SBOS344D September 2005 – November 2023 XTR117
PRODUCTION DATA
Refer to the PDF data sheet for device specific package drawings
The external transistor, Q1, conducts the majority of the full-scale output current. Power dissipation in this transistor can approach 0.8 W with high loop voltage (40 V) and 20-mA output current. The XTR117 is designed to use an external transistor to avoid on-chip, thermal-induced errors. Heat produced by Q1 still causes ambient temperature changes that can influence the XTR117 performance. To minimize these effects, locate Q1 away from sensitive analog circuitry, including the XTR117. Mount Q1 so that heat is conducted to the outside of the transducer housing.
The XTR117 is designed to use virtually any NPN transistor with sufficient voltage, current, and power rating. Case style and thermal mounting considerations often influence the choice for any given application. Several possible choices are listed in Figure 6-1. A MOSFET transistor does not improve the accuracy of the XTR117 and is not recommended. Although the XTR117 can be used without an additional external transistor, this configuration is not always practical at higher loop voltages and currents because of self-heating concerns.