CMX878 Ver la hoja de datos (PDF) - CML Microsystems Plc

Número de pieza

componentes Descripción

Fabricante

CMX878

Line Powered Modem plus DAA

CML Microsystems Plc 

Line Powered Modem plus DAA

Power Supply Arrangement

CMX878

Figure 2b Recommended Power Supply Connections and De-coupling

This device is capable of detecting and decoding small amplitude signals. To achieve this DVDD, AVDD

and VBIAS should be decoupled and the receive path protected from extraneous in-band signals. It is

recommended that the printed circuit board is laid out with both AVSS and DVSS ground planes in the

CMX878 area, as shown in Figure 2b, with provision to make a link between them close to the CMX878.

To provide a low impedance connection to ground, the decoupling capacitors must be mounted as close

to the CMX878 as possible and connected directly to their respective ground plane. This will be achieved

more easily by using surface mounted capacitors.

VBIAS is used as an internal reference for detecting and generating the various analogue signals. It must

be carefully decoupled, to ensure its integrity. Apart from the decoupling capacitor, no other loads are

allowed. If VBIAS needs to be used to set external analogue levels, it must be buffered with a high input

impedance buffer.

The DVSS connections to the Xtal oscillator capacitors C1 and C2 should also be of low impedance and

preferably be part of the DVSS ground plane to ensure reliable start up of the oscillator.

In a line powered application it is important to prevent noise from the circuit being coupled onto the line;

careful board layout should be employed to minimise this. It is also important to minimise power supply

noise currents from causing undesirable modulation of the line; the circuit configuration shown in

Figure 4a will minimise this effect.

© 2002 Consumer Microcircuits Limited

9

D/878/2

Share Link: