Richtek RT8532GQW Schematic [ru]

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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 LEDstring. 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

VIN

 

L1

 

D1

 

 

 

 

 

 

VOUT

 

 

 

 

COUT

 

 

 

 

 

 

CIN

 

LX

 

 

 

 

 

 

 

 

 

ROVP2

 

 

 

 

 

 

 

Chip Enable

 

VIN

 

 

 

 

 

 

 

 

RT8532

 

:

:

:

:

:

:

 

 

EN

OVP

 

 

 

 

 

 

:

:

:

:

:

:

 

 

PWM

 

ROVP1

COVP

:

:

:

:

:

:

 

 

 

 

 

 

 

 

 

 

 

PWM Signal

MIX

MIX

 

LED1

 

 

 

 

 

 

 

 

 

COMP

 

 

 

 

 

 

 

 

 

 

 

LED2

 

 

 

 

 

 

 

CC

RCOMP

 

 

 

 

 

 

 

 

 

 

 

LED3

 

 

 

 

 

 

 

 

CCOMP

 

 

LED4

 

 

 

 

 

 

 

 

 

 

LED5

 

 

 

 

 

 

 

 

 

ISET

 

 

 

 

 

 

 

 

 

 

 

LED6

 

 

 

 

 

 

 

RISET

FREQ

 

 

 

 

 

 

 

 

 

AGND PGND

 

 

 

 

 

 

 

 

RFSW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8532-04 January 2014

www.richtek.com

 

1

89=YM DNN
RT8532
Ordering Information

Pin Configurations

RT8532

Package Type

 

 

(TOP VIEW)

 

 

 

 

COMP VIN VDC PWM LX

 

 

QW : WQFN-20L 3x3 (W-Type)

 

 

 

 

Lead Plating System

 

 

 

 

 

 

20 19 18 17 16

 

Note :

G : Green (Halogen Free and Pb Free)

EN

1

 

 

 

 

15

LX

 

FREQ

2

 

GND

14

PGND

Richtek products are :

ISET

3

 

13

PGND

MIX

4

 

 

 

21

12

OVP

RoHS compliant and compatible with the current require-

 

 

 

AGND

5

 

 

 

 

11

LED1

ments of IPC/JEDEC J-STD-020.

 

 

6

7

8

9

10

 

 

 

LED6 LED5 LED4 LED3 LED2

 

Suitable for use in SnPb or Pb-free soldering processes.

 

 

 

 

 

 

 

 

Marking Information

 

 

WQFN-20L 3x3

 

 

 

 

 

 

 

 

 

89= : Product Code

YMDNN : Date Code

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

and AGND to set the switching frequency.

 

25

 

k

 

 

RFSW 1.1

 

 

6

 

 

F

(MHz)

 

 

SW

 

 

 

 

LED Current Setting. LED current is set by the resistor RISET connected from the

3

ISET

ISET pin to ground.

 

 

ILED mA

 

 

240

 

 

 

 

 

 

 

 

 

 

RISET k

 

 

 

 

 

 

 

Dimming Mode Selection. There is an internal pull high 400k resistor connected to

4

MIX

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.

5

AGND

Analog Ground of LED Driver.

 

6, 7, 8, 9, 10,

LED6 to

Current Sink for LED String. (Leave the pin unconnected or short to GND, if not

11

LED1

used.)

 

 

 

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 Boost 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

Compensation Note for Boost Converter. Connect a compensation network to this pin

for stability.

 

 

 

 

 

 

 

 

21

GND

Ground. The Exposed Pad must be Soldered to a Large PCB and Connected to GND

(Exposed Pad)

for Maximum Power Dissipation.

 

 

 

 

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

 

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

 

 

 

 

 

 

DS8532-04 January 2014

2

 

 

 

 

 

 

 

Richtek RT8532GQW Schematic

RT8532

Function Block Diagram

 

VIN VDC

FREQ

 

 

OVP

 

 

 

 

 

 

+

1.2V

 

 

 

 

 

-

LX

 

 

OSC

 

 

S

Q

 

EN

LDO

 

 

 

R

Q

 

 

 

 

 

 

 

 

 

 

 

 

 

 

OCP

 

OTP

PWM

 

+

+

 

PGND

 

Controller

 

-

 

 

 

 

 

 

 

 

 

 

 

 

GND

 

 

 

 

 

+

0.6V

COMP

 

 

 

 

6

 

 

 

 

-

Mini LED

 

 

 

 

 

 

 

 

 

 

 

Selection

 

PWM

PWM-to-DC

PWMO

MUX

 

LED Open

Generator

 

 

 

 

 

 

 

 

 

Detection

MIX

 

 

 

 

 

 

 

 

 

DAC

 

 

 

 

LED1

 

 

 

 

 

 

 

LED2

 

 

 

 

 

 

 

……

 

+

 

+

 

+

 

LED6

 

 

 

……

+

 

-

 

-

 

-

-

ISET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AGND

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 than 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.

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-

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 minimum voltage to EA (ErrorAmplifier). This function can guarantee the lowest of LED pin voltage is around 600mV and VOUT can be boost to the highest forward voltage of LED strings.

LED Open Detection

If the voltage at LEDx pin is lower than 100mV, this channel is defined as open channel and the Minimum LED Selection function will discard it to regulate other used channels in proper voltage.

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8532-04 January 2014

www.richtek.com

 

3

RT8532

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

Supply Input Voltage, VIN to GND ------------------------------------------------------------------------------------

 

 

 

−0.3V to 26.5V

EN, PWM, ISET, COMP, MIX, FREQ to GND ----------------------------------------------------------------------

 

 

−0.3V to 26.5V

LX, OVP, LED1 to LED6 to GND ---------------------------------------------------------------------------------------

 

 

 

−0.3V to 48V

LX toGND -------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

−0.3V to 48V

< 500ns ----------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

−1V to 48V

VDC to GND ----------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

−0.3V to 7V

Power Dissipation, PD @ TA = 25°C

 

 

 

 

 

 

 

WQFN−20L 3x3

------------------------------------------------------------------------------------------------------------

 

 

 

 

 

1.471W

 

Package Thermal Resistance (Note 2)

 

 

 

 

 

 

 

WQFN−20L 3x3, θJA ------------------------------------------------------------------------------------------------------

 

 

 

 

68°C/W

 

WQFN−20L 3x3, θJC ------------------------------------------------------------------------------------------------------

 

 

 

 

7.5°C/W

 

Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------

 

 

 

260°C

 

Junction Temperature -----------------------------------------------------------------------------------------------------

 

 

 

 

150°C

 

Storage Temperature 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 Temperature Range --------------------------------------------------------------------------------------------

 

 

 

 

−40°C to 125°C

Ambient Temperature Range --------------------------------------------------------------------------------------------

 

 

 

 

−40°C to 85°C

Electrical Characteristics

 

 

 

 

 

 

 

(VIN = 5V, TA = 25°C, unless otherwise specified)

 

 

 

 

 

 

Parameter

 

Symbol

Test Conditions

Min

Typ

Max

 

Unit

VIN Quiescent Current

 

IVIN

PWM = COMP = 0V, Not Switching

--

3

--

 

mA

 

IVIN_SW

PWM = COMP = 2V, Switching

--

4

--

 

 

 

 

 

 

VIN Shutdown Current

 

ISHDN

VIN = 4.5V, EN = 0V

--

--

10

 

A

VIN Under Voltage Lockout

 

VUVLO

VIN Rising

 

--

2.3

--

 

V

Threshold

 

 

VIN Falling

 

--

2.1

--

 

 

 

 

 

 

 

PWM Dimming Frequency

 

fPWM

 

 

0.1

--

20

 

kHz

Control Input

 

 

 

 

 

 

 

 

 

 

EN, PWM Input

High

 

VIH

VIN = 2.5V to 24V

1.3

--

24

 

V

Voltage

Low

 

VIL

VIN = 2.5V to 24V

--

--

0.5

 

 

 

 

Boost Converter

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.8

1

1.2

 

 

Switching Frequency

 

fSW

RFSW = 22k

 

 

 

 

 

MHz

 

RFSW = 51k

 

0.4

0.5

0.6

 

 

 

 

 

 

 

 

LX On Resistance

 

RLX

VIN > 4.5V

 

0.18

0.2

0.22

 

 

(N-MOSFET)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Copyright ©2014 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

 

www.richtek.com

DS8532-04 January 2014

4

 

RT8532

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

Minimum On-Time

tON(MIN)

FSW = 1MHz

40

60

80

ns

Maximum Duty

DMAX

FSW = 1MHz

90

93

96

%

LX Current Limit

ILIM

 

2.2

2.5

2.8

A

Regulated VLEDx

VLEDx

Highest LED String, ILED = 20mA

0.5

0.6

0.7

V

Low Dropout Linear Regulator

 

 

 

 

 

LDO Output Voltage Range

VDC

 

3.6

3.8

4

V

LED Current Programming

 

 

 

 

 

 

LED Current Accuracy

ILEDA

2V > VLEDx > 0.5V, RISET = 12k

19.4

20

20.6

mA

LED Current Matching

ILEDM

2V > VLEDx > 0.5V, RISET = 12k ,

--

--

2

%

Formulated by (ILEDx IAVG) / IAVG x 100%

 

 

 

 

 

 

ISET Pin Voltage

VISET

 

0.76

1

1.24

V

Fault Protection

 

 

 

 

 

 

OVP Threshold

VOVP

 

1.16

1.2

1.24

V

OVP UVLO Threshold

VOVPF

 

--

50

--

mV

Thermal Shutdown

TSD

 

--

150

--

C

Temperature

 

 

 

 

 

 

 

OTP Hysteresis

TOTP_Hys

 

--

30

--

C

 

 

 

 

 

 

 

LED Pin Under Voltage

VLSD

Un-Connection

--

0.1

--

V

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. 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.

is a registered trademark of Richtek Technology Corporation.

DS8532-04 January 2014

www.richtek.com

 

5

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