ADR280

–6–

ADR280

–7–

Negative Reference

A negative reference can be precisely configured without using

any expensive tight tolerance resistors, as shown in Figure 10.

is at virtual ground, U2 will close the loop by forcing the V– pin

to be the negative reference output.

V+

0.1F

V–

ADR280

U1

+5V

V+

V–

–2.7V

AD8541

–1.2V

U2

C1

Figure 10. Negative Reference

Boosted Reference with Scalable Output

A precision user defined output with boosted current capabil-

ity can be implemented with the circuit shown in Figure 11. In

regulating the turn-on of M1; the load current is therefore fur-

nished 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 config-

uration, 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.

V+

V–

ADR280

U1

5V

V+

V–

U2

R1

R2

RL

25

10.8k 0.1%

10k 0.1%

C2

1pF

1.2V

AD8541

0.1F

C1

M1

2.5V/100mA

M1 = FDB301N, 2N7000, 2N7002, OR EQUIVALENT

Figure 11. 2.5 V Boosted Reference

GSM and 3G Mobile Station Applications

The ADR280 voltage reference is ideal for use with analog base-

band ICs in GSM and 3G mobile station applications. Figure 12

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 and audio codecs, voltage

regulators, and a battery charger. Besides low current consump-

tion and a small footprint, the ADR280 is optimized for excellent

power supply rejection ratio (PSRR) necessary for optimum

AD6535 device performance when the main battery voltage

fluctuates during RF power amplifier activity.

DIGITAL

BASEBAND

AD6535 ANALOG

BASEBAND

BASEBAND CODEC

AUDIO CODEC

POWER

MANAGEMENT

RADIO

ADR280

VOLTAGE REFERENCE

Figure 12. GSM Mobile Station Application

REV. A

REV. A