M2080/81/82 Datasheet Rev 0.4

9 of 14

Revised 30Jul2004

M2080/81/82, M2085/86/87

Preliminar y In f o r m atio n

Integrated

Circuit

Systems, Inc.

External Loop Filter

To provide stable PLL operation, the M2080/81/82

requires the use of an external loop filter. This is

provided via the provided filter pins (see Figure 5).

The loop filter is implemented as a differential circuit

to minimize system noise interference.

Figure 5: External Loop Filter

PLL bandwidth is affected by loop filter component

values, “Mfec” and “Mfin” values, and the “PLL Loop

Constants” listed in AC Characteristics on pg. 12.

loop bandwidth in a given application. See “Mfec and

Rfec Divider Look-Up Tables (LUTs)” on pg. 3.

See Table 11, Example Values for Loop Filter External

Components, below.

PLL Simulator Tool Available

A free PC software utility is available on the ICS website

(www.icst.com). The M2000 Timing Modules PLL

Simulator is a downloadable application that simulates

PLL jitter and wander transfer characteristics. This

enables the user to set appropriate external loop

component values in a given application.

Refer to the M208x Series product web page at

www.icst.com/products/summary/m2080-2087.htm

for additional product information.

C

POST

C

POST

VC

nVC

R

POST

nOP_OUT

OP_OUT

R

POST

R

LOOP

R

LOOP

C

LOOP

C

LOOP

OP_IN

nOP_IN

6

7

5

49

8

for Particular M208x Series Devices

Device

Device Configuration

Example External Component Values

Nominal Performance With These Values

(MHz)

F

VCSO

(MHz)

FIN_SEL

1:0

MRSEL

1:0

R loop

C loop

R post

C post

PLL Loop

Bandwidth

Damping

Factor

Passband

M2080

622.08

1 1

0 1

5.6

k

Ω

10

µF

68

k

Ω

470

pF

530

Hz

6.5

0.05

M2080

669.3266

1 0

1 0 0243.0

k

Ω

0.1

µF

34

k

Ω

470

pF

1k

Hz

5.9

0.06

M2081

77.76

622.08

0 1

0 1

8.2

k

Ω

10

µF

100

k

Ω

470

pF

360

Hz

6.5

0.05

M2081

19.44

622.08

0 0

1 1

8.2

k

Ω

10

µF

100

k

Ω

470

pF

360

Hz

6.5

0.05

Table 11: Example Values for Loop Filter External Components

Note 1: K

VCO , VCSO Bandwidth, M Divider Value, and External Loop Filter Component Values determine Loop Bandwidth, Damping Factor, and

Passband Peaking. For PLL Simulator software, go to www.icst.com.