AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 3

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

Mixed Voltage Systems
MOTOROLA
Timer
Timer
ADC
ADC
IRQ
IRQ
SCI
SCI
I/O
I/O
Flash / ROM
Flash / ROM
Memory
Memory
RAM
RAM
CPU
CPU
Figure 1. 3V and 5V parts in a dual voltage design
In a mixed voltage application, parts must be able to translate from one voltage
to another. A typical scenario is shown in
supply, the EEPROM memory and the various I/O parts are powered at 5V, and
a voltage converter provides the interfacing between the two sub-systems.
The disadvantages of mixed voltage systems are mainly due to the increased
number of components required for interfacing parts operating at different
voltages. Possibly, also, the need for multiple voltage power supplies, which in
turn produces additional current consumption.
The additional parts required in a mixed voltage system increase the overall
system power dissipation, mainly due to the power absorbed by the interfacing
components. Also, the output high level (V
the current consumption of the driven part.
For example when using ACT or HCT logic for 3V to 5V translation, if a TTL-
compatible 5V CMOS device is driven by voltages lower than V
is an additional current consumption that needs to be taken into account: the
leakage current from V
is negligible if the applied input voltage approaches V
voltage applied moves away from the full power rail values, the p-channel and
the n-channel transistors that form the typical CMOS input stage of a device will
Freescale Semiconductor, Inc.
For More Information On This Product,
5V to 3V Design Considerations
3 Volt Bus
3 Volt Bus
Go to: www.freescale.com
DD
to V
SS
(Ground) of the receiving device, I
5 Volt Bus
5 Volt Bus
Figure
OH
) of the driving device influences
1, where an MCU uses a 3V
DD
LEDs, Relays,
LEDs, Relays,
or V
Other I/Os
Other I/Os
EEPROM
EEPROM
Crossing
Crossing
Buttons
Buttons
Speed
Speed
Motor
Motor
Motor
Motor
Mixed Voltage Systems
Drive
Drive
Zero
Zero
SS
DD
. But if the
– 2.1V there
DD
AN2433/D
. I
DD
3