LTC2917/LTC2918
Voltage Supervisor with
27 Selectable Thresholds
and Watchdog Timer
DESCRIPTION
FEATURES
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9 Selectable Supply Voltages
12V, 5V, 3.3V, 2.5V, 1.8V
1.5V, 1.2V, 1V, +ADJ (0.5V)
3 Selectable Tolerances
–5%, –10%, –15% (LTC2917)
Manual Reset Input (LTC2918)
1.5V to 5.5V Supply Operation
Adjustable Watchdog Timeout
Windowed Watchdog Timeout for Higher Reliability
Applications (LTC2917-B, LTC2918-B)
6.2V Shunt Regulator for High Voltage Operation
Guaranteed Operation to 125°C
Guaranteed Threshold Accuracy: ±1.5%
Low Quiescent Current: 30μA Typical
Power Supply Glitch Immunity
Guaranteed RST for VCC ≥ 0.8V
10-Lead MSOP Packages and (3mm × 2mm) DFN
Packages
APPLICATIONS
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Handheld Devices
Cell Phone Base Stations
Automotive Control Systems
Network Servers
Optical Networking Systems
The LTC®2917-A/LTC2917-B and LTC2918-A/LTC2918-B
are low voltage single-supply monitors with selectable
thresholds and an adjustable watchdog timer. The parts
operate from 1.5V to 5.5V and consume a quiescent current of only 30μA.
Two three state inputs select one of nine internally programmed thresholds without the need for external resistors.
For the LTC2917, an additional three state input determines
the tolerance (–5%, –10%, –15%). The tolerance for the
LTC2918 is fixed at –5%. Threshold accuracy is guaranteed
at ±1.5% over the entire operating temperature range.
Glitch filtering ensures reliable reset operation without
false triggering.
The reset timeout and the watchdog timeout may be set
with no external components, or adjusted using an external capacitor. A windowed watchdog feature is available
for high-reliability applications (B1 versions). A separate
manual reset input on the LTC2918-A/LTC2918-B allows
a simple push button interface.
Operation to 125°C makes the LTC2917-A/LTC2917-B
and LTC2918-A/LTC2918-B suitable for automotive
applications.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
1.8V Supply Monitor with Manual
Reset and Internal Timers Selected
Monitor Selection Table
1.8V
0.1μF
10k
VCC
LTC2918-A
μP
VM
RST
RST
RT
WDI
I/O
WT
SEL1
MR
SEL2
29178 TA01
GND
tWDU = 1.6s
tRST = 200ms
NOMINAL VOLTAGE
SEL1
SEL2
12V
VCC
VCC
5V
VCC
Open
3.3V
VCC
GND
2.5V
Open
VCC
1.8V
Open
Open
1.5V
Open
GND
1.2V
GND
VCC
1V
GND
Open
ADJ (0.5V)
GND
GND
29178fb
1
LTC2917/LTC2918
ABSOLUTE MAXIMUM RATINGS (Note 1, 2)
Terminal Voltages
VCC (Note 3).......................................... –0.3V to 5.7V
SEL1, SEL2, TOL, WDI, MR, RST ......... –0.3V to 7.5V
VM ......................................................... –0.3V to 15V
RT, WT.......................................–0.3V to (VCC + 0.3)V
Terminal Currents
VCC (Note 3).......................................................±5mA
Operating Temperature Range
LTC2917C/LTC2918C ............................... 0°C to 70°C
LTC2917I/LTC2918I.............................. –40°C to 85°C
LTC2917H/LTC2918H ......................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MSOP ............................................................... 300°C
PIN CONFIGURATION
LTC2917
LTC2917
GND 1
TOP VIEW
GND
TOL
SEL2
SEL1
VM
10
9
8
7
6
1
2
3
4
5
TOP VIEW
9
RT
8
WT
SEL1 4
7
WDI
VM 5
6
VCC
SEL2 3
MS PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 11) PCB GND
CONNECTION OPTIONAL
LTC2917
LTC2918
LTC2918
TOP VIEW
GND 1
TOP VIEW
1
2
3
4
5
11
DDB PACKAGE
10-LEAD (3mm s 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 200°C/W
LTC2917
GND
MR
SEL2
SEL1
VM
10 RST
TOL 2
RST
RT
WT
WDI
VCC
10
9
8
7
6
MS PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 200°C/W
LTC2918
RST
RT
WT
WDI
VCC
10 RST
MR 2
9
RT
8
WT
SEL1 4
7
WDI
VM 5
6
VCC
SEL2 3
11
DDB PACKAGE
10-LEAD (3mm s 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 11) PCB GND
CONNECTION OPTIONAL
LTC2918
29178fb
2
LTC2917/LTC2918
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2917CMS-B1#PBF
LTC2917CMS-B1#TRPBF
LTCQP
10-Lead Plastic MSOP
0°C to 70°C
LTC2917IMS-B1#PBF
LTC2917IMS-B1#TRPBF
LTCQP
10-Lead Plastic MSOP
–40°C to 85°C
LTC2917HMS-B1#PBF
LTC2917HMS-B1#TRPBF
LTCQP
10-Lead Plastic MSOP
–40°C to 125°C
LTC2917CMS-A1#PBF
LTC2917CMS-A1#TRPBF
LTDGD
10-Lead Plastic MSOP
0°C to 70°C
LTC2917IMS-A1#PBF
LTC2917IMS-A1#TRPBF
LTDGD
10-Lead Plastic MSOP
–40°C to 85°C
LTC2917HMS-A1#PBF
LTC2917HMS-A1#TRPBF
LTDGD
10-Lead Plastic MSOP
–40°C to 125°C
LTC2918CMS-B1#PBF
LTC2918CMS-B1#TRPBF
LTDCT
10-Lead Plastic MSOP
0°C to 70°C
LTC2918IMS-B1#PBF
LTC2918IMS-B1#TRPBF
LTDCT
10-Lead Plastic MSOP
–40°C to 85°C
LTC2918HMS-B1#PBF
LTC2918HMS-B1#TRPBF
LTDCT
10-Lead Plastic MSOP
–40°C to 125°C
LTC2918CMS-A1#PBF
LTC2918CMS-A1#TRPBF
LTDGG
10-Lead Plastic MSOP
0°C to 70°C
LTC2918IMS-A1#PBF
LTC2918IMS-A1#TRPBF
LTDGG
10-Lead Plastic MSOP
–40°C to 85°C
LTC2918HMS-A1#PBF
LTC2918HMS-A1#TRPBF
LTDGG
10-Lead Plastic MSOP
–40°C to 125°C
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2917CDDB-B1#TRMPBF
LTC2917CDDB-B1#TRPBF
LCQR
10-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2917IDDB-B1#TRMPBF
LTC2917IDDB-B1#TRPBF
LCQR
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2917HDDB-B1#TRMPBF
LTC2917HDDB-B1#TRPBF
LCQR
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LTC2917CDDB-A1#TRMPBF
LTC2917CDDB-A1#TRPBF
LDGF
10-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2917IDDB-A1#TRMPBF
LTC2917IDDB-A1#TRPBF
LDGF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2917HDDB-A1#TRMPBF
LTC2917HDDB-A1#TRPBF
LDGF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LTC2918CDDB-B1#TRMPBF
LTC2918CDDB-B1#TRPBF
LDCV
10-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2918IDDB-B1#TRMPBF
LTC2918IDDB-B1#TRPBF
LDCV
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2918HDDB-B1#TRMPBF
LTC2918HDDB-B1#TRPBF
LDCV
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LTC2918CDDB-A1#TRMPBF
LTC2918CDDB-A1#TRPBF
LDGH
10-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2918IDDB-A1#TRMPBF
LTC2918IDDB-A1#TRPBF
LDGH
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2918HDDB-A1#TRMPBF
LTC2918HDDB-A1#TRPBF
LDGH
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
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/
29178fb
3
LTC2917/LTC2918
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 2.5V, unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
VCC(MIN)
Minimum Supply Voltage
RST in Correct Logic State
MIN
VCC(UVLO)
Supply Undervoltage Lockout
VCC(SHUNT)
Shunt Regulation Voltage
IVCC = 0.5mA
●
ICC
VCC Pin Current
SEL1, SEL2, TOL, MR = Open
SEL1, SEL2, TOL = GND (LTC2917)
MR = VCC (LTC2918)
●
●
●
TYP
MAX
0.8
V
●
5.7
UNITS
1.5
V
6.2
7.0
V
30
45
50
80
μA
μA
Monitor Input (VM)
VMT120
12V, 5% Reset Threshold
12V, 10% Reset Threshold
12V, 15% Reset Threshold
●
●
●
11.04
10.44
9.84
11.22
10.62
10.02
11.40
10.80
10.20
V
V
V
VMT50
5V, 5% Reset Threshold
5V, 10% Reset Threshold
5V, 15% Reset Threshold
●
●
●
4.600
4.350
4.100
4.675
4.425
4.175
4.750
4.500
4.250
V
V
V
VMT33
3.3V, 5% Reset Threshold
3.3V, 10% Reset Threshold
3.3V, 15% Reset Threshold
●
●
●
3.036
2.871
2.706
3.086
2.921
2.756
3.135
2.970
2.805
V
V
V
VMT25
2.5V, 5% Reset Threshold
2.5V, 10% Reset Threshold
2.5V, 15% Reset Threshold
●
●
●
2.300
2.175
2.050
2.338
2.213
2.088
2.375
2.250
2.125
V
V
V
VMT18
1.8V, 5% Reset Threshold
1.8V, 10% Reset Threshold
1.8V, 15% Reset Threshold
●
●
●
1.656
1.566
1.476
1.683
1.593
1.503
1.710
1.620
1.530
V
V
V
VMT15
1.5V, 5% Reset Threshold
1.5V, 10% Reset Threshold
1.5V, 15% Reset Threshold
●
●
●
1.380
1.305
1.230
1.403
1.328
1.253
1.425
1.350
1.275
V
V
V
VMT12
1.2V, 5% Reset Threshold
1.2V, 10% Reset Threshold
1.2V, 15% Reset Threshold
●
●
●
1.104
1.044
0.984
1.122
1.062
1.002
1.140
1.080
1.020
V
V
V
VMT10
1V, 5% Reset Threshold
1V, 10% Reset Threshold
1V, 15% Reset Threshold
●
●
●
0.920
0.870
0.820
0.935
0.885
0.835
0.950
0.900
0.850
V
V
V
VMTADJ
ADJ (0.5V), 5% Reset Threshold
ADJ (0.5V), 10% Reset Threshold
ADJ (0.5V), 15% Reset Threshold
●
●
●
460.0
435.0
410.0
467.5
442.5
417.5
475.0
450.0
425.0
mV
mV
mV
RVM
VM Input Impedance (Note 4)
Fixed Threshold Modes
●
0.5
8
MΩ
IVM(ADJ)
ADJ Input Current
VM = 0.5V
●
±15
nA
0.5
V
Three-State Inputs (SEL1, SEL2), (TOL, LTC2917)
VTPIN,LOW
Low Level Input Voltage
●
VTPIN,HIGH
High Level Input Voltage
●
VTPIN,Z
Pin Voltage when Open
ITPIN,Z
Allowable Leakage in Open State
ITPIN,H/L
Pin Input Current
1.4
I = 0μA
V
0.9
V
●
±5
μA
VTPIN = 0V, VCC
●
±20
μA
Reset Timer Control (RT)
IRT(UP)
RT Pull-Up Current
VRT = 0.25V
●
–2
–3
–4
μA
IRT(DOWN)
RT Pull-Down Current
VRT = 1.1V
●
2
3
4
μA
IRT(INT)
Internal RT VCC Detect Current
VRT = VCC
●
1
8
μA
VRT(INT, LH)
RT Internal Timer Threshold
VRT Rising, Referenced to VCC
●
–100
–160
–300
mV
29178fb
4
LTC2917/LTC2918
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 2.5V, unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
tRST(INT)
Internal Reset Timeout Period
VRT = VCC
●
150
200
260
ms
tRST(EXT)
Adjustable Reset Timeout Period
CRT = 2.2nF
●
16
20
25
ms
tUV
VM Undervoltage Detect to RST
Asserted
VM Less Than Reset Threshold
VMTX by More Than 5%
●
10
80
150
μs
VOL
Output Voltage Low RST
VCC = 3.3V, IRST = 2.5mA
VCC = 1V, IRST = 100μA
VCC = 0.8V, IRST = 15μA
●
●
●
0.15
0.15
0.05
0.4
0.3
0.2
V
V
V
IOH(RST)
RST Output Voltage High Leakage
RST = VCC
●
±1
μA
Reset Output (RST)
Watchdog Timer Control (WT)
IWT(UP)
WT Pull-Up Current
VWT = 0.25V
●
–2
–3
–4
μA
IWT(DOWN)
WT Pull-Down Current
VWT = 1.1V
●
2
3
4
μA
VWT(INT, LH)
WT Internal Timer Threshold
VWT Rising, Referenced to VCC
●
–100
–160
–300
mV
●
1
8
μA
IWT(INT)
Internal WT VCC Detect Current
VWT = VCC
IWT(DIS)
Watchdog Disable Hold Current
VWT = 0V
–3.5
μA
Watchdog Input (WDI)
tWDU(INT)
Internal Watchdog Upper Boundary
VWT = VCC
●
1.3
1.6
2
tWDL(INT)
Internal Watchdog Lower Boundary
(Note 5)
B Versions, VWT = VCC
●
37.5
50
62.5
ms
tWDU(EXT)
External Watchdog Upper Boundary
CWT = 2.2nF
●
130
160
200
ms
tWDL(EXT)
External Watchdog Lower Boundary
(Note 5)
B Versions, CWT = 2.2nF
●
VIL(WDI)
Input Low Voltage
●
VIH(WDI)
Input High Voltage
●
1.1
V
tPW(WDI)
Input Pulsewidth
●
400
ns
WDI Leakage Current
●
±1
μA
0.2 • VCC
V
tWDU(EXT)/32
s
ms
0.4
V
Manual Reset Input (LTC2918)
VIL(MR)
Input Low Voltage
●
VIH(MR)
Input High Voltage
●
0.8 • VCC
RPU
Pull-Up Resistance
●
50
tPW(MR)
Pulsewidth
●
250
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: VCC maximum pin voltage is limited by input current. Since the
VCC pin has an internal 6.2V shunt regulator, a low impedance supply
which exceeds 5.7V may exceed the rated terminal current. Operation
V
100
150
kΩ
ns
from higher voltage supplies requires a series dropping resistor. See
Applications Information.
Note 4: Input impedance is dependent on the configuration of the SEL
pins.
Note 5: In the LTC2917-B/LTC2918-B, edges must occur on WDI with a
period between the lower and upper boundary or RST is invoked. For the
LTC2917-A/LTC2918-A, the edges must simply occur before the upper
boundary. See Applications Information.
29178fb
5
LTC2917/LTC2918
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Supply Current vs
Temperature
1.5
QUIESCENT SUPPLY CURRENT, ICC (μA)
40
NORMALIZED VMTnn (%)
1.0
0.5
VMTADJ
0
–0.5
VMT25
VMT120
–1.0
–1.5
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
SEL1 = 0V
SEL2 = 2.5V
TOL = OPEN
35
VCC = 5.5V
VCC = 2.5V
30
VCC = 1.5V
25
20
–50
125
–25
75
0
25
50
TEMPERATURE (°C)
100
RESET TIMEOUT PERIOD, tRST(INT) (ms)
RESET TIMEOUT PERIOD, tRST(EXT) (ms)
250
1000
100
10
1
0.01
0.1
1
10
100
RT PIN CAPACITANCE, CRT (nF)
RT = VCC
230
210
190
170
150
–50
1000
–25
50
25
0
75
TEMPERATURE (°C)
100
29178 G04
100
50
0
1
10
100
0.1
GLITCH PERCENTAGE PAST THRESHOLD (%)
29178 G03
Internal Watchdog Timeout
Period vs Temperature
125
2.0
1.6
1.4
1.2
1.0
–50
100
10
100
29178 G07
–25
50
25
0
75
TEMPERATURE (°C)
100
Shunt Regulation Voltage vs
Supply Current
6.4
ICC = 5mA
6.3
ICC = 1mA
ICC = 100μA
6.2
6.1
–50
–25
0
25
50
75
TEMPERATURE (°C)
125
29178 G06
SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V)
SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V)
1000
WT = VCC
1.8
Shunt Regulation Voltage vs
Temperature
10000
RESET OCCURS
ABOVE CURVE
150
29178 G05
Watchdog Timeout Period vs
Capacitance
WATCHDOG TIMEOUT PERIOD, tWDU(EXT) (ms)
200
Internal Reset Timeout Period vs
Temperature
10000
0.01
0.1
1
10
WT PIN CAPACITANCE, CWT (nF)
250
125
WATCHDOG TIMEOUT PERIOD, tWDU(INT) (ms)
Reset Timeout Period vs RT
Capacitance
1
0.001
300
29178 G02
29178 G01
0.1
0.001
Allowable Glitch Duration vs
Magnitude
MAXIMUM ALLOWABLE GLITCH DURATION (μs)
Threshold Voltage vs
Temperature
100
125
29178 G08
7.0
6.8
6.6
6.4
6.2
6.0
0.01
1
0.1
10
SUPPLY CURRENT, ICC (mA)
100
29178 G09
29178fb
6
LTC2917/LTC2918
TYPICAL PERFORMANCE CHARACTERISTICS
RST Pull-Down Current vs VCC
RST Output Voltage vs VCC
6
4
3
2
1
0
1
2
3
4
SUPPLY VOLTAGE, VCC (V)
5
5
NO PULL-UP R
VCC = 2.5V
0.8
RST VOLTAGE (V)
PULL-DOWN CURRENT, IRST (mA)
RST VOLTAGE (V)
10k PULL-UP R TO VCC
SEL1 = SEL2 = TOL = 0V
5 VM = 0.5V
0
RST VOL vs IRST
1.0
6
4
RST AT 150mV
3
2
1
TA = 125°C
0.6
0.2
RST AT 50mV
0
0
0
1
2
3
4
SUPPLY VOLTAGE, VCC (V)
29178 G10
TA = 25°C
0.4
5
29178 G11
TA = –40°C
0
2
6
4
IRST (mA)
8
10
29178 G12
PIN FUNCTIONS
GND: Device Ground.
MR (LTC2918 only): Manual Reset Input (Active Low). A low
level on the MR input causes the part to issue a reset, which
is released one reset timeout after the input goes high. The pin
has an internal 100k pull-up to VCC, and thus may interface
directly to a momentary pushbutton. Leave open if unused.
RST: Open Drain RST Output. Asserts low when VM is
below the threshold selected by SEL1, SEL2 and TOL input
pins. Held low for an adjustable timeout after VM input is
above threshold.
RT: Reset Timeout Control Pin. Attach an external capacitor
(CRT) to GND to set a reset timeout of 9ms/nF. Leave RT open
to generate a reset timeout of approximately 400μs. Tie RT to
VCC to generate a reset timeout of approximately 200ms.
SEL1, SEL2: Monitor Voltage Select Three-State Input.
SEL1, and SEL2 control the nominal threshold voltage
that VM is set to monitor. Connect to VCC, GND or leave
unconnected in open state. (See Table 1).
that the part is out of under voltage lockout and that the
voltage thresholds are accurate. Operates as a direct supply
input for voltages up to 5.5V. Operates as a shunt regulator
for supply voltages greater than 5.7V and should have a
resistor between this pin and the supply to limit VCC input
current to no greater than 5mA. When used without a current-limiting resistor, pin voltage must not exceed 5.7V.
VM: Voltage Monitor Input to RST comparator. SEL1, SEL2
and TOL inputs select the exact threshold that asserts the
RST output.
WDI: Watchdog Input. This pin must be driven to change
state within a time less than the watchdog upper boundary time, or RST will be asserted low. On the LTC2917-B,
LTC2918-B, the period must also be greater than the
watchdog lower boundary time, and only falling edges
are considered. Tie WT and WDI to GND to disable the
watchdog timer.
TOL (LTC2917 only): Three-State Input for Supply Tolerance
Selection (–5%, –10% or –15%). Controls the tolerance
band at which the VM supply is monitored. Connect to VCC,
GND, or leave unconnected in open state. (See Table 2)
WT: Watchdog Timer Control Pin. Attach an external
capacitor (CWT) to GND to set a watchdog upper boundary timeout time of 72ms/nF. Tie WT to VCC to generate a
timeout of approximately 1.6s. Leave WT open to generate
a timeout of approximately 3.2ms. Tie WT and WDI to GND
to disable the watchdog timer.
VCC: Power Supply input. Bypass this pin to ground with a
0.1μF ceramic capacitor. A minimum of 1.5V on VCC ensures
Exposed Pad (DFN Only): Exposed Pad may be left open
or connected to device ground.
29178fb
7
LTC2917/LTC2918
BLOCK DIAGRAM
LTC2917
SEL1
SEL2
LTC2918
TOL
MR
RT
VCC
3 STATE
DECODE
+
–
0.5V
VCC
6.2V
100k
INTERNAL
200ms TIMER
MONITOR
DIVIDER
MATRIX
VM
VCC
VCC DETECT
RST
–
+
RESET
DRIVER LOGIC
REFERENCE
DIVIDER
MATRIX
GND
ADJUSTABLE
RESET TIMER
INTERNAL
1.6 SECOND
TIMER
WATCHDOG
LOGIC
ADJUSTABLE
WATCHDOG
TIMER
VCC DETECT
WT
WDI
29178 BD
TIMING DIAGRAMS
Monitor Input Timing
VMTx
VM
tUV
RST
tRST
1V
29178 TD01
Watchdog Timing (LTC2917-A, LTC2918-A)
WDI
RST
tWDU
29178 TD01
tRST
Watchdog Timing (LTC2917-B, LTC2918-B)
WDI
RST
t > tWDL
t < tWDL
tRST
tWDU
29178 TD03
tRST
29178fb
8
LTC2917/LTC2918
APPLICATIONS INFORMATION
Supply Monitoring
Monitor Threshold Control
The LTC2917/LTC2918 are low voltage single supply
monitors with selectable thresholds. Two three-state inputs
select one of nine internally programmed thresholds. For
the LTC2917, a third three-state input selects the tolerance
at which the supply connected to the VM pin is monitored
(–5%, –10%, –15%). The tolerance for the LTC2918 is
fixed at –5%. Threshold accuracy is guaranteed at ±1.5%
over the entire operating temperature range.
The monitor threshold on the VM pin is controlled by
the SEL1, SEL2 and TOL three-state pins. The SEL1 and
SEL2 pins select one of nine preset nominal voltages
(including one externally adjustable threshold) as shown
in Table 1.
The LTC2917/LTC2918 asserts the RST output low when
VM is below the programmed threshold, and for a reset
timeout period (tRST) after VM goes above the threshold.
The reset timeout can be configured to use one of two
internal timers with no external components, or an adjusted timer programmed by placing an external capacitor
from RT to ground. Glitch filtering ensures reliable reset
operation without false triggering.
Power-Up
VCC powers the drive circuits for the RST pin. Therefore,
as soon as VCC reaches 0.8V during power up, the RST
output asserts low.
Until VCC reaches the undervoltage lockout threshold
(guaranteed less than 1.5V), RST is held low regardless
of the state of VM.
Once VCC is above the undervoltage lockout threshold
and VM is above the programmed threshold, the reset
timer is started. After the reset timeout, the open drain
pull-down releases RST and the external pull-up resistor
pulls high.
Power-Down
On power-down, once VM drops below its threshold or
VCC drops below the undervoltage lockout, RST asserts
logic low.
The SEL1 and SEL2 three-state input pins should be connected to GND, VCC or left unconnected during normal
operation. Note that when left unconnected, the maximum
leakage allowable from the pin to either GND or VCC is
±5μA.
The tolerance at which the monitored supply is measured
is set by the TOL pin (LTC2917 only) as shown in Table 2.
If desired (e.g. for margining purposes), the TOL pin may
be driven by a three-state buffer. That three-state buffer
must have a VOL and VOH which meet the VIL and VIH of
the TOL pin specified in the Electrical Characteristics, and
maintain less than 5μA of leakage in the open state.
Table 1. Voltage Threshold Settings
NOMINAL VOLTAGE
SEL1
SEL2
12V
VCC
VCC
5V
VCC
Open
3.3V
VCC
GND
2.5V
Open
VCC
1.8V
Open
Open
*1.5V
Open
GND
*1.2V
GND
VCC
*1V
GND
Open
*ADJ (0.5V)
GND
GND
*Require a separate supply for VCC
Table 2. System Voltage Tolerance Settings
TOLERANCE
TOL
–5%
VCC
–10%
Open
–15%
GND
29178fb
9
LTC2917/LTC2918
APPLICATIONS INFORMATION
Threshold Accuracy
The trip threshold for the supplies monitored is selected
by configuring the three-state input pins. When using the
adjustable input, a external resistive divider sets the trip
threshold, allowing the user complete control over the
trip point. Selection of this trip voltage is crucial to the
reliability of the system.
Any power supply has some tolerance band within which
it is expected to operate (e.g. 5V±10%). It is generally
undesirable that a supervisor issue a reset when the power
supply is inside this tolerance band. Such a “nuisance”
reset reduces reliability by preventing the system from
functioning under normal conditions.
To prevent nuisance resets, the supervisor threshold must
be guaranteed to lie outside the power supply tolerance
band. To ensure that the threshold lies outside the power
supply tolerance range, the nominal threshold must lie outside that range by the monitor’s accuracy specification.
All 27 of the selectable thresholds have the same relative
threshold accuracy of ±1.5% of the programmed nominal
input voltage (over the full operating temperature range).
Consider the example of monitoring a 5V supply with a 10%
tolerance. The nominal threshold internal to the LTC2917
is 11.5% below the 5V input at 4.425V. With ±1.5% accuracy, the trip threshold range is 4.425V±75mV over
temperature (i.e. 10% to 13% below 5V). The monitored
system must thus operate reliably down to 4.35V or 13%
below 5V over temperature.
Glitch Immunity
The above discussion is concerned only with the DC
value of the monitored supply. Real supplies also have
relatively high-frequency variation, from sources such as
load transients, noise, and pickup. These variations should
not be considered by the monitor in determining whether
a supply voltage is valid or not. The variations may cause
spurious outputs at RST, particularly if the supply voltage
is near its trip threshold.
Two techniques are used to combat spurious reset without
sacrificing threshold accuracy. First, the timeout period
helps prevent high-frequency variation whose frequency
is above 1/ tRST from appearing at the RST output.
When the voltage at VM goes below the threshold, the
RST pin asserts low. When the supply recovers past
the threshold, the reset timer starts (assuming it is not
disabled), and RST does not go high until it finishes. If
the supply becomes invalid any time during the timeout
period, the timer resets and starts a fresh when the supply
next becomes valid.
While the reset timeout is useful at preventing toggling
of the reset output in most cases, it is not effective at
preventing nuisance resets due to short glitches (due to
load transients or other effects) on a valid supply.
To reduce sensitivity to these short glitches, the comparator
has additional anti-glitch circuitry. Any transient at the input
of the comparator needs to be of sufficient magnitude and
duration tUV before it can change the monitor state.
The combination of the reset timeout and anti-glitch circuitry prevents spurious changes in output state without
sacrificing threshold accuracy.
Adjustable Input
When the monitor threshold is configured as ADJ, the
internal comparator input is connected to the pin without
a resistive divider, and the pin is high-impedance. Thus,
any desired threshold may be chosen by attaching VM to
a tap point on an external resistive divider between the
monitored supply and ground, as shown in Figure 1.
VMON
R2
–
VM
+
R1
+
–
0.5V
29178 F01
Figure 1. Setting the Trip Point Using the
Adjustable Threshold.
29178fb
10
LTC2917/LTC2918
APPLICATIONS INFORMATION
Typically, the user will pick a value of R1 based on acceptable current draw. Current used by the resistor divider will
be approximately:
10000
RESET TIMEOUT PERIOD, tRST (EXT) (ms)
The reference input of the comparator is controlled by the
tolerance pin. The external resistive divider should make
the voltage at VM = 0.5V when the supply is at nominal
value. The actual threshold of VM accounts for the supply tolerance of ±1.5% guaranteed over the full operating
temperature range. The resulting tolerances are –6.5%,
–11.5%, –16.5% which correspond to 0.468V, 0.443V,
0.418V respectively.
1000
100
10
1
0.1
0.001
0.01
0.1
1
10
100
RT PIN CAPACITANCE, CRT (nF)
1000
29178 F02
⎛ 0.5V ⎞
R1= ⎜
⎝ I ⎟⎠
Recommended range of R1 is 1k—1M. Higher values of
resistance exacerbate the degradation of threshold accuracy due to leakage currents.
If the nominal value of the supply being monitored is
VNOM, then
R2 = R1(2VNOM – 1)
Figure 2. Reset Timeout Period vs RT Capacitance
RST Output Characteristics
The DC characteristics of the RST pull-down strength
are shown in the Typical Performance Characteristics
section. RST is an open-drain pin and thus requires an
external pull-up resistor to the logic supply. RST may be
pulled above VCC, providing the voltage limits of the pin
are observed.
Resistor tolerances must be taken into account when
determining the overall accuracy.
The open-drain of the RST pin allows for wired-OR connection of several LTC2917/LTC2918’s.
Selecting the Reset Timing Capacitor
Watchdog
The reset timeout period can be set to one of two fixed
internal timers or set with a capacitor in order to accommodate a variety of applications. Connecting a capacitor,
CRT, between the RT pin and ground sets the reset timeout
period, tRST. The following formula approximates the value
of capacitor needed for a particular timeout:
LTC2917-A/LTC2918-A
CRT = tRST • 110 [pF/ms]
For example, using a standard capacitor value of 2.2nF
would give a 20ms timeout.
Figure 2 shows the desired reset timeout period as a
function of the value of the timer capacitor.
Leaving RT open with no external capacitor generates a
reset timeout of approximately 400μs. Shorting RT to VCC
generates a reset timeout of approximately 200ms.
A standard watchdog function is used to ensure that the
system is in a valid state by continuously monitoring
the microprocessor’s activity. The microprocessor must
toggle the logic state of the WDI pin periodically (within
upper boundary) in order to clear the watchdog timer. If
timeout occurs, the LTC2917-A/LTC2918-A asserts RST
low for the reset timeout period, issuing a system reset.
Once the reset timeout completes, RST is released to go
high and the watchdog timer starts again.
During power-up, the watchdog timer remains cleared while
RST is asserted low. As soon as the reset timer times out,
RST goes high and the watchdog timer is started.
29178fb
11
LTC2917/LTC2918
APPLICATIONS INFORMATION
LTC2917-B/LTC2918-B
Manual Reset (LTC2918 Only)
For applications in which reliability is even more critical,
the LTC2917-B/LTC2918-B implements a windowed watchdog function by adding a lower boundary condition to the
standard watchdog function. If the WDI input receives a
falling edge prior to the watchdog lower boundary, the
part considers this a watchdog failure, and asserts RST
low (releasing again after the reset timeout period as
described above). The LTC2917-B/LTC2918-B WDI input
only responds to falling edges.
The LTC2918 includes the MR pin for applications where a
manual reset is desired. MR is internally pulled up, making
it ready to interface with a push button with no external
components required. Asserting MR low when RST is high
initiates a reset, resulting in RST being asserted low for
the reset timeout time.
Setting the Watchdog Timeout Period
The watchdog timeout period is adjustable and can be
optimized for software execution. The watchdog timeout
period is adjusted by connecting a capacitor between WT
and ground. Given a specified watchdog timeout period,
the capacitor is determined by:
CWT = tWD • 13.8 [nF/s]
For example, using a standard capacitor value of 0.047μF
would give a 3.4s watchdog timeout period.
Leaving WT open with no external capacitor generates
a timeout of approximately 3.2ms. Shorting WT to VCC
generates a timeout of approximately 1.6s. Connecting
WT to GND disables the watchdog function.
Shunt Regulator
The LTC2917 and LTC2918 contain an internal 6.2V shunt
regulator on the VCC pin to allow operation from a high
voltage supply. To operate the part from a supply higher
than 5.7V, the VCC pin must have a series resistor, RCC,
to the supply. See Figure 3. This resistor should be sized
according to the following equation:
VS(MAX ) − 5.7 V
VS(MIN) − 7 V
≤ RCC ≤
5mA
250μA
where VS(MIN) and VS(MAX) are the operating minimum
and maximum of the supply.
As an example, consider operation from an automobile
battery which might dip as low as 10V or spike to 60V. We
must then pick a resistance between 10.86k and 12k.
(VTRIP = 10.64V)
12V
3.3V
R2
1.15M
RPU
10k
RCC
11k
CBYPASS
0.1μF
VCC
VCC
LTC2917
R1
49.9k
μP
VM
RST
RST
SEL1
WDI
I/O
SEL2
TOL
GND
GND
29178 F03
WT
RT
CWT
CRT
Figure 3. 12V Supply Monitor Powered From 12V, Utilizing
the Internal Shunt Regulator with 3.3V Logic Out
29178fb
12
LTC2917/LTC2918
TYPICAL APPLICATIONS
1V Supply Monitor with Windowed Watchdog Timeout
and Internal Timers Selected
12V Supply Monitor with 20ms Reset Timeout and 3.4s
Watchdog Timeout, with 3.3V Logic Out
3.3V
3.3V
CBYPASS
0.1μF
CBYPASS
0.1μF
RPU
10k
VCC
μP
VM
RST
RST
SEL1
WDI
I/O
SEL2
TOL
GND WT
VCC
VCC
LTC2917-B
1V
VCC
LTC2917-A
12V
GND
μP
VM
RST
RST
SEL1
WDI
I/O
SEL2
29178 TA02
TOL
GND
RT
3.3V
RPU
10k
29178 TA03
WT
RT
CWT
0.047μF
tWDU = 1.6s
tWDL = 50ms
tRST = 200ms
GND
CRT
0.0022μF
9V, –15% Tolerance Supply Monitor ith 1.8V Logic Out
1.8V
CBYPASS
0.1μF
9V
R2
866k
RPU
10k
VCC
VCC
LTC2917-A
R1
51.1k
μP
VM
RST
RST
SEL1
WDI
I/O
SEL2
TOL
GND
GND
29178 TA04
WT
RT
CWT
CRT
29178fb
13
LTC2917/LTC2918
TYPICAL APPLICATIONS
3.3V, –10% Tolerance Supply Monitor
with Disabled Watchdog
1.8V, –5% Supply Monitor with Manual Reset
3.3V
1.8V
CBYPASS
0.1μF
CBYPASS
0.1μ F
RPU
10k
VCC
VCC
LTC2917
RST
SEL1
WDI
VCC
LTC2918
RST
GND
SEL2
TOL
GND
VCC
μP
VM
RPU
10k
29178 TA06
μP
VM
RST
RST
SEL1
WDI
I/O
SEL2
GND
29178 TA07
MR
WT
10k*
RT
CRT
GND
RT
WT
MANUAL RESET
PUSHBUTTON
CWT
CRT
*OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE
1.5V Supply Monitor with Tolerance Control for Margining,
–5% Operation with –15% Margining
3.3V
CBYPASS
0.1μF
RPU
10k
VCC
VCC
LTC2917
1.5V
μP
VM
RST
RST
SEL1
WDI
I/O
SEL2
TOL
I/O
–15% –5%
GND
WT
GND
29178 TA08
RT
CWT
CRT
29178fb
14
LTC2917/LTC2918
PACKAGE DESCRIPTION
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
3.00 p 0.102
(.118 p .004)
(NOTE 3)
0.254
(.010)
0.889 p 0.127
(.035 p .005)
10 9 8 7 6
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
DETAIL “A”
0.497 p 0.076
(.0196 p .003)
REF
0° – 6° TYP
GAUGE PLANE
1 2 3 4 5
5.23
(.206)
MIN
0.53 p 0.152
(.021 p .006)
3.20 – 3.45
(.126 – .136)
0.86
(.034)
REF
1.10
(.043)
MAX
DETAIL “A”
0.18
(.007)
0.50
0.305 p 0.038
(.0197)
(.0120 p .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.1016 p 0.0508
(.004 p .002)
0.50
(.0197)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
MSOP (MS) 0307 REV E
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 p0.05
(2 SIDES)
3.00 p0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
6
0.40 p0.10
10
0.70 p0.05
2.55 p0.05
1.15 p0.05
PACKAGE
OUTLINE
0.25 p0.05
0.50 BSC
2.39 p0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
2.00 p0.10
(2 SIDES)
0.75 p0.05
0.64 p 0.05
(2 SIDES)
5
0.25 p 0.05
0 – 0.05
PIN 1
R = 0.20 OR
0.25s45°
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 p0.05
(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
29178fb
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.
15
LTC2917/LTC2918
TYPICAL APPLICATION
Dual Supply Monitor (1.8V and 12V) with Manual Reset
1.8V
CBYPASS
0.1μF
C1
0.1μF
VCC
VCC
LTC2916
VM
MANUAL RESET
PUSH BUTTON
RPU
10k
VCC
LTC2917-B
RST
12V
μP
VM
RST
RST
SEL1
SEL1
WDI
I/O
SEL2
SEL2
MR
TOL
GND WT
GND
RT
1.8V
GND
29178 TA10
RT
1.8V
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690
5V Supply Monitor, Watchdog Timer and Battery Backup
4.65V Threshold
LTC694-3.3
3.3V Supply Monitor, Watchdog Timer and Battery Backup
2.9V Threshold
LTC1232
5V Supply Monitor, Watchdog Timer and Push-Button Reset
4.37V/4.62V Threshold
LTC1326
Micro Power Precision Triple Supply Monitor
4.725V, 3.118V, 1V Threshold (±0.75%)
LTC1536
Precision Triple Supply Monitor for PCI Applications
Meets PCI tFALL Timing Specifications
LTC1726
Micro Power Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable RESET and Watchdog Time-Outs
LTC1727
Micro Power Triple Supply Monitor with Open-Drain Reset
Individual Monitor Outputs in MSOP
LTC1728
Micro Power Triple Supply Monitor with Open-Drain Reset
5-Lead SOT-23 Package
LTC2900
Programmable Quad Supply Monitor
Adjustable RESET, 10-Lead MSOP and 3mm × 3mm 10-Lead DFN
LTC2901
Programmable Quad Supply Monitor
Adjustable RESET and Watchdog Timer, 16-Lead SSOP Package
LTC2902
Programmable Quad Supply Monitor
Adjustable RESET and Tolerance, 16-Lead SSOP Package, Margining
LTC2903
Precision Quad Supply Monitor
6-Lead SOT-23 Package, Ultra Low Voltage Reset
LTC2904
3-State Programmable Precision Dual Supply Monitor
Adjustable Tolerance, 8-Lead SOT-23 Package
LTC2905
3-State Programmable Precision Dual Supply Monitor
Adjustable RESET and Tolerance, 8-Lead SOT-23 Package
LTC2906
Precision Dual Supply Monitor 1 Selectable and 1 Adjustable
Separate VCC Pin, RST/RST Outputs
LTC2907
Precision Dual Supply Monitor 1 Selectable and 1 Adjustable
Separate VCC Pin, Adjustable Reset Timer
LTC2908
Precision Six Supply Monitor (Four Fixed and 2 Adjustable)
8-Lead SOT-23 and DDB Packages
LTC2909
Precision Triple/Dual Input UV, OV
2 ADJ Inputs
LTC2910
Octal Positive/Negative Voltage Monitor
16-Lead SSOP and 5mm × 3mm DFN Packages
LTC2912
Single UV/OV Voltage Monitor, Adjustable UV and OV
8-Lead TSOT and 3mm × 2mm DFN Packages
LTC2913
Dual UV/OV Voltage Monitor
10-Lead MSOP and 3mm × 3mm DFN Packages
LTC2914
Qual UV/OV Positive/Negative Voltage Monitor
16-Lead SSOP and 5mm × 3mm DFN Packages
LTC2915
Single Supervisor with 27 Selectable Thresholds
10-Lead MSOP and 3mm × 2mm DFN-10 Packages
LTC2916
Single Supervisor with 9 Selectable Thresholds
Manual Reset, 10-Lead MSOP and 3mm × 2mm DFN-10 Packages
29178fb
16 Linear Technology Corporation
LT 0208 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
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