DS8302 01

®
RT8302
60V, 4-CH, Programmable Current Sink LED Driver for
1D/2D/3D Dimming Applications
General Description
Features
The RT8302 is a 4-CH constant current sink LED driver
which can drive 4-CH constant current with good matching
ability.
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The RT8302 provides ±3% high accuracy current each
channel. The range of the constant current output is
programmable from 30mA to 360mA by SPI interface. It
also supports the local dimming and scan dimming by 4
independent PWM generators with programmable PWM
duty cycle, period and delay. The dropout voltage of output
channel is 0.5V as the output constant current is 150mA
which can accept wide range VF variation. Moreover, the
RT8302 provides Dynamic Headroom Control (DHC)
function which can generate feedback signal to DC/DC
control loop and regulate the output voltage.
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The RT8302 also provides LED open/short protection. If
there is any channel open or short, the FLT pin will pull
low and the output channel will be turned off individually.
The RT8302 is available in the WDFN 5x5-16L and DIP-18
packages to achieve optimized solution for PCB space.
Wide Input Supply Voltage Range : 5V to 26V
Wide Current Range : 30mA to 360mA (8-Bit
Resolution)
Programmable Channel Current
Low Dropout Voltage : 500mV at 150mA
±3% High Accuracy Current for 60mA to 120mA
±2% Current Matching for 60mA to 120mA
Fault Detection for LED Open/Short
Under-Voltage Lockout and Thermal Shutdown
Integrated Dynamic Headroom Control (DHC)
Support 1D/2D/3D Dimming (Programmable
Channel Delay, Individual PWM Duty Control,
Automatic VSYN Synchronization)
Flexible Daisy-Chained SPI Interface
RoHS Compliant and Halogen Free
Applications
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LCD TV, MNT Display Backlight
DC/DC or AC/DC LED Driver Applications
General Purpose Constant Current Source
Architectural and Decorative LED Lighting
LED Street Lighting
Simplified Application Circuit
L1
D1
VLED
VIN
CIN
RT8525
DRV
VIN
CDC
VDC
M1
COUT
RSLP
ISW
VIN
RS
Enable
EN
SS
CSS
PGND
FB
AGND
RFB1
CFB
RFB2
VIN
COMP
EN
RPWMI
RIF
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
LED1 LED2 LED3 LED4
VFB
PWMI
RC
CC1
VPH
CIN
RFB3
MCU
CS
SCL
VSYN
MOSI
MISO
RPH
FLT
EN
CS
SCL
VSYN
SDI
IFB
RT8302
PWMO
SDO
GND
is a registered trademark of Richtek Technology Corporation.
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1
RT8302
Ordering Information
Pin Configurations
RT8302
(TOP VIEW)
Package Type
QW : WDFN-16L 5x5 (W-Type)
N : DIP-18
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
SDI
SCL
VSYN
PWMO
EN
VFB
FLT
SDO
16
15
1
2
3
4
5
6
7
8
14
13
GND
12
11
10
17
9
CS
LED4
LED3
LED2
LED1
IFB
VREG
VIN
Richtek products are :
`
WDFN-16L 5x5
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
PWMO
18
VSYN
EN
2
17
SCL
VFB
3
16
SDI
FLT
4
15
CS
SDO
5
14
GND
GND
6
13
LED4
VIN
7
12
LED3
VREG
8
11
LED2
IFB
9
10
LED1
Marking Information
RT8302GQW
RT8302GQW : Product Number
RT8302
GQW
YMDNN
YMDNN : Date Code
RT8302GN
RichTek
RT8302
GNYMDNN
RT8302GN : Product Number
YMDNN : Date Code
DIP-18
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Functional Pin Description
Pin No.
Pin Name
Pin Function
WDFN-16L 5x5
DIP-18
1
16
SDI
Serial Interface Data Input.
2
17
SCL
Serial Interface Clock Input.
3
18
VSYN
Video Sync Signal or External Clock Input.
4
1
PW MO
PWM Output.
5
2
EN
Enable Control Input (Active High).
6
3
VFB
Feedback Control Voltage Output.
7
4
FLT
Open-Drain Output for Fault Detection.
8
5
SDO
Serial Digital Data Output.
9
7
VIN
Power Supply Input.
10
8
VREG
Shunt Regulator Supply.
11
9
IFB
Feedback Control Current Output.
12
10
LED1
Constant Current Sink Output.
13
11
LED2
Constant Current Sink Output.
14
12
LED3
Constant Current Sink Output.
15
13
LED4
Constant Current Sink Output.
16
15
CS
Chip Select.
17 (Exposed Pad)
6, 14
GND
Ground. The exposed pad must be soldered to a large PCB
and connected to GND for maximum thermal dissipation.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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RT8302
Function Block Diagram
VFB
25MHz Oscillator
EN
SDI
DHC
Function
LDO
OTP
SDO
CS
UVLO
Daisy Chain SPI
Interface
SCL
PWM
Control
VREG
GND
Fault
Detection
Channel
Select
VSYN
VIN
FLT
LED1
LED2
LED3
236-step Current
Setting
LED4
IFB
Soft-Start Circuit
Constant Current Control Circuit
PWMO
Operation
The RT8302 is a 4-CH constant current sink LED driver
with 12-bit depth for PWM control. The daisy chain Serial
Peripheral Interface (SPI) bus control can shift the input
data into each channel buffer with dependent pixel gray
scale and shift out input data to output pin SDO. The
RT8302 supports local and scan dimming by PWM Control
and Channel Select block. In PWM Control block, there
are four independent PWM generators with programmable
PWM duty cycle, period and delay. Channel Select block
can decide which channel should be enabled.
The RT8302 provides ±3% high accurate current for each
channel by Constant Current Control Circuit block. The
dropout voltage of output channel is 0.5V as the output
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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constant current is 150mA which can accept wide range
VF variation. The range of the constant current output is
from 30mA to 360mA which is adjusted by 236-step
Current Setting block. Besides, a Dynamic Headroom
Control (DHC) function is designed to generate a feedback
signal for DC/DC control loop and regulate the output
voltage.
Furthermore, the RT8302 provides LED open/short and
OTP protection by Fault Detection block. If there is any
channel open/short, the FLT pin will pull low and the output
channel will be turned off individually. If the internal junction
temperature exceeds 150°C, all output channels will be
turned off.
is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VIN -----------------------------------------------------------------------------------------------Output Voltage LED1 to LED4 -----------------------------------------------------------------------------------------Other Pins -------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-16L 5x5 -------------------------------------------------------------------------------------------------------------DIP-18 ------------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-16L 5x5, θJA -------------------------------------------------------------------------------------------------------WDFN-16L 5x5, θJC -------------------------------------------------------------------------------------------------------DIP-18, θJA ------------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Storage Temperature Range ---------------------------------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 31V
−0.3V to 70V
−0.3V to 28V
3.47W
1.97W
28.8°C/W
4.4°C/W
50.6°C/W
260°C
150°C
−65°C to 150°C
(Note 3)
Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 5V to 26V
Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Input Power Supply
Supply Current
ION
EN = High, VLEDx open
--
2
5
mA
Shutdown Current
ISHDN
EN = Low
--
--
5
μA
Under Voltage Lockout
Threshold Voltage
VUVLO
VIN Rising
--
3.7
--
VIN Falling
--
3.2
--
UVLO Hysteresis
VHYS
--
0.5
--
V
VREG Output
VREG
--
3.8
--
V
V
Enable
EN Input
Voltage
Logic-High
VIH
TA = −40°C to 85°C
2
--
--
Logic-Low
VIL
TA = −40°C to 85°C
--
--
0.8
V
Shutdown Delay
TSHDN
--
32
--
ms
EN Sink Current
IIH
2
--
20
μA
Power On Reset Time
tRESET
--
256
--
μs
Soft-Start Time
tSS
--
128
--
ms
Fault Blanking Time
tFB
--
256
--
ms
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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RT8302
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
±0.5
±3
%
Current Sink
ILEDx = 60mA to 120mA;
VLEDx = 0.5V
Current Accuracy of Output
Current
IACC
Channel to Channel Matching
IMAT
I
−I
IMAT = LEDx AVE × 100%
IAVE
--
±0.5
±2
%
Output Current of Each
Channel
ILEDx
Programmable 236-Step Current
Setting
30
--
360
mA
Output Voltage
VLEDx
VLED1 to VLED4, All Channels Off
--
--
60
V
Output Leakage Current
IO LEAK
VLEDx = 50V, All Channels Off
--
--
0.5
μA
VVFBH
IVFBH = 50μA
--
3.3
--
VVFBL
IVFBL = 50μA
--
0.2
--
IVFBH
VVFBH = 3.3V
--
50
--
μA
IVFBL
VVFBL = 0.2V
--
1
--
mA
100
--
--
μA
--
--
115
μA
I
−I
IACC = LEDx TAR ×100%
ITAR
Output Pins Capability
Feedback Voltage of VFB pin
Output Current of VFB Pin
PWMO Source Current
Is, PWM
Output Current of IFB Pin
IIFB
V
Protection
OTP Threshold
VOTP
Junction Temperature
--
150
--
°C
OTP Hysteresis
VOTPHYS
Junction Temperature
--
30
--
°C
2-Bit Programmable (Code = 00)
--
3
--
2-Bit Programmable (Code = 01)
--
6
--
2-Bit Programmable (Code = 10)
--
9
--
2-Bit Programmable (Code = 11)
--
12
--
--
50
--
LSP
VLSP
OLP
VOLP
V
mV
Digital Input (SPI Interface)
Input Voltage
High Level
VIH
SDI, VSYN, SCL, CS Input
2
--
--
Low Level
VIL
SDI, VSYN, SCL, CS Input
--
--
1
--
--
10
MHz
V
Maximum SCL Frequency
F_SCL
Setup Time SDI, SCL
ts_SDISCL
SPI Interface Mode
15
--
--
ns
Hold Time SCL, SDI
th_SCLSDI
SPI Interface Mode
15
--
--
ns
Setup Time CS, SCL
ts_CSSCL
SPI Interface Mode
15
--
--
ns
Hold Time SCL, CS
th_SCLCS
SPI Interface Mode
15
--
--
ns
High-Level
VOH
SDO Output
--
VREG
--
Low-Level
VOL
SDO Output
--
0.4
--
SDO Output
Voltage
V
VSYNC Pulse Width On-Time
tVSYNC_ON
150
--
--
ns
Delay Time SCL, SDI
td_SCLSDI
15
--
--
ns
VSYNC Pulse Width Off-Time
tVSYNC_OFF
150
--
--
ns
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of the package.
Note 3. The device is not guaranteed to function outside its operating conditions.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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Copyright © 2013 Richtek Technology Corporation. All rights reserved.
RFSW
56k
RIF
1k
VDC
PWMI
COMP
FSW
SS
EN
L1
33µH
AGND
OOVP
FAULT
FB
PGND
ISW
RT8525
DRV
VIN
220k
Dimming Input
CSS
0.33µF/16V
CDC
1µF/16V
R1
100
CC1
27nF/16V
RC
32k
Enable
C1
1µF/50V
CIN
10µF/50V
VIN
12V
RS
50m
CFB
0.1µF/25V
RFLT
100k
RSLP
2.7k
M1
D1
EN
VSYN
MISO
CS
SCL
MCU
MOSI
ROVP2
ROVP1
RFB1
COUT
100µF/
100V
RFB2
RFB3
200pF
200
CREG
10µF/25V
CVIN
0.1µF/25V
12V
EN
CS
SCL
SDI
VSYN
GND
FLT
IFB
VFB
SDO
PWMO
LED1
RT8302
LED4
Max 360mA
VREG
VIN
VLED
60V (Max)
12V
CREG
10µF/25V
CVIN
0.1µF/25V
RPH
47k
VPH
EN
CS
SCL
SDI
VSYN
GND
FLT
IFB
VFB
SDO
PWMO
LED1
RT8302
LED4
Max 360mA
VREG
VIN
VLED
60V (Max)
RPH
47k
VPH
RT8302
Typical Application Circuit
is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Timing Diagram
SPI Interface
CS
SCL
SDI
0
MSB
6
1
2
5
3
4
4
3
5
2
6
LSB
0
1
7 Bit Register Address
SDO
7
8
9
10
11
12
13
14
15
1
R/W
MSB
7
Previous Data
6
5
4
3
2
1
13
14
LSB
0
8 Bit Data Output
Figure 1. Read Sequence
CS
SCL
SDI
0
MSB
6
1
2
5
4
3
4
3
2
5
1
6
LSB
0
7 Bit Register Address
SDO
7
0
8
MSB
7
9
10
6
5
7
6
5
R/W
Previous Data
11
4
12
3
2
1
15
LSB
0
2
1
0
1 Bit Data Byte
4
3
Register Address
Figure 2. Write Sequence
CS
SCL
8 Clks
8 Clks
8 Clks
8 Clks
8 Clks
MOSI/SDI1
WR IC
Data IC4
Data IC3
Data IC2
Data IC1
SDO1/SDI2
X
WR IC
Data IC4
Data IC3
Data IC2
SDO2/SDI3
X
X
WR IC
Data IC4
Data IC3
SDO3/SDI4
X
X
X
WRIC
Data IC4
1st Execution
Figure 3. Daisy Chain Write Sequence
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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RT8302
CS
SCL
8 Clks
8 Clks
8 Clks
8 Clks
8 Clks
8 Clks
8 Clks
8 Clks
MOSI/SDI1
RD IC
X
X
X
X
X
X
X
SDO1/SDI2
X
RD IC
X
X
IC1 OUT
X
X
X
SDO2/SDI3
X
X
RD IC
X
IC2 OUT
IC1 OUT
X
X
SDO3/SDI4
X
X
X
RD IC
IC3 OUT
IC2 OUT
IC1 OUT
X
SDO4/MISO
X
X
X
X
IC4 OUT
IC3 OUT
IC2 OUT
IC1 OUT
1st Execution
Figure 4. Daisy Chain Read Sequence (only request a read command of the same address for all ICs)
ts_CSSCL
th_CSSCL
CS
td_SCLSDI
ts_SCLSDI
SCL
th_SCLSDI
SDI
MSB
LSB
DATA
Figure 5
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Typical Operating Characteristics
VREG vs. Input Voltage
5
4
4
VREG (V)
Supply Current (mA)
Supply Current vs. Input Voltage
5
3
2
3
2
1
1
No current source work
ILED = 120mA
0
0
5
10
15
20
5
25
10
15
LED Current vs. Input Voltage
EN Level vs. Temperature
130
1.8
V IH
1.6
128
LED Current (mA)
1.4
EN Level
1.2
VIL
1.0
0.8
0.6
0.4
125
123
120
LED1
LED2
LED3
LED4
118
115
113
0.2
VIN = 24V
ILED = 120mA, fSYNC = 120Hz
110
0.0
-50
-25
0
25
50
75
100
5
125
10
15
20
25
Input Voltage (V)
Temperature (°C)
LED Current vs. PWM Duty Cycle
ILED vs. Temperature
60
121.0
48
120.6
36
I LED (mA)
LED Current (mA)
25
Input Voltage (V)
Input Voltage (V)
24
12
120.2
119.8
119.4
VIN = 24V, fSYNC = 120Hz
0
VIN = 24V, fSYNC = 120Hz
119.0
0
20
40
60
80
PWM Duty Cycle (%)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
20
October 2013
100
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
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11
RT8302
DHC Rising Response
DHC Falling Response
VFB
(2V/Div)
VFB
(2V/Div)
I LED
(500mA/Div)
I LED
(500mA/Div)
VIN = 24V, fSYNC = 120Hz
VIN = 24V, fSYNC = 120Hz
Time (50ms/Div)
Time (50ms/Div)
VSYNC Dimming Mode
ILED Synchronous with VSYNC
VSYNC
(2V/Div)
CSN
(5V/Div)
PWMO
(5V/Div)
VSYNC
(2V/Div)
I LED
(100mA/Div)
I LED
(200mA/Div)
VIN = 24V, fSYNC = 120Hz, no delay
VIN = 24V, fSYNC = 120Hz, delay = 6.25ms
Time (2.5ms/Div)
Time (2.5ms/Div)
Power On from EN
Power Off from EN
EN
(5V/Div)
SCL
(5V/Div)
EN
(10V/Div)
SDI
(5V/Div)
I LED
(20mA/Div)
I LED
(20mA/Div)
VIN = 24V, fSYNC = 120Hz
Time (250μs/Div)
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VIN = 24V, fSYNC = 120Hz
Time (10ms/Div)
is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Application Information
The RT8302 is a 4-CH LED current source controller with
SPI interface control. The RT8302 regulates the lowest
voltage of the LED strings and generates a feedback control
signal to a primary controller to regulate the LED current.
Each channel constant current which ensures the
difference in output current value of 4 channels and ICs is
smaller than 3% and 3% in SYNC and ASYNC mode LED
brightness control, respectively. The range of the constant
current output is programmable from 30mA to 360mA by
SPI interface. Moreover, the RT8302 also provides Dynamic
Headroom Control (DHC) function which can generate
feedback signal to DC/DC control loop and regulate the
output voltage of the RT8302. The RT8302 also features
several protections including Short-LED Protection (SLP),
Open-LED Protection (OLP), and Over-Temperature
Protection (OTP).
SYNC Mode Dimming : When the PWM_Control register
is set to 0x10h, the dimming mode operates in SYNC
Mode. During the PWM dimming, the current source turns
on/off according to the VSYNC signal. The LED current
frequency is equivalent to VSYNC frequency. In this mode,
the VSYNC and ILED dimming cycle will delay one period
as shown in the following Figure 6.
SYNC Mode and ASYNC Mode Brightness Dimming
ASYNC Mode Dimming : When the PWM_Control register
is set to 0x15h, the dimming mode operates in ASYNC
Mode. During the PWM dimming, the current source turns
on/off according to the internal clock, as shown in the
following Figure 7.
The LED current high time and delay time can be
calculated as follows :
PWM_HT_Data
× Sampled CLK
High Time =
4096
PWM_Delay_ Data
× Sampled CLK
Delay Time =
4096
The sampled CLK equals VSYNC period. PWM High +
delay time can exceed VSYNC period to fulfill complex
scanning requirements if PWM_HT_Data is FFFh.
PWM_Delay_Data should be 000h.
The RT8302 allows two ways of controlling the LED
brightness.
60Hz, 120Hz, 180Hz, 240Hz
VSYNC
Sampled CLKs 1
Internal Clock
(Fixed 25MHz)
Sampled CLKs 2
Sampled CLKs 3
Sampled CLKs 4
CHn_Delay_VSYNC
CHn Pwm data
512
CHn Pwm OUT
0
100
2000
(512/4096) x sampled CLKs_1
(100/4096) x sampled CLKs_2
PWM On Time
1000
400
PWM On Time
(2000/4096) x sampled CLKs_3
PWM On Time
PWM On Time
tD1
tD2
tD3
tD4
Td1 = (Dn / 4096) x
sampled CLKs_1
tD2 = (Dn / 4096) x
sampled CLKs_2
tD3 = (Dn / 4096) x
sampled CLKs_3
tD4 = (Dn / 4096) x
sampled CLKs_4
Figure 6. SYNC Mode
2. Update PWM grayscale
data of buffers
1. Load data from SDI
3. The next data is updated and start counting as
the last data has finished one PWM period cycle.
CS
SCL
SDI
0
1
2
3
DAddr DAddr DAddr DAddr
(7)
(6)
(5)
(4)
18
19
20
21
22
23
D(n) D(n) D(n) D(n) D(n) D(n)
5
4
3
2
1
0
Next Data
Next Data
VSYNC or Internal
clock 500kHz
CURREGX_DELAY
PWM_Period
Curregx_HT (Internal)
CH1_4 PWM
PWM Data (n - 1)
PWM Data (n)
CH1-4 PWM Output (n - 1)
CH1-4 PWM Output (n)
PWM outputs are switching according to previous data D (n - 1)
(PWM outputs are finished one period cycle.)
PWM outputs are switching according to data D (n)
Figure 7. ASYNC Mode
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
is a registered trademark of Richtek Technology Corporation.
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13
RT8302
The LED current high time can be obtained as follows :
High Time =
VLED
PWM_HT_Data
× Sampled CLK
PWM_Period
RF1
where
Converter VREF
Sampled CLK : internal clock period.
PWM_Period : PWM period register data
RF3
VFB
0.2V to 3.3V
RF2
Dynamic Headroom Control Function (DHC)
The Dynamic Headroom Control (DHC) function is used
to generate feedback signal to primary DC/DC control loop
and regulate the LED current of the RT8302. This function
can improve IC's thermal performance and efficiency. The
RF1, RF2 and RF3 selection is shown in below
equations :
VLED(Default) = VREF × (1+ RF1 )
RF2
V
− 0.2
VLED(MAX) = VLED(Default) +RF1× ( REF
)
RF3
V
− 3.3
VLED(MIN) = VLED(Default) +RF1× ( REF
)
RF3
RF3(MIN) =
VFB − VREF
,
IFB (typ.)
VLED(MAX) − VLED(MIN)
< 0.15 (typ.)
256
where VLED is converter output voltage, VREF is converter
reference voltage and typical IFB is 50μA. The connection
is shown as the following Figure 8.
VIN
0V
Figure 8
Power-On and Power-Off Sequence
When power converter output voltage and supply voltage
of the RT8302 are both ready, EN pulled high will enable
the RT8302. Then, IC will check whether the channel is
unused or not in power on reset time (256μs) in the first
period. The unused channel needs to be short to GND or
the FLT pin will be turned on. The second period is softstart time (128ms), and the RT8302 feedback voltage is
3.3V in this period. Then, IC gets into the third period,
fault blanking time (256ms), and the fault signal would be
ignored even LED in Short/Open condition. After the fault
blanking time, the fault function will be turned on. As for
power off sequence, IC will be shut down when the EN pin
is pulled low for 32ms. The power on sequence is shown
in Figure 9.
24V
By CPU
UVLO
EN
256µs (check
unused CHs
Clear
Registers
POR
Status
SS 128ms
Pulled low
PWMO
Floating
Receive start-up
commands LED
current, PWM, etc
Fault blanking 256ms
Boost
activated
3.3V
In regulation
VFB
VOUT nominal
DHC VOUT min
BOOST VOUT
24V
Assuming pull down
resistor at PWMO
Requested ILED
ILED
(Depends on DHC setting
and LED string)
Figure 9. Power-On Sequence
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Over-Temperature Protection (OTP)
Short-LED Protection (SLP)
The RT8302 has an over-temperature protection function
to prevent overheating due to excessive power dissipation.
The OTP will disable all channels if the junction
temperature exceeds 150°C and send a fault signal. The
channels are re-enabled when the junction temperature
cools down by approximately 30°C.
If the voltage of VLEDx is > VSLP after fault blanking
period, the SLP function will be triggered. Moreover, there
is an adjustable blanking time on every rising part of current
regulator on. When the counter accumulates to 2μs, this
short channel will be off and latched. The FLT pin will be
pulled low. The fault state can only be released by current
regulator off after 32ms. The operation and protection flow
is shown as the following Figure 10.
Open-LED Protection (OLP)
If the VLEDx is < 50mV after a fault blanking period, the
counter will be triggered when PWM is high. Moreover,
there is an adjustable blanking time on every rising part of
current regulator on. When the counter accumulates to
2μs, only this open channel will be off but not latched.
The FLT pin will be pulled low.
VIN and PWMI
Power-On Start
(RESET)
PWMI = low after
32ms or VIN < UVLO
Disable this
Channel
Un-used
VFB = 0.2
Status of Channel
is VLEDx Floating?
(Un-used channel need
short to GND)
4 channels
open
LED OLP
Soft-Start Function
and ILED Turn-On
(128ms)
Over-Temperature
Protection ?
Tj >140°C
Turn-Off All Channel
FLT Pulled Low
Follow the
Normal Flow
SLP : Fault pulled low, only this
channel off and latch
OLP : Fault pulled low, only this
channel off and non-latch
VFB = 3.3V
OLP = SLP = L
Fault Blacking Time VFB = 0.2V to 3.3V
(256ms)
OLP = SLP = L
Tj < 90°C
Auto-recovery
Normal Operation
TF <2µs
TF > 2µs
Open / Short
Detection Time
4 channels
DHC open
LED Short / Open
Latch
Protection ?
Figure 10
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
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15
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-16L 5x5 package, the thermal resistance, θJA, is
Maximum Power Dissipation (W)1
RT8302
4.0
Four-Layer PCB
WDFN-16L 5x5
3.2
2.4
DIP-18
1.6
0.8
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 11. Derating Curve of Maximum Power
Dissipation
28.8°C/W on a standard JEDEC 51-7 four-layer thermal
test board. For DIP-18 package, the thermal resistance,
θJA, is 50.6°C/W on a standard JEDEC 51-7 four-layer
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (28.8°C/W) = 3.47W for
WDFN-16L 5x5 package
PD(MAX) = (125°C − 25°C) / (50.6°C/W) = 1.97W for
DIP-18 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 11 allows
the designer to see the effect of rising ambient temperature
on the maximum power dissipation.
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Layout Consideration
Place the current sensing register
as close as possible to IC PGND.
Place the power components as close as possible. The traces
should be wide and short especially for the high-current loop.
VIN
PGND
L1
VOUT
The compensation circuit should be
kept away from the power loops and
should be shielded with a ground
trace to prevent any noise coupling.
D1
CIN
COUT
RT8525
1
VDC
2
VIN
DRV
M1
14
RS
RC
CC1
PGND 13
3 COMP
EN
12
4
SS
ISW
11
5
FSW
PGND
RSLP
IFB
RIF
6
AGND
PWMO 7
PWMI
ROVP1
OOVP 10
FB
VFB
RFB1
9
FAULT 8
CFB
ROVP2
RFB2
AGND
The feedback voltage-divider resistors
must near the feedback pin. The divider
center trace must be short and avoid
the trace near any switching nodes.
CS
MOSI
MCU
VOUT
SCL
VSYN
EN
RT8302
MISO
1
SDI
2
SCL
LED4 15
CS
3
VSYN
LED3 14
PWMO4 PWMO
The SPI signals path must be
kept away from noise and be short
enough to connect to the RT8302.
16
LED2 13
GND
VFB
RFB3
5
EN
6
VFB
7
FLT
8
SDO
LED1 12
IFB
11
CREG
IFB
VREG 10
PGND
VIN
9
PGND
CVIN
VIN
Locate the CVIN and CREG
as close to VIN as possible.
Figure 12. PCB Layout Guide for WDFN-16L 5x5 Package
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October 2013
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RT8302
Place the power components as close as possible. The traces
should be wide and short especially for the high-current loop.
VIN
L1
VOUT
PGND
The compensation circuit should be
kept away from the power loops and
should be shielded with a ground
trace to prevent any noise coupling.
D1
CIN
M1
COUT
RT8525
1 VDC
2
DRV 14
PGND 13
VIN
3 COMP
EN
12
4
ISW
11
SS
5 FSW
ROVP1
RS
PGND
OOVP 10
RC
6 AGND
CC1
RFB1
RSLP
FB
7 PWMI
9
FAULT 8
ROVP2
RIF
RFB3
RFB2
0
The feedback voltage-divider resistors
must near the feedback pin. The divider
center trace must be short and avoid
the trace near any switching nodes.
CFB
EN
VSYN
PWMO
1
18
VSYN
EN
2
17
SCL
SCL MCU
VFB
3
16
SDI
MOSI
FLT
4
15
CS
CS
SDO
5
14
GND
GND
6
13
LED4
VIN
7
12
LED3
VREG
8
11
LED2
IFB
9
10
LED1
RT8302
CVIN
CREG
Locate the CVIN and CREG
as close to VIN as possible.
The IFB trace must be placed
close to compensation circuit
for reducing noise coupling.
The SPI signals path must be kept
away from noise and be Short
enough to connect to the RT8302.
Place the currentsensing resistor
as close as possible to IC PGND.
Figure 13. PCB Layout Guide for DIP-18 Package
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DS8302-01
October 2013
RT8302
Name
Page
Addr Write Default
Addr.
Reg Control1
02h
EFh
Feedback
Control
04h
01h
Voltage Fault 1
09h
00h
Curreg_Control
0Dh
00h
Reference_DAC
_Voltage
0Eh
00h
PWM-Control
0Fh
15h
PWM_Period_LSB
10h
FFh
PWM_Period_MSB
11h
00h
Curreg1_HT_LSB
12h
22h
00h
Curreg1_HT_MSB
13h
23h
00h
Curreg2_HT_LSB
14h
24h
00h
Curreg2_HT_MSB
15h
25h
00h
Curreg3_HT_LSB
16h
26h
00h
Curreg3_HT_MSB
17h
27h
00h
Curreg4_HT_LSB
18h
28h
00h
Curreg4_HT_MSB
19h
29h
00h
Curreg1_Delay_LSB
32h
42h
00h
Curreg1_Delay_MSB 33h
43h
00h
Curreg2_Delay_LSB
34h
44h
00h
Curreg2_Delay_MSB 35h
45h
00h
Curreg3_Delay_LSB
36h
46h
00h
Curreg3_Delay_MSB 37h
47h
00h
Curreg4_Delay_LSB
38h
48h
00h
Curreg4_Delay_MSB 39h
49h
00h
DHC Timing Control
54h
00h
Overtemp Control
55h
00h
B7
October 2013
B5
B4
B3
Curreg4
_ON
IC Version
B2
B1
Fault
_Reg4
Fault_Reg3
Peak
current
with
VSYNC
B0
Curreg3 Curreg2 Curreg1
_ON
_ON
_ON
SHORT_LED SHORT
OPEN
Detect
_LED
_LED
Voltage
_DET_ON _DET_ON
Fault_Reg2
Feedback
_ON
Fault_Reg1
SR_Control
Vref_DAC_Code
Scrambled
PWM
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
B6
Hysteretic
VSYNC
PWM
_INVERT _INT/EXT
PWM_MODE
PWM_Period_LSB
PWM_Period_MSB
Curreg1_HT_LSB
Curreg1_HT_MSB
Curreg2_HT_LSB
Curreg2_HT_MSB
Curreg3_HT_LSB
Curreg3_HT_MSB
Curreg4_HT_LSB
Curreg4_HT_MSB
Curreg1_Delay_LSB
Curreg1_Delay_MSB
Curreg2_Delay_LSB
Curreg2_Delay_MSB
Curreg3_Delay_LSB
Curreg3_Delay_MSB
Curreg4_Delay_LSB
Curreg4_Delay_MSB
DHC_T
ov_temp
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RT8302
Current Regulator On/Off Control
Addr : 02h
Bit
Bit Name
3:0
Curreg1_ON to
Curreg4_ON
7:4
IC Version
RT8302 Register Control
This Register enables or disable the curreg1 to curreg4
Default
Access
Description
Enables or disables the current regulators
1111
R/W
1 = regulator on
0 = regulator off
Define the IC version
1110
R/W
1110 = RT8302
Feedback Mode Control
Addr : 04h
Bit
Bit Name
0
Feedback on
2
Open_LED_Det_on
3
Short_det_on
5:4
Short LED Detect
Voltage (VSL)
RT8302 Feedback Control
Enables and Disables the Different Feedback modes
Default
Access
Description
1 = Feedback Circuit is Active
1
R/W
0 = The entire feedback loop is disabled
Enables open LED detection comparators
0
R/W
0 = Open LED Detection enabled
1 = Open LED Detection disabled
Enables short LED detection
0
R/W
0 = Short LED Detection on.
1 = Short LED Detection off.
Short LED detection trip voltage (de-bounced 3ms)
00 = 3V
00
R/W
01 = 6V
10 = 9V
11 =12V
Voltage Fault Register Status Read
RT8302 Voltage Fault
Addr : 09h
This register shows a fault on any LED string
Bit
Bit Name
Default
Access
Description
Shows an error on any LED string
00 = no fault
1 : 0 Fault_Reg 1
00
R
01 = open LED
10 = short LED
11 = channel un-used
Shows an error on any LED string
00 = no fault
3 : 2 Fault_Reg 2
00
R
01 = open LED
10 = short LED
11 = channel un-used
Shows an error on any LED string
00 = no fault
5 : 4 Fault_Reg 3
00
R
01 = open LED
10 = short LED
11 = channel un-used
Shows an error on any LED string
00 = no fault
7 : 6 Fault_Reg 4
00
R
01 = open LED
10 = short LED
11 = channel un-used
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Current Regulator Slew Rate Control
Addr : 0Dh
Bit
3 :2
7
Bit Name
RT8302 Curreg Control
Controls Rise and Fall times of the Curreg.
Default
Access
SR_Control
00
R/W
Peak current with
VSYNC
0
R/W
Description
SLEW_RATE_Control. Adjusts the rise and fall time of the
current switching
00 = typ. 1μs
01 = typ. 2μs
10 = typ. 4μs
11 = typ. 8μs
0 = Update Synchronous with next VSYNC
1 = Update Directly after CS Transition
Reference DAC Voltage Control
RT8302 Ref_DAC_Voltage
Addr : 0Eh
The Regulation Current can be chosen in this register
Bit
7:0
Bit Name
Ref_DAC_Voltage
Default
00000000
Access
R/W
Description
00000000 = 30mA
…..
00010100 = 30mA
…..
10000000 = 181.4mA
…..
11111111= 360mA
PWM Mode Control
Addr : 0Fh
Bit
Bit Name
RT8302 PWM Mode
Control the different PWM modes and internal or external PWM
Default
Access
1 :0
PWM_MODE
01
R/W
2
PWM INT/EXT
1
R/W
3
VSYNC_INVERT
0
R/W
5 :4
PWM Hysteretic
Control
01
R/W
7 :6
Scrambled PWM
00
R/W
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
Description
00 SYNC mode
01 ASYNC mode
10 not used
11 not used
Note : SYNC mode can only be used with PWM INT = 0.
0 PWM generator uses external H and VSYNC clock
1 PWM generator uses internal 500kHz clock.
0 VSYNC active high (PWM triggers on rising edge)
1 VSYNC active low (PWM triggers on falling edge)
00 : No Hysteretic
01 : PWM varied range < ± 1 clock cycle
10 : PWM varied range < ± 2 clock cycle
11 : PWM varied range < ± 3 clock cycle
00 : 1 times refresh rate
01 : 2 times refresh rate
10 : 4 times refresh rate
11 : 8 times refresh rate
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RT8302
PWM Period Control
Addr : 10h
Bit
Bit Name
7:0
PWM_PERIOD
_LSB
RT8302 PWM Period-LSB
Defines PWM – Period
Default
Access
11111111
R/W
Description
Defines the period of the PWM
PWM Period Control
Addr : 11h
RT8302 PWM Period-MSB
Defines PWM – Period
Bit
Bit Name
Default
Access
3:0
PWM_PERIOD_MSB
0000
R/W
Description
Defines the period of the PWM
PWM High Time Control
Addr : 12h, 14h, 16h, 18h
Bit
7:0
Bit Name
CurregX_HT_LSB
Addr : 13h, 15h, 17h, 19h
Bit
3:0
Bit Name
CurregX_HT_MSB
RT8302 CURREGX PWM-High Time-LSB
Defines High Time of PWM
Default
Access
00000000
R/W
Description
Defines PWM high time
RT8302 CURREGX PWM-High Time-MSB
Defines High Time of PWM
Default
Access
0000
R/W
Description
Defines PWM high time
PWM Delay Time Control
Addr : 32h, 34h, 36h, 38h
Bit
7:0
Bit Name
CurregX_DELAY
RT8302 CURREGX Delay Time-LSB
Defines delay of the different PWM’s
Default
Access
00000000
R/W
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Description
Defines the delay time of the PWM
is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Addr : 33h, 35h, 37h, 39h
Bit
3:0
Bit Name
CurregX_DELAY
RT8302 CURREGX Delay Time-MSB
Defines delay of the different PWM’s
Default
Access
0000
R/W
Description
Defines the delay time of the PWM
DHC Timing Control
Addr : 54h
Bit
5
Bit Name
DHC_T
RT8302 DHC Timing Control
Enable, disable and timing setup some function of RT8302
Default
Access
0
R/W
Description
DHC one step time
0 = 1ms
1 = 128μs
Over Temperature Control
Addr : 55h
Bit
1
Bit Name
ov_temp
RT8302 Over Temperature Control
Controls the temperature function
Default
0
Access
R/W
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8302-01
October 2013
Description
Displays temperature status
0 = Normal operation
1 = Over temperature shutdown
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23
RT8302
Outline Dimension
2
1
2
1
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.200
0.300
0.008
0.012
D
4.900
5.100
0.193
0.201
D2
4.350
4.450
0.171
0.175
E
4.900
5.100
0.193
0.201
E2
3.650
3.750
0.144
0.148
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 16L DFN 5x5 Package
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is a registered trademark of Richtek Technology Corporation.
DS8302-01
October 2013
RT8302
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
3.700
5.330
0.146
0.210
A1
0.381
0.710
0.015
0.028
A2
3.200
3.600
0.126
0.142
b
0.360
0.560
0.014
0.022
b1
1.143
1.778
0.045
0.070
D
22.350
23.368
0.880
0.920
E
6.200
6.600
0.244
0.260
E1
7.620
8.255
0.300
0.325
2.540
e
L
2.920
0.100
3.800
0.115
0.150
18-Lead DIP Plastic Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
DS8302-01
October 2013
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