TP3054WM datasheet(12/16 Pages) NSC

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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

ground point to VCC and VBB as close to the device as

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

This common ground point should be decoupled to VCC and

VBB with 10 mF capacitors

RECEIVE GAIN ADJUSTMENT

For applications where a TP305X family CODECfilter re-

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

than g25V is required the receive gain can be easily ad-

justed by inserting a matched T-pad or q-pad at the output

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

R1 e Z1

2 a 1

N2 b 1

J b20Z1Z2 N

N2 b 1

R2 e 2

0Z1Z2

N2 b 1

Where N e

0 POWERIN

POWER OUT

and

S e

0Z1Z2

Also Z e

0ZSC ZOC

Where ZSC e impedance with short circuit termination

and ZOC e impedance with open circuit termination

q-Pad Attenuator

TLH5510 – 5

R3 e

0Z1Z2

2 b 1

R3 e Z1

2 b 1

N2 b 2NS a 1

Note

See Application Note 370 for further details

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