A controller, for a voltage regulator module including a power unit and providing, at an output, an output current, I out, at an output voltage, V out, from an input current at an input voltage, the voltage regulator module being configured for use in a multi-module voltage regulator having at least one neighbouring voltage regulator module having a respective output connected in parallel with the output, the controller comprising: a reference voltage source for providing a reference voltage (V ref); a current balancing unit, configured to receive a respective output current from each of the at least one neighbouring voltage regulator module and to determine an adjusted reference voltage, V ref ', from the reference voltage and for balancing the output current, I out, with the at least one respective output current; and a control unit configured to use the adjusted reference voltage to control the voltage regulator module, to provide the output current, I out, at the output voltage from the input current at the input voltage, based on adaptive voltage positioning, AVP, regulation; wherein the current balancing module is configured to determine a difference, the difference being a difference between the output current and the sum of half the output currents from each of two neighbouring voltage regulator modules, and to adjust the reference voltage in proportion to the difference to provide the adjusted reference voltage; characterised in that the current balancing module is further configured to detect a failure of communication from a one of the two neighbouring voltage regulator modules, and in response to the failure of communication determine the difference to be a difference between the output current, I out, and the output current from the other of the two neighbouring voltage regulator modules. for a voltage regulator module including a power unit and providing, at an output, an output current, I out, at an output voltage, V out, from an input current at an input voltage, the voltage regulator module being configured for use in a multi-module voltage regulator having at least one neighbouring voltage regulator module having a respective output connected in parallel with the output, the controller comprising: a reference voltage source for providing a reference voltage (V ref); a current balancing unit, configured to receive a respective output current from each of the at least one neighbouring voltage regulator module and to determine an adjusted reference voltage, V ref ', from the reference voltage and for balancing the output current, I out, with the at least one respective output current; and a control unit configured to use the adjusted reference voltage to control the voltage regulator module, to provide the output current, I out, at the output voltage from the input current at the input voltage, based on adaptive voltage positioning, AVP, regulation; wherein the current balancing module is configured to determine a difference, the difference being a difference between the output current and the sum of half the output currents from each of two neighbouring voltage regulator modules, and to adjust the reference voltage in proportion to the difference to provide the adjusted reference voltage; a reference voltage source for providing a reference voltage (V ref); a current balancing unit, configured to receive a respective output current from each of the at least one neighbouring voltage regulator module and to determine an adjusted reference voltage, V ref ', from the reference voltage and for balancing the output current, I out, with the at least one respective output current; and a control unit configured to use the adjusted reference voltage to control the voltage regulator module, to provide the output current, I out, at the output voltage from the input current at the input voltage, based on adaptive voltage positioning, AVP, regulation; wherein the current balancing module is configured to determine a difference, the difference being a difference between the output current and the sum of half the output currents from each of two neighbouring voltage regulator modules, and to adjust the reference voltage in proportion to the difference to provide the adjusted reference voltage; characterised in that the current balancing module is further configured to detect a failure of communication from a one of the two neighbouring voltage regulator modules, and in response to the failure of communication determine the difference to be a difference between the output current, I out, and the output current from the other of the two neighbouring voltage regulator modules.