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ADR293GRZ-REEL7 数据表(PDF) 10 Page - Analog Devices |
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ADR293GRZ-REEL7 数据表(HTML) 10 Page - Analog Devices |
10 / 12 page ADR293 Rev. D | Page 10 of 12 THEORY OF OPERATION The ADR293 uses a new reference generation technique known as XFET, which yields a reference with low noise, low supply current, and very low thermal hysteresis. The core of the XFET reference consists of two junction field effect transistors, one of which has an extra channel implant to raise its pinch-off voltage. By running the two JFETs at the same drain current, the difference in pinch-off voltage can be amplified and used to form a highly stable voltage reference. The intrinsic reference voltage is around 0.5 V with a negative temperature coefficient of about –120 ppm/K. This slope is essentially locked to the dielectric constant of silicon and can be closely compen- sated by adding a correction term generated in the same fashion as the proportional-to-temperature (PTAT) term used to compensate band gap references. The big advantage over a band gap reference is that the intrinsic temperature coefficient is some 30 times lower (therefore, less correction is needed) and this results in much lower noise, because most of the noise of a band gap reference comes from the temperature compensation circuitry. The simplified schematic in Figure 21 shows the basic topology of the ADR293. The temperature correction term is provided by a current source with value designed to be proportional to absolute temperature. The general equation is ()() R3 I R1 R3 R2 R1 V V PTAT P OUT + ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + + Δ = where: ΔVP is the difference in pinch-off voltage between the two FETs. IPTAT is the positive temperature coefficient correction current. The process used for the XFET reference also features vertical NPN and PNP transistors, the latter of which are used as output devices to provide a very low dropout voltage. VOUT VIN IPTAT GND R1 R2 R3 I1 I1 1 1 EXTRA CHANNEL IMPLANT VOUT =× ∆VP + IPTAT × R3 R1 + R2 + R3 R1 ∆VP Figure 21. Simplified Schematic DEVICE POWER DISSIPATION CONSIDERATIONS The ADR293 is guaranteed to deliver load currents to 5 mA with an input voltage that ranges from 5.5 V to 15 V. When this device is used in applications with large input voltages, care should be exercised to avoid exceeding the published specifications for maximum power dissipation or junction temperature that could result in premature device failure. The following formula should be used to calculate a device’s maximum junction temperature or dissipation: JA A J D T T P θ − = where: TJ and TA are the junction temperature and ambient temperature, respectively. PD is the device power dissipation. θJA is the device package thermal resistance. BASIC VOLTAGE REFERENCE CONNECTIONS References, in general, require a bypass capacitor connected from the VOUT pin to the GND pin. The circuit in Figure 22 illustrates the basic configuration for the ADR293. Note that the decoupling capacitors are not required for circuit stability. NC NC NC NC VOUT NC 0.1µF 0.1µF 10µF + NC = NO CONNECT 1 2 3 4 8 7 6 5 ADR293 Figure 22. Basic Voltage Reference Configuration NOISE PERFORMANCE The noise generated by the ADR293 is typically less than 15 μV p-p over the 0.1 Hz to 10 Hz band. The noise measure- ment is made with a band-pass filter made of a 2-pole high-pass filter with a corner frequency at 0.1 Hz and a 2-pole low-pass filter with a corner frequency at 10 Hz. TURN-ON TIME Upon application of power (cold start), the time required for the output voltage to reach its final value within a specified error band is defined as the turn-on settling time. Two components normally associated with this are the time for the active circuits to settle and the time for the thermal gradients on the chip to stabilize. Figure 15 shows the typical turn-on time for the ADR293. |
类似零件编号 - ADR293GRZ-REEL7 |
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类似说明 - ADR293GRZ-REEL7 |
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