DS8565 01

RT8565
Small Package, High Performance, Diode Embedded,
Asynchronous Boost, 6 WLEDs Driver
General Description
Features
The RT8565 is a high efficiency LED driver IC capable of
driving 6 LEDs. The RT8565 integrates 26V/0.9A power
switch with an internal Schottky diode.
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The RT8565 is a current mode boost converter which is
fixed at 600kHz operating frequency and has a wide input
voltage range from 2.8V to 4.5V.
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During brightness dimming, the RT8565 does not burst
the LED current. Therefore, no audible noises are
generated on the output capacitor. The RT8565 also has
internal over voltage protection setting to prevent the output
from exceeding the absolute maximum ratings during open
LED conditions.
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Applications
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GPS, Portable DVD Backlight
Mobile Phone, Smart Phone
Pin Configurations
(TOP VIEW)
NC
The LED current is set with an external resistor and the
feedback voltage is regulated to 200mV. During operation,
an internal 6-bit DAC is used for brightness control. Users
can easily configure up to 64 steps of LED current via the
EN pin.
Internal Schottky Diode
Internal Soft-Start and Compensation
200mV Reference Voltage
64-Step Pulse Dimming
Open LED Protection
Internally Set Over Voltage Protection
Over Temperature Protedtion
Current Limit Protection
RoHS Compliant and Halogen Free
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The RT8565 is available in a small WQFN-8L 1.6x1.6
package.
FB
1
7
VIN
VOUT
2
6
EN
GND
3
5
LX
4
NC
Ordering Information
RT8565
Package Type
QW : WQFN-8L 1.6x1.6 (COL) (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
WQFN-8L 1.6x1.6 (COL)
Marking Information
C0 : Product Code
C0W
W : Date Code
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
DS8565-01 April 2011
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1
RT8565
Typical Application Circuit
VOUT 2
L
10µH
VIN
2.8V to 4.5V
CIN
1µF
COUT
1µF
5 LX
RT8565
:
: 6 LEDs
:
:
7 VIN
FB
6 EN
Chip Enable
1
RSET
GND
3
Timing Diagram
1ms < tIH
0
0.5µs < tIH
1
100%
2
63/64
0.5µ < tIH < 500µs
3
4
5
4ms < tSHDN
62
63
0
1
100%
62/64
61/64
63/64
60/64
2/64
1/64
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
FB
Feedback Voltage Input. Connect a resistor from this pin to GND to set the LED current.
2
VOUT
Boost Converter Output.
3
GND
Ground.
4, 8
NC
No Internal Connection.
5
LX
Switch Node of Boost Converter.
6
EN
Chip Enable (Active High).
7
VIN
Power Supply Input.
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DS8565-01 April 2011
RT8565
Function Block Diagram
VOUT
OVP
OTP
Soft-Start
LX
OCP
VIN
PWM
Control
UVLO
OSC
Shutdown
Delay
+
+
-
EN
EN Control
Dimming
+
-
Soft-Start
VREF
OCP
Error
AMP
Internal
Compensation
GND
OTP
FB
DS8565-01 April 2011
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3
RT8565
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VIN to GND ------------------------------------------------------------------------------------- −0.3V to 5.4V
EN, FB to GND ------------------------------------------------------------------------------------------------------------ −0.3V to 5.4V
LX, VOUT to GND --------------------------------------------------------------------------------------------------------- −0.3V to 40V
Power Dissipation, PD @ TA = 25°C
WQFN−8L 1.6x1.6 (COL) -----------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WQFN−8L 1.6x1.6 (COL), θJA -----------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------
Recommended Operating Conditions
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0.833W
120°C/W
260°C
150°C
−65°C to 150°C
(Note 3)
Supply Input Voltage ------------------------------------------------------------------------------------------------------ 2.8V to 4.5V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3.6V, TA = 25°C, unless otherwise specified)
Parameter
Under Voltage Lockout Threshold
Symbol
VUVLO
Test Conditions
VIN Rising
Under Voltage Lockout Hysteresis ΔV UVLO
Min
Typ
Max
Unit
2
2.2
2.45
V
--
0.1
--
V
IVCC
FB = 1.5V, Not Switching
--
850
--
μA
IVCC_SW
FB = 0V, Switching
--
--
3
mA
ISHDN
VIN = 4V, VEN ≤ 0.8V
--
1
4
μA
VIH
VIL
1.5
--
---
-0.4
V
IIH
1
--
10
μA
Logic-Low
tIL
0.5
--
500
Logic-High
tIH
0.5
--
--
tSHDN
4
--
--
ms
Switching Frequency
fOSC
−20%
0.6
20%
MHz
LX On-Resistance (N-MOSFET)
RDS(ON)
--
0.5
0.7
Ω
Minimum ON Time
tON
--
100
--
ns
Maximum Duty
DMAX
--
92
--
%
Feedback Reference Voltage
VREF
−5%
200
5%
mV
VIN Quiescent Current
VIN Shutdown Current
Control Input
EN Threshold
Voltage
Logic-High
Logic-Low
EN Sink Current
EN Dimming
Time
Shutdown Delay Time
μs
Boost Converter
Fault Protection
LX Current Limit
ILIM
--
0.9
--
A
Over Voltage Protection
V OVP
--
26
--
V
Thermal Shutdown Temperature
Thermal Shutdown
Hysteresis
T SD
--
160
--
°C
ΔTSD
--
30
--
°C
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DS8565-01 April 2011
RT8565
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 thermal conductivity four-layer test board of
JEDEC 51-7 thermal measurement standard.
Note 3. The device is not guaranteed to function outside its operating conditions.
DS8565-01 April 2011
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5
RT8565
Typical Operating Characteristics
Quiescent Current vs. Input Voltage
1800
1050
1700
Quiescent Current (μA)
Quiescent Current (μA)
Quiescent Current vs. Input Voltage
1100
1000
950
900
850
800
750
700
1600
1500
1400
1300
1200
1100
650
No Switching
600
2.8
3.1
3.4
3.7
4.0
4.3
Switching
1000
2.8
4.6
3.1
3.4
4.0
4.3
4.6
Input Voltage (V)
Input Voltage (V)
OVP vs. Input Voltage
Feedback Voltage vs. Temperature
199.5
25.9
199.3
Feedback Voltage (V)
26.0
25.8
OVP (V)
3.7
25.7
25.6
199.1
198.9
198.7
25.5
198.5
25.4
198.3
VIN = 3.7V
2.8
3.1
3.4
3.7
4.0
4.3
4.6
-50
-25
0
25
50
75
100
Input Voltage (V)
Temperature (°C)
Power Off
Pulse Dimming for LED Current
125
VEN
(2V/Div)
VEN
(2V/Div)
VFB
(200mV/Div)
I LED
(10mA/Div)
VIN = 3.7V, 6 WLEDs with 20mA
Time (500μs/Div)
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6
I LED
(5mA/Div)
VIN = 3.7V, 6 WLEDs with 20mA
Time (10ms/Div)
DS8565-01 April 2011
RT8565
Soft-Start
Line Transient Response
VEN
(5V/Div)
VIN 4.2
(V)
3.2
VLX
(10V/Div)
I LED
(10mA/Div)
I LED
(10mA/Div)
VIN = 3.7V, 6 WLEDs with 20mA
VIN = 3.2V to 4.2V, 6 WLEDs with 20mA
Time (1ms/Div)
Time (1ms/Div)
Efficiency vs. Load Current
90
80
80
70
VIN = 4.2V
VIN = 3.7V
VIN = 3V
60
Load = 10mA
Load = 20mA
Load = 30mA
70
Efficiency (%)
Efficiency (%)
Efficiency vs. Input Voltage
90
50
40
30
20
60
50
40
30
20
10
VOUT = 20V, L = 10μH
0
10
VOUT = 20V, L = 10μH
0
0
5
10
15
20
Load Current (mA)
DS8565-01 April 2011
25
30
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
Input Voltage (V)
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RT8565
Application Information
Soft-Start
The function of Soft-Start is to avoid high inrush current
during start-up
LED Current
the major concerns for portable devices, such as for mobile
phone. The inductor should have low core loss at 600kHz
and low DCR for better efficiency. The inductor saturation
current rating should be able to cover the inductor peak
current.
The loop control of the boost converter keeps VFB equal
to a reference voltage VREF. Therefore, when RSET is
connected between the FB pin and GND, the LED current
will be determined by the current through RSET, which is
equal to VFB / RSET.
Brightness Dimming
The RT8565 implements a pulse dimming method to
control the brightness of the white LEDs. Users can easily
configure the LED current with a serial pulse. The dimming
of white LED current can be achieved by applying a pulse
signal to the EN pin. There are a total of 64 steps of current
levels that can be set by users. The detail operation of
the brightness dimming is shown in Timing Diagram.
Current Limiting
The current flowing through the inductor during the
charging period is detected by a current sensing circuit.
If the value over the current limit, the N-MOSFET will be
turned off. The inductor will then be forced to leave charging
stage and enter discharging stage. Therefore, the inductor
current will not increase over the current limit.
Shutdown Delay
When the EN voltage is in logic-low for 4ms typical during
for pulse dimming, the system will enter shutdown.
OVP/UVLO/OTP
When the output voltage is higher than a specified value
or input voltage is lower than a specified value, the IC will
enter protection mode to prevent abnormal operation. If
the die temperature > 160°C, the IC will also enter
protection mode. The power MOSFET will be turned off
during protection mode to prevent abnormal operation.
Inductor Selection
The recommended Inductor value for 6-WLED applications
is from 10μH to 22μH. Small size and better efficiency are
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Capacitor Selection
Input ceramic capacitor of 1μF and output ceramic capacitor
of 1μF are recommended for driving 6-WLED applications.
For better voltage filtering, ceramic capacitors with low
ESR are recommended. X5R and X7R types are suitable
because of their wide voltage and temperature ranges.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications of
the RT8565, the maximum junction temperature is 125°C
and TA is the ambient temperature. The junction to ambient
thermal resistance, θ JA , is layout dependent. For
WQFN-8L 1.6x1.6 packages, the thermal resistance, θJA,
is 120°C/W on a standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for
WQFN-8L 1.6x1.6 package
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
resistance. For the RT8565 package, the derating curve
in Figure 1 allows the designer to see the effect of rising
ambient temperature on the maximum power dissipation.
DS8565-01 April 2011
RT8565
0.75
The inductor should be placed as close
as possible to the switch pin to minimize
the noise coupling into other circuits.
The LX node copper area should be
minimized for reducing EMI.
NC
Four-Layer PCB
COUT should be connected
directly from Pin 2 to ground
rather than across the LEDs
8
FB
1
7
VIN
VOUT
2
6
EN
GND
3
5
LX
COUT
0.50
Battery
L
CIN
4
CIN should be placed as
close as possible to the
VIN pin for good filtering.
NC
Maximum Power Dissipation (W)
1.00
0.25
GND
RSET
0.00
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve for the RT8565 Package
FB node copper area should be
minimized and kept far away from
noise sources (LX pin) and RSET
should be placed as close as
possible to the FB pin.
Figure 2. PCB Layout Guide
Layout Consideration
For best performance of the RT8565, the following
guidelines must be strictly followed :
`
Input and output capacitors should be placed close to
the IC and connected to the ground plane to reduce
noise coupling.
`
GND and Exposed Pad should be connected to a strong
ground plane for heat sinking and noise protection.
`
Keep the main current traces as short and wide as
possible.
`
LX node of DC/DC converter experiences high frequency
voltage swings. It should be kept in a small area.
`
Place the feedback components as close as possible
to the IC and away from the noisy devices.
DS8565-01 April 2011
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9
RT8565
Outline Dimension
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
0.250
0.006
0.010
D
1.550
1.650
0.061
0.065
E
1.550
1.650
0.061
0.065
e
L
0.400
0.350
0.016
0.450
0.014
0.018
W-Type 8L QFN 1.6x1.6 (COL) 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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DS8565-01 April 2011
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