AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 12

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

AN2433/D
Interfacing to
Microcontroller
Outputs
3V CMOS Output to
5V TTL Input
3V CMOS to 5V
CMOS
12
And typically, for the high current I/O Ports, the sink current capability is as
follows:
@ V
@ V
For the 3V only MC68HC9S08GB60 MCU the current sink and source
specifications, at full drive, are as follows:
Therefore, it can be concluded that moving from 5V to 3V technology will not
jeopardise the output high voltage and low voltage provided by the
microcontrollers. For some applications the sourcing and sinking capability
required might be quite demanding, therefore, as lower V
effect of reducing the current sourcing and sinking capability of the devices,
some signal amplification could provide assistance. Some examples will be
illustrated in the following paragraphs.
Interfacing 3V CMOS devices to 5V TTL devices causes no problems because
the 3V device outputs have enough margin to drive 5V TTL-device inputs. For
other technologies or voltage levels, such as 3V CMOS to 5V CMOS, some
level shifting may be necessary.
The maximum input voltage level permissible for TTL technology for a logical
"0", V
must be
required for interfacing.
Interfacing a 3V MCU output to a 5V CMOS input requires extra drive to prevent
current leakage.
For CMOS technology the input switching levels are defined as:
V
Therefore for 5V V
and the minimum input level for logical "1" must be
A simple resistor and diode are sufficient to provide a 0.6V upward level shift of
the MCU’s output voltage, see
the 3V device is outputting a logic zero level, there will be an inherent current
drawn via R and D.
IL
Freescale Semiconductor, Inc.
DD
DD
For More Information On This Product,
IL
(0.3 * V
, must be 0.8V, and the minimum input voltage level for logical "1", V
= 5.5V,
= 2.7V,
2.0V. Since MCU outputs are TTL compatible, no special circuitry is
5V to 3V Design Considerations
DD
Go to: www.freescale.com
), and V
V
V
V
V
DD
OL
OL
OH
OL
the maximum input level for logical "0" must be
< 1.0V at sink current of 15mA
< 0.8V at sink current of 10mA
< 0.4V at sink current of 10mA
> (V
IH
DD
(0.7 * V
– 0.8V) at source current of 10mA
Figure 9
DD
).
. The only disadvantage is that when
3.5V.
DDS
will have the
MOTOROLA
1.5V
IH
,