Datasheet

Operation description LED7707
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5.3.1 FAULT pin
The FAULT pin is an open-collector output, (with 4 mA current capability) active low, which
gives information regarding faulty conditions eventually detected. This pin can be used
either to drive a status LED or to warn the host system.
The FAULT pin status is strictly related to the MODE pin setting (see
Ta ble 6 for details).
5.3.2 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 LED7707 can manage a faulty condition
in two different ways, according to the application needs.
Table 6 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).
5.3.3 Open LED fault
In case a row is not connected or a LED fails open, the device has two different behaviors
according to the MODE pin status. If the MODE pin is high (i.e. connected to AVCC), the
FAULT pin is set high as soon as the device recognizes the event; the open row is excluded
from the control loop and the device continues to work properly with the remaining rows.
Thus, if less than six rows are used in the application, the MODE pin must be set high.
Connecting the MODE pin to SGND, the LED7707 behaves in a different manner: as soon
as an open row is detected the FAULT pin is tied low and the device is turned off. The
internal logic latches this status: to restore the normal operation, the device must be
restarted by toggling the EN pin or performing a power-on reset (POR occurs when the
voltage at the LDO5 pin falls below the lower UVLO threshold and subsequently rises above
the upper one).
Table 6. 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.
LED short circuit
FAULT pin LOW, device turned
OFF (100s masking time),
latched condition (Vth = 4.0 V)
-
Open row(s)
FAULT pin LOW
Device turned OFF at first
occurrence, latched condition
FAULT pin HIGH faulty row(s)
disconnected.