Richtek RT9284A-15PJ6, RT9284A-15PJ6E, RT9284A-20GJ6E, RT9284A-20PJ6, RT9284A-20PJ6E Schematic [ru]
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RT9284A/B
Tiny Package, High Performance, Constant Current
Switching Regulator for White LED
General Description
The RT9284A/B is a compact, high efficient and high
integration LED driver . Internal 22V MOSFET can support
2 to 5 White LEDs for ba cklighting a nd ca mera fla shing.
Highly integration and internal compensation network
minimizes as 5 external component counts. Optimized
operation frequency can meet the requirement of small
LC filters value and low operation current with high
efficiency . Internal soft start function ca n reduce the inrush
current. Tiny pa ckage type of TSOT-23-5 a nd TSOT -23-6
pack ages provide the best solution for PCB spa ce saving
and total BOM cost.
Ordering Information
-
RT9284
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.
( )
Package Type
J5 : TSOT-23- 5
J6 : TSOT-23- 6
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
OVP Voltage
15 : 15V
20 : 20V
FB Voltage
A : 1.235V
B : 0.25V
Features
zz
z V
Operating Range : 2.7V to 5.5V
zz
IN
zz
z Maximum Output Voltage up to 20V
zz
zz
z Dimming with Zero-inrush and Wide Frequency
zz
Range of 100 to 100kHz
zz
z Over Voltage Protection
zz
zz
z Output Current up to 100mA at V
zz
zz
z Zero Shutdown Supply Current
zz
zz
z Minimize the External Component
zz
zz
z Small LC Filter
zz
zz
z Internal Soft Start
zz
zz
z RoHS Compliant and 100% Lead (Pb)-Free
zz
OUT
: 12V
Applications
z Camera Fla sh White LED
z Mobile Phone, Smart Phone LED Ba cklight
z PDA LED Ba cklight
z Digital Still Camera
z Ca mcorder
Pin Configurations
TOP VIEW
VDD EN
5
LX GND FB
TSOT-23-5
VDD OVP EN
4
23
4
56
Marking Information
For marking information, conta ct our sales representative
directly or through a Richtek distributor located in your
area.
DS9284A/B-07 April 2011
23
LX GND FB
TSOT-23-6
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1
RT9284A/B
Typical Application Circuit
L1
4.7uH to 22uH
D1
SS0520
OVP
15V
V
IN
2.7V to 5.5V
Dimming
Control
V
IN
2.7V to 5.5V
Dimming
Control
+
100Hz-100kHz
C1
1uF
RT9284
6
VDD
4
EN
2
GND
LX
OVP
FB
1
5
3
Figure 1. Application for Driving 3 Series WLEDs
SS0520
1
5
OVP 15V
3
D1
600k
+
100Hz-100kHz
C1
1uF
4.7uH to 22uH
RT9284
6
VDD
4
EN
2
GND
L1
LX
OVP
FB
Figure 2. Application for Driving 4 Series WLEDs
R2
OVP
18V
1uF/25V
C2
1uF/16V
C2
R1
R1
I
I
LED
LED
V
IN
2.7V to 5.5V
Dimming
Control
V
IN
2.7V to 5.5V
D1
SS0520
VFB = 0.25V
+
100Hz-100kHz
C1
1uF
4.7uH to 22uH
RT9284B
6
VDD
4
EN
2
GND
L1
LX
OVP
FB
1
5
3
Figure 3. Application for Driving 5 Series WLEDs
L1
4.7uH to 22uH
+
C1
1uF
6
4
2
RT9284A
VDD
EN
GND
LX
OVP
FB
D1
SS0520
1
5
3
OVP
15V
OVP
20V
C2
1uF/25V
R1
130k
V
FB
R2
15k
C2
1uF/16V
= 1.235V
R1
I
LED
V
12V
OUT
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2
Figure 4. Application f or Constant Output V oltage
DS9284A/B-07 April 2011
Pin Description
RT9284A/B
Pin No.
Pin Name Pin Function
TSOT-23-5 TSOT-23-6
1 1 LX
Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track
area to reduce EMI.
2 2 GND Ground Pin
Feedback Reference Voltage Pin. Series connect a resistor between WLED
3 3 FB
and ground as a current sense. Sense the current feedback voltage to set
the current rating.
Chip Enable (Active High). Voltage sensing input to trigger the function of
4 4 EN
over voltage protection. Note that this pin is high impedance. There should
be a pull low 100kΩ resistor connected to GND when the control signal is
floating.
-- 5 OVP
5 6 VDD
Over Voltage Protection Pin. Voltage sensing input to trigger the function of
over voltage protecti on. Leave it unconnecte d to disable this function.
Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input
noise.
Function Block Diagram
VDD
OVP
EN
Current Bias
BandGap
Protection Circuit
OVP
UVLO
Timer
5ms
ibias
V
REF
1.2MHz OSC
OCP
750mA
Soft Start
PWM
Logic
LX
+
-
Buffer
+
-
FB
V
REF
GND
DS9284A/B-07 April 2011
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3
RT9284A/B
Absolute Maximum Ratings (Note 1)
z Supply Input V oltage ---------------------------------------------------------------------------------------------------- −0.3V to 7V
z LX Input V oltage---------------------------------------------------------------------------------------------------------- −0.3V to 22V
z OVP Voltage -------------------------------------------------------------------------------------------------------------- −0.3V to 22V
z The Other Pins ----------------------------------------------------------------------------------------------------------- −0.3V to 6V
z Power Dissipation, P
TSOT-23-5 ----------------------------------------------------------------------------------------------------------------- 0.455W
TSOT-23-6 ----------------------------------------------------------------------------------------------------------------- 0.455W
z Package Thermal Resistance (Note 2)
TSOT-23-5, θJA------------------------------------------------------------------------------------------------------------ 220°C/W
TSOT-23-6, θJA------------------------------------------------------------------------------------------------------------ 220°C/W
z Lead T emperature (Soldering, 10 sec.) ----------------------------------------------------------------------------- 260°C
z Junction T emperature --------------------------------------------------------------------------------------------------- 150°C
z Storage T emperature Range------------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Mode)--------------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------------------- 200V
@ T
D
= 25°C
A
Recommended Operating Conditions (Note 4)
z Supply Input V oltage ---------------------------------------------------------------------------------------------------- 2.7V to 5.5V
z Junction T emperature Range ------------------------------------------------------------------------------------------ −40°C to 125°C
z Ambient T emperature Range ------------------------------------------------------------------------------------------ −40°C to 85°C
Electrical Characteristics
(V
= 3.7V, T
IN
System Supply Input
Operation voltage Range
Under Voltage Lock Out
Quiescent Current
Supply Current
Shut Do wn Current
Line Regulation
Oscillator
Operation Frequency
= 25°C unless otherwise specified)
A
Parameter Symbol Test Conditions Min Typ Max Unit
V
DD
V
DD
I
DD
I
DD
V
I
DD
f
OSC
2.7 -- 5.5 V
1.8 2.2 2.5 V
FB = 1.5V, No switch 50 300 1000 uA
FB = 0V, Switch 0.1 2 3 mA
< 0.4V
EN
V
: 3.0~4.3V
IN
-- -- 1 uA
-- 3 -- %
0.9 1.2 1.5 MHz
Maxi mum Du ty Cyc le 85 - - -- %
Dimming Frequency 100 -- 100k Hz
Reference Voltage
RT9284A 1.173 1.235 1.296
Feedback Voltage (Note 5)
V
RT9284B 0.237 0.25 0.263
T o be continued
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4
DS9284A/B-07 April 2011
MOSFET
RT9284A/B
Parameter Symbol Test Condition Min Typ Max Unit
On Resistance of MOSFET
R
DS(ON)
-- 0.75 --
Ω
Protection
for 2,3,4 WLEDs application 14 15 16
OVP Threshold
V
OVP
for 5 WLED application 19 20 21
V
OVP Sink Cur rent -- 5 -- μA
OCP -- 750 -- mA
Shut Down Voltage
Enable Voltage
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 recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Floating the OVP pin to disable OVP function.
is measured in the natural convection at T
JA
JEDEC 51-3 thermal measurement standard.
V
EN
V
EN
1.5 -- -- V
-- -- 0.4 V
= 25°C on a low effective thermal conductivity test board of
A
DS9284A/B-07 April 2011
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5
RT9284A/B
Typical Operating Characteristics
Enable Voltage vs. Input Voltage
1.2
1.1
1.0
0.9
0.8
0.7
Enable Voltage (V)
0.6
0.5
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
-45°C
25°C
85°C
Inp ut Vo ltage (V )
Efficiency vs. Input Voltage
84
I
= 20mA, L = 4.7μH, DCR = 0.15Ω
LED
83.5
3WLEDs
4WLEDs
Efficiency (%)
83
82.5
82
81.5
81
Shut Down Voltage vs. Input Voltage
1.2
1.1
1
0.9
0.8
0.7
Shut Down Voltage (V )
0.6
0.5
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
-45°C
25°C
85°C
In p ut Volta g e (V)
LED Current vs . Inpu t Voltage
22
4WLEDs, L = 10μH
21.5
21
20.5
20
19.5
LED Current ( m A)
19
18.5
80.5
3 3.2 3.4 3.6 3.8 4 4.2 4.4
91%
91
90%
90
89%
89
88%
88
87
87%
86
86%
Maximum Duty Cycle (%)
85
85%
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
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Input Voltage ( V)
Maximum Duty Cycle vs. V
VDD (V)
DD
18
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
Inp ut Voltage (V)
POR (Rising/Falling) vs. Temperature
2.7
2.5
2.3
2.1
POR (V)
1.9
1.7
1.5
-40-30-20-100 102030405060708090
Rising
Falling
Temperature
(°C)
DS9284A/B-07 April 2011
RT9284A/B
Switching Current vs. Input Voltage
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
Switching Current (mA)
0.2
0
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
-45°C
Input Voltage (V)
Feedback Voltage vs. Temperature
252.2
252
251.8
251.6
251.4
25°C
85°C
Switching Frequency vs. Temperature
1.5
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
Switching Frequency (MHz)
1.05
1
-40-30-20-10 0 102030405060708090
Temperature
(°C)
Dimming Operation
4WLEDs, VIN = 3.7V, I
EN
I
IN
(5V/Div)
(50mA/Div)
= 20mA, L = 10μH
LED
251.2
251
Feedback Vol tage (m V)
250.8
250.6
-40-30-20-100 102030405060708090
Temperature
(°C)
Dimming Operation
4WLEDs, VIN = 3.7V, I
EN
(5V/Div)
I
IN
(100mA/Div)
I
LED
(10mA/Div)
Time (400μs/Div)
= 20mA, L = 10μH
LED
f = 1kHz, Duty = 50%
I
LED
4WLEDs, VIN = 3.7V, I
EN
(5V/Div)
I
IN
(100mA/Div)
I
(10mA/Div)
LED
(10mA/Div)
f = 100Hz, Duty = 50%
Time (2ms/Div)
Dimming Operation
= 20mA, L = 10μH
LED
f = 10kHz, Duty = 50%
Time (40μs/Div)
DS9284A/B-07 April 2011
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RT9284A/B
4WLEDs, VIN = 3.7V, I
EN
(5V/Div)
I
IN
(100mA/Div)
I
(10mA/Div)
LED
4WLEDs, VIN = 3.0V, I
(2V/Div)
EN
(2V/Div)
V
IN
(5V/Div)
Dimming Operation
= 20mA, L = 10μH
LED
f = 100kHz, Duty = 50%
Time (4μs/Div)
Inrush Current
= 20mA, L = 4.7μH
LED
L = 10μH
(10V/Div)
V
OUT
I
LX
(500mA/Div)
LX
(20V/Div)
4WLEDs, VIN = 4.3V, I
(2V/Div)
EN
(2V/Div)
(5V/Div)
V
IN
OCP
Time (25μs/Div)
Inrush Current
= 20mA, L = 4.7μH
LED
V
OUT
I
IN
(100mA/Div)
Time (500μs/Div)
Normal Operation
(5V/Div)
(2V/Div)
V
OUT
(10V/Div)
V
IN
LX
I
IN
(100mA/Div)
Time (400ns/Div)
4WLEDs, VIN = 3.0V
I
= 20mA, L = 10μH
LED
V
OUT
I
IN
(100mA/Div)
Time (500μs/Div)
Normal Operation
(5V/Div)
OUT
V
(2V/Div)
(10V/Div)
IN
V
LX
I
IN
(100mA/Div)
Time (400ns/Div)
4WLEDs, VIN = 3.7V
I
= 20mA, L = 10μH
LED
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DS9284A/B-07 April 2011
RT9284A/B
Normal Operation
OUT
V
LX
I
IN
IN
(5V/Div)
(2V/Div)
(10V/Div)
(100mA/Div)
(5V/Div)
(2V/Div)
V
OUT
(10V/Div)
V
IN
4WLEDs, VIN = 4.3V
I
= 20mA, L = 10μH
LED
V
LX
I
IN
(100mA/Div)
Time (400ns/Div)
Normal Operation
4WLEDs, VIN = 5.5V
I
= 20mA, L = 10μH
LED
Time (400ns/Div)
DS9284A/B-07 April 2011
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9
RT9284A/B
Application Information
Power Sequence
The RT9284A/B must take notice of the power sequence.
The power sequence of RT9284A/B ha s to V DD early than
EN or else the RT9284A/B maybe fall into the unknown
state to result in RT9284A/B turn off.
> 2.7V
V
DD
V
DD
EN > 1.5V
EN < 0.4V
EN
V
OUT
Figure 5
LED Current Control
The RT9284A/B regulates the LED current by setting the
current sense resistor (R1) connecting to feedba ck and
ground. As shown in Table 1, the RT9284A feedback
voltage (VFB) is 1.235V and the R T9284B feedback voltage
(VFB) is 0.25V. The LED current (I
) can be set by a
LED
resistor R1. In order to have an accurate LED current, a
precision resistor is preferred (1% is recommended).
b. Using a DC V oltage
Using a variable DC voltage to adjust the brightness is a
popular method in some a pplications. The dimming control
using a DC voltage circuit is shown in Figure 6. According
to the Superposition Theorem, as the DC voltage
increases, the voltage contributed to VFB increases and
the voltage drop on R2 decreases, i.e. the LED current
decreases. For example, if the VDC range is from 0V to
2.8V, the selection of resistors in Figure 6 sets dimming
control of LED current from 20mA to 0mA.
D1
SS0520
1
5
3
R3
13k
VDC Dimming
0V to 2.8V
C2
R2
10k
R1
110
I
LED
2.7V to 5.5V
V
V
< 0.4V
V
EN
IN
EN
C1
> 1.5V
L1
4.7uH to 22uH
RT9284A
6
4
2
VDD
EN
GND
LX
OVP
FB
Figure 6. Di mming Control Using a DC V oltage for
RT9284A
Table 1
Version
Feedback Reference
Voltage V
FB
(V)
RT9284A 1.235
RT9284B 0.25
LED Current
Setting I
I
LED
I
LED
LED
= 1.235/R1
= 0.25/R1
(A)
Dimming Control
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the R T9284A/B can
perform the dimming control by applying a PWM signal
to EN pin. The internal soft start and the wide range
dimming frequency from100 to100kHz can eli minate inrush
current and audio noise when dimming. The average LED
current is proportional to the PWM signal duty cycle. The
magnitude of the PWM signal should be higher than the
maximum enable voltage of EN pin, in order to let the
dimming control perform corre ctly .
The LED current can be calculated by the following
equation.
R2 (V V )
×−
V
I =
LED
FB
−
DC FB
R3
R1
c. Using a Filtered PWM signal:
Another common application is using a filtered PWM
signal a s an adjustable DC voltage for LED dimming control.
A filtered PWM sign al a cts a s the DC voltage to regulate
the output current. The recommended a pplication circuit
is shown in the Figure 7. In this circuit, the output ripple
depends on the frequency of PWM signal. For smaller
output voltage ripple (<100mV), the recommended
frequency of 2.8V PWM signal should be above 2kHz. T o
fix the frequency of PWM signal and change the duty
cycle of PWM signal can get different output current.
Figure 8. shows the relationship between LED current and
PWM duty cycle.
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10
DS9284A/B-07 April 2011
RT9284A/B
V
EN
V
< 0.4V
IN
EN
2.7V to 5.5V
V
C1
> 1.5V
L1
4.7uH to 22uH
RT9284A
6
VDD
4
EN
OVP
2
GND
LX
FB
SS0520
1
5
3
2.8V
0V
PWM Signal
D1
R3
10k
R
3k
DC
C2
R2
10k
C
1uF
DC
R1
110
I
Figure 7. Filtered PWM Signal for LED Dimming Control
of RT9284A
The LED current can be calculated by the following
equation.
R2 (V Duty V )
××−
V
−
FB
I =
LED
20
18
16
14
12
10
8
6
LED Current (mA)
4
2
0
0 102030405060708090100
PWM FB
R3 + R
DC
R1
PWM Duty (%)
Capacitor Selection
Input and output ceramic capacitors of 1μF are
recommended for RT9284A/B applications. For better
LED
voltage filtering, ceramic capacitors with low ESR are
recommended. X5R and X7R type s are suitable because
of their wider voltage and temperature ra nges.
Diode Selection
Schottky diode is a good choice for RT9284A/B because
of its low forward voltage drop and fa st reverse recovery .
Using Schottky diode can get better eff iciency . The highspeed rectification is also a good characteristic of
Schottky diode for high switching frequency . Current rating
of the diode must meet the root mean s quare of the peak
current and output average current multiplication as
following :
)I(I(RMS)I
×≈
PEAKOUTD
The diode’ s reverse breakdown voltage should be larger
than the output voltage. SS0520 is recommended Schottky
diode for rectifier .
Layout Guide
z A full GND plane without ga p brea k.
z VCC to GND noise bypa ss–Short and wide connection
for the 1μF MLCC ca pa citor between Pin6 and Pin2.
z Minimized LX node copper area to reduce EMI.
z Minimized FB node copper area a nd keep far away from
noise sources.
Figure 8
Inductor Selection
The recommended value of inductor for 3 to 5 WLEDs
applications are 4.7 to 22μH. Small size and better
efficiency are the ma jor concerns for portable device, such
as R T9284A/B used for mobile phone. The inductor should
have low core loss at 1.2MHz and low DCR for better
efficiency . T o avoid inductor saturation current rating should
be considered.
DS9284A/B-07 April 2011
Figure 9. T op Layer
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11
RT9284A/B
Figure 10. Bottom Layer
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DS9284A/B-07 April 2011
Outline Dimension
RT9284A/B
H
D
L
C
b
A
e
Dimensions In Millimeters Dimensions In Inches
Symbol
Min Max Min Max
A 0.700 1.000 0.028 0.039
A1 0.000 0.100 0.000 0.004
B 1.397 1.803 0.055 0.071
b 0.300 0.559 0.012 0.022
C 2.591 3.000 0.102 0.118
B
A1
DS9284A/B-07 April 2011
D 2.692 3.099 0.106 0.122
e 0.838 1.041 0.033 0.041
H 0.080 0.254 0.003 0.010
L 0.300 0.610 0.012 0.024
TSOT-23-5 Surface Mount Package
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RT9284A/B
H
D
L
C
b
A
e
B
A1
Dimensions In Millim eters Dimensions In Inches
Symbol
Min Max Min Max
A 0.700 1.000 0.028 0.039
A1 0.000 0.100 0.000 0.004
B 1.397 1.803 0.055 0.071
b 0.300 0.559 0.012 0.022
C 2.591 3.000 0.102 0.118
D 2.692 3.099 0.106 0.122
e 0.838 1.041 0.033 0.041
H 0.080 0.254 0.003 0.010
L 0.300 0.610 0.012 0.024
TSOT-23-6 Surface Mount Package
Richtek Technology Corporation
Headquarter
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
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.
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Richtek Technology Corporation
Taipei Office (Marketing)
5F, No. 95, Minchiuan Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: (8862)86672399 Fax: (8862)86672377
Email: marketing@richtek.com
DS9284A/B-07 April 2011
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