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OP250GRU データシート(PDF) 10 Page - Analog Devices |
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OP250GRU データシート(HTML) 10 Page - Analog Devices |
10 / 16 page OP250/OP450 REV. 0 –10– Output Phase Reversal The OPx50 is immune to output voltage phase reversal with an input voltage within the supply voltages of the device. However, if either of the device’s inputs exceeds 0.6 V outside of the sup- ply rails, the output could exhibit phase reversal. This is due to the ESD protection diodes becoming forward biased, thus caus- ing the polarity of the input terminals of the device to switch. The technique recommended in the Input Overvoltage Protec- tion section should be applied in applications where the possibil- ity of input voltages exceeding the supply voltages exists. Output Short Circuit Protection To achieve high quality rail-to-rail performance, the outputs of the OPx50 family are not short-circuit protected. Although these amplifiers are designed to sink or source as much as 250 mA of output current, shorting the output directly to ground could damage or destroy the device when excessive volt- ages or currents are applied. If to protect the output stage, the maximum output current should be limited to ±250 mA. By placing a resistor in series with the output of the amplifier as shown in Figure 28, the output current can be limited. The minimum value for RX can be found from Equation 2. R V mA X SY ≥ 250 (2) For a +5 V single supply application, RX should be at least 20 Ω. Because R X is inside the feedback loop, VOUT is not af- fected. The trade-off in using RX is a slight reduction in output voltage swing under heavy output current loads. RX will also increase the effective output impedance of the amplifier to RO + RX, where RO is the output impedance of the device. THEORY OF OPERATION The OPx50 family of amplifiers are CMOS rail-to-rail input and output single supply amplifiers designed for low cost and high output current drive. These features make the OPx50 op amps ideal for multimedia and telecom applications. Figure 27 shows the simplified schematic for an OPx50 ampli- fier. Two input differential pairs consisting of an n-channel pair (M1–M2) and a p-channel pair (M3–M4) provide a rail-to-rail input common-mode range. The outputs of the input differen- tial pairs are combined in a compound folded-cascode stage, which drives the input to a second differential pair gain stage. The outputs of the second gain stage provide the gate voltage drive to the rail-to-rail output stage. The rail-to-rail output stage consists of M15 and M16, which are configured in a complementary common-source configura- tion. As with any rail-to-rail output amplifier, the gain of the output stage, and thus the open loop gain of the amplifier, is de- pendent on the load resistance. Also, the maximum output volt- age swing is directly proportional to the load current. The difference between the maximum output voltage to the supply rails, known as the dropout voltage, is determined by the OPx50’s output transistors’ on-channel resistance. The output dropout voltage is given in Figures 1 and 2. Input Voltage Protection Although not shown on the simplified schematic, there are ESD protection diodes connected from each input to each power supply rail. These diodes are normally reversed biased, but will turn on if either input voltage exceeds either supply rail by more than 0.6 V. Should this condition occur the input current should be limited to less than ±5 mA. This can be done by placing a resistor in series with the input. The minimum resistor value should be: R V mA IN IN MAX ≥ , 5 (1) VEE VCC VOUT –VIN +VIN M1 M2 M3 M4 BIAS M5 M6 BIAS BIAS Figure 27. OPx50 Simplified Schematic |
同様の部品番号 - OP250GRU |
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同様の説明 - OP250GRU |
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