EM773 datasheet(37/45 Pages) NXP

37 / 45 page

EM773

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Objective data sheet

Rev. 1 — 1 September 2010

37 of 45

NXP Semiconductors

EM773

Energy metering IC

11.2 XTAL Printed Circuit Board (PCB) layout guidelines

The crystal should be connected on the PCB as close as possible to the oscillator input

and output pins of the chip. Take care that the load capacitors Cx1, Cx2, and Cx3 in case of

third overtone crystal usage have a common ground plane. The external components

must also be connected to the ground plain. Loops must be made as small as possible in

Fig 22. Oscillator modes and models: oscillation mode of operation and external crystal

model used for CX1/CX2 evaluation

Table 13.

Recommended values for CX1/CX2 in oscillation mode (crystal and external

components parameters) low frequency mode

Fundamental oscillation

frequency FOSC

Crystal load

capacitance CL

Maximum crystal

series resistance RS

External load

capacitors CX1, CX2

1 MHz - 5 MHz

10 pF

< 300

18 pF, 18 pF

20 pF

< 300

39 pF, 39 pF

30 pF

< 300

57 pF, 57 pF

5 MHz - 10 MHz

10 pF

< 300

18 pF, 18 pF

20 pF

< 200

39 pF, 39 pF

30 pF

< 100

57 pF, 57 pF

10 MHz - 15 MHz

10 pF

< 160

18 pF, 18 pF

20 pF

< 60

39 pF, 39 pF

15 MHz - 20 MHz

10 pF

< 80

18 pF, 18 pF

Table 14.

Recommended values for CX1/CX2 in oscillation mode (crystal and external

components parameters) high frequency mode

Fundamental oscillation

frequency FOSC

Crystal load

capacitance CL

Maximum crystal

series resistance RS

External load

capacitors CX1, CX2

15 MHz - 20 MHz

10 pF

< 180

18 pF, 18 pF

20 pF

< 100

39 pF, 39 pF

20 MHz - 25 MHz

10 pF

< 160

18 pF, 18 pF

20 pF

< 80

39 pF, 39 pF

em773_002aaf424

EM773

XTALIN

XTALOUT

CX2

CX1

XTAL

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