FAN7346 Datasheet, PDF (13/19 Pages) Fairchild Semiconductor – 4-Channel LED Current Balance Controller

7. Over-Voltage Regulation (OVR)
To prevent LED driving voltage from exceeding the
withstanding voltage of system components, the
FAN7346 controls LED driving voltage with OVR pin
voltage. The FAN7346 senses output LED driving
voltage through the OVR pin voltage. Resistor divided
output voltage is applied to the OVR pin voltage.
In FAN7346, OVR voltage uses two kinds of feedback
and control: and regulating output voltage during enable
off and clamping output voltage during enable on.
When ENA pin is LOW, the FAN7346 controls FB voltage
to maintain OVR voltage as 1.0V. Through this output
voltage control during ENA off, the FAN7346 reaches
adequate LED driving voltage before turning ENA on.
After ENA pin is HIGH, OVR pin voltage is used for over-
voltage regulation. If OVR pin voltage is lower than
1.42V, the FB pin voltage follows headroom control to
maintain minimum voltage of drain voltages as 1V. If
OVR pin voltage is higher than 1.42V, the FAN7346
controls FB (FB is pulled LOW). Through feedback
regulation, OVR pin voltage cannot exceed 1.42V.
8. Over-Current Protection (OCP)
Through over-current protection, the FAN7346 can
protect external balance switches from shorted over-
current damage. To sense over-current condition, the
FAN7346 monitors FBx (FB1~FB4) pin voltage.
If FBx voltage is higher than 1V for 20µs, CHx is
considered an over-current condition. After sensing OCP
condition, CHx dimming switch is turned off.
OCP is channel individual and latched protection. If one
channel is in OCP condition, other channels keep
operating. OCP channel is restarted after UVOL is reset.
9. Error Flag (FO)
To make error flag signal, the FAN7346 uses the FO pin.
FO pin is open-drain type.
During normal operation, the FO pin is open. If using an
external pull-up resistor, this signal is HIGH.
If used OLP / OCP / SLP protection, the FO pin is
connected to ground. If using an external pull-up resistor,
this signal is LOW.
If a single channel is in protection condition, error-flag
signal is detected. Only if all channels are operating
normally is the FO pin pulled HIGH.
© 2011 Fairchild Semiconductor Corporation
FAN7346 • 1.0.0
13
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