ncp1597 ON Semiconductor, ncp1597 Datasheet - Page 5

• Manufacturer Part Number: ncp1597
• Description: 1 Mhz, 2.0 A Synchronous Buck Regulator
• Manufacturer: ON Semiconductor

Overview
incorporates all the control and protection circuitry
necessary to satisfy a wide range of applications. The
NCP1597/A employs current mode control to provide fast
transient response, simple compensation, and excellent
stability. The features of the NCP1597/A include a precision
reference, fixed 1 MHz switching frequency,
transconductance error amplifier, an integrated high−side
P−channel MOSFET and low−side N−Channel MOSFET,
internal soft−start, and very low shutdown current. The
protection features of the NCP1597/A include internal
soft−start, pulse−by−pulse current limit, hiccup mode
short−circuit protection, and thermal shutdown.
Reference Voltage
allows output voltages as low as 0.8 V. The tolerance of the
internal reference is guaranteed over the entire operating
temperature range of the controller. The reference voltage is
trimmed using a test configuration that accounts for error
amplifier offset and bias currents.
Oscillator Frequency
frequency range is 1 MHz with $13% variation.
Transconductance Error Amplifier
is to regulate the converter’s output voltage using a resistor
divider connected from the converter’s output to the FB pin
of the controller, as shown in the applications Schematic. A
series RC compensation network must be connected from
the error amplifier’s output (COMP pin) to GND to stabilize
the converter. In some applications, a lower value capacitor
may be connected from the COMP pin to GND to reduce the
loop gain at higher frequencies. However, if this capacitor
is too large the phase margin of the converter will be
reduced. If a Fault occurs, the COMP pin is immediately
pulled to GND and PWM switching is inhibited.
Internal Soft−Start
circuit is used to ramp up the reference voltage from 0 V to
its final value linearly. The internal soft start time is 1 ms
typically.
Output MOSFETs
P−channel and low−side N−channel MOSFETs capable of
delivering up to 2.0 A of current. When the controller is
disabled or during a Fault condition, the controller’s output
stage is tri−stated by turning OFF both the upper and lower
MOSFETs.
The NCP1597/A is a synchronous PWM controller that
The NCP1597/A incorporates an internal reference that
A fixed precision oscillator is provided. The oscillator
The transconductance error amplifier’s primary function
To limit the startup inrush current, an internal soft start
The NCP1597/A includes low R
DS(on)
, both high−side
DETAILED DESCRIPTION
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a
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Adaptive Dead Time Gate Driver
required between the low side drive signal and high side
drive signal to avoid shoot through. During the dead time,
the body diode of the low side FET freewheels the current.
The body diode has much higher voltage drop than that of
the MOSFET, which reduces the efficiency significantly.
The longer the body diode conducts, the lower the
efficiency. In NCP1597/A, the drivers and MOSFETs are
integrated in a single chip. The parasitic inductance is
minimized. Adaptive dead time control method is used in
NCP1597/A to prevent the shoot through from happening
and minimizing the diode conduction loss at the same time.
Pulse Width Modulation
as low as 50 ns, is included in the NCP1597/A. The inverting
input of the comparator is connected to the output of the
error amplifier. The non−inverting input is connected to the
the current sense signal. At the beginning of each PWM
cycle, the CLK signal sets the PWM flip−flop and the upper
MOSFET is turned ON. When the current sense signal rises
above the error amplifier’s voltage then the comparator will
reset the PWM flip−flop and the upper MOSFET will be
turned OFF.
high side FET will be ON all the time (100% duty cycle) and
the part operates in a low dropout mode
Low Dropout Mode operation
each other, the NCP1597/A enters into LDO (low dropout)
mode. The high side FET is turned on 100% for one or more
cycles. With further decreasing of input voltage, the high
side FET will be on completely. In this case, the converter
offers a low voltage difference. This is particularly useful in
battery−powered applications to achieve longest operation
time by taking full advantage of the whole battery voltage
range.
Power Save Mode
power save mode operation automatically. During power
save mode, the converter skips switching and operates with
reduced frequency, which minimizes the quiescent current
and maintain high efficiency.
Current Sense Amplifier
current in the upper MOSFET. The current signal is required
by the PWM comparator, the pulse−by−pulse current
limiter, and the hiccup mode/over current counter.
In a synchronous buck converter, a certain dead time is
A high−speed PWM comparator, capable of pulse widths
When input and output voltage gets close to each other, the
When the input voltage and output voltage come close to
If the load current decreases, the converter will enter
A high−bandwidth current sense amplifier monitors the
.