Protection Features - Broadcom ACPL-355JC Reference Manual

ACPL-355JC Reference Manual
The next step in choosing the right gate resistor is checking the power dissipation of the ACPL-355JC 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-355JC data sheet.
Finally, switching performance, especially the turn-off speed, must be measured since the fast-switching transients in
combination with parasitic inductances in the switching loop can generate high over-voltages and oscillations.
To ensure the constraints described above during the worst-case conditions, based on FF6MR12KM1, the EB1200M62-
355JC comes with 4.03Ω gate resistors for positive and 4.03Ω for negative gating. Both resistances are realized with two
parallel resistors to increase the power dissipation capacity of the gate circuit. In addition, the evaluation board is designed
to enable Broadcom customers to evaluate switching characteristics of the semiconductors by changing or combining the
turn-on/off resistors.
Additionally, Schottky diode D5, placed between the gate and the V
shunt parasitic Miller current during the off cycle.

3.2.3 Protection Features

V and V will remain functional until OC or UVLO protection features are activated.
OUTP OUTN
3.2.3.1 OC
The OC pin monitors the MOSFET drain-source voltage. OC fault detection circuitry must remain disabled for a short period
of time following the turn-on of the MOSFET to allow the drain-source voltage to settle down and fall below the OC threshold.
This period, called the OC blanking time, is determined by the blanking capacitor and the internal current source provided
in the gate driver IC. The total blanking time is calculated in terms of the internal blanking time (t
capacitance (C ), the FAULT threshold voltage (V
BLANK
C corresponds to capacitance C2 (C12 for the low-side driver) in
BLANK
9V, and the I OC charge current is 1 mA. The nominal blanking time also represents the longest time it takes for the
CHG
driver to respond to the OC fault condition. Once the OC fault is detected and the blanking time has passed, both V
V will go low and a soft shutdown will start. The soft shutdown resistor R7 (R20) should be small enough to speed up
OUTN
the shutdown of the MOSFET to prevent overheating.
When the OC conditions are met, an internal feedback channel is activated, which brings the FAULT output from high to low.
Once the fault is detected, V
must be kept low for t
OC(RESET)
will return to the High-Z state. If the LED goes high during t
need to be kept low for another t
The total voltage measured at the OC pin is the sum of the drain-source voltage across the MOSFET switch and the total
voltage drop on following components: R4 (R17), D3 (D13), D4 (D14), D2 (D12). The drain-source voltage threshold value
for OC triggering is equal to 9V – (I
D3 and D4, and V is the blocking voltage of Zener diode D2. The function of the high-voltage diodes D3 (D13) and D4
D2
(D14) is to conduct the current from the OC pin through the MOSFET when it is in the on state, allowing for drain-source
voltage sensing, and to block high voltages when the MOSFET is in the off state. Proper adjustment of the OC detection
level can be performed by choosing the correct voltage rating of Zener diode D2.
Broadcom
and V are set to the High-Z state for the t
OUTP OUTN
before the fault condition is cleared. The FAULT status will return to high, and the SS output
. Figure 15
OC(RESET)
x R4) – V – V
CHG D3
pin, is used together with the CLAMP function to
OUTP
), and the blanking capacitor charge current (I
OC
Figure 14, the V
, the t
OC(RESET) OC(RESET)
depicts the circuit behavior during the over-current event.
– V , where V and V
D4 D2 D3
62-mm SiC Module EB1200M62-355JC Evaluation Board
OC(BLANKING)
fault threshold voltage is nominally
OC
time. After this time, the LED input
OC(MUTE)
timing will reset, and the LED input will
are the forward voltage drops of diodes
D4
ACPL-355JC-62mmSiC-RM100
), the external
) as follows:
CHG
and
OUTP
21