USERS MANUAL ISL28133ISENSEV1Z AN1480 Rev.2.00 Evaluation Board User Guide Jul 18, 2011 The ISL28133ISENSEV1Z evaluation board contains a cases, limiting these transient even further will improve complete precision current sense amplifier using the amplifier response and overload settling time. The optional ISL28133 chopper amplifier in a high side, low side of floating Schottky diode transient clamp D2 reduces transients let supply current sense application. through by the common mode clamp from 6V down to ~ 0.3V, which improves overload recovery time. Capacitors The advantages of the ISL28133 in this application include very C7 and C9 provide common mode noise filtering and capacitor low offset voltage (2V typical) and offset drift (0.07V/C), C8 can be used to filter the current sense signal. rail-to-rail input and output, and low power consumption (18A typical). These features provide a very high degree of precision Current Sense Gain Equations for use in 5V, low power applications. The current sense amplifier in Figure 1 forms a trans-impedance amplifier whose gain is in units of V/A and is Reference Documents determined by the ratios of resistor pairs. R11:R8 and R14: Data Sheet (ISL28133) R9. Resistor R11 is set equal to R14 and R8 is set equal to R9. This matching cancels the input offset voltage errors caused Evaluation Board Key Features by the op amp input bias currents, leaving behind only the offset voltage errors caused by the ISL28133 input offset The ISL28133ISENSEV1Z operates from a single 1.65VDC to current (I ). OS +5.5VDC supply. The current sense function is configured as a single stage, balanced input, trans-impedance amplifier. A The I to V DC transfer function is given by Equation 1: SENSE OUT 0.1 0.1% current sense resistor is used convert the incoming R14 ----------- V = I R + V (EQ. 1) OUT SENSE SENSE REF R9 current to a voltage which is applied to a precision differential amplifier with a gain of 100. The overall current to voltage where: transfer ratio is 10V/A, and a bidirectional current range of R11 = R14 and R6 + R8 = R7 + R9 0.25A is achieved when operating from a +5V supply, using a 2.5V reference voltage (V ). At +25C, the ISL28133 On the evaluation board, the R12, R9 resistor ratio is 100:1 REF achieves a total full scale offset error of 0.038% (when a (499k : 4.9k ), and R is 0.1 for a trans-impedance SENSE precision external reference is used) and approximately 0.15% gain given by Equation 2: V using the internal 0.1% resistors. SENSE V -------------------- = 10 --- (EQ. 2) I A The total current draw from the amplifier power is less than SENSE 35A and the total leakage current from the current sense input is less than 3A. Input Range and Offset Error Analysis The ISL28133 output swings from rail-to-rail, and the evaluation Power Supply and Protection Features board has a bi-directional output range of V 2.5V when REF External power connections are made through the +V, and operated from a +5V supply and V is set to V /2. The REF S ground jacks. The single supply input is overvoltage protected evaluation board contains a jumper-selectable, internal V /2 S using a series 100resistor and a 5.6V Zener diode (D1). reference or an external reference (V pin). With V set to REF REF Reverse polarity protection uses the 100 resistor and two +2.5, the full scale output range is 0 0.25A. protection diode pairs (D3, D4). These also provide input The very low offset voltage (8V +25C max) and offset common mode voltage protection to the op amp. current (300pA +25C max) of the ISL28133 enable the use of very high values resistors for low current consumption while Input Protection Clamp Options maintaining excellent precision in battery operated circuits. Included on the evaluation board are optional input protection The total offset voltage contribution of the ISL28133 is the circuits that illustrate the best methods to limit input common sum of the input offset voltage (V ) and the offset voltage OS mode and differential transient voltage spikes in exposed or produced by the input offset current (IOS) through the gain electrically hazardous applications. The ISL28133 can handle resistors and using the evaluation board resistor values and input common mode and differential transients to a diode drop the data sheet maximum +25C V gives the total input OS beyond the rails, or to a range of -0.5V to +5.5V when operating offset voltage as shown in Equations 3, 4 and 5: from a single 5V supply. R14 R9 ------------------------- V = IOS + VOS (EQ. 3) OSTotal R14 + R9 Clamp diodes D3A, B, D4A, B and input resistors R6, R7, R8, R9 form a current limiting, 6V common mode and differential R14 R9 voltage clamp. This clamp provides sufficient protection for the V = 3e 10 ------------------------- + 8 V (EQ. 4) OSTotal R14 + R9 ISL28133 for common mode fault voltages far beyond the power supply rails. These diodes also provide the same 6V V =3e 10 4950 + 8 V9= .5 V (EQ. 5) OSTotal protection against large differential transients. High speed current sensing may involve filtering repetitive current transients with high peak to average values. In these AN1480 Rev.2.00 Page 1 of 7 Jul 18, 2011ISL28133ISENSEV1Z Multiplying the ISL28133 input offset voltage by the amplifier pin defines the amplifier output The voltage applied to the V REF gain allows the input offset error to be expressed as a percent of zero current level, and must be between 0V and +5V. For full scale output voltage. bi-directional current sensing, a reference midway between the ground and the supply voltage will maximize the output span. For R14 ----------- V example, a V = +2.5V would be the best choice for +5V power OS REF R9 (EQ. 6) --------------------------------- % F.S. Error = = 0.038% supply. The jumper selectable internal voltage divider is provided 2.5V for this internal reference. The +2.5V will establish an output current scale setting 0A = +2.5V, but the accuracy is determined Using the Evaluation Board by the voltage divider accuracy (0.1% resistors on the evaluation board). Connecting the jumper to the external reference position The evaluation board has separate connections for the amplifier enables an external reference source to be used. power supply, an output zero reference (V ),and the current REF sense terminals. The correct inter-connection between the I- Figure 2 shows the connections to implement a high side, SENSE terminals and the V terminals are needed to bi-directional current sense with the ability to monitor the REF implement the different types of current sense configurations. charging current. Figure 3 shows the connection for uni-directional ground referenced current sensing. The ISL28133 The I-SENSE + and I-SENSE - connections to the measured circuit maintains precision performance from rail-to-rail making determine the polarity of the amplifier output voltage. precision ground-side sensing possible. 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. V S R15 1.65V TO +5.5V 100 R12A, B C4 1M 1nF V /2 JUMPER EXT I-SENSE+ S D3A D4A REFERENCE REFERENCE V REF R11 R6 R8 499k 10 4.99k R13 3 5 + 0 V+ 1 D2 C8 ISL28133 I SENSE R1 R2 R3 R4 R5 4 V- 10nF OUT - R14 DNP DNP 0.1 DNP DNP R7 R9 2 10 499k 4.99k D1 C2 C10 C7 C9 R10A, B 5.6V 4.7F OPEN 1nF 1nF C20 1M D3B D4B OPEN I-SENSE- GND FIGURE 1. ISL28133 DIFFERENTIAL CURRENT SENSE AMPLIFIER AN1480 Rev.2.00 Page 2 of 7 Jul 18, 2011