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AD8569ARM-R2 Fiches technique(PDF) 9 Page - Analog Devices |
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AD8569ARM-R2 Fiches technique(HTML) 9 Page - Analog Devices |
9 / 12 page –9– AD8568/AD8569/AD8570 REV. C APPLICATIONS Theory of Operation This family of buffers is designed to drive large capacitive loads in LCD applications. Each has high output current drive and rail- to-rail input/output operation and can be powered from a single 16 V supply. They are also intended for other applications where low distortion and high output current drive are needed. Input Overvoltage Protection As with any semiconductor device, whenever the input exceeds either supply voltage, attention needs to be paid to the input overvoltage characteristics. As an overvoltage occurs, the amplifier could be damaged, depending on the voltage level and the magnitude of the fault current. When the input voltage exceeds either supply by more than 0.6 V, the internal pn junctions will allow current to flow from the input to the supplies. This input current is not inherently damaging to the device as long as it is limited to 5 mA or less. If a condition exists using the buffers where the input exceeds the supply by more than 0.6 V, an external series resistor should be added. The size of the resis- tor can be calculated by using the maximum overvoltage divided by 5 mA. This resistance should be placed in series with the input exposed to an overvoltage. Output Phase Reversal The buffer family is immune to phase reversal. Although the device’s output will not change phase, large currents due to input overvoltage could damage the device. In applications where the possibility exists of an input voltage exceeding the supply voltage, overvoltage protection should be used as described in the previous section. Power Dissipation The maximum allowable internal junction temperature of 150 °C limits the device’s maximum power dissipation. As the ambient temperature increases, the maximum power dissipated by the device must decrease linearly to maintain the maximum junc- tion temperature. If this maximum junction temperature is exceeded momentarily, the device will still operate properly once the junction temperature is reduced below 150 °C. If the maximum junction temperature is exceeded for an extended period of time, overheating could lead to permanent damage of the device. The maximum safe junction temperature, TJMAX, is 150 °C. Using the following formula, we can obtain the maximum power that the buffer family can safely dissipate as a function of temperature. PT T DISS A A =− () JMAX J / θ where: PDISS = the power dissipation. TJMAX = the maximum allowable junction temperature (150 °C). TA = the ambient temperature of the circuit. θJ A = the AD856x package thermal resistance, junction-to-ambient. The power dissipated by the device can be calculated as PV V I DISS S OUT LOAD =− () × where: VS = the supply voltage. VOUT = the output voltage. ILOAD = the output load current. Figure 1 shows the maximum power dissipation versus temperature. To achieve proper operation, use the previous equation to calculate PDISS for a specific package at any given temperature, or see Figure 1. AMBIENT TEMPERATURE – C 1.00 0.75 0 35 85 15 525 4565 0.50 0.25 10-LEAD MSOP 6-LEAD SOT-23 Figure 1. Maximum Power Dissipation vs. Temperature for 6- and 10-Lead Packages Total Harmonic Distortion + Noise (THD+N) The buffer family features low THD+N. The total harmonic distortion plus noise for the buffer over the entire supply range is below 0.08%. When the device is powered from a 16 V supply, the THD+N stays below 0.03%. Figure 2 shows the AD8568 THD+N versus frequency performance. FREQUENCY – Hz 20 30k 100 1k 10k 10 1 0.01 0.1 VS = 2.5V VS = 8V Figure 2. AD8568 THD+N vs. Frequency Short-Circuit Output Conditions The buffer family does not have internal short-circuit protection circuitry. As a precautionary measure, do not short the output directly to the positive power supply or to ground. It is not recommended to operate the AD856x with more than 35 mA of continuous output current. The output current can be limited by placing a series resistor at the output of the amplifier whose value can be derived using the following equation. R V mA X S ≥ 35 For a 5 V single-supply operation, RX should have a minimum value of 143 Ω. |
Numéro de pièce similaire - AD8569ARM-R2 |
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Description similaire - AD8569ARM-R2 |
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