THS8134, THS8134A, THS8134B

TRIPLE 8-BIT, 80 MSPS VIDEO D/A CONVERTER

WITH TRI-LEVEL SYNC GENERATION

SLVS205D – MAY 1999 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

comparison to EIA RS-343/RS-170 levels

Traditionally, video amplitude levels are specified according to the EIA RS-343 or RS-170 standards. RS-343

uses a bi-level negative going sync. Also, there is a difference between the reference blanking and black video

level. Figure 15 shows the relative amplitudes and the current drives that would be needed to generate

compliant relative amplitudes with a double-terminated 75-

Ω load, as is specified for RS-343. RS-170 compliant

levels can be reached using the same current sources but a different 150-

Ω source termination resistor, which

brings the load to 150 || 75

Ω = 50 Ω. In this case a blank-to-white level of approximately 1 V is reached

(0.714 V

× 50 ÷ 37.5) as required by RS-170.

7.5 IRE

40 IRE

92.5 IRE

BLACK Level

BLANK Level

SYNC Level

With Sync Insertion

Without Sync Insertion

V

mA

V

mA

1.000

26.67

0.714

19.05

0.340

9.05

0.340

1.44

0.286

7.62

0

0

0

0

Figure 15. RS-343 Video Definition

The video signal contains 140 IRE, equal to 1 Vpp. This is split into 40 IRE for the composite sync, 7.5 IRE for

blanking-to-black and 92.5 IRE for the active video portion.

designing with PowerPAD

™

The THS8134 is housed in a high-performance, thermally enhanced, 48-pin PowerPAD package (TI package

designator: 48-PHP). Use of the PowerPAD package does not require any special considerations except to note

that the PowerPAD, which is an exposed die pad on the bottom of the device, is a metallic thermal and electrical

conductor. Therefore, if not implementing the PowerPAD PCB features, solder masks (or other assembly

techniques) may be required to prevent any inadvertent shorting by the exposed PowerPAD of connection

etches or vias under the package. The recommended option, however, is not to run any etches or signal vias

under the device, but to have only a grounded thermal land as explained below. Although the actual size of the

exposed die pad may vary, the minimum size required for the keep-out area for the 48-pin PHP PowerPAD

package is 7 mm

× 7 mm.

It is recommended that there be a thermal land, which is an area of solder-tinned-copper, underneath the

PowerPAD package. The thermal land will vary in size, depending on the PowerPAD package being used, the

PCB construction, and the amount of heat that needs to be removed. In addition, the thermal land may or may

not contain numerous thermal vias, depending on PCB construction.

More information on this package and other requirements for using thermal lands and thermal vias are detailed

in the TI application note

PowerPAD

™ Thermally Enhanced Package Application Report, TI literature number

SLMA002, available via the TI Web pages beginning at URL: http://www.ti.com.