LTC2917HDDB-A1#PBF_技术文档

LTC2917/LTC2918

Voltage Supervisor with

27 Selectable Thresholds

and Watchdog Timer

DESCRIPTION

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.

FEATURES

■

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)

Two three state inputs select one of nine internally pro-

grammedthresholdswithouttheneedforexternalresistors.

FortheLTC2917,anadditionalthreestateinputdetermines

the tolerance (–5%, –10%, –15%). The tolerance for the

LTC2918isﬁxedat–5%.Thresholdaccuracyisguaranteed

at 1.5% over the entire operating temperature range.

Glitch ﬁltering ensures reliable reset operation without

false triggering.

■

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

■

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.

Power Supply Glitch Immunity

■

Guaranteed RST for V ≥ 0.8V

CC

■

10-Lead MSOP Packages and (3mm × 2mm) DFN

Packages

APPLICATIONS

■

Handheld Devices

Operation to 125°C makes the LTC2917-A/LTC2917-B

and LTC2918-A/LTC2918-B suitable for automotive

applications.

■

Cell Phone Base Stations

■

Automotive Control Systems

■

Network Servers

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

All other trademarks are the property of their respective owners.

■

Optical Networking Systems

TYPICAL APPLICATION

1.8V Supply Monitor with Manual

Reset and Internal Timers Selected

Monitor Selection Table

NOMINAL VOLTAGE

SEL1

SEL2

1.8V

12V

5V

V

CC

0.1μF

10k

Open

GND

V

CC

3.3V

LTC2918-A

μP

2.5V

Open

GND

V

CC

VM

RST

WDI

RST

I/O

1.8V

Open

GND

RT

1.5V

29178 TA01

WT

MR

SEL1

SEL2

1.2V

V

CC

GND

1V

Open

GND

t = 1.6s

WDU

t = 200ms

RST

ADJ (0.5V)

29178fb

1

LTC2917/LTC2918

(Note 1, 2)

ABSOLUTE MAXIMUM RATINGS

Terminal Voltages

Operating Temperature Range

V

(Note 3).......................................... –0.3V to 5.7V

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)

CC

SEL1, SEL2, TOL, WDI, MR, RST ......... –0.3V to 7.5V

VM......................................................... –0.3V to 15V

RT, WT.......................................–0.3V to (V + 0.3)V

CC

Terminal Currents

V

(Note 3)....................................................... 5mA

MSOP ............................................................... 300°C

CC

PIN CONFIGURATION

LTC2917

TOP VIEW

1

2

3

4

5

10

9

GND

TOL

RST

RT

TOP VIEW

GND

TOL

SEL2

SEL1

VM

1

2

3

4

5

10 RST

9

8

7

6

RT

11

8

SEL2

SEL1

VM

WT

WDI

CC

7

WDI

V

6

V

CC

MS PACKAGE

10-LEAD PLASTIC MSOP

DDB PACKAGE

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

T

= 125°C, θ = 200°C/W

JMAX

JA

T

JMAX

= 125°C, θ = 43°C/W

JA

LTC2917

EXPOSED PAD (PIN 11) PCB GND

CONNECTION OPTIONAL

LTC2917

TOP VIEW

LTC2918

1

2

3

4

5

10

9

GND

MR

RST

RT

TOP VIEW

GND

MR

SEL2

SEL1

VM

1

2

3

4

5

10 RST

9

8

7

6

RT

11

8

SEL2

SEL1

VM

WT

WDI

CC

7

WDI

V

6

V

CC

MS PACKAGE

10-LEAD PLASTIC MSOP

DDB PACKAGE

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

T

= 125°C, θ = 200°C/W

JMAX

JA

T

JMAX

= 125°C, θ = 43°C/W

JA

LTC2918

EXPOSED PAD (PIN 11) PCB GND

CONNECTION OPTIONAL

LTC2918

29178fb

2

LTC2917/LTC2918

ORDER INFORMATION

LEAD FREE FINISH

TAPE AND REEL

PART MARKING*

LTCQP

LTDGD

LTDCT

LTDGG

PART MARKING*

LCQR

PACKAGE DESCRIPTION

TEMPERATURE RANGE

0°C to 70°C

LTC2917CMS-B1#PBF

LTC2917IMS-B1#PBF

LTC2917HMS-B1#PBF

LTC2917CMS-A1#PBF

LTC2917IMS-A1#PBF

LTC2917HMS-A1#PBF

LTC2918CMS-B1#PBF

LTC2918IMS-B1#PBF

LTC2918HMS-B1#PBF

LTC2918CMS-A1#PBF

LTC2918IMS-A1#PBF

LTC2918HMS-A1#PBF

TAPE AND REEL (MINI)

LTC2917CMS-B1#TRPBF

LTC2917IMS-B1#TRPBF

LTC2917HMS-B1#TRPBF

LTC2917CMS-A1#TRPBF

LTC2917IMS-A1#TRPBF

LTC2917HMS-A1#TRPBF

LTC2918CMS-B1#TRPBF

LTC2918IMS-B1#TRPBF

LTC2918HMS-B1#TRPBF

LTC2918CMS-A1#TRPBF

LTC2918IMS-A1#TRPBF

LTC2918HMS-A1#TRPBF

TAPE AND REEL

10-Lead Plastic MSOP

–40°C to 85°C

–40°C to 125°C

0°C to 70°C

10-Lead Plastic MSOP

–40°C to 85°C

–40°C to 125°C

0°C to 70°C

10-Lead Plastic MSOP

–40°C to 85°C

–40°C to 125°C

0°C to 70°C

10-Lead Plastic MSOP

–40°C to 85°C

–40°C to 125°C

TEMPERATURE RANGE

0°C to 70°C

10-Lead Plastic MSOP

PACKAGE DESCRIPTION

LTC2917CDDB-B1#TRMPBF LTC2917CDDB-B1#TRPBF

LTC2917IDDB-B1#TRMPBF LTC2917IDDB-B1#TRPBF

10-Lead (3mm × 2mm) Plastic DFN

LCQR

–40°C to 85°C

–40°C to 125°C

0°C to 70°C

LTC2917HDDB-B1#TRMPBF LTC2917HDDB-B1#TRPBF

LTC2917CDDB-A1#TRMPBF LTC2917CDDB-A1#TRPBF

LCQR

LDGF

LTC2917IDDB-A1#TRMPBF

LTC2917IDDB-A1#TRPBF

LDGF

–40°C to 85°C

–40°C to 125°C

0°C to 70°C

LTC2917HDDB-A1#TRMPBF LTC2917HDDB-A1#TRPBF

LTC2918CDDB-B1#TRMPBF LTC2918CDDB-B1#TRPBF

LDGF

LDCV

LTC2918IDDB-B1#TRMPBF

LTC2918IDDB-B1#TRPBF

LDCV

–40°C to 85°C

–40°C to 125°C

0°C to 70°C

LTC2918HDDB-B1#TRMPBF LTC2918HDDB-B1#TRPBF

LTC2918CDDB-A1#TRMPBF LTC2918CDDB-A1#TRPBF

LDCV

LDGH

LTC2918IDDB-A1#TRMPBF

LTC2918IDDB-A1#TRPBF

LDGH

–40°C to 85°C

–40°C to 125°C

LTC2918HDDB-A1#TRMPBF LTC2918HDDB-A1#TRPBF

LDGH

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 T_A= 25°C. V_CC= 2.5V, unless otherwise noted. (Note 2)

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

●

V

Minimum Supply Voltage

Supply Undervoltage Lockout

Shunt Regulation Voltage

RST in Correct Logic State

0.8

V

CC(MIN)

1.5

7.0

CC(UVLO)

CC(SHUNT)

I

= 0.5mA

5.7

6.2

VCC

●

I

CC

V

CC

Pin Current

SEL1, SEL2, TOL, MR = Open

30

45

50

80

μA

SEL1, SEL2, TOL = GND (LTC2917)

MR = V (LTC2918)

CC

Monitor Input (VM)

●

V

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

MT120

MT50

MT33

MT25

MT18

MT15

MT12

MT10

MTADJ

●

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

●

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

●

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

●

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

●

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

●

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

●

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

●

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

●

R

VM Input Impedance (Note 4)

ADJ Input Current

Fixed Threshold Modes

VM = 0.5V

0.5

8

MΩ

VM

I

15

nA

VM(ADJ)

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

●

V

Low Level Input Voltage

High Level Input Voltage

Pin Voltage when Open

Allowable Leakage in Open State

Pin Input Current

0.5

V

TPIN,LOW

V

1.4

TPIN,HIGH

V

TPIN,Z

I = 0μA

0.9

V

●

I

5

μA

TPIN,Z

V

TPIN

= 0V, V

CC

20

TPIN,H/L

Reset Timer Control (RT)

●

I

RT Pull-Up Current

V

RT

V

RT

V

RT

V

RT

= 0.25V

= 1.1V

–2

2

–3

3

–4

4

μA

RT(UP)

RT Pull-Down Current

RT(DOWN)

RT(INT)

Internal RT V Detect Current

= V

1

8

CC

V

RT Internal Timer Threshold

Rising, Referenced to V

–100

–160

–300

mV

RT(INT, LH)

CC

29178fb

4

LTC2917/LTC2918

ELECTRICAL CHARACTERISTICS ^The● denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_CC= 2.5V, unless otherwise noted. (Note 2)

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Reset Output (RST)

●

t

Internal Reset Timeout Period

Adjustable Reset Timeout Period

V

C

= V

CC

150

16

200

20

260

25

ms

μs

RST(INT)

RST(EXT)

UV

RT

= 2.2nF

RT

VM Undervoltage Detect to RST

Asserted

VM Less Than Reset Threshold

10

80

150

V

by More Than 5%

MTX

●

V

Output Voltage Low RST

V

CC

V

CC

V

CC

= 3.3V, I = 2.5mA

RST

0.15

0.05

0.4

0.3

0.2

V

OL

= 1V, I

= 100μA

RST

= 0.8V, I

= 15μA

RST

●

I

RST Output Voltage High Leakage

RST = V

1

μA

OH(RST)

CC

Watchdog Timer Control (WT)

●

I

WT Pull-Up Current

V

= 0.25V

= 1.1V

–2

2

–3

3

–4

4

μA

WT(UP)

WT

WT Pull-Down Current

WT Internal Timer Threshold

V

WT

WT(DOWN)

V

WT

Rising, Referenced to V

CC

–100

–160

1

–300

8

mV

μA

WT(INT, LH)

I

Internal WT V Detect Current

V

= V

WT(INT)

WT(DIS)

CC

WT CC

I

Watchdog Disable Hold Current

V

WT

= 0V

–3.5

μA

Watchdog Input (WDI)

●

t

Internal Watchdog Upper Boundary

V

= V

CC

1.3

1.6

50

2

s

WDU(INT)

WDL(INT)

WT

Internal Watchdog Lower Boundary

(Note 5)

B Versions, V = V

37.5

62.5

ms

WT

CC

●

t

External Watchdog Upper Boundary

C

= 2.2nF

130

160

200

0.4

ms

WDU(EXT)

WT

External Watchdog Lower Boundary

(Note 5)

B Versions, C = 2.2nF

t

/32

WDU(EXT)

WDL(EXT)

WT

●

V

Input Low Voltage

Input High Voltage

Input Pulsewidth

V

IL(WDI)

IH(WDI)

PW(WDI)

1.1

t

400

ns

μA

WDI Leakage Current

1

Manual Reset Input (LTC2918)

●

V

Input Low Voltage

Input High Voltage

Pull-Up Resistance

Pulsewidth

0.2 • V

150

V

IL(MR)

IH(MR)

CC

V

0.8 • V

50

CC

R

100

kΩ

ns

PU

t

250

PW(MR)

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.

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 2: All currents into pins are positive; all voltages are referenced to

GND unless otherwise noted.

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.

Note 3: V maximum pin voltage is limited by input current. Since the

CC

V

pin has an internal 6.2V shunt regulator, a low impedance supply

CC

which exceeds 5.7V may exceed the rated terminal current. Operation

29178fb

5

LTC2917/LTC2918

TYPICAL PERFORMANCE CHARACTERISTICS

Threshold Voltage vs

Temperature

Quiescent Supply Current vs

Temperature

Allowable Glitch Duration vs

Magnitude

1.5

1.0

0.5

0

300

250

200

150

100

50

40

35

30

25

SEL1 = 0V

SEL2 = 2.5V

TOL = OPEN

V

= 5.5V

= 2.5V

CC

V

RESET OCCURS

ABOVE CURVE

MTADJ

–0.5

–1.0

–1.5

V

= 1.5V

V

MT120

CC

MT25

20

0

50

TEMPERATURE (°C)

100 125

–50 –25

0

25

50

75 100 125

0.1

1

10

100

–50 –25

0

25

75

TEMPERATURE (°C)

GLITCH PERCENTAGE PAST THRESHOLD (%)

29178 G01

29178 G02

29178 G03

Reset Timeout Period vs RT

Capacitance

Internal Reset Timeout Period vs

Temperature

Internal Watchdog Timeout

Period vs Temperature

10000

1000

100

10

250

230

210

190

170

150

2.0

1.8

1.6

1.4

1.2

1.0

RT = V

CC

WT = V

CC

1

0.1

0.001 0.01

0.1

1

10

100 1000

–50 –25

0

25

50

75 100 125

–50 –25

0

25

50

75 100 125

RT PIN CAPACITANCE, C (nF)

RT

TEMPERATURE (°C)

29178 G04

29178 G05

29178 G06

Watchdog Timeout Period vs

Capacitance

Shunt Regulation Voltage vs

Temperature

Shunt Regulation Voltage vs

Supply Current

10000

1000

100

10

6.4

6.3

6.2

6.1

7.0

6.8

6.6

6.4

6.2

6.0

I

= 5mA

CC

I

= 1mA

CC

I

= 100μA

CC

1

10

0.001

0.01

0.1

1

10

100

0.01

0.1

–50 –25

0

25

50

75 100 125

100

WT PIN CAPACITANCE, C (nF)

TEMPERATURE (°C)

SUPPLY CURRENT, I (mA)

WT

CC

29178 G07

29178 G09

29178 G08

29178fb

6

LTC2917/LTC2918

TYPICAL PERFORMANCE CHARACTERISTICS

RST Pull-Down Current vs V_CC

RST V_OLvs I_RST

RST Output Voltage vs V_CC

1.0

6

5

6

5

NO PULL-UP R

10k PULL-UP R TO V

SEL1 = SEL2 = TOL = 0V

VM = 0.5V

CC

V

= 2.5V

CC

0.8

0.6

T

= 125°C

A

4

3

4

3

RST AT 150mV

RST AT 50mV

T

= 25°C

A

0.4

0.2

0

2

1

0

2

1

0

T

= –40°C

A

0

2

4

I

6

8

10

0

1

2

3

4

5

0

1

2

3

4

5

SUPPLY VOLTAGE, V (V)

(mA)

RST

SUPPLY VOLTAGE, V (V)

CC

29178 G12

29178 G10

29178 G11

PIN FUNCTIONS

GND: Device Ground.

that the part is out of under voltage lockout and that the

voltagethresholdsareaccurate. Operatesasadirectsupply

input for voltages up to 5.5V. Operates as a shunt regulator

for supply voltages greater than 5.7V and should have a

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 V , and thus may interface

directly to a momentary pushbutton. Leave open if unused.

resistor between this pin and the supply to limit V input

CC

current to no greater than 5mA. When used without a cur-

rent-limiting resistor, pin voltage must not exceed 5.7V.

RST: Open Drain RST Output. Asserts low when VM is

belowthethresholdselectedbySEL1,SEL2andTOLinput

pins. Held low for an adjustable timeout after VM input is

above threshold.

VM:VoltageMonitorInputtoRSTcomparator.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.

RT: Reset Timeout Control Pin. Attach an external capacitor

RT

(C ) to GND to set a reset timeout of 9ms/nF. Leave RT open

togeneratearesettimeoutofapproximately400μs. TieRTto

V

CC

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 V , GND or leave

CC

WT: Watchdog Timer Control Pin. Attach an external

unconnected in open state. (See Table 1).

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

WT

TOL(LTC2917only):Three-StateInputforSupplyTolerance

ary timeout time of 72ms/nF. Tie WT to V to generate a

CC

Selection (–5%, –10% or –15%). Controls the tolerance

timeoutofapproximately1.6s. LeaveWTopentogenerate

atimeoutofapproximately3.2ms.TieWTandWDItoGND

to disable the watchdog timer.

band at which the VM supply is monitored. Connect to V ,

CC

GND, or leave unconnected in open state. (See Table 2)

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

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

CC

0.1μFceramiccapacitor.Aminimumof1.5VonV ensures

or connected to device ground.

CC

29178fb

7

LTC2917/LTC2918

BLOCK DIAGRAM

LTC2917

TOL

LTC2918

SEL1

SEL2

MR

RT

V

CC

V

CC

V

CC

V

DETECT

CC

3 STATE

DECODE

100k

6.2V

INTERNAL

200ms TIMER

MONITOR

DIVIDER

MATRIX

VM

RST

–

+

RESET

DRIVER LOGIC

REFERENCE

DIVIDER

MATRIX

GND

ADJUSTABLE

RESET TIMER

+

0.5V

–

INTERNAL

1.6 SECOND

TIMER

WATCHDOG

LOGIC

ADJUSTABLE

WATCHDOG

TIMER

V

CC

DETECT

WT

WDI

29178 BD

TIMING DIAGRAMS

Monitor Input Timing

V

VM

MTx

t

UV

t

RST

1V

29178 TD01

Watchdog Timing (LTC2917-A, LTC2918-A)

WDI

RST

t

WDU

29178 TD01

t

RST

Watchdog Timing (LTC2917-B, LTC2918-B)

WDI

RST

t > t

t

WDU

WDL

29178 TD03

t < t

t

RST

WDL

RST

29178fb

8

LTC2917/LTC2918

APPLICATIONS INFORMATION

Supply Monitoring

Monitor Threshold Control

The LTC2917/LTC2918 are low voltage single supply

monitorswithselectablethresholds.Twothree-stateinputs

select one of nine internally programmed thresholds. For

theLTC2917, athirdthree-stateinputselectsthetolerance

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

nected to GND, V or left unconnected during normal

CC

operation. Notethatwhenleftunconnected, themaximum

The LTC2917/LTC2918 asserts the RST output low when

leakage allowable from the pin to either GND or V is

CC

VM is below the programmed threshold, and for a reset

5μA.

timeout period (t ) after VM goes above the threshold.

RST

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

The reset timeout can be conﬁgured 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 ﬁltering ensures reliable reset

operation without false triggering.

must have a V and V which meet the V and V of

OL

OH

IL

IH

the TOL pin speciﬁed in the Electrical Characteristics, and

maintain less than 5μA of leakage in the open state.

Power-Up

Table 1. Voltage Threshold Settings

V

powers the drive circuits for the RST pin. Therefore,

CC

NOMINAL VOLTAGE

SEL1

SEL2

as soon as V reaches 0.8V during power up, the RST

CC

12V

V

output asserts low.

CC

5V

V

Open

GND

CC

Until V reaches the undervoltage lockout threshold

CC

3.3V

(guaranteed less than 1.5V), RST is held low regardless

2.5V

Open

GND

V

CC

of the state of VM.

1.8V

Open

GND

Once V is above the undervoltage lockout threshold

CC

*1.5V

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.

*1.2V

V

CC

*1V

Open

GND

*ADJ (0.5V)

*Require a separate supply for V

CC

Power-Down

Table 2. System Voltage Tolerance Settings

On power-down, once VM drops below its threshold or

CC

logic low.

TOLERANCE

–5%

TOL

V

drops below the undervoltage lockout, RST asserts

V

CC

–10%

Open

GND

–15%

29178fb

9

LTC2917/LTC2918

APPLICATIONS INFORMATION

Threshold Accuracy

Twotechniquesareusedtocombatspuriousresetwithout

sacriﬁcing threshold accuracy. First, the timeout period

helps prevent high-frequency variation whose frequency

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.

is above 1/ t

from appearing at the RST output.

RST

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.

Any power supply has some tolerance band within which

it is expected to operate (e.g. 5V 10%). It is generally

undesirablethatasupervisorissuearesetwhenthepower

supply is inside this tolerance band. Such a “nuisance”

reset reduces reliability by preventing the system from

functioning under normal conditions.

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.

Topreventnuisanceresets,thesupervisorthresholdmust

be guaranteed to lie outside the power supply tolerance

band. To ensure that the threshold lies outside the power

supplytolerancerange,thenominalthresholdmustlieout-

side that range by the monitor’s accuracy speciﬁcation.

Toreducesensitivitytotheseshortglitches,thecomparator

hasadditionalanti-glitchcircuitry.Anytransientattheinput

of the comparator needs to be of sufﬁcient magnitude and

duration t before it can change the monitor state.

UV

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).

Considertheexampleofmonitoringa5Vsupplywitha10%

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.

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

cuitry 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.

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

loadtransients,noise,andpickup.Thesevariationsshould

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.

V

MON

R2

–

+

VM

R1

+

0.5V

–

29178 F01

Figure 1. Setting the Trip Point Using the

Adjustable Threshold.

29178fb

10

LTC2917/LTC2918

APPLICATIONS INFORMATION

10000

1000

100

10

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.

1

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

able current draw. Current used by the resistor divider will

be approximately:

0.1

0.001 0.01

0.1

1

10

100 1000

RT PIN CAPACITANCE, C (nF)

RT

29178 F02

0.5V

I

⎛

⎞

Figure 2. Reset Timeout Period vs RT Capacitance

R1=

⎜

⎝

⎟

⎠

RST Output Characteristics

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

resistance exacerbate the degradation of threshold ac-

curacy due to leakage currents.

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

If the nominal value of the supply being monitored is

V

, then

NOM

pulled above V , providing the voltage limits of the pin

CC

are observed.

R2 = R1(2V

– 1)

NOM

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

nection of several LTC2917/LTC2918’s.

Resistor tolerances must be taken into account when

determining the overall accuracy.

Watchdog

Selecting the Reset Timing Capacitor

LTC2917-A/LTC2918-A

The reset timeout period can be set to one of two ﬁxed

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

modate a variety of applications. Connecting a capacitor,

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.

C , between the RT pin and ground sets the reset timeout

RT

period,t .Thefollowingformulaapproximatesthevalue

RST

of capacitor needed for a particular timeout:

C

= t

• 110 [pF/ms]

RT

RST

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.

Duringpower-up,thewatchdogtimerremainsclearedwhile

RST is asserted low. As soon as the reset timer times out,

RST goes high and the watchdog timer is started.

Leaving RT open with no external capacitor generates a

reset timeout of approximately 400μs. Shorting RT to V

generates a reset timeout of approximately 200ms.

CC

29178fb

11

LTC2917/LTC2918

APPLICATIONS INFORMATION

LTC2917-B/LTC2918-B

Manual Reset (LTC2918 Only)

For applications in which reliability is even more critical,

theLTC2917-B/LTC2918-Bimplementsawindowedwatch-

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.

The LTC2918 includes the MR pin for applications where a

manualresetisdesired. MRisinternallypulledup, making

it ready to interface with a push button with no external

componentsrequired.AssertingMRlowwhenRSTishigh

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 V pin to allow operation from a high

CC

Setting the Watchdog Timeout Period

voltage supply. To operate the part from a supply higher

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:

than 5.7V, the V pin must have a series resistor, R ,

CC CC

to the supply. See Figure 3. This resistor should be sized

according to the following equation:

V_S(MAX)−5.7V

V_S(MIN)−7V

≤R_CC≤

5mA

250μA

C

= t • 13.8 [nF/s]

WD

WT

where V

and V

are the operating minimum

S(MIN)

S(MAX)

For example, using a standard capacitor value of 0.047μF

would give a 3.4s watchdog timeout period.

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.

Leaving WT open with no external capacitor generates

a timeout of approximately 3.2ms. Shorting WT to V

CC

generates a timeout of approximately 1.6s. Connecting

WT to GND disables the watchdog function.

(V

= 10.64V)

TRIP

12V

3.3V

R2

1.15M

R

PU

10k

CC

11k

C

BYPASS

0.1μF

V

CC

V

CC

LTC2917

μP

VM

RST

WDI

RST

I/O GND

SEL1

SEL2

TOL

R1

49.9k

29178 F03

GND WT

RT

C

RT

WT

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

C

BYPASS

0.1μF

R

PU

10k

BYPASS

PU

0.1μF

10k

V

CC

LTC2917-B

μP

LTC2917-A

μP

1V

12V

VM

RST

WDI

RST

I/O GND

VM

RST

WDI

RST

I/O GND

SEL1

SEL2

TOL

SEL1

SEL2

TOL

29178 TA02

29178 TA03

GND WT

RT

GND WT

RT

C

RT

0.0022μF

3.3V

t

= 1.6s

WT

WDU

WDL

RST

0.047μF

= 50ms

= 200ms

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

1.8V

C

R

BYPASS

PU

0.1μF

10k

9V

R2

866k

V

CC

LTC2917-A

μP

VM

RST

WDI

RST

I/O GND

SEL1

SEL2

TOL

29178 TA04

R1

51.1k

GND WT

RT

C

RT

WT

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

C

R

BYPASS

PU

BYPASS

PU

0.1μF

10k

0.1μ F

10k

V

CC

V

CC

LTC2917

μP

LTC2918

μP

VM

RST

WDI

RST

VM

RST

WDI

RST

I/O GND

SEL1

SEL2

TOL

GND

SEL1

SEL2

MR

29178 TA06

29178 TA07

10k*

GND WT RT

GND

WT

RT

C

MANUAL RESET

PUSHBUTTON

RT

C

RT

WT

*OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE

1.5V Supply Monitor with Tolerance Control for Margining,

–5% Operation with –15% Margining

3.3V

C

R

BYPASS

PU

0.1μF

10k

V

CC

LTC2917

μP

1.5V

VM

RST

I/O

SEL1

SEL2

WDI

TOL

I/O GND

–15% –5%

29178 TA08

GND

WT

C

RT

C

WT

RT

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)

0.497 p 0.076

(.0196 p .003)

REF

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”

0.254

0.889 p 0.127

(.035 p .005)

(.010)

0° – 6° TYP

GAUGE PLANE

1

2

3

4 5

0.53 p 0.152

(.021 p .006)

5.23

3.20 – 3.45

(.206)

0.86

(.034)

REF

1.10

(.043)

MAX

(.126 – .136)

MIN

DETAIL “A”

0.18

(.007)

0.50

(.0197)

BSC

0.305 p 0.038

(.0120 p .0015)

TYP

SEATING

PLANE

0.17 – 0.27

(.007 – .011)

TYP

0.1016 p 0.0508

(.004 p .002)

RECOMMENDED SOLDER PAD LAYOUT

0.50

(.0197)

BSC

MSOP (MS) 0307 REV E

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

DDB Package

10-Lead Plastic DFN (3mm × 2mm)

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

R = 0.115

0.64 p 0.05

(2 SIDES)

0.40 p 0.10

3.00 p 0.10

(2 SIDES)

TYP

6

R = 0.05

TYP

10

0.70 p 0.05

2.55 p 0.05

1.15 p 0.05

2.00 p 0.10

PIN 1 BAR

(2 SIDES)

TOP MARK

PIN 1

R = 0.20 OR

(SEE NOTE 6)

0.25 s 45°

PACKAGE

OUTLINE

0.64 p 0.05

(2 SIDES)

0.25 p 0.05

CHAMFER

5

1

(DDB10) DFN 0905 REV Ø

0.25 p 0.05

0.75 p 0.05

0.200 REF

0.50 BSC

2.39 p 0.05

(2 SIDES)

0 – 0.05

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

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 representa-

tion 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

C

C1

0.1μF

R

BYPASS

PU

0.1μF

10k

V

CC

LTC2916

LTC2917-B

μP

VM

RST

12V

VM

RST

WDI

RST

I/O GND

SEL1

SEL2

MR

SEL1

SEL2

TOL

29178 TA10

GND

RT

1.8V

GND WT RT

MANUAL RESET

PUSH BUTTON

1.8V

RELATED PARTS

PART NUMBER

LTC690

DESCRIPTION

COMMENTS

5V Supply Monitor, Watchdog Timer and Battery Backup

3.3V Supply Monitor, Watchdog Timer and Battery Backup

4.65V Threshold

2.9V Threshold

LTC694-3.3

LTC1232

LTC1326

LTC1536

LTC1726

LTC1727

LTC1728

LTC2900

LTC2901

LTC2902

LTC2903

LTC2904

LTC2905

LTC2906

LTC2907

LTC2908

LTC2909

LTC2910

LTC2912

LTC2913

LTC2914

LTC2915

LTC2916

5V Supply Monitor, Watchdog Timer and Push-Button Reset 4.37V/4.62V Threshold

Micro Power Precision Triple Supply Monitor

4.725V, 3.118V, 1V Threshold ( 0.75%)

Meets PCI tFALL Timing Speciﬁcations

Precision Triple Supply Monitor for PCI Applications

Micro Power Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable RESET and Watchdog Time-Outs

Micro Power Triple Supply Monitor with Open-Drain Reset

Programmable Quad Supply Monitor

Individual Monitor Outputs in MSOP

5-Lead SOT-23 Package

Adjustable RESET, 10-Lead MSOP and 3mm × 3mm 10-Lead DFN

Adjustable RESET and Watchdog Timer, 16-Lead SSOP Package

Adjustable RESET and Tolerance, 16-Lead SSOP Package, Margining

6-Lead SOT-23 Package, Ultra Low Voltage Reset

Adjustable Tolerance, 8-Lead SOT-23 Package

Programmable Quad Supply Monitor

Precision Quad Supply Monitor

3-State Programmable Precision Dual Supply Monitor

Adjustable RESET and Tolerance, 8-Lead SOT-23 Package

Precision Dual Supply Monitor 1 Selectable and 1 Adjustable Separate V Pin, RST/RST Outputs

CC

Precision Dual Supply Monitor 1 Selectable and 1 Adjustable Separate V Pin, Adjustable Reset Timer

CC

Precision Six Supply Monitor (Four Fixed and 2 Adjustable)

Precision Triple/Dual Input UV, OV

8-Lead SOT-23 and DDB Packages

2 ADJ Inputs

Octal Positive/Negative Voltage Monitor

16-Lead SSOP and 5mm × 3mm DFN Packages

8-Lead TSOT and 3mm × 2mm DFN Packages

10-Lead MSOP and 3mm × 3mm DFN Packages

16-Lead SSOP and 5mm × 3mm DFN Packages

10-Lead MSOP and 3mm × 2mm DFN-10 Packages

Manual Reset, 10-Lead MSOP and 3mm × 2mm DFN-10 Packages

Single UV/OV Voltage Monitor, Adjustable UV and OV

Dual UV/OV Voltage Monitor

Qual UV/OV Positive/Negative Voltage Monitor

Single Supervisor with 27 Selectable Thresholds

Single Supervisor with 9 Selectable Thresholds

29178fb

LT 0208 REV B • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

16

●

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


型号：	LTC2917HDDB-A1#PBF
厂家：	Linear
描述：	LTC2917 - Voltage Supervisor with 27 Selectable Thresholds and Watchdog Timer; Package: DFN; Pins: 10; Temperature Range: -40°C to 125°C 光电二极管
文件：	总16页 (文件大小：155K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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