ADP221ACBZ2828-R7 datasheet(11/20 Pages) AD

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Data Sheet

ADP220/ADP221

Rev. H | Page 11 of 20

THEORY OF OPERATION

The ADP220/ADP221 are low quiescent current, low dropout

linear regulators that operate from 2.5 V to 5.5 V and provide

up to 200 mA of current from each output. Drawing a low 120 μA

quiescent current (typical) at full load makes the ADP220/

ADP221 ideal for battery-operated portable equipment. Shut-

down current consumption is typically 100 nA.

Optimized for use with small 1 µF ceramic capacitors, the

ADP220/ADP221 provide excellent transient performance.

THERMAL

SHUTDOWN

EN1

EN2

GND

CURRENT

LIMIT

CURRENT

LIMIT

60Ω

REFERENCE

ADP221

ONLY

CONTROL

LOGIC

AND

ENABLE

VIN

VOUT1

VOUT2

ADP220

Figure 28. Internal Block Diagram

Internally, the ADP220/ADP221 consist of a reference, two error

amplifiers, two feedback voltage dividers, and two PMOS pass

transistors. 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 flow 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 flow and decreasing the output voltage.

The ADP221 also includes an active pull-down circuit to rapidly

discharge the output load capacitance when each output is

disabled.

The ADP220/ADP221 are available in multiple output voltage

options ranging from 0.8 V to 3.3 V. The ADP220/ADP221 use

the EN1/EN2 pins to enable and disable the VOUT1/VOUT2

pins under normal operating conditions. When EN1/EN2 are high,

VOUT1/VOUT2 turn on; when EN1/EN2 are low, VOUT1/

VOUT2 turn off. For automatic startup, EN1/EN2 can be tied

to VIN.

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