Datasheet

Data Sheet ADP222/ADP223/ADP224/ADP225
Rev. D | Page 17 of 24
THEORY OF OPERATION
The ADP222/ADP223/ADP224/ADP225 are low quiescent
current, fixed and adjustable dual output, low dropout linear
regulators that operate from 2.5 V to 5.5 V and provide up to
300 mA of current from each output. Drawing a low 300 μA
quiescent current (typical) at full load make the ADP222/
ADP223/ADP224/ADP225 ideal for battery-operated portable
equipment. Shutdown current consumption is typically 200 nA.
Optimized for use with small 1 μF ceramic capacitors, the
ADP222/ADP223/ADP224/ADP225 provide excellent
transient performance.
THERMAL
SHUTDOWN
EN1
EN2
G
ND
CURRENT
LIMIT
CURRENT
LIMIT
REFERENCE
ADP225 ONLY
CONTROL
LOGIC
AND
ENABLE
VIN VOUT1
140Ω
VOUT2
ADP223/ADP225
ADJ1
ADJ2
09376-062
140Ω
Figure 62. Internal Block Diagram, ADP223/ADP225
THERMAL
SHUTDOWN
EN1
EN2
GND
CURRENT
LIMIT
CURRENT
LIMIT
REFERENCE
ADP224
ONLY
CONTROL
LOGIC
AND
ENABLE
VIN VOUT1
140Ω
VOUT2
ADP222/ADP224
SENSE1
SENSE2
09376-063
140Ω
Figure 63. Internal Block Diagram, ADP222/ADP224
Internally, the ADP222/ADP223/ADP224/ADP225 consist of a
reference, two error amplifiers, 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.
EN1
VOUT1
VIN
EN2
GND
6
4
3
2
ADJ2 VOUT2
1 8
5
7
ADJ1
ADP223/
ADP225
R1
R4
R2
ON
OFF
ON
OFF
V
IN
= 4.2V
+
C1
1µF
+
C3
1µF
+
C2
1µF
VOUT1 = 2.8V
VOUT2 = 2.0V
R3
09376-064
Figure 64. Typical Application Circuit for Setting Output Voltages,
ADP223/ADP225
The ADP223/ADP225 are exactly the same as the ADP222/
ADP224 except that the output voltage dividers are internally
disconnected and the feedback input of the error amplifiers is
brought out for each output. The output voltages can be set
according to the following equations:
V
OUT1
= 0.50 V(1 + R1/R2)
V
OUT2
= 0.50 V(1 + R3/R4)
The value of R1 and R3 should be less than 200 kΩ to minimize
errors in the output voltage caused by the ADJx pin input 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 ADJx
pin input current is 2 mV or 0.20%, assuming a typical ADJx pin
input current of 10 nA at 25°C.
The output voltage of the ADP223/ADP225
may be set from
0.5 V to 5.0 V.
The ADP222/ADP224 are available in multiple output voltage
options ranging from 0.8 V to 3.3 V.
The ADP224/ADP225 are identical to the ADP222/ADP223
with the addition of a quick output discharge (QOD) feature.
This allows the output voltage to start up from a known state.
The ADP222/ADP223/ADP224/ADP225 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.