ANALOG DEVICES LTC 1799 CS 5 Datasheet

Resistor Set SOT-23 Oscillator

1kHz ≤ f

≤ 33MHz

3k ≤ R

OPEN

UNITS (%)

25

1.25

1799 TA02

FEATURES DESCRIPTION

n

One External Resistor Sets the Frequency

n

Fast Start-Up Time: <1ms

n

1kHz to 33MHz Frequency Range

n

Frequency Error ≤1.5% 5kHz to 20MHz

= 25°C)

(T

A

n

Frequency Error ≤2% 5kHz to 20MHz

= 0°C to 70°C)

(T

A

n

±40ppm/°C Temperature Stability

n

0.05%/V Supply Stability

n

50% ±1% Duty Cycle 1kHz to 2MHz

n

50% ±5% Duty Cycle 2MHz to 20MHz

n

1mA Typical Supply Current

n

100Ω CMOS Output Driver

n

Operates from a Single 2.7V to 5.5V Supply

n

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

n

AEC-Q100 Qualified for Automotive Applications

APPLICATIONS

n

Low Cost Precision Oscillator

n

Switching Power Supply Clock Reference

n

Clocking Switched Capacitor Filters

n

Fixed Crystal Oscillator Replacement

n

Ceramic Oscillator Replacement

All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents including 6342817 and 6614313.

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

). The LTC1799 has been designed for high accuracy

(R

SET

operation (≤1.5% frequency error) without the need for
external trim components.

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
feedback loop that linearizes the relationship between R
and frequency, eliminating the need for tables to calculate
frequency. The oscillator can be easily programmed using
the simple formula outlined below:

⎛

f

OSC

= 10MHz •

⎜

N •R

⎝

10k

LTC1799

1kHz to 33MHz

⎧

DIV Pin = V

100,

⎪
⎨

10,

DIV Pin = Open

⎪

1,

DIV Pin = GND

⎩

SET

⎞

, N =

⎟
⎠

-

-

SET

+

TYPICAL APPLICATION

Basic Connection

SET

5V

0.1µF

≤ 1M

TSOT-23 Actual Size

1

2

3

+

V

LTC1799

GND

SET

OUT

DIV

1799 TA01

Typical Distribution of Frequency Error,

TA = 25°C (5kHz ≤ f

OSC

5

5V

÷100

4

÷10

÷1

For more information www.analog.comDocument Feedback

20

15

10

5

0
–1.25 –0.75 –0.25 0 0.25 0.75

FREQUENCY ERROR (%)

≤ 20MHz, V+ = 5V)

OSC

Rev. E

1

LTC1799

TOP VIEW

5-LEAD PLASTIC TSOT-23

GND

OUT

(Note 1)

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

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

+

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

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

+ 0.3V)

+

+ 0.3V)

SET

+

1

V

2
3

5

4

DIV

Operating Temperature Range

1799C ................................................ 0°C to 70°C

LTC

1799I .............................................–40°C to 85°C

LTC

1799H .......................................... –40°C to 125°C

LTC

S5 PACKAGE

= 150°C, θJA = 256°C/W

T

JMAX

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

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

ORDER INFORMATION

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

LTC1799CS5#TRMPBF LTC1799CS5#TRPBF LTND 5-Lead Plastic TSOT-23 0°C to 70°C
LTC1799IS5#TRMPBF LTC1799IS5#TRPBF LTNE 5-Lead Plastic TSOT-23 –40°C to 85°C
LTC1799HS5#TRMPBF LTC1799HS5#TRPBF LTND 5-Lead Plastic TSOT-23 –40°C to 125°C

AUTOMOTIVE PRODUCTS**

LTC1799IS5#WTRMPBF LTC1799IS5#WTRPBF LTNE 5-Lead Plastic TSOT-23 –40°C to 85°C
LTC1799HS5#WTRMPBF LTC1799HS5#WTRPBF LTND 5-Lead Plastic TSOT-23 –40°C to 125°C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.

Contact the factory for parts specified with wider operating temperature ranges.
Contact the factory for information on lead based finish parts.

Tape and reel specifications

**Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These

models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
thesemodels.

. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.

2

Rev. E

For more information www.analog.com

LTC1799

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V+ = 2.7V to 5.5V, RL = 5k, CL = 5pF, unless otherwise noted. All
voltages are with respect to GND.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

∆f Frequency Accuracy

(Notes 2, 3)

R

f

MAX

f

MIN

SET

Frequency-Setting Resistor Range |∆f| < 1.5% V+ = 5V

Maximum Frequency |∆f| < 2.5%, Pin 4 = 0V V+ = 5V

Minimum Frequency |∆f| < 2.5%, Pin 4 = V
∆f/∆T Freq Drift Over Temp (Note 3) R
∆f/∆V Freq Drift Over Supply (Note 3) V

Timing Jitter

(Note 4)

Long-T

erm Stability of Output Frequency 300 ppm/√kHr

Duty Cycle (Note 7) Pin 4 = V

V
I

V
V
I

+

S

IH

IL

DIV

Operating Supply Range

Power Supply Current R

High Level DIV Input Voltage

Low Level DIV Input Voltage

DIV Input Current (Note 5) Pin 4 = V

+

= 5V 5kHz ≤ f ≤ 20MHz

V

5kHz ≤ f ≤ 20MHz, LTC1799C
5kHz ≤ f ≤ 20MHz, LTC1799I/H
1kHz ≤ f ≤ 5kHz
20MHz ≤ f ≤ 33MHz

+

= 3V 5kHz ≤ f ≤ 10MHz

V

5kHz ≤ f ≤ 10MHz, LTC1799C
5kHz ≤ f ≤ 10MHz, LTC1799I/H
1kHz ≤ f ≤ 5kHz
10MHz ≤ f ≤ 20MHz

+

= 31.6k

SET
+

= 3V to 5V, R

+

= V

Pin 4

SET

= 31.6k

Pin 4 = Open
Pin 4 = 0V

+

Pin 4 = 0V (DIV by 1), R

R

or Open (DIV Either by 100 or 10)

= 5k to 200k

SET

= 200k, Pin 4 = V+, RL = ∞ V+ = 5V

SET

= 10k, Pin 4 = 0V, RL = ∞ V+ = 5V

SET

+

Pin 4 = 0V

+

V

+

V

+

V

+

V

+

V

= 3V

= 3V

= 3V

= 5V
= 5V

l
l

±0.5

±

1.5

±2

±2.5
±2.5
±2.5

l
l

±0.5

±

1.5

±2

±2.5
±2.5
±2.5

5

10

200
200

33
20

1 kHz

l

l

±0.004 %/°C

0.05 0.1 %/V

0.06

0.13

0.4

l

49

l

45

l

2.7 5.5 V

l

l
l

l

V+ – 0.4 V

l

l
l

–8

50
50

51
55

0.7 1.1 mA

2.4
2

0.5 V

5

8 µA

–5

kΩ
kΩ

MHz
MHz

mA
mA

µA

%
%
%
%
%

%
%
%
%
%

%
%
%

%
%

For more information www.analog.com

Rev. E

3

LTC1799

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V+ = 2.7V to 5.5V, RL = 5k, CL = 5pF, unless otherwise noted. All
voltages are with respect to GND.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

OH

High Level Output Voltage (Note 5) V+ = 5V,

LTC1799C/I

+

= 5V,

V
LTC1799H

+

= 3V,

V
LTC1799C/I

V+ = 3V,
LTC1799H

V

OL

Low Level Output Voltage (Note 5) V+ = 5V,

LTC1799C/I

+

= 5V,

V
LTC1799H

+

= 3V,

V
LTC1799C/I

+

= 3V,

V
LTC1799H

t

r

OUT Rise Time

V+ = 5V Pin 4 = V+ or Floating, RL = ∞

(Note 6)

+

= 3V Pin 4 = V+ or Floating, RL = ∞

V

IOH = –1mA
I

= –4mA

OH

IOH = –1mA
I

= –4mA

OH

IOH = –1mA
I

= –4mA

OH

IOH = –1mA
I

= –4mA

OH

IOL = 1mA
I

= 4mA

OL

IOL = 1mA
I

= 4mA

OL

IOL = 1mA
I

= 4mA

OL

IOL = 1mA
I

= 4mA

OL

Pin 4 = 0V, RL = ∞

Pin 4 = 0V, RL = ∞

t

f

OUT Fall Time
(Note 6)

V+ = 5V Pin 4 = V+ or Floating, RL = ∞

Pin 4 = 0V, RL = ∞

+

= 3V Pin 4 = V+ or Floating, RL = ∞

V

Pin 4 = 0V, RL = ∞

l
l

l
l

l
l

l
l

l
l

l
l

l
l

l
l

4.8

4.5

4.75

4.40

2.7

2.2

2.65

2.10

4.95

4.8

4.95

4.75

2.9

2.6

2.90

2.55

0.05

0.2

0.05

0.25

0.1

0.4

0.10

0.45
14

7

19
11

13

6

19
10

0.15

0.4

0.20

0.50

0.3

0.7

0.35

0.80

V
V

V
V

V
V

V
V

V
V

V
V

V
V

V
V

ns
ns

ns
ns

ns
ns

ns
ns

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: Frequencies near 100kHz and 1MHz may be generated using two
different values of R

(see the Table 1 in the Applications Information

SET

section). For these frequencies, the error is specified under the following
assumption: 10k < R

≤ 100k. The frequency accuracy for f

SET

= 20MHz

OSC

is guaranteed by design and test correlation.
Note 3: Frequency accuracy is defined as the deviation from the

equation.

f

OSC

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
a pin is arbitrarily given as a negative value.

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.

4

Rev. E

For more information www.analog.com

TYPICAL PERFORMANCE CHARACTERISTICS

4

1000

1799 G01

VARIATION (%)

VARIATION (%)

1.00

1799 G02

JITTER (%)

0.7

100M

1799 G03

SUPPLY CURRENT (mA)

4.5

100M

1799 G04

OUTPUT RESISTANCE (Ω)

140

1799 G05

6.0

12.5ns/DIV

1V/DIV

1799 G06

25ns/DIV

1V/DIV

1799 G07

LTC1799

Frequency Variation
vs R

SET

TA = 25°C
GUARANTEED LIMITS APPLY

3

OVER 5k TO 200k RANGE

2

1

0

–1

–2

–3

–4

1 10 100

TYPICAL

HIGH

TYPICAL

LOW

R

(kΩ)

SET

Peak-to-Peak Jitter vs Frequency

0.6

0.5

0.4

0.3

0.2

0.1

0

1k 100k 1M 10M

÷10

÷100

10k
OUTPUT FREQUENCY, f

÷1

(Hz)

OUT

Frequency Variation
Over Temperature

R

= 31.6k

SET

÷1 OR ÷10 OR ÷100

0.75

0.50

0.25

–0.25

–0.50

–0.75

–1.00

0

–40

TYPICAL

HIGH

TYPICAL

LOW

–20 0

TEMPERATURE (°C)

Supply Current
vs Output Frequency

TA = 25°C

= 5pF

C

4.0

L

= 1M

R

L

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

÷100 (5V)

÷100 (3V)

1k 100k 1M

÷10 (3V)

10k
OUTPUT FREQUENCY, f

40 80

20 60

÷1 (5V)

÷10 (5V)

÷1 (3V)

OUT

10M

(Hz)

Output Resistance
vs Supply Voltage

120

OUTPUT SOURCING CURRENT

100

80

60

OUTPUT SINKING CURRENT

40

2.5 3.0

3.5
SUPPLY VOLTAGE (V)

4.0

4.5

5.0

T

A

= 25°C

5.5

LTC1799 Output Operating at
20MHz, VS = 5V

V+ = 5V, R

For more information www.analog.com

= 5k, CL = 10pF

SET

LTC1799 Output Operating at
10MHz, VS = 3V

V+ = 3V, R

= 10k, CL = 10pF

SET

Rev. E

5

LTC1799

1799 BD

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
bypassed directly to a ground plane with a

0.1µF capacitor.

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

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

+

of the resistor connected between this pin and V

deter­mines the oscillator frequency. The voltage on this pin is
held by the

+

voltage. For best performance, use a precision metal

V

LTC1799 to approximately 1.13V below the

film resistor with a value between 10k and 200k and limit
the capacitance on this pin to less than 10pF.

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 4 should be tied
to GND for the ÷1 setting, the highest frequency range.

BLOCK DIAGRAM

Floating Pin 4 divides the master oscillator by 10. Pin 4

+

should be tied to V

for the ÷100 setting, the lowest fre­quency range. To detect a floating DIV pin, the LTC1799
attempts to pull the pin toward midsupply
with two internal current sources, one tied to V

. This is realized

+

and Pin
4 and the other one tied to ground and Pin 4. Therefore,
driving the DIV pin high requires sourcing approximately
5µA. Likewise, driving DIV low requires sinking 5µA.
When Pin 4 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.

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.

= 1.13V ±25%

V

RES

+

V

1

I

+

–

RES

GAIN = 1

R

SET

I

RES

SET

3

+

V

BIAS

–

GND

+

– V

)

(V

SET

MASTER OSCILLATOR

I

= 100MHz • kΩ •

ƒ

MO

RES

(V+ – V

SET

)

PROGRAMMABLE

DIVIDER

(÷1, 10 OR 100)

DIVIDER

SELECT

THREE-STATE
INPUT DETECT

OUT

V

5µA

DIV

5µA

GND

5

+

42

6

Rev. E

For more information www.analog.com

THEORY OF OPERATION

+

1.4

1000

1799 F01

R

(kΩ)

1799 F02

1000

100M

LTC1799

As shown in the Block Diagram, the LTC1799’s master
oscillator is controlled by the ratio of the voltage between

+

and SET pins and the current entering the SET pin

the V

). The voltage on the SET pin is forced to approximately

(I

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.
A resistor R

“locks together” the voltage (V

, connected between the V+ and SET pins,

SET

+

– V

SET

) and current, I

RES

,
variation. This provides the LTC1799’s high precision. The
master oscillation frequency reduces to:

ƒMO= 10MHz •

⎛
⎜
⎝

10kΩ

R

SET

⎞
⎟
⎠

The LTC1799 is optimized for use with resistors between
10k and 200k, corresponding to master oscillator frequen­cies between 0.5MHz and 10MHz. Accurate frequencies up

= 5k) are attainable if the supply voltage

to 20MHz

(R

SET

is greater than 4V.

(Pin 5). The divide-by value is determined by the state of
the DIV input (Pin 4). 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

+

range, ÷100, is selected by tying DIV to V

+

within 0.4V of V

, divider setting and output frequency, including the

R

SET

. Figure 2 shows the relationship between

or driving it to

overlapping frequency ranges near 100kHz and 1MHz.
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 ÷100 modes, where the output frequency is much lower,
slew rate control circuitry in the output driver increases
the rise/fall times to typically 14ns for a 5V supply and
19ns for a 3V supply. The reduced slew rate lowers EMI
(electromagnetic interference) and supply bounce.

To extend the output frequency range, the master oscillator
signal may be divided by 1, 10 or 100 before driving OUT

TA = 25°C

1.3

V+ = 5V

V+ = 3V

10 100

I

RES

SET

(µA)

Variation with I

RES

1.2

SET

– V

1.1

= V

RES

V

1.0

0.9

0.8
1

Figure 1. V+ – V

100

SET

10

1

1k 100k 1M 10M

Figure 2. R

÷100 ÷10 ÷1

10k

DESIRED OUTPUT FREQUENCY (Hz)

vs Desired Output Frequency

SET

MOST

ACCURATE

OPERATION

Rev. E

For more information www.analog.com

7

LTC1799

400kHz TO 21MHz

(APPROXIMATE, SEE TEXT)

5µA TO 200µA

CONTROL

+

0V TO 1.13V

( )

APPLICATIONS INFORMATION

SELECTING THE DIVIDER SETTING AND RESISTOR

The LTC1799’s master oscillator has a frequency range
spanning 0.1MHz to 33MHz. However, accuracy may suffer
if the master oscillator is operated at greater than 10MHz
with a supply voltage lower than 4V. A programmable
divider extends the frequency range to greater than three
decades. Table 1 describes the recommended frequencies
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.

general, any given oscillator frequency (f

In

) should

OSC

be obtained using the lowest master oscillator frequency.
Lower master oscillator frequencies use less power and
are more accurate. For instance, f
obtained by either R

10MHz or R

tor =
1MHz. The R

= 100k is preferred for lower power and

SET

= 10k, N = 100, master oscilla-

SET

= 100k, N = 10, master oscillator =

SET

= 100kHz can be

OSC

better accuracy.

Table 1. Frequency Range vs Divider Setting

DIVIDER SETTING FREQUENCY RANGE

÷1 ⇒ DIV (Pin 4) = GND >500kHz*
÷10 ⇒ DIV (Pin 4) = Floating 50kHz to 1MHz
÷100 ⇒ DIV (Pin 4) = V
*At master oscillator frequencies greater than 10MHz (R

LTC1799 may suffer reduced accuracy with a supply voltage less than 4V.

+

<100kHz

< 10kΩ), the

SET

After choosing the proper divider setting, determine the
correct frequency-setting resistor. Because of the linear
correspondence between oscillation period and resistance,
a simple equation relates resistance with frequency.

⎧

R

= 10k •

SET

(R
R

SETMAX

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

SETMIN

= 1M)

Any resistor, R
the oscillator, f

⎛

10MHz

⎜

N • f

⎝

, tolerance adds to the inaccuracy of

SET

.

OSC

⎞

, N =

⎟
⎠

OSC

⎪
⎨

⎪

⎩

100
10
1

ALTERNATIVE METHODS OF SETTING THE OUTPUT
FREQUENCY OF THE LTC1799

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
resistor R

is replaced by the ratio of 1.13V/I

SET

OSC

CONTROL

-

, the

.

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.

Figure 4 shows the LTC1799 configured as a VCO. A voltage
source is connected in series with an external 10k resis
tor. The output frequency, f
that is the voltage source connected between V

, will vary with V

OSC

CONTROL

+

and the

­,

SET pin. Again, this circuit decouples the relationship

+

between the input current and the voltage between V
and SET; the frequency accuracy will be degraded. The
oscillator frequency, however, will monotonically increase
with decreasing V

+

V

I

CONTROL

Figure 3. Current Controlled Oscillator

V

V

CONTROL

+
–

Figure 4. Voltage Controlled Oscillator

CONTROL

0.1µF

0.1µF

R

SET

10k

.

1

+

V

LTC1799

2

GND

3

SET

10MHz

ƒ

≅

OSC

N

I

EXPRESSED IN (A)

1

+

V

LTC1799

2

GND

3

SET

10MHz

ƒ

≅

OSC

• • 1 –

N

OUT

DIV

1799 F03

10kΩ

• • I

1.13V

OUT

DIV

1799 F04

10k

R

SET

5

4

CONTROL

5

4

V

N = 1

N = 1

CONTROL

1.13V

8

Rev. E

For more information www.analog.com

APPLICATIONS INFORMATION

FREQUENCY DEVIATION (%)

0.15

1799 F05

5.5

60

1799 F06

600

FREQUENCY ERROR (%)

1799 F07

( )

)

LTC1799

POWER SUPPLY REJECTION

Low Frequency Supply Rejection (Voltage Coefficient)

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

–0.05

.

R

= 31.6k

SET

PIN 4 = FLOATING (÷10)

0.10

0.05

0

2.5

3.0 3.5 4.0 4.5
SUPPLY VOLTAGE (V)

Figure 5. Supply Sensitivity

25°C

–40°C

85°C

5.0

High Frequency Power Supply Rejection

START-UP TIME

The start-up time and settling time to within 1% of the
final value can be estimated by t

START

≅ R

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

(2.8µs/kΩ)

SET

SET

and it
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

is connected in parallel with set resistor R

R

SET2

SET1

via
switch S1. When switch S1 is open, the output frequency
of the LTC1799 depends on the value of the resistor R

SET1

.
When switch S1 is closed, the output frequency of the
LTC1799 depends on the value of the parallel combination
of R

SET1

and R

SET2

.

The start-up time and settling time of the LTC1799 with
switch S1 open (or closed) is described by t

START

shown
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.

TA = 25°C

+

= 5V

50

V

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
a switching power supply is used to power up the LTC1799,
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.

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.

40

30

. If

OSC

-

–10

20

10

0

0

200k

10k

31.6k

100 200

TIME AFTER POWER APPLIED (µs)

400

300 500

Figure 6. Start-Up Time

S1

R

SET1

R

SET2

3V OR 5V

1

2

3

+

V

LTC1799

GND

SET

OUT

DIV

5

÷100

4

÷1

f

= 10MHz •

OSC

OR

+

V

f

= 10MHz •

OSC

÷10

N • R

(

N • R

10k

SET1

10k

SET1

//R

SET2

Figure 7.

Rev. E

For more information www.analog.com

9

LTC1799

10MHz

10k

1

5

1799 F08

OPEN

1

5

1799 F09

OPEN

APPLICATIONS INFORMATION

Jitter

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.

A Ground Referenced Voltage Controlled Oscillator

The LTC1799 output frequency can also be programmed
by steering current in or out of the SET pin, as conceptually
shown in Figure 8. This technique can degrade accuracy

+

as the ratio of (V

– V

dependent of the value of R

SET

) / I

is no longer uniquely

RES

, as shown in the LTC1799

SET

Block Diagram. This loss of accuracy will become notice­able when the magnitude of I

is comparable to I

PROG

RES

.

The frequency variation of the LTC1799 is still monotonic.
Figure 9 shows how to implement the concept shown in

Figure 8 by connecting a second resistor, R
the SET pin and a ground referenced voltage source, V

, between

IN

IN

.

For a given power supply voltage in Figure 9, the output
frequency of the LTC1799 is a function of V

+

and (V

f

OSC

⎡
⎢
⎢

1+

⎢
⎢

⎣

– V

=

( )

) = V

SET

N

IN

V

− V

RES

+

V

RES

•
RINR

⎛
⎜
⎜

•

⎜

1+

⎜
⎝

:

•

SET

⎤

⎞

⎥

⎟

1

⎥

⎟

R

⎥

⎟

IN

⎟

⎥

R

⎠

⎦

SET

, RIN, R

IN

SET

(1)

When V

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

IN

sumes the highest value and it is set by the parallel com­bination of R

, is independent of the value of V

f

OSC

the accuracy of f
When V

and R

IN

OSC

is less than V+, and especially when VIN ap-

IN

. Also note, the output frequency,

SET

= (V+ – V

RES

SET

is within the data sheet limits.

) so

proaches the ground potential, the oscillator frequency,

, assumes its lowest value and its accuracy is affected

f

OSC

by the change of V

RES

= (V+ – V
by ±8%, assuming the variation of V
perature coefficient of V

is 0.02%/°C.

RES

By manipulating the algebraic relation for f

). At 25°C V

SET

+

is ±5%. The tem-

RES

above, a

OSC

varies

simple algorithm can be derived to set the values of external
resistors R

and RIN, as shown in Figure 9.

SET

1. Choose the desired value of the maximum oscillator

frequency, f
voltage V

IN(MAX)

OSC(MAX)

, occurring at maximum input

≤ V+.

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

quency, f

IN(MIN)

≥ 0.

V

3. Choose V

OSC(MIN)

RES

, occurring at minimum input voltage

= 1.1 and calculate the ratio of RIN/R

SET

from the following:

R

IN

=

R

SET

V

IN(MAX)

( )

− V

V

+

RES

⎛

f

OSC(MAX)

⎜

−
⎜

f

OSC(MIN)

⎝

⎡

f

( )

OSC(MAX)

⎢

f

⎢

OSC(MIN)

⎣

⎞
⎟

V

IN(MIN)

( )

⎟

− V

⎠

⎤
⎥

− 1

⎥

⎦

+

− 1

(2)

+

V

0.1µF

R

SET

I

RES

I

PR

Figure 8. Concept for Programming via Current Steering Figure 9. Implementation of Concept Shown in Figure 8 Steering

10

+

V

OUT

LTC1799

2

GND

3

SET

DIV

5V

÷100

4

÷10

÷1

For more information www.analog.com

+

V

+

0.1µF

V

R

SET

RES

–

R

IN

+

V

IN

–

2

3

+

V

LTC1799

GND

SET

OUT

DIV

f

OSC

5V

÷100

4

÷10

÷1

Rev. E

APPLICATIONS INFORMATION

10MHz

10k

3V

0.1µF

( )

SET

LTC1799

Once RIN/R

R

SET

⎡

V

⎢

IN(MAX)

( )

⎢
⎢
⎢
⎣

is known, calculate R

SET

=

N

− V

V

+

RES

•
f

OSC(MAX)

+ V

RES

⎛

R

IN

⎜

R

⎝

SET

from:

SET

•

⎛

1+

⎜
⎝

⎞
⎟

⎠

⎤

⎞

R

IN

⎥

⎟

R

⎠

⎥

SET

(3)

⎥
⎥
⎦

Maximum VCO Modulation Bandwidth

The maximum VCO modulation bandwidth is 10kHz; that
is, the LTC1799 will respond to changes in VIN at a rate
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

TYPICAL APPLICATION

is the master oscillator frequency divided by 20, (f

OSC

/20).
In general, for minimum output jitter the modulation fre­quency should be limited to f

/20 or 10kHz, whichever

OSC

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

when V

Table 2. Variation of V

RIN || R

10k 0.98V 1.06V

20k 1.03V 1.11V
40k 1.09V 1.17V
80k 1.13V 1.21V
160k 1.16V 1.24V
V

Note: All of the calculations above assume V

completeness, Table 2 shows the variation of V

of R

approximation of V

should be the master oscillator frequency (N=1)

OSC

is at the lowest level.

IN

for Various Values of RIN || R

RES

(VIN = V+) V

SET

= Voltage across R

RES

and R

(VIN = V+). Calculate first with V

IN

SET

RES

SET

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

, V+ = 3V V

RES

= 1.1V, although V

RES

against various parallel combinations

RES

≈ 1.1V, then use Table 2 to get a better

RES

RES

≈ 1.1V. For

RES

SET

, V+ = 5V

RES

.

C1

R

SET

1

+

V

LTC1799

2

GND

3

SET

800Hz ≤ f
80Hz ≤ f

5

OUT

SW1

4

DIV

8kHz, N = 10

SINE

800Hz, N = 100

SINE

3V

OPEN, N = 10

C2

0.1µF

Low Power 80Hz to 8kHz Sine Wave Generator (IQ < 4mA)

f

OSC

3V, N = 100

3V

R61

10k

0.1µF

C3

R31 51.1k

C4

÷2

÷4

÷8

÷16

÷32

÷64

÷128

÷256

1µF

R11

100k

f

OSC

64

74HC4520

1

3V

2

16

10

7

8

9

15

CLOCK A

ENABLE A

V

DD

ENABLE B

RESET A

V

SS

CLOCK B

RESET B

Q1A

Q2A

Q3A

Q4A

Q1B

Q2B

Q3B

Q4B

3

4

5

6

11

12

13

14

LTC1067-50

1

+

V

2

NC

3

+

V

4

R51 5.11k

R21 20k

A STOPBAND NOTCH AT THE 3rd HARMONIC

SA

5

LPA

6

BPA

7

HPA/NA

8

INV A

CLOCK-TUNABLE LOWPASS FILTER WITH

CLK

AGND

V

SB

LPB

BPB

HPB/NB

INV B

R

249k

H1

51.1k

R

L1

f

OSC

• 3

64

16

15

R62 14k

14

–

13

12

11

10

9

R32 51.1k

R22 20k

R52

5.11k
SINEWAVE

OUT

f

SINE

1799 TA05

10MHz

= •

N

64R

10k

Rev. E

For more information www.analog.com

11

LTC1799

S5 Package

5-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1635)

PACKAGE DESCRIPTION

S5 Package

5-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1635)

0.62

MAX

3.85 MAX

0.20 BSC

DATUM ‘A’

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

2.62 REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.30 – 0.50 REF

0.95
REF

1.22 REF

1.4 MIN

0.09 – 0.20
(NOTE 3)

2.80 BSC

1.50 – 1.75
(NOTE 4)

1.00 MAX

PIN ONE

0.95 BSC

0.80 – 0.90

2.90 BSC
(NOTE 4)

0.30 – 0.45 TYP
5 PLCS (NOTE 3)

0.01 – 0.10

1.90 BSC

S5 TSOT-23 0302

12

Rev. E

For more information www.analog.com

LTC1799

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

C 1/11 Revised part number in Maximum VCO Modulation Bandwidth section. 10
D 07/16 Updated T
E 01/20 Added AEC-Q100 Qualified Note

Added W Grade Automotive Products to Order Information

(150°C) 2

JMAX

(Revision history begins at Rev C)

1
2

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

For more information www.analog.com

Rev. E

13

LTC1799

5V

THERMISTOR

T

10k

1799 TA04

1400

90

FREQUENCY (kHz)

ON

5V

1799 TA08

OUT

TYPICAL APPLICATIONS

Shutting Down the LTC1799

Temperature-to-Frequency Converter

C1

T

0.1µF

: YSI 44011 800 765-4974

R

100k

R

1

2

3

+

V

LTC1799

GND

SET

OUT

DIV

5

4

1799 TA03

f

OSC

/SHDN

=

10MHz

10

•

R

T

74AC04

R1

10k

0.1µF

1

+

C1

2

3

V

LTC1799

GND

SET

OUT

DIV

5

4

Output Frequency vs Temperature

MAX

1200

1000

800

600

400

200

0

–20 –10 0 10 20 30 40 50 60 70 80

TYP
MIN

TEMPERATURE (°C)

14

For more information www.analog.com

Rev. E

01/20

www.analog.com

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