RT8301 - Richtek

®
RT8301
8-CH Constant Current LED Driver for Display Backlight
General Description
The RT8301 is a 8-CH constant current sink LED drivers
with Dynamic Headroom Control (DHC) function. RT8301
can provide well current matching ability, adjustable VSET
to choose the suitable dropout voltage across the MOS /
BTJ. Beside that, DHC will provide the stable VFB
dimming, thus voltage ripple is kept as small even during
the dimming.
The RT8301 provides four channel constant currents with
less than 3% differences in output current value among
the 8-CH and ICs respectively. The constant current is
adjustable by each channel external resistor (RISET). The
LED brightness can also be adjusted via the EN/PWM
pin with PWM dimming duty from 1% to 100%. The RT8301
can operate with external components for high current
applications.
The DHC function generates feedback signal to DC/DC
control loop and regulate the output voltage. When RT8301
selects the LED string with the highest forward voltage,
and then the COMP is defined according to that particular
string. The COMP voltage is then compared with the
voltage of VSET to determine the voltage level of VFB,
which therefore control the switching of the primary
controller.
RT8301's protection features include Short LED Protection
(SLP), Open LED Protection (OLP) and Over Temperature
Protection (OTP). When any channel triggers protection
function, LED will be turned off and the FAULT pin will pull
low.
The RT8301 is available in SOP-24 package to achieve
optimized solution for PCB space.
Simplified Application Circuit
VOUT
COUT
8 x NLEDs
DSL11
VCC
FAULT
RSLP
RT8301
VCC
RSET1
DSL18
……
Q1
ZD2
SLP
CVCC1
SLP
VSET
VSET
RSET2
VCC
COMP
RCOMP
VFB
COMP
FAULT
RFAULT
VCC
FAULT
OUT1
CCOMP
DC11
DC18
D1
……
COMP1
M11
PWM Signal
……
CS1
EN/PWM
OUT8
……
CS8
……
GND
RS11
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8301-03 April 2013
M18
RS18
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1
RT8301
Features
Ordering Information
Wide Input Supply Voltage Range : 5V to 24V
z Adjustable Channel Current
z 3% Current Sense Amplifier Input Offset
z VCC Under Voltage Lockout
z Thermal Shutdown
z Adjustable Dynamic Headroom Control (DHC)
Function
z LED Open/Short Protection
z RoHS Compliant and Halogen Free
RT8301
z
Applications
z
z
z
z
z
Package Type
S : SOP-24
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
LCD TV, MNT Display Backlight
DC/DC or AC/DC LED Driver Application
General Purpose Constant Current Source
Architectural and Decorative LED Lighting
LED Street Lighting
(TOP VIEW)
VFB
COMP
EN/PWM
VCC
OUT1
CS1
OUT3
CS3
OUT5
CS5
OUT7
CS7
Marking Information
RT8301GS : Product Number
RT8301
GSYMDNN
YMDNN : Date Code
24
2
23
3
22
4
21
5
20
6
19
7
18
8
17
9
16
10
15
11
14
12
13
VSET
SLP
FAULT
GND
OUT2
CS2
OUT4
CS4
OUT6
CS6
OUT8
CS8
SOP-24
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
VFB
Feedback Signal Output.
2
COMP
LED String Voltage Sense.
3
EN/PWM
Chip Enable (Active High) and PWM Pulse Dimming Input.
4
VCC
Power Supply Input.
5
OUT1
Channel 1 Current Gate Driver Output.
6
CS1
Channel 1 Current Sense Input.
7
OUT3
Channel 3 Current Gate Driver Output.
8
CS3
Channel 3 Current Sense Input.
9
OUT5
Channel 5 Current Gate Driver Output.
10
CS5
Channel 5 Current Sense Input.
11
OUT7
Channel 7 Current Gate Driver Output.
12
CS7
Channel 7 Current Sense Input.
13
CS8
Channel 8 Current Sense Input.
14
OUT8
Channel 8 Current Gate Driver Output.
15
CS6
Channel 6 Current Sense Input.
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DS8301-03 April 2013
RT8301
Pin No.
Pin Name
Pin Function
16
OUT6
Channel 6 Current Gate Driver Output.
17
CS4
Channel 4 Current Sense Input.
18
OUT4
Channel 4 Current Gate Driver Output.
19
CS2
Channel 2 Current Sense Input.
20
OUT2
Channel 2 Current Gate Driver Output.
21
GND
Power Ground.
22
FAULT
Open Drain Output for Fault Detection.
23
SLP
Short LED Protection Sense Input.
24
VSET
Highest Voltage LED String.
Function Block Diagram
VCC
BandGap
Reference
UVLO
0.6V
+
OUT1
-
4V
Regulator
-
VDD
+
8
CS1
0.4V
+
OUT2
-
VDD
2.5V
SLP
CS2
VCC
OTP
COMP
+
VSET
-
+
OUT3
-
+
CS3
……
+
Fault
Logic
……
EN/PWM
-
OUT8
-
VFB
DHC
GND
CS8
FAULT
Operation
The RT8301 is a 8-CH LED driver integrated with a feedback
controller. When EN/PWM is go high and VCC is exceeded
the voltage of the UVLO, it will start-up. During the first
256μs, RT8301 will detect which channels are using. If
the CS pin < 0.4V, that channel is defined as “USED”
channel. Otherwise, the channel is defined as “UN-USED”
if CS pin > 0.4V. And the diver of this channel will be
turned off after the un-used checking.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8301-03 April 2013
Then RT8301 will enter the soft-start state, VFB is kept
as 3.3V. After that period, RT8301 selects the LED string
with the highest forward voltage, and then COMP is defined
according to that particular string. The voltage of COMP
will further compare with the voltage of VSET and
determine the voltage level of VFB.
Beside that, the protection function is activated after the
fault blanking period. If the LED string is broken or shorted,
RT8301 will turn off channels. The internal MOS of the
FAULT will be turned-on, users could add an external pullhigh resistor to get this alarm signal.
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RT8301
Timing Diagram
VCC
EN/PWM
Status
Fault Blanking
~ 256ms
SS Start VFB = 3.3V
~ 128ms
Normal
Operation
IC Reset (Checking Unused CHs) ~ 256µs
The Time of Startup Depends on VOUT
ILED
Figure 1. Power On by EN/PWM Pin Signals
VCC
EN/PWM
Status
Shutdown Delay
~ 32ms
Shutdown
ILED
Figure 2. Power Off by EN/PWM Pin Signals
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is a registered trademark of Richtek Technology Corporation.
DS8301-03 April 2013
RT8301
Absolute Maximum Ratings
z
z
z
z
z
z
z
z
z
z
(Note 1)
Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------CS1 to CS8 ----------------------------------------------------------------------------------------------------------------SLP, EN/PWM, COMP, VSET ----------------------------------------------------------------------------------------(OUT1 to OUT8), VFB, FAULT ----------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
−0.3V to 30V
−0.3V to 7V
−0.3V to 16V
−0.3V to 16V
SOP-24 ---------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOP-24, θJA ---------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------
1.111W
Recommended Operating Conditions
z
z
z
90°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------- 5V to 24V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Supply Current
IVCCON
VEN/PWM = 4V
--
6
--
mA
Shutdown Current
ISHDN
VEN/PWM = 0V
--
20
--
μA
Under Voltage Lockout
Threshold
VUVLO
--
3.7
--
V
Under Voltage Lockout
Threshold Hysteresis
ΔVUVLO
--
500
--
mV
Logic-High VIH
2
--
--
Logic-Low
VIL
--
--
1
Shutdown Delay
tSHDN
--
32
--
ms
EN/PWM Sink Current
IIH
2
--
20
μA
PWM Dimming Frequency
fPWM
90
--
500
Hz
1
--
100
%
582
600
618
mV
--
2.5
--
%
Enable / PWM
EN/PWM Input
Threshold Voltage
PWM Dimming Duty
PWM Frequency = 500Hz
V
Current Sink
CSx Reference Voltage
VREF
VEN/PWM = 4V
Channel to Channel Accuracy
VMATCH
PWM Frequency = 500Hz,
Duty = 80%
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8301-03 April 2013
(Note 5)
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RT8301
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Output Pins Capability
OUTx Source Current
IGsr
5
10
22
mA
OUTx Sink Current
IGsk
--
5
--
mA
VSET Voltage Range
VSET
2
--
10
V
VFB(MAX)
VVSET = 2V, VCOMP = 3V
--
3.3
--
V
VFB(MIN)
VVSET = 3V, VCOMP = 2V
--
12
--
mV
VFB Source Current
IFBsr
VVSET = 2V, VCOMP = 3V ,
VVFB = 1.5V
--
100
--
μA
VFB Sink Current
IFBsk
VVSET = 3V, VCOMP = 2V, VFB = 1.5V
--
1.8
--
mA
VFB Output Voltage Range
Protection
Short LED Protection
VSLP
2.5
--
--
V
Current Sink of SLP
ISLP
--
100
--
μA
Open LED Protection
VOLP
--
0.4
--
V
Over Temperature Protection
TOTP
--
140
--
°C
OTP Hysteresis
ΔTOTP
--
30
--
°C
Reset
tRESET
--
256
--
μs
Soft-Start
tSS
(Note 6)
--
128
--
ms
Fault Blanking Time
tFB
(Note 7)
--
256
--
ms
Timing
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 low effective thermal conductivity single-layer test board per JEDEC 51-3.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. CSX should be left floating for unused channel(s).
Note 6. During tSS, VFB = 3.3V and the protection function SLP and OLP are disabled.
Note 7. The protection function SLP and OLP are disabled. Before the end of tFB.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8301-03 April 2013
RT8301
Typical Application Circuit
For General Application
VOUT
COUT
100µF
8 x NLEDs
12V
RSET1
100k
DSL1
DSL2
DSL3
DSL4
DSL5
DSL6
DSL7
DSL8
ZD1
Q1
DC1
DC2
DC3
DC4
DC5
DC6
DC7
DC8
RT8301
CVCC1
0.1µF
FAULT RSLP
30k
4 VCC
CVCC2
10µF
24
SLP 23
VCC
VSET
RSET2
24k
RCOMP
COMP
3 EN/PWM
90Hz to 500Hz
2
510k
OUT1 5
CS1 6
D1
CCOMP
22nF
M1
OUT2 20
CS2 19
M2
OUT3 7
CS3 8
VCC
RFAULT
300k
22
1
21
FAULT
VFB
GND
M3
OUT4 18
CS4 17
M4
OUT5 9
10
CS5
16
OUT6
15
CS6
11
OUT7
12
CS7
OUT8 14
M5
M6
M7
M8
CS8 13
RS1
4.99
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8301-03 April 2013
RS2
4.99
RS3
4.99
RS4
4.99
RS5
4.99
RS6
4.99
RS7
4.99
RS8
4.99
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Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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VAC
90V to 265V
CCOMP1
22nF
CDD1
10µF
COMP
CDD2
1µF
CX1
0.22µF
COMP CS
GND
R7732
VDD GATE
R4
10
R2
1M
R1
1M
RSW1
1k
R5
22
D2
D1
C1
3.3nF
CSW1
100pF
Q2
Q1
CIN
330µF
RSW2
0.05
M1
R3
100k
TL431
COUT
220µF
RS2
1k
RS1
8.2k
ZD1
60V
VREF
RCOMP1 CCOMP1
0.22µF
22k
PC817
COMP Photo
Coupler
D3
RSET2
24k
RSET1
100k
SLP
RT8301
4 VCC
24 VSET
CVCC1
1µF
ZD2
Q1 6V8S
DSL11
510k
CCOMP2
22nF
COMP1
SLP
23
VCC
DC11
COMP
12V
D4
RCOMP2
FAULT R
SLP
30k
FAULT
COMP 2
RFAULT
300k
22 FAULT
FAULT
5
OUT1
RFB3
51k
1 VFB
CS1 6
CVFB1
33nF
RFB2
OUT8 14
FPWM
7.5k
3
EN/PWM
90Hz to 500Hz
CS8 13
GND
21
VSET
RFB1
300k
VCC
12V
……
CS1
RS3
0.22nF 50
M18
RS18
4.99
……
……
RS11
4.99
M11
……
DC18
……
DSL18
8 x NLEDs
RT8301
For Application Using Fly-Back Converter System
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DS8301-03 April 2013
VIN
24V
DS8301-03 April 2013
CCOMP2
1nF
CDC
10µF
Chip Enable
5V
CSS
0.33µF
RCOMP1
82k
CCOMP1
27nF
CIN2 VIN
1µF 12V
RFSW
200k
CIN1
120µF
EN
SS
FSW
COMP
VDC
PWMI
OOVP
FAULT
FB
GND
PGND
ISW
RT8525
DRV
VIN
RSW2
0.05
90Hz to 500Hz
RFAULT
300k VCC
12V
FAULT
RSW1
2.7k
M1
D1
ROVP2
9.1k
ROVP1
430k
COUT
220µF
RFB2
68k
CVCC1
1µF
24
4
CVFB1
33nF
3
1
RSET2
24k
FAULT
RFAULT
300k
22
RFB1
2M
RFB3 VCC
51k
VSET
RSET1
100k
VCC
12V
SLP
5
2
CS8
OUT8
SLP
Q1
RSLP
30k DSL11
FAULT
13
14
CCOMP3
22nF
COMP1
ZD 6V8S
VCC
12V
COMP
DC11
RCOMP2
D2
510k
23
CS1 6
OUT1
GND
21
EN/PWM
VFB
FAULT COMP
VSET
VCC
RT8301
……
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
RS11
4.99
……
……
M11
……
DC18
……
DSL18
RS18
4.99
M18
8 x NLEDs
4
3
1
22
24
CVFB2
33nF
FAULT
VSET
CVCC2
1µF
VCC
12V
CS1
OUT1
COMP
OUT8
GND CS8
21
EN/PWM
VFB
FAULT
VSET
SLP
RT8301
VCC
……
L1
33µH
SLP
13
14
6
5
COMP
2
23
COMP1
DC21
DSL21
RS21
4.99
……
……
M21
……
DC28
……
DSL28
RS28
4.99
M28
8 x NLEDs
RT8301
For Application Using Multi-Chip Boost Converter System
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RT8301
Typical Operating Characteristics
Supply Current vs. Temperature
7.0
6.5
6.5
Supply Current (mA)
Supply Current (mA)
Supply Current vs. Input Voltage
7.0
6.0
5.5
5.0
6.0
5.5
5.0
4.5
4.5
VEN/PWM = 4V
VEN/PWM = 4V
4.0
4.0
5
9
13
17
21
25
-50
-25
0
50
75
100
125
LEDx Current vs. PWM Duty Cycle
1.8
120
1.6
100
LEDx Current (mA)
Threshold Voltage (V)
EN/PWM Threshold Voltage vs. Input Voltage
V IH
1.4
VIL
1.2
25
Temperature (°C)
Input Voltage (V)
1.0
0.8
ILED1
ILED2
ILED3
ILED4
ILED5
ILED6
ILED7
ILED8
80
60
40
20
VEN/PWM = 4V
VEN/PWM = 4V, FPWM = 160Hz
0.6
0
5
9
13
17
21
25
0
20
Input Voltage (V)
40
60
80
100
PWM Duty Cycle (%)
CSx Reference Voltage vs. Input Voltage
LEDx Current vs. Input Voltage
150
0.7
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
0.5
0.4
0.3
LEDx Current (mA)
Reference Voltage (V)
0.6
0.2
120
ILED1
ILED2
ILED3
ILED4
ILED5
ILED6
ILED7
ILED8
90
60
30
0.1
VEN/PWM = 4V
VEN/PWM = 4V
0
0.0
5
9
13
17
21
Input Voltage (V)
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10
25
5
9
13
17
21
25
Input Voltage (V)
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DS8301-03 April 2013
RT8301
Power On
VFB Output Voltage vs. Input Voltage
4.0
Output Voltage (V)
VEN/PWM = 4V
3.2
VCC = 12V, ILED1 = 120mA
V FB(MAX)
VEN/PWM
(2V/Div)
2.4
VFB
(2V/Div)
1.6
0.8
I LED1
(100mA/Div)
V FB(MIN)
0.0
5
9
13
17
21
Time (1ms/Div)
25
Input Voltage (V)
Power Off
DHC Function
VCC = 12V, ILED1 = 120mA
VCOMP = VSET = 1.8V, VFB = 2.3V
TSHDN = 32ms
VEN/PWM
(2V/Div)
VCOMP
(1V/Div)
VFB
(2V/Div)
VSET
(1V/Div)
VFB
(2V/Div)
I LED1
(100mA/Div)
Time (25ms/Div)
Time (10μs/Div)
Open Protection
Short Protection
VCC = 12V, VEN/PWM = 4V, ILED1 = 120mA
VEN/PWM
(5V/Div)
VCS1
(100mV/Div)
VEN/PWM
(5V/Div)
TFB = 256ms
TSHDN = 32ms
VFB
(2V/Div)
VCC = 12V, VEN/PWM = 4V, ILED1 = 120mA
VSLP
(2V/Div)
TSS = 128ms
I LED1
(100mA/Div)
I LED2
(100mA/Div)
Time (100ms/Div)
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DS8301-03 April 2013
Time (250ms/Div)
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RT8301
Applications Information
The RT8301 is an 8-CH LED current source controller.
This device can also drive an external N-MOSFET for
various applications. The RT8301 regulates the lowest
cathode voltage of the LED strings and generates a
feedback control signal to a primary controller to regulate
the LED current. Each LED channel current is accurately
matched and controlled by sensing an external resistor in
series with the MOSFET. All channels' LED brightness
can be precisely controlled by applying a PWM signal to
the EN/PWM pin. The RT8301 also features several
protection functions including LED short protection, LED
open protection, and over temperature protection. The
device is totally turned off by pulling the EN/PWM pin low
after 32ms.
The feedback level of the whole system is defined by the
resistive voltage divider (RSET1, RSET2) at the VSET pin.
The minimum setting of the VSET pin voltage is according
to the following equation :
Minimum VVSET = VF + VDS + 0.6
Where VF = VD1 + VDC1
VCC
VOUT
DC1
COMP
D1
……
+ VF -
COMP 2
COMP1
+
VDS
-
Under Voltage Lockout
To prevent abnormal device operation caused by low input
voltages, an under voltage lockout is included which
shutdown the device at voltages lower than 3.7V. All
functions will be turned off in this state.
LED Current Setting
Figure 3. COMP Circuit
where VF (VD1 + VDC1) is the forward voltage of the diodes
and VDS is the dropout voltage of the external MOSFET.
Besides, it can improve thermal performance of external
MOSFET by VSET pin voltage setting.
The loop structure keeps the CS pin voltage, VCSx (x = 1
to 8), equal to the reference voltage, VREF. Therefore, by
connecting the resistor, RSx (x = 1 to 8) between the CS
pin and GND, the LED current can be determined via the
value of RSx. The maximum LED current is calculated
according to the following equation :
V
ILEDx = CSx
RSx
The R1, R2 and R3 selection is shown in below equation :
Brightness Control
Where VOUT is converter output voltage, VREF is converter
reference voltage and typical IFB is 100μA. The connection
is shown as the following Figure 4.
The RT8301 provides a PWM dimming function. The LED
string current sinks are turned on/off by the PWM signals
applied at the EN/PWM pin. Thus, the average LED current
can be calculated according to the following equation :
V
Average ILEDx = CS x duty
RSx
where duty is the duty cycle of the PWM signal.
Dynamic Headroom Control Function
The Dynamic Headroom Control (DHC) function is used
to generate feedback signal to adjust primary converter
output voltage with regulate the LED current of the RT8301.
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12
VOUT(default) = ( R2 + 1) × VREF
R1
R2
+
VOUT (MAX.) = (
) × (VREF − 12m) + VOUT(default)
R3
VOUT −(MIN.) = ( R2 ) × (VREF − 3.3) + VOUT(default)
R3
R3(MIN.) =
VFB − VREF
IFB,SR(MAX)
Output Voltage of Converter
(VOUT)
R2
R3
Reference Voltage of
Converter (VREF)
VFB Output Voltage
(10m to 3.3V) of RT8301
R1
Figure 4. DHC Function Setting Circuit
is a registered trademark of Richtek Technology Corporation.
DS8301-03 April 2013
RT8301
Chip Enable and PWM Dimming Operation
Pull the EN/PWM pin low to drive the device into shutdown
mode. Drive the EN pin high to turn on the device again.
To control LED brightness, the RT8301 can perform
dimming function by applying a PWM signal to the EN/
PWM pin. The average LED current is proportional to the
PWM signal duty cycle.
MOSFET Selection
The RT8301 is designed to drive on external N-MOSFET
pass element. MOSFET selection criteria include
threshold voltage, VGS(TH), maximum continuous drain
current, ID, on resistance, RDS(ON). ,maximum drain-tosource voltage, VDS(MAX), and package thermal resistance,
θJA.
Input Capacitors Selection
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. A
ceramic capacitor is recommended for the input capacitor
due to its high ripple current, high voltage rating and low
ESR, which makes them ideal for switching regulator
applications. A 10μF capacitance is sufficient for most
applications. Nevertheless, a higher or lower value may
be used depending on the noise level from the input supply
and the input current to the converter. Note that the voltage
rating of the input capacitor must be greater than the
maximum input voltage. For better voltage filtering, ceramic
capacitors with low ESR are recommended. X5R and X7R
types are suitable because of their wide voltage and
temperature ranges.
Diode Selection
The reverse voltage rating is important parameters for
consideration when making a diode selection. Make sure
that the diode's reverse voltage rating exceeds the
maximum output voltage.
Power On/Off Sequence
When converter's output and VCC is already ready. EN/
PWM pulled high will enable the RT8301, and IC will check
channel unused or not in first period (256μs).The unused
channel must be floating. The second period is 128ms
soft start time, the RT8301 feedback voltage is 3.3V in
this period. Then, IC gets into the fault blanking time
(32ms) when PWM duty is 100% since fault blanking
counter depends on the PWM on period. After the third
period, fault function will turn on. About power off
sequence, IC will shut down after 32ms when EN/PWM
pin is pulled low. The power on/off flow-chart are shown
as the following Figure 5.
VCC and EN/PWM
Power on Start
(RESET)
Disable that Channel
Un-used
(Un-used channel must
be float.)
IC Latched
Power Reset
YES
Status of
Channel
Is CSx floating ?
(256µs)
EN/PWM = L
TSHDN > 32ms ?
Used
VFB = 3.3V
OLP = SLP = L
Start-up Soft-start
Function and ILED
Turn on (128ms)
OLP = SLP = L
Fault Blacking Time
(256ms)
Over Temperature
Protection ?
Normal Operation
FAULT = H
Tj > 140
Turn off All Channel
FAULT = L
YES
NO
OLP (TF < 20µs)
OPEN / SHORT
OLP(TF > 20µs)
SLP(TF > 2µs)
SLP (TF < 2µs)
Tj < 110
Auto-recovery
NO
LED
OPEN/SHORT
Protection ?
VSLP > 2.5V
VOLP < 0.4V
Turn-off All Channel
YES
Figure 5. Power On/Off Flow Chart
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DS8301-03 April 2013
is a registered trademark of Richtek Technology Corporation.
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13
RT8301
If the CS pin < 0.4V after a fault blanking period, the counter
will be triggered when PWM is high. Moreover, there is a
4μs blanking time on every rising part of PWM. When the
counter accumulates to 20μs, all channels will be off and
latched. The FAULT will be pulled low. The fault state can
only be released by pulling the EN/PWM pin low for 32ms.
Short Protection
If the SLP pin > 2.5V after a fault blanking period, the
counter will be triggered when PWM is high. Moreover,
there is a 4μs blanking time on every rising part of PWM
. When the counter accumulates to 2μs, all channels will
be off and latched. The FAULT will be pulled low. The fault
state can only be released by pulling the EN/PWM pin for
32ms.
The maximum power dissipation at TA = 25°C can be
calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (90°C/W) = 1.111W for
SOP-24 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 6 allow the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
1.2
Maximum Power Dissipation (W)1
Open Protection
Over Temperature
The RT8301 has an Over Temperature Protection (OTP)
function to prevent excessive power dissipation from
overheating the device. The OTP shuts down switching
operation and disables all channels if the junction
temperature exceeds 140°C and sends a fault signal. The
channels are re-enabled when the junction temperature
cools down by approximately 30°C.
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.
Single-Layer PCB
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 6. Derating Curve of Maximum Power Dissipation
Layout Consideration
Follow the PCB layout guidelines for optimal performance
of the RT8301.
`
Keep the traces of the main current paths as short and
wide as possible.
`
Put the input capacitor as close as possible to the device
pins (VCC and GND).
`
The VFB path must be kept away from noise and short
enough to connect VREF.
`
The drain pad must large enough to reduce thermal on
MOSFET.
`
In order maintain ILEDx current match, the grounding paths
of each RSx should as similar as possible.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOP-24 package, the thermal resistance, θJA, is 90°C/W
on a standard JEDEC 51-3 single-layer thermal test board.
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14
is a registered trademark of Richtek Technology Corporation.
DS8301-03 April 2013
RT8301
The VFB path must be kept away from noise and
short enough to connect VREF.
VREF Reference
Voltage
OF Converter
VOUT
OF Converter
R2
R1
CVCC capacitor must
be placed as close to
the IC as possible.
RSET1
VFB
0
CCOMP
0 is use to
write jump.
RCOMP
24
VSET
COMP
2
23
SLP
EN/PWM
3
22
FAULT
VCC
4
21
GND
OUT1
5
20
OUT2
CS1
6
19
CS2
OUT3
7
18
OUT4
CS3
8
17
CS4
OUT5
9
16
OUT6
CS5
10
15
CS6
OUT7
11
14
OUT8
CS7
12
13
CS8
RSET2
CVCC
0
0
0
M1
RS1
M3
0
RS3
0
M2
0
RS4
0
M6
RS5
0
M7
0
0
0
M4
M5
0
0
RS2
0
RS6
0
M8
0
RS8
RS7
0
Q1
0
RSLP
ZD
0
0
VOUT
of Converter
In order maintain ILEDx current match, the grounding
COUT
paths of each RSx should as similar as possible.
The drian pad must large enough to reduce
thermal on MOSFET.
Figure 7. PCB Layout Guide for Single-clad Board
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8301-03 April 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT8301
Outline Dimension
H
A
M
B
J
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
15.189
15.596
0.598
0.614
B
7.391
7.595
0.291
0.299
C
2.362
2.642
0.093
0.104
D
0.330
0.508
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.229
0.330
0.009
0.013
I
0.102
0.305
0.004
0.012
J
10.008
10.643
0.394
0.419
M
0.381
1.270
0.015
0.050
24–Lead SOP Plastic Package
Richtek Technology Corporation
5F, No. 20, Taiyuen 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.
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DS8301-03 April 2013