AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 20

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

AN2433/D
Driving TRIACs
20
Driving of TRIACs does not bring any issues for 5V to 3V transition, except that
the value of R1 in
in order to have enough TRIAC gate current.
The number of MCU pins should be chosen according to the driving capability
of the MCU outputs to comply with the TRIAC minimum gate current
requirement, which is 15mA for MAC4DC type for example. The circuitry on
Figure 17
When galvanic isolation is necessary, the standard opto-triac or opto-coupler
can be used for connection to the TRIAC. With a 3.3V MCU the situation is the
same as in the 5V system, only the resistor limiting the opto-coupler current
should be lowered to get the same driving current as in the 5V system.
The situation is similar for driving LEDs, although considering that the LED
forward voltage drop is in the range of 1.6–2V there is a smaller headroom for
the MCU output pin voltage drop compared to 5V system.
Therefore, the output characteristic of the MCU must be taken into
consideration in these circumstances.
Freescale Semiconductor, Inc.
For More Information On This Product,
3.3V MCU
3.3V MCU
has a galvanic connection to the power outlets.
5V to 3V Design Considerations
Go to: www.freescale.com
OUT
OUT
OUT
OUT
OUT
OUT
Figure 17
V
V
V
V
DD
DD
SS
SS
Figure 17. Driving of TRIAC
should be lowered compared to that in a 5V system
R1
R1
GND
GND
R2
R2
MAC4DC
MAC4DC
L
L
N
N
MOTOROLA