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PDF NCP1597B Data sheet ( Hoja de datos )

Número de pieza NCP1597B
Descripción 2 A Synchronous Buck Regulator
Fabricantes ON Semiconductor 
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NCP1597B
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1 MHz, 2 A Synchronous
Buck Regulator
The NCP1597B is a fixed 1 MHz, highoutputcurrent,
synchronous PWM converter that integrates a lowresistance,
highside Pchannel MOSFET and a lowside Nchannel MOSFET.
The NCP1597B utilizes current mode control to provide fast transient
response and excellent loop stability. It regulates input voltages from
4.0 V to 5.5 V down to an output voltage as low as 0.8 V and is able to
supply up to 2 A.
The NCP1597B has features including fixed internal switching
frequency (FSW), and an internal softstart to limit inrush current.
Using the EN pin, shutdown supply current is reduced to 3 mA
maximum.
Other features include cyclebycycle current limiting;
shortcircuit protection, low dropout mode, power saving mode and
thermal shutdown.
Features
Input Voltage Range: from 4.0 V to 5.5 V
Internal 140 mW HighSide Switching PChannel MOSFET and
90 mW LowSide NChannel MOSFET
Fixed 1 MHz Switching Frequency
CyclebyCycle Current Limiting
Overtemperature Protection
Internal SoftStart
Startup with PreBiased Output Load
Adjustable Output Voltage Down to 0.8 V
Power Saving Mode During Light Load
Low Dropout Mode Operation to Extend the Battery Life
These are PbFree Devices
Applications
DSP Power
Hard Disk Drivers
Computer Peripherals
Home Audio
SetTop Boxes
Networking Equipment
LCD TV
Wireless and DSL/Cable Modem
USB Power Devices
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DFN10
CASE 485C
MARKING
DIAGRAM
1597B
ALYWG
G
1597B = Specific Device Code
A = Assembly Location
L = Wafer Lot
Y = Year
W = Work Week
G = PbFree Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
EN
VCC
VCCP
AGND
FB
1
2
3
4
5
10 PGND
9 PGND
8 LX
7 LX
6 NC
(Top View)
ORDERING INFORMATION
Device
Package
Shipping
NCP1597BMNTWG DFN10 3000 / Tape &
(PbFree)
Reel
NCP1597BMNTXG DFN10 3000 / Tape &
(PbFree)
Reel
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications
Brochure, BRD8011/D.
This document contains information on a product under development. ON Semiconductor
reserves the right to change or discontinue this product without notice.
© Semiconductor Components Industries, LLC, 2009
October, 2009 Rev. P0
1
Publication Order Number:
NCP1597B/D

1 page




NCP1597B pdf
NCP1597B
DETAILED DESCRIPTION
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Overview
The NCP1597B is a synchronous PWM controller that
incorporates all the control and protection circuitry
necessary to satisfy a wide range of applications. The
NCP1597B employs current mode control to provide fast
transient response, simple compensation, and excellent
stability. The features of the NCP1597B include a precision
reference, fixed 1 MHz switching frequency, a
transconductance error amplifier, an integrated highside
Pchannel MOSFET and lowside NChannel MOSFET,
internal softstart, and very low shutdown current. The
protection features of the NCP1597B include internal
softstart, pulsebypulse current limit, and thermal
shutdown.
Reference Voltage
The NCP1597B incorporates an internal reference that
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
A fixed precision oscillator is provided. The oscillator
frequency range is 1 MHz with $13% variation.
Transconductance Error Amplifier
The transconductance error amplifier’s primary function
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. If
a Fault occurs, the COMP pin is immediately pulled to GND
and PWM switching is inhibited.
Internal SoftStart
To limit the startup inrush current, an 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
The NCP1597B includes low RDS(on), both highside
Pchannel and lowside Nchannel 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 tristated by turning OFF both the upper and lower
MOSFETs.
Adaptive Dead Time Gate Driver
In a synchronous buck converter, a certain dead time is
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 NCP1597B, the drivers and MOSFETs are
integrated in a single chip. The parasitic inductance is
minimized. Adaptive dead time control method is used in
NCP1597B to prevent the shoot through from happening
and minimizing the diode conduction loss at the same time.
Pulse Width Modulation
A highspeed PWM comparator, capable of pulse widths
as low as 50 ns, is included in the NCP1597B. The inverting
input of the comparator is connected to the output of the
error amplifier. The noninverting input is connected to the
the current sense signal. At the beginning of each PWM
cycle, the CLK signal sets the PWM flipflop 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 flipflop and the upper MOSFET will be
turned OFF.
When input and output voltage gets close to each other, the
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
When the input voltage and output voltage come close to
each other, the NCP1597B 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
batterypowered applications to achieve longest operation
time by taking full advantage of the whole battery voltage
range.
Power Save Mode
If the load current decreases, the converter will enter
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
A highbandwidth current sense amplifier monitors the
current in the upper MOSFET. The current signal is required
by the PWM comparator, the pulsebypulse current
limiter.
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