MIC4605 Datasheet, PDF (21/25 Pages) Micrel Semiconductor – 85V Half-Bridge MOSFET Drivers

Micrel, Inc.
MIC4605
Figure 15. Three-Phase Brushless DC
Motor Driver − 24V Block Diagram
The MIC4605 is offered in a small 2.5mm × 2.5mm TDFN
package for applications that are space constrained and
an SOIC-8 package for ease of manufacturing. The motor
trend is to put the motor control circuit inside the motor
casing, which requires small packaging because of the
size of the motor.
The MIC4605 offers low UVLO threshold and
programmable gate drive, which allows for longer
operation time in battery operated motors such as power
hand tools.
Cross conduction across the half bridge can cause
catastrophic failure in a motor application. Engineers
typically add dead time between states that switch
between high input and low input to ensure that the low-
side MOSFET completely turns off before the high-side
MOSFET turns on and vice versa. The dead time
depends on the MOSFET used in the application, but
200ns is typical for most motor applications.
Power Inverter
Power inverters are used to supply AC loads from a DC
operated battery system, mainly during power failure. The
battery voltage can be 12VDC, 24VDC, or up to 36VDC,
depending on the power requirements. There two popular
conversion methods, Type I and Type II, that convert the
battery energy to AC line voltage (110VAC or 230VAC).
Figure 16. Type I Inverter Topology
As shown in Figure 16, Type I is a dual-stage topology
where line voltage is converted to DC through a
transformer to charge the storage batteries. When a
power failure is detected, the stored DC energy is
converted to AC through another transformer to drive the
AC loads connected to the inverter output. This method is
simplest to design but tends to be bulky and expensive
because it uses two transformers.
Type II is a single-stage topology that uses only one
transformer to charge the bank of batteries to store the
energy. During a power outage, the same transformer is
used to power the line voltage. The Type II switches at a
higher frequency compared to the Type I topology to
maintain a small transformer size.
Both types require a half bridge or full bridge topology to
boost the DC to AC. This application can use two
MIC4605s. The 85V operating voltage offers enough
margin to address all of the available banks of batteries
commonly used in inverter applications. The 85V
operating voltage allows designers to increase the bank
of batteries up to 72V, if desired. The MIC4605 can sink
as much as 1A, which is enough current to overcome the
MOSFET’s input capacitance and switch the MOSFET up
to 50kHz. This makes the MIC4605 an ideal solution for
inverter applications.
As with all half bridge and full bridge topologies, cross
conduction is a concern to inverter manufactures
because it can cause catastrophic failure. This can be
remedied by adding the appropriate dead time between
transitioning from the high-side MOSFET to the low-side
MOSFET and vice versa.
Grounding, Component Placement, and Circuit
Layout
Nanosecond switching speeds and ampere peak currents
in and around the MIC4605 drivers require proper
placement and trace routing of all components. Improper
placement may cause degraded noise immunity, false
switching, excessive ringing, or circuit latch-up.
November 11, 2013
21
Revision 1.0