic output with weak pull-up to
VCC3. Asserted when VCC3 is above VRT3. Can be pulled
greater than VCC3 using an external pull-up.
Rev. E
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7
LTC1727/LTC1728
BLOCK DIAGRAMS
LTC1727-5/LTC1727-2.5
VCC3
6µA
–
VCC3 1
8
COMP3
7
COMP25/
COMP5
6
RST
5
COMPA
+
VCC3
POWER
DETECT
6µA
VCC INTERNAL
VCC5/
2
VCC25
–
VCC3
+
6µA
VCCA 3
GND 4
–
200ms PULSE GENERATOR
200ms
DELAY
+
VCC3
6µA
BANDGAP
REFERENCE
1727 BD1
Rev. E
8
For more information www.analog.com
LTC1727/LTC1728
BLOCK DIAGRAMS
LTC1728-5/LTC1728-2.5/LTC1728-1.8/LTC1728-3.3
–
VCC3 5
+
POWER
DETECT
VCC INTERNAL
VCC3
VCC5/
VCC25/ 4
VCC18
6µA
–
200ms PULSE GENERATOR
1
RST
200ms
DELAY
+
–
VCCA 3
+
GND 2
BANDGAP
REFERENCE
1727 BD2
TIMING DIAGRAM
VCC Monitor Timing
VCCX
RST
VRTX
tUV
tRST
1.5V
COMPX
1727 TD01
Rev. E
For more information www.analog.com
9
LTC1727/LTC1728
APPLICATIONS INFORMATION
Supply Monitoring
Power-Down
The LTC1727 is a low power, high accuracy triple supply monitoring circuit with three monitor outputs and a
200ms microprocessor reset output.
On power-down, once any of the VCC inputs drop below
its threshold, RST is held at a logic low. A logic low of
0.3V is guaranteed until both VCC3 and VCC5/VCC25/VCC18
drop below 1V.
All three VCC inputs must be above predetermined thresholds for reset not to be invoked. The LTC1727/LTC1728 will
assert reset during power-up, power-down and brownout
conditions on any one or all of the VCC inputs.
Power Detect
The LTC1727/LTC1728 are powered from the 3.3V/3V input
pin (VCC3), the 1.8V input pin (VCC18), the 2.5V input pin
(VCC25) or the 5V input pin (VCC5), whichever pin has the
highest potential. This ensures the part pulls the RST pin
low as soon as either input pin is ≥ 1V.
Power-Up
Upon power-up, either the VCC5 /VCC25/VCC18 or VCC3 pin,
can power the part. This ensures that RST will be low
when either VCC5/VCC25/VCC18 or VCC3 reaches 1V. As long
as any one of the VCC inputs is below its predetermined
threshold, RST will stay a logic low. Once all of the VCC
inputs rise above their thresholds, an internal timer is
started and RST is released after 200ms.
RST is reasserted whenever any one of the VCC inputs
drops below its predetermined threshold and remains
asserted until 200ms after all of the VCC inputs are above
their thresholds.
On the LTC1727, each of the comparator outputs will be
low until the VCC input that is monitored by that comparator rises above the appropriate predetermined threshold.
The COMP3, and COMP5/COMP25 outputs are guaranteed to be in the correct logic state for either VCC3 or
VCC5/VCC25 greater than 1V. The COMPA output requires
the internal bandgap reference to be valid before the
correct logic state can be output. Therefore, the COMPA
output will be held low until VCCA is above 1V and VCC3
or VCC5/VCC25 is greater than 2V (typ).
Glitch Immunity
The RST output of the LTC1727/LTC1728 have two forms
of glitch immunity built in. First, the input monitors require
the input voltage to transition at least 10% of the input
threshold (0.1 • VRTH) below the input threshold for approximately 50µs in order to force the monitor output low.
The duration of the transition must be longer for voltage
transitions of lesser magnitude (see Figure 1). Secondly,
the reset pulse width of approximately 200ms acts to
debounce the RST output ensuring that the RST output
will always be in the correct state.
The individual monitor outputs of the LTC1727 do not have
hysteresis and will track the monitor inputs relative to the
monitor’s input threshold (VRTA, VRT25, VRT3 and VRT5). A
very slow moving input voltage with ripple riding on it may
cause the individual monitor outputs (COMPA, COMP25,
COMP3 and COMP5) to toggle on the ripple as the input
voltage passes the input threshold. The slow response
time of the LTC1727’s input monitors has a tendency to
integrate signals on the inputs improving their immunity
to noise and ripple.
450
400
TRANSIENT DURATION (µs)
The LTC1728 is a low power, high accuracy triple supply
monitoring circuit with a single 200ms microprocessor
reset output.
350
300
250
200
150
100
50
0
1
10
100
0.1
RESET MONITOR OVERDRIVE VOLTAGE (% OF VCC)
1727/28 F01
Figure 1. Transient Duration vs Comparator Overdrive
Rev. E
10
For more information www.analog.com
LTC1727/LTC1728
APPLICATIONS INFORMATION
Override Functions (5V Versions Only)
When monitoring either 3.3V or 5V with VCC3 strapped
to VCC5 (see Figure 2), the part determines which is the
appropriate range. The part handles this situation as
shown in Figure 3. Above 1V and below VRT3, RST is held
low. From VRT3 to approximately 4.15V the part assumes
3.3V supply monitoring and RST is deasserted. Above
approximately 4.15V the part operates as a 5V monitor.
In most systems the 5V supply will pass through the
3.1V to 4.15V region in
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