EM783 datasheet(47/58 Pages) NXP

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EM783

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Product data sheet

Rev. 2 — 17 January 2014

47 of 58

NXP Semiconductors

EM783

Energy metering IC; 32 kB flash, 8 kB SRAM, 4 kB EEPROM

12. Application information

12.1 XTAL input

The input voltage to the on-chip oscillators is limited to 1.8 V. If a clock in slave mode

drives the oscillator, it is recommended that the input is coupled through a capacitor with

Ci = 100 pF. To limit the input voltage to the specified range, choose an additional

capacitor to ground Cg which attenuates the input voltage by a factor Ci/(Ci + Cg). In slave

mode, a minimum of 200 mV(RMS) is needed.

In slave mode, the input clock signal should be coupled using a capacitor of 100 pF

(Figure 22), with an amplitude between 200 mV (RMS) and 1000 mV (RMS). This

corresponds to a square wave signal with a signal swing of between 280 mV and 1.4 V.

The XTALOUT pin in this configuration can be left unconnected.

External components and models used in oscillation mode are shown in Figure 23 and in

Table 22 and Table 23. Since the feedback resistance is integrated on chip, for

fundamental mode oscillation, only connect a crystal and the capacitances CX1 and CX2

externally. L, CL and RS define the fundamental frequency. Capacitance CP in Figure 23

represents the parallel package capacitance and should not be larger than 7 pF.

Parameters FOSC, CL, RS and CP are supplied by the crystal manufacturer (see Table 22).

Fig 22. Slave mode operation of the on-chip oscillator

Fig 23. Oscillation mode of operation and external crystal model used for CX1/CX2

evaluation

aaa-009613

EMxxx

100 pF

XTALIN

aaa-009614

EMxxx

XTALOUT

XTAL

CX2

CX1

XTALIN

EM783 Datasheet(PDF) 47 Page - NXP Semiconductors