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PDF RT8450 Data sheet ( Hoja de datos )
| Número de pieza | RT8450 | |
| Descripción | High Voltage Multi-Topology LED Driver | |
| Fabricantes | Richtek | |
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®
RT8450/B
High Voltage Multi-Topology LED Driver
General Description
The RT8450/B is a current mode PWM regulator for LED
driving applications. With an 1.5A switch on board and
wide input (4.5V to 40V) and/or output (up to 50V)ranges
the RT8450/B can operate in any of the three common
topologies : Buck, Boost or Buck-Boost.
With 800k/500kHz operating frequency, the external PWM
inductor and input/output capacitors can all be small. High
efficiency is achieved by a 190mV current sensing.
Dimming can be done either analog or PWM signal. An
unique built-in clampping comparator and filtering resistor
allow easy low noise analog dimming conversion from
PWM signal with only one external capacitor.
The RT8450/B is available in a TSSOP-16 (Exposed Pad)
and WDFN-12L 3x3 packages.
Ordering Information
RT8450/B
Package Type
CP : TSSOP-16 (Exposed Pad)
QW : WDFN-12L 3x3 (W-Type)
(Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Switching Frequency
500kHz
800kHz
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.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Features
High Voltage : VIN Up to 40V, VOUT Up to 50V
1.5A Switch Current
Buck, Boost or Buck-Boost Operation
Current Mode PWM with 800kHz (RT8450) and
500kHz (RT8450B) Switching Frenquency
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 to Limit
Output Voltage
VIN Under Voltage Lockout and Thermal Shutdown
RoHS Compliant and Halogen Free
Applications
GPS, Portable DVD Backlight
Desk Lights and Room Lighting
Industrial Display Backlight
Pin Configurations
(TOP VIEW)
ISP
ISN
VC
ACTL
DCTL
EN
OVP
SS
16
2 15
3 14
4
5
GND
13
12
6 17 11
7 10
89
VCC1
VCC2
SW
SW
GND
GND
GND
GND
TSSOP-16 (Exposed Pad)
ISP 1
ISN 2
VC 3
ACTL 4
DCTL 5
EN 6
GND
13
12 VCC2
11 VCC1
10 SW
9 GND
8 SS
7 OVP
WDFN-12L 3x3
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8450/B-05 August 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT8450/B
Absolute Maximum Ratings (Note 1)
Supply Input Voltage, VCC1, VCC2 ---------------------------------------------------------------------------------------- 45V
SW Pin Voltage at Switching Off, ISP, ISN ---------------------------------------------------------------------------- 55V
DCTL, ACTL, OVP Pin Voltage ------------------------------------------------------------------------------------------ 8V (Note 2)
EN Pin Voltage --------------------------------------------------------------------------------------------------------------- 20V
Power Dissipation, PD @ TA = 25°C
TSSOP-16 --------------------------------------------------------------------------------------------------------------------- 2.66W
WDFN-12L 3x3 --------------------------------------------------------------------------------------------------------------- 1.667W
Package Thermal Resistance (Note 3)
TSSOP-16, θJA --------------------------------------------------------------------------------------------------------------- 47°C/W
WDFN-12L 3x3, θJA --------------------------------------------------------------------------------------------------------- 60°C/W
WDFN-12L 3x3, θJC --------------------------------------------------------------------------------------------------------- 8.2°C/W
Junction Temperature ------------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------------- 260°C
Storage Temperature Range ---------------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 4)
HBM (Human Body Mode) ------------------------------------------------------------------------------------------------ 2kV
MM (Machine Mode) -------------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 5)
Junction Temperature Range ---------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC1 = VCC2 = 12V, No Load on any Output, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Overall
Supply Voltage
Supply Voltage VCC2 for Switch
Base Drive
VCC1
VCC2
Supply Current
IVCC1
VC 0.4V (Switching off)
Supply Current
IVCC2
VCC1 = VCC2 = 24V, ISW 1A
Shutdown Current
ISHDN_VCC1 VEN 0.7V
Shutdown Threshold
EN Input Current
VEN
VEN = 3V
Current Sense Amplifier
Input Threshold (VISP VISN)
4.5V common mode 50V
Input Current
IISP VISP = 24V
Input Current
Output Current
VC Threshold for PWM Switch Off
IISN
IVC
VISN = 24V
2.4V > VC > 0.2V
Min Typ Max Unit
4.5 -- 40 V
3 -- 40 V
-- 4 6 mA
-- ISW/70 ISW/40 A
-- 12 -- A
1 1.4 --
V
-- -- 0.5 A
170 190 210 mV
-- 100 --
A
-- 40 -- A
-- 20 --
A
-- 0.7 --
V
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8450/B-05 August 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
Application Information
The RT8450/B is specifically designed to be operated in
buck, buck -boost and boost converter applications. This
device uses a fixed frequency, current mode control
scheme to provide excellent line and load regulation. The
control loop has a current sense amplifier to sense the
voltage between the ISP and ISN pins and provides an
output voltage at the VC pin. A PWM comparator then
turns off the internal power switch when the sensed power
switch current exceeds the compensated VC pin voltage.
The power switch will not reset by the oscillator clock in
each cycle. If the comparator does not turn off the switch
in a cycle, the power switch is on for more than a full
switching period until the comparator is tripped. In this
manner, the programmed voltage across the sense
resistor is regulated by the control loop.
The current through the sense resistor is set by the
programmed voltage and the sense resistance. The voltage
across the sense resistor can be programmed by either
the analog or PWM signals at the ACTL pin, or the PWM
signal at the DCTL pin.
The protection schemes in the RT8450/B include over
temperature, input voltage under voltage, output voltage
over-voltage, and switch current limit.
Loop Compensation
The RT8450/B has an external compensation pin (VC)
allowing the loop response optimized for specific
application. An external resistor in series with a capacitor
is connected from the VC pin to GND to provide a pole
and a zero for proper loop compensation. The
recommended compensation resistance and capacitance
for the RT8450/B are 10k and 3.3nF.
Soft-Start
The soft-start of the RT8450/B 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 value of the soft-start capacitor
is user-defined to satisfy the designer’ s requirement.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8450/B-05 August 2014
RT8450/B
LED Current Setting
The LED current could be calculated by the following
equation :
ILED,MAX
=
V(ISP-ISN)
R2
Where V(ISP-ISN) is the voltage between ISP and ISN
(190mV typ. if ACTL or DCTL dimming is not applied) and
the R2 is the resister between ISP and ISN.
Brightness / Dimming Control
The RT8450/B features both analog and digital dimming
control. Analog dimming is linearly controlled by an
external voltage (0.3V < VACTL < 1.2V). With an on-chip
output clamping amplifier and a resistor, PWM dimming
signal fed at DCTL pin can be easily low-pass filtered to
an analog dimming signal with one external capacitor from
ACTL pin to GND for noise-free PWM dimming. A very
high contrast ratio true digital PWM dimming can be
achieved by driving ACTL pin with a PWM signal from
100Hz to 10kHz.
Output Over Voltage Setting
The RT8450/B is equipped with over voltage protection
(OVP) function. When the voltage at OVP pin exceeds a
threshold of approximately1.2V, the power switch is turned
off. The power switch can be turned on again once the
voltage at OVP pin drops below 1.2V.
For the Boost Application, the output voltage could be
clamped at a certain voltage level. The OVP voltage can
be set by the following equation :
VOUT,OVP
= 1.2 x (1 +
R3
R4
)
Where R3 and R4 are the voltage divider from VOUT to
GND with the divider center node connected to OVP pin.
Current-Limit Protection
The RT8450/B can limit the peak switch current by the
internal over current protection feature. In normal operation,
the power switch is turned off when the switch current
hits the loop-set value. The over current protection function
will turn off the power switch independent of the loop control
when the peak switch current reaches around 1.5A.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8450.PDF ] | |
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