FDL300E/FDL300D
Page 8
Figure 2. Circuit schematic for interface between a T1 1394b PHY and Firecomms FOTs.
FDL300E/FDL300D (Preliminary) Revision P13
Firecomms assumes no responsibility for inaccuracies or omissions in the information
contained in this document. Specifications are subject to change without notice.
No patent rights are granted to any of the circuits described herein.
IEEE 1394 APPLICATION CIRCUIT
Figure 2 illustrates the correct configuration for the interface between the Texas Instruments 1394b PHY (part number
TSB41BA3B) and the Firecomms Tx and Rx FOT pair, part numbers FDL300E and FDL300D.
Note on Reduced Power Consumption
Firecomms FOTs do not need a level-shifting circuit between the PHY and FOT as the differential I/O swings have
been matched. The result of this PHY and FOT I/O matching is the elimination of power consumption by the level
shifting circuit. Previously, FOT designs required a level shifting network (LVDS to LVPECL) which consumed
approximately 33 mA from the power rail (Vcc) for each I/O. In that design, power consumption continued
irrespective of the PHY IC and even if the FOTs were powered down or in sleep states. With the Firecomms FOT
solution, this power consumption has been eliminated.
In the circuit shown in Figure 2, once the PHY and FOTs enter a sleep state the power consumption is reduced to the
data sheet values for PHY and FDL300 sleep states. There is no residual power consumption from the interface circuit.
Similarly, if the PHY and the FOTS experience a hard power-down, current consumption goes to zero.
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