LTC6900CS5 Linear Technology, LTC6900CS5 Datasheet - Page 9

• Manufacturer Part Number: LTC6900CS5
• Manufacturer: Linear Technology
• Type: Silicon Oscillatorr

Specifications of LTC6900CS5

• Mounting Style: Surface Mount
• Screening Level: Industrial
• Product Length (mm): 2.9mm
• Product Depth (mm): 1.75mm
• Product Height (mm): 0.9mm
• Package / Case: TSOT-23
• Lead Free Status / RoHS Status: Not Compliant

APPLICATIO S I FOR ATIO
A Ground Referenced Voltage Controlled Oscillator
The LTC6900 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
dependent of the value of R
Block Diagram. This loss of accuracy will become notice-
able when the magnitude of I
The frequency variation of the LTC6900 is still monotonic.
Figure 9 shows how to implement the concept shown in
Figure 8 by connecting a second resistor, R
SET pin and a ground referenced voltage source, V
For a given power supply voltage in Figure 9, the output
frequency of the LTC6900 is a function of V
and (V
S1
R
R
f
SET2
OSC
SET1
1
Figure 8. Concept for Programming via Current Steering
3V OR 5V
+
– V
V
V
+
I
R
IN
PR
10
V
SET
SET
RES
MHz
N
1
2
3
V
) = V
0.1 F
+
V
GND
SET
LTC6900
+
– V
I
RES
•
•
U
RES
R R
OUT
DIV
IN
SET
1
20
:
1
2
3
) / I
Figure 7
5
4
R
k
U
1
V
GND
SET
SET
R
LTC6900
+
SET
SET
100
IN
PROG
1
RES
V
, as shown in the LTC6900
•
OUT
DIV
+
6900 F07
10
is no longer uniquely
f
OR
f
5
4
is comparable to I
OSC
OSC
W
100
= 10MHz •
= 10MHz •
1
5V
IN
10
, between the
IN
N • R
N • R
OPEN
6900 F08
, R
U
20k
SET1
SET1
IN
20k
, R
//R
IN
SET2
RES
.
SET
(1)
.
When V
assumes the highest value and it is set by the parallel
combination of R
quency, f
V
When V
proaches the ground potential, the oscillator frequency,
f
by the change of V
by 8%, assuming the variation of V
perature coefficient of V
By manipulating the algebraic relation for f
simple algorithm can be derived to set the values of
external resistors R
1. Choose the desired value of the maximum oscillator
2. Set the desired value of the minimum oscillator fre-
3. Choose V
R
OSC
R
SET
V
SET
IN MAX
frequency, f
age V
quency, f
V
from the following:
IN
, assumes its lowest value and its accuracy is affected
IN(MIN)
Figure 9. Implementation of Concept Shown in Figure 8
(
) so the accuracy of f
+
–
IN
IN
IN(MAX)
V
)
OSC
IN
is less than V
= V
V
R
OSC(MIN)
RES
+
IN
V
V
, is independent of the value of V
V
0.
RES
RES
OSC(MAX)
+
–
+
, the output frequency of the LTC6900
= 1.1 and calculate the ratio of R
IN
0.1 F
R
V
RES
SET
+
SET
, occurring at minimum input voltage
f
and R
f
.
OSC MAX
f
OSC MIN
f
OSC MAX
OSC MIN
= (V
, occurring at maximum input volt-
and R
RES
(
OSC
(
(
+
(
, and expecially when V
SET
1
2
3
+
is within the data sheet limits.
– V
is 0.02%/ C.
)
V
GND
SET
)
IN
)
. Also note, the output fre-
LTC6900
)
+
, as shown in Figure 9.
SET
V
1
OUT
DIV
IN MIN
). At 25 C V
(
+
5
4
is 5%. The tem-
LTC6900
f
100
)
OSC
1
5V
V
OSC
10
RES
RES
OPEN
above, a
6900 F09
IN
= (V
1
IN
varies
/R
9
6900f
ap-
SET
+
(2)
–