CTD203 Crocus

CTD203 Users Manual Current Sensing Demo Board Relevant Products: CT219 Dieren al Current Sensor Introduc on This document provides general informa on about the design and use of the Crocus evalua on board for dieren al current sensing with either a current carrying trace and adjustable bus bar. General Descrip on The CTD203 Dieren al Current Sensor Demonstra on Board is designed to demonstrate the current sensing capa- bili es of the Crocus magne c sensor for dierent ranges of currents. This demo board includes one CT219 current sensor that is used in dieren al mode. This sensor is physically mounted on top of the PCB over the current carrying trace and under a ver cally adjustable bus bar. The bus bar height can be adjusted above the sensor, and there are two areas iden ed on the board which are marked for adding concentrators. With either AC or DC current passing through the bus bar, the sensor senses the magne c ux generated by the current and provides an output voltage that is directly propor onal to the current. The CT219 sensor by nature is connected in a half-bridge congura on as part of a closed-loop circuit as shown in Figure 1. The output voltage of the half-bridge is used in the circuit to provide feedback currents to the inputs of the sensor se ng the biasing point. The PCB is designed with several test points and signal output points terminated by SMA connectors on the demo board. This allows the user to probe the circuit at every stage of the signal chain. 2016 Crocus Technology Page 1 Doc : CTD203 - Users Manual Note Rev 0.1 CTD203 Users Manual Current Sensing Demo Board Closed-Loop Circuit The closed-loop circuit shown in Figure 1 is designed to provide a feedback path for the bias current for CT219 sensor so that the device is kept at the same bias point. This is accomplished by rst sensing the output voltage of the half- bridge circuit and then zeroing the sensor output by changing the input currents of the sensor. The feedback in the eld line current is used to essen ally cancel the eects of the external magne c eld and keep the sensor at the same bias point. By way of circuit analysis, the CT219 sensor is comprised of a voltage divider (Rs1 & Rs2) that is biased by the sensor supply (+5 VDC). In an ini al state of no current on the trace (or the bus bar) and no external magne c eld, the sensor supply voltage is split by the dieren al sensor half-bridge circuit (+5V / 2 = 2,500 mV DC). This value changes as exter- nal current (external magne c ux) ows through the trace. Therefore, to zero the output of each sensor exposed to the external magne c eld, the feedback currents will need to cancel, one to decrease and the other to increase. For this purpose, output of the half-bridge is rst buered via U1A Op-Amp and then compared to a 2.5 VDC (generated with adjus ng the POT) and amplied via U1B. Since the quiescent output of the half-bridge is approxi- mately +2.5VDC, oset biasing is necessary prior to amplica on. The poten ometer (R3) is used to zero the sensor oset voltage before amplica on. The output of the amplier is then fed back into the Crocus sensor in order to keep the sensors in their linear region. The output signal of the comparing circuit (U1B) is the signal out of the closed-loop circuit. A Sallen-Key low-pass lter monitors the output of the circuit. Figure 1: Closed-loop Circuit Schema c 2016 Crocus Technology Page 2 Doc : CTD203 - Users Manual Note Rev 0.1