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PDF RT8452 Data sheet ( Hoja de datos )
| Número de pieza | RT8452 | |
| Descripción | High Voltage High Current LED Driver Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8452
High Voltage High Current LED Driver Controller for Buck
Boost or Buck-Boost Topology
General Description
The RT8452 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 the maximum
operating input voltage of 36V and output voltage up to
48V, the RT8452 is ideal for Buck, Boost or Buck-Boost
operation.
With 350kHz operating frequency, the external inductor
and capacitors can be small while maintaining high
efficiency.
Dimming can be done by either analog or digital. A built-in
clamping comparator and filter allow easy low noise analog
dimming conversion from digital signal with only one
external capacitor. An unique True PWM dimming control
is made easy with MOSFET under LED string. A very high
dimming ratio can be achieved by adopting both analog/
digital dimming and True PWM dimming together.
The RT8452 is available in WQFN-16L 3x3 and SOP-16
packages.
Ordering Information
RT8452
Package Type
S : SOP-16
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Features
z High Voltage Capability : VIN Up to 36V, VOUT Up to
48V
z Buck, Boost or Buck-Boost Operation
z Current Mode PWM with 350kHz Switching
Frenquency
z Easy Dimming Control : Analog or Digital
Converting to Analog with One External Capacitor
z True PWM Dimming : External FET Driver is Build-
in
z Programmable Soft Start to Avoid Inrush Current
z Programmable Over Voltage Protection
z VIN Undervoltage Lockout and Thermal Shutdown
z 16-Lead WQFN and SOP Packages.
z RoHS Compliant and Halogen Free
Applications
z General Industrial High Power LED Lighting
z Desk Lights and Room Lighting
z Building and Street Lighting
z Industrial Display Backlight
Pin Configurations
(TOP VIEW)
GBIAS
GATE
PWMOUT
ISW
PWMDIM
ISP
ISN
VC
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SOP-16
GND
VCC
OVP
EN
NC
SS
DCTL
ACTL
16 15 14 13
GBIAS
GATE
PWMOUT
ISW
1
2
3
4
GND
17
12 NC
11 SS
10 DCTL
9 ACTL
5678
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8452-03 May 2012
WQFN-16L 3x3
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
Function Block Diagram
RT8452
EN
VCC
OVP
VC
SS
DCTL
1.4V
4.5V
1.2V
5.7V +
+ Shutdown
-
-
-
OSC
S
+
R
+R
- RR
VOC
5V
100k GBIAS
- 100mV
+
6µA
1.2V
+
-
-
GM
+
1.2V
+
-
GBIAS
GATE
PWMOUT
PWMDIM
ISW
ISN
ISP
GND
ACTL
VISP – VISN
(mV)
190
0 0.2
1.2
Figure 6
VACTL (V)
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8452-03 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
Applications Information
The RT8452 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 RT8452
can be up to 36V and the output voltage can be up to 48V.
The RT8452 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. The value of a
1μF capacitor will be adequate for many 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
RT8452 from excessive on-chip power dissipation.
The GBIAS pin has its own under-voltage disable (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, will 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 besides RT8452, typically the extra GBIAS load
should be limited to less than 10mA.
Loop Compensation
The RT8452 uses an internal error amplifier whose
compensation pin (VC) allowing the loop response
optimized for specific application. The external inductor,
output capacitor and the 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, and 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
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8452-03 May 2012
RT8452
from the VC pin to GND to provide a pole and a zero for
proper loop compensation. The typical compensation
forthe RT8452 is 10k and 3.3nF.
Soft-Start
The soft-start of the RT8452 can be achieved by connecting
a capacitor from 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 :
TSS
=
CSS
×
2.4V
6μA
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 an GBIAS under-voltage event.
LED current Setting
The LED current is programmed by placing an appropriate
value 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 :
ILED = (VACTL - 0.2)× 0.19
RSENSE
Where,
RSENSE is the resister between ISP and ISN.
When the voltage of ACTL is higher than 1.2V, the LED
current is regulated to :
ILED(MAX)
=
190mV
RSENSE
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet RT8452.PDF ] | |
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