LTC6902IMS#TR Linear Technology, LTC6902IMS#TR Datasheet - Page 6

• Manufacturer Part Number: LTC6902IMS#TR
• Description: IC OSC MULTIPHASE PREC LP 10MSOP
• Manufacturer: Linear Technology
• Type: Oscillator, Siliconr

Specifications of LTC6902IMS#TR

• Frequency: 20MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 2.5mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Count: -

QUICK DESIG GUIDE
PI FU CTIO S
LTC6902
Step 3. Calculating the R
The R
setting set the output frequency (f
quency applications. For SSFM applications, the maxi-
mum frequency excursion (f
V
should be kept free from noise and ripple. It should be
bypassed directly to a ground plane with a 0.1 F capacitor
placed as close to the pin as possible.
DIV (Pin 2): Divider Setting Input. This three-state input
selects among three divider settings determining the value
of N in the frequency equation. Pin 2 should be tied to GND
for the 1 setting, the highest frequency range. Floating
Pin 2, leaving it open, divides the master oscillator by 10.
Tie Pin 2 to V
range. To detect a floating DIV pin, the LTC6902 places the
pin at the midsupply point with active circuitry. Therefore,
driving the DIV pin high requires sourcing approximately
2 A. Similarly, driving the DIV pin low requires sinking
2 A. When the DIV pin is floated, it should be bypassed by
a 1nF capacitor to GND or it should be surrounded by a
6
+
R
N
M
(Pin 1): Supply Voltage ( 2.7V V
U
SET
SET
100
10
1
1
4
3
resistor, the multiphase mode and the divider
U
20
+
k
DIV Pin V
DIV Pin
DIV Pin 0
(4 - Phase Output) PH Pin V
(3 - Phase Output) P Pin
(2 - Phase Output) P Pin 0
for the 100 setting, the lowest frequency
U
N M f
U
•
10
Open
MHz
V
SET
•
OUT
MAX
Resistor Value
) is equal to f
OUT
H
H
+
) for constant fre-
5.5V). The supply
Open
V
OUT
.
Step 4. Calculating the R
(Note: For constant frequency applications R
required. Disable SSFM by connecting the MOD pin to
GND)
where the Spreading Percentage is defined by the
following:
where f
R
frequency excursion.
Example
For a 4-phase, 250kHz clock with 40% spreading:
ground shield to prevent excessive coupling from other
PCB traces.
PH (Pin 3): Phase Setting Input. This three-state input
selects among three multiphase options. This sets the
outputs to produce 2-phase, 3-phase or 4-phase signals.
It also sets the value of M in the frequency equation. Pin 3
should be tied to GND for the 2-phase setting. This is the
highest frequency range with M set to 1. Floating Pin 3,
leaving it open, selects the 3-phase setting. This also sets
M to 3. Tie Pin 3 to V
lowest frequency range as M is set to 4. To detect a floating
PH pin, the LTC6902 places the pin at the midsupply point
with active circuitry. Therefore, driving the PH pin high
requires sourcing approximately 2 A. Similarly, driving
the PH pin low requires sinking 2 A. When the PH pin is
floated, it should be bypassed by a 1nF capacitor to GND
SET
Connect PH Pin to V
Leave DIV Pin Open
R
R
R
Spreading Percentage
SET
MOD
MOD
value calculated in Step 3) and f
MAX
= 20k
= 10k
20 •
is the highest frequency excursion (set by the
Spreading Percentage
Sets f
Sets Spreading to 40%
+
for the 4-phase setting. This is the
+
OUT
R
MOD
N = 10
SET
= f
Selects 4-Phase Mode, M = 4
100 •
MAX
Resistor Value
= 250kHz
f
MAX
f
MAX
MIN
–
f
MIN
is the lowest
MOD
is not
6902f