LTC6907HS6#TRM Linear Technology, LTC6907HS6#TRM Datasheet - Page 7

• Manufacturer Part Number: LTC6907HS6#TRM
• Description: SC-Timing, Low Power 10kHz - 1MHz Resistor Programmable Osc
• Manufacturer: Linear Technology

Specifications of LTC6907HS6#TRM

• Lead Free Status / Rohs Status: Not Compliant

THEORY OF OPERATIO
Table 1. Output Frequency Equations
The LTC6907 is a precision, resistor programmable oscil-
lator (see 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 equilibrum, this circuit ensures
that the current in the SET pin, I
is proportional to the master oscillator frequency, so we
have the relationship:
Where C
Solving for the oscillator period:
This is the fundamental equation for the LTC6907. It holds
regardless of how the SET pin is driven. When a resistor,
R
the relationship:
SET
I
C
t
SET
V
I
OSC
OSC
SET
SET
, is connected from the SET pin to ground, we have
PART NUMBER
= I
LTC6907
= 5pF for the LTC6907
=
OSC
=
FB
ƒ
R
OSC
= V
SET
is a precision internal capacitor:
1
SET
=
V
I
• ƒ
SET
SET
OSC
SET
•
ƒ
C
• C
OUT
. A feedback circuit measures
OSC
OSC
SET
=
FREQUENCY
4
, is balanced by I
MHz
N
U
•
⎛
⎝ ⎜
R
50
SET
k
⎞
⎠ ⎟
FB
. I
(1)
(2)
(3)
FB
t
OUT
so
The period and frequency are determined exclusively by
R
value of V
accuracy even though V
voltage.
The digital dividers shown in the Block Diagram further
divide the master oscillator frequency by 1, 3 or 10
producing:
and
Table 1 gives specific frequency and period equations for
the LTC6907. The Applications Information section gives
further detail and discusses alternative ways of setting the
LTC6907 output frequency.
=
SET
N
t
t
ƒ
OUT
•
OSC
OUT
and the precision internal capacitor. Importantly, the
250
PERIOD
= N • t
=
=
SET
ns
ƒ
ƒ
OSC
OSC
•
1
N
is immaterial, and the LTC6907 maintains its
⎛
⎝ ⎜
OSC
R
50
SET
=
k
R
SET
⎞
⎠ ⎟
•
SET
C
OSC
N
is not a precision reference
=
⎧
⎪
⎨
⎪
⎩
10
1
3
DIVIDER RATIOS
,
,
,
DIV Pin V
DIV Pin
DIV Pin GND
LTC6907
=
=
=
Open
+
6907fa
7
(4)
(5)
(6)