TSB21LV03

IEEE 1394-1995 TRIPLE-CABLE TRANSCEIVER/ARBITER

SLLS230A – MARCH 1996 – REVISED DECEMBER 1996

25

POST OFFICE BOX 655303

APPLICATION INFORMATION

DC/DC

Converter

Regulator

Host

Power

Supply

LLC

Phy

D0 – D7

CTL0,

CTL1

LREQ

SYSCLK

D0 – D7

CTL0,

CTL1

LREQ

SYSCLK

0.1

µF

1 M

Ω

B

W

G

12 V

5 V

TPA+

TPA–

TPB+

TPB–

12 V

5 V

Isolation Boundary

Cable Shield

Terminals 7

and 8

Cable Ground

Cable Power

1394 Host Design

0.001

µF

0.1

µF

1 M

Ω

Bus

Holder

Bus

Holder

1

6

4

2

5

3

LLC

GND

Phy

GND

Figure 15. External Implementation of Bus-Holder Isolation

When either the phy or the LLC had internal bus holders present, then the device without bus holders would

require an external bus holder to be implemented on its side of the isolation barrier. There are several choices

for external bus holders. Depending on the application, the least expensive approach can be to use the inputs

to buffer circuits that have bus holders built into their inputs. Several alternative devices that have bus holder

circuits on the inputs are available. For 3.3-V applications, the SN74LVCH244, SN74LVCH245, and

SN74LVCH16244 are available. For 5-V applications, the SN74ABTH245, SN74ACT1071, or SN74ACT1073

are available. Figure 16 and Figure 17 show the implementation of the bus-holder isolation for a

monodirectional signal.

NOTE:

A bus holder is only required on the receiving side of the isolation capacitor, regardless

of whether that side is in the LLC power domain or the phy power domain.