LTC1799IS5#TRMPBF Linear Technology, LTC1799IS5#TRMPBF Datasheet - Page 7

• Manufacturer Part Number: LTC1799IS5#TRMPBF
• Description: IC OSCILLATOR RES SET TSOT23-5
• Manufacturer: Linear Technology
• Type: Oscillator, Siliconr

Specifications of LTC1799IS5#TRMPBF

• Frequency: 33MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 7mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: TSOT-23-5, TSOT-5, TSOP-5
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Count: -
• Other names: LTC1799IS5#TRMPBFTR

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.
In general, any given oscillator frequency (f
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
tor = 10MHz or R
1MHz. The R
better accuracy.
Table 1. Frequency Range vs Divider Setting
DIVIDER SETTING
÷1
÷10
÷100 ⇒
*At master oscillator frequencies greater than 10MHz (R
LTC1799 may suffer reduced accuracy with a supply voltage less than 4V.
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.
Any resistor, R
the oscillator, f
applicaTions inForMaTion
(R
R
R
SETMAX
SET
SETMIN
⇒
⇒
= 10k •
DIV (Pin 4) = GND
DIV (Pin 4) = Floating
DIV (Pin 4) = V
= 1M)
= 3k (5V Supply), 5k (3V Supply),
SET
OSC
SET

 
= 100k is preferred for lower power and
SET
N • f
10MHz
.
, tolerance adds to the inaccuracy of
SET
= 100k, N = 10, master oscillator =
OSC
+
= 10k, N = 100, master oscilla-

 
, N =



 
100
10
1
OSC
FREqUENCY RANGE
= 100kHz can be
50kHz to 1MHz
>500kHz*
<100kHz
SET
OSC
< 10kΩ), the
) should
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
As already explained in the “Theory of Operation,” the
voltage difference between V
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
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
5µA TO 200µA
0V TO 1.13V
V
I
CONTROL
CONTROL
SET
Figure 4. Voltage Controlled Oscillator
Figure 3. Current Controlled Oscillator
is replaced by the ratio of 1.13V/I
V
V
+
–
+
+
CONTROL
0.1µF
0.1µF
R
10k
SET
ƒ
OSC
ƒ
I
CONTROL
OSC
≅
≅
10MHz
.
1
2
3
10MHz
1
2
3
OSC
N
EXPRESSED IN (A)
N
V
GND
SET
V
GND
SET
+
LTC1799
+
+
LTC1799
, will vary with V
•
and SET is approximately
R
•
10k
SET
1.13V
10k
OUT
OUT
1799 F03
1799 F04
DIV
DIV
• 1 –
(APPROXIMATE, SEE TEXT)
(
5
4
5
4
• I
400kHz TO 21MHz
LTC1799
CONTROL
V
CONTROL
N = 1
N = 1
1.13V
)
+
CONTROL
CONTROL
OSC
and the
, the
1799fc
7
+
.
,