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RT8510GQW
Schematic [ru]
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Richtek RT8510GQW Schematic [ru]

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43V 4-CH LED Driver
RT8510
General Description
Features
zz
Wide Input Voltage : 4.2V to 24V
z
zz
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z High Output V oltage : Up to 43V
zz
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z Adjustable Channel Current : 10mA to 40mA
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z Channel Current Accuracy :
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z Channel Current Matching :
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z PWM Dimming Frequency : 120Hz to 30kHz
zz
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z Adjustable Switching Frequency : 500kHz to 2MHz
zz
zz
z Built-In Soft-Start
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z Disconnects LED in Shutdown
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z Open Current Sink Detection
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z Adjustable Over Voltage Protection
zz
zz
z Over Temperature Protection
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zz
z Current Limit Protection
zz
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z Thin 16-Lead WQFN Package
zz
zz
z RoHS Compliant and Halogen Free
zz
±±
±3%
±±
±±
±2%
±±
Applications
z UMPC and Notebook Computer Ba cklight z GPS, Portable D V D Ba cklight
Pin Configurations
(TOP VIEW)
The RT8510 is available in a WQFN-16L 3x3 pa ckage.
Ordering Information
RT8510
Package Type QW : WQFN-16L 3x3 (W-Type)
AGND
COMP
ISET
RT
CH4
CH3
CH1
CH2
13141516
1 2
GND
3 4
12
OVP
11
PGND
10
17
PGND
9
LX
8765
Lead Plating System
LX
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.
DS8510-03 June 2011 www.richtek.com
EN
VIN
PWM
WQFN-16L 3x3
1
RT8510
Marking Information
HU= : Product Code
HU=YM
DNN
Typical Application Circuit
V
4.2V to 24V
1nF
IN
PWM Dimming
C4
YMDNN : Date Code
C
IN
10µF
Chip Enable
R3 10k
R
C3
10nF
51k
RT
R2 10
C2
1µF
100k
R
ISET
4.75k
7
6
5 2
4 3
VIN
EN
PWM COMP
RT ISET
PGND
10, 11
L
10µH
RT8510
AGND
LX
OVP
CH1 CH2
CH3 CH4
1
8, 9 12
13 14 15
16
D1
R 2M
R 62k
OVP2
OVP1
C
OUT
10µF
: : : :
V
OUT
43V MAX
:
:
:
:
:
:
:
:
:
10 LED String
: : :
PWM Dimming
C4
1nF
V
BATT
2.7V to 24V
Chip Enable
R3 10k
C3
10nF
5V
R 51k
Figure 1. General Application Circuit
RT
100k
C 10µF
C2
1µF
R
ISET
4.75k
L
10µH
IN
RT8510
7
VIN
6
EN
5
PWM
2
COMP
4
RT
3
ISET
PGND
10, 11
OVP
CH1 CH2
CH3 CH4
AGND
1
LX
12
13 14 15
16
D1
8, 9
Figure 2. Low Input V oltage Application Circuit
R 2M
R 62k
OVP2
OVP1
C
OUT
10µF
(V
depends on D
OUT
: : : :
V
OUT
23V MAX
:
:
:
:
:
:
:
:
)
MAX
:
10 LED String
: : :
DS8510-03 June 2011www.richtek.com
2
Function Pin Description
Pin No. Pin Name Pin Function
1 AGND Analog Ground of LED Driver. 2 COMP
3 ISET
4 RT 5 PWM Dimming Control Input.
Compensation Pin for Error Amplifier. Connect a compensation network to ground. LED Current Set Pin. LED current is set by the value of the resistor R connected from the ISET pin to ground. Do not short the ISET pin. V typic al ly 0.6V.
I =
LED
R
95
ISET
Frequency Adj ust Pin. This pin allows setting the switching frequency with a resistor to 500kHz to 2MHz.
RT8510
ISET
is
ISET
6 EN
Chip Enable (Active High). Note that this pin is high impedance. There should be a pull low 100kΩ resistor connected to GND when the control signal is floating.
7 VIN Power Supply Input.
8, 9 LX Switching Pin of Boost Converter.
10, 11 PGND P ower Ground of Boost Co nverter.
12 OVP Sense Input for Over Voltage Protection. The detecting threshold is 1.2V.
13, 14, 15, 16 CH1 to CH 4 Current Sink for LED. Leave the pin unconnected, if not used.
17 (Exposed Pad) GND
Th e e xpo se d p ad m us t be s old er e d to a large PC B and c on nec ted to G N D f o r max imu m pow er dis si pat ion .
Function Block Diagram
RT
COMP
PWM
OSC
PWM
Controller
+
1.2
-
QS
R
Q
+
-
+
EA
-
+
0.6V
+
-
-
0.4V
LXOVP
+
-
EN
Regulator
LED
Detection
OCP
OTP
VIN
:
4
+
:
-
PGND
CH1 CH2
CH3 CH4
ISET
AGND
DS8510-03 June 2011 www.richtek.com
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RT8510
Absolute Maximum Ratings (Note 1)
z Supply Input V oltage to GND------------------------------------------------------------------------------------------ −0.3V to 26.5V z EN, PWM, ISET, COMP, RT to GND -------------------------------------------------------------------------------- −0.3V to 26.5V z LX, OVP , CH1, CH2, CH3, CH4 to GND ---------------------------------------------------------------------------- −0.3V to 48V z Power Dissipation, P
WQFN-16L 3x3----------------------------------------------------------------------------------------------------------- 1.471W
z Package Thermal Resistance (Note 2)
WQF N-16L 3x3, θJA----------------------------------------------------------------------------------------------------- 68°C/W WQF N-16L 3x3, θJC----------------------------------------------------------------------------------------------------- 7.5°C/W
z Lead T emperature (Soldering, 10 sec.) ----------------------------------------------------------------------------- 260°C z Junction T emperature --------------------------------------------------------------------------------------------------- 150°C z Storage T emperature Range------------------------------------------------------------------------------------------- −65°C to 150°C z ESD Susceptibility (Note 3)
HBM ------------------------------------------------------------------------------------------------------------------------ 2kV MM-------------------------------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
@ T
D
= 25°C
A
z Supply Input Voltage, V z Junction T emperature Range ------------------------------------------------------------------------------------------ −40°C to 125°C z Ambient T emperature Range ------------------------------------------------------------------------------------------ −40°C to 85°C
---------------------------------------------------------------------------------------------- 4.2V to 24V
IN
Electrical Characteristics
(V
= 4.5V, T
IN
VIN Quiesce nt Current IQ VIN Shutdown Current I
VIN Under Voltage Lockout UVLO
Control Input
EN, PWM Threshold
Voltage
PWM Dimming Frequency f EN, PWM Leakage Current I EN Shutdown Delay tEN R
Boost Converte r
LX On Resistance (N-MOSFET) R M inimu m O N Time t
M aximum Duty D LX Current Limit I
= 25°C unless otherwise specified)
A
Parameter Symbol Test Conditions Min Typ Max Unit
V V
VIN = 4.5V , EN = 0V -- -- 10 μA
SHDN
Rising -- 2.2 -­Falling -- 2.1 --
Logic-High VIH 2 -- -­Logic-Low V
IL
PWM
2 -- 6 μA
LKG
V
120 -- 30k Hz
= 0V, No Switching -- 1 1.5
COMP
= 2V, Switching 2 3
COMP
mA
V
= 4.2V to 24V
IN
= 51kΩ -- 32 -- ms
RT
-- -- 0.8
V
RRT = 25kΩ -- 2 --
OSC
DS(ON)_N VIN
-- 120 -- ns
MON
MAX
-- 2 -- A
LIM
RRT = 51kΩ -- 1 -- Switching Frequency f
= 102kΩ -- 0.5 --
R
RT
> 4.5V -- 0.2 0.32 Ω
V
COMP
= 2V, Switching -- 90 -- %
MHz
T o be continued
DS8510-03 June 2011www.richtek.com
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RT8510
Parameter Symbol Test Conditions Min Typ Max Unit
LED Current Programming
2V > CHx > 0.4V Calculating
LED Current Matching I
ISET Pin Voltage V LED Current I
(I
LEDM
-- 0.6 -- V
ISET
2V > CHx > 0.4V, R
CHx
(MAX)
R
ISET
− I
= 4.75kΩ
(AVG)
) / I
x 100%,
(AVG)
= 4.75kΩ 19.4 20 20.6 mA
ISET
Fault Protection
OVP T hreshold V OVP F ail Thr eshold V
1.16 1.2 1.24 V
OVP
-- 50 -- mV
OVPF
Thermal Shutdown Temperature TSD -- 160 -- °C LED Pin Under Voltage
Threshold
Regu la t ed V
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or a ny other conditions beyond those indicated in the operation al sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability.
Note 2. θ
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. Guaranteed by design; not subject to production testing.
is mea sured in natural convection at T
JA
51-7 thermal measurement standard. The measurement case position of θ
V
CHx
No Connection -- 50 -- mV
V
LSD
Highest LE D String Vol tage,
CHx
A
= 4.75kΩ
R
ISET
= 25°C on a high-effective thermal conductivity four-layer test board of JEDEC
is on the exposed pad of the package
JC
-- -- ±2 %
-- 0.4 -- V
DS8510-03 June 2011 www.richtek.com
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RT8510
Typical Operating Characteristics
Efficiency vs. Input Voltage
100
90 80 70 60 50 40
Efficiency (%)
30 20 10
0
4 8 12 16 20 24
10 x 4 LEDs, f
Input Voltage (V)
LED Current vs. Temperature
26
24
22
OSC
= 1MHz
LED Current vs. Input Voltage
26
24
22
20
18
LED Current ( m A)
16
14
4 9 14 19 24
Input Volt age (V)
V
vs. Temperature
0.70
0.65
0.60
ISET
CH1
CH2
CH3
CH4
f
OSC
= 1MHz
20
18
LED Current ( m A)
16
14
VIN = 12V, f
-50 -25 0 25 50 75 100 125
OSC
Temperature (°C)
V
vs. Input Voltage
0.8
0.7
0.6
ISET
(V)
ISET
0.5
V
0.4
f
0.3 4 8 12 16 20 24
OSC
Input Volt age (V)
= 1MHz
= 1MHz
(V)
0.55
ISET
V
0.50
0.45
0.40
VIN = 12V, f
-50-250 255075100125
OSC
= 1MHz
Temperature (°C)
LED Current vs. PWM Duty Cycle
90 80 70 60 50 40 30
LED Current (mA)
20 10
0
0 102030405060708090100
10 x 4 LEDs, f
Dut y Cycle (%)
PWM = 30kHz
PWM = 10kHz
PWM = 1kHz
PWM = 120Hz
OSC
= 1MHz
DS8510-03 June 2011www.richtek.com
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RT8510
OVP Threshold vs. Input Voltage
1.5
1.4
1.3
1.2
OVP Threshold (V)
1.1
1.0 4 8 12 16 20 24
Input Voltage (V)
Line Transient Response
f
OSC
= 1MHz
Switch Off Current vs. Temperature
1.5
1.3
1.1
0.9
0.7
Switch Off Current (mA)
f
= 1MHz, VIN = 4.5V
0.5
-50-25 0 25 50 75100125
OSC
Temperature (°C)
Line Transient Response
V
IN
(5V/Div)
I
OUT
(50mA/Div)
VIN = 11V to 14V, f
Time (50ms/Div)
OSC
= 1MHz
V
IN
(2V/Div)
I
OUT
(50mA/Div)
VIN = 4.5V to 5.5V, f
Time (50ms/Div)
OSC
= 1MHz
DS8510-03 June 2011 www.richtek.com
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RT8510
Application Information
The RT8510 is a general purpose 4-CH LED driver ca pable of delivering an adjustable 10 to 40mA LED current. The IC is a current mode boost converter integrated with a 43V/2A power switch a nd can cover a wide V
4.2V to 24V . The switching frequency is a djustable by an external resistor from 500kHz to 2MHz. The part integrates built-in soft start, with PWM dimming control; moreover, it provides over voltage, over temperature a nd current limiting protection features.
Soft-Start
The RT8510 equips a built-in soft-start feature to prevent high inrush current during start-up. The soft-start function prevents excessive input current and input voltage droop during power on state.
Compensation
The control loop can be compensates by adjusting the external components connected to the COMP pin. The COMP pin is the output of the internal error a mplifier . The compensation capacitors, C3 and C4, will adjust the integrator zero and pole respectively to maintain stability . Moreover, the resistor, R3, will adjust the frequency integrator gain for fa st tran sient response.
Switching Frequency
range from
IN
T2
Normal Operation
T3
Pulse Skipped
CLK
Output of PWM
Comparator
PWM Pulse
T1
Normal Operation
Figure 3. Pulse Skip Mode
Setting and Regulation of LED Current
The LED current can be calculated by the following equation :
I
LED
where R
95
≅
R
ISET
is the resistor between the ISET pin and GND.
ISET
This setting is the reference for the LED current at channel 1-4 and represents the sensed LED current for ea ch string. The DC/DC converter regulates the LED current according to R
ISET
.
Power Sequence
LED Driver is without power sequence concern. Figure 4, Figure 5 and Figure 6 are different power sequences respectively . There is no concern in the above condition.
VIN
T4
Normal Operation
The LED driver switching frequency is able to a djusted as the following equation :
f (MHz)
OSC
51k
≅
R
RT
LED Connection
The RT8510 equips 4-CH LED divers with ea ch cha nnel supporting up to 12 LEDs. If the boost converter input voltage too close to the output voltage, V increa sed. T o prevent this phenomenon, plea se keep V
ripple will be
OUT
OUT
higher than 1.2 x VIN. The LED strings are connected from the output of the boost converter to pins 13, 14, 15 and 16 respectively . If one of the LED channel is not used, the LED pin should be opened directly.
Duty pulse close to minimum on time and small than 120ns, we will skip duty clock. The Figure 3. shows the pulse skipped time diagram.
8
VOUT
EN
PWM
Power On Mode 1
VIN
VOUT
EN
PWM
Power On Mode 2
Figure 4
DS8510-03 June 2011www.richtek.com
RT8510
VIN
VOUT
EN
PWM
VIN
VOUT
EN
PWM
Power Off Mode 1
Power Off Mode 2
Figure 5
Over Voltage Protection
The RT8510 integrates over voltage protection (OVP) function. When the voltage at the OVP pin reaches the threshold voltage, the internal switch will be turned off. The internal switch will be turned on again once the voltage at OVP pin drops below its threshold voltage.
The OVP threshold voltage is adjustable and can be clamped at a certain voltage level a nd it ca n be calculated by the following equation :
⎛⎞
R
VV1
OUT(OVP) OVP
where V R
OVP1
=×+
= 1.2V (typ.).
OVP
and R
are the resistors in the voltage divider
OVP2
OVP2
⎜⎟
R
OVP1
⎝⎠
connected to the OVP pin. If at lea st one string is in normal operation, the controller will automatically ignore the open strings and continue to regulate the current for the strings in normal operation. It is suggested to use 2MΩ for R
OVP2
to reduce loading effect.
VIN
VOUT
EN
PWM
VIN
VOUT
EN
PWM
UVLO
Power On Mode 3
UVLO
Power On Mode 3
Figure 6
Current Limit Protection
The RT8510 can limit the peak current to achieve over current protection. The RT8510 senses the inductor current during the “ON” period that flows through the LX pin. The duty cycle depends on the current signal and internal slope compensation in comparison with the error signal. The internal switch will be turned off when the current signal is larger than the internal slope compensation. In the “OFF” period, the inductor current will be decrea sed until the internal switch is turned on by the oscillator.
Brightness Control
The RT8510 brightness dimming control is determined by the signal on the PWM pin with a suggested PWM frequency range from 120Hz to 30kHz. However , the LED current cannot be 100% proportional to duty cycle especially f or high frequency and low duty ratio because of physical limitation caused by inductor rising time. Plea se refer to T a ble 1 and Figure 7.
DS8510-03 June 2011 www.richtek.com
9
RT8510
η
Table 1.
Dimming Frequency (Hz) Duty (Min.) Duty (Max.)
120 < f 500 < f 1k < f 2k < f 5k < f 10k < f
Note : The minimum duty in Table 1 is ba sed on the a pplication circuit and does not consider the devi ation of current linearity.
≤ 500 0.2% 100%
PWM
≤ 1k 0.4% 100%
PWM
≤ 2k 0.8% 100%
PWM
≤ 5k 1.5% 100%
PWM
≤ 10k 3% 100%
PWM
≤ 30k 10% 100%
PWM
LED Current vs. PWM Duty Cycle
90 80 70 60 50 40 30
LED Current (mA)
20 10
0
0 102030405060708090100
VIN = 12V, V
Dut y Cycle (%)
PWM = 30kHz
PWM = 10kHz
PWM = 1kHz
PWM = 120Hz
= 0V to 3V
PWM
Figure 7
Over Temperature Protection
The RT8510 ha s over temperature protection function to prevent the IC from overheating due to excessive power dissipation. The OTP function will shutdown the IC when junction temperature exceeds 160°C .
Inductor Selection
The value of the inductance L can be a pproximated by the following equation, where the transition is from discontinuous conduction mode (DCM) to continuous conduction mode (CCM) :
D(1D) V
×− ×
L
=
2f I
2
OUT
××
OSC OUT
The duty cycle can be calculated a ccording to the following equation :
VV
−
OUT IN
D
=
V
OUT
where V minimum input voltage, f and I
OUT
is the maximum output voltage, VIN is the
OUT
is the operating frequency
OSC
is the total current from all LED strings.
The boost converter operates in DCM over the entire in put voltage range when the inductor value is below this value L. When inductance greater is than L, the converter operates in CCM at the minimum input voltage a nd may be discontinuous at higher voltages.
The inductor must be selected with a saturated current rating that is greater than the peak current provided by the following equation :
VI VDT
×××
I
PEAK
OUT OUT IN
=+
V2L
××
η
IN
where η is the eff iciency of the power converter a nd T is the operating period.
Diode Selection
Schottky diodes are recommended for most a pplication s because of their fa st recovery time a nd low forward voltage. The power dissipation, reverse voltage rating and pulsating peak current are the important parameters for Schottky diode selection. Ma ke sure that the diode's peak current rating exceeds I
and reverse voltage rating exceeds
PEAK
the maximum output voltage.
Output Capa citor Sele ction
The input ca pacitor reduce s current spikes from the input supply and minimizes noise in jection to the converter. For most applications, a 10 μF ceramic ca pa citor is suf ficient. A value higher or lower may be used depending on the noise level from the input supply and the input current to the converter.
For lower output voltage ripple, a low ESR cera mic capa citor is recommended. The output voltage ripple consists of two components: one is the pulsating output ripple current flowing through the ESR, and the other is
VV V
RIPPLE RIPPLE_ESR RIPPLE_C
I R
=+
⎛⎞
IVV
≅×+
PEAK ESR
PEAK AVDD IN1
CVf
⎜⎟ ⎝⎠
OUT1 AVDD
− ××
DS8510-03 June 2011www.richtek.com
10
RT8510
)
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 a mbient temperature. The maximum power dissipation can be calculated by the following formula :
P where T
the a mbient temperature, and θ
D(MAX)
= (T
J(MAX)
− TA) / θ
J(MAX)
JA
is the maximum junction temperature, T
is the junction to ambient
JA
A
thermal resistance. For recommended operating condition specifications of
RT8510, the maximum junction temperature is 125°C a nd TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For WQF N­16L 3x3 packages, the thermal resistance, θJA, is 68°C/ W on a standard JEDEC 51-7 f our-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula :
P
= (125°C − 25°C) / (68°C/W) = 1.471W for
D(MAX)
WQF N-16L 3x3 pa ckage The maximum power dissipation depends on the operating
ambient temperature for fixed T
and thermal
J(MAX)
resistance, θJA. For RT8510 pa ckage, the derating curve in Figure 8 allows the designer to see the effect of rising ambient te mperature on the maximum power dissipation.
1.60
1.40
Four-Layer PCB
Layout Considerations
PCB layout is very important f or designing switching power converter circuits. The following layout guides should be strictly followed for best perf ormance of the RT8510.
` The power components, L1, D1, C
, C
IN
placed a s close a s possible to reduce current loop. The PCB trace between power components must be a s short and wide a s possible.
` Place L1 and D1as close as possible to LX pin . The
is
trace should be a s short a nd wide as possible.
` The compensation circuit should be kept away from
the power loops and should be shielded with a ground trace to prevent any noise coupling. Place the compensation components as close as possible to COMP pin.
` The exposed pad of the chip should be connected to
ground plane for thermal con sideration.
The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling.
GND
C3
C4
R3
AGND
COMP
ISET
RT
CH4
CH3
CH1
CH2
13141516
1 2
GND
3 4
17
8765
LX
EN
VIN
PWM
C2
GND
Place the power components as close as possible. The traces should be wide and short especially for the high­current loop.
12
OVP
11
PGND
10
PGND
9
LX
D1
R2
L1
Figure 9. PCB Layout Guide
C
+
V
must be
OUT
IN
IN
V
OUT
C
OUT
GND
1.20
1.00
0.80
0.60
0.40
0.20
Maximum Power Dissipation (W
0.00 0 25 50 75 100 125
Ambient Temperature ( °C)
Figure 8. Derating Curve f or RT8510 Pa ckage
DS8510-03 June 2011 www.richtek.com
11
RT8510
Outline Dimension
D
D2
L
SEE DETAIL A
1
E
e
A
A3
A1
E2
1
b
2
1 2
DET AIL A
Pin #1 ID a nd T ie 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 0.180 0.300 0.007 0.012
D 2.950 3.050 0.116 0.120
D2 1.300 1.750 0.051 0.069
E 2.950 3.050 0.116 0.120 E2 1.300 1.750 0.051 0.069
e 0.500 0.020 L 0.350 0.450
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
0.014 0.018
W-Type 16L QFN 3x3 Package
Richtek Technology Corporation
Taipei Office (Marketing) 5F, No. 95, Minchiuan Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)86672399 Fax: (8862)86672377 Email: marketing@richtek.com
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
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