ADR280ART-REEL7 Просмотр технического описания (PDF) - Analog Devices
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ADR280ART-REEL7 Datasheet PDF : 12 Pages
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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).
U1
5V
V+
5V
U2 +
V+
V– –
ADR280
V–
VOUT
C1
0.1µF
RSET
230Ω
RL
500Ω
+
1.2V
–
IL
5mA
5V
– U3
V+
+ V–
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.
U1
+5V
V+
ADR280
C1
0.1µF
V–
VOUT
U2
– V+
AD8541
+ V–
–VREF
–1.2V
–2.7V
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
ADR280
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.
2.5V/100mA
VO
RL
25Ω
5V
M1*
U1
V+
ADR280
V–
R2
10.8kΩ ± 0.1% C2
1pF
U2
+
V+
AD8541
V– –
VREF
1.2V
VOUT
C1
0.1µF
R1 *M1 = FDB301N, 2N7000, 2N7002, OR EQUIVALENT.
10kΩ ± 0.1%
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.
DIGITAL
BASEBAND
AD6535
ANALOG BASEBAND
RADIO
BASEBAND CODEC
AUDIO CODEC
POWER
MANAGEMENT
ADR280
VOLTAGE REFERENCE
Figure 21. GSM Mobile Station Application
Rev. C | Page 9 of 12
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