LTC2911
Precision Triple Supply
Monitor with Power-Fail
Comparator
DESCRIPTION
FEATURES
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Ultralow Voltage Reset: VCC = 0.5V Guaranteed
Monitors Three Inputs Simultaneously:
3.3V, 5V, ADJ (LTC2911-1)
3.3V, 2.5V, ADJ (LTC2911-2)
3.3V, 1.8V, ADJ (LTC2911-3)
3.3V, 1.2V, ADJ (LTC2911-4)
3.3V, ADJ, ADJ (LTC2911-5)
±1.5% Threshold Accuracy
Power-Fail Monitor
RST State Can Be Held for Margining
Low Supply Current: 30µA Typical
Input Glitch Immunity
Adjustable Reset Timeout Period
Selectable Internal Timeout Saves Components
Space Saving 8-Lead TSOT-23 and 3mm × 2mm DFN
Packages
APPLICATIONS
Network Servers
Desktop and Notebook Computers
n Automotive and Industrial Electronics
The LTC®2911 is a low power, high accuracy triple supply
monitor with a power-fail comparator. Reset timeout may
be selected with an external capacitor or set to an internally
generated 200ms.
The V1 pin monitors a 3.3V supply. The V2 pin monitors a
5V, 2.5V, 1.8V, 1.2V or adjustable supply. A third adjustable
input has a nominal 0.5V threshold allowing a resistive
divider to configure its threshold. All three comparators
feature a tight 1.5% threshold accuracy over the entire
operating temperature range while a glitch filter ensures
reliable reset operation.
A spare comparator can be configured to provide early
warning of a low voltage condition. It causes the PFO output
to pull low when the voltage of the PFI input falls below 0.5V,
allowing the power-fail threshold to be configured with
a resistive divider. A latch feature on the TMR pin allows
the RST output to be latched to prevent system resets,
simplifying margin testing.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6949965, 7292076.
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TYPICAL APPLICATION
RST Output Voltage With 10k Pull-Up to V1
3.3V
6
2.5V
DC/DC
CONVERTER 1.0V
SYSTEM
LOGIC
76.8k
+
Li-Ion
BATTERY
STACK
576k
RST
V2
PFO
LTC2911-2
ADJ
RESET
LOBAT
100k
PFI
100k
5
10k
4
VRST (V)
TMR
V1
V1 = V2
3
2
1
GND
tRST = 200ms
2911 TA01a
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
V1 (V)
2911 TA01b
2911f
1
LTC2911
ABSOLUTE MAXIMUM RATINGS (Notes 1, 2, 3)
Supply Voltages
V1, V2.................................................... –0.3V to 6.5V
Input Voltages
ADJ........................................................ –0.3V to 6.5V
PFI............................................................ –0.3V to 2V
TMR.............................................–0.3V to (V1 + 0.3V)
Output Voltages
RST, PFO............................................... –0.3V to 6.5V
Operating Temperature Range
LTC2911C................................................. 0°C to 70°C
LTC2911I.............................................. –40°C to 85°C
LTC2911H........................................... –40°C to 125°C
Storage Temperature Range.................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
TSOT-23............................................................. 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
PFI 1
ADJ 2
TMR 3
GND 4
V2 1
8 V2
7 V1
6 PFO
5 RST
V1 2
PFO 3
8 PFI
9
GND
RST 4
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
7 ADJ
6 TMR
5 GND
DDB PACKAGE
8-LEAD (3mm × 2mm) PLASTIC DFN
TJMAX = 150°C, θJA = 195°C/W
TJMAX = 150°C, θJA = 76°C/W
EXPOSED PAD (PIN 9) IS GND, PCB CONNECTION OPTIONAL
ORDER INFORMATION
LTC2911 C
DDB –1
#TRM
PBF
LEAD FREE DESIGNATOR
PBF = Lead Free Finish Parts
None = Lead Based Finish Parts
TAPE AND REEL
#TR = Tape and Reel
#TRM = 500-Piece Tape and Reel
PRODUCT SELECTION
–1, –2, –3, –4, –5
See Product Selection Guide for Details
PACKAGE TYPE
DDB = 8-Lead (3mm × 2mm) Plastic DFN
TS8 = 8-Lead Plastic TSOT-23
TEMPERATURE GRADE
C = Commercial Temperature Range (0°C to 70°C)
I = Industrial Temperature Range (–40°C to 85°C)
H = Automotive Temperature Range (–40°C to 125°C)
PRODUCT PART NUMBER
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
2911f
2
LTC2911
PRODUCT SELECTION GUIDE
PART NUMBER
PART MARKING
PACKAGE DESCRIPTION
V1
V2
LTC2911-1
LFHZ
8-Lead (3mm × 2mm) Plastic DFN
3.3V
5V
LTC2911-2
LFPG
8-Lead (3mm × 2mm) Plastic DFN
3.3V
2.5V
LTC2911-3
LFPJ
8-Lead (3mm × 2mm) Plastic DFN
3.3V
1.8V
LTC2911-4
LFPM
8-Lead (3mm × 2mm) Plastic DFN
3.3V
1.2V
LTC2911-5
LFPP
8-Lead (3mm × 2mm) Plastic DFN
3.3V
ADJ
LTC2911-1
LTFJB
8-Lead Plastic TSOT-23
3.3V
5V
LTC2911-2
LTFPH
8-Lead Plastic TSOT-23
3.3V
2.5V
LTC2911-3
LTFPK
8-Lead Plastic TSOT-23
3.3V
1.8V
LTC2911-4
LTFPN
8-Lead Plastic TSOT-23
3.3V
1.2V
LTC2911-5
LTFPQ
8-Lead Plastic TSOT-23
3.3V
ADJ
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VADJ = 0.55V, VPFI = 0.55V, V1 = 3.3V unless otherwise noted. (Notes 2, 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VRT33
3.3V, 5% Reset Threshold
V1 Input
l
3.036
3.086
3.135
V
VRT50
5V, 5% Reset Threshold
V2 Input (LTC2911-1)
l
4.600
4.675
4.750
V
VRT25
VRT18
2.5V, 5% Reset Threshold
V2 Input (LTC2911-2)
l
2.300
2.338
2.375
V
1.8V, 5% Reset Threshold
V2 Input (LTC2911-3)
l
1.656
1.683
1.710
V
VRT12
1.2V, 5% Reset Threshold
V2 Input (LTC2911-4)
l
1.104
1.122
1.140
V
VRTA
ADJ Pin Threshold
ADJ Input and V2 Input of
LTC2911-5
l
492.5
500
507.5
mV
VPFT
PFI Pin Threshold
PFI Input Threshold (Falling)
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492.5
500
507.5
mV
∆VPFT
PFI Hysteresis
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10
15
19
mV
VCC,OP
Minimum Operating Voltage to Guarantee PFO
High (Note 3)
VPFI = 0.55V
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2.3
V
IV1
V1 input Current (Note 4)
V1 = 3.3V, V1 > V2
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10
30
80
µA
V1 = 3.3V, V1 < V2
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3
10
30
µA
V2 = 5V (LTC2911-1)
V2 = 2.5V (LTC2911-2)
V2 = 1.8V (LTC2911-3)
V2 = 1.2V (LTC2911-4)
V2 = 0.55V (LTC2911-5)
C-Grade/I-Grade
H-Grade
l
l
l
l
10
3
2
2
35
10
10
10
80
30
30
30
µA
µA
µA
µA
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±15
±40
nA
nA
IV2
V2 Input Current (Note 4)
IADJ
ADJ Input Current
VADJ = 0.55V (C-Grade) (I-Grade)
VADJ = 0.55V (H-Grade)
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±15
±40
nA
nA
IPFI
PFI Input Current
VPFI = 0.55V (C-Grade) (I-Grade)
VPFI = 0.55V (H-Grade)
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±15
±40
nA
nA
ITMR(UP)
TMR Pull-Up Current
VTMR = 1V
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–1.5
–2.2
–2.9
µA
ITMR(DOWN)
TMR Pull-Down Current
VTMR = 1V
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1.5
2.2
2.9
µA
IPU
RST, PFO Pull-Up Current
VPIN = 0V
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–20
–29
–40
µA
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LTC2911
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VADJ = 0.55V, VPFI = 0.55V, V1 = 3.3V unless otherwise noted. (Notes 2, 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
tP,PF
PFI Comparator Propagation Delay to PFO
VPFI Driven Beyond Threshold
VPFT by More Than 10%
tUV
V1, V2, ADJ Undervoltage Detect to RST Low
VOH
UNITS
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8
30
80
µs
VX Less Than Threshold VRTX by
More Than 10%
l
8
30
80
µs
RST, PFO Output Voltage High (Note 5)
IRST = –1µA
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V1 – 1
V1
V
VOL
RST, PFO Output Voltage Low (Note 6)
VCC = 0.5V, I = 5µA
VCC = 1V, I = 100µA
VCC = 3V, I = 2.5mA
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l
l
0.01
0.01
0.10
0.15
0.15
0.30
V
V
V
tRST(EXT)
Reset Timeout Period, External
CTMR = 2.2nF
l
15
20
27
ms
tRST(INT)
Reset Timeout Period, Internal
VTMR = V1
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140
200
280
ms
VTMR(INT)
Timer Internal Mode Threshold
VTMR Rising
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V1 – 0.40
V1 – 0.020
V1 – 0.10
∆VTMR(INT)
Timer Internal Mode Hysteresis
VTMR Falling
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40
100
160
mV
VTMR(LATCH)
Timer Latch Mode Threshold
VTMR Falling
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0.10
0.20
0.40
V
∆VTMR(LATCH) Timer Latch Mode Hysteresis
VTMR Rising
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40
75
160
mV
0.5
3
µs
V
tP, LR
Latch Release Propagation Delay to RST Low
VTMR Rising, Step 0V to 0.6V
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tSU,MON
Monitor Input Setup Time to Latch Enable (Note 7) VTMR Falling, Step 0.6V to 0V
Monitor Input Setup Time to Latch Release
VTMR Rising, Step 0V to 0.6V
Monitor Input Hold Time to Latch Enable
VTMR Falling, Step 0.6V to 0V
Monitor Input Hold Time to Latch Release
VTMR Rising, Step 0V to 0.6V
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2
ms
l
0
µs
tHD, MON
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 currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
Note 3: The internal supply voltage (VCC) is generated from the greater of
the voltages on the V1 and V2 inputs. VCC = V1 for the LTC2911-5.
Note 4: Under typical operating conditions, quiescent current is drawn
from the greater of the voltages on the V1 and V2 inputs. For the
LTC2911‑5 only V1 supplies the quiescent current.
Note 5: The RST and PFO output pins on the LTC2911 have internal pullups to V1. However, for faster rise times or for VOH voltages greater than
V1, use an external pull-up resistor.
Note 6: The RST and PFO pull-down currents are derived from V1 and V2
except for the LTC2911-5 where the pull-down strength is derived only
from V1.
Note 7: tSU,MON is required to latch a low RST state and tSU,MON + tRST is
required to latch a high RST state.
2911f
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LTC2911
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Supply Current
vs Temperature
60
1.010
1.005
1.000
0.995
0.990
0.985
–50
–25
75
0
50
25
TEMPERATURE (°C)
100
500
IV2 FOR LTC2911-1
50
400
40
30
20
–25
75
0
50
25
TEMPERATURE (°C)
2911 G01
16.0
15.5
15.0
1.0
220
INTERNAL
200
EXTERNAL
CTMR = 22nF
180
75
100
140
–50
125
–25
75
0
50
25
TEMPERATURE (°C)
RST, PFO Voltage Output High
vs Source Current
6
V1 = 3.135V, V2 = 5V FOR RST
5
VOLTAGE OUTPUT HIGH (V)
2.5
1.5
1.0
0.5
V1 = V2 = ADJ = PFI
10k PULL-UP TO VCC
RST FOR
LTC2911-1
4
3
2
1
PFO
RST FOR
LTC2911-2
LTC2911-3
LTC2911-4
LTC2911-5
0
0
5
20
15
25
10
SOURCE CURRENT (µA)
30
35
2911 G07
0.6
0.4
–40°C
25°C
85°C
125°C
150°C
0.2
0
5
10
15
20
SINK CURRENT (mA)
25
–1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
2911 G08
30
2911 G06
RST, PFO Voltage Output High
vs VCC
2.0
0.8
0
125
VCC = 3V
2911 G05
2911 G04
3.0
100
RST, PFO Pin Source Current
vs V1
100
OUTPUT SOURCE CURRENT (µA)
50
25
TAMB (°C)
100
RST, PFO Voltage Output Low
vs Sink Current
160
14.5
0
10
2911 G03
VOLTAGE OUTPUT LOW (V)
TIMEOUT PERIOD (ms)
HYSTERESIS (mV)
16.5
1
0.1
OVERDRIVE (%)
240
17.0
VOLTAGE OUTPUT HIGH (V)
0
125
260
17.5
0
100
Reset Timeout Period vs
Temperature
18.0
–25
200
2911 G02
PFI Hysteresis vs Temperature
14.0
–50
300
100
10
0
–50
125
Allowable Glitch Duration
vs Overdrive
GLITCH DURATION (µs)
1.015
QUIESCENT SUPPLY CURRENT (µA)
NORMALIZED THRESHOLD VOLTAGE (V/V)
Normalized Reset and Power-Fail
Threshold Voltages vs Temperature
80
60
40
20
0
PFO
0
1
2
RST
3
V1 (V)
4
5
6
2911 G09
2911f
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LTC2911
PIN FUNCTIONS
ADJ: Adjustable Voltage Monitor Input. Input to a voltage
monitor comparator with a 0.5V nominal threshold. Tie
to V1 if unused.
Exposed Pad (DFN Only): Exposed pad may be left open
or connected to device ground.
GND: Device Ground.
PFI: Power-Fail Voltage Monitor Input. Input to the powerfail comparator with a 500mV threshold at the falling
edge and a 515mV threshold at the rising edge, giving
a 3% hysteresis for noise rejection. Tie to V1 or GND if
unused.
PFO: Power-Fail Logic Output. This pin asserts low when
the PFI input voltage is below its threshold and goes high
when the PFI input voltage is above its threshold. This pin
provides a weak pull-up current to V1. This current is typically 29µA at V1 = 3.3V. The pin can be pulled to voltages
higher than V1 by external pull-up resistors. PFO provides
an early warning signal of a system power failure.
RST: Reset Logic Output. This pin asserts low when any
of the V1, V2, or ADJ inputs are below their reset thresholds. Pulls high when all the monitored inputs are above
their thresholds for longer than a timeout period. This pin
provides a weak pull-up current to V1. This current is typically 29µA at V1 = 3.3V. The pin can be pulled to voltages
higher than V1 by external pull-up resistors. The status of
RST can be latched by holding the TMR pin at GND.
TMR: Reset Timeout Control. Attach an external capacitor,
CTMR, to GND to set a reset timeout period of 9.4ms/nF. A
low leakage ceramic capacitor is recommended for timer
accuracy. A 2.2nF capacitor generates a 20ms timeout.
Leaving the TMR pin open without a capacitor generates
a minimum timeout of approximately 400µs which will
vary depending on the parasitic capacitance on the pin.
Tying this pin to V1 enables the internal 200ms timeout.
Pulling this pin to GND latches the reset state.
V1: 3.3V Monitor and Power Supply Input. V1 is an accurate 3.3V, –5% undervoltage supply monitor. The internal
VCC is generated from the greater of the voltages at the
V1 and V2 inputs for the LTC2911-1/LTC2911‑2/LTC29113/LTC2911-4 options. The LTC2911-5 option always derives
its power supply from the V1 pin. Bypass this pin to GND
with a 0.1µF (or greater) capacitor for the LTC2911-2
through LTC2911-5.
V2: Voltage Monitor and Power Supply Input. V2 is a
–5% undervoltage supply monitor for a 5V, 2.5V, 1.8V
or 1.2V supply for the LTC2911-1/LTC2911‑2/LTC29113/LTC2911‑4 options, respectively. Because the internal
VCC is generated from the greater of the V1 and V2 inputs
for these options, the V2 pin should be bypassed to GND
with a 0.1µF (or greater) capacitor for the LTC2911-1. The
V2 pin of the LTC2911-5 is a high impedance input with a
0.5V threshold, allowing the trip threshold of the monitored
supply to be configured with a resistive divider.
2911f
6
LTC2911
BLOCK DIAGRAM
V1
V1
V2*
POWER
DETECT
114k
VCC
–
PFI
PFO
+PFI COMP
VCC
LOW
VOLTAGE
PULL-DOWN
TMR
1.36M
V1
–
263k
THREE-STATE
DECODE
V1 COMP
+
V1
114k
RX**
V2
ADJUSTABLE
PULSE
GENERATOR
–
231k**
V2 COMP
LATCH
+
200ms
PULSE
GENERATOR
–
ADJ
RST
VCC
LOW
VOLTAGE
PULL-DOWN
ADJ COMP
+
0.5V
+
–
MONITORED VOLTAGES
GND
LTC2911 LTC2911-1 LTC2911-2 LTC2911-3 LTC2911-4 LTC2911-5
V2
5V
2.5V
1.8V
1.2V
ADJ
RX
1.93M
850k
547k
288k
**
*FOR OPTIONS LTC2911-1 THROUGH LTC2911-4 ONLY. **OMIT THE RESISTIVE DIVIDER FOR THE LTC2911-5.
2911 BD
2911f
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LTC2911
TIMING DIAGRAMS
Power-Fail Timing
Undervoltage and Reset Timing
VX
PFI
VRTX
tUV
tP,PF
tRST
RST
VPFT
tP,PF
PFO
1.0V
2911 TD03
1.0V
2911 TD01
Latch Release to RST Low Timing
TMR
0.4V
tP,LR
1.0V
RST
2911 TD02
NOTE: ADJ FORCED LOW BEFORE TMR RELEASE
Latching RST High
Input Valid to Latch Enable
Setup and Hold Timing
TMR
VTMR(LATCH) +
∆VTMR(LATCH)
VTMR(LATCH)
tRST
ADJ, V1, V2
Input Valid to Latch Release
Setup Timing
tSU,MON
tHD,MON
VRTX
3% OVERDRIVE
t > tSU,MON
MARGINING
–3% OVERDRIVE
RST
POWER UP
2911 TD04
1V
LATCH IN
NOTE: FOR THE LTC2911-5, V1 LOW RESETS RST TO A LOW STATE
INPUT RETURNING TO ABOVE VRTX
FOR t > tSU,MON, RST PIN STAYS HIGH
Latching RST Low
Input Invalid to Latch Enable
Setup and Hold Timing
TMR
RST
VTMR(LATCH) +
∆VTMR(LATCH)
VTMR(LATCH)
tHD,MON
tSU,MON
tUV
ADJ, V1, V2
Input Invalid to Latch
Release Setup Timing
t > tSU,MON
3% OVERDRIVE
MARGINING
VRTX
–3% OVERDRIVE
1V
–3% OVERDRIVE
VRTX
LATCH IN
NOTE: FOR THE LTC2911-5, V1 LOW RESETS RST TO A LOW STATE
2911 TD05
INPUT RETURNING TO BELOW VRTX
FOR t > tSU,MON, RST PIN STAYS LOW
2911f
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LTC2911
APPLICATIONS INFORMATION
The LTC2911 is a low power, high accuracy triple supply
monitor with power-fail comparator. For the LTC2911-1,
LTC2911-2, LTC2911-3 and LTC2911‑4 options, the V1
and V2 pins monitor two supplies. Their thresholds are
preset internally based on the option chosen. A resistive
divider connected to the ADJ pin configures the third
threshold. For the LTC2911-5, the V2 pin is a high impedance adjustable input similar to the ADJ pin.
Reset timeout of the device may be selected with an external
capacitor or set to an internally generated 200ms. The ADJ,
V1 and V2 inputs must be valid (above their thresholds)
for longer than the reset timeout period before the RST
pin transitions high.
The LTC2911 uses proprietary low voltage drive circuitry
for the RST and PFO pins which holds them low with
VCC (the higher of V1 and V2) as low as 0.5V. This helps
prevent indeterminate voltages from appearing on the
outputs during power-up. For additional details refer to
the Output Pin Characteristics section.
When V1 and V2 are ramped simultaneously (for
LTC2911‑1/LTC2911-2/LTC2911-3/LTC2911-4), the pulldown current from the RST and PFO pins is about twice
the current available when V1 or V2 is grounded.
Power Down
The power-fail comparator causes the PFO pin to pull
low when the PFI pin falls below 0.5V. A resistive divider
connected to the PFI pin configures the threshold of the
monitored voltage. The PFO output typically provides
an early warning of imminent power failure so that the
system may begin shutdown procedures such as supply
sequencing and/or storage of system state in nonvolatile
memory.
On power-down, when the voltage monitored by the powerfail comparator falls below the threshold configured by its
resistive divider, the PFO pin pulls low to provide an early
warning of imminent power failure. In a typically configured system, this occurs before the supplies monitored
by V1, V2 or ADJ fall below their thresholds and cause
the RST pin to pull low. The RST and PFO pins maintain
a logic low output for VCC as low as 0.5V. See the Output
PIn Characteristics section for additional details.
Power-Up
Power-Fail Monitoring and PFO Signaling
The LTC2911-1, LTC2911-2, LTC2911-3 and LTC2911-4
supervisors are powered from the V1 and V2 pins, automatically selecting the pin with the higher potential. The
exception in the device family, the LTC2911-5, derives
its internal supply voltage (VCC) only from V1. When all
monitor inputs are above their thresholds, the quiescent
supply current drawn from VCC is typically 30µA (35µA
for the LTC2911-1). When the three monitor inputs (V1,
V2 and ADJ) rise above their thresholds, the appropriate
timeout delay begins, after which RST pulls to V1. Once
the PFI input rises above 515mV, the PFO output signals
high indicating that the supply or voltage monitored by
PFI is above threshold.
The LTC2911’s PFI input monitors a voltage through a
resistive divider and compares it to the internal power-fail
threshold. When PFI drops below 0.50V (the power-fail
threshold) the PFO output pulls low to provide an early
warning of a low voltage condition. When the PFI pin rises
above 0.515V again, the PFO output signals high indicating
a valid supply condition.
The PFI input typically monitors the primary power supply
of a system. For example, the PFI pin may monitor the
input supply of a DC/DC converter or a Li-Ion battery stack
voltage. The PFO output typically provides a warning to
the system that the power supply is on the verge of failing so that it can prepare for a controlled shutdown. For
2911f
9
LTC2911
APPLICATIONS INFORMATION
example, the PFO pin may connect to a processor nonmaskable interrupt. When the battery pack voltage drops
below the shutdown threshold, as sensed at PFI, the PFO
pin pulls low to issue an interrupt. Next, the processor
begins shutdown procedures which may include supply
sequencing and/or storage/erasure of system state in
nonvolatile memory.
Threshold Accuracy
Specifying the minimum supply voltage for a system
requires the designer to consider three factors: minimum
supply voltage for proper operation, power supply tolerance, and supervisor reset threshold accuracy. Highly
accurate supervisors ease the design challenge by decreasing the overall voltage margin required for reliable
system operation.
The reset threshold band and the power supply tolerance
bands should not overlap. This prevents false or nuisance
resets when the power supply is actually within its specified
tolerance band. The actual reset threshold of supervisors
varies over a specified band. The LTC2911 supervisor
varies ±1.5% around its nominal threshold voltage over
temperature.
3.3V
The system must operate reliably a little below 3.036V
(or 3.3V, –8%), or risk malfunction before a reset signal
is properly issued. A less accurate supervisor increases
the supply voltage tolerance requirements and the risk
of system malfunction. The LTC2911’s ±1.5% threshold
voltage specification minimizes these requirements.
V1 and V2 Supply Monitors
All the LTC2911 options have a V1 threshold equal to
3.086V (3.3V – 6.5%). The V2 thresholds are 4.675V
(5V – 6.5%), 2.338V (2.5V – 6.5%), 1.683V (1.8V – 6.5%)
and 1.122V (1.2V – 6.5%) for options LTC2911-1,
NOMINAL
SUPPLY
VOLTAGE
SUPPLY TOLERANCE
MINIMUM
RELIABLE
SYSTEM
VOLTAGE
±1.5%
THRESHOLD
BAND
Figure 1 illustrates a typical 3.3V monitor. The LTC2911
has ±1.5% reset threshold accuracy. The nearest practical
supervisor trip point is the sum of power supply tolerance and the LTC2911 tolerance. So a “5%” threshold
is typically set to –6.5%, excluding resistor errors. Thus
for a 3.3V “5%” threshold, the practical supervisor trip
point is at 3.086V. The threshold is guaranteed to lie in
the band between 3.036V and 3.135V over the operating
temperature range. This 3.135V maximum threshold is at
the lower limit of supply tolerance (3.3V – 5%) to prevent
false tripping.
IDEAL
SUPERVISOR
THRESHOLD
3.135V
–5%
3.086V
–6.5%
3.036V
–8%
REGION OF POTENTIAL MALFUNCTION
2911 F01
Figure 1. 1.5% Threshold Accuracy Improves System Reliability
2911f
10
LTC2911
APPLICATIONS INFORMATION
LTC2911‑2, LTC2911-3 and LTC2911-4 respectively. V2
of the LTC2911‑5 option is a high impedance input with
a nominal 0.5V threshold.
To minimize errors arising from the ADJ input bias current,
a value of less than 100k is recommended for R1.
R2 is then chosen by:
Input Noise Filtering for RST
The V1, V2 and ADJ comparators have a response time that
is inversely proportional to overdrive. This characteristic
is illustrated in the Typical Performance Characteristics
as the graph Allowable Glitch Duration versus Overdrive.
The ADJ and the LTC2911-5’s V2 pin may be bypassed
with a capacitor to increase the filtering in applications that
demand it. The resultant RC lowpass filter at the inputs will
further reject high frequency components, at the cost of
slowing the monitor’s response to fault conditions.
The threshold of the supply monitored by the ADJ pin is
configured with an external resistive divider (R2 and R1)
connected between the supply and ground. The tap point
for the divider is connected to the adjustable input (ADJ)
which has a 0.5V threshold. (See Figure 2)
Normally, the user selects a trip voltage based on the supply and acceptable tolerances, and a value of R1 based on
current drawn. For a given current, I, R1 is given by:
where, VTRIP_ADJ is the supply threshold when the ADJ
pin falls below its 0.5V threshold.
For accurate monitoring, the resistor tolerance should be
as small as possible. Resistor tolerance of 0.1% or some
trimming of components should be considered for R2/R1
in applications that require an accurate trip point.
Resistor Selection for PFI
Resistor Selection for ADJ
R1=
V
R2 = R1• TRIP_ ADJ – 1
0.5V
0.5V
I
An external resistive divider (R3 and R4) connected between
the supply and ground configures the threshold of the
supply monitored by the power-fail comparator. The tap
point for the divider is connected to the PFI input which
has a 0.5V threshold. (See Figure 3a)
Resistor selection follows a process similar to that for
the ADJ pin.
R3 is given by:
R3 =
0.5V
I
VTRIP
R2
–
ADJ
R1
LTC2911
+
0.5V
+
–
2911 F02
Figure 2. Setting the Adjustable (ADJ) Trip Point
2911f
11
LTC2911
APPLICATIONS INFORMATION
R5
V1
VTRIP
R4
V1
LTC2911
114k
VTRIP
–
PFI
R3
PFO
+
0.5V
R4
LTC2911
–
PFI
R3
+
–
114k
V1
PFO
R6
+
0.5V
2911 F03a
+
–
2911 F03b
Figure 3a. Setting the Power-Fail (PFI) Trip Point
Figure 3b. Increasing Power-Fail Hysteresis
Again, to minimize errors arising from the PFI input bias
current, a value of less than 100k is recommended for
R3.
R4 can be chosen either using the PFI falling threshold or
the PFI rising threshold.
For the falling edge threshold, use the equation:
V
R4 = R3 • TRIP_ PFI_ FALL – 1
0.5V
Increasing the Power-Fail Hysteresis
Alternatively, for the rising edge threshold, use the
equation:
V
R4 = R3 • TRIP_ PFI_ RISE – 1
0.515V
edges. The nominal threshold is 500mV at the falling edge
and 515mV at the rising edge. The hysteresis prevents
oscillation when the monitored voltage passes through
the thresholds. If the PFI pin is connected to an external
resistive divider, it may be bypassed with a capacitor for
additional noise filtering.
where VTRIP_PFI_FALL is the supply threshold when the PFI
pin falls below the 0.5V falling threshold, and VTRIP_PFI_RISE
is the supply threshold when the PFI pin rises above the
0.515V rising threshold.
Note that VTRIP_PFI_RISE is typically 3% above the
VTRIP_PFI_FALL due to the fact that the PFI 515mV rising
threshold is 3% above its 500mV falling threshold.
In applications that require an accurate trip point, the R4
and R3 resistors should have small tolerances.
Hysteresis for Power-Fail Comparator
The power-fail comparator uses a positive 3% accurate
hysteresis to combat spurious triggering while maintaining accurate thresholds for both the rising and falling
The power-fail comparator hysteresis can be increased by
adding two resistors, R5 and R6, as shown in Figure 3b.
When PFO is low, R5 sinks current from the center tap
of the R3 and R4 resistive divider. The upper threshold is
therefore given by:
R4 R4
VH = 0.515V 1+ +
R3 R5
When PFO is high, the series combination of R5 and R6
sources current into the center tap of the R3 and R4 resistive divider. This leads to a lower threshold of:
R4 ( 3.3V – 0.5V )R4
VL = 0.5V 1+ –
R3
R5 +R6
The addition of R5 and R6 increases the hysteresis to:
VHYST = VH – VL
R4
R4 ( 3.3V – 0.5V )R4
= 0.015 1+ + 0.515 +
R3
R5
R5 +R6
2911f
12
LTC2911
APPLICATIONS INFORMATION
Resistor Selection for Combined Reset
and Power-Fail Divider
When the power-fail and reset signals are based on the
same supply, the PFI and ADJ inputs may be connected
to a single resistive divider formed from three resistors.
The configuration is shown in Figure 4. For a given bias
current I, RA, RB and RC can be calculated from:
0.5V
I
V
RB = R A • TRIP_ PFI_ FALL – 1
VTRIP _ ADJ
RA =
V
V
RC = R A • TRIP_ ADJ – 1 • TRIP_ PFI_ FALL
0.5V
VTRIP_ ADJ
For example, consider monitoring a 5V, ±5% supply with
VTRIP_PFI_FALL = 4.5V and VTRIP_ADJ = 4V. The resulting
VTRIP_PFI_RISE is equal to 4.63V or 3% above VTRIP_PFI_FALL.
The maximum VTRIP_PFI_RISE should not overlap the minimum power supply voltage level for PFO to deassert when
the supply recovers. Mathematically, after factoring in the
sum of the power supply tolerance and the LTC2911 tolerance, the VTRIP_PFI_RISE should be lower than 5V – 6.5%.
Setting the Reset Timeout
RST goes high after the V1, V2 and ADJ inputs are above
their thresholds for a reset timeout period. Connecting
the TMR pin to V1 enables the internal 200ms timer.
To configure a different reset timeout period connect a
capacitor between the TMR pin and ground.
The following formula approximates the value of capacitor
needed for a particular timeout:
CTMR = tRST • 106.5 [pF/ms]
Leaving the TMR pin open with no external capacitor
generates a reset timeout of approximately 400µs. Larger
capacitors may be used to increase the timeout, but the
capacitor leakage current must not exceed 500nA. Otherwise, the timer accuracy will be severely affected.
Suitable values of CTMR for a given tRST may be selected
from Figure 5.
10000
VTRIP
–
ADJ
LTC2911
1000
EXTERNAL TIMEOUT, tRST (ms)
RC
See Threshold Accuracy section for more details. In the
design, if we wish to consume about 5µA in the divider,
RA = 100k. We then find RB = 12.4k and RC = 787k (nearest
1% standard values).
+
RB
–
PFI
RA
+
0.5V
+
–
100
10
1
0.1
10p
2911 F04
Figure 4. Combining PFI/ADJ Monitoring of One Supply
with Three Resistors
100p
1n
10n
CTMR (F)
100n
1µ
2911 F05
Figure 5. External Timeout vs CTMR
2911f
13
LTC2911
APPLICATIONS INFORMATION
Reset Latch Mode
At any time, the TMR pin can be pulled low to latch the
RST pin status, overriding the reset operation. This feature
is useful when testing a system at supply voltages that
might otherwise cause the RST pin to assert.
If the RST pin is unasserted (high) before the latch is
enabled (by pulling the TMR pin low), RST will remain
unasserted after the TMR pin is released. This is true
provided that all reset monitor inputs are valid when TMR
releases, regardless of their state while the TMR pin was
low. However, if RST was unasserted before TMR was
pulled low, and now one of the inputs is invalid when TMR
is released, RST will assert after a tPL,LR propagation delay
(see Figure 6a). Conversely, if RST was asserted (low)
before TMR was pulled low, and all inputs are valid when
TMR is released, RST will deassert (go high) after a tRST
delay (see Figures 6b and 6c). The RST pin remains asserted for a full tRST timeout after the TMR pin is released,
regardless of the state of the tRST timer before the latch
was enabled. The reset latch mode is useful for performing supply margining tests without resetting the system
(see Figure 6d).
At least 2.9µA of pull-up or pull-down current is required
to hold the TMR pin high or low to configure the internal
timer or reset latch mode. However, during the timer mode
transition, 100µA will be required to switch the TMR floating state to ground or V1. Connecting the TMR pin to any
voltage other than ground or V1 may have unpredictable
results.
LATCH RELEASE
TMR
ADJ, V1, V2
LATCH RELEASE
VTMR(LATCH) + ∆VTMR
VTMR(LATCH)
TMR
VRTX
VTRM(LATCH)
ADJ, V1, V2
RST
1.0V
t > tSU,MON
VRTX
RST
tP,LR
Figure 6c. Timer Latched Before Timeout. After Latch Release,
RST Stays Low for a Full Timeout Before Going High
LATCH RELEASE
VTMR(LATCH) +
∆VTMR
VTMR(LATCH)
TMR
VRTX
ADJ, V1, V2
t > tSU,MON
RST
1.0V
2911 F06c
LATCH RELEASE
ADJ, V1, V2
tRST
t < tRST
2911 F06a
Figure 6a. Input Toggled Low While Timer Latched.
RST Goes Low tP,LR After Latch Release
TMR
VTMR(LATCH) +
∆VTMR
tRST
1.0V
RST
MARGINING
VTRX
t > tHD,MON
tRST
1.0V
2911 F06b
t > tRST
Figure 6b. Input Toggled High While Timer Latched.
RST Goes High tRST After Latch Release
VTMR(LATCH)
+ ∆VTMR
VTRM(LATCH)
t > tSU,MON
2911 F06d
NO
RECOUNTING
Figure 6d. Timer Latched After Timeout and RST High.
RST Stays High After Margining if Inputs are Restored
Before Release
2911f
14
LTC2911
APPLICATIONS INFORMATION
During power-up, with a capacitor connected to the TMR
pin, the part remains in the reset latch mode described
above until the 2.2µA flowing out of the TMR pin charges
the capacitor beyond the VTMR(LATCH) threshold. For this
reason, large capacitors will extend the RST timeout during
power-up. For example, if CTMR = 1µF, the LTC2911 leaves
the reset latch mode 90ms after power-up and the RST
pin goes high after a 9 second timeout.
Figures 7a and 7b show how the TMR pin can be driven
low to latch the state of the RST pin or floated or driven
high for external and internal reset timing, respectively.
TMR
SYSTEM
LOGIC
Figure 7a. Open-Drain (or Three-State Buffer) Output.
Grounds TMR to Latch the State of RST. Floats TMR for
External Reset Timing
V1
TMR
2911 F07b
Figure 7b. V1 Powered Inverter. Grounds TMR
to Latch the State of RST. Drives TMR High for
Internal Reset Timing
The open-drain output pins (RST and PFO) contain weak
pull-up circuitry to V1. Use an external pull-up resistor
when the outputs need to pull beyond V1 and/or require
a faster rise time. Use external pull-up resistor values of
100k or less.
When output pins are externally pulled up to voltages higher
than V1, an internal network automatically protects the
weak pull-up circuitry from reverse currents. For a given
external load capacitance or CLOAD, the rise and fall times
can be estimated using Figure 9. The output pins have very
strong pull-down capability. With a 150pF load capacitance
the reset line can pull down in about 30ns.
10m
VCC = 0.5V
1m
1600
tRISE LTC2911-1
100µ
tFALL OR tRISE (s)
VOLTAGE OUTPUT LOW (mV)
2000
The DC characteristics of the RST and PFO pull-down
strength are shown in the Typical Performance Characteristics. The circuits that drive the pull-down of the output
pins are powered by the internal VCC (the greater voltage
of V1 or V2). During power-up, a VCC of at least 0.5V ensures a low output state. The VOL voltage depends on the
current sunk by RST and PFO as shown in the Figure 8.
The open-drain nature of the RST and PFO pins allows for
wire-ORed connections. For example, multiple LTC2911s
may be wire-ORed to monitor additional supplies, or opendrain logic can be connected to allow other conditions to
issue the reset and/or power-fail signals.
Output Pin Rise and Fall Time
2911 F07a
SYSTEM
LOGIC
Output Pin Characteristics
1200
800
10µ
1µ
tFALL LTC2911-1
100n
400
0
10n
0
10 20 30 40 50 60 70 80 90 100
ISINK (µA)
2911 F08
Figure 8. Voltage Output Low vs ISINK at VCC = 0.5V
1n
10p
100p
1n
10n
CLOAD (F)
2911 F09
Figure 9. tRISE and tFALL vs CLOAD
2911f
15
LTC2911
TYPICAL APPLICATIONS
Triple Supply Monitor and Overtemperature Signal
3.3V
3.3V
5V
5V
12V
12V
VTRIP = 10.75V
V1
RESET
RST
LTC2911-1
0.1µF
R4
200k
OVERTEMP
PFO
TRIP TEMPERATURE = 90°C
RECOVER TEMPERATURE = 89°C
PFI
R2
2.05M
C1**
10nF
R3
R31*
270k
V2
ADJ
TMR
CTMR
2.2nF
GND
R1
100k
2911 TA02
tRST = 20ms
*THERMISTOR MURATA NTC NCP15WM474J03RC TOLERANCE 5%.
NTC RESISTANCE IS 474k AT ROOM, 35.8k AT 85°C
**OPTIONAL BYPASS CAPACITOR FOR SUPPLY TRANSIENT NOISE FILTERING
Quad Supply Monitor
3.3V
V1
0.1µF
2.5V
12V
VTRIP = 10.5V
R6
383k
VTRIP = 4.53V
R1
100k
D1
BAS119
RESET
LTC2911-2
V2
R4
806k
5V
R5
1.62M
RST
PFO
PFI
R3
100k
ADJ
TMR
GND
CTMR
2.2nF
tRST = 20ms
2911 TA03
2911f
16
LTC2911
TYPICAL APPLICATIONS
48V Telecom UV/OV Monitor with Hysteresis
VIN
36V TO 72V
RCC
27k
0.25W
R2A
1.43M
0.1µF
16V
5.6V
M1
R2B
169k
5V
TMR V1 V2
R4
1.87M
LTC2911-1
R1
18.7k
ADJ
RST
PFI
PFO
R3
13.7k
UV
RPU1
10k
OV
GND
2911 TA04
M1: FDG6301N OR SIMILAR
VUV(RISING) = 43.3V
VUV(FALLING) = 38.7V
VOV(RISING) = 70.8V
VOV(FALLING) = 68.8V
4-Cell NiMH Stack Voltage Monitor with Input Overvoltage Signaling
FROM
CHARGER
1N5817
+
+
+
+
0.1µF
1.2V
1.2V
R2
576k
V1
V2
TMR
LTC2911-2
R4
1.18M
1.2V
1.2V
ADJ
RST
PFI
PFO
R3
102k
R1
100k
LOBAT
OV
GND
tRST = 200ms
BATTERY LOW RESET THRESHOLD = 3.38V
OVERVOLTAGE TRIP THRESHOLD = 6.47V
OVERVOLTAGE RECOVER THRESHOLD = 6.28V
2911 TA05
4-Cell Alkaline Stack Voltage Monitor with Early Power-Fail Warning
+
+
+
+
0.1µF
1.5V
1.5V
1.5V
1.5V
RC
665k
RB
15k
RA
100k
V1
V2
TMR
LTC2911-2
ADJ
RST
PFI
PFO
RESET
LOBAT
GND
tRST = 200ms
2911 TA06
POWER-FAIL FALLING THRESHOLD = 3.90V
POWER-FAIL RISING THRESHOLD = 4.02V
RESET THRESHOLD = 3.39V
2911f
17
LTC2911
PACKAGE DESCRIPTION
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.95 BSC
TS8 TSOT-23 0802
2911f
18
LTC2911
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 ±0.05
(2 SIDES)
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(2 SIDES)
R = 0.115
TYP
5
R = 0.05
TYP
0.40 ± 0.10
8
2.00 ±0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.56 ± 0.05
(2 SIDES)
0.200 REF
0.75 ±0.05
0 – 0.05
4
0.25 ± 0.05
1
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
(DDB8) DFN 0905 REV B
0.50 BSC
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
2911f
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.
19
LTC2911
TYPICAL APPLICATION
Triple Supply Monitor with Early Power-Fail Warning (With Manual Reset and Latchable Reset for Margining)
3.3V
1.8V
DC/DC
CONVERTER 1.0V
SYSTEM
LOGIC
VTRIP = 0.88V
V1
0.1µF
RESD*
10k
VTRIP = 3.37V
+
Li-Ion
R2
76.8k
RST
RESET
LTC2911-3
V2
PFO
LOBAT
ADJ
R1
100k
R4
1.43M
PFI
R3
249k
TMR
GND
VN2222
CTMR
2.2nF
2911 TA07
*OPTIONAL RESISTOR FOR ADDED ESD PROTECTION
RST_LATCH
SIGNAL HIGH
TO PERFORM
MARGINING
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1326/LTC1326-2.5
Micropower Precision Triple Supply Monitor for 5V/2.5V,
3.3V and ADJ
4.725V, 3.118V, 1V Threshold (±0.75%)
LTC1536
Precision Triple Supply Monitor for PCI Applications
Meets PCI tFAIL Timing Specifications
LTC1726-2.5/LTC1726-5 Micropower Triple Supply Monitor for 2.5V/5V, 3.3V
and ADJ
Adjustable Reset and Watchdog Timeouts
LTC1727/LTC1728
Micropower Triple Supply Monitor With Open-Drain Reset
Individual Monitor Outputs in MSOP/5-Lead SOT-23
LTC1985-1.8
Micropower Triple Supply Monitor with Push-Pull Reset
Output
5-Lead SOT-23 Package
LTC2909
Precision, Triple/Dual Input UV, OV and Negative Voltage
Monitor
8-Lead SOT-23 and DFN Packages
LTC2912/LTC2913/
LTC2914
Single/Dual/Quad UV and OV Voltage Monitors
Separate VCC Pin, Adjustable Reset Timer, H-Grade Temperature
Range
LTC2915/LTC2916/
LTC2917/LTC2918
Single Voltage Monitor With 27 Unique Thresholds
Manual Reset, Watchdog, TSOT-8/MSOP-10 and 3mm × 2mm DFN
Packages, H-Grade Temperature Range
LTC2919
Precision, Triple/Dual Input UV, OV and Negative Voltage
Monitor
10-Lead 3mm × 2mm and MSOP Packages, H-Grade Temperature
Range (Individual Outputs for ADJ Comparators and System RST)
2911f
20 Linear Technology Corporation
LT 0910 • PRINTED IN USA
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(408) 432-1900 ● FAX: (408) 434-0507
●
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