Datasheet

ADP7104 Data Sheet
Rev. F | Page 16 of 28
THEORY OF OPERATION
The ADP7104 is a low quiescent current, low-dropout linear
regulator that operates from 3.3 V to 20 V and provides up to
500 mA of output current. Drawing a low 1 mA of quiescent
current (typical) at full load makes the ADP7104 ideal for
battery-operated portable equipment. Typical shutdown
current consumption is 40 μA at room temperature.
Optimized for use with small 1 µF ceramic capacitors, the
ADP7104 provides excellent transient performance.
SHUTDOWN
VIN
GND
EN/
UVLO
VOUT
R1
R2
1.22V
REFERENCE
VREG
PGOOD
PG
SENSE
SHORT-CIRCUIT,
THERMAL
PROTECT
10µA
09507-055
Figure 59. Fixed Output Voltage Internal Block Diagram
SHUTDOWN
VIN
GND
EN/
UVLO
VOUT
R2
1.22V
REFERENCE
VREG
PGOOD
PG
ADJ
SHORT-CIRCUIT,
THERMAL
PROTECT
10µA
09507-056
Figure 60. Adjustable Output Voltage Internal Block Diagram
Internally, the ADP7104 consists 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 ADP7104 is available in seven fixed output voltage options,
ranging from 1.5 V to 9 V and in an adjustable version with an
output voltage that can be set to between 1.22 V and 19 V by an
external voltage divider. The output voltage can be set according
to the following equation:
V
OUT
= 1.22 V(1 + R1/R2)
V
OUT
= 5V
V
IN
= 8V
PG
VOUTVIN
PG
GND
ADJ
EN/
UVLO
RPG
100kΩ
R4
100kΩ
R3
100kΩ
COUT
1µF
CIN
1µF
ON
OFF
R2
13kΩ
++
R1
40.2kΩ
09507-075
Figure 61. Typical Adjustable Output Voltage Application Schematic
The value of R2 should be less than 200 kΩ to minimize errors
in the output voltage caused by the ADJ pin input current. For
example, when R1 and R2 each equal 200 kΩ, the output voltage
is 2.44 V. The output voltage error introduced by the ADJ pin input
current is 2 mV or 0.08%, assuming a typical ADJ pin input
current of 10 nA at 25°C.
The ADP7104 uses the EN/UVLO pin to enable and disable
the VOUT pin under normal operating conditions. When
EN/UVLO is high, VOUT turns on, when EN is low, VOUT
turns off. For automatic startup, EN/UVLO can be tied to VIN.
The ADP7104 incorporates reverse current protections circuitry
that prevents current flow backwards through the pass element
when the output voltage is greater than the input voltage. A
comparator senses the difference between the input and output
voltages. When the difference between the input voltage and
output voltage exceeds 55 mV, the body of the PFET is switched
to V
OUT
and turned off or opened. In other words, the gate is
connected to VOUT.