AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 19

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

Controlling IGBTs &
MOSFETs with
Drivers
Controlling MOSFETs
without Drivers
MOTOROLA
In motor control applications, the MCU output signals serve as user interface
(LED, display), communication and control signals (IGBT / MOSFET control,
Triac control, etc). The IGBTs / MOSFETs and Triacs are key control parts in
motor control applications, so the implication of moving to lower operating
voltages will be analysed in the following paragraphs.
IGBTs and MOSFETs are mostly used in the power stage design. Both types
of power switches are controlled in the same way using high side and low side
drivers.
The input characteristics of the drivers are very important for the power stage
topology and its interface to 3.3V control signals.
The logic level requirement that is the key factor for the selection of the driver
type is “1”, because the logic level “0” requirement is near to the ground voltage
and it is satisfied by all types of drivers.
For direct interfacing to a 3.3V MCU, the driver logic “1” threshold level, V
should be well below 3.3V. This condition is met by drivers that have TTL
compatible input levels with V
International Rectifier, which has V
For other types of drivers with logic “1” input voltage close or even above
V
leakage. An example of this is the MC74VHC1GT50 buffer, as shown in
CMOS to 5V CMOS
Small power MOSFETs can sometimes be driven directly without drivers, such
as the IR2181 and similar.
In these circumstances, because of the large MOSFET gate capacitance, the
transient response is considerably slower than when a driver IC is used. This
is due to the fact that an MCU has a lower output current and voltage rating
compared to the output of a driver, therefore this solution is appropriate only for
slow changing outputs, i.e. controlling lamps, solenoids, etc. Also if the
transition from the on to the off state and vice versa is slow, switching losses
increase and they have to be taken into account during design.
For direct driving, the MOSFET used should have a gate threshold voltage
V
Semiconductor MMDF6N03HD dual 6A N channel MOSFET in SO8 package
and similar types and the International rectifier IRF7501 dual N channel
MOSFET in Micro8 package with R
marked as "3V drive" types.
DD3min
GTH
Freescale Semiconductor, Inc.
For More Information On This Product,
well below V
, a level shifter needs to be used in order to prevent the current
5V to 3V Design Considerations
Go to: www.freescale.com
DD3min
.
(3.0V). Among suitable MOSFET types are the On
IH
< V
IH
DS(ON)
DD3min
= 2.7V.
=0.135ohm at V
(3.0V), such as the IR2181 from
Interfacing to Motor Control Parts
GS
=2.7V and others
AN2433/D
3V
IH
,
19