Datasheet

Data Sheet ADP1752/ADP1753
Rev. F | Page 11 of 20
THEORY OF OPERATION
The ADP1752/ADP1753 are low dropout linear regulators that
use an advanced, proprietary architecture to provide high power
supply rejection ratio (PSRR) and excellent line and load transient
response with only a small 4.7 µF ceramic output capacitor.
Both devices operate from a 1.6 V to 3.6 V input rail and
provide up to 0.8 A of output current. Supply current in
shutdown mode is typically 2 µA.
UVLO
VOUTVIN
SENSE
SS
SHORT-CIRCUIT
AND THERMAL
PROTECTION
R1
0.5V
REF
R2
SHUTDOWN
EN
PG
GND
ADP1752
REVERSE POLARITY
PROTECTION
PG
DETECT
0.9µA
07718-019
Figure 24. ADP1752 Internal Block Diagram
UVLO
VOUTVIN
ADJ
SS
SHORT-CIRCUIT
AND THERMAL
PROTECTION
0.5V
REF
SHUTDOWN
EN
PG
GND
ADP1753
REVERSE POLARITY
PROTECTION
PG
DETECT
0.9µA
07718-020
Figure 25. ADP1753 Internal Block Diagram
Internally, the ADP1752/ADP1753 consist of a reference, an error
amplifier, a feedback voltage divider, and a PMOS pass transistor.
Output current is delivered via the PMOS pass transistor, 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 ADP1752 is available in seven fixed output voltage options
between 0.75 V and 2.5 V. The ADP1752 allows for connection
of an external soft start capacitor that controls the output voltage
ramp during startup. The ADP1753 is the adjustable version
with an output voltage that can be set to a value between 0.75 V
and 3.3 V by an external voltage divider. Both devices are con-
trolled by an enable pin (EN).
SOFT START FUNCTION (ADP1752/ADP1753)
For applications that require a controlled startup, the ADP1752/
ADP1753 provide a programmable soft start function. The
programmable soft start is useful for reducing inrush current
upon startup and for providing voltage sequencing. To implement
soft start, connect a small ceramic capacitor from SS to GND.
Upon startup, a 0.9 µA current source charges this capacitor.
The ADP1752/ADP1753 start-up output voltage is limited by
the voltage at SS, providing a smooth ramp-up to the nominal
output voltage. The soft start time is calculated as follows:
t
SS
= V
REF
× (C
SS
/I
SS
) (1)
where:
t
SS
is the soft start period.
V
REF
is the 0.5 V reference voltage.
C
SS
is the soft start capacitance from SS to GND.
I
SS
is the current sourced from SS (0.9 µA).
When the ADP1752/ADP1753 are disabled (using EN), the soft
start capacitor is discharged to GND through an internal 100 Ω
resistor.
2.50
0
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
0 2 4 6 8 10
VOLTAGE (V)
TIME (ms)
EN
1nF
4.7nF
10nF
07718-021
Figure 26. V
OUT
Ramp-Up with External Soft Start Capacitor