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ADR280 Datasheet(PDF) 9 Page - Analog Devices |
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ADR280 Datasheet(HTML) 9 Page - Analog Devices |
9 / 12 page ADR280 Rev. C | Page 9 of 12 Boosted Current Source Adding one more buffer to the previous circuit boosts the current to the level that is limited only by the buffer U2 current handling capability (see Figure 18). V+ V– ADR280 U1 5V C1 V+ V– 5V U3 V+ V– 5V U2 1.2V + – + – VOUT 0.1µF RSET 230Ω RL 500Ω IL 5mA IL = 1.2V/RSET U2 = U3 = AD8542, AD822 Figure 18. Precision Current Source Negative Reference A negative reference can be precisely configured without using any expensive tight tolerance resistors, as shown in Figure 19. The voltage difference between VOUT and V− is 1.2 V. Since VOUT is at virtual ground, U2 closes the loop by forcing the V− pin to be the negative reference output. V+ V– ADR280 U1 +5V V+ V– –2.7V AD8541 –1.2V U2 –VREF VOUT – + C1 0.1µF Figure 19. Negative Reference Boosted Reference with Scalable Output A precision user defined output with boosted current capability can be implemented with the circuit shown in Figure 20. In this circuit, U2 forces VO to be equal to VREF × (1 + R2/R1) by regu- lating the turn-on of M1; the load current is therefore furnished by the 5 V supply. For higher output voltage, U2 must be changed and the supply voltage of M1 and U2 must also be elevated and separated from the U1 input voltage. In this configuration, a 100 mA load is achievable at a 5 V supply. The higher the supply voltage, the lower the current handling is because of the heat generated on the MOSFET. For heavy capacitive loads, additional buffering is needed at the output to enhance the transient response. *M1 = FDB301N, 2N7000, 2N7002, OR EQUIVALENT. V+ V– ADR280 U1 5V V+ V– U2 C2 1pF VREF 1.2V AD8541 M1* VOUT 2.5V/100mA VO RL 25Ω R2 10.8kΩ ± 0.1% R1 10kΩ ± 0.1% C1 0.1µF + – Figure 20. 2.5 V Boosted Reference GSM and 3G Mobile Station Applications The ADR280 voltage reference is ideal for use with analog baseband ICs in GSM and 3G mobile station applications. Figure 21 illustrates the use of the ADR280 with the AD6535 GSM analog baseband. The AD6535 provides all of the data converters and power management functions needed to implement a GSM mobile station, including baseband codecs, audio codecs, voltage regulators, and a battery charger. Besides low current consumption and a small footprint, the ADR280 is optimized for excellent PSRR, which is necessary for optimum AD6535 device performance when the main battery voltage fluctuates during RF power amplifier activity. RADIO BASEBAND CODEC AUDIO CODEC POWER MANAGEMENT ADR280 VOLTAGE REFERENCE AD6535 ANALOG BASEBAND DIGITAL BASEBAND Figure 21. GSM Mobile Station Application |
Similar Part No. - ADR280_15 |
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Similar Description - ADR280_15 |
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