Datasheet

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
60Ω
REFERENCE
ADP221
ONLY
CONTROL
LOGIC
AND
ENABLE
VIN
VOUT1
VOUT2
ADP220
07572-028
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.