LTC6902 查看數據表（PDF） - Linear Technology

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LTC6902

Multiphase Oscillator with Spread Spectrum Frequency Modulation

Linear Technology 

LTC6902

PI FU CTIO S

or it should be surrounded by a ground shield to prevent

excessive coupling from other PCB traces.

OUT1, OUT2, OUT3, OUT4 (Pins 4, 5, 6 and 7): Oscillator

Outputs. These pins can drive 5kΩ and/or 10pF loads.

Larger loads may cause inaccuracies due to supply bounce

at high frequencies.

GND (Pin 8): Ground. Should be tied to a ground plane for

best performance.

SET (Pin 10): Frequency Setting Resistor Input. The value

of the resistor (RSET) connected between Pin 10 and V+

determines the oscillator frequency. The voltage on this

pin is held at approximately 1.13V below the V+ voltage.

For best performance, use a precision metal film resistor

with a value between 10k and 2M and limit the capacitance

on this pin to less than 10pF.

MOD (Pin 9): Spread Spectrum Frequency Modulation

Setting Resistor Input. The value of the resistor (RMOD)

connected between Pin 9 and V+ determines the amount

of frequency modulation. The output frequency is always

modulated down from the frequency set by the RSET resis-

tor. For best performance, use a precision metal film resis-

tor with a value between 10k and 2M and limit the

capacitance on this pin to less than 10pF. The voltage on

this pin is not static. Limiting the capacitance on this pin

is important for the part to perform properly. To disable

the modulation, connect this pin to GND. Grounding the

MOD pin disables the modulation and shuts down the

modulation circuitry to save power. Leaving the pin open

to disable the modulation is not recommended. While

leaving the pin open, RMOD ≈ ∞, gives the mathematical

result of 0% modulation, the open pin is susceptible to

external noise coupling that can effect frequency accuracy.

BLOCK DIAGRA

RSET

IMOD

V+

1

ISET

SET

10

ISET

RMOD

MOD

9

IMOD

V+ – VSET = 1.1V ±25%

+

–

G=1

+– VBIAS

ISET

MASTER OSCILLATOR

fMASTER

=

10MHz

•

20kΩ

•

IMASTER

(V+ – VSET)

IMASTER

2

DIV

3

PH

PROGRAMMABLE

DIVIDER ÷N

(N = 1, 10 OR 100)

MULTIPHASE

CIRCUIT

SELECTS BETWEEN

MULTIPHASE

OPTIONS AND ÷M

2-PHASE (M = 1)

3-PHASE (M = 3)

4-PHASE (M = 4)

OUT1

4

OUT2

5

OUT3

6

OUT4

7

IMOD

VSET

REF

MULTIPLYING

DAC

7

9-BIT PRBS

GENERATOR

÷ 3200

8 GND

CURRENT MIRROR

6902 BD

6902f

7

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