SL28SRC01

DOC#: SP-AP-0015 (Rev. 0.2)

Page 2 of 11

Pin Definitions

The SL28SRC01 requires a Parallel Resonance Crystal.

Substituting a series resonance crystal causes the

SL28SRC01 to operate at the wrong frequency and violates

the ppm specification. For most applications there is a

300-ppm frequency shift between series and parallel crystals

due to incorrect loading.

Crystal Loading

Crystal loading plays a critical role in achieving low ppm perfor-

mance. To realize low ppm performance, use the total capac-

itance the crystal sees to calculate the appropriate capacitive

loading (CL).

Figure 1

shows a typical crystal configuration using the two

trim capacitors. It is important that the trim capacitors are in

series with the crystal. It is not true that load capacitors are in

parallel with the crystal and are approximately equal to the

load capacitance of the crystal.

Calculating Load Capacitors

In addition to the standard external trim capacitors, consider

the trace capacitance and pin capacitance to calculate the

crystal loading correctly. Again, the capacitance on each side

is in series with the crystal. The total capacitance on both side

is twice the specified crystal load capacitance (CL). Trim

Pin No.

Name

Type

Description

1

XIN

I

14.318 MHz Crystal input.

2

VDD

PWR 3.3V power supply

3

VDD

PWR 3.3V power supply

4

VSS

GND

Ground

5

VDD

PWR 3.3V power supply

6

VSS

GND

Ground

7

SRC1

O, DIF 100 MHz Differential serial reference clocks.

8

SRC1#

O, DIF 100 MHz Differential serial reference clocks.

9

VSS

GND

Ground

10

VDD

PWR 3.3V power supply

11

VDD

PWR 3.3V power supply

12

VSS

GND

Ground

13

VDD

PWR 3.3V power supply

14

SSON

I

3.3V LVTTL input for enabling spread spectrum clock

0 = Disable, 1 = Enable (-0.5% SS)

Extrenal 10K ohm pull-up or pull-down resistor required

15

VSS

GND

Ground

16

XOUT

O

14.318 MHz Crystal output.

Table 1. Crystal Recommendations

Frequency

(Fund)

Cut

Loading

Load Cap

Drive

(max.)

Shunt Cap

(max.)

Motional

(max.)

Tolerance

(max.)

Stability

(max.)

Aging

(max.)

14.31818 MHz

AT

Parallel

20 pF

0.1 mW

5 pF

0.016 pF

35 ppm

30 ppm

5 ppm

Figure 1. Crystal Capacitive Clarification