RT8482 - Farnell

®
RT8482
High Voltage High Current LED Driver Controller for Buck
Boost, or Buck-Boost Topology
General Description
Features
The RT8482 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 a maximum
operating input voltage of 36V and output voltage up to
48V, the RT8482 is ideal for Buck, Boost or Buck-Boost
operation.
z
With 350kHz operating frequency, the external inductor
and capacitors can be small while maintaining high
efficiency.
z
z
z
z
z
z
z
z
Dimming can be either analog or PWM digital. The unique
built-in clamping comparator and filter allow easy low
noise analog dimming conversion from PWM signal with
only one external capacitor.
Applications
z
z
The RT8482 is available in WQFN-16L 3x3 and
SOP-16 packages.
Ordering Information
RT8482
Package Type
S : SOP-16
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
High Voltage Capability : VIN Up to 36V, VOUT Up to
48V
Buck, Boost or Buck-Boost Operation
Current Mode PWM with 350kHz Switching
Frequency
Easy Dimming : Analog, PWM Digital or PWM
Converting to Analog with One External Capacitor
Programmable Soft Start to Avoid Inrush Current
Programmable Over Voltage Protection
VIN Under Voltage Lockout and Thermal Shutdown
16-Lead WQFN and SOP Packages
RoHS Compliant and Halogen Free
z
z
General Industrial High Power LED Lighting
Desk Lights and Room Lighting
Building and Street Lighting
Industrial Display Backlight
Marking Information
RT8482GS
RT8482GS : Product Number
RT8482
GSYMDNN
YMDNN : Date Code
Note :
Richtek products are :
`
H9= : Product Code
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
RT8482GQW
H9=YM
DNN
YMDNN : Date Code
Suitable for use in SnPb or Pb-free soldering processes.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8482-02 May 2012
is a registered trademark of Richtek Technology Corporation.
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1
RT8482
Pin Configurations
GND
VCC
OVP
EN
NC
SS
DCTL
ACTL
16
15
2
3
14
4
5
13
12
6
7
11
10
8
9
16 15 14 13
GBIAS
GATE
NC
ISW
1
12
2
11
GND
3
10
17
4
9
5
6
7
NC
SS
DCTL
ACTL
8
NC
ISP
ISN
VC
GBIAS
GATE
NC
ISW
NC
ISP
ISN
VC
GND
VCC
OVP
EN
(TOP VIEW)
SOP-16
WQFN-16L 3x3
Typical Application Circuit
L1
47µH
VIN
4.5V to 36V
CIN
10µF
RT8482
VCC
13 EN
5V
Analog
Dimming
RVC
10k
CVC
3.3nF
11
SS
GBIAS 1
CSS
0.1µF
VOUT
48V (Max.)
RSW
0.05
ISW 4
6
ISP
7
ISN
14
OVP
9 ACTL
10 DCTL
8 VC
COUT
1µF
M1
GATE 2
15
RSENSE
0.09
D1
R1
VOUT
R2
CB
1µF
GND
16, 17 (Exposed Pad)
Figure 1. Analog Dimming in Boost Configuration
L1
47µH
VIN
4.5V to 36V
CIN
10µF
RT8482
15
13 EN
5V
PWM
Dimming control
RVC
10k
CVC
3.3nF
VCC
10 DCTL
8 VC
11
CSS
0.1µF
SS
9 ACTL
CA
0.47µF
RSENSE
0.09
D1
GATE 2
ISW 4
6
ISP
7
ISN
14
OVP
GBIAS 1
COUT
1µF
M1
VOUT
48V (Max.)
RSW
0.05
R1
CB
1µF
VOUT
R2
GND
16, 17 (Exposed Pad)
Figure 2. PWM to Analog Dimming in Boost Configuration
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DS8482-02 May 2012
RT8482
L1
47µH
VIN
4.5V to 36V
D1
VOUT
48V (Max.)
CIN
10µF
RT8482
15
5V
Analog
Dimming
13 EN
ISW 4
9 ACTL
10 DCTL
ISN
8 VC
11
SS
RVC
10k
CSS
0.1µF
CVC
3.3nF
COUT
1µF
M1
GATE 2
VCC
RSW
0.05
RSENSE
0.09
7
ISP 6
OVP 14
GBIAS 1
R1
CB
1µF
VOUT
R2
GND
16, 17 (Exposed Pad)
Figure 3. Analog Dimming in Buck-Boost Configuration
D1
COUT
1µF
RSENSE
VIN
CIN
10µF
0.09
RT8482
VCC
13 EN
5V
Analog
Dimming
CVC
3.3nF
ISN 7
9 ACTL
10 DCTL
RVC
10k
CSS
0.1µF
GATE
M1
2
RSW
0.05
ISW 4
8 VC
11
SS
1 GBIAS
CB
1µF
L1
47µH
ISP 6
15
OVP 14
GND
16, 17 (Exposed Pad)
Figure 4. Analog Dimming in Buck Configuration
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3
RT8482
Functional Pin Description
Pin No.
Pin Name
Pin Function
SOP-16
WQFN-16L 3x3
1
1
GBIAS
Internal Gate Driver Bias. A good bypass capacitor is required.
2
2
GATE
External MOSFET Switch Gate Driver Output.
3, 5, 12
3, 5, 12
NC
No Internal Connection.
4
4
ISW
External MOSFET Switch Current Sense. Connect the current sense
resistor between external N-MOSFET switch and the ground.
6
6
ISP
LED Current Sense Amplifier Positive Input.
7
7
ISN
LED Current Sense Amplifier Negative Input. Voltage threshold
between ISP and ISN is 190mV.
8
8
VC
PWM Control Loop Compensation.
9
9
ACTL
10
10
DCTL
11
11
SS
13
13
EN
14
14
OVP
15
15
VCC
16
16,
17 (Exposed Pad)
GND
Analog Dimming Control. The effective programming voltage range
of the pin is between 0.2V and 1.2V.
By adding signal on DCTL pin can be averaged and converted into
analog dimming signal on the ACTL pin following the formula below. a
0.47μF filtering capacitor on ACTL pin, the PWM dimming
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 1.2V.
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.
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DS8482-02 May 2012
RT8482
Function Block Diagram
VOC
8.5V
EN
+
2V
+
-
Shutdown
GBIAS
-
4.5V
S
OSC
-
VCC
GATE
5V
+
R
OVP
1.18V
+
R
-
R
100k
R
+
-
-
110mV
+
VC
ISW
GM
+
6µA
ISN
ISP
SS
1.2V
DCTL
1.2V
+
+
-
-
GND
ACTL
VISP – VISN
(mV)
190
0
0.2
1.2
VACTL (V)
Figure 4
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5
RT8482
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------GBIAS, GATE -------------------------------------------------------------------------------------------------------------z ISW --------------------------------------------------------------------------------------------------------------------------z ISP, ISN ---------------------------------------------------------------------------------------------------------------------z DCTL, ACTL, OVP Pin Voltage ---------------------------------------------------------------------------------------z EN Pin Voltage ------------------------------------------------------------------------------------------------------------z Power Dissipation, PD @ TA = 25°C
SOP-16 ---------------------------------------------------------------------------------------------------------------------WQFN-16L 3x3 ------------------------------------------------------------------------------------------------------------z Package Thermal Resistance (Note 3)
SOP-16, θJA ----------------------------------------------------------------------------------------------------------------WQFN-16L 3x3, θJA ------------------------------------------------------------------------------------------------------WQFN-16L 3x3, θJC -----------------------------------------------------------------------------------------------------z Junction Temperature ----------------------------------------------------------------------------------------------------z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------z Storage Temperature Range -------------------------------------------------------------------------------------------z ESD Susceptibility (Note 4)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------z
z
Recommended Operating Conditions
z
z
38V
10V
1V
54V
8V (Note 2)
20V
1.176W
1.471W
85°C/W
68°C/W
7.5°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
(Note 5)
Supply Input Voltage Range, VCC ------------------------------------------------------------------------------------- 4.5V to 36V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Electrical Characteristics
(VCC = 24V, No Load on any Output, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Overall
Supply Current
IVCC
VC ≤ 0.4V (Switching off)
--
6
7.2
mA
Shutdown Current
ISHDN
VEN ≤ 0.7V
--
12
--
μA
EN Threshold
Voltage
Logic-High
VIH
2
--
--
Logic-Low
VIL
--
--
0.5
--
--
1.2
μA
180
190
200
mV
--
140
--
μA
--
±20
--
μA
--
0.7
--
V
VACTL = 1.2V
--
1
--
VACTL = 0.2V
--
10
--
VEN ≤ 3V
EN Input Current
V
Current Sense Amplifier
Input Threshold (VISP − VISN)
12V ≤ common mode ≤ 36V
ISP / ISN Input Current
IISP / IISN
VC Output Current
IVC
4.5V ≤ VISP = VISN ≤ 48V
VISP − VISN = 190mV,
0.5V ≤ VC ≤ 2.4V
VC Threshold for PWM Switch
Off
LED Dimming
Analog Dimming ACTL Pin
Input Current
IACTL
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μA
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DS8482-02 May 2012
RT8482
Parameter
Min
Typ
Max
Unit
--
0.3
--
V
--
--
0.5
μA
280
350
420
kHz
--
250
--
ns
IGBIAS = 20mA
--
8.5
--
V
IGate = −50mA
--
7.2
--
IGate = −100μA
--
7.8
--
IGate = 50mA
--
0.25
--
IGate = 100μA
--
0.1
--
1nF Load at GATE
--
15
--
ns
ISW_LIM
--
110
--
mV
OVP Threshold
VOVP_th
--
1.18
--
V
OVP Input Current
IOVP
0.7V ≤ V OVP ≤ 1.5V
--
--
0.1
μA
Soft-Start Pin Current
ISS
VSS ≤ 2V
--
6
--
μA
--
145
--
°C
--
10
--
°C
LED Current Off Threshold at
ACTL
DCTL Input Current
Symbol
Test Conditions
VACTL_OFF
IDCTL
0.3V ≤ V DCTL ≤ 6V
PWM Control
Switching Frequency
Minimum Off Time
fSW
(Note 6)
Switch Gate Driver
GBIAS Voltage
VGBIAS
Gate Voltage High
VGate_H
Gate Voltage Low
VGate_L
GATE Drive Rise and Fall Time
PWM Switch Current Limit
Threshold
V
V
OVP and Soft-Start
Thermal Protection
Thermal Shutdown Temperature TSD
Thermal Shutdown Recovery
ΔTSD
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. If connected with a 20kΩ serial resistor, ACTL and DCTL can go up to 36V.
Note 3. 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 4. Devices are ESD sensitive. Handling precaution is recommended.
Note 5. The device is not guaranteed to function outside its operating conditions.
Note 6. When the natural maximum duty cycle of 350kHz switching frequency is reached, the switching cycle will be skipped (not
reset) as the operating condition requires to effectively stretch and achieve higher on cycle than the natural maximum
duty cycle set by the 350kHz switching frequency.
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RT8482
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Input Voltage
90
90
Efficiency (%)
100
Efficiency (%)
100
80
70
80
70
Boost Application, VOUT = 48V, IOUT = 1A
Boost Application, VIN = 24V, VOUT = 48V
60
60
0
200
400
600
800
1000
1200
9
12
15
Output Current(mA)
Current (mA)
21
24
27
30
Switching Frequency vs. Temperature
Switching Frequency vs. Input Voltage
400
Switching Frequency (kHz)1
400
Switching
Frequency(kHz
Switching Frequency
(kHz)
18
Input Voltage (V)
380
360
340
320
380
360
340
320
VIN = 24V
300
300
4
8
12
16
20
24
28
32
-50
36
-25
0
25
50
75
100
125
Temperature (°C)
Input Voltage (V)
Shutdown Current vs. Input Voltage
Supply Current vs. Input Voltage
30
10
Supply Current (mA)
Shutdown Current
Current(μA)
(uA)
Shutdown
9
25
20
15
10
5
8
7
6
5
4
3
2
1
0
0
4
8
12
16
20
24
28
32
Input Voltage (V)
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8
36
4
8
12
16
20
24
28
32
36
Input Voltage (V)
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RT8482
LED Current vs. DCTL Duty
2.5
2.0
2.0
LED Current (A)
LED Current (A)
LED Current vs. ACTL
2.5
1.5
1.0
DCTL high level is 3V and low level is 0V,
DCTL = 10kHz, VIN = 24V, RSENS = 90mΩ
1.5
1.0
0.5
0.5
VIN = 24V, RSENS = 90mΩ
0.0
0.0
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
0
1.1 1.2 1.3 1.4
10
20
30
50
60
70
80
90
100
DCTL Duty (%)
ACTL (V)
OVP vs. Input Voltage
OVP vs. Temperature
1.21
1.21
1.20
1.20
1.19
OVP_H
1.18
OVP_L
OVP_H
OVP_L
1.19
OVP (V)
OVP (V)
40
1.17
1.18
1.17
1.16
1.16
1.15
1.15
VIN = 24V
4
8
12
16
20
24
28
32
36
-40 -25 -10
5
20
35
50
65
80
Input Voltage (V)
Temperature (°C)
Power Off from EN
Power On from EN
95 110 125
Boost Application, VIN = 24V, VOUT = 48V
IOUT
(500mA/Div)
IOUT
(200mA/Div)
VOUT
(50V/Div)
VOUT
(20V/Div)
EN
(2V/Div)
VGATE
(10V/Div)
EN
(2V/Div)
VGATE
(10V/Div)
Time (250μs/Div)
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Time (250μs/Div)
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RT8482
Applications Information
The RT8482 is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications. The LED current can be programmed by an
external resistor. The input voltage range of the RT8482
can be up to 36V and the output voltage can be up to 48V.
The RT8482 provides analog and PWM dimming to achieve
LED current control.
GBIAS Regulator and Bypass Capacitor
The GBIAS pin requires a capacitor for stable operation
and to store the charge for the large GATE switching
currents. Choose a 10V rated low ESR, X7R or X5R
ceramic capacitor for best performance. A 1μF capacitor
will be adequate for most applications.
Place the capacitor close to the IC to minimize the trace
length to the GBIAS pin and also to the IC ground. An
internal current limit on the GBIAS output protects the
RT8482 from excessive on chip power dissipation.
The GBIAS pin has its own Under Voltage Lockout (UVLO)
set to 4.3V (typical) to protect the external FETs from
excessive power dissipation caused by not being fully
enhanced. If the input voltage, VIN, does not exceed 8V,
then the GBIAS pin should be connected to the input
supply. Be aware if GBIAS supply is used to drive extra
circuits in addition to the RT8482. Typically, the extra
GBIAS load should be limited to less than 10mA.
Loop Compensation
The RT8482 uses an internal error amplifier via the
compensation pin (VC) to optimize the loop response for
specific application. The external inductor, output capacitor,
and compensation resistor and capacitor determine the
loop stability. The inductor and output capacitor are chosen
based on performance, size and cost. The compensation
resistor and capacitor at VC are selected to optimize
control loop response and stability. For typical LED
applications, a 3.3nF compensation capacitor at VC is
adequate. A series resistor should always be used to
increase the slew rate on the VC pin to maintain tighter
regulation of LED current during fast transients on the input
supply to the converter. An external resistor in series with
a capacitor is connected from the VC pin to GND to provide
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10
a pole and a zero for proper loop compensation. The typical
compensation for the RT8482 is 10kΩ and 3.3nF.
Soft-Start
The soft-start of the RT8482 can be achieved by connecting
a capacitor from the SS pin to GND. The built-in soft-start
circuit reduces the start-up current spike and output
voltage overshoot. The soft-start time is determined by
the external capacitor charged by an internal 6μA constant
charging current. The SS pin directly limits the rate of
voltage rise on the VC pin, which in turn limits the peak
switch current.
The soft-start interval is set by the soft-start capacitor
selection according to the equation :
2.4V
tSS = CSS ×
6μ A
A typical value for the soft-start capacitor is 0.1μF. The
soft-start capacitor is discharged when EN/UVLO falls
below its threshold, during an over-temperature event or
during a GBIAS under-voltage event.
LED Current Setting
The LED current is programmed by placing an appropriate
valued current sense resistor between the ISP and ISN
pins. Typically, sensing of the current should be done at
the top of the LED string. The ACTL pin should be tied to
a voltage higher than 1.2V to get the full-scale 190mV
(typical) threshold across the sense resistor. The ACTL
pin can also be used to dim the LED current to zero,
although relative accuracy decreases with the decreasing
voltage sense threshold. When the ACTL pin voltage is
less than 1.2V, the LED current is :
(VACTL − 0.2) × 0.19
ILED =
RSENSE
where,
RSENSE is the resistor between ISP and ISN.
When the voltage of ACTL is higher than 1.2V, the LED
current is regulated to :
ILED(MAX) =
190mV
RSENSE
The ACTL pin can also be used in conjunction with a
thermistor to provide over-temperature protection for the
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DS8482-02 May 2012
be set by the following equation :
RT8482
LED load, or with a resistive voltage divider to VIN to reduce
output power and switching current when VIN is low. The
presence of a time varying differential voltage signal (ripple)
across ISP and ISN at the switching frequency is expected.
The amplitude of this signal is increased by high LED load
current, low switching frequency and/or a smaller value
output filter capacitor. The compensation capacitor on the
VC pin filters the signal so the average difference between
ISP and ISN is regulated on the user-programmed value.
and Buck-Boost applications, the output voltage can be
set by the following equation :
⎛ R1 ⎞
VOUT, OVP = 1.18 × ⎜1 +
⎟
⎝ R2 ⎠
where,
R1 and R2 are the voltage divider resistors from VOUT to
GND with the divider center node connected to the OVP
pin.
ISW Sense Resistor Selection
Dimming Control
For LED applications where a wide dimming range is
required, two competing methods are available: analog
dimming and PWM dimming. The easiest method is to
simply vary the DC current through the LED by analog
dimming.
However, the better dimming method is PWM dimming,
which switches the LED on and off by different duty cycle
to control the average LED current. The PWM dimming
offers several advantages over analog dimming and is much
preferred by LED manufacturers. One advantage is the
chromatic ity of the LEDs which remains unchanged in
this scheme since the LED current is either zero or at
programmed current. Another advantage of PWM dimming
over analog dimming is that a wider dimming range is
possible.
The RT8482 features both analog and digital dimming
control. Analog dimming is linearly controlled by an
external voltage (0.2V < VACTL < 1.2V). With an on-chip
output clamping amplifier and a resistor. PWM dimming
signal fed at the DCTL pin can be easily low-pass filtered
to an analog dimming signal with one external capacitor
from the ACTL pin to GND for noise-free PWM dimming. A
very high contrast ratio true digital PWM dimming can be
achieved by driving the ACTL pin with a PWM signal from
100Hz to10kHz.
Output Over Voltage Setting
The RT8482 is equipped with an Over Voltage Protection
(OVP) function. When the voltage at the OVP pin exceeds
a threshold of approximately 1.18V, the power switch is
turned off. The power switch can be turned on again once
the voltage at the OVP pin drops below 1.18V. For Boost
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The resistor, RSW, between the source of the external
N-MOSFET and GND should be selected to provide
adequate switch current to drive the application without
exceeding the 110mV (typical) current limit threshold on
the ISW pin of the RT8482. For real applications, select a
resistor that gives a switch current at least 30% greater
than the required LED current.
For Buck application, select a resistor according to :
⎛ 0.08V ⎞
RSW, Buck = ⎜
⎟
⎝ IOUT ⎠
For Buck-Boost application, select a resistor according
to :
⎛
⎞
VIN × 0.08V
RSW, Buck-Boost = ⎜
⎟
⎝ (VIN + VOUT ) × IOUT ⎠
For Boost application, select a resistor according to :
⎛ VIN × 0.08V ⎞
RSW, Boost = ⎜
⎟
⎝ VOUT × IOUT ⎠
The placement of RSW should be close to the source of
the N-MOSFET and GND of the RT8482. The ISW pin
input to the RT8482 should be a Kelvin connection to the
positive terminal of RSW.
Over Temperature Protection
The RT8482 has an Over Temperature Protection (OTP)
function to prevent excessive power dissipation from
overheating the device. The OTP function will shut down
switching operation when the die junction temperature
exceeds 150°C. The chip will automatically start to switch
again when the die junction temperature cools off.
Inductor Selection
The inductor used with the RT8482 should have a
saturation current rating appropriate to the maximum
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RT8482
switch current selected with the RSW resistor. Choose an
Capacitor Selection
inductor value based on operating frequency, input and
output voltage to provide a current mode ramp of
approximately 20mV magnitude on the ISW pin during
the switch on-time of approximately 20mV magnitude. The
following equations are useful to estimate the inductor
value. For Buck application :
RSW × VOUT × ( VIN − VOUT )
LBuck =
0.02 × VIN × fSW
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. For
most of the RT8482 applications, a 10μF ceramic capacitor
is sufficient. 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 Boost application
LBoost =
RSW × VIN × ( VOUT − VIN )
0.02 × VOUT × fSW
For Buck-Boost application
LBuck −Boost =
RSW × VIN × VOUT
0.02 × ( VIN + VOUT ) × fSW
Power MOSFET Selection
For applications operating at high input or output voltages,
the power N-MOSFET switch is typically chosen for drain
voltage, VDS, rating and low gate charge. Consideration of
switch on-resistance, R DS(ON), is usually secondary
because switching losses dominate power loss. The
GBIAS regulator on the RT8482 has a fixed current limit
to protect the IC from excessive power dissipation at high
VIN, so the N-MOSFET should be chosen such that the
product of Qg at 5V and switching frequency does not
exceed the GBIAS current limit.
Schottky Diode Selection
The Schottky diode, with their low forward voltage drop
and fast switching speed, is necessary for the RT8482
applications. In addition, power dissipation, reverse voltage
rating and pulsating peak current are also important
parameters for the Schottky diode selection. Choose a
suitable Schottky diode with reverse voltage rating greater
than the maximum output voltage. The diode's average
current rating must exceed the average output current.
The diode conducts current only when the power switch
is turned off (typically less than 50% duty cycle). If using
the PWM feature for dimming, it is important to consider
diode leakage, which increases with temperature, from
the output during the PWM low interval. Therefore, a
Schottky diode with sufficiently low leakage current is
suggested.
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12
In Boost application, the output capacitor is typically a
ceramic capacitor and is selected based on the output
voltage ripple requirements. The minimum value of the
output capacitor, COUT, is approximately given by the
following equation :
IOUT × VOUT
COUT =
VIN × VRIPPLE × fSW
For LED applications, the equivalent resistance of the LED
is typically low and the output filter capacitor should be
sized to attenuate the current ripple. Use of X7R type
ceramic capacitors is recommended. Lower operating
frequencies will require proportionately higher capacitor
values.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
Where T J(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance θJA is layout dependent. For
WQFN-16L 3x3 packages, the thermal resistance θJA is
68°C/W on the standard JEDEC 51-7 four layers thermal
test board. For SOP-16 packages, the thermal resistance
θJA is 85°C/W on the standard JEDEC 51-7 four layers
thermal test board. The maximum power dissipation at
TA = 25°C can be calculated by following formula :
is a registered trademark of Richtek Technology Corporation.
DS8482-02 May 2012
RT8482
PD(MAX) = (125°C − 25°C) / (68°C/W) = 1.471W for
WQFN-16L 3x3 packages
PD(MAX) = (125°C − 25°C) / (85°C/W) = 1.176W for
SOP-16 packages
Maximum Power Dissipation (W)1
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
resistance θJA. The Figure 5 of derating curves allows the
designer to see the effect of rising ambient temperature
on the maximum power allowed.
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Four Layers PCB
Layout Consideration
PCB layout is very important when designing power
switching converter circuits. Some recommended layout
guidelines are suggested as follows :
`
The power components L1, D1, CIN, M1 and COUT must
be placed as close to each other as possible to reduce
the ac current loop area. The PCB trace between power
components must be as short and wide as possible
due to large current flow through these traces during
operation.
`
The input capacitor CVCC must be placed as close to
VCC pin as possible.
`
Place the compensation components as close to VC
pin as possible to avoid noise pick up.
`
Connect GND pin and Exposed Pad to a large ground
plane for maximum power dissipation and noise
reduction.
WQFN-16L 3x3
SOP-16
Place these components as close to each other as possible
D1
0
25
50
75
100
L1
VIN
125
Ambient Temperature (°C)
Figure 5. Derating Curve of Maximum Power Dissipation
CIN
M1
COUT
RSW
GND
RSENS
GBIAS
GATE
NC
ISW
NC
ISP
ISN
VC
2
16
15
3
14
4
5
13
12
6
7
11
10
8
9
GND
VCC
OVP
EN
NC
SS
DCTL
ACTL
Locate input
capacitor as
close to VCC
as possible
CVCC
CSS
RVC
CVC
GND
Locate the compensation components as
close to VC pin as possible
Figure 6. PCB Layout Guide
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS8482-02 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8482
Outline Dimension
H
A
M
B
J
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
9.804
10.008
0.386
0.394
B
3.810
3.988
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.508
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.178
0.254
0.007
0.010
I
0.102
0.254
0.004
0.010
J
5.791
6.198
0.228
0.244
M
0.406
1.270
0.016
0.050
16–Lead SOP Plastic Package
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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14
is a registered trademark of Richtek Technology Corporation.
DS8482-02 May 2012
RT8482
D
SEE DETAIL A
D2
L
1
E
E2
e
1
2
DETAIL A
Pin #1 ID and Tie Bar Mark Options
b
A
A1
1
2
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
A3
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
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 16L QFN 3x3 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.
DS8482-02 May 2012
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15