LTC2905HDDB#TRMPBF - ANALOG DEVICES

LTC2904/LTC2905

29045fd

TYPICAL APPLICATION

DESCRIPTION

Precision Dual Supply

Monitors with Pin-Selectable

Thresholds

The LTC

2904/LTC2905 are dual supply monitors in-

tended for systems with two supply voltages. The dual

supply monitors have a common reset output with delay

(200ms for the LTC2904 and adjustable using an exter-

nal capacitor for the LTC2905). This product provides a

precise, space-conscious and micropower solution for

supply monitoring.

The LTC2904/LTC2905 feature a tight 1.5% threshold

accuracy over the whole operating temperature range, and

glitch immunity to ensure reliable reset operation without

false triggering. The open drain RST output is guaranteed

to be in the correct state for inputs down to 1V.

The LTC2904/LTC2905 also feature three programming

input pins, which program the threshold and tolerance level

without requiring any external components. These three

programming pins provide a total of 27 different voltage

level and tolerance combinations, eliminating the need to

have different parts for development and implementation

of different systems with different voltage levels requiring

monitoring function.

5V, 3.3V Dual Supply Monitor with 5% Tolerance

FEATURES

APPLICATIONS

n Monitors Two Inputs Simultaneously

n Nine Threshold Combinations

n Three Supply Tolerances (5%, 7.5%, 10%)

n Guaranteed Threshold Accuracy: ±1.5% of

Monitored Voltage Over Temperature

n Internal VCC Auto Select

n Power Supply Glitch Immunity

n 200ms Reset Time Delay (LTC2904 Only)

n Adjustable Reset Time Delay (LTC2905 Only)

n Open Drain RST Output

n Guaranteed RST for V1 ≥ 1V or V2 ≥ 1V

n Low Proﬁ le (1mm) SOT-23 (ThinSOT™) and

Plastic (3mm × 2mm) DFN Packages

n Desktop and Notebook Computers

n Handheld Devices

n Network Servers

n Core, I/O Monitor

Table 1. Voltage Threshold Programming

V1 V2 S1 S2

5.0 3.3 V1 V1

3.3 2.5 Open GND

3.3 1.8 V1 Open

3.3 1.5 Open V1

3.3 1.2 Open Open

2.5 1.8 GND GND

2.5 1.5 GND Open

2.5 1.2 GND V1

2.5 1.0 V1 GND

TOL

TMR

GND

RST

LTC2905

22nF

0.1μF0.1μF

DC/DC

CONVERTER

SYSTEM

LOGIC

29045 TA01

3.3V

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

LTC2904/LTC2905

29045fd

ABSOLUTE MAXIMUM RATINGS

Terminal Voltages

V1, V2 ...................................................... –0.3V to 7V

S1, S2, TOL ................................–0.3V to (VCC +0.3V)

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

RST (LTC2904) ........................................ –0.3V to 7V

TMR (LTC2905) ....................................... –0.3V to 7V

(Note 1, 2)

ORDER INFORMATION

TOP VIEW

DDB8 PACKAGE

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

EXPOSED PAD IS GND (PIN 9),

MUST BE SOLDERED TO PCB

1GND

RST

RST/TMR*

TOL

* RST FOR LTC2904

TMR FOR LTC2905

TJMAX = 150°C, θJA = 76°C/W

V2 1

RST/TMR* 2

RST 3

GND 4

8 V1

7 S2

6 S1

5 TOL

TOP VIEW

TS8 PACKAGE

8-LEAD PLASTIC TSOT-23

* RST FOR LTC2904

TMR FOR LTC2905

TJMAX = 150°C, θJA = 195°C/W

PIN CONFIGURATION

Operating Temperature Range

LTC2904C/LTC2905C .............................. 0°C to 70°C

LTC2904I/LTC2905I .............................–40°C to 85°C

LTC2905H .......................................... –40°C to 125°C

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

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

Lead Free Finish

TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2904CDDB#TRMPBF LTC2904CDDB#TRPBF LBCZ 8-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C

LTC2904IDDB#TRMPBF LTC2904IDDB#TRPBF LBDB 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C

LTC2905CDDB#TRMPBF LTC2905CDDB#TRPBF LAJF 8-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C

LTC2905HDDB#TRMPBF LTC2905HDDB#TRPBF LBCY 8-Lead (3mm × 2mm) Plastic DFN –40°C to 125°C

LTC2905IDDB#TRMPBF LTC2905IDDB#TRPBF LBCY 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C

LTC2904CTS8#TRMPBF LTC2904CTS8#TRPBF LTBCJ 8-Lead Plastic TSOT-23 0°C to 70°C

LTC2904ITS8#TRMPBF LTC2904ITS8#TRPBF LTBCK 8-Lead Plastic TSOT-23 –40°C to 85°C

LTC2905CTS8#TRMPBF LTC2905CTS8#TRPBF LTAJD 8-Lead Plastic TSOT-23 0°C to 70°C

LTC2905HTS8#TRMPBF LTC2905HTS8#TRPBF LTAJE 8-Lead Plastic TSOT-23 –40°C to 125°C

LTC2905ITS8#TRMPBF LTC2905ITS8#TRPBF LTAJE 8-Lead Plastic TSOT-23 –40°C to 85°C

TRM = 500 pieces. *Temperature grades are identiﬁ ed by a label on the shipping container.

Consult LTC Marketing for parts speciﬁ ed with wider operating temperature ranges.

Consult LTC Marketing for information on 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/

LTC2904/LTC2905

29045fd

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VRT50 5V, 5% Reset Threshold

5V, 7.5% Reset Threshold

5V, 10% Reset Threshold

V1 Input Threshold l

4.600

4.475

4.350

4.675

4.550

4.425

4.750

4.625

4.500

VRT33 3.3V, 5% Reset Threshold

3.3V, 7.5% Reset Threshold

3.3V, 10% Reset Threshold

V1, V2 Input Threshold l

3.036

2.954

2.871

3.086

3.003

2.921

3.135

3.053

2.970

VRT25 2.5V, 5% Reset Threshold

2.5V, 7.5% Reset Threshold

2.5V, 10% Reset Threshold

V1, V2 Input Threshold l

2.300

2.238

2.175

2.338

2.275

2.213

2.375

2.313

2.250

VRT18 1.8V, 5% Reset Threshold

1.8V, 7.5% Reset Threshold

1.8V, 10% Reset Threshold

V2 Input Threshold l

1.656

1.611

1.566

1.683

1.638

1.593

1.710

1.665

1.620

VRT15 1.5V, 5% Reset Threshold

1.5V, 7.5% Reset Threshold

1.5V, 10% Reset Threshold

V2 Input Threshold l

1.380

1.343

1.305

1.403

1.365

1.328

1.425

1.388

1.350

VRT12 1.2V, 5% Reset Threshold

1.2V, 7.5% Reset Threshold

1.2V, 10% Reset Threshold

V2 Input Threshold l

1.104

1.074

1.044

1.122

1.092

1.062

1.140

1.110

1.080

VRT10 1V, 5% Reset Threshold

1V, 7.5% Reset Threshold

1V, 10% Reset Threshold

V2 Input Threshold l

0.920

0.895

0.870

0.935

0.910

0.885

0.950

0.925

0.900

VCCMIN Minimum Internal Operating Voltage (Note 2) RST in Correct Logic State l1V

IV1 V1 Input Current Includes Input Current to Three-State Pins l65 130 μA

IV2 V2 Input Current l0.4 1.0 μA

ITMR(UP) TMR Pull-Up Current LTC2905 VTMR = 0V l–1.5 –2.1 –2.7 μA

ITMR(DOWN) TMR Pull-Down Current LTC2905

LTC2905H

VTMR = 1.4V l

1.5

1.4

2.1

2.0

2.7

μA

tRST Reset Timeout Period LTC2904 l140 200 260 ms

tRST Reset Timeout Period LTC2905

LTC2905H

CTMR = 22nF l

140

200 260

295

tUV Vx Undervoltage Detect to

RST or RST

Vx Less than Reset Threshold VRTX

by More than 1%

150 μs

VOL Output Voltage Low RST, RST I = 2.5mA

I = 100μA; V1 = 1V (RST Only)

0.15

0.05

0.4

0.3

VOH Output Voltage High RST, RST

(Notes 2, 5)

I = –1μA lVCC–1 V

Three-State Inputs S1, S2, TOL

VIL Low Level Input Voltage l0.4 V

VIH High Level Input Voltage l1.4 V

VZPin Voltage When Left in Open State I = –10μA

I = 0μA

I = 10μA

0.7

0.9

1.1

2905H I = –10μA

I = 0μA

I = 10μA

0.65

0.9

1.15

IVPG Programming Input Current (Note 6) l±25 μA

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

temperature range, otherwise speciﬁ cations are at TA = 25°C. V1 = 2.5V, V2 = 1V, S1 = TOL = V1, S2 = 0V, unless otherwise noted.

(Notes 2, 3)

LTC2904/LTC2905

29045fd

TYPICAL PERFORMANCE CHARACTERISTICS

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT50 (V)

29045 G01

4.75

4.70

4.65

4.60

4.55

4.50

4.45

4.40

4.35

–50 100

25 75

–25 050

7.5%

10%

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT33 (V)

3.120

3.070

3.020

2.970

2.920

2.870

29045 G02

–50 100

25 75

–25 050

7.5%

10%

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT25 (V)

29045 G03

2.375

2.325

2.275

2.225

2.175–50 100

25 75

–25 050

7.5%

10%

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT18 (V)

29045 G04

1.705

1.685

1.665

1.645

1.625

1.605

1.585

1.565

–50 100

25 75

–25 050

7.5%

10%

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT15 (V)

29045 G05

1.425

1.405

1.385

1.365

1.345

1.325

1.305

–50 100

25 75

–25 050

7.5%

10%

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT12 (V)

1.135

1.125

1.115

1.105

1.095

1.085

1.075

1.065

1.055

1.045

29045 G06

–50 100

25 75

–25 050

7.5%

10%

1.8V Threshold Voltage

vs Temperature

1.5V Threshold Voltage

vs Temperature

1.2V Threshold Voltage

vs Temperature

5V Threshold Voltage

vs Temperature

3.3V Threshold Voltage

vs Temperature

2.5V Threshold Voltage

vs Temperature

Speciﬁ cations are at TA = 25°C unless otherwise noted.

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

Note 3: All currents into pins are positive; all voltages are referenced to

GND unless otherwise noted.

Note 4: For reset thresholds test conditions refer to the voltage threshold

programming table in the Applications Information section.

Note 5: The output pins RST and RST have an internal pull-up to VCC of

typically –6μA. However, an external pull-up resistor may be used when

faster rise time is required or for VOH voltages greater than VCC.

Note 6: The input current to the three-state input pins are the pull-up

and the pull-down current when the pins are either set to V1 or GND

respectively. In the open state, the maximum leakage current to V1 or GND

permissible is 10μA.

ELECTRICAL CHARACTERISTICS

LTC2904/LTC2905

29045fd

TEMPERATURE (oC)

THRESHOLD VOLTAGE, VRT10 (V)

29045 G07

0.950

0.940

0.930

0.920

0.910

0.900

0.890

0.880

0.870

–50 100

25 75

–25 050

7.5%

10%

TEMPERATURE (oC)

IV1 (MA)

21.5

21.0

20.5

20.0

19.5

19.0

29045 G08

–50 100

25 75

–25 050

V1 = 5V

V2 = 3.3V

S1 = S2 = TOL = 1.4V

TEMPERATURE (oC)

IV2 (MA)

29045 G09

1.8

1.7

1.6

1.5

1.4

1.3

1.2

–50 100

25 75

–25 050

V1 = 5V

V2 = 3.3V

S1 = S2 = TOL = 1.4V

TYPICAL PERFORMANCE CHARACTERISTICS

TEMPERATURE (oC)

IV2 (MA)

29045 G10

20.0

19.5

19.0

18.5

18.0

17.5

17.0

–50 100

25 75

–25 050

V1 = 2.5V

V2 = 3.3V

S1 = S2 = TOL = 1.4V

COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)

0.1

TYPICAL TRANSIENT DURATION (Ms)

700

600

500

400

300

200

100

1 10 100

29045 G11

RESET OCCURS

ABOVE CURVE

CTMR (FARAD)

10p 100p 1n 10n 100n 1M

RESET TIME OUT PERIOD, tRST (ms)

29045 G12

10000

1000

100

0.1

TEMPERATURE (oC)

RESET TIME-OUT PERIOD, tRST (ms)

29045 G13

235

230

225

220

215

210

205

200

195

–50 100

25 75

–25 050

CRT = 22nF

(FILM)

V1 (V)

RST OUTPUT VOLTAGE (V)

–1 1234

29045 G14

V2 = S1 = S2 = TOL = V1

10k PULL-UP RESISTOR

V1 (V)

RST OUTPUT VOLTAGE (V)

–1 1234

29045 G15

V2 = S1 = S2 = TOL = V1

10k PULL-UP RESISTOR

Reset Timeout Period (tRST)

vs Temperature RST Output Voltage vs V1 RST Output Voltage vs V1

IV2 vs Temperature

Typical Transient Duration

vs Comparator Overdrive (V1, V2)

Reset Time Out Period (tRST)

vs Capacitance (CTMR)

1V Threshold Voltage

vs Temperature IV1 vs Temperature IV2 vs Temperature

Speciﬁ cations are at TA = 25°C unless otherwise noted.

LTC2904/LTC2905

29045fd

RST PULL-DOWN CURRENT, IRST (mA)

RST OUTPUT VOLTAGE LOW, VOL (V)

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

29045 G19

10 50 604030

25oC

85oC

–40oC

V1 = 5V

V2 = 3V

S1 = S2 = TOL = V1

NO PULL-UP R

RST PULL-DOWN CURRENT, IRST (mA)

RST OUTPUT VOLTAGE LOW, VOL (V)

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

29045 G20

10 50 604030

25oC

85oC

–40oC

V1 = 5V

V2 = 3.3V

S1 = S2 = TOL = V1

NO PULL-UP R

SUPPLY VOLTAGE, VCC (V)

2.0

RST PULL-UP CURRENT, IRST (MA)

4.0

–18

–16

–14

–12

–10

–8

–6

–4

–2

29045 G21

3.0 5.0

2.5 4.5

3.5

VRT25 VRT33 VRT50

TOL = GND

SUPPLY VOLTAGE, VCC (V)

2.0 4.0

29045 G22

3.0 5.0

2.5 4.5

3.5

RST PULL-UP CURRENT, IRST (MA)

–16

–14

–12

–10

–8

–6

–4

–2

TOL = V1

VRT25 VRT33 VRT50

OUTPUT SOURCE CURRENT, IRST (MA)

–12

RST OUTPUT VOLTAGE HIGH, VOH (V)

3.0

2.5

2.0

1.5

1.0

0.5

–10 –8 –6 –4

29045 G23

–2 0

V1 = 3.3V

V2 = 1.8V

S1 = TOL =V1

S2 = OPEN

NO PULL-UP R

25oC

85oC

–40oC

OUTPUT SOURCE CURRENT, IRST (MA)

–7

RST OUTPUT VOLTAGE HIGH, VOH (V)

3.5

3.0

2.5

2.0

1.5

1.0

0.5

–1

–8 –6 –3–4–5

29045 G24

–2 0

V1 = 3.3V

V2 = 1.5V

S1 = TOL = V1

S2 = OPEN

NO PULL-UP R

25oC

85oC

–40oC

RST Pull-Up Current (IRST)

vs Supply Voltage (VCC)

RST Output Voltage High (VOH)

vs RST Output Source Current (IRST)

RST Output Voltage High (VOH)

vs RST Output Source Current (IRST)

RST Output Voltage Low (VOL)

vs RST Pull-Down Current (IRST)

RST Output Voltage Low (VOL)

vs RST Pull-Down Current (IRST)

RST Pull-Up Current (IRST)

vs Supply Voltage (VCC)

TYPICAL PERFORMANCE CHARACTERISTICS

Speciﬁ cations are at TA = 25°C unless otherwise noted.

V1 (V)

RST OUTPUT VOLTAGE (V)

–1 1234

29045 G16

V2 = S1 = S2 = TOL = V1

10pF CAPACITOR AT RST

SUPPLY VOLTAGE, VCC (V)

RST PULL-DOWN CURRENT, IRST (mA)

29045 G17

123 5

RST AT 150mV

RST AT 50mV

V2 = S1 = S2 = TOL = V1

NO PULL-UP R

SUPPLY VOLTAGE, VCC (V)

RST PULL-DOWN CURRENT, IRST (mA)

29045 G18

123 5

RST AT 150mV

RST AT 50mV

S1 = V2 = V1

TOL = S2 = GND

NO PULL-UP R

RST Output Voltage vs V1

RST Pull-Down Current (IRST)

vs Supply Voltage (VCC)

RST Pull-Down Current (IRST)

vs Supply Voltage (VCC)

LTC2904/LTC2905

29045fd

PIN FUNCTIONS

V2 (Pin 1/Pin 4): Voltage Input 2. Input for V2 monitor.

Select from 3.3V, 2.5V, 1.8V, 1.5V, 1.2V or 1.0V. Refer to

Table 1 for details. The greater of V1, V2 is also the internal

supply voltage, VCC. Bypass this pin to ground with a 0.1μF

(or greater) capacitor.

RST (Pin 2/Pin 3): (LTC2904 Only) Reset Logic Output.

When all voltage inputs are above the reset threshold for

at least the programmed delay time, this pin pulls low. This

pin has a weak pull-up to VCC and may be pulled above

VCC using an external pull-up.

TMR (Pin 2/Pin 3): (LTC2905 Only) Reset Delay Time

Programming Pin. Attach an external capacitor (CTMR) to

GND to set a reset delay time of 9ms/nF. Leaving the pin

open generates a minimum delay of approximately 200μs. A

22nF capacitor will generate a 200ms reset delay time.

RST (Pin 3/Pin 2): Inverted Reset Logic Output. Pulls low

when any voltage input is below the reset threshold and is

held low for programmed delay time after all voltage inputs

are above threshold. This pin has a weak pull-up to VCC

and may be pulled above VCC using an external pull-up.

GND (Pin 4/Pin 1, Pin 9): Ground.

TOL (Pin 5/Pin 8): Three-state Input for Supply Tolerance

Selection (5%, 7.5% or 10%). See the Applications Infor-

mation section for tolerance selection chart (Table 2).

S1 (Pin 6/Pin 7): Voltage Threshold Select Three-State

Input. Connect to V1, GND or leave unconnected in open

state (See Table 1).

S2 (Pin 7/Pin 6): The Second Voltage Threshold Select

Three-State Input. Connect to V1, GND or leave uncon-

nected in open state (See Table 1).

V1 (Pin 8/Pin 5): Voltage Input 1. Input for V1 monitor.

Select from 5V, 3.3V, or 2.5V. See Table 1 for details.

The greater of V1, V2 is also the internal supply voltage,

VCC. Bypass this pin to ground with a 0.1μF (or greater)

capacitor.

(TS8/DDB8)

TEMPERATURE (oC)

IS1, IS2, ITOL (MA)

29045 G25

–50 100

25 75

–25 050

S1 = S2 = TOL = 3.3V

TEMPERATURE (oC)

IS1, IS2, ITOL (MA)

–20

–19

–18

–17

–16

–15

–14

–13

–12

–11

–10

29045 G26

–50 100

25 75

–25 050

S1 = S2 = TOL = GND

IS1, IS2, ITOL vs Temperature IS1, IS2, ITOL vs Temperature

TYPICAL PERFORMANCE CHARACTERISTICS

Speciﬁ cations are at TA = 25°C unless otherwise noted.

LTC2904/LTC2905

29045fd

BLOCK DIAGRAM

–

RESET PULSE

GENERATOR

THREE-STATE DECODER

RESISTOR

NETWORK

POWER

DETECT

BAND GAP

REFERENCE

VCC

LTC2905

2905 BD

S1 TOLS2

TMR

RST

GND

6μA

–

200ms

RESET PULSE

GENERATOR

THREE-STATE DECODER

RESISTOR

NETWORK

POWER

DETECT

BAND GAP

REFERENCE

VCC

LTC2904

2904 BD

S1 TOLS2

RST

VCC

GND

6μA

LTC2904/LTC2905

29045fd

APPLICATIONS INFORMATION

RST

tUV tRST

VRTX

29045 TD

VX Monitor Timing

TIMING DIAGRAM

Supply Monitoring

The LTC2904/LTC2905 are low power, high accuracy dual

supply monitors with a common reset output and selectable

thresholds. Reset delay is set to a nominal of 200ms for

the LTC2904 and is adjustable using an external capacitor

for the LTC2905.

The two 3-state input pins (S1 and S2) select one of nine

possible threshold voltage combinations. Another three-

state input pin sets the supply tolerance (5%, 7.5% or

10%). Both input voltages (V1 and V2) must be above

predetermined thresholds for the reset not to be invoked.

The LTC2904/LTC2905 assert the reset outputs during

power-up, power-down and brownout conditions on either

of the voltage inputs.

Power-Up

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

VCC powers the drive circuits for the RST pin. Therefore as

soon as V1 or V2 reaches 1V during power-up, the RST

output asserts low.

VCC also powers the drive circuits for the RST pin in the

LTC2904. Therefore, RST weakly pulls high when V1 or

V2 reaches at least 1V.

Threshold programming is complete when V1 reaches

at least 2.17V. After programming, if either V1 or V2 falls

below its programmed threshold, RST asserts low (RST

weakly pulls high) as long as VCC is at least 1V.

Once V1 and V2 rise above their thresholds, an internal

timer is started. After the programmed delay time, RST

weakly pulls high (RST asserts low).

LTC2904/LTC2905

29045fd

APPLICATIONS INFORMATION

Power-Down

On power-down, once either V1 or V2 inputs drops below

its threshold, RST asserts logic low and RST weakly pulls

high. VCC of at least 1V guarantees a logic low of 0.4V at

RST.

Programming Pins

The three 3-state input pins: S1, S2 and TOL should be

connected to GND, V1 or left unconnected during normal

operation. Note that when left unconnected, the maximum

leakage current allowable from the pin to either GND or

V1 is 10μA.

In margining applications, all the 3-state input pins can be

driven using a tri-state buffer. Note however the low and

high output of the tri-state buffer has to satisfy the VIL and

VIH of the 3-state pin listed in the Electrical Characteristics

Table. Moreover, when the tri-state buffer is in the high

impedance state, the maximum leakage current allowed

from the pin to either GND or V1 is 10μA.

Monitor Programming

Connecting S1 and S2 to GND, V1 or leaving them open

selects the LTC2904/LTC2905 input voltage combina-

tions. Table 1 shows the nine possible combinations of

nominal input voltages and their corresponding S1, S2

connections.

Table 1. Voltage Threshold Programming

V1 V2 S1 S2

5.0 3.3 V1 V1

3.3 2.5 Open GND

3.3 1.8 V1 Open

3.3 1.5 Open V1

3.3 1.2 Open Open

2.5 1.8 GND GND

2.5 1.5 GND Open

2.5 1.2 GND V1

2.5 1.0 V1 GND

Note: Open = open circuit or driven by a three state buffer in high

impedance state with leakage current less than 10μA.

Tolerance Programming

The three-state input pin, TOL programs the common

supply tolerance for both V1 and V2 input voltages (5%,

7.5% or 10%). The larger the tolerance the lower the trip

threshold. Table 2 shows the tolerances selection corre-

sponding to a particular connection at the TOL pin.

Table 2. Tolerance Programming

Tolerance TOL

5% V1

7.5% Open

10% GND

Threshold Accuracy

Reset threshold accuracy is of the utmost importance in a

supply sensitive system. Ideally such a system should not

reset while supply voltages are within a speciﬁ ed margin

below the rated nominal level. Both of the LTC2904/LTC2905

inputs have the same relative threshold accuracy. The

speciﬁ cation for LTC2904/LTC2905 is ±1.5% of the pro-

grammed nominal input voltage (over the full operating

temperature range).

For example, when the LTC2904/LTC2905 are programmed

to handle a 5V input with 10% tolerance (S1 = S2 = V1 and

TOL = GND, refer to Table 1 and Table 2), it does not issue

a reset command when V1 is above 4.5V. The typical 10%

trip threshold is at 11.5% below the nominal input voltage

level. Therefore, the typical trip threshold for the 5V input

is 4.425V. With ±1.5% accuracy, the trip threshold range is

4.425V ±75mV over temperature (i.e. 10% to 13% below

5V). This implies that the monitored system must operate

reliably down to 4.35V over temperature.

The same system using a supervisor with only ±2.5%

accuracy needs to work reliably down to 4.25V (4.375V

±125mV) or 15% below 5V, requiring the monitored system

to work over a much wider operating voltage range.

LTC2904/LTC2905

29045fd

In any supervisory application, supply noise riding on

the monitored DC voltage can cause spurious resets,

particularly when the monitored voltage is near the reset

threshold. A less desirable but common solution to this

problem is to introduce hysteresis around the nominal

threshold. Notice however, this hysteresis introduces an

error term in the threshold accuracy. Therefore, a ±2.5%

accurate monitor with ±1.0% hysteresis is equivalent to

a ±3.5% monitor with no hysteresis.

The LTC2904/LTC2905 takes a different approach to solve

this problem of supply noise causing spurious reset. The

ﬁ rst line of defense against this spurious reset is a ﬁ rst

order low pass ﬁ lter at the output of the comparator. Thus,

the comparator output goes through a form of integration

before triggering the output logic. Therefore, any kind of

transient at the input of the comparator needs to be of

sufﬁ cient magnitude and duration before it can trigger a

change in the output logic.

The second line of defense is the programmed delay time

tRST (200ms for LTC2904 and using an external capacitor

for LTC2905). This delay will eliminate the effect of any

supply noise whose frequency is above 1/tRST on the RST

and RST output.

When either V1 or V2 drops below its programmed thresh-

old, the RST pin asserts low (RST weakly pulls high). Then

when the supply recovers above the programmed thresh-

old, the reset-pulse-generator timer starts counting.

If the supply remains above the programmed threshold

when the timer ﬁ nishes counting, the RST pin weakly

pulls high (RST asserts low). However, if the supply falls

below the programmed threshold any time during the

period when the timer is still counting, the timer resets

and it starts fresh when the supply next rises above the

programmed threshold.

Note that this second line of defense is only effective

for a rising supply and does not affect the sensitivity of

the system to a falling supply. Therefore, the ﬁ rst line of

defense that works for both cases of rising and falling is

necessary. These two approaches prevent spurious reset

caused by supply noise without sacriﬁ cing the threshold

accuracy.

APPLICATIONS INFORMATION

Selecting the Reset Timing Capacitor

The reset timeout period for LTC2905 is adjustable in order

to accommodate a variety of microprocessor applications.

Connecting a capacitor, CTMR, between the TMR pin and

ground sets the reset timeout period, tRST. The following

formula determines the value of capacitor needed for a

particular reset timeout period:

TMR = tRST • 110 • 10–9 [F/s]

For example, using a standard capacitor value of 22nF

would give a 22000/110 = 200ms delay.

Figure 1 shows the desired delay time as a function of the

value of the timer capacitor that should be used:

Leaving the TMR pin open with no external capacitor gen-

erates a reset timeout of approximately 200μs. For long

reset timeout, the only limitation is the availability of large

value capacitor with low leakage. The TMR capacitor will

never charge if the leakage current exceeds the minimum

TMR charging current of 2.1μA (typical).

Figure 1. Reset Timeout Period vs Capacitance

CTMR (FARAD)

10p 100p 1n 10n 100n 1μ

RESET TIME OUT PERIOD, tRST (ms)

29045 F01

10000

1000

100

0.1

LTC2904/LTC2905

29045fd

APPLICATIONS INFORMATION

Output Rise and Fall Time Estimation

The RST and RST outputs have strong pull-down capabil-

ity. The following formula estimates the output fall time

(90% to 10%) for a particular external load capacitance

(CLOAD):

FALL ≈ 2.2 • RPD • CLOAD

where RPD is the on-resistance of the internal pull-down

transistor estimated to be typically 40Ω at room tempera-

ture (25°C) and CLOAD is the external load capacitance on

the pin. Assuming a 150pF load capacitance, the fall time

is about 13ns.

The rise time, on the RST and RST pins is limited by weak

internal pull-up current sources to VCC. The following

formula estimates the output rise time (10% to 90%) at

the RST and RST pins:

RISE ≈ 2.2 RPU • CLOAD

where RPU is the on-resistance of the pull-up transistor.

Notice that this pull-up transistor is modeled as a

6μA current source in the Block Diagram as a typical

representation.

The on-resistance as a function of the VCC = Max (V1, V2)

voltage (for VCC > 1V) at room temperature is estimated

as follows:

RMAX V V V

PU =Ω

610

12 1

•

(,)–

At VCC = 3.3V, RPU is about 260k. Using 150pF for load

capacitance, the rise time is 86μs. An external pull-up

resistor may be used if the output needs to pull up faster

and/or to a higher voltage, for example: the rise time re-

duces to 3.3μs for a 150pF load capacitance, when using

a 10k pull-up resistor.

RST and RST Output Characteristics

The DC characteristics of the RST and RST pull-up and

pull-down strength are shown in the Typical Performance

Characteristics section. Both RST and RST have a weak

internal pull-up to VCC = Max (V1, V2) and a strong pull-

down to ground.

The weak pull-up and strong pull-down arrangement allow

these two pins to have open-drain behavior while possess-

ing several other beneﬁ cial characteristics.

The weak pull-ups eliminate the need for external pull-up

resistors when the rise time on these pins is not critical. On

the other hand, the open-drain RST conﬁ guration allows

for wired-OR connections and can be useful when more

than one signal needs to pull down on the RST line.

As noted in the Power-Up and Power-Down sections the

circuits that drive RST and RST are powered by VCC. During

fault condition, VCC of at least 1V guarantees a maximum

VOL = 0.4V at RST. However, at VCC = 1V the weak pull-up

current on RST is barely turned on. Therefore, an external

pull-up resistor of no more than 100k is recommended on

the RST pin if the state and pull-up strength of the RST

pin is crucial at very low VCC.

Note however, by adding an external pull-up resistor, the

pull-up strength on the RST pin is increased. Therefore,

if it is connected in a wired-OR connection, the pull-down

strength of any single device needs to accommodate this

additional pull-up strength.

LTC2904/LTC2905

29045fd

2.5V, 1.2V Supply Monitor, 10% Tolerance 3.3V, 1.2V Dual Supply Monitor with LED Power Good Indicator,

7.5% Tolerance and Adjustable Timer

TYPICAL APPLICATIONS

5V, 3.3V Dual Supply Monitor with Voltage

Margining for Automated On-Board Testing

GND

RST

TOL

LTC2904

3.3V

1.2V

0.1μF

29045 TA03

510Ω

LED

SYSTEM

RESET

TOL

TMR

GND

RST

LTC2905

0.1μF

22nF

0.1μF

29045 TA04

VIN

SUPPLY

CONTROLLER

THREE-STATE

DC/DC

CONVERTER

SYSTEM

LOGIC

3.3V

RST

GND

TOL

LTC2904

2.5V1.2V

0.1μF

SYSTEM

RESET

29045 TA02

3.3V, 1.2V Dual Supply Monitor with Asymmetric Hysteresis, 5%

Tolerance (Supplies Rising), 10% Tolerance (After RST Goes Low)

GND

RST

TOL

RST

LTC2904

3.3V1.2V

0.1μF

SYSTEM

RESET

29045 TA05

10k

LTC2904/LTC2905

29045fd

PACKAGE DESCRIPTION

DDB Package

8-Lead Plastic DFN (3mm × 2mm)

(Reference LTC DWG # 05-08-1702 Rev B)

2.00 ±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 ± 0.10

BOTTOM VIEW—EXPOSED PAD

0.56 ± 0.05

(2 SIDES)

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

2.15 ±0.05

(2 SIDES)

3.00 ±0.10

(2 SIDES)

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

0.200 REF

0 – 0.05

(DDB8) DFN 0905 REV B

0.25 ± 0.05

2.20 ±0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.61 ±0.05

(2 SIDES)

1.15 ±0.05

0.70 ±0.05

2.55 ±0.05

PACKAGE

OUTLINE

0.25 ± 0.05

0.50 BSC

PIN 1

R = 0.20 OR

0.25 × 45°

CHAMFER

0.50 BSC

LTC2904/LTC2905

29045fd

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

TS8 Package

8-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1637)

1.50 – 1.75

(NOTE 4)

2.80 BSC

0.22 – 0.36

8 PLCS (NOTE 3)

DATUM ‘A’

0.09 – 0.20

(NOTE 3) TS8 TSOT-23 0802

2.90 BSC

(NOTE 4)

0.65 BSC

1.95 BSC

0.80 – 0.90

1.00 MAX 0.01 – 0.10

0.20 BSC

0.30 – 0.50 REF

PIN ONE ID

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

3. DIMENSIONS ARE INCLUSIVE OF PLATING

4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

5. MOLD FLASH SHALL NOT EXCEED 0.254mm

6. JEDEC PACKAGE REFERENCE IS MO-193

3.85 MAX

0.52

MAX

0.65

REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

1.4 MIN

2.62 REF

1.22 REF

LTC2904/LTC2905

29045fd

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

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

LT 1109 REV D • PRINTED IN USA

RELATED PARTS

TYPICAL APPLICATION

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 Pushbutton Reset 4.37V/4.62V Threshold

LTC1326/LTC1326-2.5 Micropower Precision Triple Supply Monitor

for 5V/2.5V, 3.3V and ADJ

4.725V, 3.118V, 1V Threshold (±0.75%)

LTC1536 Precision Triple Supply Monitor for PCI Applications Meets PCI tFAIL Timing Speciﬁ cations

LTC1726-2.5/LTC1726-5 Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Adjustable RESET and Watchdog Timeouts

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

LTC1728-1.8/LTC1728-3.3 Micropower Triple Supply Monitor with Open-Drain Reset 5-Lead SOT-23 Package

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

LTC1985-1.8 Micropower Triple Supply Monitor with Push-Pull Reset Output 5-Lead SOT-23 Package

LTC2900 Programmable Quad Supply Monitor Adjustable RESET, 10-Lead MSOP, DFN Packages

LTC2901 Programmable Quad Supply Monitor Adjustable RESET and Watchdog Timer,

16-Lead SSOP Package

LTC2902 Programmable Quad Supply Monitor Selectable Tolerance, RESET Disable for Margining

Functions, 16-Lead SSOP Package

LTC2903-1 Precision Quad Supply Monitor Ultralow Voltage RESET, 6-Lead SOT-23 Package

LTC2906 Dual Supply Monitor with One Pin-Selectable Threshold and

One Adjustable Input

0.5V Adjustable Threshold and Three Supply

Tolerances, 8-Lead SOT-23 and DFN Packages

LTC2907 Dual Supply Monitor with One Pin-Selectable Threshold and

One Adjustable Input

0.5V Adjustable Threshold, Adjustable RESET Timer

and Three Supply Tolerances, 8-Lead SOT-23 and

DFN Packages

LTC2908 Precision Six Supply Monitors Ultralow Voltage RESET, 8-Lead SOT-23 and DFN

Packages

3.3V, 1.2V Dual Supply Monitor with LED Power Good Indicator,

7.5% Tolerance and Adjustable Timer

TMR

GND

TOL

RST

LTC2905

TMR

GND

RST

TOL

LTC2905

3.3V

2.5V

1.8V

1.2V

0.1μF

29045 TA06

22nF

22nF 510Ω

LED