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PDF RT8532 Data sheet ( Hoja de datos )
| Número de pieza | RT8532 | |
| Descripción | 6-String 43V White LED Driver | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8532
6-String 43V White LED Driver with Boost Regulator
General Description
The RT8532 is a high efficiency white LED driver. It is
designed for LCD panel that employs a LED array as the
lighting source. An integrated switch current mode Boost
controller drives six strings in parallel and supports up to
10 pieces of LEDs per string. The internal current sinks
support maximum ±2% current matching for excellent
brightness uniformity in each LED string. To provide enough
headroom for the operating of current sink, the Boost
controller monitors the minimum voltage of feedback pins
and regulates an optimized output voltage for power
efficiency.
The RT8532 has wide input voltage range from 2.5V to
24V and provides adjustable 5mA to 50mA LED current.
The internal 200mΩ, 43V power switch with current-mode
control provides cycle-by-cycle over current protection.
The RT8532 also integrates PWM and analog dimming
functions for accurate LED current control. The input PWM
dimming frequency can be operated operate from 100Hz
to 20kHz without any inrush current in LED.
The RT8532 is available in WQFN-20L 3x3 package.
Features
Wide Input Voltage : VIN 2.5V to 24V
High Output Voltage : VOUT up to 43V
Programmable Full Channel Current from 5mA to
50mA and Matched to 2%
Channel Current Regulation with ±3% Accuracy
Dimming Controls
Direct PWM Dimming up to 20kHz and Minimum
On-Time to 500ns
PWM to Mixed Analog and PWM Dimming up to
20kHz with Maximum 9 bit Resolution
Built-In Soft Start to Prevent Inrush Current without
External Capacitor
Disconnects LED in Shutdown
Protection
Strings Open Detection
Current Limit Protection
Programmable Over Voltage Protection
Over Temperature Protection
20-Lead WQFN Package
RoHS Compliant and Halogen Free
Applications
UMPC and Notebook Computer Backlight
Simplified Application Circuit
L1 D1
VIN
Chip Enable
CIN LX
VIN
EN RT8532 OVP
PWM Signal
MIX
CC RCOMP
CCOMP
RISET
RFSW
PWM
MIX
COMP
LED1
LED2
LED3
LED4
LED5
ISET
LED6
FREQ
AGND PGND
COUT
VOUT
ROVP2
ROVP1
::::::
::::::
COVP : : : : : :
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8532-04 January 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT8532
Parameter
Symbol
Test Conditions
Min Typ Max Unit
Minimum On-Time
tON(MIN)
Maximum Duty
DMAX
LX Current Limit
ILIM
Regulated VLEDx
VLEDx
Low Dropout Linear Regulator
FSW = 1MHz
FSW = 1MHz
Highest LED String, ILED = 20mA
40 60 80
90 93 96
2.2 2.5 2.8
0.5 0.6 0.7
ns
%
A
V
LDO Output Voltage Range VDC
LED Current Programming
3.6 3.8 4
V
LED Current Accuracy
LED Current Matching
ISET Pin Voltage
ILEDA
ILEDM
VISET
2V > VLEDx > 0.5V, RISET = 12k
19.4 20 20.6 mA
2V > VLEDx > 0.5V, RISET = 12k,
-- -- 2 %
Formulated by (ILEDx IAVG) / IAVG x 100%
0.76 1 1.24 V
Fault Protection
OVP Threshold
VOVP
1.16 1.2 1.24 V
OVP UVLO Threshold
Thermal Shutdown
Temperature
VOVPF
TSD
-- 50 -- mV
-- 150 -- C
OTP Hysteresis
TOTP_Hys
-- 30 -- C
LED Pin Under Voltage
Threshold
VLSD
Un-Connection
-- 0.1 --
V
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 ©2014 Richtek Technology Corporation. All rights reserved.
DS8532-04 January 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
RT8532
Brightness Control
The RT8532 features the digital dimming control scheme.
A very high contrast ratio true digital PWM dimming can
be achieved by driving PWM pin with a PWM signal and
the recommended PWM frequency is 100Hz to 10kHz.
Dimming frequency can be sufficiently adjusted from
100Hz to 20kHz. However, LED current cannot be 100%
proportional to duty cycle especially for high frequency
and low duty ratio because of physical limitation caused
by inductor rising time. Please refer to Table 1 and Table2.
Table 1. Mixed Dimming Mode
Dimming Frequency (Hz) Duty (Min) Duty (Max)
100 < fPWM 200
200 < fPWM 500
500 < fPWM 1k
1k < fPWM 2k
2k < fPWM 5k
5k < fPWM 10k
10k < fPWM 20k
0.18%
0.18%
0.2%
0.2%
0.3%
0.3%
0.6%
100%
100%
100%
100%
100%
100%
100%
Table 2. PWM Dimming Mode
Dimming Frequency (Hz) Duty (Min) Duty (Max)
100 < fPWM 200
0.02%
100%
200 < fPWM 500
0.02%
100%
500 < fPWM 1k
0.04%
100%
1k < fPWM 2k
0.06%
100%
2k < fPWM 5k
0.15%
100%
5k < fPWM 10k
0.3%
100%
10k < fPWM 20k
0.6%
100%
Note : The minimum duty in Table 1 and Table 2 is based
on the application circuit and does not consider the
deviation of current linearity when fPWM > 10kHz, ILED
may not achieve setting current in duty (min.) due to
different VOUT / VIN ratio at VIN = 12V.
Over Temperature Protection
The RT8532 includes an Over Temperature Protection
(OTP) feature to prevent overheating due to excessive
power dissipation from damaging the device. The OTP
function will shut down LED driver when the junction
temperature exceeds 150°C. It will reactivate the device
when powered on again. To maintain continuous operation,
the junction temperature should be kept below 125°C.
LED Driver Over Voltage Protection
The LED driver equips an Over Voltage Protection (OVP)
function. When the voltage at the OVP pin reaches a
threshold of approximately 1.2V, the driver will turn off.
The drivers turn on again once the voltage at OVP drops
below the threshold voltage. Thus, the output voltage can
be clamped at a certain voltage level. This voltage level
can be calculated by the following equation :
VOUT,
OVP
VOVP
1
ROVP2
ROVP1
where ROVP1 and ROVP2 are the resistors in the voltage
divider connected to the OVP pin. It is suggested to use
500kΩ for ROVP2 to reduce loading effect.
LED Channel Open Circuit Protection
If at least one channel is in normal operation, the LED
driver will automatically ignore the open channels and
continue to regulate current for the channels in normal
operation.
Under Voltage Lockout (UVLO)
The UVLO circuit compares the LED driver input voltage
at VIN with the UVLO threshold to ensure the input voltage
is high enough for reliable operation. The 200mV (typ.)
hysteresis prevents supply transients from causing a
shutdown. Once VIN exceeds the UVLO rising threshold,
the LED soft-start will begin after a several ms delay. When
VIN falls below the UVLO falling threshold, the controller
turns off all LED driver functions.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8532-04 January 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT8532.PDF ] | |
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