APPLICATION NOTES CONTINUED
BRAKE -
is a pin for commanding the output bridge
into a motor BRAKE mode. When pulled low, nor-
mal operation commences. When pulled high, the
3 high side bridge switches turn off and the 3 low
side bridge switches turn on, causing rapid decel-
eration of the motor and will cease motor operation
until pulled high again. Logic levels for this input
are TTL compatible. It is internally pulled high.
DIS -
is a pin for externally disabling the output
bridge. A TTL logic low will enable the bridge and a
TTL logic high will disable it. It is internally pulled
up by a 100 µAmp pullup.
60/120-
is a pin for selecting the orientation of the
commutation scheme of the motor. A high state
will produce 60/300 degree commutation, whereas
a low state will produce 120/240 degree commuta-
tion. Logic levels for this input are TTL compatible.
It is internally pulled high.
VOLTAGE REGULATOR POWER DISSIPATION -
To figure volt-
age regulator power dissipation and junction temperature, use
the following as an example:
Given:
V+ = 28V, MSK 4362 +15V IQ = 85mA, -15V IQ = 40mA.
External Loads: +15V = 25 mA, -15V = 25 mA
-15V Converter Efficiency = 50%
P
DISS
due to +15V IQ,85 mA x 13V = 1.11 W
P
DISS
due to -15V IQ, (40 mA / 0.5) x 13V = 1.04 W
P
DISS
due to +15V Ext load, 25 mA x 13V = 325 mW
P
DISS
due to -15V Ext load, (25 mA / 0.5) x 13V = 650 mW
P
DISS
Total = 1.11 W + 1.04 W + 325 mW+650 mW=3.13W
3.13 W x 9°C/W = 28.1°C RISE above case temperature
Maximum Case Temperature = 150°C - 28.1°C = 121.9°C
To lower power dissipation in the regulator, a dropping resistor
can be added in series from V+ to the +REG IN pin. Using the
above example, if V+ = 39V and there is no dropping resistor,
total power dissipation rises to about 5.76 watts. Temperature
rise is now 51.8°C above case temperature, limiting maximum
case temperature to 98.2°C. By adding a dropping resistor to
lower the +REG IN pin voltage to 24.1V, the regulator power
dissipation is lowered to 2.19 watts. Temperature rise is now
19.7°C above case temperature, allowing a maximum case tem-
perature all the way to +125°C.
ALTERNATE REGULATOR CONNECTION OPTIONS
By connecting the regulators in different ways, various capabilities can be obtained.
1.
Higher than 55 volt operation -
For operation at higher than 55 volt motor bus voltages, there are three options available:
4
Rev. G 2/05
MSK [ M.S. KENNEDY CORPORATION ]
