DA9283.006
13 July 2006
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
10
ppm
pF
Crystal Load Capacitance
CL
1)
Crystal Shunt Capacitance (Typical)
C0/C1 Ratio (Typical)
C0
2
pF
≤ 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
pF
Crystal load
8
9
0
12.5
-105
15
Offset / ppm (MAS9283AA – AE, AN – AR, VC=1.65 V)
+30
-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,
27.00 MHz
27.00 MHz +
×
(−105
)
= 26.997165 MHz
.
106
4 (14)
MAS [ MICRO ANALOG SYSTEMS ]
