Applications Information

POWER SUPPLIES

While the pins of the TP305X family are well protected

against electrical misuse it is recommended that the stan-

dard CMOS practice be followed ensuring that ground is

connected to the device before any other connections are

made In applications where the printed circuit board may be

plugged into a ‘‘hot’’ socket with power and clocks already

present an extra long ground pin in the connector should

be used

All ground connections to each device should meet at a

common point as close as possible to the GNDA pin This

minimizes the interaction of ground return currents flowing

through a common bus impedance 01 mF supply decou-

pling capacitors should be connected from this common

possible

For best performance the ground point of each CODEC

FILTER on a card should be connected to a common card

ground in star formation rather than via a ground bus

RECEIVE GAIN ADJUSTMENT

For applications where a TP305X family CODECfilter re-

ceive output must drive a 600X load but a peak swing lower

Table II lists the required resistor values for 600X termina-

tions As these are generally non-standard values the equa-

tions can be used to compute the attenuation of the closest

practical set of resistors It may be necessary to use un-

equal values for the R1 or R4 arms of the attenuators to

achieve a precise attenuation Generally it is tolerable to

allow a small deviation of the input impedance from nominal

while still maintaining a good return loss For example a 30

dB return loss against 600X is obtained if the output imped-

ance of the attenuator is in the range 282X to 319X (as-

suming a perfect transformer)

T-Pad Attenuator

J

J

POWER OUT

and

TLH5510 – 5

2

N

J

J

Note

See Application Note 370 for further details

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