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AD8534AN датащи(PDF) 11 Page - Analog Devices |
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AD8534AN датащи(HTML) 11 Page - Analog Devices |
11 / 16 page AD8531/AD8532/AD8534 REV. D –11– A High Output Current, Buffered Reference/Regulator Many applications require stable voltage outputs relatively close in potential to an unregulated input source. This “low drop- out” type of reference/regulator is readily implemented with a rail-to-rail output op amp, and is particularly useful when using a higher current device such as the AD8531/AD8532/AD8534. A typical example is the 3.3 V or 4.5 V reference voltage devel- oped from a 5 V system source. Generating these voltages requires a three terminal reference, such as the REF196 (3.3 V) or the REF194 (4.5 V), both which feature low power, with sourcing outputs of 30 mA or less. Figure 38 shows how such a reference can be outfitted with an AD8531/AD8532/AD8534 buffer for higher currents and/or voltage levels, plus sink and source load capability. C2 0.1 F R2 10k 1% VOUT1 = 3.3V @ 100mA R5 0.2 C5 100 F/16V TANTALUM R1 10k 1% C1 0.1 F VS 5V VOUT2 = 3.3V C4 1 F 6 2 3 4 VOUT COMMON C3 0.1 F VC ON/OFF CONTROL INPUT CMOS HI (OR OPEN) = ON LO = OFF VS COMMON R3 (SeeText) R4 3.3k U2 AD8531 U1 REF196 Figure 38. A High Output Current Reference/Regulator The low dropout performance of this circuit is provided by stage U2, an AD8531 connected as a follower/buffer for the basic reference voltage produced by U1. The low voltage saturation characteristic of the AD8531/AD8532/AD8534 allows up to 100 mA of load current in the illustrated use, as a 5 V to 3.3 V converter with good dc accuracy. In fact, the dc output voltage change for a 100 mA load current delta measured less than 1 mV. This corresponds to an equivalent output impedance of < 0.01 W. In this application, the stable 3.3 V from U1 is applied to U2 through a noise filter, R1–C1. U2 replicates the U1 voltage within a few millivolts, but at a higher current output at VOUT1, with the ability to both sink and source output current(s) —unlike most IC references. R2 and C2 in the feedback path of U2 provide additional noise filtering. Transient performance of the reference/regulator for a 100 mA step change in load current is also quite good and is largely determined by the R5–C5 output network. With values as shown, the transient is about 20 mV peak and settles to within 2 mV in less than 10 ms for either polarity. Although room exists for optimizing the transient response, any changes to the R5–C5 network should be verified by experiment to preclude the possi- bility of excessive ringing with some capacitor types. To scale VOUT2 to another (higher) output level, the optional resistor R3 (shown dotted) is added, causing, the new VOUT1 to become: VOUT1 =VOUT 2 ¥ 1+ R2 R3 Ê ËÁ ˆ ¯˜ The circuit can either be used as shown, as a 5 V to 3.3 V reference/regulator, or with ON/OFF control. By driving Pin 3 of U1 with a logic control signal as noted, the output is switched ON/OFF. Note that when ON/OFF control is used, resistor R4 must be used with U1 to speed ON-OFF switching. A Single-Supply, Balanced Line Driver The circuit in Figure 39 is a unique line driver circuit topology used in professional audio applications and has been modified for automotive and multimedia audio applications. On a single 5 V supply, the line driver exhibits less than 0.7% distortion into a 600 W load from 20 Hz to 15 kHz (not shown) with an input signal level of 4 V p-p. In fact, the output drive capability of the AD8531/AD8532/AD8534 maintains this level for loads as small as 32 W. For input signals less than 1 V p-p, the THD is less than 0.1%, regardless of load. The design is a transformer- less, balanced transmission system where output common-mode rejection of noise is of paramount importance. As with the transformer-based system, either output can be shorted to ground for unbalanced line driver applications without changing the circuit gain of 1. Other circuit gains can be set according to the equation in the diagram. This allows the design to be easily configured for inverting, noninverting or differential operation. RL 600 C1 22 F A2 7 6 5 3 1 2 A1 5V R1 10k R2 10k R11 10k R7 10k 6 7 5 A1 12V 5V R8 100k R9 100k C2 1 F R12 10k R14 50 A2 1 2 3 R3 10k R6 10k R13 10k C3 47 F VO1 VO2 C4 47 F A1, A2 = 1/2 AD8532 GAIN = R3 R2 SET: R7, R10, R11 = R2 SET: R6, R12, R13 = R3 VIN R10 10k R5 50 Figure 39. A Single-Supply, Balanced Line Driver for Multimedia and Automotive Applications |
Аналогичный номер детали - AD8534AN |
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Аналогичное описание - AD8534AN |
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