LTC6906HS6 Linear Technology, LTC6906HS6 Datasheet - Page 7

• Manufacturer Part Number: LTC6906HS6
• Manufacturer: Linear Technology
• Type: Silicon Oscillatorr

Specifications of LTC6906HS6

• Mounting Style: Surface Mount
• 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

THEORY OF OPERATION
Table 1. Output Frequency Equations
The LTC6906 is a precision, resistor programmable oscilla-
tor (see the Block Diagram). It generates a square wave at
the OUT pin with a period directly proportional to the value
of an external resistor, R
and controls the oscillator frequency to achieve the high-
est possible accuracy. In equilibrium, this circuit ensures
that the current in the SET pin, I
I
we have the relationship:
where C
Solving for the oscillator period:
This is the fundamental equation for the LTC6906. It holds
regardless of how the SET pin is driven. When a resistor,
R
the relationship:
so
FB
SET
I
C
t
t
V
is proportional to the master oscillator frequency, so
SET
I
OSC
OSC
OSC
SET
SET
, is connected from the SET pin to ground, we have
= I
OSC
= 10pF for the LTC6906
=
=
PART NUMBER
= R
FB
ƒ
ƒ
LTC6906
OSC
OSC
is a precision internal capacitor:
= V
SET
1
1
SET
=
= R
V
I
• ƒ
SET
SET
SET
OSC
SET
• C
• C
• C
. A feedback circuit measures
OSC
OSC
OSC
SET
ƒ
OUT
, is balanced by I
FREQUENCY
=
1MHz
N
•

 

R
100k
SET

 

(1)
(2)
(3)
(4)
FB
.
The period and frequency are determined exclusively by
R
value of V
its accuracy even though V
voltage.
The digital dividers shown in the Block Diagram further
divide the master oscillator frequency by 1, 3 or 10 pro-
ducing:
and
Table 1 gives specific frequency and period equations for
the LTC6906. The Applications Information section gives
further detail and discusses alternative ways of setting the
LTC6906 output frequency.
SET
t
ƒ
OUT
t
OUT
OUT
and the precision internal capacitor. Importantly, the
= N • t
= N • 1µs •
=
PERIOD
SET
ƒ
OSC
N
OSC
is immaterial, and the LTC6906 maintains



R
100k
SET



SET
is not a precision reference
N =





DIVIDER RATIOS
10,
3,
1,
LTC6906
DIV Pin = V
DIV Pin = Open
DIV Pin = GND
+
6906fb
7
(5)
(6)