7.3.1.3 Differential Driver for the Internal Compensation Coil

The differential compensation coil driver provides the current for the internal compensation coil at the DRV1 and DRV2 pins. The driver is capable of sourcing up to ±250 mA with a 5-V supply, or up to ±150 mA with a 3.3-V supply. The current capability is not internally limited. The actual value of the compensation coil current depends on the magnetic field strength, and is limited by the sum of the resistance of the internal compensation coil and the external shunt resistor value. The internal compensation coil resistance depends on temperature (see Figure 17), and this dependancy must be taken into account when designing the system. Select the value of the shunt resistor to avoid OR pin trip levels in normal operation.

The common-mode voltage of the compensation coil driver outputs is set by the RSEL pins; see the Voltage Reference section. Thus, the common-mode voltage of the shunt-sense amplifier is matched if the internal reference is used.

Consider the polarity of the compensation coil connection to the output of the compensation coil driver. If the polarity is incorrect, then the driver output drives to the power-supply rails, even at low primary-current levels. In this case, interchange the connection of the DRV1 and DRV2 pins to the compensation coil.