LTC1985ES5-1.8#PBF - Linear Technology

LTC1985-1.8

APPLICATIO S

DESCRIPTIO

FEATURES

TYPICAL APPLICATION

Micropower Precision

Triple Supply Monitor

with Push-Pull Reset Output

in a 5-Lead SOT-23 Package

■

Monitors Three Inputs Simultaneously:

3V, 1.8V and Adjustable

■

±1.5% Threshold Accuracy Over Temperature

■

Very Low Supply Current: 10µA Typ

■

200ms Reset Time Delay

■

Power Supply Glitch Immunity

■

Guaranteed RESET for V

CC3

≥ 1V or V

CC18

≥ 1V

■

3V Active-Low Push-Pull Reset Output

■

5-Lead SOT-23 Package

The LTC

1985-1.8 is a triple supply monitor intended for

systems with multiple supply voltages. The reset output

remains low until all three supplies have been in compli-

ance for 200ms. Tight 1.5% accuracy specifications and

glitch immunity ensure reliable reset operation without

false triggering.

The RST output is guaranteed to be in the correct state for

CC18

or V

CC3

down to 1V. The LTC1985 may also be

configured to monitor any one or two V

inputs instead

of three, depending on system requirements.

Very low (10µA typical) supply current makes the LTC1985

ideal for power conscious systems.

The LTC1985 is available in a 5-lead SOT-23 package.

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

■

Desktop Computers

■

Notebook Computers

■

Intelligent Instruments

■

Portable Battery-Powered Equipment

■

Network Servers

CC3

CC18

CCA

RST

LTC1985-1.8

GND

1985-1.8 TA01

1.8V

2.5V

0.1µF

130k

100k

DC/DC

CONVERTER SYSTEM

LOGIC

0.1µF

LTC1985-1.8

(Notes 1, 2)

CC3

, V

CC18

, V

CCA

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

RST .......................................... –0.3V to (V

CC3

+ 0.3V)

Operating Temperature Range

(Note 3) ............................................. –40°C to 85°C

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

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

Consult factory for Industrial and Military grade parts.

JMAX

= 125°C, θ

= 250°C/W

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

RT3

Reset Threshold V

CC3

Input Threshold ●2.760 2.805 2.850 V

RT18

Reset Threshold V

CC18

Input Threshold ●1.656 1.683 1.710 V

RTA

Reset Threshold V

CCA

Input Threshold ●0.985 1.000 1.015 V

CCOP

CC3

, V

CC18

Operating Voltage RST in Correct Logic State ●17V

VCC3

CC3

Supply Current V

CC18

> V

CC3

●12 µA

CC18

< V

CC3

, V

CC3

= 3V (Note 4) ●10 20 µA

VCC18

CC18

Supply Current V

CC18

< V

CC3

, V

CC18

= 1.8V (Note 4) ●12 µA

VCCA

CCA

Input Current V

CCA

= 1V ●–15 0 15 nA

RST

Reset Pulse Width RST Low (Note 5) ●140 200 280 ms

Undervoltage Detect to RST V

CC18

, V

CC3

or V

CCA

Less Than Reset (Note 5) 110 µs

Threshold V

by More Than 1%

Output Voltage Low, RST I

SINK

= 2.5mA, V

CC3

= 3V, V

CC18

= 0V ●0.15 0.4 V

SINK

= 100µA, V

CC3

= 1V, V

CC18

= 0V ●0.05 0.3 V

SINK

= 100µA, V

CC3

= 0V, V

CC18

= 1V ●0.05 0.3 V

SINK

= 100µA, V

CC3

= 1V, V

CC18

= 1V ●0.05 0.3 V

Output Voltage High, RST I

SOURCE

= 200µA●0.8V

CC3

The ● denotes specifications which apply over the full operating

temperature range, otherwise specificaitons are at TA = 25°C. VCC3 = 3V, VCC18 = 1.8V, VCCA = VCC3 unless otherwise noted.

ORDER

PART NUMBER

LTC1985ES5-1.8

S5 PART MARKING

ELECTRICAL CHARACTERISTICS

ABSOLUTE AXI U RATI GS

WWWU

PACKAGE/ORDER I FOR ATIO

LTNM

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

of the device may be impaired.

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

Note 3: The LTC1985E is guaranteed to meet specified performance from

0°C to 70°C and is designed, characterized and assured to meet the

extended temperature limits of –40°C to 85°C but are not tested at these

temperatures.

Note 4: Both V

CC3

and V

CC18

can act as the supply depending on which pin

has the greatest potential.

Note 5: Measured from when input passes through the input threshold

voltage (V

RTX

) until RST passes through 1.5V.

RST 1

GND 2

TOP VIEW

S5 PACKAGE

5-LEAD PLASTIC SOT-23

CCA

5 V

CC3

4 V

CC18

LTC1985-1.8

TYPICAL PERFOR A CE CHARACTERISTICS

IVCC18 vs Temperature VCCA Input Current

vs Input Voltage

TEMPERATURE (°C)

–60

0.5

VCC18

(µA)

0.6

0.8

0.9

1.0

1.5

1.2

–20 20 40

1985-18 G02

0.7

1.3

1.4

1.1

–40 0 60 80 100

CC3

= 3V

CCA

= 3V

CC18

= 1.8V

INPUT VOLTAGE (V)

0.80 0.85 0.95 1.05 1.15

INPUT CURRENT (nA)

1.0

1.20

1985-18 G03

–1.0

–2.0

–0.5

–1.5

0.90 11.10

2.0

0.5

1.5

= 25°C

VCCA Threshold Voltage

vs Temperature

Reset Pulse Width

vs Temperature

Typical Transient Duration

vs Comparator Overdrive

VCC3 Threshold Voltage

vs Temperature

IVCC3 vs Temperature

TEMPERATURE (°C)

–60

0.985

CCA

THRESHOLD VOLTAGE, V

RTA

(V)

0.990

0.995

1.000

1.005

–20 20 60 100

1985-18 G04

1.010

1.015

–40 0 40 80

TEMPERATURE (°C)

–60

CC3

THRESHOLD VOLTAGE, V

RT3

(V)

–20 20 40

1985-18 G05

2.845

2.835

2.825

2.815

2.805

2.795

2.785

2.775

2.765 –40 0 60 80 100

RESET COMPARATOR OVERDRIVE VOLTAGE (% OF V

)

0.1

250

TYPICAL TRANSIENT DURATION (µs)

300

350

400

450

1 10 100

1985-18 G07

200

150

100

RESET OCCURS

ABOVE CURVE

= 25°C

TEMPERATURE (°C)

–60 –40

RESET PULSE WIDTH, t

RST

(ms)

220

240

260

1985-18 G08

200

180

–20 20 40 800 100

160

140

280

TEMPERATURE (°C)

–60

VCC3

(µA)

–20 20 40

1985-18 G01

–40 0 60 80 100

VCC18 Threshold Voltage

vs Temperature

TEMPERATURE (°C)

–60

1.650

CC18

THRESHOLD VOLTAGE, V

RT18

(V)

1.660

1.670

1.680

1.690

–20 20 60 100

1985-18 G06

1.700

1.710

–40 0 40 80

CC3

OR V

CC18

(V)

0 0.5

SINK

(mA)

1.0 2.01.5 2.5 3.0

1985-18 • G09

= 25°C

= 0.4V

= 0.2V

ISINK vs Supply Voltage

LTC1985-1.8

RST (Pin 1): Reset Logic Output. Active low, 3V push-

pull output. Asserted when one or all of the supplies are

below trip thresholds and held for 200ms after all sup-

plies become valid.

GND (Pin 2): Ground.

CCA

(Pin 3): 1V Sense, High Impedance Input. If unused

it can be tied to either V

CC3

or V

CC18

PI FU CTIO S

CC18

(Pin 4): 1.8V Sense Input and Power Supply Pin.

This pin is used on the LTC1985 to provide power to the

part when the voltage on V

CC18

is greater than the voltage

on V

CC3

. Bypass to ground with a ≥0.1µF ceramic

capacitor.

CC3

(Pin 5): 3V Sense Input and Power Supply Pin. This

pin provides power to the part when the voltage on V

CC3

is greater than the voltage on V

CC18

. Bypass to ground

with a ≥0.1µF ceramic capacitor.

ISOURCE (mA)

0 0.2 0.4 0.6 1.0 1.4 1.8 2.0 2.2

VOH (V)

3.5

3.0

2.5

2.0

1.5

1.0

0.5

1985-81 G10

0.8 2.4

1.2 1.6

85°C

25°C

–40°C

VCC3 = VCC18 = VCCA = 3.0V

SINK

(mA)

02 68 12

(V)

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

1985-81 G11

414

85°C

25°C

–40°C

CC3

= V

CC18

= 1.8V

CCA

= 0V

SINK

(mA)

(V)

10 20 25 45

1985-81 G12

515 30 35 40

3.0

2.5

2.0

1.5

1.0

0.5

85°C

25°C

–40°C

CC3

= V

CC18

= 3V

CCA

= 0V

RST High Level Output Voltage vs

Output Source Current

TYPICAL PERFOR A CE CHARACTERISTICS

RST Voltage Output Low vs

Output Sink Current RST Voltage Output Low vs

Output Sink Current

LTC1985-1.8

VCC Monitor Timing

RST

1985-18 TD

RTX

CCX

RST 1.5V

TI I G DIAGRA

UWW

200ms

DELAY

INTERNAL

BANDGAP

REFERENCE

POWER

DETECT

200ms PULSE GENERATOR

–

CC3

CC18

CCA

2GND

1985-18 BD

1RST

LTC1985-1.8

CC3

BLOCK DIAGRA

LTC1985-1.8

Supply Monitoring

The LTC1985 is a low power, high accuracy triple supply

monitoring circuit with a single 200ms microprocessor

reset output.

All three V

inputs must be above predetermined thresh-

olds for reset not to be invoked. The LTC1985 will assert

reset during power-up, power-down and brownout condi-

tions on any one or all of the V

inputs.

3V or 1.8V Power Detect

The LTC1985 is powered from the 3V input pin (V

CC3

) or

the 1.8V input pin (V

CC18

), whichever pin has the highest

potential. This ensures the part pulls the RST pin low as

soon as either input pin is ≥1V.

Power-Up

Upon power-up, either the V

CC18

or V

CC3

pin, can power

the part. This ensures that RST will be low when either

CC18

or V

CC3

reaches 1V. As long as any one of the V

inputs is below its predetermined threshold, RST will stay

a logic low. Once all of the V

inputs rise above their

thresholds, an internal timer is started and RST is driven

high after 200ms.

RST is reasserted whenever any one of the V

inputs

drops below its predetermined threshold and remains

asserted until 200ms after all of the V

inputs are above

their thresholds.

Power-Down

On power-down, once any of the V

inputs drop below its

threshold, RST is held at a logic low. A logic low of 0.3V is

guaranteed until both V

CC3

and V

CC18

drop below 1V.

APPLICATIO S I FOR ATIO

WUUU

CC3

CC18

CCA

GND

RST

LTC1985-1.8

1985-18 TA06

1.8V

ADJUSTABLE

SUPPLY

100k

CC3

(V)

RST VOLTAGE (V)

1985-18 TA06b

0123

CC3

= V

CC18

= V

CCA

Resistor on RST Output to Ground Ensures RST Valid to VCC = 0V

Figure 1. Typical Application Showing

Resistor on RST Output to Ground Figure 2. RST Voltage vs VCC3 with

a 100k Resistor on RST to Ground

Override Functions

The V

CCA

pin, if unused, can be tied to either V

CC3

or V

CC18

This is an obvious solution since the trip points for V

CC3

and V

CC18

will always be greater than the trip point for

CCA

. Likewise, the V

CC18

, if unused, can be tied to V

CC3

must always be used. Tying V

CC3

to V

CC18

and

operating off of a 1.8V supply will result in the continuous

assertion of RST.

Ensuring RST Valid for Supply Voltages Under 1V

When the supplies drops below 1V the RST output current

sink capability is drastically reduced. The combination of

stray currents and stray capacitance to signals other than

ground can cause the RST output pin to float around. In a

lot of applications this is not a problem since most

microprocessors and other circuits do not operate with

the supply voltage less than 1V. In applications where the

RST output must be valid down to 0V the addition of a pull-

down resistor from RST to ground will ensure RST is held

low. The circuit in Figure 1 shows an application employ-

ing this technique. The value chosen for the pull-down

resistor (R3) is a trade-off between pull-down strength

and loading of the RST pin. If the value of the resistor is too

large the pin may still float and if the resistor value is too

low it may load down the RST as well as burn excess

supply current, a value of 100k is a good compromise.

LTC1985-1.8

Using VCCA Tied to DC/DC Feedback Divider

TYPICAL APPLICATIO S

CC3

CC18

CCA

GND

RST

LTC1985-1.8

3V SYSTEM RESET

1.8V

22.6k

1985-18 TA05

27.4k

LTC1435

ADJUSTABLE

RESET TRIP

THRESHOLD 2.31V

2.5V

2.26k

OSENSE

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-

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

Dual Supply Monitor (3V Plus Adjustable)

CC3

CC18

CCA

GND

RST

LTC1985-1.8

SYSTEM RESET

R2*

1985-18 TA04

R1*

ADJUSTABLE

SUPPLY

*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL

COMBINATION OF R1 AND R2 ≤ 66.5k

Triple Supply Monitor (3V, 1.8V and Adjustable) Dual Supply Monitor (3V and 1.8V, Defeat VCCA Input)

CC3

CC18

CCA

GND

RST

LTC1985-1.8

3V SYSTEM RESET

1.8V

1985-18 TA03

CC3

CC18

CCA

GND

RST

LTC1985-1.8

3V SYSTEM RESET

*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL

COMBINATION OF R1 AND R2 ≤ 66.5k

1.8V

R2*

R1*

1985-18 TA02

ADJUSTABLE SUPPLY

OR DC/DC FEEDBACK

DIVIDER

LTC1985-1.8

PART NUMBER DESCRIPTION COMMENTS

LTC690 5V Supply Monitor, Watchdog Timer and Battery Backup 4.65V Threshold

LTC694-3.3 3.3V Supply Monitor, Watchdog Timer and Battery Backup 2.9V Threshold

LTC699 5V Supply Monitor and Watchdog Timer 4.65V Threshold

LTC1232 5V Supply Monitor, Watchdog Timer and Push-Button Reset 4.37V/4.62V Threshold

LTC1326 Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ 4.725V, 3.118V, 1V Thresholds (±0.75%)

LTC1326-2.5 Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and ADJ 2.363V, 3.118V, 1V Thresholds (±0.75%)

LTC1536 Precision Triple Supply Monitor for PCI Applications Meets PCI t

FAIL

Timing Specifications

LTC1726-2.5 Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Adjustable RESET and Watchdog Time Outs

LTC1726-5 Micropower Triple Supply Monitor for 5V, 3.3V and ADJ Adjustable RESET and Watchdog Time Outs

LTC1727-2.5/1727-5 Micropower Triple Supply Monitor with Open-Drain Reset Individual Monitor Outputs in MSOP

LTC1728-1.8 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package

LTC1728-2.5/1728-5 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package

RELATED PARTS

TYPICAL APPLICATIO

Triple Supply Monitor with Manual Reset Button

S5 Package

5-Lead Plastic SOT-23

(LTC DWG # 05-08-1633)

PACKAGE DESCRIPTIO

Dimensions in inches (millimeters) unless otherwise noted.

1.50 – 1.75

(0.059 – 0.069)

0.35 – 0.55

(0.014 – 0.022)

S5 SOT-23 0599

0.09 – 0.20

(0.004 – 0.008)

(NOTE 2)

2.60 – 3.00

(0.102 – 0.118)

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DIMENSIONS ARE INCLUSIVE OF PLATING

3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

4. MOLD FLASH SHALL NOT EXCEED 0.254mm

5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)

0.35 – 0.50

(0.014 – 0.020)

FIVE PLACES (NOTE 2)

0.90 – 1.45

(0.035 – 0.057)

0.90 – 1.30

(0.035 – 0.051)

0.00 – 0.15

(0.00 – 0.006)

0.95

(0.037)

REF

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

1.90

(0.074)

REF

 LINEAR TECHNO LOGY CORPORATION 2000

1985f LT/TP 0900 4K • PRINTED IN THE USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900

●

FAX: (408) 434-0507

●

www.linear-tech.com

CC3

CC18

CCA

RST

LTC1985-1.8

GND

1985-18 TA07

100nF

1.8V 3V

2.5V

TRIP

= 2.3V

100k

0.1%

*OPTIONAL RESISTOR RECOMMENDED

TO EXTEND ESD TOLERANCE

R3*

10k

MANUAL

RESET BUTTON

(NORMALLY OPEN)

130k

0.1% 100nF

TRIP

= (R1 + R2)

R1 = R2 – 1

CCA

()

TRIP

CCA

SYSTEM

RESET