The DACx760 voltage output includes an internal circuit to typically regulate the load current to about 30 mA. However, this parameter is not production tested or trimmed. Optionally, use an external current limiting circuit on VOUT. However, if the VOUT, IOUT and +VSENSE pins are tied together, this circuit must be placed in the VOUT path before the circuit is tied together to the other pins at the common pin. The nature of the current-limiting circuit depends on the application and load. An example of a unidirectional current limiter is shown in Figure 9-5.
Under normal operation, most current in this circuit flows through Q1 and into R3. As current increases through R3, so does the voltage drop across R3, which increases the base-emitter voltage of Q2. Eventually the base-emitter voltage of Q2 becomes high enough to turn on Q2, which turns off Q1 and reduce the current that can pass from VIN to VOUT. The value of R3 sets the current limit. Be aware that this example is very simple and only applies for sourcing current into a resistive load. For cases involving both sourcing and sinking current as well as nonresistive loads, more complex circuits are required to achieve bidirectional current limiting.