AMS2576
Application Information
It is required that VIN must be bypassed with at
least a 100µF electrolytic capacitor for stability.
Also, it is strongly recommended the capacitor’s
leads must be dept short, and located near the
regulator as possible.
For low operating temperature range, for example,
below -25℃, the input capacitor value may need
to be larger. This is due to the reason that the
be located close to the
AMS2576
using short leads
and short printed circuit traces as possible.
capacitance value of electrolytic capacitors
decreases and the ESR increases with
lower temperatures and ago. Paralleling a
ceramic or solid tantalum capacitor will
increase the regulator stability at cold
temperatures.
Output Capacitor
An output capacitor is also required to filter
the output voltage and is needed for loop
stability. The capacitor should be located
near the
AMS2576
using short PC board traces.
To satisfy the need to fast switching speed and
low forward voltage drop, Schottky diodes are
widely used to provide the best efficiency,
especially in low output voltage switching
regulators (less than 5V). Beside, Fast-Recovery,
high-efficiency, or ultra fast recovery diodes are
also suitable. But some types with an abrupt
turn-off characteristic may cause instability and
EMI problems. A fast recovery diode with soft
recovery characteristics is better choice.
Inductor Selection
The
AMS2576
can be used for either continuous or
Low ESR types capacitors are recommended for
low output ripple voltage and good stability.
Generally, low value or low voltage (less than12V)
electrolytic capacitors usually have higher ESR
numbers, For example, the lower capacitor
values (220µF - 1000µF) will yield typically 50mV
to 150mV of output ripple voltage, while
larger-value capacitors will reduce the ripple to
approximately 20mV to 50mV.
The amount of output ripple voltage is primarily a
function of the ESR (Equivalent Series
Resistance) of the output capacitor and the
amplitude of the inductor ripple current (△IIND)
Output Ripple Voltage = (
△
IIND) x (ESR of
COUT) Some capacitors called “high-frequency”,
“low-inductance”, or “low-ESR” are recommended
to use to further reduce the output ripple voltage
to 10mV or 20mV. However, very low ESR
capacitors, such as tantalum capacitors, should
be carefully evaluated.
Catch Diode
This diode is required to return path for the
inductor current when the switch is off. It should
Advanced Monolithic Systems
discontinuous modes of operation. Each mode
has distinctively different operating characteristics,
which can affect the regulator performance and
requirements.
With relatively heavy load currents, the circuit
operates in the continuous mode (inductor current
always flowing). But under light Load conditions,
the circuit will be force to the discontinuous mode
(inductor current falls to zero for a period of time).
For light loads (less than approximately 300mA) it
may be desirable to operate the regulator in the
discontinuous mode, primarily because of the
lower inductor values required for the
discontinuous mode.
Indictors are available in different styles such as
pot core, toroid, E-frame, bobbin core, et., as well
as different core materials such as ferrites and
powdered iron. The least expensive, the bobbin
core type, consists of wire wrapped on a ferrite
rod core. This type of construction makes for an
inexpensive inductor, but since the magnetic flux
is not completely contained within the core, it
generates more electromagnetic interference
(EMI). This EMI can cause problems in sensitive
circuits, or can give incorrect scope readings
because of induced voltage in the scope probe.
An inductor should not be operated beyond its
maximum rated current because it may saturate.
When an inductor begins to saturate, the
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