RICHTEK RT9385B

RT9385B
5 Channels 125mA x1/x1.5/x2 Charge Pump White LED Driver
General Description
Features
The RT9385B is a 5 channel WLED driver with auto mode
selection of x1, x1.5 and x2 mode with low dropout voltage
in current sources. The RT9385B can power up to 5 white
LEDs with regulated constant current for uniform intensity.
Each channel (LED1 to LED5) can support up to 25mA.
The part maintains highest efficiency by utilizing x1/x1.5/
x2 fractional charge pump and low dropout current
regulators. An internal 5-bit DAC is used for brightness
control. Users can easily configure up to 32 steps of LED
current by enable pin.
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85% Average Efficiency Over Li-ion Battery
Discharge
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Support Up to 5 White LEDs
Support Up to 25mA/Per Channel
Support Up to 125mA Output Current
Flexible 32 Step Brightness Control
60mV Current Source Dropout
1% LED Current Accuracy
0.7% LED Current Matching
Automatic x1/x1.5/x2 Charge Pump Mode
Transition
Low Input Noise and EMI Charge Pump
5V Over Voltage Protection
Power On/Mode Transition Inrush Protection
1MHz Frequency Oscillator
0.4μ
μA Low Shutdown Current
RoHS Compliant and Halogen Free
provides the best backlighting solution with high efficiency
and smallest board space for portable application.
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Ordering Information
RT9385B
Package Type
QW : WQFN-16L 2x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
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RoHS compliant and compatible with the current require-
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Applications
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Camera Phone, Smart Phone
White LED Backlighting
Pin Configurations
(TOP VIEW)
ments of IPC/JEDEC J-STD-020.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
LED2
LED1
VIN
Suitable for use in SnPb or Pb-free soldering processes.
16 15 14
LED3
LED4
LED5
VOUT
PGND
1
13
2
12
GND
3
4
17
5
11
10
9
6
C2N
`
AGND
NC
VIN
EN
C2P
7 8
C1P
The RT9385B is available in a WQFN-16L 2x3 package.
Small 1μF capacitors can be used for fly capacitors. It
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WQFN-16L 2x3
DS9385B-01 April 2011
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1
RT9385B
Typical Application Circuit
CFLY2
1µF
CFLY1
1µF
7
8
C1P
14,11
CIN
1µF
6
9
C1N C2P C2N
VIN
Pulse Input
10 EN
LED1
LED2
LED3
LED4
LED5
RT9385B
4 VOUT
COUT
1µF
AGND
13
15
16
1
2
3
PGND
5
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
LED3
Current Sink for LED3. (If not in use, this pin should be connected to VIN)
2
LED4
Current Sink for LED4. (If not in use, this pin should be connected to VIN)
3
LED5
Current Sink for LED5. (If not in use, this pin should be connected to VIN)
4
VOUT
Charge Pump Output.
5
PGND
Ground.
6
C2N
Fly Capacitor 2 Negative Connection.
7
C1N
Fly Capacitor 1 Negative Connection.
8
C1P
Fly Capacitor 1 Positive Connection.
9
C2P
Fly Capacitor 2 Positive Connection.
10
EN
Chip Enable (Active High).
11, 14
VIN
Power Input.
12
NC
No Internal Connection.
13
AGND
Ground.
15
LED1
Current Sink for LED1. (If not in use, this pin should be connected to VIN)
16
LED2
Current Sink for LED2. (If not in use, this pin should be connected to VIN)
The exposed pad must be soldered to a large PCB and connected to GND for
maximum power dissipation.
17 (Exposed Pad) GND
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DS9385B-01 April 2011
RT9385B
Function Block Diagram
C1P
C1N C2P C2N
VIN
VOUT
Soft Start
Circuit
OVP
UVLO
Gate Driver
1MHz
OSC
Mode Decision
LED1
LED2
LED3
LED4
LED5
Pulse Dimming
Controller
EN
PGND
AGND
DS9385B-01 April 2011
Shutdown Delay
Current
Bias
Current Source
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3
RT9385B
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WQFN-16L 2x3 ----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WQFN-16L 2x3, θJA ----------------------------------------------------------------------------------------------------WQFN-16L 2x3, θJC ----------------------------------------------------------------------------------------------------Junction Temperature --------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Mode) --------------------------------------------------------------------------------------------MM (Machine Mode) ----------------------------------------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 5V
1.111W
90°C/W
15°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
(Note 4)
Junction Temperature Range ------------------------------------------------------------------------------------------ −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------------ −40°C to 85°C
Electrical Characteristics
(VIN = 3.6V, VF = 3.5V, CIN = COUT = 1μF, CFLY1 = CFLY2 = 1μF, ILED1 to LED5 = 25mA, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test C onditions
Min
Typ
Max
Units
2.8
--
4.5
V
1.8
2
2.5
V
--
100
--
mV
Input Power Supply
Input Supply Voltage
V IN
U nder-Voltage Lockout
Threshold
V UVLO
U nder-Voltage Lockout
H ysteresis
ΔV UVLO
Quiescent Current
IQ
x1 Mode
--
1
2
mA
Shutdown Current
ISHDN
VIN = 4.5V
--
0.4
2
μA
ILEDx
ILEDx = 25mA
−5
0
+5
%
ILEDx = 25mA
−2
0
+2
%
--
1000
--
kH z
VIN R ising
LED Current
LED Current Accuracy
C urrent Matching
C harge Pump
Oscillator Frequency
fOSC
Mode Decision
x1 Mode to x1.5 Mode
Transition Voltage (V IN Falling)
IOUT = 125mA, ILEDx = 25mA
--
3.65
3.8
V
Mode Transition Hystersis
IOUT = 125mA, ILEDx = 25mA
--
200
--
mV
4.5
5
5.5
V
Protection
OVP
VIN – VO UT
To be continued
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DS9385B-01 April 2011
RT9385B
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
3
--
--
ms
D imming
EN Low to Shutdown Delay
EN Low Time for Dimming
TIL
0.5
--
500
μs
EN High T ime for Dimming
T IH
0.5
--
--
μs
En Pull Low Current
IEN
--
2
--
μA
Logic-Low Voltage
V IL
--
--
0.2
V
Logic-High Voltage
V IH
1
--
4.5
V
--
2
EN
Threshold
EN Pull Low Current
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. θJA is measured in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of
JEDEC 51-7 thermal measurement standard. The case point of θJC is on the exposed pad for 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.
DS9385B-01 April 2011
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RT9385B
Typical Operating Characteristics
LED Current vs. Input Voltage
Efficiency vs. Input Voltage
100
90
LED Current (mA)
80
Efficiency (%)
70
60
50
40
30
20
10
LED VF = 3.02V
0
2.8
3
3.2 3.4 3.6 3.8
4
4.2 4.4 4.6 4.8
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
LED1
LED2
LED3
LED4
LED5
LED VF = 3.02V
2.8
5
3
4
4.2 4.4 4.6 4.8
5
Input Voltage (V)
Input Voltage (V)
x1 Mode Quiescent Current vs. Input Voltage
x2 Mode Quiescent Current vs. Input Voltage
4.5
1.30
1.25
Quiescent Current (mA)
Quiescent Current (mA)
3.2 3.4 3.6 3.8
1.20
1.15
1.10
1.05
1.00
4.0
3.5
3.0
2.5
2.0
2.8
3
3.2 3.4 3.6 3.8
4
4.2 4.4 4.6 4.8
2.8
5
3
3.2 3.4 3.6 3.8
4
4.2 4.4 4.6 4.8
Input Voltage (V)
Input Voltage (V)
Shutdown Current vs. Input Voltage
x1 Mode Inrush Current Response
5
1
Shutdown Current (μA)
0.9
EN
(5V/Div)
0.8
0.7
VOUT
(1V/Div)
0.6
0.5
C2P
(2V/Div)
0.4
0.3
0.2
IIN
(200mA/Div)
0.1
VIN = 3.2V
0
2.8
3
3.2 3.4 3.6 3.8
4
4.2 4.4 4.6 4.8
5
Time (100μs/Div)
Input Voltage (V)
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DS9385B-01 April 2011
RT9385B
x1.5 Mode Inrush Current Response
x2 Mode Inrush Current Response
EN
(5V/Div)
VIN = 3.15V
EN
(5V/Div)
VIN = 3.1V
VOUT
(1V/Div)
VOUT
(1V/Div)
C2P
(2V/Div)
C2P
(2V/Div)
IIN
(200mA/Div)
IIN
(200mA/Div)
Time (100μs/Div)
Time (100μs/Div)
Pulse Dimming Operation
Ripple & Spike
VIN
(50mV/Div)
VIN = 3.7V
EN
(2V/Div)
VOUT
(50mV/Div)
C2P
(5V/Div)
ILED
(10mA/Div)
IIN
(200mA/Div)
Time (5ms/Div)
DS9385B-01 April 2011
VIN = 3.1V
Time (1μs/Div)
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RT9385B
Applications Information
The RT9385B uses a fractional switched capacitor charge
pump to power up to five white LEDs with a programmable
current for uniform intensity. The part integrates current
sources and automatic mode selection charge pump. It
maintains the high efficiency by utilizing an x1/x1.5/x2
fractional charge pump and current sources. The small
equivalent x1 mode open loop resistance and ultra-low
dropout voltage of current source extend the operating
time of x1 mode and optimize the efficiency in white LED
applications.
Input UVLO
The input operating voltage range of the LED driver is from
2.8V to 4.5V. An input capacitor at the VIN pin could reduce
ripple voltage. It is recommended to use a ceramic 1μF or
larger capacitance as the input capacitor. The RT9385B
provides an under voltage lockout (UVLO) function to
prevent it from unstable issue when startup. The UVLO
threshold of input rising voltage is set at 2V typically with
a hysteresis of 100mV.
Soft Start
The charge pump 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
clamps the input current over a typical period of 50us.
Mode Decision
The RT9385B uses a smart mode selection method to
decide the working mode for optimizing the efficiency.
Mode decision circuit senses the output and LED voltage
for up/down selection. The RT9385B automatically
switches to x1.5 or x2 mode whenever the dropout
condition is detected from the current source and returns
to x1 mode whenever the dropout condition releases.
Capacitors Selecting
To get the better performance of the RT9385B, the
selection of peripherally appropriate capacitor and value
is very important. These capacitors determine some
parameters such as input/output ripple voltage, power
efficiency and maximum supply current by charge pump.
To reduce the input and output ripple effectively, the low
ESR ceramic capacitors are recommended. For LED driver
applications, the input voltage ripple is more important
than output ripple. Input ripple is controlled by input
capacitor CIN, increasing the value of input capacitance
can further reduce the ripple. Practically, the input voltage
ripple depends on the power supply impedance. The flying
capacitor CFLY1 and CFLY2 determine the supply current
capability of the charge pump to influence the overall
efficiency of the system. The lower value will improve
efficiency. However, it will limit the LED's current at low
input voltage. For 5x25mA load over the entire input range
of 2.8V to 4.5V, it is recommended to use a 1μF ceramic
capacitor on the flying capacitor CFLY1 and CFLY2.
Brightness Control
The RT9385B implements a pulse dimming method to
control the brightness of white LEDs. Users can easily
configure the LED current by a serial pulse. The dimming
of white LEDs' current can be achieved by applying a pulse
signal to the EN pin. There are totally 32 steps of current
could be set by users. The detail operation of brightness
dimming is shown in the Figure 1.
30us < tIH, INIT
EN
Shutdown
ILEDX
0
1
0.5us < tIH
2
3
0.5us < tIL < 500us
4
5
30
100% 31/32
30/32 29/32
28/32 3/32
3ms < tSHDN
31
0
1
100%
2/32
31/32
1/32
Shutdown
LED connection
The RT9385B supports up to 5 white LEDs. The 5 LEDs
are connected from VIN to pin1, 2, 3, 15 and 16
respectively. If the LED is not used, the LED pin should
be connected to VIN directly.
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Figure 1. 32 Step Pulse Dimming and Shutdown Delay
DS9385B-01 April 2011
RT9385B
Thermal Considerations
Layout Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
following formula :
For best performance of the RT9385B, the following layout
guidelines should be strictly followed :
`
Output Capacitor (COUT) should be placed close to VOUT
and connected to ground plane to reduce noise coupling
from charge pump to LEDs.
`
All the traces of LED pins running from chip to LED's
should be wide and short to reduce the parasitic
connection resistance.
`
Input capacitor (CIN) should be placed close to VIN and
connected to ground plane. The trace of VIN in the PCB
should be placed far away from the sensitive devices or
shielded by the ground.
`
The traces running from pins to flying capacitor should
be short and wide to reduce parasitic resistance and
prevent noise radiation.
PD(MAX) = ( TJ(MAX) − TA ) / θJA
Where T J(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification of
the RT9385B, The maximum junction temperature is
125°C. The junction to ambient thermal resistance θJA is
layout dependent. For WQFN-16L 2x3 package, the
thermal resistance θJA is 90°C/W on the standard JEDEC
All the traces of LED pins running from
chip to LEDs should be wide and short to
reduce the parasitic connection resistance.
51-7 four layers thermal test board. The maximum power
dissipation at TA = 25°C can be calculated by following
formula :
resistance θJA. For RT9385B package, the Figure 2 of
derating curve allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation allowed.
Maximum Power Dissipation (W)
1.2
Four Layers PCB
1.1
1.0
0.9
WQFN-16L 2x3
0.8
0.7
0.6
Output capacitor
(COUT) should
be placed close
to VOUT and
connected to
ground plane to
reduce noise
coupling from
charge pump to
LEDs.
16 15 14
LED3
1
13
AGND
LED4
2
12
NC
LED5
3
11
VIN
VOUT
4
10
EN
GND
Battery
Input capacitor
(CIN) should be
6 7 8
placed close to VIN
and connected to
ground plane. The
trace of VIN in the
GND
GND PCB should be
placed far away
The traces running from pins to flying capacitor from the sensitive
should be short and wide to reduce parasitic
devices or shielded
resistance and prevent noise radiation.
by the ground.
PGND
5
17
9
C2P
C2N
C1N
C1P
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
LED2
LED1
VIN
PD(MAX) = (125°C − 25°C) / (90°C/W) = 1.111W for
WQFN-16L 2x3 package
Figure 3. PCB Layout Guide
0.5
0.4
0.3
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve for RT9385B Package
DS9385B-01 April 2011
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RT9385B
Outline Dimension
D
D2
SEE DETAIL A
e
E
E2
L
b
Symbol
1
2
2
DETAIL A
Pin #1 ID and Tie Bar Mark Options
A
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
A3
A1
1
Dimensions In Millimeters
Dimensions In Inches
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
0.250
0.006
0.010
D
1.900
2.100
0.075
0.083
D2
0.700
0.800
0.028
0.031
E
2.900
3.100
0.114
0.122
E2
1.700
1.800
0.067
0.071
e
L
0.400
0.325
0.016
0.425
0.013
0.017
W-Type 16L QFN 2x3 Package
Richtek Technology Corporation
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: [email protected]
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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DS9385B-01 April 2011