®
RT8575
4-String White LED Driver with Boost Regulator
General Description
Features
The RT8575 is a high efficiency LED driver with 40V I/O
support. It is designed for LCD panel that employs an array
of LEDs as the lighting source. An integrated switch
current mode Boost controller drives four strings in parallel
and supports up to 18 pieces of LEDs per string. The
internal current sinks support typical ±1% current
mismatching for excellent brightness uniformity in each
LED string. To provide enough headroom for the operating
of current sink, Boost controller monitors the minimum
voltage of feedback pins and regulates an optimized output
voltage for power efficiency.
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Input Operating Voltage Range 4.2V to 24V
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60V Maximum Output Voltage
Adjustable Switching Frequency : 150kHz to 500kHz
Support Up to 4 LED Strings
50mA to 150mA LED Current Per Channel
1% Typical LED Current Accuracy
1% Typical LED Current Matching
Programmable Over Voltage Protection
Built-in Soft-Start, OTP
LED Short/Open Detection
RoHS Compliant and Halogen Free
The RT8575 has a wide input voltage operating range from
4.2V to 24V and provides adjustable 50mA to 150mA LED
current. The internal 150mΩ, 60V power switch with
current-mode control provides cycle-by-cycle over current
protection. RT8575 also integrates PWM dimming function
for accurate LED current control. The input PWM dimming
frequency can operate from 120Hz to 1kHz without
inducing any inrush current in LEDs or inductor. The
switching frequency of RT8575 is adjustable from 150kHz
to 500kHz, which allows the trade-off between efficiency
and component size.
Applications
The RT8575 is available in WDFN-16L 5x5 and DIP-16
(BW) packages to achieve optimized solution for PCB
space.
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White LED Backlighting
Ordering Information
RT8575
Package Type
QW : WDFN-16L 5x5 (W-Type)
N : DIP-16 (BW)
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.
Simplified Application Circuit
D1
L1
VIN
VOUT
CIN1
COUT
R1
LX
VIN
CIN2
RT8575
ROVP2
ISET
Chip Enable
EN
CCOMP
RT
RSW
:
:
:
:
:
:
GND
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8575-00 January 2013
:
:
:
CH1
CH2
CH3
CH4
COMP
RCOMP
:
:
:
RISET
PWM
PWM Signal
ROVP1
OVP
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1
RT8575
Marking Information
Pin Configurations
(TOP VIEW)
RT8575GQW
RT8575GQW : Product Number
RT8575
GQW
YMDNN
CH1
CH2
CH3
CH4
AGND
ISET
COMP
RT
YMDNN : Date Code
16
15
1
2
3
4
14
13
PGND
5
6
7
12
11
10
17
8
9
OVP
PGND
PGND
LX
LX
VIN
EN
PWM
WDFN-16L 5x5
RT8575GN
RichTek
RT8575
GNYMDNN
RT8575GN : Product Number
EN
14
PWM
YMDNN : Date Code
VIN
2
13
RT
LX
3
12
COMP
GND
4
11
GND
OVP
5
10
ISET
CH1
6
9
CH4
CH2
7
8
CH3
DIP-16 (BW)
Functional Pin Description
Pin No.
Pin Name
Pin Function
WDFN-16L 5x5
DIP-16 (BW)
1 to 4
6 to 9
5
--
AGND
Analog Ground.
6
10
ISET
LED current is set by the value of the resistor RISET connected
from the ISET pin to ground. Do not short the ISET pin. VISET is
typically 1V.
7
12
COMP
8
13
RT
9
14
PWM
10
1
EN
Chip Enable (Active High). Note that this pin is high impedance.
There should be a 100kΩ pull low resistor connected to GND
when the control signal is floating.
11
2
VIN
Power Supply Input.
12, 13
3
LX
The Switching Pin for Boost Converter.
14, 15,
17 (Exposed Pad)
--
PGND
16
5
OVP
--
4, 11
GND
CH1 to CH4 Current Sink for LED. (Connect to GND, if not used)
Compensation Pin for Error Amplifier. Connect a compensation
network to ground.
Switching Frequency Selection Input. The switching frequency is
adjustable from 150kHz to 500kHz.
Dimming Control Input.
Power Ground of Boost Converter. The exposed pad must be
soldered to a large PCB and connected to PGND for maximum
power dissipation.
Over Voltage Protection for Boost Converter. The detecting
threshold is 1.2V.
Ground.
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is a registered trademark of Richtek Technology Corporation.
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RT8575
Function Block Diagram
OVP
RT
+
OTP
1.2V
-
OSC
VIN
5V LDO
LX
S
Q
R
Q
OCP
EN
+
PWM
Controller
PGND
+
-
LED Open & Short Detection
+
COMP
-
PWM
VREF
4
Mini LED
Selection
……
CH1
CH2
CH4
+
-
1V
+
+
-
-
……
+
-
AGND
(Only for WDFN Package)
ISET
Operation
The RT8575 integrates 4 linear LED drivers and a Boost
converter. When EN is High and VIN is higher than the
voltage of UVLO, the RT8575 will start operation and detect
which channels are using. If the channel is connected to
ground, it would be defined as un-used channel. And the
diver of this channel will be turned off after the un-used
checking.
Then, RT8575 will enter the soft-start mode. VISET will
increase to be 1V slowly, which represents that the ILED
also increases slowly. Beside that the OCP is clamped
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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at lower level, just prevents a large inrush current. RT8575
will choose the min. value of VLED as the feedback voltage
of Boost converter, the un-used channel is out of the list.
During normal operation, when LED string is defined as
short, the driver of that channel will be turned off. In order
to protect the system, “SHORT” status of the channel
should only be released by re-start of the system. When
LED string is defined as open, the driver of that channel
will be turned off, and auto-recovery when “OPEN” is
released.
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RT8575
Absolute Maximum Ratings
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z
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(Note 1)
Supply Input Voltage, VIN to GND -------------------------------------------------------------------------------------EN, ISET, COMP, OVP, RT to GND -----------------------------------------------------------------------------------CH1 to CH4, LX to GND -------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-16L 5x5 -------------------------------------------------------------------------------------------------------------DIP-16 (BW) ----------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-16L 5x5, θJA -------------------------------------------------------------------------------------------------------WDFN-16L 5x5, θJC -------------------------------------------------------------------------------------------------------DIP-16 (BW), θJA ----------------------------------------------------------------------------------------------------------DIP-16 (BW), θJC ----------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 44V
−0.3V to 44V
−0.3V to 66V
3.47W
1.8W
28.8°C/W
4.4°C/W
55.7°C/W
8.3°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 4.2V to 24V
Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 19V, CIN2 = 1μF, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Input Supply Voltage
VIN
Under Voltage Lockout
Threshold
VUVLO
Under Voltage Lockout
Hysteresis
DVUVLO
VIN Rising
Typ
Max
Unit
4.2
--
24
V
--
3.8
--
V
--
500
--
mV
IVCC
COMP = 0V, Not Switching
--
2.5
--
COMP = 2V, Switching
--
3.3
--
ISHDN
VIN = 4.5V, EN = 0
--
--
20
Logic-High
VIH
VIN = 4.2V to 24V
2
--
--
Logic-Low
VIL
VIN = 4.2V to 24V
--
--
0.8
120
--
1k
Hz
224
280
336
kHz
--
0.15
--
Ω
--
220
--
ns
--
92
--
%
2.8
3.3
3.8
A
Shutdown Current
PWM Dimming Frequency
FPWM
Switching Frequency
FOSC
RSW = 51.1kΩ
LX On-Resistance (N-MOSFET)
RLX
VIN > 4.5V
Minimum On-Time
TMON
Maximum Duty
DMAX
LX Current Limit
ILIM
VCOMP = 2V, Switching
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Min
IVCC_SW
Quiescent Current
EN, PWM
Input Voltage
Test Conditions
mA
μA
V
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RT8575
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
LED Current Accuracy
ILEDA
0.4V < CHx < 2V, RISET = 7.5kΩ
116.4
120
123.6
mA
LED Current Matching
ILEDM
0.4V < CHx < 2V, RISET = 7.5kΩ
--
±1
±3
%
ISET Pin Voltage
VISET
--
1
--
V
OVP Threshold
VOVP
1.17
1.2
1.23
V
Thermal Shutdown Temperature
TOTP
--
150
--
°C
Thermal Shutdown Hysteresis
TOTP_hys
--
20
--
°C
Un-Connected LED Detection
VUSE
--
0.2
--
V
Opened LED Protection
VOLP
--
0.1
--
V
Shorted LED Protection
VSLP
--
5.6
--
V
Shutdown Delay Time
TSD
--
28
--
ms
Un-Connection
fOSC = 280kHz
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. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8575-00 January 2013
is a registered trademark of Richtek Technology Corporation.
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RT8575
Typical Application Circuit
L1
22µH
VIN
4.2V to 24V
CIN1
47μF/35V
D1
R1
10
CIN2
1µF
COUT
47μF/100V
LX
VIN
RT8575
OVP
Chip Enable
EN
COVP
100pF
VOUT
60V(MAX)
ROVP1
300k
ROVP2
6.2k
:
:
:
:
:
:
:
:
:
:
:
:
ILED
150mA (MAX)
PGND
GND
AGND
PWM
PWM Signal
RCOMP
0
CCOMP
100nF
COMP
RT
RSW
51.1k
ISET
RISET
7.5k
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CH1
CH2
CH3
CH4
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RT8575
Typical Operating Characteristics
Efficiency vs. Input Voltage
100
90
90
Efficiency (%)
Efficiency (%)
Efficiency vs. Input Voltage
100
80
70
60
80
70
60
6S4P, ILEDx = 120mA, fOSC = 280kHz, PWM = 3.3V
14S4P, ILEDx = 120mA, fOSC = 280kHz, PWM = 3.3V
50
50
12
14
15
17
18
20
21
23
24
4
5
6
Input Voltage (V)
LED Current vs. Input Voltage
9
10
11
12
LED Current vs. Input Voltage
160
150
150
CH1
CH2
CH3
CH4
140
130
LED Current (mA)
LED Current (mA)
8
Input Voltage (V)
160
120
110
100
14 LEDs per channel,
RISET = 7.5kΩ, fOSC = 280kHz, PWM = 3.3V
90
CH1
CH2
CH3
CH4
140
130
120
110
100
6 LEDs per channel,
RISET = 7.5kΩ, fOSC = 280kHz, PWM = 3.3V
90
80
80
0
5
10
15
20
25
30
4
5
6
Input Voltage (V)
7
8
9
10
11
12
Input Voltage (V)
LED Current vs. Temperature
LED Current vs. Dimming Duty
120
160
150
100
LED1
LED2
LED3
LED4
140
130
120
LED Current (mA)
LED Current (mA)
7
110
100
90
fOSC
14S4P, RISET = 7.5kΩ,
= 280kHz, VIN = 19V, PWM = 3.3V
80
200Hz
500Hz
1kHz
80
60
40
20
14S4P, fOSC = 280kHz, VIN = 19V
0
-50
-25
0
25
50
75
100
Temperature (°C)
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DS8575-00 January 2013
125
0
10
20
30
40
50
60
70
80
90
100
Dimming Duty (%)
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RT8575
Quiescent Current vs. Input Voltage
5.0
1.35
4.5
Quiescent Current (mA)
OVP Voltage (V)
OVP Voltage vs. Input Voltage
1.40
1.30
1.25
1.20
1.15
1.10
4.0
3.5
2.5
2.0
1.0
0.5
1.00
0.0
6
8
10
12
14
16
18
20
22
Not Switching
1.5
1.05
4
Switching
3.0
VIN = 19V, fOSC = 280kHz
4
24
6.5
9
Input Voltage (V)
14
16.5
19
21.5
24
Input Voltage (V)
Quiescent Current vs. Temperature
LED Current vs. RISET
5.0
160
4.5
140
4.0
3.5
LED Current (mA)
Quiescent Current (mA)
11.5
Switching
3.0
2.5
2.0
Not Switching
1.5
1.0
0.5
VIN = 19V, fOSC = 280kHz
0.0
120
100
80
60
40
20
VIN = 19V
0
-40
-20
0
20
40
60
80
100
125
5
7.5
10
12.5
15
17.5
Temperature (°C)
RISET (k Ω )
Switching Frequency vs. RSW
Line Transient Response
20
Switching Frequency (kHz)1
600
500
400
300
200
100
VIN = 19V
VIN
(4V/Div)
IOUT
(200mA/Div)
fOSC = 280kHz, VIN = 17.1V to 20.9V,
PWM = 3.3V, RISET = 7.5kΩ
0
20
30
40
50
60
70
80
90 100 110 120 130
Time (25ms/Div)
RSW (k Ω )
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RT8575
Power Off from PWM
Power On from PWM
VPWM
(5V/Div)
VPWM
(5V/Div)
VOUT
(50V/Div)
VLX
(50V/Div)
VOUT
(50V/Div)
VLX
(50V/Div)
IOUT
(300mA/Div)
IOUT
(300mA/Div)
fOSC = 280kHz, VIN = 19V, 14S4P, EN = 3.3V,
Dimming Duty = 50%, Dimming Frequency = 200Hz
fOSC = 280kHz, VIN = 19V, 14S4P, EN = 3.3V,
Dimming Duty = 50%, Dimming Frequency = 200Hz
Time (10ms/Div)
Time (10ms/Div)
Power On from EN
Power Off from EN
VEN
(5V/Div)
VEN
(5V/Div)
VOUT
(50V/Div)
VLX
(50V/Div)
VOUT
(50V/Div)
VLX
(50V/Div)
IOUT
(300mA/Div)
IOUT
(300mA/Div)
fOSC = 280kHz, VIN = 19V, 14S4P, PWM = 3.3V
fOSC = 280kHz, VIN = 19V, 14S4P, PWM = 3.3V
Time (5ms/Div)
Time (5ms/Div)
Power On from VIN
Power Off from VIN
VIN
(12V/Div)
VIN
(12V/Div)
VOUT
(50V/Div)
VLX
(50V/Div)
VOUT
(50V/Div)
VLX
(50V/Div)
IOUT
(300mA/Div)
fOSC = 280kHz, 14S4P, PWM = EN = 3.3V
Time (5ms/Div)
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DS8575-00 January 2013
IOUT
(300mA/Div)
fOSC = 280kHz, 14S4P, PWM = EN = 3.3V
Time (5ms/Div)
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RT8575
Application Information
The RT8575 is a general purpose 4-CH LED driver capable
of delivering an adjustable 50mA to 150mA LED current.
The IC is a current mode Boost converter integrated with
a 60V/4A power switch and can cover a wide VIN range
from 4.2V to 24V. The switching frequency is adjustable
by an external resistor from 150kHz to 500kHz. The part
integrates built-in soft-start, with PWM dimming control;
moreover, it provides over voltage, over temperature, short
LED and cycle-by-cycle over current protection features.
Compensation
Supply Voltage Capacitor Selection
LED Connection
The RT8575 equips a built-in LDO linear regulator to
provide the internal logic of IC power. The output of LDO
is the pin out of VIN. The VIN pin is recommended to
connect at least a 1μF/25V bypass capacitor. The bypass
capacitor should be used with X5R or X7R type, to assure
the bypass capacitance remains stable in over voltage or
over temperature.
The RT8575 equips 4-CH LED drivers and each channel
supports up to 18 LEDs (Vf = 3V). The LED strings are
connected from the output of the Boost converter to pin
CHx (x = 1 to 4) respectively. If one of the current sink
channels is not used, the CHx pin should be connected
to GND. If the un-used channel is not connected to GND,
it will be considered that the LED string is opened, the
channel will turn light when the LED string is recovering
connected.
Soft-Start
The RT8575 equips a 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.
LED Current Setting
LED current of each channel can be calculated by following
equation :
ILED ≅ 900
RISET
Where the RISET resistor is connected between the ISET
pin and GND. This setting is the reference for the LED
current at the LED pin and represents the sensed LED
current for each string. The LED driver regulates the LED
current according to the setting.
Switching Frequency
The LED driver switching frequency is adjusted by the
external resistor, RSW. The switching frequency can be
calculated by the following equation :
9
fOSC ≅ 14.3 × 10
RSW
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10
The regulator loop can be compensated by adjusting the
external components connected to the COMP pin. The
COMP pin is the output of the internal error amplifier. The
compensation capacitor will adjust the integrator zero to
maintain stability and the resistor value will adjust the
frequency integrator gain for fast transient response.
Typical values of the compensation components are
RCOMP = 0Ω, CCOMP = 100nF.
Over Voltage Protection
The RT8575 integrates over voltage protection. When the
voltage at the OVP pin rises above the threshold voltage
of approximately 1.2V, The internal switch will be turned
off. Once the voltage of OVP pin drop below its threshold
voltage, the internal switch will be turned on again. The
output voltage can be clamped at a certain voltage level
and can be calculated by the following equations :
R
VOUT(OVP) ≅ VOVP × ⎛⎜ 1+ OVP1 ⎞⎟
⎝ ROVP2 ⎠
where VOVP = 1.2V (typ.).
ROVP1 and ROVP2 are the resistors in the voltage divider
connected to the OVP pin. If at least 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 near 300kΩ
for ROVP1, and use a 100pF bypass capacitor at ROVP2.
Current Limit Protection
The RT8575 can limit the peak current to achieve over
current protection. The RT8575 senses the inductor
current during the “ON” period that flows through the LX
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DS8575-00 January 2013
RT8575
pin. The duty cycle depends on the current signal and
internal slope compensation in comparison with the error
signal. The internal switch of Boost converter will be turned
off when the peak current value of inductor current is larger
than the threshold current 3.3A (typ.). In the “OFF” period,
the inductor current will be decreased until the internal
switch is turned on by the oscillator.
Short LED Protection
Brightness Control
Open LED Protection
The RT8575 features a digital dimming control scheme. A
very high contrast ratio true digital PWM dimming is
achieved by driving the PWM pin with a PWM signal. The
recommended PWM frequency is 120Hz to 1kHz. The
LED current can be approximately 100% proportional to
duty cycle, but the linearity is not ideal on the high
frequency and lower duty ratio.
If the CHx pin voltage is low at 0.1V, the LED driver will
determine whether the channel is open. The CHx pin
voltage will not be regulated and not latch, until the CHx
pin is recovering connected, the CHx pin will start normal
work again. If all CHx pins are open (floating), the output
voltage will be clamped to the setting voltage of OVP
(VOUT(OVP)).
Over Temperature Protection
Power On/Off Sequence
The RT8575 has over temperature protection function to
prevent the IC from overheating due to excessive power
dissipation. The OTP function will shut down the IC when
junction temperature exceeds 150°C. When junction
temperature cools down to 130°C (TOTP_hys = 20°C), the
LED driver will return to normal work.
LED driver is without power sequence concern. Mode1,
Mode2 and Mode3 are different power sequences
respectively. There is no concern in the above condition.
VIN
The RT8575 integrates Short LED Protection (SLP). If one
or more of the CH1 to CH4 pin voltages exceeds the
threshold of approximately 5.6V during normal operation,
the channels will be closed and latch. If the LED of all
channels is shorted circuit, the internal switch of Boost
converter will be turned off.
VIN
VOUT
VOUT
EN
EN
PWM
PWM
Power On Mode1
Power Off Mode1
VIN
VIN
VOUT
VOUT
EN
EN
PWM
PWM
Power On Mode2
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Power Off Mode2
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RT8575
VIN
VIN
UVLO
UVLO
VOUT
VOUT
EN
EN
PWM
PWM
Power On Mode3
Power Off Mode3
Figure 1. Power On/Off Sequence
Shutdown Delay Time
Inductor Selection
The EN shutdown delay is about 32ms, it is in intended
to prevent the glitch of EN. When EN has glitch happening
(Tglitch < 32ms), the IC will not need to recover soft-start
again. But the LED current sources will be closed
immediately. And after about 32ms, the IC will be shut
down. Please refer to the Figure 2.
The value of the inductance, L, can be approximated by
the following equation, where the transition is from
Discontinuous Conduction Mode (DCM) to Continuous
Conduction Mode (CCM) :
EN
TEN < 32ms
L=
The duty cycle, D, can be calculated as the following
equation :
D=
ILED
VISET
VLX
TEN < 32ms
TEN ≈ 32ms
D × (1− D)2 × VOUT
2 × fOSC × IOUT
VOUT − VIN
VOUT
Where VOUT is the maximum output voltage, VIN is the
minimum input voltage, fOSC is the operating frequency,
and IOUT is the sum of current from all LED strings. The
Boost converter operates in DCM over the entire input
voltage range when the inductor value is less than this
value, L. With an inductance greater than L, the converter
operates in CCM at the minimum input voltage and may
be discontinuous at higher voltages.
EN
The inductor must be selected with a saturated current
rating that is greater than the peak current as provided by
the following equation :
ILED
IPEAK =
VISET
VOUT × IOUT VIN × D × TOSC
+
2×L
η × VIN
where η is the efficiency of the power converter.
VLX
Diode Selection
TEN > 32ms
Figure 2. Shutdown Delay Time
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12
Schottky diodes are recommended for most applications
because of their fast recovery time and low forward voltage.
Power dissipation, reverse voltage rating, and pulsating
is a registered trademark of Richtek Technology Corporation.
DS8575-00 January 2013
RT8575
peak current are important parameters for consideration
when making a Schottky diode selection. Make sure that
the diode's peak current rating exceeds IPEAK and reverse
voltage rating exceeds the maximum output voltage.
ΔIL
Input Current
Inductor Current
Input Capacitor Selection
Low ESR electrolytic capacitors are recommended for
input capacitor applications. Low ESR will effectively
reduce the input voltage ripple caused by switching
operation. A 47μF/35V is sufficient for most applications.
Nevertheless, this value can be decreased for lower output
current requirement. Another consideration is the voltage
rating of the input capacitor must be greater than the
maximum input voltage.
Output Capacitor Selection
Output ripple voltage is an important index for estimating
the performance. This portion consists of two parts, one
is the ESR voltage of output capacitor, the other part is
formed by charging and discharging process of output
capacitor. Refer to Figure 3, evaluate ΔVOUT1 by ideal energy
equalization. According to the definition of Q, the Q value
can be calculated as following equation :
⎡
⎤
Q = 1 × ⎢⎛⎜ IIN + 1 ΔIL − IOUT ⎞⎟ + ⎛⎜ IIN − 1 ΔIL − IOUT ⎞⎟ ⎥
2 ⎣⎝
2
2
⎠ ⎝
⎠⎦
V
× IN × 1 = COUT × ΔVOUT1
VOUT fOSC
where fOSC is the switching frequency, and ΔIL is the
inductor ripple current. Move COUT to the left side to
estimate the value of ΔVOUT1 as the following equation :
ΔVOUT1 =
D × IOUT
η × COUT × fOSC
Then, take the ESR into consideration, the ESR voltage
can be determined as the following equation :
I
V × D × TOSC ⎞
ΔVESR = ⎛⎜ OUT + IN
⎟ × RESR
1
−
D
2L
⎝
⎠
Finally, the total output ripple ΔVOUT is combined from the
ΔVOUT1 and ΔVESR. In the general application, the output
capacitor is recommended to use a 47μF/63V electrolytic
capacitor.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8575-00 January 2013
Output Current
Time
(1-D)TS
Output Ripple
Voltage (ac)
Time
ΔVOUT1
Figure 3. The Output Ripple Voltage without the
Contribution of ESR
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
28.8°C/W on a standard JEDEC 51-7 four-layer thermal
test board. For DIP-16 (BW) package, the thermal
resistance, θJA, is 55.7°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
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13
RT8575
PD(MAX) = (125°C − 25°C) / (55.7°C/W) = 1.8W for
DIP-16 (BW) 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 4 allow the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Layout Consideration
PCB layout is very important for designing switching power
converter circuits. The following layout guides should be
strictly followed for best performance of the RT8575.
`
The power components, L1, D1, CIN1 and COUT must be
placed as close as possible to reduce power loop. The
PCB trace between power components must be as short
and wide as possible.
`
Place L1 and D1 as close as possible to LX pin. The
trace should be as short and wide as possible.
`
The compensation circuit (RCOMP, CCOMP) 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 LED current setting resistor (RISET) should be kept
away from the power loops and should be shielded with
a ground trace. Place the LED current resistor as close
as possible to ISET pin.
Maximum Power Dissipation (W)1
4.0
Four-Layer PCB
3.5
WDFN-16L 5x5
3.0
2.5
DIP-16 (BW)
2.0
1.5
1.0
0.5
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 4. Derating Curve of Maximum Power Dissipation
Locate the CIN2 as close to VIN as possible.
The compensation circuit and
RISET resistor should be kept
away from the power loops
and should be shielded with a
ground trace to prevent any
noise coupling.
GND
COUT
VOUT
CIN2
RT8575
EN
14 PWM
RSW
VIN
D1
VIN
L1
2
13
3
12 COMP
RT
R1
RCOMP
LX
CCOMP
VIN
CIN1
GND
4
11
OVP
5
10 ISET
CH1
6
9
CH4
CH2
7
8
CH3
GND
RISET
GND
Place the power components as close as
possible. The traces should be wide and
short especially for the high-current loop.
Figure 5. PCB Layout Guide for DIP-16 (BW) Package
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14
is a registered trademark of Richtek Technology Corporation.
DS8575-00 January 2013
RT8575
Place the power components as
close as possible. The traces
should be wide and short
especially for the high-current loop.
VOUT
16 OVP
CH1
The compensation circuit and
RISET resistor should be kept away
from the power loops and should
CH2
be shielded with a ground trace to
prevent any noise coupling.
CH3
2
15 PGND
3
14 PGND
CH4
4
D1
PGND
AGND
COUT
RT8575
13
PGND
LX
L1
VIN
LX
AGND
5
12
ISET
6
11 VIN
RCOMP
COMP
7
10 EN
RT
8
9
RISET
CCOMP
CIN1
R1
VIN
CIN2
RRT
Separate power ground (PGND) and analog
ground (AGND). Connect AGND and PGND
islands at a single end. Make sure there are
no other connections between these separate
ground planes.
PWM
Locate the CIN2 as close to VIN
as possible.
PGND
The exposed pad of the chip should be connected
to ground plane for thermal consideration.
Figure 6. PCB Layout Guide for WDFN-16L 5x5 Package
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8575-00 January 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT8575
Outline Dimension
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
3.700
4.320
0.146
0.170
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
b2
2.920
3.100
0.115
0.122
C
0.204
0.360
0.008
0.014
D
18.800
19.300
0.740
0.760
E
6.200
6.600
0.244
0.260
E1
7.320
7.920
0.288
0.312
E2
8.350
9.250
0.329
0.364
2.540
e
L
3.000
0.100
3.600
0.118
0.142
16-Lead DIP (BW) Plastic Package
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16
is a registered trademark of Richtek Technology Corporation.
DS8575-00 January 2013
RT8575
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.
Symbol
Dimensions In Millimeters
Dimensions In Inches
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
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.
DS8575-00 January 2013
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