USERS MANUAL ISL28133EVAL1Z AN1499 Rev.0.00 High Gain Evaluation Board User Guide Oct 2, 2009 Introduction Reference Documents The maximum useful signal range of a high gain DC Data Sheet (ISL28133) amplifier is limited by the amplifiers own DC offset and low frequency noise. For battery powered amplifiers Evaluation Board Key Features the problem is further compounded due to limits of low The ISL28133EVAL1Z is designed to enable the IC to battery voltage. For example, the useful input voltage operate from a single supply, +2.4VDC to +5.5VDC or range of an ideal amplifier with 10kV/V gain operating from split supplies, 1.2VDC to 2.75V. The board is from a 3V Lithium cell would be 300V, which would configured for a single op amp connected for drive the to the maximum possible +3V output. A single-ended or differential input with a closed loop standard low offset amplifier with 100V VOS would gain of 10,000. A single external reference voltage reduce the maximum useful input voltage range from (VREF) pin and provisions for a user-selectable voltage 300V to 200V, since the input offset voltage alone divider-filter are included. would drive the amplifier output to 10k times that, taking up 1V of the 3V total available voltage range. Power Supplies (Figure 2) Further reductions due to offset voltage drift, low External power connections are made through the V+, frequency 1/f noise, and the inability to swing the V-, VREF, and Ground connections on the evaluation output close to the power supply rails can limit the best board. For single supply operation, the -V and Ground amplifiers to DC gains no higher than several hundred pins are tied together to the power supply negative V/V. terminal. For split supplies, +V and -V terminals The ISL28133 chopper stabilized rail-to-rail op amp connect to their respective supply terminals. De- features a low 8V maximum VOS over-temperature coupling capacitors C2 and C4 provide low-frequency and a 0.1Hz 1/f noise corner frequency enabling very power-supply filtering, while four additional capacitors, high gain single-stage DC amplifiers that can operate C1, C5, C7 and C8, which are connected close to the from single cell batteries while consuming only 20A of part, filter out high frequency noise. Anti-reverse current. The ISL28133EVAL1Z evaluation board is diodes D1 and D2 (optional) protect the circuit in the configured as a precision high-gain (G = 10,000) case of accidental polarity reversal. differential amplifier and demonstrates the level of The circuit can operate from a single supply or from performance possible with this type of amplifier while dual supplies. The VREF pin can be connected to operating from battery voltages as low as 2.4V. ground to establish a ground referenced input for split supply operation, or can be externally set to any reference level for single supply operation. RF ISL28133 1M IN - VP RIN- IN- - IN- 0 V+ 100 VOUT V- RIN+ IN+ + IN+ VM 100 IN + VCM RL RG VREF OPEN 1M 0 OPEN VREF GND FIGURE 1. BASIC AMPLIFIER CONFIGURATION AN1499 Rev.0.00 Page 1 of 5 Oct 2, 2009ISL28133EVAL1Z User-selectable Options V+ VREF V- J8 J7 J10 (Figures 3 and 4) J13 J11 J9 Component pads are included to enable a variety of C2 1F C4 1F user-selectable circuits to be added to the amplifier S1AB D1 S1AB D2 inputs, the VREF input, outputs and the amplifier feedback loops. A voltage divider and filter option (Figure 3) can be added to establish a power supply-tracking common mode reference at the VREF input. The inverting and non-inverting inputs have additional resistor placements FIGURE 2. POWER SUPPLY CIRCUIT for adding input attenuation, or to establish input DC offsets through the VREF pin. Amplifier Configuration The output (Figure 4) also has additional resistor and (Figure 2) capacitor placements for filtering and loading. The schematic of the op amp with the components NOTE: Operational amplifiers are sensitive to output supplied is shown in Figure 2, with a closed loop gain of capacitance and may oscillate. In the event of oscillation, 10,000. The circuit implements a Hi-Z differential input reduce output capacitance by using shorter cables, or with unbalanced common mode impedance. The add a resistor in series with the output. differential amplifier gain is expressed in Equation 1: OPEN (EQ. 1) R5 R9 R11 V = V V R R + V FROM OUT OUT IN+ IN- F IN REF J1 IN - R1 0 10k 100k DNP where: R = R and R = R and the differential F G IN+ IN- input impedance is ~1M with V at GND. The IN- input TO IN - REF connects to the amplifier summing junction and its IN + R12 TO IN + impedance to ground is a low 100The impedance of the J2 R2 10k IN+ input to ground is much higher at 1.001Mto VREF. DNP VREF R13 R15 For single-ended input inverting operation (G = -10001), DNP 100k the IN+ input is grounded and the signal is supplied to the IN- input. V must be connected to a reference REF FIGURE 3. INPUT STAGE voltage between the V+ and V- supply rails. For non-inverting operation (G = 10,000), the IN- input is R18 grounded and the signal is supplied to the IN+ input. The OUTPUT J12 0 non-inverting gain is strongly dependent on any resistance from IN- to GND. For good gain accuracy, a 0 resistor should be installed on the empty R7 pads. FIGURE 4. OUTPUT STAGE TABLE 1. ISL28133EVAL1Z COMPONENTS PARTS LIST DEVICE DESCRIPTION COMMENTS C2, C4 CAP, SMD, 0603, 1F, 25V, 10%, X7R, ROHS Power Supply Decoupling C1, C5 CAP, SMD, 0603, 0.1F, 25V, 10%, X7R, ROHS Power Supply Decoupling C7, C8 CAP, SMD, 0603, 0.01F, 25V, 10%, X7R , ROHS Power Supply Decoupling C3, C6 CAP, SMD, 0603, DNP-PLACE HOLDER, ROHS User selectable capacitors - not populated D1, D2 DIODE-RECTIFIER, SMD, SOD-123, 2P, 40V, 0.5A, ROHS Reverse Power Protection U1 (ISL28133EVAL1Z) ISL28133FHZ-T7, IC-RAIL-TO-RAIL OP AMP, SOT-23, ROHS R1-R4, R6-R8, R10, R13, RESISTOR, SMD, 0603, 0.1%, MF, DNP-PLACE HOLDER User selectable resistors - not populated R14, R16, R17, R19, R21 R5, R18 RES, SMD, 0603, 0 , 1/10W, TF, ROHS 0 user selectable resistors R9, R12 RES, SMD, 0603, 100, 1/10W, 1%, TF, ROHS Gain resistors R11, R15 RES, SMD, 0603, 1M, 1/10W, 1%, TF, ROHS Gain resistors AN1499 Rev.0.00 Page 2 of 5 Oct 2, 2009 R4 DNP C1 0.01F C7 0.1F C5 0.01F C8 0.1F R16 DNP C6 OPEN R17 DNP R7 DNP