Broadcom
ACPL-352J-EB1200-RM100
18
ACPL-352J
Reference Manual
Infineon EconoPIM™ 3 IGBT Module EB1200-352J Evaluation Board
To isolate the collector from the gate driver circuit when the IGBT is off and to be able to adjust the sensed saturation voltage
between the collector and the emitter, OC diodes (D4 and D5 in
) are added in the circuit. By changing the forward
voltage value of the mentioned diodes, the user can modify threshold level of the saturation voltage. This configuration can
be also changed by retaining only one diode and placing a 0Ω resistor in place for the other diode. By increasing the total
forward voltage (the sum of the forward voltages of both diodes), the user can decrease the OC threshold voltage. When
using two diodes instead of one, the same type of diodes must be used, and the blocking voltage rating of these diodes can
be half of the maximum reverse voltage. Additionally, the OC threshold voltage is adjusted by adding a low-voltage Zener
diode (ZD1 in
When IGBT is switching off, a reverse current flows for a short time, which prevents the diode from achieving its blocking
capability until the charge in the junction is depleted. During this time, the positive voltage slope between the collector and
the emitter results in current that tends to charge the blanking capacitor. The minimization of this current and the avoidance
of false OC triggering are achieved with fast diodes. Aside from OC and Zener diodes in series, there is one more component
that ensures the safety of the driver—a 1-kΩ resistor (R21 in
) in series with the previous components. This resistor
limits the current caused by negative voltage spikes (generated by inductive loads or reverse recovery spikes of the
free-wheeling diode) on the OC pin, thus preventing damage to the driver. To additionally prevent false fault signals caused
by negative voltage spikes on the OC pin, connect the Zener and Schottky diode between the OC and the V
E
pin.
In addition to the described protection mechanism during short circuit behavior, the status of the IGBT gate voltage is
monitored by output pins VOUTP and VOUTN. The GFAULT feedback signal output goes low when the gate voltage does
not correspond to the LED input logic. The status of the gate is checked after a minimum delay time t
GFAULT
to allow enough
time for the gate to charge or discharge to its final level. When the LED input logic is high, VOUTN is sensed to check if the
gate voltage is higher than V
DD2
– 2V after a t
GFAULT
delay. The G
FAULT
output goes low if the gate voltage is lower than
V
DD2
– 2V. Likewise, when the LED input logic is low, VOUTP is sensed to check if the gate voltage is lower than V
SS2
+ 2V.
GFAULT output returns to high upon an input logic change or if the gate voltage manages to cross the threshold of V
DD2
–
2V or V
SS2
+ 2V. Because the VOUTP and CLAMP functions share the same pin, the gate voltage is continuously monitored
by VOUTP whether it is in a high impedance state or a CLAMP state when the LED input logic is low.
4.2.4 Gate Resistor Consideration
The first step in choosing the appropriate gate resistor is to calculate its minimal value from the I
O(PEAK)
specification. The
IGBT and the gate resistor can be analyzed as a simple RC circuit with a voltage supplied by the ACPL-352J.
Note that R
DS(MIN)
can be different for high-side and low-side power switches. Therefore, calculations for both are necessary.
This external gate resistor combined with an internal minimal turn-on resistance ensures that the output current does not
exceed the device absolute maximum rating of 4A.
The next step in choosing the correct gate resistor is to check the power dissipation of the ACPL-352J gate driver. If the
power dissipation is too high, the resistance of the gate resistor should be increased. For detailed instructions on choosing
the gate resistor, refer to the ACPL-352J data sheet.
The final step in the turn-off gate resistor selection is ensuring that during turn-off, the transient at the maximal allowed
collector current, IGBT collector-emitter voltage does not exceed the blocking voltage on the IGBT device. The criteria for
the turn-on gate resistor are the maximal collector current peak, related to the reverse recovery of the opposite freewheeling
diode. This peak must not exceed double the value of the nominal collector current.
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Содержание ACPL-352J
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