6

®

PWS725A/726A

full load while drawing only 3mA from the negative supply.

Under these conditions, the PWS725A/726A could supply

power for up to five devices (80mA

÷ 16mA ≈ 5). Thus, the

PWS725A/726A can power more circuits than is at first

apparent.

ISOLATION VOLTAGE RATINGS

Because a long-term test is impractical in a manufacturing

situation, the generally accepted practice is to perform a

production test at a higher voltage for some shorter period of

time. The relationship between actual test conditions and the

continuous derated maximum specification is an important

one. Burr-Brown has chosen a deliberately conservative

one: VDC

ten seconds. This choice is appropriate for conditions where

real voltages are well-defined or where the isolation voltage

is not continuous, the user may choose a less conservative

derating to establish a specification from the test voltage.

OUTPUT SYNC SIGNAL

To allow synchronization of an ISO120 or ISO121 isolation

amplifier, the PWS725A and PWS726A have an OUTPUT

SYNC signal at pin 29. It should be connected as shown in

Figure 5 to keep capacitive loading of pin 29 to a minimum.

If output sync is not used, leave pin open.

FIGURE 5. Synchronization with ISO120 or ISO121 Isola-

tion Amplifier.

29

PWS725A/726A

20k

Ω

4

20pF

Ext Osc

Connection

of

ISO120

or

ISO121

NOTE: (1) Reference National Electrical Manufacturers Association (NEMA)

Standards Parts ICS I-109 and ICS I-111.