RT8475 Datasheet PDF - Richtek

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RT8475
Richtek

Part Number RT8475
Description High Voltage High Current LED Driver Controller
Page 16 Pages


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®
RT8475
High Voltage High Current LED Driver Controller for
Buck, Boost or Buck-Boost Topology
General Description
The RT8475 is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications. With a current sense amplifier threshold of
190mV, the LED current is programmable with one
external current sense resistor. With the maximum
operating input voltage of 36V and output voltage up to
90V, the RT8475 is ideal for buck, boost or buck-boost
operation.
With the switching frequency programmable over 100kHz
to 1MHz, the external inductor and capacitors can be small
while maintaining high efficiency.
Dimming can be done by either analog or digital. The built-
in clamping comparator and filter allow easy low noise
analog dimming conversion from digital signal with only
one external capacitor.
The RT8475 is available in SOP-14 and WQFN-16L 3x3
packages.
Ordering Information
RT8475
Package Type
S : SOP-14
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Features
z High Voltage Capability : VIN Up to 36V, LED Sensing
Threshold Common Mode Voltage Up to 90V
z Buck, Boost or Buck-Boost Operation
z Programmable Switching Frequency
z Easy Dimming Control : Analog or Digital
Converting to Analog with One External Capacitor
z Programmable Soft-Start to Avoid Inrush Current
z Programmable Over Voltage Protection
z VIN Under Voltage Lockout and Thermal Shutdown
z RoHS Compliant and Halogen Free
Applications
z General Industrial High Power LED Lighting
z Desk Lights and Room Lighting
z Building and Street Lighting
z Industrial Display Backlight
Pin Configurations
(TOP VIEW)
RSET
ISW
ISP
ISN
VC
ACTL
DCTL
2
3
4
5
6
7
14 GATE
13 GBIAS
12 GND
11 VCC
10 OVP
9 EN
8 SS
SOP-14
16 15 14 13
RSET
ISW
ISP
ISN
1
2
3
4
GND
17
12 GND
11 VCC
10 OVP
9 EN
5 678
WQFN-16L 3x3
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8475-03 October 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1



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RT8475
Marking Information
RT8475GS
RT8475
GSYMDNN
RT8475GS : Product Number
YMDNN : Date Code
RT8475ZS
RT8475
ZSYMDNN
RT8475ZS : Product Number
YMDNN : Date Code
RT8475ZQW
5A YM
DNN
5A : Product Code
YMDNN : Date Code
Typical Application Circuit
VIN
4.5V to 36V
5V
Analog
Dimming
1R0VkC
3C.V3CnF
L1
22µH
1C0INµF
RT8475
11 VCC
GATE 14
M1
9 EN
ISW 2
6 ACTL
7 DCTL
5 VC
ISP 3
ISN 4
OVP 10
CSS
0.1µF
8 SS
13 GBIAS
RRSET
RSET 1 30k
GND
C1µBF 12
D1
RSENSE
0.47
COUT
1µF
RSW
0.05
R1
R2
VOUT
VOUT
90V (Max.)
LEDs
Figure 1. Analog Dimming in Boost Configuration
D1
VIN1
4.5V to 36V 1C0IµNF1
5V
Analog
Dimming
1R0VkC
3C.V3CnF
CSS
0.1µF
VIN2
90V (max)
CIN2
RSENSE
0.47
RT8475
11 VCC
ISP 3
9 EN
ISN 4
6 ACTL
GATE 14
7 DCTL
ISW 2
5 VC
RSET 1 RRSET
8 SS
13 GBIAS
OVP 10
CB
1µF
GND
12
COUT
1µF
LEDs
L1
22µH
M1
RSW
0.05
Figure 2. Analog Dimming in Buck Configuration
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS8475-03 October 2012



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RT8475
VIN
4.5V to 36V
5V
Analog
Dimming
1R0VkC
3C.V3CnF
L1
22µH
CIN
10µF
RT8475
11 VCC
GATE 14
9 EN
ISW 2
C0.S1SµF
6 ACTL
7 DCTL
5 VC
8 SS
13 GBIAS
C1µBF
ISN 4
ISP 3
OVP 10
RSET 1
GND 12
M1
RRSET
D1
RSW
0.05
COUT
1µF
RSENSE
0.47
R1
R2
VOUT
VOUT
90V (max)
LEDs
Figure 3. Analog Dimming in Buck-Boost Configuration
Functional Pin Description
Pin No.
SOP-14 WQFN-16L 3x3
11
22
33
44
55
66
77
Pin Name
RSET
ISW
ISP
ISN
VC
ACTL
DCTL
Pin Function
Switch Frequency Set Pin. Connect a resistor from RSET to GND.
RRSET = 30kΩ will set fSW = 350kHz.
External MOSFET Switch Current Sense. Connect the current sense
resistor between external N-MOSFET switch and the ground.
LED Current Sense Amplifier Positive Input with Common Mode Up to
90V.
LED Current Sense Amplifier Negative Input. Voltage threshold
between ISP and ISN is 190mV with common mode voltage up to 90V.
PWM Control Loop Compensation.
Analog Dimming Control. The effective programming voltage range of
the pin is between 0.2V and 1.2V.
By adding a 0.47μF filtering capacitor on ACTL pin, the PWM dimming
signal on DCTL pin can be averaged and converted into analog
dimming signal on the ACTL pin.
8 8 SS
9 9 EN
10 10 OVP
11 11 VCC
12
17
12,
(Exposed
Pad)
GND
13 13 GBIAS
14 14 GATE
Soft-Start. A capacitor of at least 10nF is required for proper soft-start.
Chip Enable (Active High). When this pin voltage is low, the chip is in
shutdown mode.
Over Voltage Protection. The PWM converter turns off when the
voltage of the pin goes to higher than 1.18V.
Power Supply Pin of the Chip. For good bypass, a low ESR capacitor
is required.
Ground. The Exposed Pad must be Soldered to a Large PCB and
Connected to GND for Maximum Power Dissipation.
Internal Gate Driver Bias. A good bypass capacitor is required.
External MOSFET Switch Gate Driver Output.
--
15, 16
NC
No Internal Connection.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8475-03 October 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3



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RT8475
Function Block Diagram
EN
RSET
VCC
OVP
VC
SS
DCTL
1.4V
4.5V
1.18V
+
-
-
+
+
-
6µA
1.2V
+
-
8.5V +
Shutdown
-
OSC
SQ
R
R
R
VOC
- 110mV
+
-
GM
+
1.2V
+
-
ACTL
VISP – VISN
(mV)
190
V
GBIAS
GATE
ISW
ISN
ISP
GND
0 0.2
1.2
Figure 4
VACTL (V)
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
is a registered trademark of Richtek Technology Corporation.
DS8475-03 October 2012



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