PCA5007 datasheet(28/112 Pages) PHILIPS

28 / 112 page

1998 Oct 07

Philips Semiconductors

Product speciﬁcation

Pager baseband controller

PCA5007

6.10

76.8 kHz oscillator

6.10.1

FUNCTION

The oscillator produces a reference frequency of 76.8 kHz.

The frequency offset is compensated for by a separate

digital clock correction block. The oscillator operates

directly on VBAT and is always enabled.

6.10.2

OSCILLATOR CIRCUITRY

The on-chip inverting oscillator amplifier is a single NMOS

transistor supplied with a constant current. The amplitude

visible at terminals XTL1 and XTL2 is therefore not a full

rail swing with a very high impedance. To reduce the

power consumption, the input Schmitt trigger buffer is

limited to approximately 100 kHz maximum frequency.

The whole circuit operates directly at the battery supply.

The 76.8 kHz oscillator cannot be disabled. It also

continues its operation during DC/DC converter off or

8051 stop mode.

The simplest application configuration is shown in Fig.12a.

C1 and C2 can be added to operate a crystal at its

optimum load condition. The resulting capacitance of the

series connection of C1 and C2 must be smaller than 5 pF

for a guaranteed start-up of the oscillator.

Fig.12 Oscillator circuit.

handbook, full pagewidth

MGR115

2 M

Ω

76.8 kHz

10 pF

(a)

(b)

(c)

10 pF

76.8 kHz

XTL1

XTL2

76.8 kHz

10 pF

XTL1

XTL2

2 M

Ω

VP = VBAT

fmax = 100 kHz

10 pF

XTL1

XTL2

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