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ADR280 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADR280
Beschreibung 1.2 V Ultralow Power High PSRR Voltage Reference
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
ADR280 Datasheet, Funktion
FEATURES
1.2 V Precision Output
Excellent Line Regulation, 2 ppm/V Typical
High Power Supply Ripple Rejection, –80 dB at 220 Hz
Ultralow Power, Supply Current 16 A Maximum
Temperature Coefficient, 40 ppm/oC Maximum
Low Noise, 12.5 nV/÷Hz Typical
Operating Supply Range, 2.4 V to 5.5 V
Compact 3-Lead SOT-23 and SC70 Packages
APPLICATIONS
GSM, GPRS, 3G Mobile Stations
Portable Battery-Operated Electronics
Low Voltage Converter References
Wireless Devices
GENERAL DESCRIPTION
The ADR280 is a 1.2 V band gap core reference with excellent
line regulation and power supply rejection designed specifically
for applications experiencing heavy dynamic supply variations,
such as data converter references in GSM, GPRS, and 3G
mobile station applications. Devices such as the AD6535, which
has an analog baseband IC with on-board baseband and audio
codecs, voltage regulators, and battery charger, rely on the
ADR280’s ability to reject input battery voltage variations during
RF power amplifier activity.
In addition to mobile stations, the ADR280 is suitable for a
variety of general-purpose applications. Most band gap refer-
ences include internal gain for specific outputs, which simplifies
the user’s design but compromises on the cost, form factor, and
flexibility. The ADR280, on the other hand, optimizes the band
gap core voltage and allows users to tailor the voltage, current, or
transient response by simply adding their preferred op amps.
The ADR280 operates on a wide supply voltage range from 2.4V
to 5.5 V. It is available in compact 3-lead SOT-23 and SC70
packages. The device is specified over the extended industrial
temperature range of –40°C to +85°C.
1.2 V Ultralow Power
High PSRR Voltage Reference
ADR280
PIN CONFIGURATIONS
3-Lead SOT-23
(RT Suffix)
V+ 1
ADR280 3 V–
VOUT 2
3-Lead SC70
(KS Suffix)
VOUT 1
ADR280 3 V–
V+ 2
15
10
5
3V TO 5V
0
–5
–10
–15
–40
–20
0
20 40
60
TEMPERATURE (C)
80 100
Figure 1. Line Regulation vs.Temperature
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
that may result from its use. No license is granted by implication or oth-
erwise under any patent or patent rights of Analog Devices.Trademarks
and registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© 2003 Analog Devices, Inc. All rights reserved.






ADR280 Datasheet, Funktion
ADR280
Negative Reference
A negative reference can be precisely configured without using
any expensive tight tolerance resistors, as shown in Figure 10.
The voltage difference between VOUT and V– is 1.2 V. Since VOUT
is at virtual ground, U2 will close the loop by forcing the V– pin
to be the negative reference output.
U1
+5V V+
ADR280
C1
0.1F
VOUT
U2
V+
AD8541
V–
V– –VREF
–1.2V
–2.7V
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
this circuit, U2 forces VO to be equal to VREF (1 + R2/R1) by
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.
VO 2.5V/100mA
RL
25
5V
M1
U1
V+
ADR280
V–
R2
10.8k 0.1%
C2
1pF
U2 V+
AD8541
V–
1.2V
C1
VOUT
0.1F
R1
10k 0.1%
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
RADIO
AUDIO CODEC
POWER
MANAGEMENT
ADR280
VOLTAGE REFERENCE
Figure 12. GSM Mobile Station Application
–6– REV. A

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