RT9285A/B

®
RT9285A/B
Tiny Package, High Performance, Diode Embedded White
LED Driver
General Description
Features
The RT9285 is a high frequency asynchronous boost
converter with internal diode, which can support 2 to 5
White LEDs for backlighting and OLED power supply. The
Internal soft start function can reduce the inrush current.
The device operates with 1MHz fixed switching frequency
to allow small external components and to simplify possible
EMI problems. The device comes with 20V over voltage
protection to allow inexpensive and small-output capacitors
with lower voltage rating. The LED current is initially set
with the external sense resistor RSET, and the feedback
z
VIN Operating Range : 2.7V to 5.5V
z
voltage is 250mV. Tiny package type TSOT-23-6 and
WDFN-8L 2x2 packages provide the best solution for PCB
space saving and total BOM cost.
z
Up to 85% Efficiency
22V Internal Power N-MOSFET
1MHz Switching Frequency
Built-in Diode
Digital Dimming with Zero-Inrush
Input UVLO Protection
Output Over Voltage Protection
Internal Soft Start and Compensation
TSOT-23-6 and 8-Lead WDFN Package
RoHS Compliant and 100% Lead (Pb)-Free
z
z
z
z
z
z
z
z
Applications
z
Ordering Information
z
RT9285
z
Package Type
QW : WDFN-8L 2x2 (W-Type)
J6 : TSOT-23-6
z
z
z
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Cellular Phones
Digital Cameras
PDAs and Smart Phones
Porbable Instruments
MP3 Player
OLED Power
Pin Configurations
(TOP VIEW)
Dimming
A : Digital Pulse Dimming
B : PWM Clock Dimming
VDD VOUT EN
Note :
AGND
LX
NC
PGND
Richtek products are :
`
RoHS compliant and compatible with the current require-
Simplified Application Circuit
RT9285A/B
VDD
VOUT
EN
GND
5
5
4
2
3
TSOT-23-6
VIN
L1
Chip Enable
9
6
FB
EN
VOUT
VDD
WDFN-8L 2x2
Suitable for use in SnPb or Pb-free soldering processes.
LX
4
8
7
6
LX GND FB
ments of IPC/JEDEC J-STD-020.
`
1
2
3
C1
C2
FB
RSET
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS9285A/B-06 August 2012
is a registered trademark of Richtek Technology Corporation.
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1
RT9285A/B
Marking Information
RT9285APQW
RT9285BPQW
D0 : Product Code
D1 : Product Code
W : Date Code
D0W
RT9285AGQW
RT9285BGQW
FW : Product Code
J9 : Product Code
W : Date Code
FWW
W : Date Code
D1W
J9W
W : Date Code
RT9285BPJ6
RT9285APJ6
AN- : Product Code
AM- : Product Code
AM-DNN
AN-DNN
DNN : Date Code
RT9285AGJ6
DNN : Date Code
RT9285BGJ6
AM= : Product Code
AM=DNN
AN= : Product Code
AN=DNN
DNN : Date Code
DNN : Date Code
Functional Pin Description
Pin No.
Pin Name
Pin Function
WDFN-8L
TSOT-23-6
1
--
AGND
Analog Ground.
2
1
LX
LX Pin. Connect this Pin to an inductor. Minimize the track area to
reduce EMI.
--
2
GND
Ground.
3, 9 (Exposed Pad)
--
NC
No Internal Connection.
4
--
PGND
Power Ground.
5
6
VDD
Supply Input Voltage. Bypass 1μF capacitor to GND to reduce the
input ripple.
6
5
VOUT
Output Voltage. The pin internally connects to OVP diode to limit
output voltage while LEDs are disconnected.
7
4
EN
Chip Enable (Active High). Note that this pin has an internal
pull-down resistance around 300kΩ.
8
3
FB
--
GND
Feedback. Series connecting a resistor between WLED and ground
as a current sense. Sense the current feedback voltage to set the
current rating.
Exposed pad should be soldered to PCB board and connected to
GND.
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DS9285A/B-06 August 2012
RT9285A/B
Function Block Diagram
1.0MHz OSC
Current
Sense
Slope
Compensation
OCP
LX
PWM
Logic
OVP
VOUT
UVLO/P
GOOD
VDD
EN
FB
VREF
+
Timer
Dimming
Controller
+
-
Soft
Start/Cla
mping
GND
Operation
Soft-Start
LED Current Setting
The Soft-Start function is made by clamping the output
voltage of error amplifier with another voltage source that
is increased slowly from zero to near VIN in the Soft-Start
period. Therefore, the duty cycle of the PWM will be
increased from zero to maximum in this period. The softstart time is decided by a timer of 1.5ms. The charging
time of the inductor will be limited as the smaller duty so
that the inrush current can be reduced to an acceptable
value.
The RT9285 regulates the LED current by setting the
current sense resistor (RSET) connecting to feedback and
ground. The internal feedback reference voltage is 0.25V.
The LED current can be set from following equation easily.
ILED (mA) = 0.25/RSET
In order to have an accurate LED current, precision
resistors are preferred (1% is recommended). The table
for RSET selection is shown below.
Table 1. RSET Value Selection
Over Voltage Protection
The Over Voltage Protection is detected by a junction
breakdown detecting circuit. Once VOUT goes over the
detecting voltage, LX pin stops switching and the power
NMOS is turned off. Then, the VOUT is clamped to be near
VOVP.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS9285A/B-06 August 2012
ILED (mA)
RSET (Ω)
5
49.9
10
24.9
12
21
15
16.5
20
12.4
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RT9285A/B
Digital Pulse Dimming (RT9285A)
PWM Dimming (RT9285B)
The digital pulse dimming is implemented by checking
the low-level duration time of EN pin. As the duration time
is in the range of TUP, the LED current will increase 1/16. If
the duration time is in the range of TDOWN, the LED current
will decrease 1/16. The high-level duration time of EN pin
needs larger than TDELAY to make sure the logic can be
detected correctly. As the LED current is set to MAX (16/
16), it will keep MAX until the decreasing signal is
detected. On the other hand, as the LED current is set to
MIN (1/16), it will keep MIN until the increasing signal is
detected. When the chip turns on, the initial state of LED
current is MAX.
For controlling the LED brightness, the RT9285B can
perform the dimming control by applying a PWM signal
to EN pin. A low pass filter is implemented inside chip to
reduce the slew rate of ILED to prevent the audio noise.
The average LED current is proportional to the PWM signal
duty cycle. The magnitude of the PWM signal should be
higher than the logic high voltage of enable pin, in order to
let the dimming control perform correctly.
Feedback Voltage
Time
Symbol
Increase
0.5μs to 75μs
TUP
Decrease
180μs to 300μs
TDOWN
Delay between steps
> 0.5μs
TDELAY
Shutdown
> 1ms
TS HDN
TDELAY
EN
TUP
IWLED, AVG = Duty of EN
IWLED
Table 2
TDOWM
EN
Figure 2
Current Limiting
The current flow through the inductor as charging period
is detected by a current sensing circuit. As the value over
the current limiting, the N-MOSFET will be turned-off so
that the inductor will be forced to leave charging stage
and enter discharging stage. Therefore, the inductor current
will not increase over the current limiting.
TSHDN
Shut-down
Shut-down
100%
15/16
100%
IWLED
Figure 1
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DS9285A/B-06 August 2012
RT9285A/B
Absolute Maximum Ratings
(Note 1)
Supply Voltage, VIN -------------------------------------------------------------------------------------------------- −0.3 to 6V
LX Input Voltage ------------------------------------------------------------------------------------------------------- − 0.3V to 22V
z Output Voltage --------------------------------------------------------------------------------------------------------- − 0.3V to 21V
z The other pins ---------------------------------------------------------------------------------------------------------- − 0.3V to 6V
z Power Dissipation, PD @ TA = 25°C
TSOT23-6 --------------------------------------------------------------------------------------------------------------- 0.455W
WDFN-8L 2x2 ---------------------------------------------------------------------------------------------------------- 0.606W
z Package Thermal Resistance (Note 2)
TSOT23-6, θJA ---------------------------------------------------------------------------------------------------------- 220°C/W
WDFN-8L 2x2, θJA ----------------------------------------------------------------------------------------------------- 165°C/W
z Junction Temperature ------------------------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C
z Storage Temperature Range ---------------------------------------------------------------------------------------- − 65°C to 150°C
z
z
Recommended Operating Conditions
z
z
(Note 3)
Operation Junction Temperature Range -------------------------------------------------------------------------- −40°C to 125°C
Operation Ambient Temperature Range -------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3.7V, FREQ left floating, TA = 25° C, unless otherwise specification)
Parameter
System Supply Input
Symbol
Test Conditions
Min
Typ
Max
Unit
Operation voltage Range
V IN
2.7
--
5.5
V
Under Voltage Lock Out
V UVLO
1.7
2
2.3
V
Quiescent Current
Supply Current
IQ
IIN
FB = 1.5V, No switch
FB = 0V, Switch
---
300
--
450
2
μA
mA
Shut Down Current
ISHDN
V EN < 0.4V
--
2
5
μA
V IN = 3V to 4.3V
--
--
3
%
fOSC
-85
1
90
---
MHz
%
V REF
0.237
0.25
0.263
V
--
0.9
--
V
0.5
0.75
1
Ω
---
20
400
---
V
mA
Output
Line Regulation
Oscillator
Operation Frequency
Maximum Duty Cycle
Reference Voltage
Feedback Reference Voltage
Diode
Forward Voltage
V FW
MOSFET
On Resistance of MOSFET
RDS(ON)
IFW = 100mA
Protection
OVP Threshold
OCP
VOVP
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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RT9285A/B
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Control Interface
EN Threshold
Logic-Low
VIL
--
--
0.4
V
Voltage
Logic-High
VIH
1.4
--
--
V
Digital Dimming (for RT9285A)
Up Brightness Time
TUP
Refer to Figure 1
0.5
--
75
μs
Down Brightness Time
TDOWN
Refer to Figure 1
180
--
300
μs
Delay Between Steps Time
TDELAY
Refer to Figure 1
0.5
--
--
μs
Shut Down Delay Time
TSHDN
Refer to Figure 1
1
--
--
ms
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 low effective thermal conductivity single-layer test board per JEDEC 51-3.
Note 3. The device is not guaranteed to function outside its operating conditions.
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RT9285A/B
Typical Application Circuit
L1
10µH to 22µH
RT9285A/B
LX
EN
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS9285A/B-06 August 2012
C1
1µF
VDD
VOUT
Chip Enable
GND
VIN
2.7V to 5.5V
FB
C2
0.22µF to 1µF
RSET
12.5
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RT9285A/B
Typical Operating Characteristics
OVP vs. Input Voltage
20.8
90
90%
20.4
85
85%
4W-LED
80
80%
Efficiency (%)
20
OVP (V)
Efficiency vs. Input Voltage
19.6
19.2
18.8
75
75%
70
70%
65
65%
60%
60
18.4
55%
55
18
50%
50
2.6
3
3.4
3.8
4.2
4.6
5
5.4
5.8
6.2
2.5
3
3.5
Input Voltage (V)
5
5.5
6
Frequency vs. Input Voltage
Quiescent Current vs. Input Voltage
1.02
1.00
400
-40°C
350
25°C
300
85°C
250
200
Frequency (MHz)
Quiescent Current (uA)
4.5
Input Voltage (V)
450
0.98
0.96
0.94
0.92
0.90
150
0.88
100
2.6
2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
3.1
3.6
4.1
4.6
5.1
5.6
Input Voltage (V)
Input Voltage (V)
Output Voltage vs. Output Current
Enable Voltage vs. Input Voltage
17
0.84
0.83
16
0.81
0.80
0.79
0.78
Shutdown Voltage
0.77
0.76
Output Voltage (V)
Enable Voltage
0.82
Enable Voltage (V)
4
15
14
13
12
11
0.75
0.74
10
2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
Input Voltage (V)
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5
15
25
35
45
55
65
75
Output Current (mA)
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DS9285A/B-06 August 2012
RT9285A/B
Feedback Reference Voltage vs. Input Voltage
Dimming Operation @ Decrease
Feedback Reference Voltage (mV)
253.5
VIN
(2V/Div)
VOUT
(5V/Div)
253.0
252.5
VIN = 3.7V
252.0
251.5
251.0
EN
(2V/Div)
250.5
250.0
ILED
(10mA/Div)
249.5
249.0
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
5.5
Time (500μs/Div)
Input Voltage (V)
Dimming Operation @ Increase
VIN
(2V/Div)
VOUT
(5V/Div)
VIN = 3.7V
Inrush Current Response
VIN
(2V/Div)
VIN = 3.7V
VOUT
(5V/Div)
EN
(2V/Div)
EN
(2V/Div)
IIN
(100mA/Div)
ILED
(10mA/Div)
Time (500μs/Div)
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Time (500μs/Div)
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RT9285A/B
Application Information
LED Current Control
The RT9285A/B regulates the LED current by setting the
current sense resistor (RSET) connecting to feedback and
ground. The RT9284A/B feedback voltage (VFB) is 0.25V.
The LED current (ILED) can be set by a resistor RSET.
ILED = 0.25/RSET
In order to have an accurate LED current, a precision
resistor is preferred (1% is recommended).
L1
10µH to 22µH
RT9285A/B
LX
EN
Capacitor Selection
Input and output ceramic capacitors of 1μF are recommended for RT9285A/B applications. For better voltage filtering,
ceramic capacitors with low ESR are recommended. X5R
and X7R types are suitable because of their wider voltage
and temperature ranges.
Output Voltage Control
The output voltage of R9285 can be adjusted by the divider
circuit on FB pin. Figure 6 shows a 2-level voltage control
circuit for OLED application. The output voltage can be
calculated by the following equations in Figure 6.
C1
1µF
VDD
VOUT
Chip Enable
GND
VIN
2.7V to 5.5V
The inductor saturation current rating should be considered
to cover the inductor peak current.
C2
0.22µF to 1µF
VIN
2.7V to 5.5V
L1
10µH to 22µH
FB
RSET
12.5
RT9285A/B
Figure 3. Application for Driving 4 Series WLEDs
L1
10µH to 22µH
VOUT
EN
Chip Enable
LX
EN
VOUT = 0.25 ×
VDD
VOUT
Chip Enable
GND
C1
1µF
C2
0.22µF to 1µF
VOUT
15V
VDD
LX
VIN
2.7V to 5.5V
GND
RT9285A/B
C1
1µF
R1
590k
C2
0.22µF to 1µF
FB
R2
10k
R1 + R2
; R2 > 10k
R2
Figure 5. Application for Constant Output Voltage
FB
RSET
12.5
GPIO
VIN
RT9285A/B
VDD
Figure 4. Application for Driving 5 Series WLEDs
VOUT
RA R
GPIO
Inductor Selection
The recommended value of inductor for 4 to 5WLEDs
applications are 10μH to 22μH. For 3WLEDs, the
recommended value of inductor is 4.7μH to 22μH. Small
size and better efficiency are the major concerns for
portable device, such as RT9285A/B used for mobile
phone. The inductor should have low core loss at 1MHz
and low DCR for better efficiency.
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LX
FB
EN
GND
OLED
RB
VEN
Figure 6. Application Circuit for Output Voltage Control
and Related Equations
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DS9285A/B-06 August 2012
RT9285A/B
VOUT = RA x {(FB/RB) + (FB-GPIO)/RGPIO} + FB
(1)
`
LX node copper area should be minimized for reducing
EMI. (*1)
`
The input capacitor C1 should be placed as closed as
possible to Pin 6. (*2)
`
The output capacitor C2 should be connected directly
from the Pin 5 to ground rather than across the LEDs.
(*3)
`
FB node copper area should be minimized and keep
far away from noise sources (Pin 1, Pin 5, Pin 6). (*4)
`
The Inductor is far away receiver and microphone.
`
The voice trace is far away RT9285.
`
The embedded antenna is far away and different side
RT9285.
`
R1 should be placed as close as RT9285.
`
The through hole of RT9285's GND pin is recommended
as large and many as possible.
As GPIO = 0V,
VOUT = RA x {(0.25/RB) + (0.25/RGPIO)} + 0.25
(2)
As GPIO = 2.8V,
VOUT = R A x {(0.25/R B) + (0.25-2.8)/R GPIO)} + 0.25
(3)
As GPIO = 1.8V, VOUT = RA x {(0.25/RB) + (0.25-1.8)/
RGPIO)} + 0.25
(4)
For Efficiency Consideration :
Set RA = 990kΩ,
If 2 levels are 16V (GPIO = 0V) and 14V (GPIO = 1.8V)
Get RB = 16kΩ, RGPIO = 890kΩ
Table 3. Suggested Resistance for Output Voltage
Control
RB
RGPIO
RA
Conditions
(kΩ)
(kΩ)
(kΩ)
Case A :
Normal Voltage = 16V
(GPIO = 0V)
1100
18
495
Dimming Voltage = 12V
(GPIO = 1.8V)
Case B :
Normal Voltage = 16V
(GPIO = 0V)
1200
19.5
840
Dimming Voltage = 12V
(GPIO = 2.8V)
Considering the output voltage deviation from the GPIO
voltage tolerance, as GPIO voltage vibrated by 0 ± 50mV
and 1.8(2.8) ±5% ,the output voltage could be kept within
±2.5%.
L1
VIN
C1
*1
*2
LX
1
6
VDD
GND
2
5
VOUT
3
4
EN
C2
*3
GND
RSET
WLEDs
*4
FB
EN
Figure 7. TOP
Layout guide
`
A full GND plane without gap break.
`
Traces in bold need to be routed first and should be
kept as short as possible.
`
VDD to GND noise bypass : Short and wide connection
for the 1μF MLCC capacitor between Pin 6 and Pin 2.
Figure 8. Bottom
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RT9285A/B
Outline Dimension
H
D
L
C
B
b
A
A1
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
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
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is a registered trademark of Richtek Technology Corporation.
DS9285A/B-06 August 2012
RT9285A/B
D2
D
L
E
E2
1
e
SEE DETAIL A
b
2
1
2
1
A
A1
A3
DETAIL A
Pin #1 ID and Tie Bar Mark Options
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
0.200
0.300
0.008
0.012
D
1.950
2.050
0.077
0.081
D2
1.000
1.250
0.039
0.049
E
1.950
2.050
0.077
0.081
E2
0.400
0.650
0.016
0.026
e
L
0.500
0.300
0.020
0.400
0.012
0.016
W-Type 8L DFN 2x2 Package
Richtek Technology Corporation
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
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