AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 24

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

AN2433/D
24
Input Power
Figure 20. Typical Step-down Switching Voltage Regulator Schematic With External MOSFET
Figure 19. Typical Step-down Switching Voltage Regulator Schematic With Internal MOSFET
Input Power
+
Input Bypass
5uF to 100uF
+
Input Bypass
5uF to 100uF
1
Figure 20
external MOSFET power device.
In summary, designing a power supply for 3.3 V microcontroller systems
requires looking at the system as a whole. Power requirements of the system
will dictate if a linear or switching voltage regulator will satisfy the system’s
power requirements. Most systems will have 3.3 and 5 V logic mixed in them.
Deriving small amounts of current for the 3.3 V portion of the system from the
5 V regulated power supply with a linear voltage regulator is a simple choice.
In the case where higher amounts of power are necessary for the 3.3 V portion
of the system, a close look at a switching voltage regulator will be prudent. If
the system only has the requirement for a 3.3 V power supply, the components
in this document will suffice for those needs as well.
Self Contained Switcher
VIN
1
Freescale Semiconductor, Inc.
VIN
For More Information On This Product,
Switcher
OUT
Vfb
Pdrive
Vfb
shows a basic schematic for a switching voltage regulator using an
8
3
5V to 3V Design Considerations
8
3
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Inductor
Inductor
+
10uF to
1000uF
Output Bypass
+
10uF to
1000uF
Output Bypass
Small bypass Capacitors
100pF to 1000pf
Small bypass Capacitors
100pF to 1000pf
3.3 Volt output
MOTOROLA
3.3 Volt output