DS125BR820 Datasheet, PDF (52/62 Pages) Texas Instruments – Low-Power 12.5 Gbps 8-Channel Linear Repeater

DS125BR820
SNLS491B – JULY 2014 – REVISED FEBRUARY 2015
www.ti.com
9 Power Supply Recommendations
Two approaches are recommended to ensure that the DS125BR820 is provided with an adequate power supply.
First, the supply (VDD) and ground (GND) pins should be connected to power planes routed on adjacent layers
of the printed circuit board. The layer thickness of the dielectric should be minimized so that the VDD and GND
planes create a low inductance supply with distributed capacitance. Second, careful attention to supply
bypassing through the proper use of bypass capacitors is required. A 0.1 μF bypass capacitor should be
connected to each VDD pin such that the capacitor is placed as close as possible to the DS125BR820. Smaller
body size capacitors can help facilitate proper component placement. Additionally, capacitor with capacitance in
the range of 1 μF to 10 μF should be incorporated in the power supply bypassing design as well. These
capacitors can be either tantalum or an ultra-low ESR ceramic.
The DS125BR820 has an optional internal voltage regulator to provide the 2.5 V supply to the device. In 3.3 V
mode operation, the VIN pin = 3.3 V is used to supply power to the device. The internal regulator then provides
the 2.5 V to the VDD pins of the device and a 0.1 μF cap is needed at each of the five VDD pins for power
supply de-coupling (total capacitance should equal 0.5 μF). The VDD_SEL pin must be tied to GND to enable the
internal regulator. In 2.5 V mode operation, the VIN pin should be left open and 2.5 V supply must be applied to
the five VDD pins to power the device. The VDD_SEL pin must be left open (no connect) to disable the internal
regulator.
3.3 V mode
2.5 V mode
Enable
VDD_SEL
Internal
voltage
regulator
2.5 V
VIN
VDD
VDD
VDD
3.3 V
Capacitors can be
either tantalum or an
ultra-low ESR ceramic.
0.1 µF
0.1 µF
0.1 µF
Disable
VDD_SEL
open
Internal
voltage
regulator
VIN
open
VDD
0.1 µF
2.5 V
VDD
VDD
0.1 µF
Capacitors can be
either tantalum or an
ultra-low ESR ceramic.
0.1 µF
VDD
0.1 µF
VDD
0.1 µF
VDD
0.1 µF
VDD
0.1 µF
Place 0.1 µF close to VDD Pin
Total capacitance should be % 0.5 µF
Place capacitors close to VDD Pin
Figure 49. 3.3 V or 2.5 V Supply Connection Diagram
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