ncp1400a ON Semiconductor, ncp1400a Datasheet - Page 12

• Manufacturer Part Number: ncp1400a
• Description: 100ma, Fixed Frequency Pwm Step-up Micropower Switching Regulator
• Manufacturer: ON Semiconductor

Operation
regulators optimized for applications where power drain
must be minimized. These devices operate as fixed
frequency, voltage mode boost regulator and is designed to
operate in the discontinuous conduction mode. Potential
applications include low powered consumer products and
battery powered portable products.
voltage−mode PWM DC−DC converters, and consist of
soft−start circuit, feedback resistor, reference voltage,
oscillator, loop compensation network, PWM control
circuit, current limit circuit and power switch. Due to the
on−chip feedback resistor and loop compensation network,
the system designer can get the regulated output voltage
from 1.8 V to 5.0 V with a small number of external
components. The quiescent current is typically 32 mA
(V
when the chip is disabled (V
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.
Oscillator
accuracy of "20% and with low temperature coefficient of
0.11%/°C. Figures 16 and 17 illustrate oscillator frequency
versus temperature.
Regulated Converter Voltage (V
This is trimmed to a selected voltage from 1.8 V to 5.0 V
range in 100 mV steps with an accuracy of "2.5%.
Note: When the duty cycle is less than about 12%, the
regulator will skip switching cycles to maintain high
efficiency at light loads. The regulated output will be raised
by 3 to 4% under this condition.
The NCP1400A series are monolithic power switching
The NCP1400A series are low noise fixed frequency
There is a soft−start circuit in NCP1400A. When power is
The oscillator frequency is internally set to 180 kHz at an
The V
OUT
= 2.7 V), and can be further reduced to about 1.5 mA
OUT
is set by an internal feedback resistor network.
CE
t 0.3 V).
OUT
)
DETAILED OPERATING DESCRIPTION
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NCP1400A
12
Compensation
conduction mode. An internal compensation circuit was
designed to guarantee stability over the full input/output
voltage and full output load range. Stability cannot be
guaranteed in continuous conduction mode.
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 PWM controller
block to terminate the output 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 150 nA pull−up current source 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.
Important: DO NOT apply a voltage between 0.3 V to
0.9 V to pin CE as this voltage will place the IC into an
undefined state and the IC may drain excessive current
from the supply.
The device is designed to operate in discontinuous
The NCP1400A series utilizes cycle−by−cycle current
The voltage across the output MOSFET is monitored and
The NCP1400A series offer IC shutdown mode by chip