ZXCT1020EV1 Evaluation Board User Guide Doc: Issue: Date: Page: ZXCT1020EV1-UG 1.2 24 April 2008 1 of 8 ZXCT1020EV1 Figure 1 Evaluation board components' layout DESCRIPTION The ZXCT1020EV1 evaluation board is intended for the evaluation of the ZXCT1020 device. The ZXCT1020 is a precision high-side current sense monitor. Using this type of device eliminates the need to disrupt the ground plane when sensing a load current. It also has an externally programmable transconductance resistor, thus making it a versatile device to use in many applications. The device produces a current output that is proportional to the current sampled by a small in-line sensing resistor, RS. The voltage output is scaled by the choice of RS (R1, R2 on the evaluation board), RGT (R4 on the evaluation board) and the load resistor (R7 on the evaluation board). The evaluation board is delivered with the values shown in Figure 2 below. As can be seen, RS consists of two resistors (R1 and R2) which are configured in parallel such that either one or both resistors could be connected by completing the solder-bridge link next to each one. R2 (0.1R) is connected by default. R3 consists of two pads with a hole in each pad and provides means for connecting an external RS. With the values shown the board produces an output of 1V/A ZDB341R2 ZXCT1020EV1 Evaluation Board User Guide Doc: Issue: Date: Page: ZXCT1020EV1-UG 1.2 24 April 2008 2 of 8 The printed circuit board is common to other devices in the ZXCT family and contains redundant component positions which will not be discussed here as they are not relevant. RS VSUPPLY (R1//R2 = 0.05R//0.1R) ILOAD V2 V1 RGT (R4=1.5k) 5 1 4 S+ SVB ZXCT1020 GND IOUT 2 3 IOUT VOUT RG (R7 = 15k) GND GND Figure 2 Equivalent circuit diagram for evaluation board ZXCT1020EV1 Operating voltage range: 2.5V to 20V ZDB341R2 ZXCT1020EV1 Evaluation Board User Guide Doc: Issue: Date: Page: ZXCT1020EV1-UG 1.2 24 April 2008 3 of 8 ORDERING INFORMATION ORDER NUMBER ZXCT1020EV1 Please note evaluation boards are subject to availability and qualified leads. PAD NAMES AND DEFINITIONS NAME DESCRIPTION/Usage V1 V2 VOUT FLAG Supply Voltage Connection to Load GND 0V / Ground SL1,SL2 Solder Links VCC Device pin S+ (connected to V1 via R4) Output Voltage Not used The target applications are battery chargers, power supply units and other applications where high side current measurement is a requirement. The input voltage (voltage on V1) range for the ZXCT1020EV1 is ranges from 2.5V to 20V. ZDB341R2 Doc: Issue: Date: Page: ZXCT1020EV1 Evaluation Board User Guide ZXCT1020EV1-UG 1.2 24 April 2008 4 of 8 ZXCT1020EV1 Summary R3 R1 0.05R SL1 ILOAD V1 V2 SL2 R2 0.1R R4 1.5k 5 1 S4 S+ VB ZXCT1020 IOUT GND 2 3 VOUT R7 15k GND GND Figure 3 Actual circuit diagram for ZXCT1020EV1 Sense resistor The board has been designed with two selectable values of sense resistor. The value of the sense resistor can be chosen by using the solder links SL1 and SL2. The board is also tracked for a user defined through hole resistor (R3). The 50mΩ resistor (R1) is selected by shorting SL1 and opening SL2. This results in an output of 0.5 V/A. The 100mΩ resistor (R2) is selected by shorting SL2 and opening SL1, resulting in an output of 1V/A. If both links are shorted the effective resistance is 33.33mΩ giving an output of 333.3mV/A. If both links are open, the optional leaded resistor R3 can be exclusively used as the sense resistor. The maximum power dissipation rating of the resistor must be appropriate to the load current level. For further information on choosing a value of sense resistor please refer to the ZXCT1020 datasheet. ZDB341R2 ZXCT1020EV1 Evaluation Board User Guide Doc: Issue: Date: Page: ZXCT1020EV1-UG 1.2 24 April 2008 5 of 8 Configuration table for ZXCT1020EV1 LOAD CURRENT (A) 1.0 1.0 1.0 RSENSE (mΩ Ω) VOUT (V) SOLDER LINK CONFIGURATION 100 50 33.33 1.0 0.5 0.33 Short SL2 Short SL1 Short SL1 & SL2 Configuration for different LOAD currents. The board can be configured for different load currents by changing the SMD resistors or fitting a suitable wire ended resistor and opening both solder links. It is important to ensure an appropriate value of RS is selected to obtain the desired accuracy for a given output current. The value of IOUT is the voltage dropped across the sensing resistor divided by RGT. Choosing a larger value for RS gives a higher output voltage for a given current resulting in better resolution but at the expense of increased voltage drop and higher dissipation in RS. Increasing the value of the gain resistor, R7, also increases the sensitivity but at the expense of a higher output impedance. The criterion for minimum input voltage still applies. The maximum practical value of the gain resistor is limited by the output conductance of the ZXCT1020 and the output voltage that can be tolerated - in practice the gain resistance should not be greater than about 40k. The ZXCT1020 is optimized for values of VSENSE around 100mV. Accuracy The ZXCT1020 has a typical 2% accuracy for a VSENSE of 100mV. The accuracy of the output voltage will be influenced by the tolerance of the external sense used. The ZXCT1020EV1 utilizes 1% sense resistors. ZDB341R2 ZXCT1020EV1 Evaluation Board User Guide Doc: Issue: Date: Page: ZXCT1020EV1-UG 1.2 24 April 2008 6 of 8 COMPONENTS LIST Ref Value Package Part Number Manufacturer Notes R1 R2 R4 R5,R6 R7 I/O’s ZXCT 50mΩ 100mΩ 1.5k 0R 15k 2512 2512 0805 Link/0805 0805 Test loops SOT23-5 LR2512-R050FW LR2512-R100FW Welwyn Welwyn SMD Sense Resistor 1% SMD Sense Resistor 1% 100-108 ZXCT1020E5 Hughes ZETEX Rapid 17-1835 SET-UP AND TEST The board is preset to give an output Voltage of 1V for a load current of 1A (SL2 is shorted to connect in the 100mΩ (R2) sense resistor). To change the board to give an output Voltage of 1V for a current of 2.0A, de-solder SL2 and short SL1. This connects the 50mΩ (R1) sense resistor. Required Equipment 1. 2. 3. 1 x 10R 5W resistor (load). 1 x adjustable bench PSU. 2 x DVMs (one for voltage measurement and one for current measurement) 500mA load test 1. Ensure SL2 is shorted. 2. Connect a resistor in series with the ammeter between the V2 and GND terminals (10R 5W resistor is suggested, if using a different value, make sure it’s power rating is P ≥ 2*I2*R). 3. Set ammeter to a suitable range for measuring up to 500mA or 600mA. 4. Set the current limit of PSU1 to 600mA, and set the voltage to 0V. 5. Connect PSU1 to V1. 6. Switch on PSU1 and increase the voltage until the ammeter reads 500mA ± 2mA 7. Measure VOUT with a DVM. The output voltage should read 0.5V ± 25mV. ZDB341R2 Doc: Issue: Date: Page: ZXCT1020EV1 Evaluation Board User Guide ZXCT1020EV1-UG 1.2 24 April 2008 7 of 8 ZXCT1020EV1 VCC FLAG VOUT DVM V1 10R 5W V2 A PSU1 GND GND Figure 4 Test diagram for ZXCT1020EV1 EVALUATION BOARD CURRENT MONITOR EVALUATION BOARD www.zetex.com Vcc FLAG ZXCT R4 C1 R5 V1 R7 R8 Vout R6 R1 SL1 R2 SL2 V2 R3 SL3 GND GND Refer to 'User Guide' for details. Bare board: ZDB341R2 Copyright Zetex PLC 2006 Top Silk ZDB341R2 Top Copper ZXCT1020EV1 Evaluation Board User Guide Doc: Issue: Date: Page: ZXCT1020EV1-UG 1.2 24 April 2008 8 of 8 Definitions Product change Zetex Semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. Customers are solely responsible for obtaining the latest relevant information before placing orders. Applications disclaimer The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is assumed by Zetex with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. 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