Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

RT8474A Datasheet(PDF) 11 Page - Richtek Technology Corporation

Part No. RT8474A
Description  High Voltage Multiple-Topology LED Driver
Download  13 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Manufacturer  RICHTEK [Richtek Technology Corporation]
Direct Link  http://www.richtek.com
Logo RICHTEK - Richtek Technology Corporation

RT8474A Datasheet(HTML) 11 Page - Richtek Technology Corporation

Back Button RT8474A Datasheet HTML 5Page - Richtek Technology Corporation RT8474A Datasheet HTML 6Page - Richtek Technology Corporation RT8474A Datasheet HTML 7Page - Richtek Technology Corporation RT8474A Datasheet HTML 8Page - Richtek Technology Corporation RT8474A Datasheet HTML 9Page - Richtek Technology Corporation RT8474A Datasheet HTML 10Page - Richtek Technology Corporation RT8474A Datasheet HTML 11Page - Richtek Technology Corporation RT8474A Datasheet HTML 12Page - Richtek Technology Corporation RT8474A Datasheet HTML 13Page - Richtek Technology Corporation  
Zoom Inzoom in Zoom Outzoom out
 11 / 13 page
background image
RT8474A
11
DS8474A-05 April 2015
www.richtek.com
©
Copyright
2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
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).

   


OUT
L
OUT
1
V
I
ESR +
8f C
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
θJAis
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.
OUT
OUT
L
IN
L
PEAK
OUT
VV
I =
1
fL
V
I
I
= I
+
2
 
 
 
 
The ripple current
ΔIL and peak current IPEAK can be
calculated :
For Boost application :
IN
IN
LOUT
VV
L =
1
fI
V

 



 
The ripple current
ΔIL and peak current IPEAK can be
calculated :
IN
IN
L
OUT
OUT
OUT
L
PEAK
IN
VV
I =
1
fL
V
IV
I
I
=
+
V2


 


 



Capacitor Selection
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. For
most RT8474A applications, a 4.7
μF 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 :
For Buck-Boost application :
OUT
OUT
LIN
OUT
VV
L =
1
If
V
+ V
 

 

 
The ripple current
ΔIL and peak current IPEAK can be
calculated :

OUT
OUT
L
IN
OUT
IN
OUT
OUT
L
PEAK
IN
VV
I =
1
Lf
V
+ V
V
+ V
I
I
I
=
+
V2
 
 
 
 






Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13 


Datasheet Download

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ] 

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Link Exchange   |   Manufacturer List
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn