Datasheet
LTC6905-XXX Series
5
6905xfa
BLOCK DIAGRA
W
–
+
–
+
+
–
1
3
GAIN = 1
V
+
V
BIAS
I
RES
I
RES
R
SET
GND
MASTER OSCILLATOR
PROGRAMMABLE
DIVIDER
(N = 1, 2 OR 4)
V
RES
= 1V ±5%
(V
+
– V
SET
)
THREE-STATE
INPUT DETECT
GND
V
+
15µA
6905x BD
15µA
OUT
OE
f
MO
DIVIDER
SELECT
5
DIV
4
2
f
OSC
=
f
MO
N
UU
U
PI FU CTIO S
V
+
(Pin 1): Voltage Supply (2.7V ≤ V
+
≤ 5.5V). This supply
must be kept free from noise and ripple. It should be
bypassed directly to the GND (Pin 2) with a 0.1µF capacitor
or higher.
GND (Pin 2): Ground. Should be tied to a ground plane for
best performance.
OE (Pin 3): Output Enable. Pull to V+ or leave floating to
enable the output driver (Pin 5). Pull low to disable the
output. The output is disabled asynchronously. Pulling OE
pin low will immediately disable the output. Pulling the OE
pin high will bring the output high on the next low to high
transition of the clock. This eliminates pulse slivers.
DIV (Pin 4): Divider-Setting Input. This three-state input
selects among three divider settings. Pin 4 should be tied
to V
+
for the ÷1 setting, the highest frequency range. Float-
ing 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 floating 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 15µA. When Pin 4 is floated, it
should be bypassed by a 1nF capacitor to ground or it should
be surrounded by a ground shield to prevent excessive cou-
pling from other PCB traces.
OUT (Pin 5): Oscillator Output. This pin can drive 5kΩ
and/or 5pF loads. For heavier loads, refer to the Applica-
tions Information section.
Table 1. LTC6905-XXX Frequency Settings
DIV SETTING LTC6905-133 LTC6905-100 LTC6905-96 LTC6905-80
V+ 133.33MHz 100MHz 96MHz 80MHz
OPEN 66.66MHz 50MHz 48MHz 40MHz
GND 33.33MHz 25MHz 24MHz 20MHz