Richtek RT8560AGQW Schematic [ru]

High Voltage 4 Channel LED Driver

RT8560A

General Description

The RT8560A is a 60V 4-channel LED driver capable of
delivering 30mA to ea ch cha nnel with 15 LEDs (3.6V per
diode) total 60 LEDs with one driver. The R T8560A is a
current mode boost converter opearated at 1MHz switching
frequency , wide V
on-chip current switch is rated at 1.5A.

The PWM output voltage loop selects and regulates the
LED pin with the highest voltage string to 0.9V allowing
voltage mismatches between LED strings. The RT8560A
automatically detects and disconnects a ny unconnected
and/or broken strings during operation from PWM loop to
prevent V

OUT

The 3% matched LED currents on all cha nnels are simply
programmed with a resistor or a current sink. Both a nalog
dimming and digitally controlled PWM dimming are
supported by RT8560A. Analog dimming is linearly
controlled by an external voltage. With a n on-chip output
clampping a mplifier a nd a 200kΩ resistor , PWM dimming
signal is easily low-pass filtered to an analog dimming
signal with one external capacitor for noise-free PWM
dimming. A very high contrast ratio true digital PWM
dimming can be achieved by driving EN pin to PWM
shutdown the chip or by driving ACTL pin.

range covers from 6V to 40V and the

IN

from over voltage.

Features

zz

High V oltage : VIN up to 40V , V

z

zz

up to 60V , Driving

OUT

up to 60 x 3.6V LEDs (15 each channel)

zz

z Channel Current Programmabe 4mA to 30mA and

zz

Matched to 3% Accuracy

zz

z Current Mode PWM 1MHz Boost Converter

zz

zz

z Easy Analog and Digital Dimming Control

zz

zz

z Programmable Soft Start

zz

zz

z Automatic Detecting Unconnected and/or Broken

zz

Channel

zz

z Programmable Over Voltage Protection

zz

zz

z Disconnects LED in Digital Dimming : Providing

zz

High Accuracy Digital Dimming by PWM at ACTL
Pin or EN Pin

zz

z V

Under Voltage Lockout

zz

IN

zz

z Over Temperature Protection

zz

zz

z Current Limiting Protection

zz

zz

z Small 20-Lead WQFN Package

zz

zz

z RoHS Compliant and Halogen Free

zz

Applications

z UMPC and Notebook Computer Backlight
z GPS, Portable DVD Backlight
z Desk Lights and Room Lighting

Other protecting features include programmable PWM
output over voltage protection, LED curren limit, PWM
switch current limit and thermal shutdown. The R T8560A
is packaged with a tiny footprint package of WQFN-20L
4x4 packages.

Ordering Information

RT8560A

Package Type
QW : WQFN-20L 4x4 (W-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)

Note :

Pin Configurations

(TOP VIEW)

GND

GND

20 19 18 1617

1

GND

2

GND

3

GND

SW
SW

GND

4
5

7

8910

6

VCC2

VCC1

LED2

LED1

21

ACTL

RISET

LED3

15

LED4

14

VC

13

SS

12

OVP

11

EN

DCTL

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.

Marking Information

For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.

WQFN-20L 4x4

DS8560A-01 April 2011 www.richtek.com

1

RT8560A

Typical Application Circuit

V

IN

6V to 40V

L

10µH

C

VIN

10µF

R

VCC1

10

C
1µF

V

OUT

V

IN

VCC1

R

R

1.8k

VCC2

10

VC

C

VC

3.9nF

C2

R1

5V

R4

C

VCC2

1µF

R3
1k

C

OUT3

1µF

R2

C1

0.1µF

4, 5

11

12

14
13

7

6

D

SW
VCC1

EN

OVP

VCC2

VC
SS

15 LED String

RT8560A

V

OUT

60V MAX

:

:

:

:

:

:

:

:

:

:

:

:

18

LED1

17

LED2

16

LED3

15

LED4

RISET

ACTL
DCTL

GND

R

ISET

5.36k

8

R5

1k

9

10

PWM Signal

1, 2, 3, 19, 20, Exposed Pad (21)

:
:

C

OUT1

:
:

I = 20mAR×

LED

C

OUT2

5.36k

ISET

Figure 1. 1MHz, 20mA Full Scale Current Digital PWM Di mming Control

V

IN

6V to 40V

R
10

C
1µF

V

OUT

V

IN

VCC1

VCC1

R

VCC2

10

R

VC

1.8k
C

VC

3.9nF

C2

5V

R1

10µH

C

VIN

10µF

L

R4

C

VCC2

1µF

R3
1k

R2

C

OUT3

1µF

4, 5

C1

0.1µF

11

12

14
13

7

6

D

SW
VCC1

EN

OVP

VCC2

VC
SS

15 LED String

RT8560A

V

OUT

60V MAX

:

:

:

:

:

:

:

:

:

:

:

:

18

LED1

17

LED2

16

LED3

15

LED4

RISET

ACTL
DCTL

GND

R

ISET

5.36k

8

R5

9

1k

10
1, 2, 3, 19, 20, Exposed Pad (21)

:
:

C

OUT1

:
:

I = 20mAR×

LED

Analog

Dimming

C

OUT2

5.36k

ISET

Figure 2. 1MHz, 20mA Full Scale Current An alog Dimming Control

DS8560A-01 April 2011www.richtek.com

2

V

IN

6V to 40V

R
10

C
1µF

V

OUT

V

IN

VCC1

VCC1

R

VCC2

10

R

VC

1.8k
C

3.9nF

VC

C3

5V

R1

10µH

C

VIN

10µF

L

R4

C
1µF

C

R3
1k

R2

VCC2

C1

0.1µF

OUT3

1µF

4, 5

11
12

14
13

7

6

D

SW
VCC1

EN

OVP

VCC2

VC
SS

15 LED String

RT8560A

V

OUT

60V MAX

:

:

:

:

:

:

:

:

:

:

:

:

18

LED1

17

LED2

16

LED3

15

LED4

RISET

ACTL

DCTL

8

9

10

R

ISET

5.36k

R5

1k

PWM Signal

1, 2, 3, 19, 20, Exposed Pad (21)

GND

:
:

C

OUT1

:
:

I = 20mAR×

LED

C

RT8560A

OUT2

5.36k

ISET

C2

0.1µF

Figure 3. 1MHz, 20mA Full Scale Current PWM to Analog Di mming Control

V

IN

V

AVDD

6V to 40V

R
10

V

OUT

V

IN

VCC1

C

VCC1

2.2µF

R

4V to 40V

C2

5V

R1

VCC2

10

R

VC

1.8k

C

VC

3.9nF

10µH

C

VIN

10µF

L

R4

C

VCC2

1µF

C

R3
1k

R2

C1

0.1µF

OUT3

1µF

4, 5

11

12

14
13

7

6

D

SW
VCC1

EN

OVP

VCC2

VC
SS

15 LED String

RT8560A

V

OUT

60V MAX

:

:

:

:

:

:

:

:

:

:

:

:

18

LED1

17

LED2

16

LED3

15

LED4

RISET

ACTL
DCTL

GND

R

ISET

5.36k

8

R5
1k

9
10

1, 2, 3, 19, 20, Exposed Pad (21)

:
:

C

OUT1

:
:

I = 20mAR×

LED

PWM Signal

C

OUT2

5.36k

ISET

Figure 4. Wide Range VIN Application by Connecting VCC1 to LCD Driver Power A V DD

DS8560A-01 April 2011 www.richtek.com

3

RT8560A

Function Block Diagram

SW

VCC1

OVP

EN

VCC2

VC

SS

DCTL

6.2V

2.5V

2V

6uA

­+

+

-

­+

1.2V

+

-

OSC

Shutdown

200k

S
R

R

+

-

V

OUT

Regulation

Unit

1.2V

+

-

+

LED1

-

LED2

+

-

LED3

+

-

5V

LED4

+

-

ACTL

RISET

DS8560A-01 April 2011www.richtek.com

4

Functional Pin Description

Pin Numbe r Pin Name Pin Function

1, 2, 3, 19, 20,

21 (Exposed Pad)

4, 5 SW

6 VCC2

7 VCC1
8 RISET

GND

Ground pin of the chip. The exposed pad must be soldered to a large PCB

and connected to GND for maximum power dissipation.

PWM boost converter switch node.
Bipolar power switch base current supply. Typical beta of the power N PN

switch is approximately 70. VCC2 can be connected either to VCC1 or to a
separate lower voltage, as low as 3V, for better s ystem efficiency and/or
heat concern. A good bypass is necessary.

Power supply of the chip. For good bypass, a low ESR capacitor is required.
A resistor or a current from DAC on this pin programs the full LED current.

RT8560A

9 ACTL

10 DCTL

11 EN
12 OVP
13 SS

14 VC

18, 17, 16, 15

LED1, LED2,
LED3, LED4

Analog / Digi tal dimming co ntrol. When using anal og dimming,

I = 20mA for V 1.2V.

LED ACTL

By adding a 0.1uF filtering capacitor on ACTL pin, the PWM dimming signal
on DCTL pin will be averaged out and converte d into analog dimming signal
on ACTL pin.

Chip enable pin, when low chip is in shutdown mode.
Over voltage protection. PWM boost converter turns off when V
higher than 2.5V.
Soft start pin, a capacitor of at least 10nF is requi red for soft start.
PWM boost converter loop compensation node.

Channel 1 to Channel 4 LED current sink. Leave the pin unconnected if not
used.

5.36k

×≥

R

ISET

OVP

goes

DS8560A-01 April 2011 www.richtek.com

5

RT8560A

Absolute Maximum Ratings (Note 1)

z Supply V oltage, VCC1, VCC2------------------------------------------------------------------------------------------ 42V
z SW Pin Voltage at Switching Off -------------------------------------------------------------------------------------- 65V
z LED1, LED2, LED3, LED4 Pin ----------------------------------------------------------------------------------------- 25V
z EN Pin Voltage ------------------------------------------------------------------------------------------------------------- 20V
z RISET Pin V oltage -------------------------------------------------------------------------------------------------------- 4V
z ACTL, DCTL, OVP , SS, VC Pins Voltage --------------------------------------------------------------------------- 8V
z Power Dissipation, P

WQFN-20L 4x4 ------------------------------------------------------------------------------------------------------------ 1.852W

z Package Thermal Re sistance (Note 2)

WQF N-20L 4x4, θJA------------------------------------------------------------------------------------------------------- 54°C/W
WQFN-20L 4x4, θJC------------------------------------------------------------------------------------------------------ 7°C/W

z Junction T emperature----------------------------------------------------------------------------------------------------- 150 °C
z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°C
z Storage T emperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)

HBM (Human Body Mode) ---------------------------------------------------------------------------------------------- 2kV
MM (Ma chine Mode)------------------------------------------------------------------------------------------------------ 200V

@ TA = 25°C

D

Recommended Operating Conditions (Note 4)

z Supply Input V oltage, VCC1, VCC2 ---------------------------------------------------------------------------------- 6V to 40V
z Junction T emperature Range--------------------------------------------------------------------------------------------
z Ambient T emperature Range--------------------------------------------------------------------------------------------

−40°C to 125°C

−40°C to 85°C

Electrical Characteristics

(V

= 17V, T

CC1

V

UVLO Threshold V

CC1

Supply Current I
Shutdown Current I

EN
Threshold

ACTL
Threshold

EN Pin Input Current IEN VEN ≤ 5V -- - - 2 μA

LED Current P rogramming

LED Cur rent I

LED´s Current Matching

RISET Pin Voltage V
Input Current of ACTL I

= 25°C, unless otherwise specified)

A

Parameter Symbol Test Conditions Min Typ Max Unit

Logic-High Voltage V

Logic-Low Voltage

Logic-High Voltage V

Logic-Low Voltage

V

UVLO

VC ≤ 0.4V (Switching off) -- 4 7 mA

VCC1

VEN ≤ 0.7V -- 12 -- μA

SHDN

2 -- 5

EN_H

-- -- 0.8

V

EN_L
ACTL_H

V

ACTL_L

LED

RISET

ACTL

-- -- 0.15

R

0.3V ≤ V

Rising -- 5.5 5.95 V

CC1

2 -- 5

2V > V
V

ACTL

2V > V
V

ACTL

(I

(MAX)

ISET

> 0.7 V, R

LED

= 5.36kΩ,

ISET

>1.28V

> 0.7 V, R

LED

= 5.36kΩ,

ISET

>1.28V, Calc ulating

− I

= 5.36kΩ, V

/ I

(MIN)

ACTL

AVERAGE

ACTL

≤ 1.2V -- -- 2 μA

x 100%)

> 1.28V -- 1.21 -- V

19 20 21 mA

-- -- 3 %

To be continued

V

V

DS8560A-01 April 2011www.richtek.com

6

RT8560A

Parameter Symbol Test Conditions Min Typ Max Unit

Threshol d of ACTL V
Input Current of DCTL I

LED Current Off -- 0.2 -- V

ACTL

0.3V ≤ V

DCTL

≤ 6V -- -- 1 μA

DCTL

PWM Boost Converte r
Switching Frequency 840 1000 1160 kHz
Maximum Duty Cycle -- 88 -- %
Minimum On Time -- 200 -- ns
Regulated V

Highest Voltag e LED Str ing -- 0 .9 -- V

LED

Amplifier gm GM -- 220 -- μA/V
Amplifier (gm) Output Current 2.4V > VC > 0.2V -- ±30 -- μA
VC Threshold PW M Switch Off -- 0.7 -- V
SW On Voltage ISW = 0.5A -- 0.4 -- V
SW Current Limit I

1.2 1.5 -- A

LIM

OVP & Soft Start
OVP Threshold V
OVP Input Current I

-- 2.5 -- V

OVP

V

OVP

≤ 2.5V -- -- 50 nA

OVP

Soft Start Current ISS VSS = 0V -- 7 -- μA

Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for

stress ratings. 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 for extended
periods may remain possibility to 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 in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of

JA

JEDEC 51-7 thermal measurement standard. The case point of θ

is on the expose pad for the WQFN package.

JC

DS8560A-01 April 2011 www.richtek.com

7

RT8560A

Typical Operating Characteristics

Efficiency vs. Input Voltage

100

90
80
70
60
50
40

Efficiency (%)

30
20
10

0

8 1216202428323640

Input Voltage (V)

LED Current v s . Te m perature

24
23
22
21
20
19
18

LED Current (mA)

17
16

-40 -15 10 35 60 85 110 135

Temperature

(°C)

60LEDs

V

= 12V

IN

LED Curre nt vs. Input Voltage

26
24
22
20
18
16

LED Current (mA)

14
12
10

8 1216202428323640

Input Volt age (V)

V

vs. Temperature

1.24

1.22

1.20

1.18

(V)

RISET

1.16

V

1.14

1.12

1.10

-40 -20 0 20 40 60 80 100 120

RISET

Temperature

(°C)

V

IN

LED1

LED2

LED3

LED4

= 12V

LED Curre nt v s. ACTL P WM Duty Cycle

20
18
16
14
12
10

8
6

LED Current (mA)

4
2
0

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100

0 10 20 30 40 50 60 70 80 90 100

ACTL = 0V to 3V, V

Duty Cycle (%)

ACTL = 200Hz

ACTL = 1kHz

ACTL = 10kHz

ACTL = 20kHz

ACTL = 30kHz

IN

= 12V

%

(V)

RISET

V

V

vs . Input Voltage

1.25

1.24

1.23

1.22

1.21

1.20

1.19

1.18

1.17

1.16

1.15
8 1216202428323640

RISET

Inpu t Voltage (V)

DS8560A-01 April 2011www.richtek.com

8

RT8560A

LED Current v s. DCTL PWM Duty Cycle

25

20

15

10

DCTL = 200Hz

DCTL = 1kHz

DCTL = 10kHz

LED Current ( m A)

5

0

20 30 40 50 60 70 80 90 100

DCTL = 0V to 3V, V

Dut y Cycle (% )

Frequency vs. Input Voltage

1.10

1.08

1.06

1.04

1.02

1.00

0.98

0.96

Frequency ( M H z)

0.94

0.92

0.90
8 1012141618202224

Inp ut Voltage (V)

IN

= 12V

LED Curre nt v s. ACTL Voltage

25

20

15

10

LED Current (mA)

5

V

0

0 0.25 0.5 0.75 1 1.25 1.5

IN

ACTL Volta ge ( V)

Shutdown Current vs. Input Voltage

40
35
30
25
20
15
10

Shutdown Current (uA)

5

V

0

8 1216202428323640

Inpu t Voltage (V)

EN

= 12V

= 0V

Switch Off Current vs. Input Voltage

5.0

4.9

4.8

4.7

4.6

4.5

4.4

4.3

4.2

Switch Off Current (mA)

4.1

4.0
8 1216202428323640

Inpu t Voltage (V)

VC = 0V

10

9
8
7
6
5
4
3

SS Current (uA)

2
1
0

-40 -20 0 20 40 60 80 100 120

SS Current vs. Temperature

V

= 12V, C

IN

Temperature

SS

(°C)

= 0.1uF

DS8560A-01 April 2011 www.richtek.com

9

RT8560A

SS Current vs. Input Voltage

10

9
8
7
6
5
4
3

SS Current (uA)

2
1
0

81216202428323640

C

SS

Inpu t Voltage (V)

OVP Voltag e vs. Input Voltage

2.8

2.7

2.6

2.5

2.4

OVP Voltage (V)

2.3

= 0.1uF

OVP Voltage vs. Temperature

2.50

2.48

2.46

2.44

2.42

2.40

2.38

2.36

OVP Voltage (V)

2.34

2.32

2.30

-40 -20 0 20 40 60 80 100 120

Temperature

(°C)

Limit Current vs. Input Voltage

2.5

2.0

1.5

1.0

Limit Current ( A)

0.5

V

IN

= 12V

10

2.2
81216202428323640

Inp ut V o ltage (V)

ACTL Voltage vs. Temperature

0.40

0.35

0.30

0.25

0.20

0.15

ACTL Volt age (V)

0.10

0.05

0.00

-40 -20 0 20 40 60 80 100 120

Temperature

(°C)

V

IN

= 12V

0.0

V

EN

(2V/Div)

V

OUT

(20V/Div)

I

IN

(500mADiv)

8 101214161820222426283032

Inpu t Voltage (V)

Power On from EN

V

= 12V, C

IN

Time (5ms/Div)

DS8560A-01 April 2011www.richtek.com

= 0.1uF

SS

RT8560A

V

IN

(5V/Div)

I

OUT

(50mA/Div)

Line Transient Response

V

= 10.8V to 13.2V, RISET = 4.8kΩ

IN

Time (50ms/Div)

V

IN

(5V/Div)

V

OUT

(20V/Div)

SW

(20V/Div)

OVP

V

= 12V, All LED Pin Open

IN

Time (2.5ms/Div)

DS8560A-01 April 2011 www.richtek.com

11

RT8560A

Applications Information

The RT8560A is a current mode boost converter operated
at 1MHz to power up to 60 white LEDs with a
programmable current for uniform intensity. The part
integrates current sources, soft-start, and easy analog
and digital dimming control. The protection block provides
the circuitry for over-temperature, over-voltage and current­limit protection features.

Input UVLO

The input operating voltage range of the RT8560A is 6V to
40V. An input capacitor at the VCC1 and VCC2 pin can
reduce ripple voltage. It is recommended to use a cera mic
10uF or larger cap acita nce as the in put cap acitor . This IC
provides an under voltage lockout (UVLO) function to
enhance the stability when startup. The UVLO threshold
of input rising voltage is around 5.5V .

Power Sequence

Please refer to the below Figure 5 and 7. The
recommended power-on sequence is that the PWM ready
before EN and/or VIN rea dy . If not, the Soft-Start function
will be disabled. As to power-off sequence, the EN/VIN
must be pulled low within 10ms to prevent “Hard-Start”
shown as Figure 7.

Abnormal Power­on sequence

UVLO

VIN

PWM

Power-on
sequence

Power-off
sequence

Power-on
sequence

VIN

PWM

EN

VOUT

Power-off
sequence

VIN must be turn ed
off early than EN and
PWM signal

Soft-Start

VIN must be
turned on late
than EN and
PWM signal

Abnormal Power­on sequence

UVLO

No Soft-Start
If PWM tu rns

on late

Figure 6. Power-On Sequence Control by VIN

EN/VIN

PWM

10ms

EN and/or VIN should be
pulled low once PWM pull low
for over 10ms

Figure 7. To Prevent “Hard-Start” Sequence

Soft Start

The RT8560A employs a soft start feature to limit the inrush
current. The soft-start circuit prevents the excessive inrush
current and input voltage droop. The soft-start time is
determined by cap acitor CSS connected to SS with a 7uA
constant current to charge CSS. The value of capacitor
CSS is user-defined to satisfy designer' requirement.

EN must be turned
off early than VIN
and PWM signal

EN

VOUT

EN must be turned
on late than VIN
and PWM signal

Soft-Start

Figure 5. Power-On Sequence Control by EN

12

No Soft-Start
If PWM turn s
on late

LED connection

The RT8560A equips 4 channel LED divers and each
channel supports up to 15 LEDs. The 4 LED strings are
connected from VOUT to pin 15, 16, 17 and 18
respectively. If one of the LED channel is not used, the
LED pin should be opened dire ctly .

Setting and Regulation of LED current

The LED current can be calculated by the following
equation :

I = 20mA

LED

5.36k

×

R

ISET

DS8560A-01 April 2011www.richtek.com

RT8560A

Where,
V

is the voltage of the RISET pin (1.21V typ.) and the

RISET

R

is the resister between RISET pin and GND.

ISET

This setting is the reference for the LED current at LED1­4 and represents the sensed LED current for ea ch string.
The DC/DC converter regulates the LED current according
to the setting.

Brightness Control

The RT8560A features both analog and digital dimming
control. Analog dimming is linearly controlled by an
external voltage (0.3V < V

< 1.2V). With an on-chip

ACTL

output clamping amplifier and a 200kΩ resistor, PWM
dimming signal is easily low-pass filtered to an analog
dimming signal with one external ca pa citor for noise-free
PWM dimming. A very high contra st ratio true digital PWM
dimming can be a chieved by driving ACTL pin with a PWM
signal and suggest PWM frequency is from 200Hz to
10kHz. Refer to Figure 8, the minimum dimming duty ca n
be as low as 1% for the frequency range from 100Hz to
300Hz. For the dimming frequency from 300Hz to 1kHz,
the duty is about 5%. If the frequency is increased to
1kHz to 30kHz, the duty will be about 10%.

LED Curre nt v s. ACTL P WM Duty Cycle

20
18
16
14
12
10

8
6

LED Current (mA)

4
2
0

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100

0 10 20 30 40 50 60 70 80 90 100

ACTL = 0V to 3V, V

Duty Cycle (%)

ACTL = 200Hz

ACTL = 1kHz

ACTL = 10kHz

ACTL = 20kHz

ACTL = 30kHz

= 12V

IN

%

Over Voltage Protection

The RT8560A equips over voltage protection (OVP)
function. When the voltage at OVP pin rea ches a threshold
of approximately 2.5V, the MOSFET drive output (SW)
will turn “OFF”. The MOSFET drive output (SW) will turn
“ON” again once the voltage at OVP drops below the
threshold of approxi mately 2.5V.

So, the output voltage can be cla mped at a certain voltage
level and it ca n be calculated by the following equation :

R1

V = 2.51+

OUT, OVP

⎛⎞

×

⎜⎟

R2

⎝⎠

Where,
R1 and R2 are the voltage divider connected to OVP pin.
If at lea st one string is in normal operation, the controller

will automatically ignore the open strings and continue to
regulate the current for the string(s) in normal operation.

Current-limit Protection

The RT8560A can limit the peak current to a chieve over
current protection. The RT8560A senses the inductor
current of on period that flows through SW pin. The duty
cycle depend on current signal and internal slope
compensation compared with error signal. The internal
N-MOSFET will be turned off when the current signal is
large than internal slope compen sation. In the off period,
the inductor current will be descended until the internal
N-MOSFET is on by the oscillator.

Over Temperature Protection

The RT8560A has over temperature protection (OTP)
function to prevent the excessive power dissipation from
overheating. OTP will shut down the IC while junction
temperature exceeds 150°C. Main converter starts
switching once the junction temperature is cooled
approxi mately 20°C.

Inductor Selection

Figure 8. LED Current vs. PWM Di mming Duty Cycle

The value of the output inductor (L), where the transition
from discontinuous to continuous mode occurs is
a pproximated by the following equation :

2

(V V V

OUT IN IN

L =

2I f V

×××

OUT OUT

DS8560A-01 April 2011 www.richtek.com

)

−×

2

13

RT8560A

Where,
V

= maximum output voltage.

OUT

VIN = minimum input voltage.
f = operating frequency .
I

= sum of current from all LED strings.

OUT

The boost converter operates in discontinuous mode over
the entire input voltage range when the L1 inductor value
is less than this value L. With a n inducta nce greater than
L, the converter operates in continuous mode at the
minimum input voltage and may be discontinuous at higher
voltages.

The inductor must be selected with a saturated current
rating that is greater than the peak current provided by
the following equation :

I =

PEAK

××−

OUT OUT IN OUT IN

η

×××

+

V2LV

IN OUT

⎛⎞
⎜⎟
⎝⎠

VI VTV V

Where,
η is the efficiency of the power converter .

Layout Guideline

PCB layout is very important f or designing power switching
converter circuits. Some recommended layout guides that
should be strictly be followed are shown a s f ollows :

` The power components L, D, C

VIN

, C

OUT1

and C

OUT2

must be placed as close as possible to reduce the ac
current loop. The PCB trace between power components
must be as short and wide as possible due to large
current stream flows through these traces during
operation.

` Place L a nd D connected to SW pin as close a s possible.

The trace should be short a nd wide a s possible.

` It is recommended to place C

V

and V

CC1

` Pin14 is the compensation point to adjust system

CC2

pins.

Vcc1

and C

close to

Vcc2

stability . Place the compensation components to pin14
as close as possible, no matter the compensation is
RC or capa cita nce.

Diode Selection

Schottky diode is a good choice for an asynchronous
Boost converter due to the small forward voltage. However ,
power dissipation, reverse voltage rating and pulsating pea k
current are the important parameters for Schottky diode
selection. Choose a suitable diode whose reverse voltage
rating is greater than the maximum output voltage.

Capacitor Selection

The input ca pacitor reduces current spikes from the input
supply and minimizes noise injection to the converter . For
most application s, a 10uF cera mic ca pa citor is sufficient.
A value higher or lower may be used depending on the
noise level from the input supply and the input current to
the converter.

It is recommended to choose a ceramic capacitor bases
on the output voltage ripple requirements. The minimum
value of the output cap acitor C

is approxi mately given

OUT

by the following equation :

C =

OUT

(V V I

OUT IN OUT

VVf

η

×××

RIPPLE OUT

)

−×

Place these components
as close as possible.

C

V

OUT

OUT3

V

OUT1

D

C

VIN

GND

IN

C

OUT2

C

Figure 9. PCB Layout Guide

GND
GND
GND

SW
SW
L

C

R

R

1
2
3
4
5

VCC2

VCC2

VCC1

GND

GND

LED2

LED1

20 19 18 1617

GND

21

7

8910

6

ACTL

VCC2

VCC1

RISET

GND

C

VCC1

Locate the C
close as possible to V
V

pin.

CC2

LED3

15
14
13
12
11

DCTL

LED4

R

VC

VC
SS
OVP

C

VC2

Locate the compensation

EN

components to VC pin as
close as possible.

and C

VCC1

CC1

VCC2

and

as

C

VC1

GND

14

DS8560A-01 April 2011www.richtek.com

Outline Dimension

RT8560A

1
2

DETAIL A

Pin #1 ID a nd T ie Bar Mark Option s

Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.

Dimensions In Millimeters Dimensions In Inches

Symbol

Min Max Min Max

A 0.700 0.800 0.028 0.031
A1 0.000 0.050 0.000 0.002
A3 0.175 0.250 0.007 0.010

b 0.150 0.300 0.006 0.012

D 3.950 4.050 0.156 0.159

D2 2.650 2.750 0.104 0.108

E 3.950 4.050 0.156 0.159
E2 2.650 2.750 0.104 0.108

1
2

e 0.500 0.020
L 0.350 0.450

0.014 0.018

W-Type 20L QFN 4x4 Package

Richtek Technology Corporation

Headquarter
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: [phone] Fax: [phone]

Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit
design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be
guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.

DS8560A-01 April 2011 www.richtek.com

Richtek Technology Corporation

Taipei Office (Marketing)
5F, No. 95, Minchiuan Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: [phone] Fax: [phone]
Email: [e-mail]

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