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PDF RT8474A Data sheet ( Hoja de datos )
| Número de pieza | RT8474A | |
| Descripción | High Voltage Multiple-Topology LED Driver | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8474A
High Voltage Multiple-Topology LED Driver
with Open Detection
General Description
The RT8474A is a current-mode LED driver supporting wide
input voltage range from 4.5V to 50V in multiple topologies.
With the internal 500kHz operating frequency, the size of
the external PWM inductor and input/output capacitors
can be minimized. High efficiency is achieved by a 100mV
current sensing control. LED dimming control can be done
from either analog or PWM signal. The RT8474A provides
an internal soft-start function to avoid inrush current and
thermal shutdown to prevent the device from overheat.
The RT8474A is available in the SOP-8 (Exposed pad)
package.
Features
High Voltage : VIN Up to 50V, VOUT Up to 50V
Support Multiple-Topologies (Buck / Boost / Buck-
Boost)
Built-In 2A Power Switch
Current-Mode PWM Control
500kHz Fixed Switching Frequency
Analog or PWM Control Signal for LED Dimming
Internal Soft-Start to Avoid Inrush Current
OVP Pin for Adjustable OVP Level Protection (for
Buck Only)
Under-Voltage Lockout
Thermal Shutdown
RoHS Compliant and Halogen Free
Ordering Information
RT8474A
Package Type
SP : SOP-8 (Exposed-Option 2)
Note :
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Applications
Desk Lights and Room Lighting
Industrial Display Backlight
Marking Information
RT8474A
GSPYMDNN
RT8474AGSP : Product Number
YMDNN : Date Code
Simplified Application Circuit
VIN
Analog Dimming
or PWM Dimming
R5 C1
RT8474A
VCC
C5 ISP
ISN
CTL
R1
R2
C2
SW
VC
CREG
OVP
C3 GND
RSENSE
L1
D1
C4 R4
R3
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS8474A-05 April 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT8474A
Parameter
Symbol
PWM Converter
Switch Frequency
Maximum Duty Cycle
Minimum On-Time
fSW
DMAX
SW RDS(ON)
SW Current Limit
ILIM_SW
Over-Voltage Protection and Soft-Start
OVP Threshold
OVP Recovery
VOVP
OVP Input Current
Soft-Start Time
IOVP
Over-Temperature Protection
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
TSD
TSD
Test Conditions
VISP VOVP
VOVP = 1.2V
VOVP 1.5V
(Note 6)
Min Typ Max Unit
440 500 540 kHz
-- -- 100 %
-- 100 200 ns
-- 0.15 --
2 2.5 --
A
1.15 1.2 1.25 V
-- 1 -- V
-- 30 -- A
-- 5.7 -- ms
-- 150 --
-- 20 --
C
C
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, PWM can go up to 40V.
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. Guarantee by design, not subject to production testing.
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS8474A-05 April 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT8474A
The ripple current ΔIL and peak current IPEAK can be
calculated :
IL
=
VOUT
f L
1
VOUT
VIN
IPEAK
=
IOUT
+
IL
2
For Boost application :
L
=
f
VIN
IL
1
VIN
VOUT
The ripple current ΔIL and peak current IPEAK can be
calculated :
IL
=
VIN
f L
1
VIN
VOUT
IPEAK
=
IOUT VOUT
VIN
+
IL
2
For Buck-Boost application :
L=
VOUT
IL f
1
VOUT
VIN + VOUT
The ripple current ΔIL and peak current IPEAK can be
calculated :
IL
=
VOUT
L f
1
VOUT
VIN + VOUT
IPEAK
=
VIN
+ VOUT IOUT
VIN
+ IL
2
where,
VOUT = output voltage.
VIN = input voltage.
IOUT = LED current.
f = switching frequency.
η = efficiency.
Schottky Diode Selection
The Schottky diode, with their low forward voltage drop
and fast switching speed, is necessary for RT8474A
applications. In addition, power dissipation, reverse voltage
rating and pulsating peak current are important parameters
of the Schottky diode that must be considered. 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).
Capacitor Selection
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. For
most RT8474A applications, a 4.7μF 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. In Buck application, the output
capacitor is typically ceramic and selection is mainly
based on the output voltage ripple requirements. The
output ripple, ΔVOUT, is determined by the following
equation :
VOUT
IL ESR +
1
8 f COUT
Thermal Considerations
For continuous operation, do not exceed the maximum
operation junction temperature 125°C. 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 TJ(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 specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOP-8 (Exposed Pad) package, the thermal resistance
θJA is 29°C/W on the standard JEDEC 51-7 four-layer
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by following formula :
PD(MAX) = (125°C − 25°C) / (29°C/W) = 3.44W for
SOP-8 (Exposed Pad) package
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. The deration curve in Figure 1 allows the
designer to see the effect of rising ambient temperature
on the maximum power allowed.
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS8474A-05 April 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet RT8474A.PDF ] | |
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