An example of in-package Hall sensors is the TMCS1100 family, shown in Figure 3-6. Within the device, the high-voltage side load current passes through the low-ohmic leadframe path. No external components, isolated supplies, or control signals are required on the high-voltage side. At the low-voltage side, the magnetic field generated by the input current is sensed by a Hall sensor and amplified by a precision signal chain.

The transfer function can be written as:

where

• S is the sensitivity
• I_in is the target current being measured
• V_{ref_x} is the reference voltage at the VREF pin

The reference voltage determines the zero-current output voltage. This zero-current output level along with sensitivity determine the measurable input current range of the device, and allows for unidirectional or bidirectional sensing. By shifting the zero current output voltage of the device, the dynamic range of measurable input current can be modified.

The input voltage on Vref pin can be provided by any external voltage source, such as a precision reference IC. The VREF pin is sampled by the internal circuitry at approximately 1 MHz, then buffered and provided to the signal chain of the device. An apparent DC load of approximately 1 µA is observed by the external reference. To prevent errors due to sampling settling, keep the source impedance below 5 kΩ, the level specified in the electrical characteristics table.