NCP1402_06 ONSEMI [ON Semiconductor], NCP1402_06 Datasheet - Page 14

• Manufacturer Part Number: NCP1402_06
• Description: 200 mA, PFM Step−Up Micropower Switching Regulator
• Manufacturer: ONSEMI [ON Semiconductor]

DETAILED OPERATING DESCRIPTION
Operation
regulators optimized for applications where power drain
must be minimized. These devices operate as variable
frequency, voltage mode boost regulators and designed to
operate in continuous conduction mode. Potential
applications include low powered consumer products and
battery powered portable products.
voltage−mode DC−DC converters, and consist of Soft−Start
circuit, feedback resistor, reference voltage, oscillator, PFM
comparator, PFM control circuit, current limit circuit and
power switch. Due to the on−chip feedback resistor network,
the system designer can get the regulated output voltage
from 1.8 V to 5 V with a small number of external
components. The operating current is typically 30 mA
(V
when the chip is disabled (V
examining the block diagram in Figure 2. PFM comparator
monitors the output voltage via the feedback resistor. When
the feedback voltage is higher than the reference voltage, the
power switch is turned off. As the feedback voltage is lower
than reference voltage and the power switch has been off for
at least a period of minimum off−time decided by PFM
oscillator, the power switch is then cycled on for a period of
on−time also decided by PFM oscillator, or until current
limit signal is asserted. When the power switch is on, current
ramps up in the inductor, storing energy in the magnetic
field. When the power switch is off, the energy in the
magnetic field is transferred to output filter capacitor and the
load. The output filter capacitor stores the charge while the
inductor current is high, then holds up the output voltage
until next switching cycle.
Important: DO NOT apply a voltage between 0.3 V and 0.9 V to pin CE as this is the CE pin’s hyteresis voltage
The NCP1402 series are monolithic power switching
The NCP1402 series are low noise variable frequency
The NCP1402 operation can be best understood by
OUT
150
125
100
75
50
25
0
= 1.9 V), and can be further reduced to about 0.6 mA
0
5.0 V
3.3 V
3.0 V
2.7 V
range. Clearly defined output states can only be obtained by applying voltage out of this range.
Figure 57. NCP1402SNXXT1 No Load Input
1.9 V
1
Current vs. Input Voltage
V
in
2
, INPUT VOLTAGE (V)
CE
< 0.3 V).
3
NCP1402SNXXT1
L = 47 mH
I
T
O
4
A
= 0 mA
= 25°C
5
http://onsemi.com
NCP1402
6
14
Soft−Start
applied to the device, the Soft−Start circuit pumps up the
output voltage to approximately 1.5 V at a fixed duty cycle, the
level at which the converter can operate normally. What is
more, the startup capability with heavy loads is also improved.
Regulated Converter Voltage (V
This is trimmed to a selected voltage from 1.8 to 5.0 V range
in 100 mV steps with an accuracy of $2.5%.
Current Limit
limiting as a means of protecting the output switch
MOSFET from overstress and preventing the small value
inductor from saturation. Current limiting is implemented
by monitoring the output MOSFET current build−up during
conduction, and upon sensing an overcurrent conduction
immediately turning off the switch for the duration of the
oscillator cycle.
compared against a reference by the VLX limiter. When the
threshold is reached, a signal is sent to the PFM controller
block to terminate the power switch conduction. The current
limit threshold is typically set at 350 mA.
Enable / Disable Operation
enable pin (CE pin) to reduce current consumption. An
internal pullup resistor tied the CE pin to OUT pin by default
i.e. user can float the pin CE for permanent “On”. When
voltage at pin CE is equal or greater than 0.9 V, the chip will
be enabled, which means the regulator is in normal
operation. When voltage at pin CE is less than 0.3 V, the chip
is disabled, which means IC is shutdown.
300
200
100
400
There is a Soft−Start circuit in NCP1402. When power is
The V
The NCP1402 series utilizes cycle−by−cycle current
The voltage across the output MOSFET is monitored and
The NCP1402 series offer IC shut−down mode by chip
0
0
Figure 58. NCP1402SNXXT1 Maximum Output
OUT
is set by an internal feedback resistor network.
1.9 V
1
Current vs. Input Voltage
3.0 V
2.7 V
V
in
, INPUT VOLTAGE (V)
2
3.3 V
OUT
3
)
5.0 V
NCP1402SNXXT1
L = 47 mH
T
A
= 25°C
4
5