LTC1799IS5#TRMPBF_技术文档

LTC1799

1kHz to 33MHz

Resistor Set SOT-23 Oscillator

FeaTures

DescripTion

n

One External Resistor Sets the Frequency

The LTC^®1799 is a precision oscillator that is easy to use

and occupies very little PC board space. The oscillator

frequency is programmed by a single external resistor

n

Fast Start-Up Time: <1ms

n

1kHz to 33MHz Frequency Range

n

Frequency Error ≤1.5% 5kHz to 20MHz

(R ). TheLTC1799hasbeendesignedforhighaccuracy

SET

(T = 25°C)

operation (≤1.5% frequency error) without the need for

A

n

Frequency Error ≤2% 5kHz to 20MHz

external trim components.

(T = 0°C to 70°C)

A

The LTC1799 operates with a single 2.7V to 5.5V power

supply and provides a rail-to-rail, 50% duty cycle square

wave output. The CMOS output driver ensures fast rise/

fall times and rail-to-rail switching. The frequency-setting

resistor can vary from 3k to 1M to select a master oscil-

lator frequency between 100kHz and 33MHz (5V supply).

The three-state DIV input determines whether the master

clock is divided by 1, 10 or 100 before driving the out-

put, providing three frequency ranges spanning 1kHz to

33MHz (5V supply). The LTC1799 features a proprietary

n

±±0ppm/°C Temperature Stability

0.05%/V Supply Stability

50% ±1% Duty Cycle 1kHz to 2MHz

50% ±5% Duty Cycle 2MHz to 20MHz

1mA Typical Supply Current

100Ω CMOS Output Driver

Operates from a Single 2.7V to 5.5V Supply

Low Profile (1mm) SOT-23 (ThinSOT™ Package)

applicaTions

feedbackloopthatlinearizestherelationshipbetweenR

SET

n

Low Cost Precision Oscillator

and frequency, eliminating the need for tables to calculate

frequency. The oscillator can be easily programmed using

the simple formula outlined below:

n

Charge Pump Driver

n

Switching Power Supply Clock Reference

n

Clocking Switched Capacitor Filters

DIV Pin = V⁺

⎧

n

Fixed Crystal Oscillator Replacement

100,

10,

1,

⎛

⎜

⎝

⎞

⎟

⎠

⎪

⎨

⎪

⎩

10k

N•R

n

Ceramic Oscillator Replacement

f_OSC= 10MHz •

, N =

DIV Pin = Open

DIV Pin = GND

n

Small Footprint Replacement for Econ Oscillators

SET

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

ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners. Protected by U.S. Patents including 63±2817 and 661±313.

Typical Distribution of Frequency Error,

T_A= 25°C (5kHz ≤ f_OSC≤ 20MHz, V⁺= 5V)

Typical applicaTion

25

20

15

10

5

Basic Connection

1kHz ≤ f

5

≤ 33MHz

OSC

5V

1

2

3

+

V

OUT

LTC1799

0.1µF

5V

3k ≤ R

≤ 1M

SET

GND

SET

÷100

÷1

÷10

4

DIV

OPEN

1799 TA01

0

TSOT-23 Actual Size

–1.25 –0.75

–0.25 0 0.25

0.75

1.25

FREQUENCY ERROR (%)

1799 TA02

1799fd

1

For more information www.linear.com/LTC1799

LTC1799

absoluTe MaxiMuM raTings

pin conFiguraTion

(Note 1)

TOP VIEW

+

Supply Voltage (V ) to GND ......................... –0.3V to 6V

+

V

1

2

3

5

4

OUT

DIV

+

DIV to GND .....................................–0.3V to (V + 0.3V)

GND

SET

SET to GND.....................................–0.3V to (V + 0.3V)

Operating Temperature Range

S5 PACKAGE

5-LEAD PLASTIC TSOT-23

= 150°C, θ = 256°C/W

LTC1799C ................................................ 0°C to 70°C

LTC1799I .............................................–±0°C to 85°C

LTC1799H.......................................... –±0°C to 125°C

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

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

T

JMAX

JA

orDer inForMaTion ^{http://www.linear.com/product/LTC1799#orderinfo}

LEAD FREE FINISH

LTC1799CS5#PBF

LTC1799IS5#PBF

LTC1799HS5#PBF

TAPE AND REEL

PART MARKING*

PACKAGE DESCRIPTION

5-Lead Plastic TSOT-23

TEMPERATURE RANGE

LTC1799CS5#TRPBF

LTC1799IS5#TRPBF

LTC1799HS5#TRPBF

LTND

0°C to 70°C

LTNE

–±0°C to 85°C

–±0°C to 125°C

LTND

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

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through

designated sales channels with #TRMPBF suffix.

elecTrical characTerisTics ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V⁺= 2.7V to 5.5V, R_L= 5k, C_L= 5pF, unless otherwise noted. All

voltages are with respect to GND.

SYMBOL PARAMETER

∆f Frequency Accuracy

CONDITIONS

MIN

TYP

MAX

UNITS

+

V = 5V

5kHz ≤ f ≤ 20MHz

±0.5

±1.5

±2

±2.5

%

l

5kHz ≤ f ≤ 20MHz, LTC1799C

5kHz ≤ f ≤ 20MHz, LTC1799I/H

1kHz ≤ f ≤ 5kHz

(Notes 2, 3)

±2.5

20MHz ≤ f ≤ 33MHz

+

V = 3V

5kHz ≤ f ≤ 10MHz

±0.5

±1.5

±2

±2.5

%

l

5kHz ≤ f ≤ 10MHz, LTC1799C

5kHz ≤ f ≤ 10MHz, LTC1799I/H

1kHz ≤ f ≤ 5kHz

±2.5

10MHz ≤ f ≤ 20MHz

+

R

Frequency-Setting Resistor Range

Maximum Frequency

|∆f| < 1.5%

V = 5V

5

10

200

kΩ

SET

MAX

MIN

+

V = 3V

+

f

|∆f| < 2.5%, Pin ± = 0V

V = 5V

33

20

MHz

+

V = 3V

+

Minimum Frequency

|∆f| < 2.5%, Pin ± = V

1

kHz

%/°C

%/V

l

∆f/∆T

∆f/∆V

Freq Drift Over Temp (Note 3)

Freq Drift Over Supply (Note 3)

R

= 31.6k

±0.00±

0.05

SET

+

V = 3V to 5V, R = 31.6k

0.1

SET

+

Timing Jitter

(Note ±)

Pin ± = V

0.06

0.13

0.±

%

Pin ± = Open

Pin ± = 0V

1799fd

2

For more information www.linear.com/LTC1799

LTC1799

elecTrical characTerisTics ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V⁺= 2.7V to 5.5V, R_L= 5k, C_L= 5pF, unless otherwise noted. All

voltages are with respect to GND.

SYMBOL PARAMETER

Long-Term Stability of Output Frequency

CONDITIONS

MIN

TYP

MAX

UNITS

300

ppm/√kHr

+

l

Duty Cycle (Note 7)

Pin ± = V or Open (DIV Either by 100 or 10)

±9

±5

50

51

55

%

Pin ± = 0V (DIV by 1), R = 5k to 200k

SET

+

l

V

Operating Supply Range

Power Supply Current

2.7

5.5

1.1

V

+

I

R

= 200k, Pin ± = V , R = ∞

V = 5V

0.7

mA

S

SET

L

+

l

= 10k, Pin ± = 0V, R = ∞

V = 5V

2.±

2

mA

L

+

V = 3V

+

l

V

High Level DIV Input Voltage

Low Level DIV Input Voltage

DIV Input Current (Note 5)

V – 0.±

V

IH

IL

0.5

8

+

l

I

Pin ± = V

V = 5V

5

–5

µA

DIV

+

Pin ± = 0V

V = 5V

–8

+

l

V

High Level Output Voltage (Note 5)

V = 5V,

I

= –1mA

= –±mA

±.8

±.5

±.95

±.8

V

OH

LTC1799C/I

+

l

V = 5V,

I

= –1mA

= –±mA

±.75

±.±0

±.95

±.75

V

OH

LTC1799H

+

l

V = 3V,

I

= –1mA

= –±mA

2.7

2.2

2.9

2.6

V

OH

LTC1799C/I

+

l

V = 3V,

I

= –1mA

= –±mA

2.65

2.10

2.90

2.55

V

OH

LTC1799H

+

l

V

Low Level Output Voltage (Note 5)

V = 5V,

I

= 1mA

= ±mA

0.05

0.2

0.15

0.±

V

OL

LTC1799C/I

+

l

V = 5V,

I

= 1mA

= ±mA

0.05

0.25

0.20

0.50

V

OL

LTC1799H

+

l

V = 3V,

I

= 1mA

= ±mA

0.1

0.±

0.3

0.7

V

OL

LTC1799C/I

+

l

V = 3V,

I

= 1mA

= ±mA

0.10

0.±5

0.35

0.80

V

OL

LTC1799H

+

t

OUT Rise Time

(Note 6)

V = 5V

Pin ± = V or Floating, RL = ∞

Pin ± = 0V, RL = ∞

1±

7

ns

r

f

+

V = 3V

Pin ± = V or Floating, RL = ∞

19

11

ns

Pin ± = 0V, RL = ∞

+

OUT Fall Time

(Note 6)

V = 5V

Pin ± = V or Floating, RL = ∞

13

6

ns

Pin ± = 0V, RL = ∞

+

V = 3V

Pin ± = V or Floating, RL = ∞

19

10

ns

Pin ± = 0V, RL = ∞

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: Jitter is the ratio of the peak-to-peak distribution of the period to

the mean of the period. This specification is based on characterization and

is not 100% tested.

Note 5: To conform with the Logic IC Standard convention, current out of

Note 2: Frequencies near 100kHz and 1MHz may be generated using two

a pin is arbitrarily given as a negative value.

different values of R (see the Table 1 in the Applications Information

section). For these frequencies, the error is specified under the following

SET

Note 6: Output rise and fall times are measured between the 10% and 90%

power supply levels. These specifications are based on characterization.

Note 7: Guaranteed by 5V test.

assumption: 10k < R ≤ 100k. The frequency accuracy for f

= 20MHz

SET

OSC

is guaranteed by design and test correlation.

Note 3: Frequency accuracy is defined as the deviation from the

equation.

f

OSC

1799fd

3

For more information www.linear.com/LTC1799

LTC1799

Typical perForMance characTerisTics

Frequency Variation

vs R_SET

Frequency Variation

Over Temperature

4

3

1.00

0.75

0.50

0.25

R

= 31.6k

T

= 25°C

SET

A

÷1 OR ÷10 OR ÷100

GUARANTEED LIMITS APPLY

OVER 5k TO 200k RANGE

2

TYPICAL

HIGH

TYPICAL

HIGH

1

0

–0.25

–0.50

–0.75

–1.00

TYPICAL

LOW

–1

–2

–3

–4

TYPICAL

LOW

40

TEMPERATURE (°C)

80

–40 –20

0

20

60

1

10

100

1000

R

SET

(kΩ)

1799 G01

1799 G02

Supply Current

vs Output Frequency

Peak-to-Peak Jitter vs Frequency

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

T

= 25°C

= 5pF

= 1M

A

L

C

R

÷1

÷1 (5V)

÷10 (5V)

÷100 (5V)

÷10

÷100

÷100 (3V) ÷10 (3V) ÷1 (3V)

1k

10k

100k

1M

10M

(Hz)

100M

1k

10k

100k

1M

10M

(Hz)

100M

OUTPUT FREQUENCY, f

OUT

1799 G03

1799 G04

Output Resistance

vs Supply Voltage

LTC1799 Output Operating at

20MHz, V_S= 5V

LTC1799 Output Operating at

10MHz, V_S= 3V

140

120

100

80

+

V

= 3V, R

= 10k, C = 10pF

L

T

A

= 25°C

V

= 5V, R = 5k, C = 10pF

SET L

SET

OUTPUT SOURCING CURRENT

1V/DIV

60

1799 G06

1799 G07

12.5ns/DIV

25ns/DIV

OUTPUT SINKING CURRENT

40

2.5 3.0 3.5 4.0 4.5

5.0 5.5 6.0

SUPPLY VOLTAGE (V)

1799 G05

1799fd

4

For more information www.linear.com/LTC1799

LTC1799

pin FuncTions

V (Pin 1): Voltage Supply (2.7V ≤ V ≤ 5.5V). This sup-

ply must be kept free from noise and ripple. It should be

bypasseddirectlytoagroundplanewitha0.1µFcapacitor.

+

Floating Pin ± divides the master oscillator by 10. Pin ±

+

should be tied to V for the ÷100 setting, the lowest fre-

quency range. To detect a floating DIV pin, the LTC1799

attempts to pull the pin toward midsupply. This is realized

GND (Pin 2): Ground. Should be tied to a ground plane

for best performance.

+

with two internal current sources, one tied to V and Pin

± and the other one tied to ground and Pin ±. Therefore,

driving the DIV pin high requires sourcing approximately

5µA. Likewise, driving DIV low requires sinking 5µA.

When Pin ± is floated, preferably it should be bypassed

by a 1nF capacitor to ground or it should be surrounded

by a ground shield to prevent excessive coupling from

other PCB traces.

SET (Pin 3): Frequency-Setting Resistor Input. The value

of the resistor connected between this pin and V deter-

+

mines the oscillator frequency. The voltage on this pin is

held by the LTC1799 to approximately 1.13V below the

+

V voltage. For best performance, use a precision metal

film resistor with a value between 10k and 200k and limit

the capacitance on this pin to less than 10pF.

OUT (Pin 5): Oscillator Output. This pin can drive 5kΩ

and/or 10pF loads. Larger loads may cause inaccuracies

due to supply bounce at high frequencies. Transients will

not cause latchup if the current into/out of the OUT pin is

limited to 50mA.

DIV (Pin 4): Divider-Setting Input. This three-state input

selects among three divider settings, determining the

value of N in the frequency equation. Pin ± should be tied

to GND for the ÷1 setting, the highest frequency range.

block DiagraM

V

= 1.13V ±±25

RES

+

PROGRAMMABLE

OUT

(V – V

)

V

SET

1

2

DIVIDER

(÷1, 10 OR 100)

+

R

SET

V

GAIN = 1

MASTER OSCILLATOR

I

RES

SET

DIVIDER

SELECT

2µA

DIV

3

±

–

I

RES

ƒ

MO

= 100MHz • kΩ •

+

(V – V

)

V

SET

BIAS

–

THREE-STATE

INPUT DETECT

GND

4

I

RES

2µA

GND

1799 BD

1799fd

5

For more information www.linear.com/LTC1799

LTC1799

Theory oF operaTion

As shown in the Block Diagram, the LTC1799’s master

(Pin 5). The divide-by value is determined by the state of

the DIV input (Pin ±). Tie DIV to GND or drive it below 0.5V

to select ÷1. This is the highest frequency range, with the

master output frequency passed directly to OUT. The DIV

pin may be floated or driven to midsupply to select ÷10,

the intermediate frequency range. The lowest frequency

oscillator is controlled by the ratio of the voltage between

+

the V and SET pins and the current entering the SET pin

(I ).ThevoltageontheSETpinisforcedtoapproximately

RES

+

1.13V below V by the PMOS transistor and its gate bias

voltage. This voltage is accurate to ±7% at a particular

input current and supply voltage (see Figure 1). The ef-

fective input resistance is approximately 2k.

+

range, ÷100, is selected by tying DIV to V or driving it to

+

within0.±VofV . Figure2showstherelationshipbetween

R

, divider setting and output frequency, including the

+

SET

A resistor R , connected between the V and SET pins,

SET

overlapping frequency ranges near 100kHz and 1MHz.

+

“locks together” the voltage (V – V ) and current, I

,

SET

RES

variation.ThisprovidestheLTC1799’shighprecision.The

The CMOS output driver has an on resistance that is typi-

cally less than 100Ω. In the ÷1 (high frequency) mode,

the rise and fall times are typically 7ns with a 5V supply

and 11ns with a 3V supply. These times maintain a clean

square wave at 10MHz (20MHz at 5V supply). In the ÷10

and÷100modes,wheretheoutputfrequencyismuchlower,

slew rate control circuitry in the output driver increases

the rise/fall times to typically 1±ns for a 5V supply and

19ns for a 3V supply. The reduced slew rate lowers EMI

(electromagnetic interference) and supply bounce.

master oscillation frequency reduces to:

⎛

⎜

⎝

⎞

⎟

⎠

10kΩ

ƒ_MO= 10MHz •

R

SET

The LTC1799 is optimized for use with resistors between

10kand200k,correspondingtomasteroscillatorfrequen-

ciesbetween0.5MHzand10MHz.Accuratefrequenciesup

to 20MHz (R = 5k) are attainable if the supply voltage

SET

is greater than ±V.

Toextendtheoutputfrequencyrange,themasteroscillator

signal may be divided by 1, 10 or 100 before driving OUT

1.4

1000

T

= 25°C

A

1.3

1.2

1.1

1.0

0.9

0.8

+

V

= 5V

MOST

ACCURATE

OPERATION

÷100

÷10

÷1

100

10

1

+

V

= 3V

1

10

100

1000

1k

10k

100k

1M

10M

100M

I

(µA)

RES

DESIRED OUTPUT FREQUENCY (Hz)

1799 F01

1799 F02

Figure 1. V⁺– V_SETVariation with I_RES

Figure 2. R_SETvs Desired Output Frequency

1799fd

6

For more information www.linear.com/LTC1799

LTC1799

applicaTions inForMaTion

SELECTING THE DIVIDER SETTING AND RESISTOR

ALTERNATIVE METHODS OF SETTING THE OUTPUT

FREꢀUENCY OF THE LTC1799

The LTC1799’s master oscillator has a frequency range

spanning0.1MHzto33MHz.However,accuracymaysuffer

if the master oscillator is operated at greater than 10MHz

with a supply voltage lower than ±V. A programmable

divider extends the frequency range to greater than three

decades. Table1describestherecommendedfrequencies

for each divider setting. Note that the ranges overlap; at

some frequencies there are two divider/resistor combina-

tions that result in the desired frequency.

The oscillator may be programmed by any method that

sources a current into the SET pin (Pin 3). The circuit in

Figure 3 sets the oscillator frequency using a program-

mable current source and in the expression for f , the

OSC

CONTROL

resistor R

is replaced by the ratio of 1.13V/I

.

SET

As already explained in the “Theory of Operation,” the

voltage difference between V and SET is approximately

+

1.13V, therefore, the Figure 3 circuit is less accurate than

if a resistor controls the oscillator frequency.

In general, any given oscillator frequency (f ) should

OSC

be obtained using the lowest master oscillator frequency.

Figure±showstheLTC1799configuredasaVCO.Avoltage

source is connected in series with an external 10k resis-

Lower master oscillator frequencies use less power and

are more accurate. For instance, f

= 100kHz can be

tor. The output frequency, f , will vary with V

,

OSC

CONTROL

+

obtained by either R

= 10k, N = 100, master oscilla-

that is the voltage source connected between V and the

SET

tor = 10MHz or R

= 100k, N = 10, master oscillator =

SET pin. Again, this circuit decouples the relationship

between the input current and the voltage between V

SET

+

1MHz. The R = 100k is preferred for lower power and

SET

better accuracy.

and SET; the frequency accuracy will be degraded. The

oscillator frequency, however, will monotonically increase

Table 1. Frequency Range vs Divider Setting

with decreasing V

.

CONTROL

DIVIDER SETTING

FREꢀUENCY RANGE

>500kHz*

÷1

⇒

DIV (Pin ±) = GND

400kHz TO 21MHz

(APPROXIMATE, SEE TEXT)

÷10

÷100

DIV (Pin ±) = Floating

50kHz to 1MHz

<100kHz

+

V

1

2

3

5

+

DIV (Pin ±) = V

V

OUT

LTC1799

0.1µF

I

*At master oscillator frequencies greater than 10MHz (R < 10kΩ), the

CONTROL

SET

GND

SET

5µA TO 200µA

LTC1799 may suffer reduced accuracy with a supply voltage less than ±V.

4

N = 1

DIV

After choosing the proper divider setting, determine the

correct frequency-setting resistor. Because of the linear

correspondencebetweenoscillationperiodandresistance,

a simple equation relates resistance with frequency.

1799 F03

10MHz 10kΩ

≅

ƒ

OSC

•

• I

CONTROL

N

1.13V

I

EXPRESSED IN (A)

CONTROL

Figure 3. Current Controlled Oscillator

⎧

100

⎛

⎜

⎝

⎞

⎟

⎠

⎪

10MHz

R_SET= 10k •

, N = 10

⎨

⎩

+

N• f

V

⎪

OSC

1

2

3

5

4

+

V

OUT

LTC1799

0.1µF

(R

= 3k (5V Supply), 5k (3V Supply),

= 1M)

V

SETMIN

SETMAX

CONTROL

+

GND

SET

–

0V TO 1.13V

R

SET

R

10k

N = 1

DIV

Any resistor, R , tolerance adds to the inaccuracy of

SET

1799 F04

the oscillator, f

.

OSC

V

10MHz 10k

≅

CONTROL

1.13V

ƒ

OSC

•

• 1–

(

)

N

R

SET

Figure 4. Voltage Controlled Oscillator

1799fd

7

For more information www.linear.com/LTC1799

LTC1799

applicaTions inForMaTion

POꢁER SUPPLY REJECTION

START-UP TIME

The start-up time and settling time to within 1% of the

Low Frequency Supply Rejection (Voltage Coefficient)

final value can be estimated by t

≅ R (2.8µs/kΩ)

START

SET

Figure 5 shows the output frequency sensitivity to power

supply voltage at several different temperatures. The

LTC1799 has a conservative guaranteed voltage coeffi-

cient of 0.1%/V but, as Figure 5 shows, the typical supply

sensitivity is lower.

+ 20µs. Note the start-up time depends on R

and it

SET

is independent from the setting of the divider pin. For

instance with R = 50k, the LTC1799 will settle with 1%

SET

of its 200kHz final value (N = 10) in approximately 160µs.

Figure 6 shows start-up times for various R resistors.

SET

Figure 7 shows an application where a second set resistor

0.15

R

= 31.6k

SET

R

is connected in parallel with set resistor R

via

PIN 4 = FLOATING (÷10)

SET2

SET1

switch S1. When switch S1 is open, the output frequency

oftheLTC1799dependsonthevalueoftheresistorR

0.10

0.05

0

.

SET1

25°C

When switch S1 is closed, the output frequency of the

LTC1799 depends on the value of the parallel combination

–40°C

85°C

of R

and R

.

SET1

SET2

The start-up time and settling time of the LTC1799 with

switch S1 open (or closed) is described by t shown

START

above. Once the LTC1799 starts and settles, and switch

S1 closes (or opens), the LTC1799 will settle to its new

output frequency within approximately 25µs.

–0.05

2.5

3.0

3.5

4.0

4.5

5.0

5.5

SUPPLY VOLTAGE (V)

1799 F05

Figure 5. Supply Sensitivity

60

T

= 25°C

= 5V

A

+

V

50

40

30

20

10

0

High Frequency Power Supply Rejection

The accuracy of the LTC1799 may be affected when its

power supply generates significant noise with frequency

contents in the vicinity of the programmed value of f . If

aswitchingpowersupplyisusedtopoweruptheLTC1799,

and if the ripple of the power supply is more than a few

tens of millivolts, make sure the switching frequency and

its harmonics are not related to the output frequency of

the LTC1799. Otherwise, the oscillator may show an ad-

ditional 0.1% to 0.2% of frequency error.

OSC

200k

200

10k

31.6k

–10

400

600

0

100

300

500

TIME AFTER POWER APPLIED (µs)

1799 F06

If the LTC1799 is powered by a switching regulator and

the switching frequency or its harmonics coincide with

the output frequency of the LTC1799, the jitter of the

oscillator output may be affected. This phenomenon will

become noticeable if the switching regulator exhibits

ripples beyond 30mV.

Figure 6. Start-Up Time

3V OR 5V

10k

N • R

1

5

+

f

= 10MHz •

OSC

V

OUT

(

)

SET1

OR

LTC1799

S1

2

3

+

10k

//R

V

R

SET1

GND

SET

f

OSC

)

N • R

SET1 SET2

÷100

÷1

R

SET2

4

÷10

DIV

1799 F07

Figure 7

1799fd

8

For more information www.linear.com/LTC1799

LTC1799

applicaTions inForMaTion

Jitter

+

When V = V , the output frequency of the LTC1799 as-

IN

sumes the highest value and it is set by the parallel com-

The typical jitter is listed in the Electrical Characteristics

and shown in the Typical Performance Characteristics.

These specifications assume that the capacitance on SET

(Pin 3) is limited to less than 10pF, as suggested in the Pin

Functions description. If this requirement is not met, the

jitter will increase. For more information, contact Linear

Technology Applications group.

bination of R and R . Also note, the output frequency,

IN

SET

+

f

, is independent of the value of V

the accuracy of f

= (V – V ) so

OSC

RES SET

is within the data sheet limits.

OSC

+

When V is less than V , and especially when V ap-

IN

proaches the ground potential, the oscillator frequency,

f

, assumes its lowest value and its accuracy is affected

OSC

+

by the change of V

= (V – V ). At 25°C V

varies

RES

SET

RES

+

A Ground Referenced Voltage Controlled Oscillator

by ±8%, assuming the variation of V is ±5%. The tem-

perature coefficient of V

is 0.02%/°C.

RES

The LTC1799 output frequency can also be programmed

bysteeringcurrentinoroutoftheSETpin,asconceptually

By manipulating the algebraic relation for f

above, a

OSC

shown in Figure 8. This technique can degrade accuracy

simplealgorithmcanbederivedtosetthevaluesofexternal

resistors R and R , as shown in Figure 9.

+

as the ratio of (V – V ) / I

is no longer uniquely

SET

RES

SET

IN

dependent of the value of R , as shown in the LTC1799

SET

1. Choose the desired value of the maximum oscillator

frequency, f , occurring at maximum input

Block Diagram. This loss of accuracy will become notice-

OSC(MAX)

able when the magnitude of I

is comparable to I

.

PROG

RES

+

voltage V

≤ V .

IN(MAX)

The frequency variation of the LTC1799 is still monotonic.

2. Set the desired value of the minimum oscillator fre-

Figure 9 shows how to implement the concept shown in

quency,f

IN(MIN)

,occurringatminimuminputvoltage

OSC(MIN)

≥ 0.

Figure 8 by connecting a second resistor, R , between

IN

V

the SET pin and a ground referenced voltage source, V .

IN

3. Choose V

= 1.1 and calculate the ratio of R /R

IN SET

RES

For a given power supply voltage in Figure 9, the output

from the following:

frequency of the LTC1799 is a function of V , R , R

IN IN SET

+

and (V – V ) = V

:

R_IN

R_SET

SET

RES

=

10MHz

10k

R_INR_SET

f_OSC

=

•

⎛

⎞

N

f_OSC(MAX)

+

V

_IN(MIN)− V⁺

⎜

⎟

V

_IN(MAX)− V −

(

)

(

)

⎜

⎟

⎡

⎢

⎤

⎞

⎛

f_OSC(MIN)

⎝

(

⎠

V − V⁺

−1

⎥

⎟

⎜

(2)

(

IN

)

1

⎜

⎡

⎢

⎣

⎤

f

⎢

⎥

⎟

)

OSC(MAX)

1+

•

(1)

⎥

V_RES

−1

R_IN

⎥

⎟

⎢

V_RES

⎜

1+

f_OSC(MIN)

⎥

⎜

⎟

⎦

⎢

⎥

R_SET

⎝

⎠

⎦

⎣

1

5

4

1

5

4

+

V

R

V

f

OUT

OSC

+

RES

0.1µF

LTC1799

2

3

2

3

5V

R

V

R

SET

GND

SET

GND

÷100

÷1

–

IN

÷10

OPEN

DIV

SET

DIV

+

–

I

÷1

RES

I

V

PR

IN

1799 F08

1799 F09

Figure 8. Concept for Programming via Current Steering

Figure 9. Implementation of Concept Shown in Figure 8

1799fd

9

For more information www.linear.com/LTC1799

LTC1799

applicaTions inForMaTion

Once R /R is known, calculate R from:

isthemasteroscillatorfrequencydividedby20, (f /20).

IN SET

SET

OSC

In general, for minimum output jitter the modulation fre-

10MHz

10k

f_OSC(MAX)

R_SET

=

•

quency should be limited to f /20 or 10kHz, whichever

OSC

N

is less. For best performance at all frequencies, the value

for f

should be the master oscillator frequency (N = 1)

IN

⎡

⎤

⎥

⎦

⎛

⎞

⎟

⎠

OSC

R_IN

R_SET

V

_IN(MAX)− V⁺+ V

1+

⎢

⎣

⎜

when V is at the lowest level.

(

)

RES

⎝

(3)

Table 2. Variation of V_RESfor Various Values of R_IN|| R_SET

⎛

⎞

R_IN

+

V_RES

⎜

⎟

R

IN

|| R (V = V )

V

, V = 3V

V

RES

, V = 5V

SET IN

RES

R

⎝

⎠

SET

10k

20k

±0k

80k

0.98V

1.03V

1.09V

1.13V

1.16V

1.06V

1.11V

1.17V

1.21V

1.2±V

Maximum VCO Modulation Bandwidth

The maximum VCO modulation bandwidth is 10kHz; that

160k

is, the LTC1799 will respond to changes in V at a rate

IN

V

RES

= Voltage across R

SET

up to 25kHz. In lower frequency applications however, the

modulation frequency may need to be limited to a lower

rate to prevent an increase in output jitter. This lower limit

Note: All of the calculations above assume V

= 1.1V, although V

RES

≈ 1.1V. For

RES

completeness, Table 2 shows the variation of V

against various parallel combinations

+

of R and R (V = V ). Calculate first with V ≈ 1.1V, then use Table 2 to get a better

IN

SET IN

approximation of V , then recalculate the resistor values using the new value for V

.

RES

1799fd

10

For more information www.linear.com/LTC1799

LTC1799

Typical applicaTion

Low Power 80Hz to 8kHz Sine ꢁave Generator (I_ꢀ< 4mA)

3V

f

OSC

1

2

5

+

V

OUT

3V

LTC1799

C1

R

SET

3V, N = 100

0.1µF

GND

SET

LTC1067-50

SW1

4

3V

C3

0.1µF

OPEN, N = 10

3

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

C4

1µF

+

DIV

V

CLK

74HC4520

CLOCK A

NC

AGND

R62 14k

÷2

÷4

1

2

3

+

–

R61

10k

Q1A

Q2A

Q3A

Q4A

Q1B

Q2B

Q3B

Q4B

V

3V

4

R52

5.11k

ENABLE A

SA

SB

LPB

BPB

R51 5.11k

R31 51.1k

÷8

16

10

7

5

SINEWAVE

OUT

V

DD

LPA

BPA

R32 51.1k

÷16

÷32

÷64

÷128

÷256

6

C2

0.1µF

ENABLE B

RESET A

10MHz

•

10k

64R

f

=

SINE

11

12

13

14

R11

N

SET

HPA/NA HPB/NB

INV A INV B

100k

R21 20k

R22 20k

8

V

SS

800Hz ≤ f

SINE

80Hz ≤ f

SINE

8kHz, N = 10

800Hz, N = 100

9

CLOCK B

RESET B

R

H1

249k

15

f

OSC

64

R

51.1k

L1

1799 TA05

CLOCK-TUNABLE LOWPASS FILTER WITH

A STOPBAND NOTCH AT THE 3rd HARMONIC

f

OSC

64

• 3

(

)

1799fd

11

For more information www.linear.com/LTC1799

LTC1799

package DescripTion

Please refer to http://www.linear.com/product/LTC1799#packaging for the most recent package drawings.

S5 Package

5-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1635)

0.62

MAX

0.95

REF

2.90 BSC

(NOTE 4)

1.22 REF

1.4 MIN

1.50 – 1.75

(NOTE 4)

2.80 BSC

3.85 MAX 2.62 REF

PIN ONE

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.30 – 0.45 TYP

5 PLCS (NOTE 3)

0.95 BSC

0.80 – 0.90

0.20 BSC

DATUM ‘A’

0.01 – 0.10

1.00 MAX

0.30 – 0.50 REF

1.90 BSC

0.09 – 0.20

(NOTE 3)

NOTE:

S5 TSOT-23 0302

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

1799fd

12

For more information www.linear.com/LTC1799

LTC1799

revision hisTory ^{(Revision history begins at Rev C)}

REV

DATE

DESCRIPTION

PAGE NUMBER

C

1/11

Revised part number in Maximum VCO Modulation Bandwidth section.

10

2

D

07/16 Updated T

(150°C)

JMAX

1799fd

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.

13

For more information www.linear.com/LTC1799

LTC1799

Typical applicaTions

Shutting Down the LTC1799

5V

74AC04

1

5

4

+

ON/SHDN

OUT

V

OUT

C1

LTC1799

R1

2

3

0.1µF

GND

SET

10k

DIV

1799 TA08

Output Frequency vs Temperature

1400

MAX

TYP

MIN

Temperature-to-Frequency Converter

1200

1000

800

600

400

200

0

5V

1

2

3

5

10MHz 10k

+

f

=

V

OUT

•

OSC

10

R

T

C1

0.1µF

LTC1799

R

T

100k

GND

SET

THERMISTOR

4

DIV

1799 TA03

R : YSI 44011 800 765-4974

T

–20 –10

0

10 20 30 40 50 60 70 80 90

TEMPERATURE (°C)

1799 TA04

1799fd

LT 0716 REV D • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7±17

14

For more information www.linear.com/LTC1799

(±08)±32-1900 FAX: (±08) ±3±-0507 www.linear.com/LTC1799

●

 LINEAR TECHNOLOGY CORPORATION 2001


型号：	LTC1799IS5#TRMPBF
厂家：	Linear
描述：	LTC1799 - 1kHz to 33MHz Resistor Set SOT-23 Oscillator; Package: SOT; Pins: 5; Temperature Range: -40°C to 85°C 光电二极管
文件：	总14页 (文件大小：226K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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