AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 23

• Manufacturer Part Number: AN2433
• Description: 5V to 3V Design Considerations
• Manufacturer: Freescale Semiconductor / Motorola

Switching Voltage
Regulators
MOTOROLA
Switching regulation is accomplished by the control of the on-time and off-time
ratio of the pass transistor in a fast switching technique. Therefore, the
switching voltage regulator operates the power device in a full-on or full-off
mode. This control technique is known as pulse width modulation (PWM) and
is commonly working at switching frequency above 20 kHz.
Switching voltage regulators have a distinct advantage over linear ones in that
their efficiencies can exceed 90%. This operation mode results in much lower
power being dissipated across the power device. Switching power supply
regulators become very cost effective when used for output powers greater
then 10 W. The disadvantage of a switching voltage regulator is that it requires
more components, including magnetics, than a linear design and is less
forgiving from a printed circuit board layout and grounding prospective (most
switching regulators do not provide isolation between the input and output
circuits). Similar to linear regulators, a switching regulator in a typical system is
powered by an input voltage that is higher than what is required to be regulated
(output voltage). In a typical 3.3 V only system, its power supply will use some
voltage source greater than 3.3 V and then regulate it down to 3.3 V. A step-
down or buck converter will be used in the application. Input bulk capacitors
and output bypass capacitors used in switching design follow the same
configuration as those in linear voltage regulators.
The following table is a partial list of switching voltage regulators appropriate
for use with 3.3 V circuits from a few manufacturers:
Figure 19
an internal MOSFET power device.
National Semiconductor
National Semiconductor
National Semiconductor
National Semiconductor
Freescale Semiconductor, Inc.
ON Semiconductor
ON Semiconductor
ON Semiconductor
Linear Technology
Linear Technology
Linear Technology
For More Information On This Product,
Manufacturer
shows a basic schematic for a switching voltage regulator containing
5V to 3V Design Considerations
Go to: www.freescale.com
LM2575D2T-3.3
LM2576D2T-3.3
Part Number
LM2574-3.3
LM1575-3.3
LM2655-3.3
LM2576-3.3
MC33163P
LTC1701
LTC1878
LTC1772
Current
500mA
500mA
600mA
Output
3.6A
2.5A
2.5A
Power Supplies for Low Voltage Systems
1A
3A
1A
3A
Ext. MOSFET Rqd.
Yes
Yes
No
No
No
No
No
No
No
No
AN2433/D
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