LTC6900CS5#TRMPBF Linear Technology, LTC6900CS5#TRMPBF Datasheet - Page 7

• Manufacturer Part Number: LTC6900CS5#TRMPBF
• Description: IC OSC PREC 1KHZ-20MHZ TSOT23-5
• Manufacturer: Linear Technology
• Type: Oscillator, Siliconr

Specifications of LTC6900CS5#TRMPBF

• Frequency: 20MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 920µA
• 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: LTC6900CS5#TRMPBFTR

APPLICATIONS INFORMATION
SELECTING THE DIVIDER SETTING AND RESISTOR
The LTC6900’s master oscillator has a frequency range
spanning 0.1MHz to 20MHz. 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
10MHz or R
The R
and better accuracy.
Table 1. Frequency Range vs Divider Setting
DIVIDER SETTING
÷1
÷10
÷100
*
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
oscillator, f
At master oscillator frequencies greater than 10MHz (R
the LTC6900 may experience reduced accuracy with a supply voltage
less than 4V.
(R
R
SET
SETMIN
SET
⇒
⇒
⇒
= 20k •
= 200k approach is preferred for lower power
DIV (Pin 4) = GND
DIV (Pin 4) = Floating
DIV (Pin 4) = V
OSC
SET
= 10k, R
SET
.
= 200k, N = 10, master oscillator = 1MHz.
⎛
⎝ ⎜
, tolerance adds to the inaccuracy of the
N • f
10MHz
SET
SETMAX
OSC
+
= 20k, N = 100, master oscillator =
⎞
⎠ ⎟
, N =
= 2M)
⎧
⎪
⎨
⎩ ⎪
100
10
1
OSC
FREQUENCY RANGE
50kHz to 1MHz
= 100kHz can be
> 500kHz
< 100kHz
SET
OSC
< 20kΩ),
*
) should
ALTERNATIVE METHODS OF SETTING THE OUTPUT
FREQUENCY OF THE LTC6900
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 programmable
current source and in the expression for f
R
explained in the Operation section, the voltage difference
between V
Figure 3 circuit is less accurate than if a resistor controls
the oscillator frequency.
Figure 4 shows the LTC6900 confi gured as a VCO. A voltage
source is connected in series with an external 20k 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
SET
1μA TO 100μA
is replaced by the ratio of 1.1V/I
I
CONTROL
0V TO 1.1V
V
CONTROL
+
Figure 4. Voltage Controlled Oscillator
Figure 3. Current Controlled Oscillator
and SET is approximately 1.1V, therefore, the
V
+
0.1μF
V
+
–
+
CONTROL
ƒ
I
0.1μF
R
CONTROL
20k
OSC
SET
TYPICAL f
±0.5%, V
±8%, V
ƒ
OSC
1
2
3
10MHz
EXPRESSED IN (A)
N
V
GND
SET
.
CONTROL
+
LTC6900
10MHz
OSC
CONTROL
1
2
3
OSC
N
•
182kHz TO 18MHz (TYPICALLY ±8%)
V
GND
SET
20kΩ
OUT
1.1V
6900 F03
, will vary with V
+
LTC6900
ACCURACY
DIV
•
= 0.5V
R
20k
= 0V
SET
5
4
OUT
• I
6900 F04
DIV
CONTROL
• 1 –
CONTROL
(
N = 1
5
4
LTC6900
V
OSC
CONTROL
N = 1
1.1V
, the resistor
. As already
)
+
CONTROL
and the
6900fa
7
+
,