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ISL28236FUZ bảng dữ liệu(PDF) 11 Page - Intersil Corporation |
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ISL28236FUZ bảng dữ liệu(HTML) 11 Page - Intersil Corporation |
11 / 15 page ISL28236 11 FN6921.2 July 24, 2014 Submit Document Feedback Applications Information Introduction The ISL28236 is a dual channel Bi-CMOS rail-to-rail input, output (RRIO) micropower precision operational amplifier. The part is designed to operate from a single supply (2.4V to 5.5V) or a dual supply (±1.2V to ±2.75V). The ISL28236 has an input common mode range that extends 0.25V above the positive rail and down to the negative supply rail. The output operation can swing within about 3mV of the supply rails with a 100kΩ load. Rail-to-Rail Input Many rail-to-rail input stages use two differential input pairs, a long-tail PNP (or PFET) and an NPN (or NFET). Severe penalties have to be paid for this circuit topology. As the input signal moves from one supply rail to another, the operational amplifier switches from one input pair to the other. Thus causing drastic changes in input offset voltage and an undesired change in magnitude and polarity of input offset current. The ISL28236 solves this problem using an internal charge pump to provide a voltage boost to the V+ supply rail driving the input differential pair. This results in extending the input common voltage rails to 0.25V beyond the V+ positive rail. The input offset voltage exhibits a smooth behavior throughout the extended common-mode input range. The input bias current versus the common-mode voltage range gives an undistorted behavior from the negative rail to 0.25V higher than the positive rail. Power Supply Decoupling The internal charge pump operates at approximately 27MHz and oscillator ripple doesn’t show up in the 5MHz bandwidth of the amplifier. Good power supply decoupling with 0.01µF capacitors at each device power supply pin, is the most effective way to reduce oscillator ripple at the amplifier output. Figure 36 shows the electrical connection of these capacitors using split power supplies. For single supply operation with V- tied to a ground plane, only a single 0.01µF capacitor from V+ is needed. When multiple ISL28236 op amps are used on a single PC board, each op amp will require a 0.01µF decoupling capacitor at each supply pin. Rail-to-Rail Output The rail-to-rail output stage uses CMOS devices that typically swing to within 3mV of the supply rails with a 100kΩ load. The NMOS sinks current to swing the output in the negative direction. The PMOS sources current to swing the output in the positive direction. Current Limiting These devices have no internal current limiting circuitry. If the output is shorted, it is possible to exceed the absolute maximum rating for output current or power dissipation, potentially resulting in the destruction of the device. Results Of Overdriving The Output Caution should be used when overdriving the output for long periods of time. Overdriving the output can occur in two ways. 1. The input voltage times the gain of the amplifier exceeds the supply voltage by a large value or, 2. The output current required is higher than the output stage can deliver. These conditions can result in a shift in the Input Offset Voltage (VOS) (as much as 1µV/hr. of exposure) under these conditions. IN+ and IN- Input Protection All input terminals have internal ESD protection diodes to both positive and negative supply rails, limiting the input voltage to within one diode beyond the supply rails. They also contain back-to-back diodes across the input terminals (see “Pin Descriptions” on page 2 - Circuit 1). For applications where the input differential voltage is expected to exceed 0.5V, an external series resistor must be used to ensure the input currents never exceed 5mA (Figure 36). Limitations of the Differential Input Protection If the input differential voltage is expected to exceed 0.5V, an external current limiting resistor must be used to ensure the input current never exceeds 5mA. For non-inverting unity gain applications, the current limiting can be via a series IN+ resistor, or via a feedback resistor of appropriate value. For other gain configurations, the series IN+ resistor is the best choice, unless the feedback (RF) and gain setting (RG) resistors are both sufficiently large to limit the input current to 5mA. Large differential input voltages can arise from several sources: 1. During open loop (comparator) operation. Used this way, the IN+ and IN- voltages don’t track, so differentials arise. 2. When the amplifier is disabled but an input signal is still present. An RL or RG to GND keeps the IN- at GND, while the varying IN+ signal creates a differential voltage. Mux Amp applications are similar, except that the active channel VOUT determines the voltage on the IN- terminal. 3. When the slew rate of the input pulse is considerably faster than the op amp’s slew rate. If the VOUT can’t keep up with the IN+ signal, a differential voltage results, and visible distortion occurs on the input and output signals. To avoid this issue, keep the input slew rate below 1.9V/µs, or use appropriate current limiting resistors. Large (>2V) differential input voltages can also cause an increase in disabled ICC. FIGURE 36. LOCAL POWER SUPPLY DECOUPLING AND INPUT CURRENT LIMITING - + RIN RL VIN VOUT V+ V- 0.01µF 0.01µF DECOUPLING CAPACITORS ISL28236 |
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Mô tả tương tự - ISL28236FUZ |
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