TLK2521

1 to 2.5 Gbps TRANSCEIVER

SLLS574B − JULY 2003 − REVISED JANUARY 2004

16

POST OFFICE BOX 655303

_

+

GND

VDD

RXP

RXN

5 k

Ω

7.5 k

Ω

TXP

TXN

Transmitter

Media

Receiver

ZO

ZO

ZO

ZO

Figure 11. High-Speed I/O Directly Coupled Mode

_

+

GND

VDD

RXP

RXN

5 k

Ω

7.5 k

Ω

TXP

TXN

Transmitter

Media

Receiver

ZO

ZO

ZO

ZO

Figure 12. High-Speed I/O AC-Coupled Mode

AC-coupling is only recommended if the parallel TX data stream is encoded to achieve a dc-balanced data

stream. Otherwise, the ac-caps can induce common-mode voltage drift due to the dc-unbalanced data stream.

designing with PowerPAD

The TLK2521 is housed in a high-performance, thermally enhanced, 64-pin HTQFP (PAP64) PowerPAD

package. 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 PowerPAD PCB features, the use of 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. It is strongly recommended that the PowerPAD be soldered to the

thermal land. The recommended convention, however, is to not 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 64-pin PAP PowerPAD package is 8 mm

×

8 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 varies 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.