DA9275.007

19 February 2004

4 (10)

EXTERNAL COMPONENT SELECTION

MAS9275 requires a minimum number of external components for proper operation.

Quartz Crystal

The MAS9275 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 oscillation of a quartz crystal is

determined by its “cut” and by the load capacitors

connected to it. MAS9275 incorporates on-chip

variable load capacitors that “pull” (change) the

frequency of the crystal. The crystal specified for

use with the MAS9275B2 is designed to have zero

frequency error when the total of on-chip + stray

capacitance is 10 pF (See Note 1 on page 2 for

other capacitance options).

Recommended Crystal Parameters:

Initial Accuracy at 25°C ±20 ppm

Temperature Stability ±30 ppm

Crystal Load Capacitance 10 pf (See Note1 below)

Crystal Shunt Capacitance, C0 2 pF Typical

C0/C1 Ratio Typical ≤ 300

Equivalent Series Resistance 20 Ω max. Crystals with higher ESR can be used if frequency is < 36 MHz. See

Note 2 under Electrical Characteristics on Page 3.

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 MAS9275. 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.

Note 1. If the crystal with a load other than the nominal Crystal Load Capacitance as defined in Recommended

Operation Conditions on page 2 is used with MAS9275, the crystal has to have frequency offset in order to

have the nominal frequency at VC = 1.65 V or at VC = 2.5 V. Please see table below for offset frequencies vs.

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

Crystal frequency

19.68

19.68

27.00

40.00

MHz

Crystal Load

8

10

12.5

16

pF

Offset in crystal frequency

A1

1.65 V

+0

-60

-150

-240

ppm

B2, C2

1.65 V

+60

0

-75

-180

ppm

B3, C3, C4

1.65 V

+85

+25

-50

-155

ppm

B3, C3, C4

2.5 V

+30

-30

-105

-210

ppm

Note: 19.68 MHz crystal with 10 pF load capacitance used with MAS9275B2 or C2 may not require frequency

offset because of small deviation

For example:

For application using MAS9275B2 or C2 with nominal frequency of 27.00 MHz a crystal with 12.5 pF load has to

have a frequency of 27.00 MHz + ((27.00 MHz/10