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MAS9275

IC FOR 10.00 – 36.00 MHz VCXO

Micro Analog Systems Oy 

EXTERNAL COMPONENT SELECTION

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

DA9275.004

23 April 2003

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 300 Typical

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 10 pF is used with MAS9275, 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.)

Crystal f/MHz

Crystal Load /pF

Offset /ppm

19.68 19.68 27.00 40.00

8

10

12.5 16

+60 +5

-90 -180

Note: 19.68 MHz crystal with 10 pF load capacitance may not require frequency offset because of small

deviation

For example:

For application 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/106) x (- 90)) = 26.99757 MHz

4 (10)

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