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ADP122 View Datasheet(PDF) - Analog Devices

Part NameADP122 ADI
Analog Devices ADI
Description5.5 V Input, 300 mA, Low Quiescent Current, CMOS Linear Regulator
ADP122 Datasheet PDF : 20 Pages
First Prev 11 12 13 14 15 16 17 18 19 20
THEORY OF OPERATION
The ADP122/ADP123 are low quiescent current, low-dropout
linear regulators that operate from 2.3 V to 5.5 V and can provide
up to 300 mA of output current. Drawing a low 170 μA of quies-
cent current (typical) at full load makes the ADP122/ADP123
ideal for battery-operated portable equipment. Shutdown current
consumption is typically 100 nA.
Optimized for use with small 1 μF ceramic capacitors, the
ADP122/ADP123 provide excellent transient performance.
Internally, the ADP122/ADP123 consist of a reference, an error
amplifier, a feedback voltage divider, and a PMOS pass transistor.
Output current is delivered via the PMOS pass device, which is
controlled by the error amplifier. The error amplifier compares
the reference voltage with the feedback voltage from the output
and amplifies the difference. If the feedback voltage is lower than
the reference voltage, the gate of the PMOS device is pulled lower,
allowing more current to pass and increasing the output voltage.
If the feedback voltage is higher than the reference voltage, the
gate of the PMOS device is pulled higher, allowing less current
to pass and decreasing the output voltage.
The adjustable ADP123 has an output voltage range of 0.8 V to
5.0 V. The output voltage is set by the ratio of two external resistors,
as shown in Figure 2. The device servos the output to maintain
the voltage at the ADJ pin at 0.5 V referenced to ground. The
current in R1 is then equal to 0.5 V/R2 and the current in R1 is
the current in R2 plus the ADJ pin bias current. The ADJ pin
bias current, 15 nA at 25°C, flows through R1 into the ADJ pin.
The output voltage can be calculated using the equation:
VOUT = 0.5 V(1 + R1/R2) + (ADJI-BIAS)(R1)
The value of R1 should be less than 200 kΩ to minimize errors
in the output voltage caused by the ADJ pin bias current. For
example, when R1 and R2 each equal 200 kΩ, the output voltage
is 1.0 V. The output voltage error introduced by the ADJ pin
bias current is 3 mV or 0.3%, assuming a typical ADJ pin bias
current of 15 nA at 25°C.
ADP122/ADP123
Note that in shutdown, the output is turned off and the divider
current is 0.
The ADP122/ADP123 use the EN pin to enable and disable the
VOUT pin under normal operating conditions. When EN is high,
VOUT turns on; when EN is low, VOUT turns off. For automatic
startup, EN can be tied to VIN.
ADP122
VIN
VOUT
SHORT CIRCUIT,
R1
GND
UVLO AND
THERMAL
PROTECT
EN
SHUTDOWN
0.5V REFERENCE
R2
NOTES
1. R1 AND R2 ARE INTERNAL RESISTORS, AVAILABLE ON
THE ADP122 ONLY.
Figure 26. ADP122 Internal Block Diagram (Fixed Output)
ADP123
VIN
VOUT
GND
SHORT CIRCUIT,
UVLO AND
THERMAL
PROTECT
EN
SHUTDOWN
0.5V REFERENCE
ADJ
Figure 27. ADP123 Internal Block Diagram (Adjustable Output)
Rev. 0 | Page 11 of 20
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GENERAL DESCRIPTION
The ADP122/ADP123 are low quiescent current, low dropout linear regulators. They are designed to operate from an input voltage between 2.3 V and 5.5 V and to provide up to 300 mA of output current. The low 85 mV dropout voltage at a 300 mA load improves efficiency and allows operation over a wide input voltage range.
The low 170 μA of quiescent current at full load makes the ADP122 ideal for battery-operated portable equipment.

FEATURES
Input voltage supply range: 2.3 V to 5.5 V
300 mA maximum output current
Fixed and adjustable output voltage versions
Very low dropout voltage: 85 mV at 300 mA load
Low quiescent current: 45 μA at no load
Low shutdown current: <1 μA
Initial accuracy: ±1% accuracy
Up to 31 fixed-output voltage options available from 1.75 V to 3.3 V
Adjustable-output voltage range 0.8 V to 5.0 V (ADP123)
Excellent PSRR performance: 60 dB at 100 kHz
Excellent load/line transient response
Optimized for small 1.0 μF ceramic capacitors
Current limit and thermal overload protection
Logic controlled enable
Compact, 5-lead TSOT package

APPLICATIONS
Digital camera and audio devices
Portable and battery-powered equipment
Automatic meter reading (AMR) meters
GPS and location management units
Medical instrumentation
Point-of-sale equipment

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