LMP8645MKEVAL/NOPB

User's Guide SNOA546C – November 2009 – Revised April 2013 AN-1975 LMP8640/LMP8645 Evaluation Board 1 Introduction This evaluation board shows a bidirectional high-side current sense made using LMP8640 (LMP8645) and optional differential amplifier in order to have a single output. 2 Connectors 2.1 Power Supply There are two banana plugs labeled GND and VCC to power the evaluation board. Moreover, a banana plug labeled VCC_Amp is used to power an optional operational amplifier that makes the difference between the outputs of the two LMP8640 (LMP8645). 2.2 Signal Connectors There are five connectors for signals. Table 1. Input signals IN It connects the non inverting input of U1 and inverting input of U2. LOAD It connects the non inverting input of U2 and inverting input of U1. The device U1 is able to sense the current when it flows in the shunt resistor from the LOAD pin to the IN pin. The device U2 is able to sense the current when it flows in the shunt resistor from IN pin to LOAD pin. Table 2. Output signals OUT+ Output of device U2, the voltage at this pin is related to the current that flows from the IN pin to the LOAD pin. OUT- Output of device U1, the voltage at this pin is related to the current that flows from the LOAD pin to the IN pin. OUT Optional Output of the difference amplifier that makes the difference between OUT+ and OUT- 3 Hardware Setup 3.1 Power Supply Setup • • High side current sense LMP8640 (LMP8645) – Connect a supply voltage in the range between 2.7 V and 12 V to the VCC and GND turrets. Optional difference amplifier – Connect a supply according to the specs of the amplifier to the VCC_Amp and GND turrets. All trademarks are the property of their respective owners. SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback AN-1975 LMP8640/LMP8645 Evaluation Board Copyright © 2009–2013, Texas Instruments Incorporated 1 Hardware Setup 3.2 www.ti.com Source and Load Setup First case: Current flows from IN to LOAD plugs. A voltage supply can be connected between the IN and the GND banana plugs, while a load is connected between the LOAD and the GND banana plugs. The voltage applied at the IN pin should not exceed the maximum common mode voltage allowed by the LMP8640/HV (LMP8645/HV). The maximum allowed common mode voltages are listed in Table 3. Second case: Current flows from LOAD to IN plugs. In this case, the voltage supply is connected between the LOAD and the GND banana plugs, while the load is connected between the IN and GND banana plugs. The voltage applied at LOAD pin should not exceed the maximum common mode voltage allowed by the LMP8640/HV (LMP8645/HV). The maximum allowed common mode voltages are listed in Table 3. Table 3. Max Common Mode Voltage DEVICE MAX VCM LMP8640 42V LMP8645 42V LMP8640HV 76V LMP8645HV 76V According to the shunt resistor (Rsns), to the gain of LMP8640 (LMP8645) and to the supply voltage different ranges of currents can be sensed with this evaluation board. 3.3 Components On the evaluation board, there are already the circuit and the footprint of a standard dual op amp (U3) to implement a differential op amp (U3.B) with reference (U3.A) in order to provide a single ended output of the bidirectional current. Table 4. Optional Differential Circuit U3 Standard Dual Op Amp 8 pin. U3.1 OUT A U3.2 -IN A U3.3 +IN A U3.4 VU3.5 +IN B U3.6 -IN B U3.7 OUT B U3.8 V+ R1, R2, R3, R4 resistors that implement the differential circuit according to Equation 1: OUT = - R4 R4 · * OUT + §1 + R1 © R1 ¹ R5, R6, C5 Vref = 2 § R2 * Vref + R3 * OUT+· R2 + R3 © R2 + R3 ¹ (1) components for voltage reference and its filter. The voltage reference is calculating according to Equation 2: R5 x VCC_ Amp R5 + R6 (2) AN-1975 LMP8640/LMP8645 Evaluation Board SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Using the Evaluation Board www.ti.com 4 Using the Evaluation Board 4.1 Input and Output Signals The evaluation board allows you to measure a bidirectional current, so the IN and LOAD banana connectors can act either as the Source or LOAD pin. If the current flows from the IN pin to the LOAD pin, a simple way to test the performance of the LMP8640 (LMP8645) is shown in Figure 1. OUT V+ V- RG +IN -IN VCC - V + DMM1 Rg1 DMM2 IN A + Rsns -IN +IN - SOURCE Rg2 + RG V- V+ OUT LOAD ohmic LOAD VCC - Figure 1. LMP8640 (LMP8645) Measurement Setup The DMM1 is configured as a voltmeter, which measures the output of the LMP8640 (LMP8645), while the DMM2 is configured as an Ammeter, which measures the current that flows in the LOAD. The source is a voltage supply that makes sure to set a voltage in the range of -2 V to +46 V for LMP8640 (LMP8645) or 2 V to +76 V for LMP8640HV (LMP8645HV). 4.2 Gain Selection of LMP8645 The evaluation board is provided with a shunt resistor Rsns (10 mΩ, @ 1%, 1W), while two gain resistors Rg1 and Rg2 (10 kΩ, @1%) ensure a gain of 2 V/V for each current sense. The Gain is evaluated according to formula in Equation 3: Gain = Rg V/ V 5k: (3) The gain resistor must be chosen such that the max output voltage does not exceed the LMP8645 max output voltage rating for a given common mode voltage (further details in the Datasheet). 4.3 Single Output In the applications where a single measurement of a bidirectional current sense is needed is possible to populate the evaluation board with two amplifiers and some resistors (see Section 3.3). For instance, in the following configuration: R1 = R2 = R3 = R4 = 10 kΩ, R5 = R6 =10 kΩ OUT = VREF +(OUT+ -OUT-) VREF = 0.5*Vcc_Amp. SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback AN-1975 LMP8640/LMP8645 Evaluation Board Copyright © 2009–2013, Texas Instruments Incorporated 3 Bill Of Materials (BOM) www.ti.com The VREF level represents the zero level; the voltages greater than VREF are related to a current that flows from IN pin to the LOAD pin while the voltages less than VREF are related to a current that flows from the LOAD pin to the IN pin. To ensure good results in the measurements, the resistors R4 and R3 and the resistors R1 and R2 need to be well matched. 5 Bill Of Materials (BOM) Table 5. Bill Of Materials Designator Component C1, C3 Capacitor C2, C6* C4 , (2) Value Tolerance Package Type 0.01 μF 5% 0603 Capacitor 1 μF 10% 3216–18 Capacitor 0.1 μF 10% 0805 C5*, C7 Capacitor 0.1 μF 10% 0603 C_Filt1*, C_Filt2* Capacitor CG1*, CG2* Capacitor R1*, R2*, R3*, R4*, R5*, R6* Resistor min 10 kΩ 1% 0603 RG1**, RG2** Resistor 10.0 kΩ 1% 0603 Rsns** Resistor 0.01 Ω 1%, 1W 2010 Rsns Resistor 0.01 Ω 0.1%, 1W 2512 R_Filt_1, R_Filt2 Resistor 5% 0805 U3* Dual Op Amp (1) (2) 4 (1) 0805 0805 SOT-8 Components Marked With (*) are not soldered on the board. Components marked with (**) are soldered only on LMP8645 board. AN-1975 LMP8640/LMP8645 Evaluation Board SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated www.ti.com Appendix A Schematic This schematic shows the evaluation board with a LMP8645 mounted on the PCB. The only difference for the version of the PCB stuffed with LMP8640 will be the gain resistors RG1, RG2. The LMP8640 is a current sense with fixed gain, so it doesn't require any external gain resistor. Figure 2. Schematic Diagram SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Schematic 5 www.ti.com Appendix B Layout Figure 3. Top Layer 6 Layout SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Appendix B www.ti.com Figure 4. Bottom Layer PCB Layout SNOA546C – November 2009 – Revised April 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Layout 7 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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