LED7706

Fault management

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8

Fault management

The main loop keeps the row having the lowest voltage drop regulated to about 400 mV.

This value slightly depends on the voltage across the remaining active rows. After the soft-

start sequence, all protections turn active and the voltage across the active current

generators is monitored to detect shorted LEDs.

8.1

FAULT pin

The FAULT pin is an open-collector output, active low, which gives information regarding

faulty conditions eventually detected. This pin can be used either to drive a status LED (with

a series resistor to not exceed 4 mA current) or to warn the host system.

The FAULT pin status is strictly related to the MODE pin setting (see Table 7 for details).

8.2

MODE pin

The MODE pin is a digital input and can be connected to AVCC or SGND in order to choose

the desired fault detection and management. The LED7706 can manage a faulty condition

in two different ways, according to the application needs. Table 7 summarizes how the

device detects and handles the internal protections related to the boost section (Over-

Current, Over-Temperature and Over-Voltage) and to the current generators section (open

and shorted LEDs).

Table 7.

Faults management summary

FAULT

MODE to GND

MODE to VCC

Internal MOSFET over

current

FAULT pin HIGH

Power MOS turned OFF

Output over voltage

FAULT pin LOW

Device turned OFF, latched condition

Thermal shutdown

FAULT pin LOW. Device turned OFF.

Automatic restart after 30 C temperature drop.

Shorted led

FAULT pin LOW

Device turned OFF,

latched condition

(Vth = 3.4 V)

FAULT pin LOW

Faulty row(s) disconnected

(Vth = 6 V)

OPEN row(s)

FAULT pin LOW

Device turned OFF at first

occurrence, latched condition

FAULT pin HIGH Faulty row(s)

disconnected