LT3008EDC#TRMPBF_技术文档

LT3008

µA I , 20mA, 45V

3

Q

Low Dropout Linear Regulator

FEATURES

DESCRIPTION

The LT^®3008 is a micropower, low dropout voltage (LDO)

linear regulator. The device supplies 20mA output current

with a dropout voltage of 300mV. No-load quiescent cur-

rent is 3μA. Ground pin current remains at less than 5% of

output current as load increases. In shutdown, quiescent

current is less than 1μA.

n

Ultralow Quiescent Current: 3μA

n

Input Voltage Range: 2.0V to 45V

n

Output Current: 20mA

n

Dropout Voltage: 300mV

n

Adjustable Output (V

= V

= 600mV)

ADJ

OUT(MIN)

n

Output Tolerance: 2% Over Load, Line and

Temperature

The LT3008 regulator optimizes stability and transient

response with low ESR ceramic capacitors, requiring a

minimum of only 2.2μF. The LT3008 does not require

the addition of ESR as is common with other regulators.

Internal protection circuitry includes current limiting,

thermal limiting, reverse-battery protection and reverse-

current protection.

Stable with Low ESR, Ceramic Output Capacitors

(2.2μF minimum)

n

Shutdown Current: <1μA

Current Limit Protection

Reverse-Battery Protection

Thermal Limit Protection

TSOT-23 and 2mm × 2mm DFN Packages

The LT3008 is ideal for applications that require moderate

outputdrivecapabilitycoupledwithultralowstandbypower

consumption. The device is available as an adjustable

device with an output voltage range down to the 600mV

reference. The LT3008 is available in the 6-lead DFN and

8-lead TSOT-23 packages.

APPLICATIONS

n

Automotive

n

Low Current Battery-Powered Systems

n

Keep-Alive Power Supplies

Remote Monitoring

Utility Meters

n

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

All other trademarks are the property of their respective owners.

n

Low Power Industrial Applications

TYPICAL APPLICATION

3.3V, 20mA Supply with Shutdown

Dropout Voltage/Quiescent Current

500

450

400

350

300

250

200

150

100

50

6

5

4

3

2

1

0

I

= 20mA

LOAD

DROPOUT

VOLTAGE

V

OUT

3.3V

IN

OUT

ADJ

V

IN

20mA

3.8V TO

45V

2.2μF

1μF

2.8M

1%

LT3008

SHDN

GND

I

Q

619k

1%

3008 TA01a

0

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3008 TA01b

3008f

1

LT3008

(Note 1)

ABSOLUTE MAXIMUM RATINGS

Operating Junction Temperature Range (Notes 2, 3)

LT3008E.............................................–40°C to 125°C

LT3008I..............................................–40°C to 125°C

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

Lead Temperature: Soldering, 10 sec

IN Pin Voltage ......................................................... 50V

OUT Pin Voltage...................................................... 50V

Input-to-Output Differential Voltage........................ 50V

ADJ Pin Voltage ...................................................... 50V

SHDN Pin Voltage (Note 8) ..................................... 50V

Output Short-Circuit Duration .......................... Indeﬁnite

TS8 Package Only............................................. 300°C

PIN CONFIGURATION

TOP VIEW

6

5

4

GND

SHDN

IN

ADJ

OUT

1

2

3

8

7

6

5

NC

SHDN

GND

1

2

3

4

ADJ

OUT

IN

7

TS8 PACKAGE

8-LEAD PLASTIC TSOT-23

DC PACKAGE

6-LEAD (2mm s 2mm) PLASTIC DFN

T

= 125°C, θ = 65°C/W TO 85°C/W*

JA

JMAX

T

JMAX

= 125°C, θ = 65°C/W TO 85°C/W*

JA

EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB

* See Applications Information Section.

ORDER INFORMATION

LEAD FREE FINISH

LT3008EDC#PBF

LT3008IDC#PBF

LT3008ETS8#PBF

LT3008ITS8#PBF

LEAD BASED FINISH

LT3008EDC

TAPE AND REEL

LT3008EDC#TRPBF

LT3008IDC#TRPBF

LT3008ETS8#TRPBF

LT3008ITS8#TRPBF

TAPE AND REEL

LT3008EDC#TR

PART MARKING*

LDPS

PACKAGE DESCRIPTION

TEMPERATURE RANGE

–40°C to 125°C

TEMPERATURE RANGE

–40°C to 125°C

6-Lead (2mm × 2mm) Plastic DFN

8-Lead Plastic TSOT-23

LDPS

LTDSX

8-Lead Plastic TSOT-23

PART MARKING*

LDPS

PACKAGE DESCRIPTION

6-Lead (2mm × 2mm) Plastic DFN

8-Lead Plastic TSOT-23

LT3008IDC

LT3008IDC#TR

LDPS

LT3008ETS8

LT3008ETS8#TR

LT3008ITS8#TR

LTDSX

LT3008ITS8

LTDSX

8-Lead Plastic TSOT-23

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

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/

3008f

2

LT3008

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_J= 25°C. (Note 2)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

l

Operating Voltage

2

45

V

ADJ Pin Voltage (Notes 3, 4)

V

= 2V, I

IN

= 100μA

594

588

600

606

612

mV

IN

LOAD

l

2V < V < 45V, 1μA < I

< 20mA

LOAD

Line Regulation (Note 3)

Load Regulation (Note 3)

0.6

3

mV

ΔV = 2V to 45V, I

= 1mA

IN

LOAD

l

V

IN

V

IN

= 2V, I

= 1μA to 10mA

= 1μA to 20mA

0.4

0.5

2

5

mV

LOAD

Dropout Voltage

IN

I

= 100μA

115

170

270

300

3

180

250

mV

LOAD

l

V

= V

(Notes 5, 6)

OUT(NOMINAL)

I

= 1mA

250

350

mV

LOAD

I

= 10mA

340

470

mV

LOAD

I

= 20mA

365

500

mV

LOAD

Quiescent Current (Notes 6, 7)

GND Pin Current

I

= 0μA

μA

LOAD

6

l

I

= 0μA

3

6

21

160

350

6

12

50

500

1200

μA

LOAD

V

= V

+ 0.5V (Notes 6, 7)

OUT(NOMINAL)

= 100μA

= 1mA

IN

= 10mA

= 20mA

Output Voltage Noise (Note 9)

ADJ Pin Bias Current

C

OUT

= 2.2μF, I

= 20mA, BW = 10Hz to 100kHz

92

μV

RMS

LOAD

l

–10

0.4

10

nA

l

Shutdown Threshold

V

OUT

V

OUT

= Off to On

= On to Off

0.67

0.61

1.5

V

0.25

l

SHDN Pin Current

V

SHDN

V

SHDN

= 0V, V = 45V

μA

1

2

IN

= 45V, V = 45V

0.65

IN

l

Quiescent Current in Shutdown

Ripple Rejection (Note 3)

V

= 6V, V

= 0V

<1

μA

dB

IN

SHDN

V

– V

= 1.5V, V

= 0.5V ,

P-P

58

22

70

75

IN

OUT

= 120Hz, I

RIPPLE

f

= 20mA

LOAD

RIPPLE

Current Limit

V

= 45V, V

= 0

mA

IN

OUT

l

= V

+ 1V, ΔV

= –5%

OUT

OUT(NOMINAL)

Input Reverse Leakage Current

Reverse Output Current

V

IN

= –45V, V

= 0

1

30

10

μA

OUT

V

OUT

= 1.2V, V = 0

0.6

IN

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 4: Operating conditions are limited by maximum junction

temperature. The regulated output voltage speciﬁcation will not apply

for all possible combinations of input voltage and output current. When

operating at the maximum input voltage, the output current range must be

limited. When operating at the maximum output current, the input voltage

must be limited.

Note 2: The LT3008 is tested and speciﬁed under pulse load conditions

such that T ≅ T . The LT3008E is 100% tested at T =25°C. Performance

J

A

at –40°C and 125°C is assured by design, characterization and correlation

with statistical process controls. The LT3008I is guaranteed over the full

–40°C to 125°C operating junction temperature range.

Note 5: Dropout voltage is the minimum input to output voltage differential

needed to maintain regulation at a speciﬁed output current. In dropout, the

output voltage equals (V – V

).

IN

DROPOUT

Note 3: The LT3008 adjustable version is tested and speciﬁed for these

conditions with the ADJ pin connected to the OUT pin.

3008f

3

LT3008

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_J= 25°C. (Note 2)

Note 6: To satisfy minimum input voltage requirements, the LT3008

adjustable version is tested and speciﬁed for these conditions with an

Note 8: The SHDN pin can be driven below GND only when tied to the IN

pin directly or through a pull-up resistor. If the SHDN pin is driven below

GND by more than –0.3V while IN is powered, the output will turn on.

external resistor divider (61.9k bottom, 280k top) which sets V

to 3.3V.

OUT

The external resistor divider adds 9.69μA of DC load on the output. This

external current is not factored into GND pin current.

Note 9: Output noise is listed for the adjustable version with the ADJ pin

connected to the OUT pin. See the RMS Output Noise vs Load Current

curve in the Typical Performance Characteristics Section.

Note 7: GND pin current is tested with V = V

+ 0.5V and a

IN

OUT(NOMINAL)

current source load. GND pin current will increase in dropout. See the GND

Pin Current curves in the Typical Performance Characteristics section.

TYPICAL PERFORMANCE CHARACTERISTICS ^T_J^{= 25°C, unless otherwise noted.}

Dropout Voltage

Minimum Input Voltage

450

400

350

300

250

200

150

100

50

450

400

350

300

250

200

150

100

50

2

1.8

1.6

1.4

1.2

1

I

= 20mA

LOAD

T

= 125°C

J

20mA

1mA

T

= 25°C

10mA

100μA

J

0.8

0.6

0.4

0.2

0

–50 –25

0

25 50 75 100 125 150

–50 –25

0

25 50 75 100 125 150

0

2

4

6

8

10 12 14 16 18 20

OUTPUT CURRENT (mA)

TEMPERATURE (°C)

3008 G01

3008 G02

3008 G03

ADJ Pin Voltage

ADJ Pin Bias Current

Quiescent Current

10

8

0.612

0.610

0.608

0.606

0.604

0.602

0.600

0.598

0.596

0.594

0.592

0.590

0.588

6

5

4

3

2

1

0

I

= 100μA

L

6

4

2

0

–2

–4

–6

–8

–10

–50 –25

0

25 50 75 100 125 150

–50 –25

0

25 50 75 100 125 150

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3008 G05

3008 G04

3008 G06

3008f

4

LT3008

TYPICAL PERFORMANCE CHARACTERISTICS ^T_J^{= 25°C, unless otherwise noted.}

Quiescent Current

GND Pin Current

GND Pin Current vs I_LOAD

400

350

300

250

200

150

100

50

1000

100

10

30

27

24

21

18

15

12

9

V

= 3.8V

V

= 3.3V

V

I

= 3.3V

= 1μA

IN

OUT

LOAD

20mA (R

= 165Ω)

LOAD

= 3.3V

10mA (R

= 330Ω)

LOAD

100μA (R

= 33k)

LOAD

6

1mA (R

= 3.3k)

3

LOAD

7

0

1

0

1

2

3

4

5

6

8

9

10

0.001

0.01

0.1

1

10

100

0

2

4

6

8

10

12

INPUT VOLTAGE (V)

LOAD (mA)

3008 G07

3008 G08

3008 G09

SHDN Pin Thresholds

SHDN Pin Input Current

2

1.8

1.6

1.4

1.2

1

1.5

1.4

1.3

1.2

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

2

1.8

1.6

1.4

1.2

1

OFF TO ON

ON TO OFF

V

SHDN

= 45V

0.8

0.6

0.4

0.2

0

0.8

0.6

0.4

0.2

0

–50

–25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3008 G12

–50

0

25 50 75 100 125 150

TEMPERATURE (°C)

3008 G10

0

5

10 15 20 25 30 35 40 45

SHDN PIN VOLTAGE (V)

3008 G11

–25

Input Ripple Rejection

Current Limit

Reverse Output Current

50

45

40

35

30

25

20

15

10

5

100

90

80

70

60

50

40

30

20

10

0

90

80

70

60

50

40

30

20

10

0

OUT = ADJ = 1.2V

IN = SHDN = GND

V

= 2.1V + 50mV

RMS

OUT

LOAD

IN

= 600mV

= 20mA

I

V

= 45V

IN

V

= 2V

IN

10μF

ADJ

2.2μF

OUT

0

–50

0

25 50 75 100 125 150

TEMPERATURE (°C)

3008 G14

–50

0

25 50 75 100 125 150

TEMPERATURE (°C)

3008 G13

–25

10

100

1000

10000 100000 1000000

FREQUENCY (Hz)

3008 G15

3008f

5

LT3008

TYPICAL PERFORMANCE CHARACTERISTICS ^T_J^{= 25°C, unless otherwise noted.}

Input Ripple Rejection

Load Regulation

Output Noise Spectral Density

80

70

60

50

40

30

20

10

0

5

4.5

4

100

10

1

C

I

= 2.2μF

= 20mA

5V

OUT

LOAD

$I = 1μA to 20mA

L

OUT

IN

3.3V

2.5V

1.8V

1.5V

1V

V

= 600mV

= 2V

3.5

3

0.6V

2.5

2

1.5

1

V

= V

(NOMINAL) + 2V + 0.5V

OUT P-P

IN

RIPPLE AT f = 120Hz

= 20mA

0.5

I

LOAD

0

0.1

–50

0

25 50 75 100 125 150

TEMPERATURE (°C)

–50

0

25

50

TEMPERATURE (°C)

75

100 125 150

–25

10

100

1k

10k

100k

–25

FREQUENCY (Hz)

3008 G17

3008 G18

3008 G16

RMS Output Noise

vs Load Current

Transient Response

500

450

C

OUT

= 10μF

5V

I

= 1mA TO 20mA

= 5.5V

OUT

IN

V

C

= 5V

OUT

400

350

= 2.2μF

V

3.3V

OUT

50mV/DIV

300

250

200

150

2.5V

1.8V

1.5V

I

OUT

20mA/DIV

1.2V

0.6V

3008 G21

100

50

0

500μs/DIV

0.01

0.1

1

100

0.001

10

I

(mA)

LOAD

3008 G19

Transient Response

Transient Response (Load Dump)

I

= 1mA TO 20mA

= 5.5V

OUT

IN

V

C

V

OUT

= 5V

OUT

50mV/DIV

= 10μF

V

OUT

45V

12V

50mV/DIV

V

I

= 5V

= 20mA

= 4.7μF

OUT

C

OUT

V

IN

10V/DIV

I

OUT

20mA/DIV

3008 G22

3008 G23

500μs/DIV

1ms/DIV

3008f

6

LT3008

PIN FUNCTIONS ^{(TSOT-23/DFN)}

SHDN (Pin 1/Pin 5): Shutdown. Pulling the SHDN pin

OUT (Pin 6/Pins 2, 3): Output. This pin supplies power

to the load. Use a minimum output capacitor of 2.2μF

to prevent oscillations. Large load transient applications

require larger output capacitors to limit peak voltage

transients. See the Applications Information section for

more information on output capacitance and reverse

output characteristics.

low puts the LT3008 into a low power state and turns the

output off. If unused, tie the SHDN pin to V . The LT3008

IN

does not function if the SHDN pin is not connected. The

SHDN pin cannot be driven below GND unless tied to the

IN pin. If the SHDN pin is driven below GND while IN is

powered, the output will turn on. SHDN pin logic cannot

be referenced to a negative rail.

ADJ (Pin 7/Pin 1): Adjust. This pin is the error ampliﬁer’s

inverting terminal. Its 400pA typical input bias current

ﬂows out of the pin (see curve of ADJ Pin Bias Current vs

Temperature in the Typical Performance Characteristics

section). TheADJpinvoltageis600mVreferencedtoGND

and the output voltage range is 600mV to 44.5V.

GND (Pins 2, 3, 4/Pin 6): Ground. Connect the bottom

of the resistor divider that sets output voltage directly to

GND for the best regulation.

IN (Pin 5/Pin 4): Input. The IN pin supplies power to the

device. The LT3008 requires a bypass capacitor at IN if

the device is more than six inches away from the main

input ﬁlter capacitor. In general, the output impedance of

a battery rises with frequency, so it is advisable to include

a bypass capacitor in battery-powered circuits. A bypass

capacitor in the range of 0.1μF to 10μF will sufﬁce. The

LT3008 withstands reverse voltages on the IN pin with re-

spect to ground and the OUT pin. In the case of a reversed

input, which occurs with a battery plugged in backwards,

the LT3008 acts as if a blocking diode is in series with its

input. No reverse current ﬂows into the LT3008 and no

reverse voltage appears at the load. The device protects

both itself and the load.

NC (Pin 8, TSOT-23 Package Only): No Connect. Pin 8

is an NC pin in the TSOT-23 package. This pin is not tied

to any internal circuitry. It may be ﬂoated, tied to V or

IN

tied to GND.

Exposed Pad (Pin 7, DFN Package Only): Ground. The

Exposed Pad (backside) of the DFN package is an electri-

cal connection to GND. To ensure optimum performance,

solder Pin 7 to the PCB and tie directly to Pin 6.

3008f

7

LT3008

APPLICATIONS INFORMATION

The LT3008 is a low dropout linear regulator with ultra-

low quiescent current and shutdown. Quiescent current is

extremely low at 3μA and drops well below 1μA in shut-

down. The device supplies up to 20mA of output current.

Dropout voltage at 20mA is typically 300mV. The LT3008

incorporatesseveralprotectionfeatures,makingitidealfor

useinbattery-poweredsystems.Thedeviceprotectsitself

against both reverse-input and reverse-output voltages.

In battery backup applications, where a backup battery

holds up the output when the input is pulled to ground,

the LT3008 acts as if a blocking diode is in series with its

output and prevents reverse current ﬂow. In applications

where the regulator load returns to a negative supply, the

output can be pulled below ground by as much as 50V

without affecting startup or normal operation.

Typical Performance Characteristics.

Speciﬁcations for output voltages greater than 0.6V are

proportional to the ratio of the desired output voltage to

0.6V:V /0.6V.Forexample,loadregulationforanoutput

OUT

current change of 100μA to 20mA is –0.5mV typical at

V

OUT

= 0.6V. At V

= 5V, load regulation is:

OUT

5V

0.6V

• (−0.5mV) = −4.17mV

Table 1 shows resistor divider values for some com-

mon output voltages with a resistor divider current of

about 1μA.

Table 1. Output Voltage Resistor Divider Values

V

R1

R2

OUT

1V

1.2V

1.5V

1.8V

2.5V

3V

604k

590k

619k

590k

402k

Adjustable Operation

590k

The LT3008 has an output voltage range of 0.6V to 44.5V.

Figure1showsthatoutputvoltageissetbytheratiooftwo

external resistors. The IC regulates the output to maintain

the ADJ pin voltage at 600mV referenced to ground. The

current in R1 equals 600mV/R1 and the current in R2 is

the current in R1 minus the ADJ pin bias current. The

ADJ pin bias current, typically 400pA at 25°C, ﬂows out

of the pin. Calculate the output voltage using the formula

in Figure 1. An R1 value of 619k sets the divider current

to 0.97μA. Do not make R1’s value any greater than 619k

to minimize output voltage errors due to the ADJ pin bias

current and to insure stability under minimum load condi-

tions. In shutdown, the output turns off and the divider

current is zero. Curves of ADJ Pin Voltage vs Temperature

and ADJ Pin Bias Current vs Temperature appear in the

887k

1.18M

1.87M

2.37M

2.8M

4.32M

3.3V

5V

Because the ADJ pin is relatively high impedance (de-

pendingontheresistordividerused),straycapacitances

atthispinshouldbeminimized.Specialattentionshould

be given to any stray capacitances that can couple ex-

ternal signals onto the ADJ pin producing undesirable

output transients or ripple.

V

OUT

IN

OUT

ADJ

V

= 600mV • (1 + R2/R1) – (I

= 600mV

= 0.4nA at 25°C

• R2)

ADJ

OUT

ADJ

V

IN

LT3008

R2

R1

I

ADJ

OUTPUT RANGE = 0.6V to 44.5V

SHDN

GND

3008 F01

Figure 1. Adjustable Operation

3008f

8

LT3008

APPLICATIONS INFORMATION

Extra care should be taken in assembly when using high

valuedresistors.Smallamountsofboardcontamination

canleadtosigniﬁcantshiftsinoutputvoltage.Appropriate

post-assembly board cleaning measures should be

implemented to prevent board contamination. If the

board is to be subjected to humidity cycling or if board

cleaningmeasurescannotbeguaranteed,consideration

shouldbegiventousingresistorsanorderofmagnitude

smaller than in Table 1 to prevent contamination from

causing unwanted shifts in the output voltage.

dielectrics,eachwithdifferentbehavioracrosstemperature

and applied voltage. The most common dielectrics are

speciﬁed with EIA temperature characteristic codes of

Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics

provide high C-V products in a small package at low cost,

but exhibit strong voltage and temperature coefﬁcients as

shown in Figures 2 and 3. When used with a 5V regulator,

a 16V 10μF Y5V capacitor can exhibit an effective value

as low as 1μF to 2μF for the DC bias voltage applied and

over the operating temperature range. The X5R and X7R

dielectrics yield more stable characteristics and are more

suitable for use as the output capacitor. The X7R type has

better stability across temperature, while the X5R is less

expensive and is available in higher values. One must still

exercise care when using X5R and X7R capacitors; the

X5R and X7R codes only specify operating temperature

rangeandmaximumcapacitancechangeovertemperature.

Capacitance change due to DC bias with X5R and X7R

capacitors is better than Y5V and Z5U capacitors, but can

still be signiﬁcant enough to drop capacitor values below

appropriate levels. Capacitor DC bias characteristics tend

toimproveascomponentcasesizeincreases,butexpected

capacitance at operating voltage should be veriﬁed.

Output Capacitance and Transient Response

The LT3008 is stable with a wide range of output capaci-

tors.TheESRoftheoutputcapacitoraffectsstability,most

notably with small capacitors. Use a minimum output

capacitor of 2.2μF with an ESR of 3Ω or less to prevent

oscillations.TheLT3008isamicropowerdeviceandoutput

loadtransientresponseisafunctionofoutputcapacitance.

Larger values of output capacitance decrease the peak

deviations and provide improved transient response for

larger load current changes.

Give extra consideration to the use of ceramic capacitors.

Manufacturers make ceramic capacitors with a variety of

20

40

20

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

0

X5R

0

–20

–40

Y5V

–60

Y5V

–80

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

–100

0

8

12 14

2

4

6

10

16

50

TEMPERATURE (°C)

100 125

–50 –25

0

25

75

DC BIAS VOLTAGE (V)

3008 F02

3008 F03

Figure 2. Ceramic Capacitor DC Bias Characteristics

Figure 3. Ceramic Capacitor Temperature Characteristics

3008f

9

LT3008

APPLICATIONS INFORMATION

Voltage and temperature coefﬁcients are not the only

sources of problems. Some ceramic capacitors have a

piezoelectric response. A piezoelectric device generates

voltage across its terminals due to mechanical stress,

similar to the way a piezoelectric accelerometer or micro-

phone works. For a ceramic capacitor, the stress can be

induced by vibrations in the system or thermal transients.

The resulting voltages produced can cause appreciable

amounts of noise, especially when a ceramic capacitor is

used for noise bypassing. A ceramic capacitor produced

Figure 4’s trace in response to light tapping from a pencil.

Similar vibration induced behavior can masquerade as

increased output voltage noise.

Thermal Considerations

The LT3008’s maximum rated junction temperature of

125°Climitsitspower-handlingcapability.Twocomponents

comprise the power dissipated by the device:

1. Output current multiplied by the input/output voltage

differential: I

• (V – V

)

OUT

IN

OUT

2. GND pin current multiplied by the input voltage:

• V

I

GND

IN

GND pin current is found by examining the GND Pin Cur-

rent curves in the Typical Performance Characteristics

section. Power dissipation is equal to the sum of the two

components listed prior.

TheLT3008regulatorhasinternalthermallimitingdesigned

to protect the device during overload conditions. For con-

tinuous normal conditions, do not exceed the maximum

junction temperature rating of 125°C. Carefully consider

all sources of thermal resistance from junction to ambi-

ent including other heat sources mounted in proximity to

the LT3008. For surface mount devices, heat sinking is

accomplished by using the heat spreading capabilities of

the PC board and its copper traces. Copper board stiffen-

ers and plated through-holes can also be used to spread

the heat generated by power devices.

V

C

LOAD

= 0.6V

= 22μF

= 10μA

OUT

I

V

OUT

500μV/DIV

3008 F04

100ms/DIV

Figure 4. Noise Resulting from Tapping

on a Ceramic Capacitor

3008f

10

LT3008

APPLICATIONS INFORMATION

The following tables list thermal resistance for several

different board sizes and copper areas. All measurements

were taken in still air on 3/32" FR-4 two-layer boards with

one ounce copper.

Calculating Junction Temperature

Example: Given an output voltage of 3.3V, an input volt-

age range of 12V 5%, an output current range of 0mA

to 20mA and a maximum ambient temperature of 85°C,

what will the maximum junction temperature be for an

application using the DC package?

PCB layers, copper weight, board layout and thermal vias

affect the resultant thermal resistance. Although Tables

2 and 3 provide thermal resistance numbers for 2-layer

boards with 1 ounce copper, modern multi-layer PCBs

provide better performance than found in these tables.

For example, a 4-layer, 1 ounce copper PCB board with

3 thermal vias from the DFN exposed backside or the

3 fused TSOT-23 GND pins to inner layer GND planes

achieves 45°C/W thermal resistance. Demo circuit DC

1388A’s board layout achieves this 45°C/W performance.

This is approximately a 30% improvement over the lowest

numbers shown in Tables 2 and 3.

The power dissipated by the device is equal to:

I

(V

– V ) + I

(V

)

OUT(MAX) IN(MAX)

OUT

GND IN(MAX)

where,

I

= 20mA

= 12.6V

OUT(MAX)

V

IN(MAX)

I

at (I = 20mA, V = 12.6V) = 0.3mA

OUT IN

GND

So,

P = 20mA(12.6V – 3.3V) + 0.3mA(12.6V) = 189.8mW

Table 2: Measured Thermal Resistance for DC Package

COPPER AREA

The thermal resistance ranges from 65°C/W to 85°C/W

dependingonthecopperarea.Sothejunctiontemperature

rise above ambient approximately equals:

BOARD

AREA

THERMAL RESISTANCE

TOPSIDE*

BACKSIDE

(JUNCTION-TO-AMBIENT)

2

2500mm

65°C/W

70°C/W

75°C/W

80°C/W

85°C/W

2

1000mm

2500mm

0.1898W(75°C/W) = 14.2°C

2

225mm

2500mm

The maximum junction temperature equals the maximum

junctiontemperatureriseaboveambientplusthemaximum

ambient temperature or:

2

100mm

2500mm

2

50mm

2500mm

*Device is mounted on the topside.

T

= 85°C + 14.2°C = 99.2°C

J(MAX)

Table 3: Measured Thermal Resistance for TSOT-23 Package

COPPER AREA

BOARD

AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE*

BACKSIDE

2

2500mm

65°C/W

67°C/W

70°C/W

75°C/W

85°C/W

2

1000mm

2500mm

2

225mm

2500mm

2

100mm

2500mm

2

50mm

2500mm

*Device is mounted on the topside.

3008f

11

LT3008

APPLICATIONS INFORMATION

voltage. Current ﬂows from the bottom resistor in the

divider and from the ADJ pin’s internal clamp through the

top resistor in the divider to the external circuitry pulling

OUT below ground. If IN is powered by a voltage source,

OUT sources current equal to its current limit capability

and the LT3008 protects itself by thermal limiting if neces-

sary. In this case, grounding the SHDN pin turns off the

LT3008 and stops OUT from sourcing current.

Protection Features

The LT3008 incorporates several protection features that

make it ideal for use in battery-powered circuits. In addition

tothenormalprotectionfeaturesassociatedwithmonolithic

regulators,suchascurrentlimitingandthermallimiting,the

devicealsoprotectsagainstreverse-inputvoltages,reverse-

output voltages and reverse output-to-input voltages.

Current limit protection and thermal overload protection

protect the device against current overload conditions at

the output of the device. For normal operation, do not

exceed a junction temperature of 125°C.

The LT3008 incurs no damage if the ADJ pin is pulled

above or below ground by 50V. If IN is left open circuit or

grounded, ADJ acts like a 100k resistor in series with a

diode when pulled above or below ground.

The IN pin withstands reverse voltages of 50V. The device

limits current ﬂow to less than 20μA (typically less than

1μA) and no negative voltage appears at OUT. The device

protects both itself and the load against batteries that are

plugged in backwards.

In circuits where a backup battery is required, several

different input/output conditions can occur. The output

voltage may be held up while the input is either pulled

to ground, pulled to some intermediate voltage or is left

open circuit. Current ﬂow back into the output follows the

curve shown in Figure 5.

The SHDN pin cannot be driven below GND unless tied to

the IN pin. If the SHDN pin is driven below GND while IN

is powered, the output will turn on. SHDN pin logic cannot

be referenced to a negative rail.

If the LT3008 IN pin is forced below the OUT pin or the

OUT pin is pulled above the IN pin, input current typically

drops to less than 1μA. This occurs if the LT3008 input is

connected to a discharged (low voltage) battery and either

a backup battery or a second regulator circuit holds up

the output. The state of the SHDN pin has no effect in the

reverse current if OUT is pulled above IN.

The LT3008 incurs no damage if OUT is pulled below

ground. If IN is left open circuit or grounded, OUT can be

pulled below ground by 50V. No current ﬂows from the

pass transistor connected to OUT. However, current ﬂows

in (but is limited by) the resistor divider that sets output

100

90

80

70

60

50

40

30

20

10

0

ADJ CURRENT

OUT CURRENT

0

1

2

3

4

5

6

7

8

9

10

OUTPUT AND ADJ VOLTAGE (V)

3008 F05

Figure 5. Reverse Output Current

3008f

12

LT3008

TYPICAL APPLICATIONS

Keep-Alive Power Supply

NO PROTECTION

DIODES NEEDED!

3.3V

V

IN

OUT

ADJ

12V

2.8M

1%

1μF

2.2μF

LT3008

LOAD:

SHDN

SYSTEM MONITOR,

VOLATILE MEMORY, ETC.

619k

1%

GND

3009 TA02

Last-Gasp Circuit

LINE POWER

V

LINE

SENSE

12V TO 15V

D

CHARGE

LINE

INTERRUPT

DETECT

R

LIMIT

TO

5V

PWR

FAULT

MONITORING

CENTER

IN

OUT

GND

4.32M

1%

SUPERCAP

1μF

2.2μF

LT3008

3008 TA03

SHDN

GND

ADJ

590k

1%

3008f

13

LT3008

PACKAGE DESCRIPTION

DC Package

6-Lead Plastic DFN (2mm × 2mm)

(Reference LTC DWG # 05-08-1703)

R = 0.115

TYP

0.56 p 0.05

(2 SIDES)

0.38 p 0.05

4

6

0.675 p 0.05

2.50 p 0.05

0.61 p 0.05

(2 SIDES)

2.00 p 0.10

(4 SIDES)

1.15 p 0.05

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

PIN 1

PACKAGE

OUTLINE

CHAMFER OF

EXPOSED PAD

(DC6) DFN 1103

3

1

0.25 p 0.05

0.50 BSC

0.75 p 0.05

0.200 REF

1.37 p 0.05

(2 SIDES)

1.42 p 0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.00 – 0.05

BOTTOM VIEW—EXPOSED PAD

NOTE:

1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2)

2. DRAWING NOT TO SCALE

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

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

3008f

14

LT3008

PACKAGE DESCRIPTION

TS8 Package

8-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1639 Rev Ø)

2.90 BSC

(NOTE 4)

0.52

MAX

0.65

REF

1.22 REF

1.50 – 1.75

(NOTE 4)

2.80 BSC

1.4 MIN

3.85 MAX 2.62 REF

PIN ONE ID

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.22 – 0.36

8 PLCS (NOTE 3)

0.65 BSC

0.80 – 0.90

0.20 BSC

DATUM ‘A’

0.01 – 0.10

1.00 MAX

0.30 – 0.50 REF

1.95 BSC

0.09 – 0.20

(NOTE 3)

TS8 TSOT-23 0802

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

3008f

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

LT3008

TYPICAL APPLICATION

Low Duty Cycle Applications

Average Power Savings for Low Duty Cycle Applications

0mA to 10mA Pulsed Load, IN = 12V

100

90

80

70

60

3.3V

V

IN

OUT

ADJ

12V

2.8M

1%

1μF

2.2μF

LT3008

LOW DUTY CYCLE

PULSED LOAD

0 TO 10mA

SHDN

GND

619k

1%

100μA I

Q

50

40

30

20

10

0

3008 TA04a

30μA I

Q

10μA I

Q

1

10

0.1

DUTY CYCLE (%)

3008 TA04b

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

: 1.8V to 20V, V

LT1761

100mA, Low Noise Micropower LDO

150mA, Low Noise Micropower LDO

500mA, Low Noise Micropower LDO

V

IN

= 1.22V, V = 0.3V, I = 20μA, I < 1μA, Low Noise < 20μV

,

OUT

DO

Q

SD

RMS

Stable with 1μF Ceramic Capacitors, ThinSOT^TMPackage

LT1762

V

: 1.8V to 20V, V

= 1.22V, V = 0.3V, I = 25μA, I < 1μA, Low Noise < 20μV

DO Q SD

IN

OUT

MS8 Package

LT1763

V

IN

: 1.8V to 20V, V

= 1.22V, V = 0.3V, I = 30μA, I < 1μA, Low Noise < 20μV

DO Q SD

S8 Package

LT1764/LT1764A

LT1962

3A, Low Noise, Fast Transient

Response LDOs

V

: 2.7V to 20V, V

= 1.21V, V = 0.34V, I = 1mA, I < 1μA, Low Noise < 40μV

,

IN

DO

Q

SD

RMS

“A” Version Stable with Ceramic Capacitors, DD and TO220-5 Packages

300mA, Low Noise Micropower LDO

V

IN

: 1.8V to 20V, V = 1.22V, V = 0.27V, I = 30μA, I < 1μA,

OUT(MIN)

DO

Q

SD

Low Noise: < 20μV

, MS8 Package

RMS

LT1963/LT1963A

1.5A, Low Noise, Fast Transient

Response LDOs

V

: 2.1V to 20V, V

= 1.21V, V = 0.34V, I = 1mA, I < 1μA,

IN

OUT(MIN) DO Q SD

RMS

Low Noise: < 40μV

, “A” Version Stable with Ceramic Capacitors, DD, TO220-5,

SOT223 and S8 Packages

LT3009

LT3020

20mA, 3μA I Micropower LDO

V

: 1.6V to 20V, Low I : 3μA, V = 0.28V, 2mm × 2mm DFN and SC-70-8 Packages

Q

IN

Q

DO

100mA, Low Voltage VLDO

V

: 0.9V to 10V, V

= 0.20V, V = 0.15V, I = 120μA, I < 1μA, 3mm × 3mm DFN

DO Q SD

IN

OUT(MIN)

and MS8 Packages

LT3021

500mA, Low Voltage VLDO

V

: 0.9V to 10V, V

= 0.20V, V = 0.16V, I = 120μA, I < 3μA, 5mm × 5mm DFN

DO Q SD

IN

OUT(MIN)

and SO8 Packages

LT3080/ LT3080-1 1.1A, Parallelable, Low Noise,

Low Dropout Linear Regulator

300mV Dropout Voltage (2-supply operation), Low Noise: 40μV

, V : 1.2V to 36V,

RMS IN

V

: 0V to 35.7V, current-based reference with 1-resistor V

set; directly parallelable

OUT

(no op amp required), stable with ceramic caps, TO-220, SOT-223, MSOP and 3 × 3 DFN

Packages; “-1” version has integrated internal ballast resistor

LT3085

500mA, Parallelable, Low Noise,

Low Dropout Linear Regulator

275mV Dropout Voltage (2-supply operation), Low Noise: 40μVRMS, V : 1.2V to 36V,

IN

V

: 0V to 35.7V, current-based reference with 1-resistor V

set; directly parallelable

OUT

(no op amp required), stable with ceramic caps, MSOP-8 and 2 × 3 DFN packages

ThinSOT is a trademark of Linear Technology Corporation.

3008f

LT 1108 • 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：	LT3008EDC#TRMPBF
厂家：	Linear
描述：	暂无描述稳压器
文件：	总16页 (文件大小：196K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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