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LT1492CN8 Datasheet(PDF) 11 Page - Linear Technology |
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LT1492CN8 Datasheet(HTML) 11 Page - Linear Technology |
11 / 16 page 11 LT1492/LT1493 APPLICATIONS INFORMATION Supply Voltage The LT1492/LT1493 op amps are fully functional and all internal bias circuits are in regulation with 2.1V of supply. The amplifiers will continue to function with as little as 1.6V, although the input common mode range and the phase margin are about gone. The minimum operating supply voltage is guaranteed by the PSRR tests that are done with the input common mode equal to 500mV and a minimum supply voltage of 2.5V. The positive supply pin of the LT1492/LT1493 should be bypassed with a small capacitor (about 0.01 µF) within an inch of the pin. When driving heavy loads and for good settling time, an additional 4.7 µF capacitor should be used. When using split supplies, the same is true for the negative supply pin. Power Dissipation The LT1492/LT1493 combine high speed and large output drive in small packages. Because of the wide supply voltage range, it is possible to exceed the maximum junction temperature under certain conditions. Maximum junction temperature (TJ) is calculated from the ambient temperature (TA) and power dissipation (PD) as follows: LT1492CN8: TJ = TA + (PD • 130°C/W) LT1492CS8: TJ = TA + (PD • 190°C/W) LT1493CS: TJ = TA + (PD • 150°C/W) Worst-case power dissipation occurs at the maximum supply current and when the output voltage is at 1/2 of either supply voltage (or the maximum swing if less than 1/2 supply voltage). For each amplifier PDMAX is: PDMAX = (V + – V–)(ISMAX) + (V+/2)2/RL Example: LT1493 at 70 °C, VS = ±15V, RL = 1k PDMAX = (30V)(930µA) + (7.5V)2/1kΩ = 84.2mW TJMAX = 70°C + (4 • 84.2mW)(150°C/W) = 121°C Inputs Typically, at room temperature, the inputs of the LT1492/ LT1493 can common mode 400mV below ground (V –) and to within 1.2V of the positive supply with the amplifier still functional. However, the input bias current will shift as shown in the characteristic curves. For full precision performance, the common mode range should be limited between ground (V –) and 1.5V below the positive supply. When either of the inputs is taken below ground (V –) by more than about 700mV, that input current will increase dramatically. The current is limited by internal 100 Ω resistors between the input pins and diodes to each supply. The output will remain low (no phase reversal) for inputs 1.3V below ground (V –). If the output does not have to sink current, such as in a single supply system with a 1k load to ground, there is no phase reversal for inputs up to 8V below ground. There are no clamps across the inputs of the LT1492/ LT1493 and therefore each input can be forced to any voltage between the supplies. The input current will re- main constant at about 50nA over most of this range. When an input gets closer than 1.5V to the positive supply, that input current will gradually decrease to zero until the input goes above the supply, then will increase due to the previously mentioned diodes. If the inverting input is held more positive than the noninverting input by 200mV or more, while at the same time the noninverting input is within 300mV to ground (V –), then the supply current will increase by 1mA and the noninverting input current will increase to about 10 µA. This should be kept in mind in comparator applications where the inverting input stays above ground (V –) and the noninverting input is at or near ground (V –). Output The output of the LT1492/LT1493 will swing to within 0.65V of the positive supply and to within 3mV of the negative supply with no load. Under loaded conditions see the Typical Performance curves for the output saturation voltage characteristics. The output of the LT1492/LT1493 has reverse-biased diodes to each supply. If the output is forced beyond either supply, unlimited currents will flow. If the current is transient and limited to several hundred milliamps, no damage will occur. |
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