722

7

SBVS016B

www.ti.com

FIGURE 3. Short-Circuit Protection.

FIGURE 2. Two-Port Isolation with Two 3650s.

+V

O1

C

1

P+

V+

E

V–

R

1

2N2219

V

IN

IN4148

100

Ω

+

3.6k

Ω

1

Ω

–V

O1

+V

O2

C

2

–V

O2

–

722

+V

O1

C

1

–V

O1

+V

O2

C

2

–V

O2

P+

V+

E

V–

C

R

1

V

IN

Com

+15V

O/P Com

O/P Com

+15V –15V

O/P Com

+15V –15V

I/P

Com #2

I/P

Com #1

722

–15V

Figure 2 illustrates how the 722 can provide isolated input

power to the input stage of two 3650s connected in the two-

port configuration. Power for the output stage is provided by

the system +15V and –15V supplies. Input stages are iso-

lated from each other and from the system supply. In this

situation, the 722 input-to-output isolation specification ap-

plies to the amplifier input-to-output voltages, whereas the

channel-to-channel 722 specification applies to the voltage

existing between I/P Com #1 and I/P Com #2.

SHORT CIRCUIT PROTECTION

The circuit in Figure 3 may be added to the input of the 722

to protect it from damage in situations where too much

current is demanded from the outputs—such as a short

circuit from an output to its common. The circuit limits input

current to approximately 150mA for an input voltage of

15VDC (for ß of 2N2219 of 50).