VSC838-01
Datasheet
ITC
VCC
TERM_CTRL
50
50
50
50
PAD
PAD
PAD
PAD
DRIVE_CTRL
H/S Input Equivalent Circuit
H/S Output Equivalent Circuit
Figure 5. Equivalent Circuits
Input Terminations
The high-speed inputs of the VSC838-01 are internally terminated by a 100Ω impedance between true and
complement inputs. Termination resistors are isolated from each other on-chip. The termination will self-bias to
+2.0V (nominal) for AC-coupled applications. The ITC pin enables direct interconnection of multiple VSC838-01
devices. With ITC tied to VCC, the center point of the 100Ω termination resistance is tied to VCC, causing the
terminations to act as loads for an open-drain or open-collector differential output. For more information about the
proper connection of the ITC pin, see Table 11, page 12.
Table 7. Allowed Input Termination Schemes
Type
Description
Comments
1
2
3
4
5
AC-coupled input
Tie ITC LOW, 100Ω differential input termination, input self-biased
Tie ITC HIGH, termination acts as 50Ω load to VCC
Tie ITC HIGH, termination acts as 50Ω load to VCC
Tie ITC LOW, 100Ω differential termination (preferred over Type 3)
DC-coupled from open-drain CML
DC-coupled from back-terminated 2.5V CML
DC-coupled from back-terminated 2.5V CML
DC-coupled from back-terminated 3.3V LVPECL Tie ITC LOW, 100Ω differential termination
Some allowed termination schemes result in additional I current and power dissipation on-chip.
CC
Output Terminations
The high-speed outputs of the VSC838-01 are internally back-terminated by 50Ω to V when the TERM_CTRL pin
CC
is HIGH. When this pin is LOW, the output driver functions as an open-drain CML driver. Setting DRIVE_CTRL
LOW (GND) saves approximately 1W under maximum power dissipation conditions. The table following table
provides more information about the allowable types of terminations and modes of operation.
Table 8. Allowed High-Speed Output Terminations and Modes of Operation
(1)
(1)
VOD
VOCM
Type
Description
DRIVE_CTRL
TERM_CTRL
(mV) typ
(V) typ
1
AC-coupled to 50Ω termination to any voltage
VCC (HIGH)
VCC (ON)
500
2.0
9 of 19
VMDS-10195 Revision 4.0
August 19, 2005
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
