NCP1597B Datasheet PDF - ON Semiconductor
| Part Number | NCP1597B | |
| Description | 2 A Synchronous Buck Regulator | |
| Manufacturers | 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, high−output−current,
synchronous PWM converter that integrates a low−resistance,
high−side P−channel MOSFET and a low−side N−channel 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 soft−start to limit inrush current.
Using the EN pin, shutdown supply current is reduced to 3 mA
maximum.
Other features include cycle−by−cycle current limiting;
short−circuit 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 High−Side Switching P−Channel MOSFET and
90 mW Low−Side N−Channel MOSFET
• Fixed 1 MHz Switching Frequency
• Cycle−by−Cycle Current Limiting
• Overtemperature Protection
• Internal Soft−Start
• Start−up with Pre−Biased 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 Pb−Free Devices
Applications
• DSP Power
• Hard Disk Drivers
• Computer Peripherals
• Home Audio
• Set−Top 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 = Pb−Free 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 &
(Pb−Free)
Reel
NCP1597BMNTXG DFN10 3000 / Tape &
(Pb−Free)
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
|
| |
 
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 high−side
P−channel MOSFET and low−side N−Channel MOSFET,
internal soft−start, and very low shutdown current. The
protection features of the NCP1597B include internal
soft−start, pulse−by−pulse 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 Soft−Start
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 high−side
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.
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 high−speed 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 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.
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
battery−powered 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 high−bandwidth current sense amplifier monitors the
current in the upper MOSFET. The current signal is required
by the PWM comparator, the pulse−by−pulse current
limiter.
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| Information | Total 9 Pages | |
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| Download | [ NCP1597B.PDF Datasheet ] | |
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