Application Note 1480 ISL28133ISENSEV1Z Evaluation Board User’s Guide The ISL28133ISENSEV1Z evaluation board contains a complete precision current sense amplifier using the ISL28133 chopper amplifier in a high side, low side of floating supply current sense application. The advantages of the ISL28133 in this application include very low offset voltage (2µV typical) and offset drift (0.07µV/°C), rail-to-rail input and output and low power consumption (18µA typical). These features provide a very high degree of precision for use in 5V, low power applications. High speed current sensing may involve filtering repetitive current transients with high peak to average values. In these cases, limiting these transient even further will improve amplifier response and overload settling time. The optional Schottky diode transient clamp D2 reduces transients let through by the common mode clamp from 6V down to ~ ±0.3V, which improves overload recovery time. Capacitors C7 and C9 provide common mode noise filtering and capacitor C8 can be used to filter the current sense signal. Current Sense Gain Equations Reference Documents • ISL28133 Data Sheet (FN6560) Evaluation Board Key Features The ISL28133ISENSEV1Z operates from a single 1.65VDC to +5.5VDC supply. The current sense function is configured as a single stage, balanced input, trans-impedance amplifier. A 0.1Ω 0.1% current sense resistor is used convert the incoming current to a voltage which is applied to a precision differential amplifier with a gain of 100. The overall current to voltage transfer ratio is 10V/A, and a bidirectional current range of ±0.25A is achieved when operating from a +5V supply, using a 2.5V reference voltage (VREF). At +25°C, the ISL28133 achieves a total full scale offset error of 0.038% (when a precision external reference is used) and approximately 0.15% using the internal 0.1% resistors. The total current draw from the amplifier power is less than 35µA and the total leakage current from the current sense input is less than 3µA. The current sense amplifier in Figure 1 forms a trans-impedance amplifier whose gain is in units of V/A and is determined by the ratios of resistor pairs. R11:R8 and R14: R9. Resistor R11 is set equal to R14 and R8 is set equal to R9. This matching cancels the input offset voltage errors caused by the op amp input bias currents, leaving behind only the offset voltage errors caused by the ISL28133 input offset current (IOS). The ISENSE to VOUT DC transfer function is given by Equation 1: R14 V OUT = I SENSE × R SENSE × ----------- + V REF R9 (EQ. 1) where: R11 = R14 and R6 + R8 = R7 + R9 On the evaluation board, the R12, R9 resistor ratio is 100:1 (499kΩ: 4.9kΩ), and RSENSE is 0.1Ω for a trans-impedance gain given by Equation 2: V SENSE V ------------------- = 10 --I SENSE A (EQ. 2) Power Supply and Protection Features Input Range and Offset Error Analysis External power connections are made through the +V, and ground jacks. The single supply input is overvoltage protected using a series 100Ω resistor and a 5.6V zener diode (D1). Reverse polarity protection uses the 100Ω resistor and two protection diode pairs (D3, D4). These also provide input common mode voltage protection to the op amp. The ISL28133 output swings from rail-to-rail, and the evaluation board has a bi-directional output range of VREF ±2.5V when operated from a +5V supply and VREF is set to VS/2. The evaluation board contains a jumper-selectable, internal VS/2 reference or an external reference (VREF pin). With VREF set to +2.5, the full scale output range is 0 ±0.25A. Input Protection Clamp Options The very low offset voltage (±8µV +25°C max) and offset current (300pA +25°C max) of the ISL28133 enable the use of very high values resistors for low current consumption while maintaining excellent precision in battery operated circuits. The total offset voltage contribution of the ISL28133 is the sum of the input offset voltage (VOS) and the offset voltage produced by the input offset current (IOS) through the gain resistors and using the evaluation board resistor values and the data sheet maximum +25°C VOS gives the total input offset voltage as shown in Equations 3, 4 and 5: Included on the evaluation board are optional input protection circuits that illustrate the best methods to limit input common mode and differential transient voltage spikes in exposed or electrically hazardous applications. The ISL28133 can handle input common mode and differential transients to a diode drop beyond the rails, or to a range of -0.5V to +5.5V when operating from a single 5V supply. Clamp diodes D3A, B, D4A, B and input resistors R6, R7, R8, R9 form a current limiting, 6V common mode and differential voltage clamp. This clamp provides sufficient protection for the ISL28133 for common mode fault voltages far beyond the power supply rails. These diodes also provide the same 6V protection against large differential transients. July 18, 2011 AN1480.2 1 R14 × R9 V OS ( Total ) = ⎛ IOS × ------------------------- ⎞ + VOS ⎝ R14 + R9 ⎠ (EQ. 3) CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas Inc. 2011. All Rights Reserved Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries. All other trademarks mentioned are the property of their respective owners. Application Note 1480 R14 × R9 V OS ( Total ) = ⎛ 3e – 10 × ------------------------- ⎞ + 8μV ⎝ R14 + R9 ⎠ (EQ. 4) V OS ( Total ) = ( 3e – 10 × 4950 ) + 8μV = 9.5μV (EQ. 5) Multiplying the ISL28133 input offset voltage by the amplifier gain allows the input offset error to be expressed as a percent of full scale output voltage. ⎛ V × R14 -----------⎞ ⎝ OS R9 ⎠ % F.S. Error = ------------------------------------- = ± 0.038% ± 2.5V (EQ. 6) Using the Evaluation Board The evaluation board has separate connections for the amplifier power supply, an output zero reference (VREF),and the current sense terminals. The correct inter-connection between the ISENSE terminals and the VREF terminals are needed to implement the different types of current sense configurations. The voltage applied to the VREF pin defines the amplifier output zero current level, and must be between 0V and +5V. For bi-directional current sensing, a reference midway between the ground and the supply voltage will maximize the output span. For example, a VREF = +2.5V would be the best choice for +5V power supply. The jumper selectable internal voltage divider is provided for this internal reference. The +2.5V will establish an output current scale setting 0A = +2.5V, but the accuracy is determined by the voltage divider accuracy (0.1% resistors on the evaluation board). Connecting the jumper to the external reference position enables an external reference source to be used. Figure 2 shows the connections to implement a high side, bi-directional current sense with the ability to monitor the charging current. Figure 3 shows the connection for uni-directional ground referenced current sensing. The ISL28133 maintains precision performance from rail-to-rail making precision ground-side sensing possible. The I-SENSE + and I-SENSE - connections to the measured circuit determine the polarity of the amplifier output voltage. Establishing a current flow from the I-SENSE + to I-SENSE causes the output voltage to increase in proportion to the input current. Reversing the I-SENSE current flow reverses the output polarity. R15 100 R12A, B 1M I-SENSE+ D3A R6 10Ω R3 R4 R5 0.1 DNP DNP R7 10Ω 3 C8 10nF 4 R9 4.99k C7 1nF C4 1nF VS/2 JUMPER EXT REFERENCE REFERENCE R8 4.99k D2 R1 R2 DNP DNP D4A C9 1nF D3B D4B VS 1.65V TO +5.5V R10A, B 1M + V+ 5 ISL28133 V- - VREF R11 499k R13 0 1 ISENSE OUT 2 R14 499k C20 OPEN D1 5.6V I-SENSE- C2 4.7µF C10 OPEN GND FIGURE 1. ISL28133 DIFFERENTIAL CURRENT SENSE AMPLIFIER 2 AN1480.2 July 18, 2011 Application Note 1480 CONNECT TO BATTERY POWER CONNECT TO EXTERNAL POWER I-SENSE+ VS 1.65V TO +5.5V VREF JUMPER GND CURRENT FLOW RSENSE VREF = +2.5V VREF VOUT = +2.5V ±2.5V FOR ISENSE = 0A ±0.25A EXT REFERENCE + VS/2 REFERENCE ISENSE OUT I-SENSE- - CHARGING CURRENT LOAD FIGURE 2. CURRENT SENSE FOR HIGH-SIDE BI-DIRECTIONAL RE-CHARGEABLE BATTERY SUPPLY CONNECT TO BATTERY POWER EXTERNAL POWER 1.65V TO +5.5V I-SENSE+ VS 1.65V TO +5.5V GND JUMPER RSENSE VREF = 0V VREF VOUT = 0V TO 5V FOR ISENSE = 0A 0.5A ISENSE OUT EXT REFERENCE CURRENT FLOW VS/2 REFERENCE LOAD 0V TO +5.5V I-SENSE- FIGURE 3. CURRENT SENSE FOR LOW SIDE UNI-DIRECTIONAL MEASUREMENT 3 AN1480.2 July 18, 2011 Application Note 1480 ISL28133ISENSEV1Z Components Parts List DEVICE # DESCRIPTION COMMENTS C2 CAP-SMD, 0805, 4.7µF, 50V, 10%, X7R, ROHS Power supply decoupling C4, C7, C9 CAP, SMD, 0603, 1000F, 25V, 10%, X7R, ROHS Power supply decoupling C8 CAP, SMD, 0603, 0.1µF, 25V, 10%, X7R, ROHS Power supply decoupling C10, C20 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS User-selectable capacitors - not populated D1 Zener Diode ROHS Reverse power protection D2- D4 DIODE-SCHOTTKY BARRIER, SMD, SOT-23, 3P, 40V, ROHS Reverse power protection R13 RESISTOR, SMD, 0603, 0Ω, 1/16W, 0.1%, TF, ROHS 0Ω user selectable resistors R1- R5 RES, SMD, 0805, 0.1Ω, 1/10W, 0.1%, TF, ROHS Current sense resistors R6, R7 RES, SMD, 0805, 10Ω, 1/10W, 0.1%, TF, ROHS Protection resistors R15 RES, SMD, 0805, 100Ω, 1/10W, 0.1%, TF, ROHS Protection resistors R8, R9 RES, SMD, 0805, 4.99kΩ, 1/10W, 0.1%, TF, ROHS 0Ω user selectable resistors R11, R14, R10A, R10B, R12A, R12B RES, SMD, 0805, 499kΩ, 1/10W, 0.1%, TF, ROHS Gain and other user selectable resistors U1 (ISL28133FHZ-T7) IC-5 MHz, RRIO OP AMP, SOT23_5, ROHS R1, R2, R4, R5 RES, SMD, 0805, DNP 4 Optional sense resistors AN1480.2 July 18, 2011 Application Note 1480 ISL28133ISENSEV1Z Schematic Diagram R1 DNP R2 DNP R3 I-SENSE + J4 I-SENSE 0.10 R4 DNP R5 R6 10 J5 R7 10 C7 DNP C8 1000pF 0.01µF C9 1000pF D2 R10B 499k R10A 499k R11 499k R12B 499k D4 D3 R12A 499k R13 J6 0 C20 OPEN R14 OPEN J1 R9 4.99k C10 V-REF R8 4.99k I-SENSE OUT 499k 1 U2 5 2 ISL28133 3 4 SOT23_5 C2 4.7µF C4 1000pF D1 R15 100 J2 GND 5 J3 VS1+ AN1480.2 July 18, 2011 Application Note 1480 FIGURE 4. ISL28133ISENSEV1Z TOP VIEW Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding. For information regarding Intersil Corporation and its products, see www.intersil.com 6 AN1480.2 July 18, 2011