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

+

–

+

–

0.1µF

230Ω

RL

500Ω

5mA

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.

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

–

+

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

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

1.2V

AD8541

M1*

2.5V/100mA

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