NCP59744
www.onsemi.com
8
APPLICATIONS INFORMATION
The NCP59744 dual−rail very low dropout voltage
regulator is using NMOS pass transistor for output voltage
regulation from V
IN
voltage. All the low current internal
controll circuitry is powered from the V
BIAS
voltage.
The use of an NMOS pass transistor offers several
advantages in applications. Unlike a PMOS topology
devices, the output capacitor has reduced impact on loop
stability. Vin to Vout operating voltage difference can be
very low compared with standard PMOS regulators in very
low Vin applications.
The NCP59744 offers programmable smooth monotonic
start-up. The controlled voltage rising limits the inrush
current what is advantageous in applications with large
capacitive loads. The Voltage Controlled Soft Start timing is
programmable by external Css capacitor value.
The Enable (EN) input is equipped with internal
hysteresis and deglitch filter.
Open Drain type Power Good (PG) output is available for
Vout monitoring and sequencing of other devices.
NCP59744 is a Adjustable linear regulator. The required
Output voltage can be adjusted by two external resistors.
Typical application schematics is shown in Figure 16.
Figure 16. Typical Application Schematics
V
OUT
+ 0.8
ǒ
1 ) R
1
ńR
2
Ǔ
Dropout Voltage
Because of two power supply inputs V
IN
and V
BIAS
and
one V
OUT
regulator output, there are two Dropout voltages
specified.
The first, the V
IN
Dropout voltage is the voltage
difference (V
IN
– V
OUT
) when V
OUT
starts to decrease by
percents specified in the Electrical Characteristics table.
V
BIAS
is high enough, specific value is published in the
Electrical Characteristics table.
The second, V
BIAS
dropout voltage is the voltage
difference (V
BIAS
– V
OUT
) when V
IN
and V
BIAS
pins are
joined together and V
OUT
starts to decrease.
Input and Output Capacitors
The device is designed to be stable for all available types
and values of output capacitors ≥ 2.2 mF. The device is also
stable with multiple capacitors in parallel, which can be of
any type or value.
In applications where low input supply impedance is
available (PCB inductance on Vin and/or Vbias as an
example) the recommended Cin and Cbias value is 1 mF or
greater. In order to avoid any excessive input voltage
transients caused i.e. by a sudden output short circuit
conditions the input capacitor value should be sized properly
for each particular application to counteract any input
inductance. For Vin of 5.5 V the recommended input
capacitance is 22 mF or greater. Ceramic or other low ESR
capacitors are recommended. For the best performance all
capacitors should be connected to the NCP59744 respective
pins directly in the device PCB copper layer, not through
vias having not negligible impedance.
Enable Operation
The enable pin will turn the regulator on or off. The
threshold limits are covered in the electrical characteristics
table in this data sheet. If the enable function is not to be used
then the pin should be connected to V
IN
or V
BIAS
.
Output Noise
When the NCP59744 device reaches the end of the
Soft−Start cycle, the Soft Start capacitor is switched to serve
as a Noise filtering capacitor.
Output Voltage Adjust
The output voltage can be adjusted from 0.8 V to 3.6 V
using resistors divider between the output and the FB input.
Recommended resistor values for frequently used voltages
can be found in the Table 6.
Programmable Soft−Start
The Soft-Start ramp time depends on the Soft Start
charging current I
SS,
Soft-Start capacitor value C
SS
and
internal reference voltage V
REF
.
The Soft –Start time can be calculated using following
equations:
t
ss
= C
SS
x (V
REF
/ I
SS
) [s, F,V,A]
or in more practical units
t
SS
= C
SS
x 0.8V / 0.44 = C
SS
x 1.82
where
t
ss
= Soft−Start time in miliseconds
C
SS
= Soft−Start capacitor value in nano Farads
Capacitor values for frequently used Soft-Start times can be
found in the Table 7.
The maximal recommended value of C
SS
capacitor is
15 nF. For higher C
SS
values the capacitor full discharging
before new Soft-Start cycle is not guaranteed.
Current Limitation
The internal Current Limitation circuitry allows the
device to supply the full nominal current and surges but
protects the device against Current Overload or Short.
Thermal Protection
Internal thermal shutdown (TSD) circuitry is provided to
protect the integrated circuit in the event that the maximum
junction temperature is exceeded. When TSD activated , the
regulator output turns off. When cooling down under the low
