NCP1410_05 ONSEMI [ON Semiconductor], NCP1410_05 Datasheet - Page 10

• Manufacturer Part Number: NCP1410_05
• Description: 250 mA Sync-Rect PFM Step-Up DC-DC Converter with Low-Battery Detector
• Manufacturer: ONSEMI [ON Semiconductor]

Low−Battery Detection
the low−battery detection function. When pin 2 (LBI) is at
a voltage, which can be defined by a resistor divider from the
battery voltage, lower than the internal reference voltage,
1.190 V, the comparator output will cause a 50 Ohm low side
switch to be turned ON. It will pull down the voltage at pin
3 (LBO) which has a hundreds kilo−Ohm of pull−high
resistance. If the pin 2 voltage is higher than 1.190 V +
30 mV, the comparator output will cause the 50 Ohm low
side switch to be turned OFF, pin 3 will become high
impedance, and its voltage will be pulled high by the
external resistor.
APPLICATIONS INFORMATION
Output Voltage Setting
external feedback network comprised of R
the relationship is given by:
resistors respectively.
Low Battery Detect Level Setting
determined by the external divider network comprised of
R
resistors respectively.
Inductor Selection
with a 22 mH inductor at V
output current up to 250 mA. For other input/output
requirements, inductance in the range 10 mH to 47 mH can be
used according to end application specifications. Selecting
an inductor is a compromise between output current
capability and tolerable output voltage ripple. Of course, the
first thing we need to obey is to keep the peak inductor
current below its saturation limit at maximum current and
the I
rule of thumb, low inductance values supply higher output
current, but also increase the ripple at output and reducing
efficiency, on the other hand, high inductance values can
improve output ripple and efficiency, however it also limit
the output current capability at the same time. One other
parameter of the inductor is its DC resistance, this resistance
can introduce unwanted power loss and hence reduce overall
efficiency, the basic rule is selecting an inductor with lowest
DC resistance within the board space limitation of the end
application.
LB1
A comparator with 30 mV hysteresis is applied to perform
The output voltage of the converter is determined by the
where R
The Low Battery Detect Voltage of the converter is
where R
The NCP1410 is tested to produce optimum performance
LIM
and R
of the device. In NCP1410, I
LB1
F2
LB2
V OUT + 1.190 V
V LB + 1.190 V
and R
and R
and the relationship is given by:
F1
LB2
are the upper and lower feedback
are the upper and lower divider
IN
= 3 V, V
1 )
1 )
R LB1
R LB2
OUT
LIM
R FB1
R FB2
= 3.3 V supplying
is set at 1 A. As a
FB1
and R
FB2
http://onsemi.com
and
NCP1410
10
Capacitors Selection
the input and output terminals sees pulsating voltage/current
waveforms. The currents flowing into and out of the
capacitors multiplying with the Equivalent Series
Resistance (ESR) of the capacitor producing ripple voltage
at the terminals. During the syn−rect switch off cycle, the
charges stored in the output capacitor is used to sustain the
output load current. Load current at this period and the ESR
combined and reflected as ripple at the output terminals. For
all cases, the lower the capacitor ESR, the lower the ripple
voltage at output. As a general guide line, low ESR
capacitors should be used. Ceramic capacitors have the
lowest ESR, but low ESR tantalum capacitors can also be
used as a cost effective substitute.
Optional Startup Schottky Diode for Low Battery
Voltage
required, however, in case you are intended to operate the
device close to 1 V level, a Schottky diode connected
between the LX and OUT pins as shown in Figure 27 can
help during startup of the converter. The effect of the
additional Schottky was shown in Figure 8.
PCB Layout Recommendations
mode power conversion. Careful PCB layout can help to
minimize ground bounce, EMI noise and unwanted
feedback that can affect the performance of the converter.
Hints in the following paragraphs, can be used as guidelines
in most situations.
Grounding
output power return ground, the input power return ground
and the device power ground together at one point. All high
current running paths must be thick enough for current
flowing through and producing insignificant voltage drop
along the path. Feedback signal path must be separated with
the main current path and sensing directly at the anode of the
output capacitor.
In all switching mode boost converter applications, both
In general operation, no external Schottky diode is
Good PCB layout plays an important role in switching
Star−ground connection should be used to connect the
Figure 27. Schottky Device Between LX and
NCP1410
OUT
L
LX
OUT Pins
MBR0502
C
OUT
V
OUT