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PDF ADP667 Data sheet ( Hoja de datos )
| Número de pieza | ADP667 | |
| Descripción | +5 V Fixed/ Adjustable Low-Dropout Linear Voltage Regulator | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
+5 V Fixed, Adjustable
Low-Dropout Linear Voltage Regulator
FEATURES
Low-Dropout: 150 mV @ 200 mA
Low Power CMOS: 20 µA Quiescent Current
Shutdown Mode: 0.2 µA Quiescent Current
250 mA Output Current
Pin Compatible with MAX667
Stable with 10 µF Load Capacitor
Low Battery Detector
Fixed +5 V or Adjustable Output
+3.5 V to +16.5 V Input Range
Dropout Detector Output
APPLICATIONS
Handheld Instruments
Cellular Telephones
Battery Operated Devices
Portable Equipment
Solar Powered Instruments
High Efficiency Linear Power Supplies
ADP667
FUNCTIONAL BLOCK DIAGRAM
IN OUT
ADP667
DD
SHDN
LBO
LBI
GND
A1
C2
1.255V
REF
SET
C1
50mV
GENERAL DESCRIPTION
The ADP667 is a low-dropout precision voltage regulator that
can supply up to 250 mA output current. It can be used to give
a fixed +5 V output with no additional external components or
can be adjusted from +1.3 V to +16 V using two external resis-
tors. Fixed or adjustable operation is automatically selected via
the SET input. The low quiescent current (20 µA) in conjunc-
tion with the standby or shutdown mode (0.2 µA) makes this
device especially suitable for battery powered systems. The
dropout voltage when supplying 100 µA is only 5 mV allowing
operation with minimal headroom and prolonging the battery
useful life. At higher output current levels the dropout remains
low increasing to just 150 mV when supplying 200 mA. A wide
input voltage range from 3.5 V to 16.5 V is allowable.
Additional features include a dropout detector and a low supply/
battery monitoring comparator. The dropout detector can be
used to signal loss of regulation, while the low battery detector
can be used to monitor the input supply voltage.
The ADP667 is a pin-compatible replacement for the MAX667.
It is specified over the industrial temperature range –40°C to
+85°C and is available in an 8-pin DIP and in narrow surface
mount (SOIC) packages.
TYPICAL OPERATING CIRCUIT
IN OUT
+6V +
INPUT
ADP667
+ C1
10µF
+5V
OUTPUT
SET GND SHDN
ORDERING GUIDE
Model
Temperature
Range
ADP667AN –40°C to +85°C
ADP667AR –40°C to +85°C
Package
Description
Package
Option
8-Pin Plastic DIP N-8
8-Lead SOIC SO-8
REV. 0
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1995
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
1 page  
ADP667
Dropout Detector
The ADP667 features an extremely low dropout voltage making
it suitable for low voltage systems where headroom is limited. A
dropout detector is also provided. The dropout detector output,
DD, changes as the dropout voltage approaches its limit. This is
useful for warning that regulation can no longer be maintained.
The dropout detector output is an open collector output from a
PNP transistor. Under normal operating conditions with the in-
put voltage more than 300 mV above the output, the PNP tran-
sistor is off and no current flows out the DD pin. As the voltage
differential reduces to less than 300 mV, the transistor switches
on and current is sourced. This condition indicates that regulation
can no longer be maintained. Please refer to Figure 10 in the
“Typical Performance Characteristics.” The current output can
be translated into a voltage output by connecting a resistor from
DD to GND. A resistor value of 100 kΩ is suitable. A digital
status signal can be obtained using a comparator. The on-chip
comparator LBI may be used if it is not being used to monitor a
battery voltage. This is illustrated in Figure 5.
+
VIN
IN OUT
ADP667
+ C1
10µF
R2
10kΩ
+5V
OUTPUT
LBI LBO
DD
SET GND SHDN
DROPOUT
STATUS
OUTPUT
R1
100kΩ
Figure 5. Dropout Status Output
Output Capacitor Selection
An output capacitor is required on the ADP667 to maintain
stability and also to improve the load transient response. Ca-
pacitor values from 10 µF upwards are suitable. All specifica-
tions are tested and guaranteed with 10 µF. Capacitors larger
than 10 µF will further improve the dynamic transient response
characteristics of the regulator. Tantalum or aluminum electro-
lytics are suitable for most applications. For temperatures below
about –25°C, solid tantalums should be used as many alumi-
num electrolytes freeze at this temperature.
Quiescent Current Considerations
The ADP667 uses a PNP output stage to achieve low dropout
voltages combined with high output current capability. Under
normal regulating conditions the quiescent current is extremely
low. However if the input voltage drops so that it is below the
desired output voltage, the quiescent current increases consider-
ably. This happens because regulation can no longer be main-
tained and large base current flows in the PNP output transistor
in an attempt to hold it fully on. For minimum quiescent cur-
rent, it is therefore important that the input voltage is main-
tained higher than the desired output level. If the device is being
powered using a battery that can discharge down below the rec-
ommended level, there are a couple of techniques that can be
applied to reduce the quiescent current, but at the expense of
dropout voltage. The first of these is illustrated in Figure 6. By
connecting DD to SHDN the regulator is partially disabled with
input voltages below the desired output voltage and therefore
the quiescent current is reduced considerably.
+
VIN
IN OUT
ADP667
DD
SET GND SHDN
+ C1
10µF
+5V
OUTPUT
R1
47kΩ
C2
0.1µF
Figure 6. IQ Reduction 1
Another technique for reducing the quiescent current near drop-
out is illustrated in Figure 7. The DD output is used to modify
the output voltage so that as VIN drops, the desired output volt-
age setpoint also drops. This technique only works when exter-
nal resistors are used to set the output voltage. With VIN greater
than VOUT, DD has no effect. As VIN reduces and dropout is
reached, the DD output starts sourcing current into the SET
input through R3. This increases the SET voltage so that the
regulator feedback loop does not drive the internal PNP transis-
tor as hard as it otherwise would. As the input voltage continues
to decrease, more current is sourced, thereby reducing the PNP
drive even further. The advantage of this scheme is that it main-
tains a low quiescent current down to very low values of VIN at
which point the batteries are well outside their useful operating
range. The output voltage tracks the input voltage minus the
dropout. The SHDN function is also unaffected and may be
used normally if desired.
+
VIN
IN OUT
ADP667
SHDN
SET
GND DD
R3
1MΩ
R2
1MΩ
+ C1
10µF
+5V
OUTPUT
R1
332kΩ
Figure 7. IQ Reduction 2
REV. 0
–5–
5 Page | ||
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| PDF Descargar | [ Datasheet ADP667.PDF ] | |
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