APPLICATION NOTES
MSK4351 PIN DESCRIPTION
+15V -
is the low voltage supply for all the internal logic and
isolated supplies which provide power to the gate drivers. A
0.1µF ceramic capacitor in parallel with a 22µF tantalum capaci-
tor is recommended for bypassing the low voltage supply to
GND.
GND -
is the low voltage supply return for the +15V. All
bypassing of the +15V should return here. Since the output
section of the hybrid is completely isolated, there are no restric-
tions for potential differences between this GND and any hi-
voltage returns, up to 500V.
AHI,BHI,CHI -
are the logic inputs for controlling the switching
of the corresponding hi-side bridge outputs. A logic high will
turn on the corresponding hi-side output. The input levels are
5V CMOS or TTL compatible. If one of these inputs are active
at the same time as the corresponding low-side bridge outputs,
neither output will be allowed to turn on until one of the inputs
is switched low. There will be a deadtime inserted before the
corresponding bridge output is switched in all cases. This pre-
vents simultaneous conduction of the output, shorting high
voltage supply and destroying the bridge.
ALO,BLO,CLO -
are the logic inputs for controlling the switching
of the corresponding low-side bridge outputs. A logic high will
turn on the corresponding low-side output. The input levels are
5V CMOS or TTL compatible. If one of these inputs are active
at the same time as the corresponding hi-side bridge outputs,
neither output will be allowed to turn on until one of the inputs
is switched low. There will be a deadtime inserted before the
corresponding bridge output is switched in all cases. This pre-
vents simultaneous conduction of the output, shorting the high
voltage supply and destroying the bridge.
RESET - is
an active low logic input for causing all switching to
cease. The input level is 5V CMOS or TTL compatible. Upon
releasing RESET, the outputs will resume after the dead time.
R/C -
is the input pin for setting the deadtime of the bridge.
Connecting a resistor between this input and OSC OUT, and a
capacitor to ground will create the time for an internal oscillator.
OSC OUT
- is a pin that brings the deadtime oscillator out to be
connected through the timing resistor to R/C. This is not an
output to be used externally, but just for the timing circuit.
AV+,BV+,CV+
- are pins for connecting the tops of each half
bridge to the high voltage supply. Each pin must be connected
individually, as there is no internal connection across the three
half bridges. Proper power supply bypassing must be connected
to these pins and the V- pins as close to the hybrid as possible
for proper filtering.
AV-,BV-,CV- -
are pins for connecting the bottoms of each half
bridge to the high voltage supply return. Each pin must be
connected individually, as there is no internal connection across
the three half bridges. Proper power supply bypassing must be
connected to these pins and the V+ pins as close to the hybrid
as possible for proper filtering.
AØ, BØ, CØ -
are the pins connecting the 3 phase bridge switch
outputs.
TEMP SENSE -
is a pin for measuring the output of a tempera-
ture sensor IC. The case temperature is depicted as a voltage
corresponding to 10mV/°C with 0 volts equating to absolute
zero, 0°K or -273°C.
3
RSENSE+ -
is the pin for connecting to the internal sense resistor.
It has a value of 0.003 ohms, 20 watts. AV-,BV- and CV- should
connect to this point for sensing the current at the bottom of the
bridge.
RSENSE- -
is the pin for connecting the internal sense resistor to
the high voltage return.
RKELVIN+ -
is the pin for connecting to the sense resistor +KELVIN
connection. This is on the same side of the resistor as RSENSE+.
RKELVIN- -
is the pin for connecting to the sense resistor -KELVIN
connection. This is on the same side of the resistor as RSENSE-.
DEADTIME SELECTION
The amount of deadtime required is based on the propagation
delay of the input to actual completion of switching of the output
transistors. Not taking all this into account can possibly allow the
opposite transistor in a half bridge to turn on before the active
transistor can turn off. Excessive current will flow through the
half bridge because this creates a momentary short across the
power supply.
Once all these factors are taken into account, the deadtime can be
determined. Allow sufficient safety factor for changes in compo-
nents over temperature, and variations from system to system in
production.
Deadtime is exactly 8 R/C clock periods. Use the formula:
Max. Clock = 8/Min. Deadtime
For clock operation below 1MHz:
Clock Frequency =
0.95
C
OSC
x R
OSC
0.95
(R
OSC
+ 30) + 3x 10
8
For clock operation above 1MHz:
Clock Frequency =
C
OSC
As an alternative, the R/C pin can be driven directly with an HCMOS
compatible clock up to 24MHz.
PRELIMINARY Rev. A
11/01
MSK [ M.S. KENNEDY CORPORATION ]
