AN-9044 - Fairchild Semiconductor

Input Signal
Protection
Circuit State
Control
Supply Voltage
Output Current
Fault Output Signal
UV BSR
7.3 Short-Circuit Protection
RESET
b1
b2
Mini DIP (SPM3) Application Note (2012-07-09)
UV BSD
High-level (no fault output)
© 2008 FAIRCHILD SEMICONDUCTOR - Smart Power Module
32
SET RESET
Figure 7.2 Timing chart of high-side under-voltage protection function
7.3.1 Timing chart of Short Circuit (SC) Protection
The LVIC has a built-in short circuit function. This IC monitors the voltage to the CSC pin and if this
voltage exceeds the VSC(ref), which is specified in the devices data sheets, then a fault signal is asserted and
the lower arm IGBTs are turned off. Typically the maximum short circuit current magnitude is gate voltage
dependant. A higher gate voltage results in a larger short circuit current. In order to avoid this potential
problem, the maximum short circuit trip level is generally set to below 1.7times the nominal rated collector
current. The LVIC short circuit protection-timing chart is shown in Figure 7.3.
(with the external shunt resistance and RC connection)
c1 : Normal operation: IGBT ON and carrying current.
c2 : Short circuit current detection (SC trigger).
c3 : Hard IGBT gate interrupt.
c4 : IGBT turns OFF softly.
c5 : Fault output timer operation starts:
The pulse width of the fault output signal is set by the external capacitor CFO.
c6 : Input “L” : IGBT OFF state.
c7 : Input “H”: IGBT ON state, but during the active period of fault output the IGBT doesn’t turn ON.
c8 : IGBT OFF state
b3
b4
b5
b6