Richtek RT8532GQW Schematic [ru]

®
6-String 43V White LED Driver with Boost Regulator
RT8532
General Description
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.
©
DS8532-04 January 2014 www.richtek.com
1
RT8532
Ordering Information
Pin Configurations
RT8532
Package Type QW : WQFN-20L 3x3 (W-Type)
Lead Plating System
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.
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.

R1.1 6 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
AGND LED1
GND
4
LED6
WQFN-20L 3x3
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
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DS8532-04 January 2014
Function Block Diagram
VIN OVP
EN
COMP
PWM
MIX
LDO
PWM-to-DC
VDC
OTP
FREQ
OSC
PWM
Controller
Generator
PWMO
RT8532
+
1.2V
-
SQ
R
Q
OCP
+
+
-
0.6V
MUX
+
-
Mini LED Selection
LED Open
Detection
6
LX
PGND GND
DAC
+
-
ISET
+
-
Operation
Enable Control
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.
DS8532-04 January 2014
©
LED Open Detection
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.
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RT8532
Absolute Maximum Ratings (Note 1)
Supply Input V oltage, VINEN, PWM, ISET, COMP , MIX, FREQ to GND ---------------------------------------------------------------------- 0.3V to 26.5VLX, OVP , LED1 to LED6 to GN D--------------------------------------------------------------------------------------- 0.3V to 48VLX 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 7VPower Dissipation, P
@ T
D
= 25°C
A
WQFN20L 3x3------------------------------------------------------------------------------------------------------------ 1.471W
Package Thermal Re sistance (Note 2)
WQFN20L 3x3, θJA------------------------------------------------------------------------------------------------------ 68°C/W WQFN20L 3x3, θJC------------------------------------------------------------------------------------------------------ 7.5°C/W
Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°CJunction T emperature----------------------------------------------------------------------------------------------------- 150°CStorage T emperature Range -------------------------------------------------------------------------------------------- 65°C to 150°CESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------------- 2kV MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.5V to 24VJunction T emperature Range-------------------------------------------------------------------------------------------- 40°C to 125°CAmbient 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.
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DS8532-04 January 2014
RT8532
A
A
Parameter Symbol Test Conditions Min Typ Max Unit
Minimum On-Time t
ON(MIN)
Maximum Duty D LX Cur rent Limi t I Regulat ed V
V
LEDx
LIM
Low Dropout Linear Regulator
LDO O utput Vol tag e Ra nge VDC 3.6 3.8 4 V
LED Current Pr ogramming
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.
DS8532-04 January 2014
©
www.richtek.com
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