6-String 43V White LED Driver with Boost Regulator
RT8532
General Description
The RT8532 is a high efficiency white LED driver. It is
designed for LCD pa nel that employs a LED array a s 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 ea ch LED string. T o provide enough
headroom for the operating of current sink, the Boost
controller monitors the minimum voltage of feedback pin s
and regulates an optimized output voltage for power
efficiency.
The RT8532 has wide input voltage range from 2.5V to
24V and provides adjusta ble 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 a ccurate 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 WQF N-20L 3x3 pack age.
Features
Wide Input Voltage : VIN 2.5V to 24V
High Output Voltage : V
Programmable Full Channel Current from 5mA to
50mA and Matched to 2%
Channel Current Regulation with
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
up to 43V
OUT
±±
±3% Accuracy
±±
Simplified Application Circuit
V
IN
C
IN
Chip Enable
R
C
ISET
MIX
R
COMP
C
C
COMP
R
FSW
PWM Signal
L1
VIN
EN
PWM
MIX
COMP
ISET
FREQ
AGND
LX
RT8532
PGND
Applications
UMPC and Notebook Computer Backlight
D1
C
OUT
R
OVP
LED1
LED2
LED3
LED4
LED5
LED6
R
OVP2
OVP1
C
OVP
:
:
:
:
:
:
:
:
:
:
:
:
V
OUT
:
:
:
:
:
:
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
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.
G : Green (Halogen Free and Pb Free)
Marking Information
89= : Product Code
89=YM
YMDNN : Date Code
DNN
Functional Pin Description
Pin No. Pin Name Pin Function
1 EN Chip Enable (Active High). There is an internal pull low resistor 400k for the EN pin.
Switching Frequency of Boost Converter Setting. Connect a resistor between this pin
2 FREQ
3 ISET
4 MIX
5 AGND Analog Ground of LED Driver.
6, 7, 8, 9, 10,
11
LED6 to
LED1
12 OVP Over Voltage Protection Sense Input. The detecting threshold is 1.2V (typ.).
13, 14 PGND Power Ground of Boost Converter.
15, 16 LX Switching Pin of B oost Converter.
17 PWM PWM Dimming Control Input.
18 VDC Internal Regulator Voltage. Connect a capacitor from this pin to ground.
19 VIN Power Supply Input.
20 COMP
21
(Ex pos ed Pad)
GND
and AGND to set the switching frequency.
R1.16 k
FSW
25
F(MHz)
SW
LED C urre nt Set ting. LED cur rent is set by the re sisto r R
ISET pin to ground.
ImA
LED
240
Rk
ISET
Dimm in g Mod e Selec tio n. Th ere is an inte r na l pul l hi gh 4 00k resistor con nec t e d to
VDC. Floating or pulling high for 25% Mixed mode dimming, pulling low for direct
PWM mode dimming. Recommended to mixed mode for high LED efficiency.
Current Sink for LED String. (Leave the pin unconnected or short to GND, if not
used.)
Compensation Note for Boost Converter. Connect a compensation network to this pin
for stability.
Ground. The Exposed Pad must be Soldered to a Large PCB and Connected to GND
for Maximum Power Dissipation.
(TOP VIEW)
VIN
LED5
LX
PWM
VDC
16
17181920
15
LX
14
PGND
13
PGND
12
21
9876
LED4
OVP
115
10
LED3
LED2
con nected from the
ISET
COMP
1
EN
2
FREQ
3
ISET
MIX
AGNDLED1
GND
4
LED6
WQFN-20L 3x3
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
When VIN is higher than the UVLO voltage and EN pin
input voltage is higher than rising threshold, the VDC will
be regulated around 3.8V if VIN is higher tha n 3.8V .
OSC
The switching frequency is adjustable by the external
resistor connected between the FREQ pin and GND.
PWM Controller
This controller includes some logic circuit to control LX
N-MOSFET on/off. This block controls the minimum on
time and max duty of LX.
LED1
LED2
……
LED6
AGND
+
-
……
+
-
MOSFET will be turned off until the temperature is lower
than the 120°C (typically).
OVP
When OVP pin voltage is higher than 1.2V, the LX
N-MOSFET is turned off immediately to protect the LX
N-MOSFET.
Minimum LED Selection
This block detects all LEDx voltage and select a minim um
voltage to EA (Error Amplifier). This function ca n guarantee
the lowest of LED pin voltage is around 600mV and V
OUT
can be boost to the highest forward voltage of LED strings.
OCP & OTP
When LX N-MOSFET peak current is higher than 2.5A
(typically), the LX N-MOSFET is turned off immediately
and resumed again at next clock pulse. When the junction
temperature is higher than 150°C (typically), the LX N-
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
If the voltage at LEDx pin is lower than 100mV, this
channel is defined a s open channel a nd the Minimum LED
Selection function will discard it to regulate other used
channels in proper voltage.
www.richtek.com
3
RT8532
Absolute Maximum Ratings (Note 1)
Supply Input V oltage, VIN
EN, PWM, ISET, COMP , MIX, FREQ to GND ---------------------------------------------------------------------- −0.3V to 26.5V
LX, OVP , LED1 to LED6 to GN D--------------------------------------------------------------------------------------- −0.3V to 48V
LX t o G ND ------------------------------------------------------------------------------------------------------------------- −0.3V to 48V
to GND------------------------------------------------------------------------------------ −0.3V to 26.5V
< 500ns ---------------------------------------------------------------------------------------------------------------------- −1V to 48V
V DC to GND ---------------------------------------------------------------------------------------------------------------- −0.3V to 7V
Power Dissipation, P
Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°C
Junction T emperature----------------------------------------------------------------------------------------------------- 150°C
Storage T emperature Range -------------------------------------------------------------------------------------------- − 65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.5V to 24V
Junction T emperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient T emperature Range-------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(V
= 5V, TA = 25°C, unless otherwise specified)
IN
Parameter Symbol Test Conditions Min Typ Max Unit
I
VIN Quiescent Current
VIN Shutdown Current I
VI N Unde r Vol tage Lock ou t
Threshold
PWM Dimm ing Frequency f
VIN
I
VIN_SW
SHDN
V
PWM
Control Input
EN, PWM Inp ut
Voltage
High V
Low VIL
Boost Converter
Switching Frequency fSW
LX On Resista nc e
(N-MOSFET)
R
UVLO
0.1 -- 20 kHz
IH
V
LX
PWM = COMP = 0V, Not Switching
-- 3 --
PWM = COMP = 2V, Sw itching -- 4 --
-- -- 10 A
-- 2.1 --
1.3 -- 24
-- -- 0.5
0.8 1 1.2
0.4 0.5 0.6
= 4.5V, EN = 0V
V
IN
V
Rising -- 2.3 --
IN
VIN Falling
= 2.5V to 24V
V
IN
= 2.5V to 24V
V
IN
R
= 22k
FSW
R
= 51k
FSW
> 4.5V 0 .18 0.2 0 .22
IN
mA
V
V
MHz
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
LED Current Accuracy I
LE D Curr en t Matc hi ng I
LEDA
LEDM
ISET Pin Voltage V
F ault Protecti on
FSW = 1MHz 40 60 80 n s
FSW = 1MHz 90 93 96 %
MAX
LEDx
ISET
Hi gh est LE D Strin g, I
2V > V
2V > V
Formulated by (I
LEDx
LEDx
> 0.5V, R
> 0.5V, R
LEDx
LED
ISET
ISET
I
= 20mA
= 12k
= 12k,
) / I
VG
x 100%
VG
2.2 2.5 2.8 A
0.5 0.6 0.7 V
19.4 20 20.6 mA
-- -- 2 %
0.76 1 1.24 V
OVP Threshol d V
OVP UVLO Threshold V
T herm al Shutdow n
Temperature
OTP H ysteresis T
LE D Pi n Unde r Vol tag e
Threshold
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. θ
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
is measured at T
JA
measured at the exposed pad of the package.
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
A
1.16 1.2 1.24 V
OVP
OVPF
T
-- 150 -- C
SD
OTP_Hys
V
LSD
-- 30 -- C
Un-Connection -- 0.1 -- V
-- 50 -- mV
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.