1B22

REV. B

–4–

Synchronizing Multiple 1B22s: In applications where mul-

tiple 1B22s are used in close proximity, radiated individual

oscillator frequencies may cause “beat frequency” related out-

put errors. These errors can be eliminated by driving the SYNC

pins of all the units with a 40 kHz clock circuit at 50% duty

cycle (Figure 5). The SYNC input typically has an input imped-

ance of 150 k

Ω 180 pF.

Figure 5. Multiple 1B22s’ Synchronization

Loop Supply Requirements: The 1B22 design allows flexible

loop supply options. The loop supply voltage required for any

value of load resistance can be calculated from the following

equation:

=

+ 780

106

This value allows for approximately 10% overrange capability.

The graph in Figure 6 shows the relationship between supply

voltage and load resistance.

Figure 6. Loop Supply vs. Load

APPLICATIONS

Isolated D/A Converter: The 1B22 offers total ground isola-

tion and protection from high voltage transients in interfacing

D/A converters to standard 4 to 20 mA current loops. The D/A

converter, such as the Analog Devices’ 12-bit AD7245

DACPORT®, should be connected for operation on the unipo-

lar 0 V to +10 V output range. This is shown in Figure 7.

Figure 7. D/A Converter–Isolated 4-20 mA Interface

Pressure Transmitter: In Figure 8, the 1B22 is used in a

pressure transmitter application to provide complete input-

output isolation and avoid signal errors due to ground loop cur-

rents. The process pressure is monitored with a strain gage type

pressure transducer interfaced by the Analog Devices’ 1B32

transducer signal conditioner. The high level voltage output of

the 1B32 is converted to the isolated 4 to 20 mA current for

transmission to a remote recorder or indicator.

Figure 8. Isolated Pressure Transmitter

DACPORT is a registered trademark of Analog Devices, Inc.