APPLICATION NOTES
THERMAL PROTECTION:
The amplifiers are equipped with thermal protection circuitry
that protects each amplifier from damage caused by excessive
junction temperature. The output is disabled when the junction
temperature reaches approximately 160°C. After the junction
temperature cools to approximately 140°C, the output is again
enabled. The thermal protection may cycle on and off depend-
ing on the output load and signal conditions; this may have an
undesirable effect on the load.
It should be noted that even though this internal protection
circuitry does protect against overload conditions, it does not
take the place of proper heat sinking. For reliable operation,
junction temperature should be limited to 150°C, maximum.
POWER SUPPLIES:
For the MSK 186 maximum total supply voltage is specified
as 60V. However, dual and unbalanced power supply operation
is permissible as long as total supply voltage does not exceed
60V.
POWER SUPPLY BYPASSING:
Power supply terminals must be effectively decoupled with a
high and low frequency bypass circuit to avoid power supply
induced oscillation. An effective decoupling scheme consists
of a 0.1µF ceramic capacitor in parallel with a 10µF tantalum
capacitor for each power supply pin to ground. In addition, it is
recommended that a 0.01µF capacitor be placed between ±Vcc
as close to the amplifiers as possible.
ENABLE/STATUS PIN:
For the MSK 186 this pin actually has a dual function. First,
when the pin is forced low, the output stage is disabled. Sec-
ond, it can be monitored to determine if the device is in thermal
shutdown. These functions can be used on the same device
with either single or dual supplies. For normal operation, the
E/S pin must be left open or pulled at least 2.4 volts above the
VR pin. In noisy applications, a small value capacitor between
the E/S pin and VR may be required.
To disable the output, the user must pull the E/S pin low, no
greater than 0.8V above VR. To once again enable the device,
the E/S pin must be brought at least 2.4 volts above VR or be
disconnected. It should be noted that when the E/S pin is high,
the internal thermal shutdown is still active.
CURRENT LIMIT:
The MSK 186 offers accurate, user-selectable current limit.
Unlike typical designs that use a power resistor in series with
the output to sense load, the MSK 186 senses the load indi-
rectly and therefore does not require a resistor to handle the full
output current. Current limit is selected by controlling the input
to the ILIM pin (0 to 633µA).
The easiest method is to use a resistor or potentiometer
connected between VR and the ILIM pin. Use the following equa-
tion to select proper resistor value:
75,000
ILIM
-7.5KΩ
RCL=
If the E/S pin is used to monitor thermal shutdown, during
normal operation the voltage on the E/S pin is typically 3.5V
above VR. Once shutdown has occurred this voltage will drop
to approximately 350mV above VR.
A low level control signal (0-633µA) can also be used to con-
trol the current level digitally. If the pin is left open, the current
is programmed to OA, while connecting ILIM directly to VR sets
the output current to it's maximum, typically 10A.
SAFE OPERATING AREA:
The safe operating area curve is a graphical representation of
the power handling capability of the amplifier under various
conditions. Power dissipation of the device is equal to the prod-
uct of the voltage across the output transistor times the output
current. As can be seen in the curve on page 5, safe operating
current decreases with an increase in temperature as well as an
increase in the voltage across the output transistor. Therefore,
for maximum amplifier performance it is important to keep case
temperature as low as possible and to keep ±Vcc as close to
the output rail as achievable.
VR PIN
The MSK 186 features a reference (VR) pin to which the ILIM
and the E/S pin are referred. VR simply provides a reference
point accessible to the user that can be set to V-, ground, or
any reference of the user's choice. VR cannot be set below the
negative supply or above (V+)-8V. If the minimum VS is used,
VR must be set at V-.
COMPENSATION:
For normal operation output compensation is not typically
required. However, if the MSK 186 is intended to be driven into
current limit the user may find that an R/C network is required.
A snubber network from the output to ground for each ampli-
fier will provide stability. If driving large capacitive or inductive
loads, a snubber network will also enhance stability. Typically
3Ω to 10Ω in series with 0.01µF is acceptable.
TYPICAL CONNECTION DIAGRAM
PRELIMINARY Rev. B 11/06
3
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