RT7304 Datasheet, PDF (5/14 Pages) Richtek Technology Corporation – Primary-Side-Regulation LED Driver Controller with Active PFC

LED Short-Circuit Protection
LED short-circuit protection can be achieved by VDD UVLO
and cycle-by-cycle current limitation. Once LED short-
circuit failure occurs, V_DD drops related to the output
voltage. When the V_DD is lower than falling UVLO threshold
(V_{TH_OFF}, 9V typ.), the converter will be shut down and it
will be auto-restarted when the output is recovered.
Output Diode Short-Circuit Protection
When the output diode is damaged as short-circuit, the
transformer will be led to magnetic saturation and the main
switch will suffer from a high current stress. To avoid the
above situation, an output diode short-circuit protection
is built-in. When CS voltage V_CS exceeds the threshold
(V_{CS_SD} 1.5 typ.) of the output diode short-circuit protection,
the RT7304 will shut down the PWM output (GD pin) in
few cycles to prevent the converter from damage. It will
be auto-restarted when the failure condition is recovered.
VDD Under-Voltage Lockout (UVLO) and
Over-Voltage Protection(VDD OVP)
The RT7304 will be enabled when VDD voltage (V_DD)
exceeds rising UVLO threshold (V_{TH_ON}, 16V typ.) and
disabled when V_DD is lower than falling UVLO threshold
(V_{TH_OFF}, 9V typ.).
When V_DD exceeds its over-voltage threshold (V_OVP, 27V
typ.), the PWM output of the RT7304 is shut down. It will
be auto-restarted when the V_DD is recovered to a normal
level.
Over-Temperature Protection (OTP)
The RT7304 provides an internal OTP function to protect
the controller itself from suffering thermal stress and
permanent damage. It's not suggested to use the function
as precise control of over temperature. Once the junction
temperature is higher than the OTP threshold (T_SD, 150°C
typ.), the controller will shut down until the temperature
cools down by 30°C (typ.). Meanwhile, if V_DD reaches falling
UVLO threshold voltage (V_{TH_OFF}), the controller will
hiccup till the over-temperature condition is removed.
RT7304
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS7304-04 February 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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