LM3464EVAL：LM3464

Hello,

In the LM3464 datasheet the pin description on page to shows the function of faultb.  There is a FAULT_CAP which sets the fault delay.

Starting at the bottom of page 18 of the LM3464 datasheet it explains the open and short LED function and fault response:

"FAULT HANDLING and INDICATION
The LM3464/64A features a complete mechanism for fault handling and indication. The LM3464/64A detects
LED failures and raises fault indication signal at the Faultb pin upon open or short circuits of LED strings,
insufficient supply voltage and so on. In order to avoid false triggering the fault detection circuitry, the
LM3464/64A features a timer for fault recognition. When a fault condition arises and sustains longer than the
time constant preset by the capacitor , CFLT, a fault is confirmed. The Faultb pin is then pulled low as an
indication. The time constant for fault detection is defined by the value of the capacitor connects across the
FAULT_CAP pin and GND, CFLT. Normally, a 2.2 nF CFLT that set a 264 us delay time is suitable for most
application. For those applications with slow response primary power supply, the value of CFLT may need to
increase accordingly. The time delay for fault detection is governed by the following equation:

OPEN CIRCUIT OF LED STRINGS
Detection of LED open circuit is achieved by detecting the voltages of the SEx pin and the internal gate control
signal being fed to the internal MOSFET gate driver. When a LED string is open circuit, the VSEx pin is pulled
down to below 30mV by the current sensing resistor. As VSEx falls below its regulated level, the LM3464/64A
increases the gate voltage of the corresponding MOSFET (VGDx) in order to maintain current regulation. Thus,
the requirement for LED open circuit is VSEx below 30mV and internal gate voltage reaches its maximum (at VGDx
about 5V). When the requirement of LED open fault is fulfilled, the LM3464/64A begins to charge up the CFLT.
When the voltage of the FAULT_CAP reaches 3V, and the condition of open fault retains, an open fault is
confirmed.
After an open fault is confirmed, the failed channel(s) will be disabled and excluded from DHC loop. To reactivate
the disabled channel(s), the EN pin can be pulled to GND for a soft reset or re-power the primary power supply
for a system reset. Either reset methods results in a system restart with startup sequence shows in Figure 16.
SHORT CIRCUIT OF LED STRINGS
If any LED string experiences partially short circuit after normal system startup, the drain voltage (DRx) of the
corresponding channel(s) will increase so as to maintain correct current regulation. When drain voltage increases
up to 8.4V higher than the drain voltages of any other channels, the shortened channel will be latched off and
excluded from the DHC loop to avoid further damages. Once a short fault is confirmed, the Faultb pin will be
pulled low no matter it is due to failure of the power source or shortening of LED strings. When a short circuit of
LED sting is confirmed, the failed channel(s) will be disabled and excluded from DHC loop. The disabled
channels can be reactivated by either pulling the EN pin to GND or system re-powering."

Best Regards,