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PDF RT7304 Data sheet ( Hoja de datos )
| Número de pieza | RT7304 | |
| Descripción | Primary-Side-Regulation LED Driver Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT7304
Primary-Side-Regulation LED Driver Controller
with Active PFC
General Description
The RT7304 is a constant current LED driver with active
power factor correction. It supports high power factor
across a wide range of line voltages, and it drives the
converter in the Quasi-Resonant (QR) mode to achieve
higher efficiency. By using Primary Side Regulation (PSR),
the RT7304 controls the output current accurately without
a shunt regulator and an opto-coupler at the secondary
side, reducing the external component count, the cost,
and the volume of the driver board.
The RT7304 embeds comprehensive protection functions
for robust designs, including LED open-circuit protection,
LED short-circuit protection, output diode short-circuit
protection, VDD Under-Voltage lockout (UVLO), VDD Over-
Voltage Protection (VDD OVP), Over-Temperature
Protection (OTP), and cycle-by-cycle current limitation.
Marking Information
0H=DNN
0H= : Product Code
DNN : Date Code
Features
Tight LED Current Regulation
No Opto-Coupler and TL431 Required
Power Factor Correction (PFC)
Quasi-Resonant
Maximum/Minimum Switching Frequency
Clamping
Maximum/Minimum On-Time Limitation
Wide VDD Voltage Range (up to 25V)
Multiple Protection Features
LED Open-Circuit Protection
LED Short-Circuit Protection
Output Diode Short-Circuit Protection
VDD Under-Voltage Lockout
VDD Over-Voltage Protection
Over-Temperature Protection
Cycle-by-Cycle Current Limit
RoHS Compliant and Halogen Free
Applications
AC/DC LED Lighting driver
Simplified Application Circuit
Flyback Converter
Buck-Boost Converter
Line
Neutral
BD
CSIN
RST
RT7304
GD
VDD
CS
RG
RPC
CVDD
CCOMP
COMP
GND
ZCD
DAUX
TX1 DOUT
VOUT+
COUT
Line
VOUT-
Q1 Neutral
RCS
RZCD2
RZCD1
BD
CSIN
RST
RT7304
GD
VDD
CS
RG
RPC
CVDD
CCOMP
COMP
GND
ZCD
DAUX
TX1
VOUT-
DOUT
COUT
VOUT+
Q1
RCS
RZCD2
RZCD1
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS7304-04 February 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
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, VDD drops related to the output
voltage. When the VDD is lower than falling UVLO threshold
(VTH_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 VCS exceeds the threshold
(VCS_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 (VDD)
exceeds rising UVLO threshold (VTH_ON, 16V typ.) and
disabled when VDD is lower than falling UVLO threshold
(VTH_OFF, 9V typ.).
When VDD exceeds its over-voltage threshold (VOVP, 27V
typ.), the PWM output of the RT7304 is shut down. It will
be auto-restarted when the VDD 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 (TSD, 150°C
typ.), the controller will shut down until the temperature
cools down by 30°C (typ.). Meanwhile, if VDD reaches falling
UVLO threshold voltage (VTH_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
5
5 Page 
Application Information
Output Current Setting
Considering the conversion efficiency, the programmed
DC level of the average output current (IOUT (t)) can be
derived as :
IOUT_CC
=
1
2
NP
NS
KCC
RCS
CTRTX1
CTRTX1
=
ISEC_PK
IPRI_PK
NS
NP
in which CTRTX1 is the current transfer ratio of the
transformer TX1, ISEC_PK is the peak current of secondary
side, and IPRI_PK is the peak current of the primary side.
CTRTX1 can be estimated to be 0.9.
According to the above parameters, current sense resistor
RCS can be determined as the following equation :
RCS
=
1
2
NP
NS
KCC
IOUT_CC
CTRTX1
Propagation Delay Compensation Design
The VCS deviation (ΔVCS) caused by propagation delay
effect can be derived as :
VCS
=
VIN tD RCS
Lm
in which tD is the delay period which includes the
propagation delay of the RT7304 and the turn-off transition
of the main MOSFET. The sourcing current from CS pin
of the RT7304 (ICS) can be expressed as :
ICS
=
KPC
VIN
NA
NP
1
RZCD1
where NA is the turns number of auxiliary winding.
RPC can be designed by :
RPC =
VCS
ICS
=
tD
RCS
Lm
RZCD1
KPC
NP
NA
RT7304
Minimum On-Time Setting
The RT7304 limits a minimum on-time (tON(MIN)) for each
switching cycle. The tON(MIN) is a function of the sample-
and-hold ZCD current (IZCD_SH) as following :
tON(MIN) IZCD_SH 375p sec A (typ.)
IZCD_SH can be expressed as :
IZCD_SH
=
VIN NA
RZCD1 NP
Thus, RZCD1 can be determined by :
RZCD1=
tON(MIN)
375p
VIN
NA
NP
(typ.)
In addition, the current flowing out of ZCD pin must be
lower than 2.5mA (typ.). Thus, the RZCD1 is also
determined by :
RZCD1 >
2
VAC(MAX)
2.5m
NA
NP
where the VAC(MAX) is maximum input AC voltage.
Output Over-Voltage Protection Setting
Output OVP is achieved by sensing the knee voltage on
the auxiliary winging. It is recommended that output OV
level (VOUT_OVP) is set at 120% of nominal output voltage
(VOUT). Thus, RZCD1 and RZCD2 can be determined by the
equation as :
VOUT
NA
NS
RZCD2
RZCD1 RZCD2
120%
=
3.1V
(typ.)
Table 2. Suggested Component Values Range
Component
CVDD
CCOMP
CZCD
CCS
RST
RGP
RG
RA UX
Range of Typical Value
10F to 33F
1F to 4.7F
10pF to 22pF
NC to 22pF
0.68M to 2M
10k to 22k
10 to 47
10 to 100
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS7304-04 February 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT7304.PDF ] | |
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