Datasheet

LTC6905
5
6905fd
PIN FUNCTIONS
V
+
(Pin 1): Voltage Supply (2.7V ≤ V
+
≤ 5.5V). This sup-
ply must be kept free from noise and ripple. It should be
bypassed directly to the GND (Pin 2) with a 0.1μF capaci-
tor or higher.
GND (Pin 2): Ground. Should be tied to a ground plane
for best performance.
SET (Pin 3): Frequency-Setting Resistor Input. The value
of the resistor connected between this pin and V
+
deter-
mines the oscillator frequency. The voltage on this pin is
held by the LTC6905 to approximately 1V below the V
+
voltage. For best performance, use a precision metal fi lm
resistor with a value between 10k and 25k and limit the
capacitance on this pin to less than 10pF.
DIV (Pin 4): Divider-Setting Input. This three-state input
selects among three divider settings, determining the value
of N in the frequency equation. Pin 4 should be tied to V
+
for the ÷1 setting, the highest frequency range. Floating
Pin 4 divides the master oscillator by 2. Pin 4 should
be tied to GND for the ÷4 setting, the lowest frequency
range. To detect a fl oating DIV pin, the LTC6905 attempts
to pull the pin toward midsupply. This is realized with two
internal current sources, one tied to V
+
and Pin 4 and the
other one tied to ground and Pin 4. Therefore, driving
the DIV pin high requires sourcing approximately 15μA.
Likewise, driving DIV low requires sinking 11μA. When
Pin 4 is fl oated, it should be bypassed by a 1nF capacitor
to ground or it should be surrounded by a ground shield
to prevent excessive coupling from other PCB traces.
OUT (Pin 5): Oscillator Output. This pin can drive 5kΩ
and/or 5pF loads. For larger loads, refer to the Applications
Information section.
TYPICAL PERFORMANCE CHARACTERISTICS
R
OUT
vs V
+
Jitter vs Frequency Frequency vs Temperature
LTC6905 Output Operating at
17.5MHz, V
S
= 3V
LTC6905 Output Operating at
170MHz, V
S
= 3V
SUPPLY VOLTAGE (V)
2.5
0
OUTPUT RESISTANCE (Ω)
5
15
20
25
4.5
45
6905 G04
10
3.5
3
5
4 5.5
30
35
40
FREQUENCY (MHz)
0
0
PEAK-TO-PEAK JITTER (%)
0.20
0.60
÷4 ÷2
÷1
0.80
1.00
40
80
100 180
6905 G05
0.40
20 60
120
140
160
1.20
TEMPERATURE (°C)
–40
–1.0
PERCENTAGE ERROR (%)
–0.8
–0.4
–0.2
0
1.0
0.4
0
40
60
6905 G08
–0.6
0.6
0.8
0.2
–20 20
80
100
120
1V/DIV
12.5ns/DIV
6905 G06
1V/DIV
1ns/DIV
6905 G07