This high-side constant-current source delivers load current of 2.5 V divided by the output resistance, provided that you choose the output resistance to ensure that the voltage between the regulator's input and ground terminals is at least 2.5 V
Figure 1. This high-side constant-current source delivers load current of 2.5 V divided by the output resistance, provided that you choose the output resistance to ensure that the voltage between the regulator's input and ground terminals is at least 2.5 V