DA9283.006

13 July 2006

4 (14)

EXTERNAL COMPONENT SELECTION

MAS9283 requires a minimum number of external components for proper operation.

Quartz Crystal

The MAS9283 VCXO function consists of the

external crystal and the integrated VCXO oscillator

circuit. To assure the best system performance

(frequency pull range) and reliability, a crystal

device with the recommended parameters (shown

below) must be used, and the layout guidelines in

the

following

section must be followed. The

frequency of the oscillation of a quartz crystal is

determined by its “cut” and by the load capacitors

connected to it. MAS9283 incorporates on-chip

variable load capacitors that “pull” (change) the

frequency of the crystal. The crystal specified for

use with the MAS9283 is designed to have zero

frequency error when the total of on-chip + stray

capacitance is 10 pF. See Note 3 on page 2 for

other capacitance options.

The external crystal must be connected as close to the chip as possible and should be on the same side

of the PCB as the MAS9283. There should be no vias between the crystal pins and the X1 and X2 device

pins. There should be no signal traces underneath or close to the crystal.

Recommended Crystal Parameters:

Parameter

Symbol

Typ

Unit

Note

Initial Accuracy at 25°C

±20

ppm

Temperature Stability

±30

ppm

Crystal Load Capacitance

10

pF

1)

Crystal Shunt Capacitance (Typical)

C0

2

pF

C0/C1 Ratio (Typical)

≤ 300

Note 1. If the crystal with a load other than 10 pF is used with MAS9283, the crystal has to have frequency offset

in order to have the nominal frequency at VC = 1.65 V. Please see table below for offset frequencies vs. crystal

load. (Values are for a typical crystal with S = 30 ppm/pF.)

Parameter

Unit

Crystal frequency

27

27

27

27

MHz

Crystal load

8

9

12.5

15

pF

Offset / ppm (MAS9283AA – AE, AN – AR, VC=1.65 V)

+30

0

-105

-180

Offset / ppm (MAS9283AG – AR, VC= 2.5V)

0

-30

-135

-210

For example:

When the desired nominal frequency of the application and the crystal load are 27.00 MHz and 12.5 pF, the

crystal nominal frequency has to be,

(

)

MHz

MHz

MHz

997165

.

26

105

10

00

.

27

00

.

27

6

=

















−

×

















+

.