TCM38C17IDL

QCombo

™ FOUR-CHANNEL (QUAD) PCM COMBO

SLWS040C – JUNE 1996 – REVISED OCTOBER 1999

18

POST OFFICE BOX 655303

APPLICATION INFORMATION

Various TCM38C17IDL output configurations are detailed in the following paragraphs.

differential configuration

For connection to a transformer, the fully differential configuration is recommended to provide maximum

possible output, or voltage swing, to the primary of an attached transformer. Figure 9 shows the QCombo in a

fully-differential mode.

PWRO +

PWRO –

GSR

Vd

R1

R2

RL

VO+

VO–

Figure 9. Fully Differential Gain-Setting Configuration

PWRO+ and PWRO – are low-impedance complementary outputs. The total output available for the output load

GSR input.

R1 + R2 should be greater than 10 k

sets the total loading. The total parasitic capacitance of the GSR input, along with the parallel combination of

R1 and R2, define a time constant that must be minimized to avoid inaccuracies in the gain calculations.

The resistor gain control actually consists of attenuating the full differential output voltage. The equation to

determine the value of the attenuation constant is given in equation 1.

A

+

1

) (R1 B R2)

4

) (R1 B R2)

which can also be expressed as shown in equation 2.

A

+

R1

) R2

4(R2

) R1 B 4)

where A = attenuation constant

Depending on the values of gain setting resistors R1 and R2, the attenuation constant (A) can have a value of

0.25 to unity (1), or approximately 12 dB of voltage adjustment.

(1)

(2)