ISPLSI 2032/A-80LTN44 - LATTICE SEMICONDUCTOR

LTC2917/LTC2918

29178fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Voltage Supervisor with

27 Selectable Thresholds

and Watchdog Timer

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 cur-

rent of only 30μA.

Two three state inputs select one of nine internally pro-

grammed 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 ﬁ xed at –5%. Threshold accuracy is guaranteed

at ±1.5% over the entire operating temperature range.

Glitch ﬁ ltering 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 exter-

nal 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.

1.8V Supply Monitor with Manual

Reset and Internal Timers Selected

■ 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

■ Handheld Devices

■ Cell Phone Base Stations

■ Automotive Control Systems

■ Network Servers

■ Optical Networking Systems

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

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

29178 TA01

WDIRT

WT SEL1

SEL2

GND

VCC

LTC2918-A μP

RST RST

I/O

10k

0.1μF

1.8V

tWDU = 1.6s

tRST = 200ms

Monitor Selection Table

LTC2917/LTC2918

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ABSOLUTE MAXIMUM RATINGS

(Note 1, 2)

Terminal Voltages

CC (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

CC (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

GND

TOL

SEL2

SEL1

RST

WDI

VCC

TOP VIEW

MS PACKAGE

10-LEAD PLASTIC MSOP

TJMAX = 125°C, θJA = 200°C/W

LTC2917

TOP VIEW

DDB PACKAGE

10-LEAD (3mm s 2mm) PLASTIC DFN

GND

TOL

SEL2

SEL1

RST

WDI

VCC

TJMAX = 125°C, θJA = 43°C/W

EXPOSED PAD (PIN 11) PCB GND

CONNECTION OPTIONAL

LTC2917

GND

SEL2

SEL1

RST

WDI

VCC

TOP VIEW

MS PACKAGE

10-LEAD PLASTIC MSOP

TJMAX = 125°C, θJA = 200°C/W

LTC2918

TOP VIEW

DDB PACKAGE

10-LEAD (3mm s 2mm) PLASTIC DFN

GND

SEL2

SEL1

RST

WDI

VCC

TJMAX = 125°C, θJA = 43°C/W

EXPOSED PAD (PIN 11) PCB GND

CONNECTION OPTIONAL

LTC2918

PIN CONFIGURATION

LTC2917

LTC2918 LTC2918

LTC2917

LTC2917/LTC2918

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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 identiﬁ ed by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based ﬁ nish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁ cations, go to: http://www.linear.com/tapeandreel/

LTC2917/LTC2918

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ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VCC(MIN) Minimum Supply Voltage RST in Correct Logic State ●0.8 V

VCC(UVLO) Supply Undervoltage Lockout ●1.5 V

VCC(SHUNT) Shunt Regulation Voltage IVCC = 0.5mA ●5.7 6.2 7.0 V

ICC VCC Pin Current SEL1, SEL2, TOL, MR = Open

SEL1, SEL2, TOL = GND (LTC2917)

MR = VCC (LTC2918)

●

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

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

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

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

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

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

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

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

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

RVM VM Input Impedance (Note 4) Fixed Threshold Modes ●0.5 8 MΩ

IVM(ADJ) ADJ Input Current VM = 0.5V ●±15 nA

Three-State Inputs (SEL1, SEL2), (TOL, LTC2917)

VTPIN,LOW Low Level Input Voltage ●0.5 V

VTPIN,HIGH High Level Input Voltage ●1.4 V

VTPIN,Z Pin Voltage when Open I = 0μA 0.9 V

ITPIN,Z Allowable Leakage in Open State ●±5 μA

ITPIN,H/L Pin Input Current 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 ●234μA

IRT(INT) Internal RT VCC Detect Current VRT = VCC ●18μA

VRT(INT, LH) RT Internal Timer Threshold VRT Rising, Referenced to VCC ●–100 –160 –300 mV

The ● denotes the speciﬁ cations which apply over the full operating

temperature range, otherwise speciﬁ cations are at TA = 25°C. VCC = 2.5V, unless otherwise noted. (Note 2)

LTC2917/LTC2918

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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Reset Output (RST)

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

0.05

0.4

0.3

0.2

IOH(RST) RST Output Voltage High Leakage RST = VCC ●±1 μA

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 ●234μA

VWT(INT, LH) WT Internal Timer Threshold VWT Rising, Referenced to VCC ●–100 –160 –300 mV

IWT(INT) Internal WT VCC Detect Current VWT = VCC ●18μA

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 s

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 ●tWDU(EXT)/32 ms

VIL(WDI) Input Low Voltage ●0.4 V

VIH(WDI) Input High Voltage ●1.1 V

tPW(WDI) Input Pulsewidth ●400 ns

WDI Leakage Current ●±1 μA

Manual Reset Input (LTC2918)

VIL(MR) Input Low Voltage ●0.2 • VCC V

VIH(MR) Input High Voltage ●0.8 • VCC V

RPU Pull-Up Resistance ●50 100 150 kΩ

tPW(MR) Pulsewidth ●250 ns

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

ELECTRICAL CHARACTERISTICS

The ● denotes the speciﬁ cations which apply over the full operating

temperature range, otherwise speciﬁ cations are at TA = 25°C. VCC = 2.5V, unless otherwise noted. (Note 2)

from higher voltage supplies requires a series dropping resistor. See

Applications Information.

Note 4: Input impedance is dependent on the conﬁ guration 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.

LTC2917/LTC2918

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TEMPERATURE (°C)

–50

NORMALIZED VMTnn (%)

0.5

1.0

1.5

25 75

29178 G01

–0.5

–25 0 50 100 125

–1.0

–1.5

VMT120

VMTADJ

VMT25

TEMPERATURE (°C)

–50

QUIESCENT SUPPLY CURRENT, ICC (μA)

–25 0 25 50

29178 G02

75 100 125

SEL1 = 0V

SEL2 = 2.5V

TOL = OPEN

VCC = 5.5V

VCC = 2.5V

VCC = 1.5V

GLITCH PERCENTAGE PAST THRESHOLD (%)

0.1

MAXIMUM ALLOWABLE GLITCH DURATION (μs)

200

250

300

1 10 100

29178 G03

150

100

RESET OCCURS

ABOVE CURVE

TEMPERATURE (°C)

–50 –25

150

RESET TIMEOUT PERIOD, tRST(INT) (ms)

190

250

050 75

29178 G05

170

230

210

25 100 125

RT = VCC

TEMPERATURE (°C)

–50 –25

1.0

WATCHDOG TIMEOUT PERIOD, tWDU(INT) (ms)

1.4

2.0

050 75

29178 G06

1.2

1.8

1.6

25 100 125

WT = VCC

WT PIN CAPACITANCE, CWT (nF)

0.001

WATCHDOG TIMEOUT PERIOD, tWDU(EXT) (ms)

100

10000

1100.10.01 100

29178 G07

1000

SUPPLY CURRENT, ICC (mA)

0.01

SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V)

6.4

6.6

100

29178 G09

6.2

6.0 0.1 110

7.0

6.8

TYPICAL PERFORMANCE CHARACTERISTICS

Threshold Voltage vs

Temperature

Quiescent Supply Current vs

Temperature

Allowable Glitch Duration vs

Magnitude

Reset Timeout Period vs RT

Capacitance

Internal Reset Timeout Period vs

Temperature

Internal Watchdog Timeout

Period vs Temperature

Watchdog Timeout Period vs

Capacitance

Shunt Regulation Voltage vs

Temperature

Shunt Regulation Voltage vs

Supply Current

RT PIN CAPACITANCE, CRT (nF)

0.001

0.1

RESET TIMEOUT PERIOD, tRST(EXT) (ms)

10000

0.10.01 1 10 100 1000

29178 G04

100

1000

TEMPERATURE (°C)

–50

6.1

SHUNT REGULATION VOLTAGE, VCC(SHUNT) (V)

6.2

6.3

6.4

–25 0 25 50

29178 G08

75 100 125

ICC = 5mA

ICC = 1mA

ICC = 100μA

LTC2917/LTC2918

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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).

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)

VCC: Power Supply input. Bypass this pin to ground with a

0.1μF ceramic capacitor. A minimum of 1.5V on VCC ensures

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 cur-

rent-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 bound-

ary 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.

WT: Watchdog Timer Control Pin. Attach an external

capacitor (CWT) to GND to set a watchdog upper bound-

ary 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.

Exposed Pad (DFN Only): Exposed Pad may be left open

or connected to device ground.

PIN FUNCTIONS

SUPPLY VOLTAGE, VCC (V)

RST VOLTAGE (V)

1234

29178 G10

10k PULL-UP R TO VCC

SEL1 = SEL2 = TOL = 0V

VM = 0.5V

SUPPLY VOLTAGE, VCC (V)

PULL-DOWN CURRENT, IRST (mA)

1234

29178 G11

RST AT 150mV

RST AT 50mV

IRST (mA)

RST VOLTAGE (V)

0.6

0.8

1.0

29178 G12

0.4

0.2

024610

TA = 125°C

TA = 25°C

TA = –40°C

NO PULL-UP R

VCC = 2.5V

TYPICAL PERFORMANCE CHARACTERISTICS

RST Output Voltage vs VCC RST Pull-Down Current vs VCC RST VOL vs IRST

LTC2917/LTC2918

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BLOCK DIAGRAM

–

GND

RST

VCC

29178 BD

SEL1 MRSEL2 RT

3 STATE

DECODE

MONITOR

DIVIDER

MATRIX

REFERENCE

DIVIDER

MATRIX

INTERNAL

200ms TIMER

ADJUSTABLE

RESET TIMER

RESET

DRIVER LOGIC

VCC DETECT

TOL

6.2V

100k

0.5V

–

WT WDI

VCC DETECT

INTERNAL

1.6 SECOND

TIMER

ADJUSTABLE

WATCHDOG

TIMER

WATCHDOG

LOGIC

LTC2918LTC2917

TIMING DIAGRAMS

RST

VMTx

tUV tRST

29178 TD01

Monitor Input Timing

WDI

RST

tWDU

tRST

29178 TD01

Watchdog Timing (LTC2917-A, LTC2918-A)

WDI

RST

tWDU

t > tWDL

tRST

29178 TD03

tRST

t < tWDL

Watchdog Timing (LTC2917-B, LTC2918-B)

LTC2917/LTC2918

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APPLICATIONS INFORMATION

Supply Monitoring

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

ﬁ xed at –5%. Threshold accuracy is guaranteed at ±1.5%

over the entire operating temperature range.

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 conﬁ gured to use one of two

internal timers with no external components, or an ad-

justed timer programmed by placing an external capacitor

from RT to ground. Glitch ﬁ ltering 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.

Monitor Threshold Control

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 SEL1 and SEL2 three-state input pins should be con-

nected 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 speciﬁ ed 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

LTC2917/LTC2918

29178fb

APPLICATIONS INFORMATION

Threshold Accuracy

The trip threshold for the supplies monitored is selected

by conﬁ guring 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 out-

side that range by the monitor’s accuracy speciﬁ cation.

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% ac-

curacy, 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

sacriﬁ cing 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 ﬁ nishes. 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 sufﬁ cient magnitude and

duration tUV before it can change the monitor state.

The combination of the reset timeout and anti-glitch cir-

cuitry prevents spurious changes in output state without

sacriﬁ cing threshold accuracy.

Adjustable Input

When the monitor threshold is conﬁ gured 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.

Figure 1. Setting the Trip Point Using the

Adjustable Threshold.

–

–0.5V

29178 F01

VMON

LTC2917/LTC2918

29178fb

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 sup-

ply 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.

Typically, the user will pick a value of R1 based on accept-

able current draw. Current used by the resistor divider will

be approximately:

105

=⎛

⎝

⎜⎞

⎠

⎟

Recommended range of R1 is 1k—1M. Higher values of

resistance exacerbate the degradation of threshold ac-

curacy due to leakage currents.

If the nominal value of the supply being monitored is

VNOM, then

R2 = R1(2VNOM – 1)

Resistor tolerances must be taken into account when

determining the overall accuracy.

Selecting the Reset Timing Capacitor

The reset timeout period can be set to one of two ﬁ xed

internal timers or set with a capacitor in order to accom-

modate 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:

RT = 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.

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.

The open-drain of the RST pin allows for wired-OR con-

nection of several LTC2917/LTC2918’s.

Watchdog

LTC2917-A/LTC2918-A

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.

APPLICATIONS INFORMATION

Figure 2. Reset Timeout Period vs RT Capacitance

RT PIN CAPACITANCE, CRT (nF)

0.001

0.1

RESET TIMEOUT PERIOD, tRST (EXT) (ms)

10000

0.10.01 1 10 100 1000

29178 F02

100

1000

LTC2917/LTC2918

29178fb

LTC2917-B/LTC2918-B

For applications in which reliability is even more critical,

the LTC2917-B/LTC2918-B implements a windowed watch-

dog 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.

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 speciﬁ ed watchdog timeout period,

the capacitor is determined by:

WT = 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.

APPLICATIONS INFORMATION

Manual Reset (LTC2918 Only)

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.

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:

mA RVV

SMAX

SMIN() ()

.−≤≤ −57

250μ

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.

Figure 3. 12V Supply Monitor Powered From 12V, Utilizing

the Internal Shunt Regulator with 3.3V Logic Out

RCC

11k

12V 3.3V

CRT

CBYPASS

0.1μF

RPU

10k

29178 F03

SEL1 GND

SEL2

TOL

VCC

(VTRIP = 10.64V)

VCC

LTC2917 μP

RST RST

WDI I/O

GND

1.15M

49.9k

CWT

LTC2917/LTC2918

29178fb

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

9V, –15% Tolerance Supply Monitor ith 1.8V Logic Out

3.3V

CBYPASS

0.1μF

RPU

10k

29178 TA02

SEL1 GND

SEL2

GND RTWT

TOL

VCC VCC

LTC2917-B μP

RST RST

WDI I/O

tWDU = 1.6s

tWDL = 50ms

tRST = 200ms

3.3V

12V

CBYPASS

0.1μF

RPU

10k

29178 TA03

SEL1 GND

SEL2

GND RTWT

TOL

VCC VCC

LTC2917-A μP

RST RST

WDI I/O

CWT

0.047μF

CRT

0.0022μF

1.8V

CBYPASS

0.1μF

RPU

10k

29178 TA04

SEL1 GND

SEL2

TOL

VCC VCC

LTC2917-A μP

RST RST

WDI I/O

GND

866k

51.1k

CRT

CWT

LTC2917/LTC2918

29178fb

TYPICAL APPLICATIONS

3.3V, –10% Tolerance Supply Monitor

with Disabled Watchdog 1.8V, –5% Supply Monitor with Manual Reset

1.5V Supply Monitor with Tolerance Control for Margining,

–5% Operation with –15% Margining

3.3V

CBYPASS

0.1μF

RPU

10k

29178 TA06

SEL1 GND

SEL2

TOL

VCC VCC

LTC2917 μP

RST

WDI

RST

GND RTWT

CRT

1.8V

CBYPASS

0.1μF

RPU

10k

29178 TA07

SEL1 GND

SEL2

VCC VCC

LTC2918 μP

RST RST

WDI I/O

GND

10k*

*OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE

CRT

MANUAL RESET

PUSHBUTTON

CWT

3.3V

1.5V

CBYPASS

0.1μF

RPU

10k

29178 TA08

SEL1

GNDSEL2

VCC VCC

LTC2917 μP

RST RST

WDI I/O

TOL I/O

GND

CRT

CWT

–5%–15%

LTC2917/LTC2918

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

PACKAGE DESCRIPTION

2.00 p0.10

(2 SIDES)

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

0.40 p0.10

BOTTOM VIEW—EXPOSED PAD

0.64 p 0.05

(2 SIDES)

0.75 p0.05

R = 0.115

TYP

R = 0.05

TYP

2.39 p0.05

(2 SIDES)

3.00 p0.10

(2 SIDES)

106

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

0.200 REF

0 – 0.05

(DDB10) DFN 0905 REV Ø

0.25 p0.05

2.39 p0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.64 p0.05

(2 SIDES)

1.15 p0.05

0.70 p0.05

2.55 p0.05

PACKAGE

OUTLINE

0.25 p 0.05

0.50 BSC

PIN 1

R = 0.20 OR

0.25s45°

CHAMFER

0.50 BSC

MSOP (MS) 0307 REV E

0.53 p 0.152

(.021 p .006)

SEATING

PLANE

0.18

(.007)

1.10

(.043)

MAX

0.17 –0.27

(.007 – .011)

TYP

0.86

(.034)

REF

0.50

(.0197)

BSC

12345

4.90 p 0.152

(.193 p .006)

0.497 p 0.076

(.0196 p .003)

REF

8910 76

3.00 p 0.102

(.118 p .004)

(NOTE 3)

3.00 p 0.102

(.118 p .004)

(NOTE 4)

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

0.254

(.010) 0° – 6° TYP

DETAIL “A”

GAUGE PLANE

5.23

(.206)

MIN

3.20 – 3.45

(.126 – .136)

0.889 p 0.127

(.035 p .005)

RECOMMENDED SOLDER PAD LAYOUT

0.305 p 0.038

(.0120 p .0015)

TYP

0.50

(.0197)

BSC 0.1016 p 0.0508

(.004 p .002)

MS Package

10-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1661)

DDB Package

10-Lead Plastic DFN (3mm × 2mm)

(Reference LTC DWG # 05-08-1722 Rev Ø)

LTC2917/LTC2918

29178fb

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 0208 REV B • PRINTED IN USA

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1.8V

CBYPASS

0.1μF

SEL1

SEL2

GND RT

VCC

LTC2916

RST

MANUAL RESET

PUSH BUTTON 1.8V 1.8V

12V

0.1μF

RPU

10k

29178 TA10

SEL1 GND

SEL2

GND WT RT

TOL

VCC VCC

LTC2917-B μP

RST RST

WDI I/O

TYPICAL APPLICATION

Dual Supply Monitor (1.8V and 12V) with Manual Reset