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AD745JR-16 датащи(PDF) 9 Page - Analog Devices |
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AD745JR-16 датащи(HTML) 9 Page - Analog Devices |
9 / 12 page REV. D AD745 –9– HOW CHIP PACKAGE TYPE AND POWER DISSIPATION AFFECT INPUT BIAS CURRENT As with all JFET input amplifiers, the input bias current of the AD745 is a direct function of device junction temperature, IB approximately doubling every 10 °C. Figure 9 shows the rela- tionship between bias current and junction temperature for the AD745. This graph shows that lowering the junction tempera- ture will dramatically improve IB. JUNCTION TEMPERATURE – C 10–6 –60 10–7 10–8 10–9 10–10 10–11 10–12 –40 –20 0 20 40 60 80 100 120 140 VS = 15V TA = 25 C Figure 9. Input Bias Current vs. Junction Temperature The dc thermal properties of an IC can be closely approximated by using the simple model of Figure 10 where current represents power dissipation, voltage represents temperature, and resistors represent thermal resistance ( θ in °C/watt). TA JA JC CA TJ PIN WHERE: PIN = DEVICE DISSIPATION TA = AMBIENT TEMPERATURE TJ = JUNCTION TEMPERATURE JC = THERMAL RESISTANCE – JUNCTION TO CASE CA = THERMAL RESISTANCE – CASE TO AMBIENT Figure 10. Device Thermal Model From this model TJ = TA+ θJA PIN. Therefore, IB can be deter- mined in a particular application by using Figure 9 together with the published data for θ JA and power dissipation. The user can modify θJA by use of an appropriate clip-on heat sink such as the Aavid #5801. Figure 11 shows bias current versus supply voltage with θ JA as the third variable. This graph can be used to predict bias current after θJA has been computed. Again bias current will double for every 10 °C. SUPPLY VOLTAGE – Volts 300 515 10 200 100 0 TA = 25 C JA = 165 C/W JA = 115 C/W JA = 0 C/W Figure 11. Input Bias Current vs. Supply Voltage for Various Values of θJA A (J TO DIE MOUNT) B (DIE MOUNT TO CASE) A + B = JC TJ TA CASE Figure 12. Breakdown of Various Package Thermal Resistance REDUCED POWER SUPPLY OPERATION FOR LOWER IB Reduced power supply operation lowers IB in two ways: first, by lowering both the total power dissipation and, second, by reduc- ing the basic gate-to-junction leakage (Figure 11). Figure 13 shows a 40 dB gain piezoelectric transducer amplifier, which operates without an ac coupling capacitor, over the –40 °C to +85 °C temperature range. If the optional coupling capacitor, C1, is used, this circuit will operate over the entire –55 °C to +125 °C temperature range. +5V –5V CT** C1* 100 10k 108 ** CT 108 TRANSDUCER *OPTIONAL DC BLOCKING CAPACITOR **OPTIONAL, SEE TEXT AD745 Figure 13. A Piezoelectric Transducer |
Аналогичный номер детали - AD745JR-16 |
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Аналогичное описание - AD745JR-16 |
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