LTC2901-2IGN_技术文档

Final Electrical Specifications

LTC2901

Programmable Quad Supply

Monitor with Adjustable Reset

and Watchdog Timers

June 2002

U

FEATURES

DESCRIPTIO

Simultaneously Monitors Four Supplies

The LTC^®2901 is a programmable supply monitor for

systemswithuptofoursupplyvoltages. Oneof16preset

or adjustable voltage monitor combinations can be se-

lected using an external resistor divider connected to the

program pin. The preset voltage thresholds are accurate

to 1.5% over temperature. All four voltage comparator

outputs are connected to separate pins for individual

supply monitoring.

■

16 User Selectable Combinations of 5V, 3.3V, 3V,

2.5V, 1.8V, 1.5V and/or ±Adjustable Voltage

Thresholds

■

Guaranteed Threshold Accuracy: ±1.5% of

Monitored Voltage Over Temperature

■

Low Supply Current: 43µA Typ

■

Adjustable Reset Time

■

Adjustable Watchdog Time

The reset and watchdog delay times are adjustable using

externalcapacitors.Tightvoltagethresholdaccuracyand

glitch immunity ensure reliable reset operation without

falsetriggering.TheRSToutputisguaranteedtobeinthe

correctstateforV_CCdownto1V.TheLTC2901-1features

an open-drain RST output, while the LTC2901-2 has a

push-pull RST output.

■

Open-Drain RST Output (LTC2901-1)

■

Push-Pull RST Output (LTC2901-2)

■

Individual Nondelayed Monitor Output for Each Supply

■

Power Supply Glitch Immunity

^{Guaranteed RST}U^{for V}

■

_CC≥ 1V

APPLICATIO S

■

The 43µA supply current makes the LTC2901 ideal for

power conscious systems and it may be configured to

monitor less than four inputs. The parts are available in

the 16-lead narrow SSOP package.

Desktop and Notebook Computers

■

Multivoltage Systems

Telecom Equipment

■

Portable Battery-Powered Equipment

■

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

Network Servers

U

TYPICAL APPLICATIO

Quadruple Supply Monitor (5V, 3.3V, 2.5V, 1.8V)

5V

3.3V

2.5V

1.8V

DC/DC

CONVERTER

SYSTEM

LOGIC

3

13

V4

R3

10k

POWER

GOOD

V3

V1

4

2

COMP1

COMP2

COMP3

COMP4

WDI

16

1

LTC2901-2

14

V2

V

15

8

C1

0.1µF

C2

0.1µF

12

11

REF

7

WDO

R1

59k

1%

6

V

RST

PG

GND CRT

10

2901 TA01

CWT

9

R2

40.2k

1%

5

t

= 216ms

= 940ms

RST

WD

C

WT

47nF

RT

47nF

2901is sn2901

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 represen-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

1

LTC2901

W W

U W

U

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

(Notes 1, 2, 3)

V1, V2, V3, V4, V_PG..................................... –0.3V to 7V

RST (LTC2901-1)........................................ –0.3V to 7V

RST (LTC2901-2).......................... –0.3V to (V2 + 0.3V)

COMPX ....................................................... –0.3V to 7V

CWT, WDO.................................................. –0.3V to 7V

ORDER PART

TOP VIEW

NUMBER

COMP3

COMP1

V3

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

COMP2

COMP4

V2

LTC2901-1CGN

LTC2901-2CGN

LTC2901-1IGN

LTC2901-2IGN

V1

V4

V

_REF, CRT, WDI ............................ –0.3V to (V_CC+ 0.3V)

CRT

V

REF

Reference Load Current (I_VREF) ............................ ±1mA

V4 Input Current (–ADJ Mode)............................. –1mA

Operating Temperature Range

LTC2901-1C/LTC2901-2C ....................... 0°C to 70°C

LTC2901-1I/LTC2901-2I .................... –40°C to 85°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)................... 300°C

RST

V

PG

GN16 PART MARKING

WDO

WDI

GND

CWT

29011

29012

29011I

29012I

GN PACKAGE

16-LEAD PLASTIC SSOP

T_JMAX= 125°C, θ_JA= 130°C/W

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_CC= 5V, unless otherwise noted. (Note 3)

SYMBOL

PARAMETER

CONDITIONS

MIN

4.600

3.036

2.760

2.300

1.656

1.380

0.492

–18

TYP

4.675

3.086

2.805

2.338

1.683

1.403

0.500

0

MAX

4.750

3.135

2.850

2.375

1.710

1.425

0.508

18

UNITS

V

5V, 5% Reset Threshold

3.3V, 5% Reset Threshold

3V, 5% Reset Threshold

2.5V, 5% Reset Threshold

1.8V, 5% Reset Threshold

1.5V, 5% Reset Threshold

ADJ Reset Threshold

V1 Input Threshold

●

V

RT50

RT33

RT30

RT25

RT18

RT15

RTA

V1, V2 Input Threshold

V2 Input Threshold

V

V2, V3 Input Threshold

V3, V4 Input Threshold

V4 Input Threshold

V

–ADJ Reset Threshold

Minimum Internal Operating Voltage

mV

V

RTAN

CC

RST, COMPX in Correct Logic State;

1

V

Rising Prior to Program

CC

PG

V

Minimum Required for Programming

Minimum Required for Comparators

Reference Voltage

Rising

Falling

●

2.42

2.32

V

CCMINP

CCMINC

REF

≥ 2.3V, I

= ±1mA, C ≤ 1000pF

1.192

0

1.210

1.228

V

VREF

CCMINP

REF

Programming Voltage Range

≥ V

V

PG

REF

I

V

Input Current

= V

REF

±20

75

2

nA

µA

VPG

V1

PG

V1 Input Current

V2 Input Current

V3 Input Current

V1 = 5V, I

V2 = 3.3V

V3 = 2.5V

= 12µA, (Note 4)

43

0.8

VREF

V2

●

0.52

1.2

15

µA

nA

V3

V3 = 0.55V (ADJ Mode)

–15

I

V4 Input Current

V4 = 1.8V

V4 = 0.55V (ADJ Mode)

V4 = –0.05V (–ADJ Mode)

●

0.34

0.8

15

µA

nA

V4

–15

I

t

CRT Pull-Up Current

CRT Pull-Down Current

Reset Time-Out Period

V

C

= 0V

●

–1.4

10

–2

20

–2.6

30

µA

CRT(UP)

CRT(DN)

RST

CRT

= 1.3V

= 1500pF

4.9

6.9

8.9

ms

RT

2901is sn2901

2

LTC2901

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_CC= 5V, unless otherwise noted. (Note 3)

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

t

V Undervoltage Detect to RST or COMPX

X

V Less Than Reset Threshold V

by More Than 1%

150

µs

UV

X

RTX

V

Output Voltage Low RST, COMPX

I

= 2.5mA; V1 = 3V, V2 = 3V;

SINK

●

0.15

0.4

V

OL

V3, V4 = 0V; V = 0V

PG

I

= 100µA; V2 = 1V; V1, V3, V4 = 0V

= 100µA; V1 = 1V; V2, V3, V4 = 0V

●

0.05

0.3

V

SINK

V

Output Voltage High RST, WDO, COMPX

(Note 5)

I

= 1µA

●

V2 – 1

V

OH

OL

OH

SOURCE

Output Voltage Low WDO

I

= 2.5mA; V1 = 5V, V2 = 3.3V;

0.15

0.4

SINK

V3, V4 = 1V; V = 0V

PG

Output Voltage High RST (LTC2901-2)

(Note 6)

I

= 200µA

0.8 • V2

SOURCE

I

t

CWT Pull-Up Current

V

C

V

= 0V

●

–1.4

10

–2

20

30

–2.6

30

µA

ms

V

CWT(UP)

CWT(DN)

WD

CWT

CWT Pull-Down Current

Watchdog Time-Out Period

WDI Input Threshold High

WDI Input Threshold Low

WDI Input Pulse Width

WDI Pull-Up Current

= 1.3V

= 1500pF

20

40

WT

CC

V

= 3.3V to 5.5V

= 3.3V

1.6

IH

IL

0.4

V

CC

t

I

150

ns

µA

WP

WDI

CC

= 0V

–10

WDI

Note 1: Absolute Maximum Ratings are those values beyond which the life of

a device may be impaired.

Note 5: The output pins RST, WDO and COMPX have internal pull-ups to V2

of typically 6µA. However, external pull-up resistors may be used when faster

rise times are required or for V voltages greater than V2.

OH

Note 2: All voltage values are with respect to GND.

Note 6: The push-pull RST output pin on the LTC2901-2 is actively pulled up

to V2.

Note 3: The greater of V1, V2 is the internal supply voltage (V ).

CC

Note 4: Under static no-fault conditions, V1 will necessarily supply quiescent

current. If at any time V2 is larger than V1, V2 must be capable of supplying

the quiescent current, programming (transient) current and reference load

current.

2901is sn2901

3

LTC2901

TEST CIRCUITS

RST, WDO

LTC2901-1

LTC2901-2

RST

OR COMPX

V1

V2

V3

V4

V1

V2

V3

V4

V1

V2

V3

V4

I

SINK

2.5mA,

RST, WDO

OR COMPX

I

SOURCE

1µA

SOURCE

200µA

100µA

2901 F01

2901 F02

2901 F03

Figure 1. RST, WDO, COMPX V_OHTest

Figure 2. RST, WDO, COMPX V_OLTest

Figure 3. Active Pull-Up RST V_OHTest

W U

W

TI I G DIAGRA S

V_XMonitor Timing

V

RTX

V

X

t

RST

t

UV

1.5V

RST

2901 TD

COMPX

Watchdog Timing

t

RST

WDI

t

WP

WDO

t

WD

2901 TD2

2901is sn2901

4

LTC2901

U W

TYPICAL PERFOR A CE CHARACTERISTICS

5V Threshold Voltage

vs Temperature

3.3V Threshold Voltage

vs Temperature

3V Threshold Voltage

vs Temperature

4.750

4.725

4.700

4.675

4.650

4.625

4.600

3.135

3.125

3.115

3.105

3.095

3.085

3.075

3.065

3.055

3.045

3.035

2.850

2.840

2.830

2.820

2.810

2.800

2.790

2.780

2.770

2.760

20

TEMPERATURE (°C)

–60 –40 –20

0

40 60 80 100

–60

20

TEMPERATURE (°C)

60 80

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

–40 –20

0

40

100

2901 G01

2901 G02

2901 G03

2.5V Threshold Voltage

vs Temperature

1.8V Threshold Voltage

vs Temperature

1.5V Threshold Voltage

vs Temperature

1.425

1.420

1.415

1.410

1.405

1.400

1.395

1.390

1.385

1.380

2.3750

2.3675

2.3600

2.3525

2.3450

2.3375

2.3300

2.3225

2.3150

2.3075

2.3000

1.710

1.705

1.700

1.695

1.690

1.685

1.680

1.675

1.670

1.665

1.660

1.655

40 60

–60 –40 –20

TEMPERATURE (°C)

80

0

20

80 100

–60

20

TEMPERATURE (°C)

60

–40 –20

0

40

100

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

2901 G05

2901 G06

2901 G04

ADJ Threshold Voltage

vs Temperature

–ADJ Threshold Voltage

vs Temperature

V_REFvs Temperature

0.508

0.506

0.504

0.502

0.500

0.498

0.496

0.494

0.492

0.018

0.012

0.006

0

1.228

1.222

1.216

1.210

1.204

1.198

1.192

–0.006

–0.012

–0.018

–60

20

TEMPERATURE (°C)

60 80

–60

20

TEMPERATURE (°C)

60 80

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

–40 –20

0

40

100

–40 –20

0

40

100

2901 G07

2901 G08

2901 G23

2901is sn2901

5

LTC2901

TYPICAL PERFOR A CE CHARACTERISTICS

U W

I_V1vs Temperature

I_V2vs Temperature

I_V3vs Temperature

100

90

80

70

60

50

40

30

20

10

0

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

V1 = 5V

V2 = 3.3V

V3 = 2.5V

V4 = 1.8V

V2 = 3.3V

V3 = 2.5V

V4 = 1.8V

V2 = 3.3V

V3 = 2.5V

V4 = 1.8V

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

80

–60

20

TEMPERATURE (°C)

60

–40 –20

0

40

100

2901 G09

2901 G10

2901 G11

Typical Transient Duration

vs Comparator Overdrive (V1, V2)

Typical Transient Duration

vs Comparator Overdrive (V3, V4)

I_V4vs Temperature

220

200

180

160

140

120

100

80

450

400

350

300

250

200

150

100

50

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

T

= 25°C

T

= 25°C

A

V1 = 5V

A

V2 = 3.3V

V3 = 2.5V

V4 = 1.8V

RESET OCCURS

ABOVE CURVE

RESET OCCURS

ABOVE CURVE

60

40

20

0

0.1

1

10

100

0.1

1

10

100

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V

)

RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V

)

RTX

2901 G13

2901 G22

2901 G12

RST Output Voltage

vs V1, V_PG= 0V

Watchdog Time-Out Period

vs Temperature

Reset Time-Out Period

vs Temperature

8.9

38

5

4

3

2

1

0

C

= 1500pF

C

= 1500pF

RT

V1 = V2 = V3 = V4

10k PULL-UP FROM RST TO V1

WT

(SILVER MICA)

8.4

7.9

7.4

6.9

6.4

5.9

5.4

4.9

36

34

32

30

28

26

24

22

T

= 25°C

A

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

V1 (V)

–60 –40 –20

0

20 40 60 80 100

–60

20

TEMPERATURE (°C)

60 80

–40 –20

0

40

100

TEMPERATURE (°C)

2901 G14

2901 G15

2901 G16

2901is sn2901

6

LTC2901

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Reset Time-Out Period

vs Capacitance

Watchdog Time-Out Period

vs Capacitance

RST, WDO, COMPX I_SINK

vs Supply Voltage

100

10

1

10

9

8

7

6

5

4

3

2

1

0

T

= 25°C

T = 25°C

A

T

= 25°C

A

V

= 0.4V

OL

1

100m

10m

1m

100m

10m

1m

V

= 0.2V

OL

100µ

100n

10p

100p

1n

10n

1µ

10p

100p

1n

10n

1µ

0

1

3

4

5

6

2

C

(FARAD)

C

(FARAD)

RT

V1 OR V2 (V)

WT

2901 G17

2901 G18

2901 G19

RST High Level Output Voltage

vs Output Source Current

(LTC2901-2)

COMPX and WDO Pull-Up

Current vs V2 (COMPX and

WDO Held at 0V)

RST, WDO, COMPX Voltage

Output Low vs Output Sink Current

20

18

16

14

12

10

8

3.0

2.5

2.0

1.5

1.0

0.5

0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

T

= 25°C

V1 = 5V

V2 = 3V

V3 = 2.5V

V4 = 1V

A

V2 = 3V

25°C

V1 = 5V

85°C

–40°C

25°C

6

85°C

4

2

0

1

3

4

4.5

0

10 20 30 40 50 60 70 80 90

(mA)

0

0.5

1

1.5

(mA)

2

2.5

1.5

2

2.5

3.5

5

V2 (V)

I

SOURCE

SINK

2901 G24

2901 G20

2901 G21

COMPX Propagation Delay vs Input

Overdrive Above Threshold

RST Pull-Up Current vs V2

(LTC2901-1)

RST Pull-Up Current vs V2

(LTC2901-2)

6

5

4

3

2

1

0

250

200

150

100

50

20

18

16

14

12

10

8

T

= 25°C

T

= 25°C

A

T

= 25°C

A

V

RT33

V

RT30

6

RT33

V1, V2

V3, V4

V

RT30

V

RT25

4

V

RT25

2

0

1000

2

2.5

3

3.5

4

4.5

5

2

2.5

3

3.5

4

4.5

5

10

100

V2 (V)

INPUT OVERDRIVE ABOVE THRESHOLD (mV)

2901 G25

2901 G26

2901 G27

2901is sn2901

7

LTC2901

U

PI FU CTIO S

COMP3 (Pin 1): Comparator Output 3. Nondelayed, active

high logic output with weak pull-up to V2. Pulls high when

V3 is above reset threshold. May be pulled greater than V2

using external pull-up.

CWT (Pin 9): Watchdog Time-Out Programming Pin.

Attach a capacitor (C_WT) between CWT and GND to set a

watchdog time-out period of 20ms/nF. Leaving the pin

open generates a minimum time-out of approximately

200µs. A 47nF capacitor will generate a 940ms watchdog

time-out period.

COMP1 (Pin 2): Comparator Output 1. Nondelayed, active

high logic output with weak pull-up to V2. Pulls high when

V1 is above reset threshold. May be pulled greater than V2

using external pull-up.

GND (Pin 10): Ground.

V_PG(Pin 11): Voltage Threshold Combination Select

Input. Connect to an external 1% resistive divider be-

tween V_REFand GND to select 1 of 16 combinations of

presetand/or±adjustablevoltagethresholds(seeTable 1).

Do not add capacitance on the V_PGpin.

V3 (Pin 3): Voltage Input 3. Select from 2.5V, 1.8V, 1.5V

or ADJ. See Table 1 for details.

V1 (Pin 4): Voltage Input 1. Select from 5V or 3.3V. See

Table 1 for details. The greater of (V1, V2) is also V_CCfor

the chip. Bypass this pin to ground with a 0.1µF (or

greater) capacitor.

V_REF(Pin 12): Buffered Reference Voltage. A 1.210V

nominal reference used for programming voltage (V_PG)

and for the offset of negative adjustable applications. The

buffered reference can source and sink up to 1mA. The

reference can drive a bypass capacitor of up to 1000pF

without oscillation.

CRT (Pin 5): Reset Delay Time Programming Pin. Attach

anexternalcapacitor(C_RT)toGNDtosetaresetdelaytime

of 4.6ms/nF. Leaving the pin open generates a minimum

delay of approximately 50µs. A 47nF capacitor will gener-

ate a 216ms reset delay time.

V4 (Pin 13): Voltage Input 4. Select from 1.8V, 1.5V, ADJ

or –ADJ. See Table 1 for details.

RST (Pin 6): Reset Logic Output. Active low with weak

pull-up to V2 (LTC2901-1) or active pull-up to V2

(LTC2901-2). Pulls low when any voltage input is below

the reset threshold and held low for programmed delay

time after all voltage inputs are above threshold. May be

pulled above V2 using an external pull-up (LTC2901-1

only).

V2 (Pin 14): Voltage Input 2. Select from 3.3V, 3V or 2.5V.

See Table 1 for details. The greater of (V1, V2) is also V_CC

forchip.Bypassthispintogroundwitha0.1µF(orgreater)

capacitor. All logic outputs (COMP1, COMP2, COMP3,

COMP4, RST, WDO) are weakly pulled up to V2

(LTC2901-1). RST is actively pulled up to V2 in the

LTC2901-2.

WDO (Pin 7): Watchdog Output. Active low logic output

with weak pull-up to V2. May be pulled greater than V2

using external pull-up. The watchdog output pulls low if

the watchdog timer is allowed to time out and remains low

until set high by the next WDI transistion or anytime RST

is low. The watchdog timer is enabled when RST is high.

COMP4 (Pin 15): Comparator Output 4. Nondelayed,

activehighlogicoutputwithweakpull-uptoV2. Pullshigh

when V4 is above reset threshold. May be pulled greater

than V2 using external pull-up.

COMP2 (Pin 16): Comparator Output 2. Nondelayed,

activehighlogicoutputwithweakpull-uptoV2. Pullshigh

when V2 is above reset threshold. May be pulled greater

than V2 using external pull-up.

WDI (Pin 8): Watchdog Input. A logic input whose rising

or falling edge must occur on this pin (while RST is high)

within the selected watchdog time-out period, prohibiting

a high-to-low transition on the WDO pin. The watchdog

time-out period is set by the value of the capacitor that is

attachedtotheCWTpin.ArisingorfallingedgeontheWDI

pin clears the voltage on the C_WTcapacitor, preventing

WDO from going low. When disabling the watchdog

function, tie CWT to GND.

2901is sn2901

8

LTC2901

W

BLOCK DIAGRA

V1

V2

POWER

DETECT

V

CC

6µA

COMP1

–

V2

2

+

–

+

V1

4

V2

14

COMP2

16

RESISTIVE

DIVIDER

V3

MATRIX

–

+

3

V4

13

GND

10

COMP3

1

–

+

V

PG

A/D

11

BUFFER

V

REF

BANDGAP

REFERENCE

12

COMP4

15

ADJUSTABLE

RESET PULSE

GENERATOR

V

CC

LTC2901-1

V2

2µA

6µA

22µA

RST

6

LTC2901-2

V2

10µA

TRANSITION

DETECT

WATCHDOG

TIMER

V

CC

RST

6

V

CC

V2

2µA

6µA

22µA

WDO

7

5

CRT

8

WDI

C

RT

9

CWT

C

WT

2901 DB-1

2901is sn2901

9

LTC2901

W U U

U

APPLICATIO S I FOR ATIO

R1

1%

Power-Up

LTC2901

12

11

10

V

REF

The greater of V1, V2 is the internal supply voltage (V_CC).

On power-up, V_CCwill power the drive circuits for the RST

andtheCOMPXpins.ThisensuresthattheRSTandCOMPX

outputs will be low as soon as V1 or V2 reaches 1V. The

RST and COMPX outputs will remain low until the part is

programmed.Afterprogramming,ifanyoneoftheV_Xinputs

isbelowitsprogrammedthreshold,RSTwillbealogiclow.

Once all the V_Xinputs rise above their thresholds, an inter-

nal timer is started and RST is released after the pro-

grammed delay time. If V_CC< (V3 – 1) and V_CC< 2.4V, the

V3 input impedance will be low (1kΩ typ).

V

PG

R2

GND

1%

2901 F04

Figure 4. Monitor Programming

150µs during which the voltage on the V_PGpin is sampled

and the monitor is configured to the desired input combi-

nation.DonotaddcapacitancetotheV_PGpin.Immediately

after programming, the comparators are enabled and

supply monitoring will begin.

Supply Monitoring

The LTC2901 is a low power, high accuracy program-

mablequadsupplymonitoringcircuitwithfournondelayed

monitor outputs, a common reset output and a watchdog

timer. Watchdog and reset timing are both adjustable

usingexternalcapacitors.Singlepinprogrammingselects

1 of 16 input voltage monitor combinations. All four

voltage inputs must be above predetermined thresholds

fortheresetnottobeinvoked. TheLTC2901willassertthe

reset and comparator outputs during power-up, power-

down and brownout conditions on any one of the voltage

inputs.

Monitor Programming

The LTC2901 input voltage combination is selected by

placing the recommended resistive divider from V_REFto

GND and connecting the tap point to V_PG, as shown in

Figure 4. Table 1 offers recommended 1% resistor values

forthevariousmodes. ThelastcolumninTable1specifies

optimum V_PG/V_REFratios (±0.01) to be used when pro-

gramming with a ratiometric DAC.

During power-up, once V1 or V2 reaches 2.4V max, the

monitor enters a programming period of approximately

The inverting inputs on the V3 and/or V4 comparators are

setto0.5Vwhenthepositiveadjustablemodesareselected

(Figure 5). The tap point on an external resistive divider,

connected between the positive voltage being sensed and

ground, is connected to the high impedance noninverting

inputs (V3, V4). The trip voltage is calculated from:

Table 1. Voltage Threshold Programming

V

PG

MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ)

V

REF

0

1

5.0

3.3

5.0

3.3

5.0

3.3

2.5

3.3

3.0

2.5

3.3

3.0

ADJ

1.5

2.5

ADJ

1.8

ADJ

–ADJ

ADJ

–ADJ

ADJ

1.8

Open

93.1

86.6

78.7

71.5

66.5

59.0

53.6

47.5

40.2

34.8

28.0

22.1

16.2

9.53

Short

9.53

16.2

22.1

28.0

34.8

40.2

47.5

53.6

59.0

66.5

71.5

78.7

86.6

93.1

Open

0.000

0.094

0.156

0.219

0.281

0.344

0.406

0.469

0.531

0.594

0.656

0.719

0.781

0.844

0.906

1.000

2

3

R3

R4

4

V_TRIP= 0.5V 1+

5

6

Inthenegativeadjustablemode, thenoninvertinginputon

the V4 comparator is connected to ground (Figure 6). The

tap point on an external resistive divider, connected be-

tween the negative voltage being sensed and the V_REFpin,

is connected to the high impedance inverting input (V4).

7

1.5

8

ADJ

1.5

9

10

11

12

13

14

15

ADJ

–ADJ

ADJ

V

_REFprovides the necessary level shift required to operate

at ground. The trip voltage is calculated from:

R3

R4

V_TRIP= –V_REF

; V_REF= 1.210V Nominal

2901is sn2901

10

LTC2901

W U U

APPLICATIO S I FOR ATIO

U

V

TRIP

Table 2. Suggested 1% Resistor Values for the ADJ Inputs

LTC2901

V

(V)

V

(V)

TRIP

R3 (kΩ)

2150

1780

1400

1300

1020

845

R4 (kΩ)

100

R3

SUPPLY

1%

12

11.25

9.4

V3 OR V4

+

R4

1%

10

8

7.5

–

7.5

6

7

+

0.5V

5.6

–

5

4.725

3.055

2.82

2.325

1.685

1.410

1.120

0.933

0.840

2901 F05

3.3

3

511

464

Figure 5. Setting the Positive Adjustable Trip Point

2.5

1.8

1.5

1.2

1

365

237

12

LTC2901

V

REF

182

R4

1%

13 V4

124

–

R3

1%

86.6

68.1

0.9

+

V

TRIP

Table 3. Suggested 1% Resistor Values for the –ADJ Input

2901 F06

V

(V)

V

(V)

TRIP

R3 (kΩ)

187

R4 (kΩ)

121

SUPPLY

Figure 6. Setting the Negative Adjustable Trip Point

–2

–1.87

–4.64

–4.87

–9.31

–5

–5.2

–10

–12

464

121

In a negative adjustable application, the minimum value

forR4islimitedbythesourcingcapabilityofV_REF(±1mA).

With no other load on V_REF, R4 (minimum) is:

487

121

931

121

–11.30

1130

121

1.21V ÷ 1mA = 1.21kΩ.

Tables 2 and 3 offer suggested 1% resistor values for

various adjustable applications.

Monitor Output Rise and Fall Time Estimation

All of the outputs (RST, COMPX, WDO) have strong pull-

down capability. If the external load capacitance (C_LOAD

for a particular output is known, output fall time (10% to

90%) is estimated using:

Although all four supply monitor comparators have built-

in glitch immunity, bypass capacitors on V1 and V2 are

recommended because the greater of V1 or V2 is also the

V_CCfor the chip. Filter capacitors on the V3 and V4 inputs

are allowed.

)

t

_FALL≈ 2.2 • R_PD• C_LOAD

where R_PDis the on-resistance of the internal pull-down

transistor. The typical performance curve (V_OLvs I_SINK

Power-Down

)

demonstrates that the pull-down current is somewhat

linear versus output voltage. Using the 25°C curve, R_PDis

estimated to be approximately 40Ω. Assuming a 150pF

load capacitance, the fall time is about 13.2ns.

On power-down, once any of the V_Xinputs drop below

their threshold, RST and COMPX are held at a logic low.

A logic low of 0.4V is guaranteed until both V1 and V2

drop below 1V. If the bandgap reference becomes invalid

(V_CC< 2V typ), the part will reprogram once V_CCrises

above 2.4V max.

Although the outputs are considered to be “open-drain,”

theydohaveaweakpull-upcapability(seeCOMPXorRST

2901is sn2901

11

LTC2901

W U U

U

APPLICATIO S I FOR ATIO

Selecting the Reset Timing Capacitor

Pull-Up Current vs V2 curve). Output rise time (10% to

90%) is estimated using:

The reset time-out period is adjustable in order to accom-

modate a variety of microprocessor applications. The

reset time-out period, t_RST, is adjusted by connecting a

capacitor, C_RT, between the CRT pin and ground. The

value of this capacitor is determined by:

t_RISE≈ 2.2 • R_PU• C_LOAD

where R_PUis the on-resistance of the pull-up transistor.

The on-resistance as a function of the V2 voltage at room

temperature is estimated using:

C

_RT= t_RST• 217.4 • 10^–9

6 •10⁵

V2 – 1

R_PU

=

Ω

withC_RTinFaradsandt_RSTinseconds. TheC_RTvalueper

millisecond of delay can also be expressed as C_RT/ms

217.4 (pF/ms).

=

with V2 = 3.3V, R_PUis about 260k. Using 150pF for load

capacitance, the rise time is 86µs. If the output needs to

pull up faster and/or to a higher voltage, a smaller

external pull-up resistor may be used. Using a 10k pull-

up resistor, the rise time is reduced to 3.3µs for a 150pF

load capacitance.

Leaving the CRT pin unconnected will generate a mini-

mum reset time-out of approximately 50µs. Maximum

reset time-out is limited by the largest available low

leakagecapacitor. Theaccuracyofthetime-outperiodwill

be affected by capacitor leakage (the nominal charging

current is 2µA) and capacitor tolerance. A low leakage

ceramic capacitor is recommended.

The LTC2901-2 has an active pull-up to V2 on the RST

output. The typical performance curve (RST Pull-Up Cur-

rent vs V2 curve) demonstrates that the pull-up current is

somewhat linear versus the V2 voltage and R_PUis esti-

mated to be approximately 625Ω. A 150pF load capaci-

tance makes the rise time about 206ns.

Selecting the Watchdog Timing Capacitor

The watchdog time-out period is adjustable and can be

optimized for software execution. The watchdog time-out

period, t_WD, is adjusted by connecting a capacitor, C_WT

between the CWT pin and ground. Given a specified

watchdogtime-outperiod, thecapacitorisdeterminedby:

,

Watchdog Timer

ThewatchdogcircuittypicallymonitorsaµP’sactivity.The

µP is required to change the logic state of the WDI pin on

a periodic basis in order to clear the watchdog timer and

preventtheWDOpinfromgoinglow.WheneverRSTislow,

the watchdog timer is cleared and WDO is set high. The

watchdogtimerisstartedwhenRSTpullshigh.Subsequent

edgesreceivedontheWDIpinwillclearthewatchdogtimer.

Thetimerwillcontinuetorununtilthewatchdogtimertimes

out. Once the watchdog timer times out, internal circuitry

will bring the WDO pin low. WDO will remain low and the

watchdog timer will remain cleared until the next edge is

received on the WDI pin or until RST goes low.

C_WT= t_WD• 50 • 10^–9

with C_WTin Farads and t_WDin seconds. The C_WTvalue per

millisecond of delay can also be expressed as C_WT/ms

50 (pF/ms).

=

Leaving the CWT pin unconnected will generate a mini-

mum watchdog time-out of approximately 200µs. Maxi-

mum time-out is limited by the largest available low

leakagecapacitor. Theaccuracyofthetime-outperiodwill

be affected by capacitor leakage (the nominal charging

current is 2µA) and capacitor tolerance. A low leakage

ceramic capacitor is recommended.

Todisablethewatchdogtimer,simplygroundtheCWTpin

(Pin9).WithCWTheldatground,anyreseteventwillforce

WDOhighindefinitely.ItissafetoleavetheWDIpin(Pin 8)

unconnectedbecausetheweakinternalpull-up(10µAtyp)

will pull WDI high. Tying WDI to V1 or ground is also

allowed, but grounding the WDI pin will force the pull-up

current to be drawn continuously.

Monitoring Power Supply Controller Activity

Figure 7 demonstrates how the LTC2901 can be used to

monitor switcher activity. The monitor is configured to

supervise 3.3V, 2.5V, 1.8V and one adjustable input.

2901is sn2901

12

LTC2901

W U U

APPLICATIO S I FOR ATIO

U

Because 2.5V does not exist in this application, the V2

input is tied to the V1 (3.3V) input. The feedback voltage

on the LTC1772 (0.8V typ) is monitored with the adjust-

able input (V4). The RST pin will go high 216ms

(C_RT= 47nF) after the 3.3V and 1.8V supplies and the

feedback voltage are above threshold. Individual input

status is available at the COMPX pins.

unconnected, the watchdog time-out is approximately

200µs. At low load currents on the 1.8V supply, the

LTC1772 will go into Burst Mode^®operation. With an

open-ciruit load, the duty cycle at the gate of M1 will drop,

and the pulse spacing will exceed the watchdog time-out

period. The WDO pin will go low indicating the low load

condition. The WDO pin will return high on the next pulse

to the gate of M1. The WDO pin will remain high if the load

is restored.

While the voltage monitors can detect low voltage or

shorted inputs, the watchdog circuit can be used to detect

an open circuit to the primary load. With the CWT pin

Burst Mode is a registered trademark of Linear Technology Corporation.

V

IN

LTC2901-2

3.3V

C1

10µF

10V

R5

4

14

3

2

3.3V MONITOR

V1

COMP1

COMP2

COMP3

COMP4

RST

0.15Ω

16

1

V2

LTC1772

PGATE

1

2

3

6

5

4

1.8V MONITOR

L1

10µH

V3

M1

I

TH

13

8

15

6

R6

V

1.8V

0.5A

OUT

FEEDBACK MONITOR

COMMON RESET OUT

LOW LOAD INDICATOR

V4

GND

V

IN

–

10k

+

C2

47µF

6V

WDI

V

SENSE

C3

220pF

FB

D1

R3

12

11

10

7

V

WDO

100k

REF

R1

28k

1%

5

V

CRT

PG

9

C1: TAIYO YUDEN CERAMIC LMK325BJ106K-T

C2: SANYO POSCAP 6TPA47M

D1: MOTOROLA MBRM120T3

L1: COILTRONICS UP1B-100

M1: Si3443DV

GND

CWT

R4

80.6k

R2

71.5k

1%

C

RT

47nF

R5: DALE 0.25W

2901 F07

Figure 7. Monitor Input, Output, Feedback Voltage and Low Load Conditions on DC/DC Controller

U

TYPICAL APPLICATIO S

Quad Supply Monitor with Watchdog Timer Disabled

5V, 3V, 1.8V, 12V (ADJ)

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

COMP3 COMP2

COMP1 COMP4

R3

2.15M

1%

1.8V

5V

V3

V2

V4

3V

LTC2901

V1

12V

V

TRIP

= 11.25V

CRT

RST

V

REF

SYSTEM

RESET

R4

100k

1%

V

PG

WDO

WDI

GND

CWT

C

RT

2901 TA02

2901is sn2901

13

LTC2901

TYPICAL APPLICATIO S

U

5V, –5V Monitor with Watchdog Timer Disabled and Unused

V2, V3 Inputs Pulled Above Trip Thresholds

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

COMP3 COMP2

COMP1 COMP4

R3

464k

1%

V3

V2

V4

5V

LTC2901

V1

–5V

V

TRIP

= –4.64V

CRT

RST

V

REF

R1

16.2k

1%

R4

121k

1%

SYSTEM

RESET

V

PG

WDO

WDI

GND

CWT

C

RT

R2

86.6k

1%

2901 TA03

Quad Supply Monitor with LED Undervoltage Indicators

5V, 3.3V, 2.5V, 1.5V

R

L4

1k

L1

L3

L2

1k

LED

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

COMP3 COMP2

COMP1 COMP4

2.5V

3.3V

1.5V

V3

V2

V4

5V

LTC2901

V1

CRT

RST

V

REF

R1

SYSTEM RESET

WATCHDOG STATUS

WDI

V

PG

53.6k

1%

WDO

WDI

GND

CWT

R2

47.5k

1%

C

WT

RT

2901 TA04

2901is sn2901

14

LTC2901

U

PACKAGE DESCRIPTIO

GN Package

16-Lead Plastic SSOP (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1641)

0.189 – 0.196*

(4.801 – 4.978)

0.009

(0.229)

REF

16 15 14 13 12 11 10 9

0.229 – 0.244

(5.817 – 6.198)

0.150 – 0.157**

(3.810 – 3.988)

1

2

3

4

5

6

7

8

0.015 ± 0.004

(0.38 ± 0.10)

× 45°

0.053 – 0.068

(1.351 – 1.727)

0.004 – 0.0098

(0.102 – 0.249)

0.007 – 0.0098

(0.178 – 0.249)

0° – 8° TYP

0.016 – 0.050

(0.406 – 1.270)

0.0250

(0.635)

BSC

0.008 – 0.012

(0.203 – 0.305)

* DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD

FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

GN16 (SSOP) 1098

2901is sn2901

15

LTC2901

U

TYPICAL APPLICATIO

Monitor Seven Supplies (12V, 5V, 3.3V, 2.5V, 1.8V, –2V, –5.2V) with

Sequenced Reset and AC Present Indication

5V

12V

10k

5V

AC/DC

DC/DC

3.3V

2.5V

1.8V

–2V

–5.2V

LTC2901-1

4

14

3

2

4

14

3

2

5V MONITOR

V1

COMP1

COMP2

COMP3

COMP4

RST

V1

COMP1

COMP2

COMP3

COMP4

RST

CONVERTERS

16

1

16

1

3.3V

1.8V

3.3V MONITOR

1.8V MONITOR

–5.2V MONITOR

2.5V MONITOR

12V MONITOR

–2V MONITOR

COMMON RESET OUT

AC PRESENT

2.5V

V2

V3

13

8

15

6

13

8

15

6

V4

WDI

120V AC

12

11

10

7

12

11

10

7

12V

V

WDO

V

WDO

REF

PG

REF

PG

LOW

5

121k 16.2k

1% 1%

2.15M

1%

121k 78.7k

1% 1%

VOLTAGE

CRT

SECONDARY

9

GND

CWT

GND

CWT

487k 86.6k

1% 1%

100k

1%

187k 22.1k

1% 1%

C

RT2

47nF

RT1

WT

680pF

100k

47nF

2901 TA05

–5.2V

–2V

1N4148

100k

t

+ t

= 432ms

Q1

2N3904

RST1 RST2

WD

= 13.6ms

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

LTC690

5V Supply Monitor, Watchdog Timer and Battery Backup

4.65V Threshold

2.9V Threshold

4.65V Threshold

LTC694-3.3

LTC699

3.3V Supply Monitor, Watchdog Timer and Battery Backup

5V Supply Monitor and Watchdog Timer

LTC1232

5V Supply Monitor, Watchdog Timer and Push-Button Reset

Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ

4.37V/4.62V Threshold

4.725V, 3.118V, 1V Thresholds (±0.75%)

LTC1326

LTC1326-2.5

LTC1536

Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and AJD 2.363V, 3.118V, 1V Thresholds (±0.75%)

Precision Triple Supply Monitor for PCI Applications

Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ

Micropower Triple Supply Monitor for 5V, 3.3V and ADJ

Micropower Triple Supply Monitors with Open-Drain Reset

Meets PCI t

Timing Specifications

FAIL

LTC1726-2.5

LTC1726-5

LTC1727-2.5/LTC1727-5

Adjustable RESET and Watchdog Time-Outs

Individual Monitor Outputs in MSOP

5-Lead SOT-23 Package

LTC1728-1.8/LTC1728-3.3 Micropower Triple Supply Monitor with Open-Drain Reset

LTC1728-2.5/LTC1728-5

LTC1985-1.8

Micropower Triple Supply Monitors with Open-Drain Reset

Micropower Triple Supply Monitor with Push-Pull Reset Output

5-Lead SOT-23 Package

2901is sn2901

LT/TP 0602 1.5K • PRINTED IN USA

16 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

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

LINEAR TECHNOLOGY CORPORATION 2002


型号：	LTC2901-2IGN
厂家：	Linear
描述：	Programmable Quad Supply Monitor with Adjustable Reset and Watchdog Timers 可编程四通道电源监视器具有可调复位和看门狗定时器监视器
文件：	总16页 (文件大小：212K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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