Inductor Design

Filter inductor design constraints
Objective:
Design inductor having a given inductance L,
which carries worst-case current Imax without saturating,
and which has a given winding resistance R, or,
equivalently

Index
- Assumed filter inductor geometry
- Constraint: maximum flux density
- Constraint: Inductance
- Constraint: Winding area
- The window utilization factor Ku
- also called the “fill factor”
- Winding resistance
- The core geometrical constant Kg
- Core geometrical constant Kg
- A step-by-step procedure

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INDUCTOR DESIGN in SWITCHING REGULATORS
Technical Bulletin
Better efficiency, reduced size, and lower costs have combined to
make the switching regulator a viable method for converting unfiltered
DC input voltages into regulated DC outputs. This brochure describes
the switching regulator and presents design information. In particular,
MAGNETICS® Ferrite and Molypermalloy Powder cores used for
the power inductor are highlighted.

DESCRIPTION

A typical circuit consists of three parts: transistor switch, diode
clamp, and an LC filter. An unregulated DC voltage is applied to
the transistor switch which usually operates at a frequency of 1 to 50
kilohertz. When the switch is ON, the input voltage, Ein, is applied to
the LC filter, thus causing current through the inductor to increase;
excess energy is stored in the inductor and capacitor to maintain
output power during the OFF time of the switch. Regulation is
obtained by adjusting the ON time, ton, of the transistor switch, using
a feedback system from the output. The result is a regulated DC
output,

index
- COMPONENT SELECTION
- INDUCTOR DESIGN
- CORE SELECTION PROCEDURE
- DESIGN EXAMPLE

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Switching Regulator Inductor Design
COILTRONICS Application Notes Magnetics
In switching regulator applications the inductor is used as
an energy storage device, when the semiconductor
switch is on the current in the inductor ramps up and
energy is stored. When the switch turns off this energy is
released into the load, the amount of energy stored is
given by;
Energy = 1/2L.I2 (Joules) (1)
Where L is the inductance in Henrys and I is the peak
value of inductor current.
The amount by which the current changes during a
switching cycle is known as the ripple current and is
defined by the equation;
V1 = L.di/dt (2)
Where V1 is the voltage across the inductor, di is the
ripple current and dt is the duration for which the voltage
is applied. From this we can see that the value of ripple
current is dependent upon the value of inductance.
Choosing the correct value of inductance is important in
order to obtain acceptable inductor and output capacitor
sizes and sufficiently low output voltage ripple.

Index
- Inductor Selection for Buck Converters
- Inductor Selection for Boost Converters
- Inductor Selection for Buck-Boost Converters

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Gate Drive for step-down switching regulator

Switching Regulator by Hysteretic PFET Buck Controller

LM3485/LM3485Q
Hysteretic PFET Buck Controller
General Description
The LM3485 is a high efficiency PFET switching regulator
controller that can be used to quickly and easily develop a
small, low cost, switching buck regulator for a wide range of
applications. The hysteretic control architecture provides for
simple design without any control loop stability concerns using
a wide variety of external components. The PFET architecture
also allows for low component count as well as ultralow
dropout, 100% duty cycle operation. Another benefit is
high efficiency operation at light loads without an increase in
output ripple.
Current limit protection is provided by measuring the voltage
across the PFET’s RDS(ON), thus eliminating the need for a
sense resistor. The cycle-by-cycle current limit can be adjusted
with a single resistor, ensuring safe operation over a range
of output currents.

Features
- Easy to use control methodology
- No control loop compensation required
- 4.5V to 35V wide input range
- 1.242V to VIN adjustable output range
- High Efficiency 93%
- ฑ1.3% (ฑ2% over temp) internal reference
- 100% duty cycle
- Maximum operating frequency > 1MHz
- Current limit protection
- MSOP-8
- LM3485Q is AEC-Q100 Grade 1 qualified and are
manufactured on an Automotive Grade Flow

LM3485 Datasheet Pdf

Circuit PCB

5A switching regulator with Adjustable Current Limit

Switching Regulator by High-Side N-Channel Controller

LM3477
High Efficiency High-Side N-Channel Controller for
Switching Regulator
Description
The LM3477/A is a high-side N-channel MOSFET switching
regulator controller. It can be used in topologies requiring a
high side MOSFET such as buck, inverting (buck-boost) and
zeta regulators. The LM3477/A’s internal push pull driver
allows compatibility with a wide range of MOSFETs. This, the
wide input voltage range, use of discrete power components
and adjustable current limit allows the LM3477/A to be optimized
for a wide variety of applications.
The LM3477/A uses a high switching frequency of 500kHz to
reduce the overall solution size. Current-mode control requires
only a single resistor and capacitor for frequency
compensation. The current mode architecture also yields
superior line and load regulation and cycle-by-cycle current
limiting. A 5µA shutdown state can be used for power savings
and for power supply sequencing. Other features include
internal soft-start and output over voltage protection.
The internal soft-start reduces inrush current. Over voltage
protection is a safety feature to ensure that the output voltage
stays within regulation.
The LM3477A is similar to the LM3477. The primary difference
between the two is the point at which the device
transitions into hysteretic mode. The hysteretic threshold of
the LM3477A is one-third of the LM3477.

Features
- 500kHz switching frequency
- Adjustable current limit
- 1.5% reference
- Thermal shutdown
- Frequency compensation optimized with a single
capacitor and resistor
- Internal softstart
- Current mode operation
- Undervoltage lockout with hysteresis
- 8-lead Mini-SO8 (MSOP-8) package

LM3477 Datasheet Pdf

Switching Regulator by Hysteretic PFET Buck Controller

5A switching regulator with Adjustable Current Limit

LM2679
5A Step-Down Voltage Regulator
with Adjustable Current Limit

Description
The LM2679 series of regulators are monolithic integrated
circuits which provide all of the active functions for a stepdown
(buck) switching regulator capable of driving up to 5A
loads with excellent line and load regulation characteristics.
High efficiency (>90%) is obtained through the use of a low
ON-resistance DMOS power switch. The series consists of
fixed output voltages of 3.3V, 5V and 12V and an adjustable
output version.
The SIMPLE SWITCHER concept provides for a complete
design using a minimum number of external components. A
high fixed frequency oscillator (260KHz) allows the use of
physically smaller sized components. A family of standard
inductors for use with the LM2679 are available from several
manufacturers to greatly simplify the design process.
Other features include the ability to reduce the input surge
current at power-ON by adding a softstart timing capacitor to
gradually turn on the regulator. The LM2679 series also has
built in thermal shutdown and resistor programmable current
limit of the power MOSFET switch to protect the device and
load circuitry under fault conditions. The output voltage is
guaranteed to a ±2% tolerance. The clock frequency is
controlled to within a ±11% tolerance.

Features
- Efficiency up to 92%
- Simple and easy to design with (using off-the-shelf
external components)
- Resistor programmable peak current limit over a range
of 3A to 7A.
- 120 mΩ DMOS output switch
- 3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
- ±2%maximum output tolerance over full line and load
conditions
- Wide input voltage range: 8V to 40V
- 260 KHz fixed frequency internal oscillator
- Softstart capability
- −40 to +125°C operating junction temperature range

LM2679 Datasheet Pdf

dual step-down switching regulator circuit

dual step-down switching regulator circuit

The output voltages
OUT1 0.9 V to 5.5 V
OUT2 0.9 V to 3.3 V

PM6680
No Rsense dual step-down controller with adjustable voltages
for notebook system power

Description
PM6680 is a dual step-down controller
specifically designed to provide extremely high
efficiency conversion, with lossless current
sensing technique. The constant on-time
architecture assures fast load transient response
and the embedded voltage feed-forward provides
nearly constant switching frequency operation. An
embedded integrator control loop compensates
the DC voltage error due to the output ripple.
Pulse skipping technique increases efficiency at
very light load. Moreover a minimum switching
frequency of 33kHz is selectable to avoid audio
noise issues. The PM6680 provides a selectable
switching frequency, allowing three different
values of switching frequencies for the two
switching sections.

Features
- 6 V to 28 V input voltage range
- Adjustable output voltages
- 5 V always voltage available deliver 100 mA
peak current
- 1.237 V ± 1% reference voltage available
- Lossless current sensing using low side
MOSFETs RDS(on)
- Negative current limit
- Soft-start internally fixed at 2ms
- Soft output discharge
- Latched OVP and UVP
- Selectable pulse skipping at light loads
- Selectable minimum frequency (33 kHz) in
pulse skip mode
- 4 mW maximum quiescent power
- Independent power good signals
- Output voltage ripple compensation

PM6680 Datasheet Pdf

10A stepdown switching regulator circuit