J14 J13 J12 J11 2 3 1 J8 J6 USERS MANUAL ISL28208SOICEVAL2Z AN1658 Rev 0.00 Evaluation Board Jul 26, 2011 Introduction Power Supplies (Figure 1) The ISL28208SOICEVAL2Z evaluation board is designed to External power connections are made through the V+, V-, VREF, evaluate the performance of the ISL28208 dual Operational and GND connections on the evaluation board. The circuit can Amplifier. The ISL28208 is a dual low power precision operate from a single supply or from dual supplies. For single amplifier that features a common mode input voltage range supply operation, the V- and GND pins are tied together to the extending to 0.5V below the V- rail, a rail-to-rail differential negative or ground reference of the power supply. For split input voltage range for use as a comparator, and rail-to-rail supplies, V+ and V- terminals connect to their respective output voltage swing, which makes it ideal for single supply supply terminals. De-coupling capacitors C2 and C4 provide applications where input operation at ground is important. low-frequency power-supply filtering, while additional With a wide operating range from 3V to 40V, in combination capacitors, C3 and C5, which are connected close to the part, with its precision, low power, and small footprint, ISL28208 filter out high frequency noise. Anti-reverse diode D1 (optional) provides the user with outstanding value and flexibility relative protects the circuit in the momentary case of accidentally to similar competitive parts. reversing the power supplies to the evaluation board. The VREF pin can be connected to ground to establish a ground referenced input for split supply operation, or can be externally Reference Documents set to any reference level for single supply operation. ISL28208 Data Sheet, FN6935 VREF V- V+ Evaluation Board Key Features 3 3 Single Supply Operation: +9V to +40V 2 2 Dual Supply Operation: 4.5V to 20V Singled-Ended or Differential Input Operation C2 C4 External VREF input 1F 1F Banana Jack Connectors for Power Supply and VREF Inputs D1 BNC Connectors for Op Amp Input and Output Terminals CLOSE TO DUT Convenient PCB Pads for Op Amp Input/Output Impedance C3 C5 Loading 0.01F 0.01F FIGURE 1. POWER SUPPLY CIRCUIT R13/R23 100k INA- 2 8 +4.5V R11/R24 INB- 6 TO +20V - V+ 1/7 10k ISL28208 V OUT INA+ 3 V- R14/R21 INB+ 5 + PRECISION 10k SENSOR GAIN = -10V/V 4 R18/R19 -4.5V TO -20V 100k V REF FIGURE 2. PRECISION AMPLIFIER WITH G = -10V/V AN1658 Rev 0.00 Page 1 of 5 Jul 26, 2011 1 2 1 R16 0 1 1 R31 2 1 1 0 1 1ISL28208SOICEVAL2Z NOTE: Operational amplifiers are sensitive to output capacitance Amplifier Configuration (Figure 3) and may oscillate. In the event of oscillation, reduce output The schematic of the op amp input stage with the components capacitance by using shorter cables, or add a resistor in series supplied is shown in Figure 3, with a closed loop gain of 10V/V. with the output. The differential amplifier gain is expressed in Equation 1: C1 (EQ. 1) V = V V R R + V OUT IN+ IN- F IN REF OPEN R4 R11 R13 FROM V OUTA IN-A J1 For single-ended input with an inverting gain G = -10V/V, the IN+ R1 0 10k 100k input is grounded and the signal is supplied to the IN- input. VREF DNP can be connected to a reference voltage between the V+ and V- TO INA - supply rails. For non-inverting operation with G = 11V/V, the IN- input is grounded and the signal is supplied to the IN+ input. The R14 TO INA + IN+A J2 non-inverting gain is strongly dependent on any resistance from R2 10k IN- to GND. For good gain accuracy, a 0 resistor should be DNP VREF installed on the empty R5 pad. R15 R18 DNP 100k User-selectable Options FIGURE 3. INPUT STAGE (Figures 3 and 4) Component pads are included to enable a variety of user-selectable circuits to be added to the amplifier inputs, the VREF input, outputs and the amplifier feedback loops. R26 V J15 OUT A OUT A A voltage divider (Figure 3, R18 and R15) can be added to 0 establish a power supply-tracking common mode reference C6 using the VREF input. The inverting and non-inverting inputs have OPEN additional resistor placements for adding input attenuation, or to establish input DC offsets through the VREF pin. FIGURE 4. OUTPUT STAGE The output (Figure 4) also has additional resistor and capacitor placements for filtering and loading. TABLE 1. ISL28208SOICEVAL2Z COMPONENTS PARTS LIST DEVICE DESCRIPTION COMMENTS C2, C4 CAP, SMD, 1206, 1F, 50V, 10%, X7R, ROHS Power Supply Decoupling C3, C5 CAP, SMD, 0603, 0.01F, 50V, 10%, X7R, ROHS Power Supply Decoupling C1, C6, C7, C8, C9, C10 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS User selectable capacitors - not populated D1 40V DUAL SERIES SCHOTTKY BARRIER DIODE Reverse Power Protection R11, R14, R21, R24 RESISTOR, SMD, 0603, 10k, 1%, 1/16W, ROHS Gain Setting Resistor R13, R23 RESISTOR, SMD, 0603, 100k, 1%, 1/16W, ROHS Gain Setting Feedback Resistor R1-R3, R5-R8, R10, R12, R15, RESISTOR, SMD, 0603, DNP-PLACE HOLDER, ROHS User selectable resistors - not populated R17, R20, R22, R28-R30, R32, R34-R36 U1 (ISL28208FBZ) ISL28208FBZ, IC PRECISION LOW NOSIE JFET OP AMP, SOIC, ROHS AN1658 Rev 0.00 Page 2 of 5 Jul 26, 2011 C8 OPEN R5 R28 DNP DNP