RT8509A [RICHTEK]
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| 型号： | RT8509A |
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RICHTEK TECHNOLOGY CORPORATION |
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®
RT8509A
4.5A Step-Up DC/DC Converter
General Description
Features
90% Efficiency
The RT8509A is a high performance switching Boost
converter that provides a regulated supply voltage for active
matrix thin film transistor (TFT) liquid crystal displays
(LCDs).
Adjustable Output Up to 24V
2.8V to 14V Input Supply Voltage
Input Supply Under-Voltage Lockout
Fixed 1.2MHz Switching Frequency
Adjustable Soft-Start
The RT8509Aincorporates current mode, fixed-frequency,
pulse width modulation (PWM) circuitry with a built in
N-MOSFET to achieve high efficiency and fast transient
response.
VOUT Over-Voltage Protection
Over-Temperature Protection
Thin 12-Lead WDFN Package
RoHS Compliant and Halogen Free
The RT8509Ahas a wide input voltage range from 2.8V to
14V. In addition, the output voltage can be adjusted up to
24V via an external resistive voltage divider. The maximum
peak current is limited to 4.5A (min.). Other features
include adjustable soft-start, over-voltage protection, and
over-temperature protection.
Applications
GIPTFT-LCDPanels
Ordering Information
RT8509A
The RT8509Ais available in the WDFN-12L 5x5 package.
Package Type
Marking Information
QW : WDFN-12L 5x5 (W-Type)
RT8509AGQW : Product Number
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
RT8509A
GQW
YMDNN : Date Code
YMDNN
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.
Simplified Application Circuit
D1
L1
V
IN
V
OUT
R4
C2
C
C
OUT
IN
LX
R1
VIN
VOUT
C3
RT8509A
R2
FB
SS
Enable
EN
C
SS
R3
GND
COMP
C1
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8509A-00 November 2013
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1
RT8509A
Pin Configurations
(TOP VIEW)
COMP
FB
12
11
1
2
3
SS
VIN
EN
10
9
VOUT
GND
LX
GND
4
5
6
GND
GND
GND
8
13
7
LX
WDFN-12L 5x5
Functional Pin Description
Pin No.
Pin Name
Pin Function
Compensation Node for Error Amplifier. Connect a series RC from COMP to
ground.
1
COMP
Feedback Voltage Input. The FB regulation voltage is 1.25V nominal. Connect an
external resistive voltage divider between the step-up regulator’s output (VOUT
and GND, with the center tap connected to FB. Place the divider close to the IC
and minimize the trace area to reduce noise coupling.
)
2
3
FB
EN
Enable Control Input. Drive EN low to turn off the Boost.
4, 5, 6, 9,
13 (Exposed Pad)
Ground. The Exposed Pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
GND
Switch Node. LX is the Drain of the internal MOSFET. Connect the
inductor/rectifier diode junction to LX and minimize the trace area for lower EMI.
7, 8
10
LX
Over-Voltage Protection Input for Boost Converter. Bypass VOUT with a
minimum 1F ceramic capacitor directly to GND.
VOUT
VIN
Supply Voltage Input. Bypass VIN with a minimum 1μF ceramic capacitor directly
to GND.
11
Soft-Start Time Setting. Connect a soft-start capacitor (CSS) to this pin. The
soft-start capacitor is charged with a constant current of 5A. The soft-start
capacitor is discharged to ground when EN is low.
12
SS
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DS8509A-00 November 2013
RT8509A
Function Block Diagram
LX
VIN
Soft
Start
Protection
SS
LX
OTP
EN
COMP
Summing
Comparator
Error Amplifier
Control
and
Driver
Logic
FB
+
-
+
-
1.25V
VOUT
OVP
V
GND
DD
Clock
Current
Sense
Slope
Compensation
Oscillator
Operation
The RT8509A is a high-performance step-up DC/DC
converter that provides a regulated and high precision
supply voltage. It incorporates current mode, fixed-
frequency, pulse-width modulation (PWM) circuitry with
a built-in N-Channel power MOSFET to achieve high
efficiency and fast transient response. The device features
an adjustable soft start time using an external soft-start
capacitor to reduce in-rush current.
Copyright 2013 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
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RT8509A
Absolute Maximum Ratings (Note 1)
LXtoGND ------------------------------------------------------------------------------------------------------------------- −0.3V to 28V
VIN, ENtoGND ------------------------------------------------------------------------------------------------------------ −0.3V to 16.5V
Other Pins------------------------------------------------------------------------------------------------------------------- −0.3V to 6.5V
Power Dissipation, PD @ TA = 25°C
WDFN-12L 5x5 ------------------------------------------------------------------------------------------------------------- 3.38W
Package Thermal Resistance (Note 2)
WDFN-12L 5x5, θJA ------------------------------------------------------------------------------------------------------- 29.5°C/W
WDFN-12L 5x5, θJC ------------------------------------------------------------------------------------------------------- 7.5°C/W
Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
Lead Temperature (Soldering, 10sec.)-------------------------------------------------------------------------------- 260°C
ESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
Ambient Temperature Range-------------------------------------------------------------------------------------------- −40°C to 85°C
Junction Temperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C
Electrical Characteristics
(VIN = 3.3V, VOUT = 10V, TA =25°C unless otherwise specified)
Parameter
Supply Current
Symbol
Test Conditions
Min
Typ
Max
Unit
Input Voltage Range
Output Voltage Range
VIN
2.8
--
--
--
14
24
V
V
VOUT
Under Voltage Lockout
Threshold
--
2.5
3
V
VUVLO
VUVLO
IQ
VIN Rising
UVLO Hysteresis
--
--
--
--
200
1
--
--
--
--
mV
VFB = 1.3V, LX Not Switching
FB = 1V, LX Switching
VIN Quiescent Current
mA
V
5
Thermal Shutdown Threshold
Temperature Rising
155
C
C
TSD
Thermal Shutdown
Hysteresis
--
--
10
26
--
--
TSD
VOUT Over Voltage
Threshold
V
VOUT Rising
Oscillator
Oscillator Frequency
Maximum Duty Cycle
Error Amplifier
1000
--
1200
90
1500
--
kHz
%
fOSC
DMAX
FB Regulation Voltage
FB Input Bias Current
FB Line Regulation
1.2312
1.25
--
1.2688
100
V
VREF
IFB
--
--
nA
0.05
0.2
%/V
Copyright 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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DS8509A-00 November 2013
RT8509A
Parameter
Transconductance
Voltage Gain
Symbol
Test Conditions
I = ±2.5μA at VCOMP = 1V
FB to COMP
Min
--
Typ
100
700
Max
--
Unit
A/V
V/V
gm
--
--
AV
N-MOSFET
Current Limit
4.5
--
5
--
A
ILIM
On-Resistance
Leakage Current
100
30
250
45
m
A
RDS(ON)
ILEAK
--
VLX = 24V
Current Sense
Transresistance
--
0.25
--
V/A
RCS
Soft-Start
Charge Current
Control Inputs
--
5
--
A
Logic-High
Logic-Low
1.5
--
--
--
--
VIH
VIL
EN Input
Voltage
V
0.5
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 high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of 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.
Copyright 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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RT8509A
Typical Application Circuit
L1
4.7µH
D1
V
IN
V
OUT
12V
18V
C
C
OUT
IN
7, 8
LX
10µF x 4
R1
134k
10µF x 3
R4
10
2
10
VOUT
C3
R2
10k
1µF
11
VIN
RT8509A
C2
1µF
FB
C
SS
33nF
3
Enable
EN
12
1
SS
COMP
R3
56k
4, 5, 6, 9,
GND
C1
1nF
13 (Exposed Pad)
Copyright 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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RT8509A
Typical Operating Characteristics
Boost Efficiency vs. Load Current
Boost Efficiency vs. Load Current
100
100
90
80
70
60
50
VIN = 5V
VIN = 14V
90
80
70
60
50
V
V
IN = 12V
IN = 10V
VIN = 3.3V
VOUT = 13.5V, fOSC = 1.2MHz
VOUT = 18V, fOSC = 1.2MHz
0.9 1.2 1.5
0
0.1
0.2
0.3
0.4
0.5
0
-50
2
0.3
0.6
Load Current (A)
Load Current (A)
Boost Reference Voltage vs. Temperature
Boost Frequency vs. Temperature
1.5
1400
1300
1200
1100
1000
900
1.4
1.3
1.2
1.1
1
VIN = 3.3V
100 125
VIN = 3.3V
100 125
-25
0
25
50
75
-50
-25
0
25
50
75
Temperature (°C)
Temperature (°C)
Boost Reference Voltage vs. Input Voltage
Boost Current Limit vs. Input Voltage
1.5
8
1.4
1.3
1.2
1.1
1
7
6
5
4
3
2
4
6
8
10
12
14
4
6
8
10
12
14
Input Voltage (V)
Input Voltage (V)
Copyright 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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RT8509A
Application Information
If CSS < 220pF, the internal soft-start function will be turned
on and period time is approximately 1ms.
The RT8509A is a high performance step-up DC/DC
converter that provides a regulated supply voltage for panel
source driver ICs. The RT8509A incorporates current mode,
fixed frequency, Pulse Width Modulation (PWM) circuitry
with a built-in N-MOSFET to achieve high efficiency and
fast transient response. The internal driver power is
supplied from the VOUT pin and that will increase efficiency
when low input voltage condition. The following content
contains detailed description and information for
component selection.
Output Voltage Setting
The regulated output voltage is shown as the following
equation :
R1
R2
V
= V
x 1
, where V
= 1.25V (typ.)
OUT
REF
REF
The recommended value for R2 should be at least 10kΩ
without some sacrificing. Place the resistive voltage divider
as close as possible to the chip to reduce noise sensitivity.
Boost Regulator
Loop Compensation
The RT8509A is a current mode Boost converter integrated
with a 24V/5A power switch, covering a wide VIN range
from 2.8V to 14V. It performs fast transient responses to
generate source driver supplies for TFT-LCDdisplay. The
high operation frequency allows the use of smaller
components to minimize the thickness of the LCD panel.
The output voltage can be adjusted by setting the resistive
voltage-divider sensing at the FB pin. The error amplifier
varies the COMP voltage by sensing the FB pin to regulate
the output voltage. For better stability, the slope
compensation signal summed with the current sense
signal will be compared with the COMP voltage to
determine the current trip point and duty cycle. The Boost
minimum gain ratio depends on minimum on-time. It's
suggested that VOUT higher than 1.2 x VIN for better
performance.
The voltage feedback loop can be compensated with an
external compensation network consisting of R3. Choose
R3 to set high frequency integrator gain for fast transient
response and C1 to set the integrator zero to maintain
loop stability. For typical application, VIN = 5V,
VOUT = 13.6V, COUT = 4.7μF x 3, L1 = 4.7μH, while the
recommended value for compensation is as follows :
R3 = 56kΩ, C1 = 1nF.
Over-Current Protection
The RT8509ABoost converter has over-current protection
to limit the peak inductor current. It prevents the inductor
and diode from damage due to large current. During the
On-time, once the inductor current exceeds the current
limit, the internal LX switch turns off immediately and
shortens the duty cycle. Therefore, the output-voltage
drops if the over current condition occurs. The current
limit is also affected by the input voltage, duty cycle, and
inductor value.
Soft-Start
The RT8509A provides soft-start function to minimize the
inrush current. When powered on, an internal constant
current charges an external capacitor. The rising voltage
rate on the COMP pin is limited from VSS = 0V to 1.24V
and the inductor peak current will also be limited at the
same time. When powered off, the external capacitor will
be discharged until the next soft-start time.
Over-Temperature Protection
The RT8509A Boost converter has thermal protection
function to prevent the chip from overheating. When the
junction temperature exceeds 155°C, the function shuts
down the device. Once the device cools down by
approximately 10°C, it will automatically restart to normal
operation. To guarantee continuous operation, do not
operate over the maximum junction temperature rating of
125°C.
The soft-start function is implemented by the external
capacitor with a 5μAconstant current charging to the soft-
start capacitor. Therefore, the capacitor should be large
enough for output voltage regulation. A typical value for
soft-start capacitor is 33nF. The available soft-start capacitor
range is from 10nF to 100nF.
Copyright 2013 Richtek Technology Corporation. All rights reserved.
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DS8509A-00 November 2013
RT8509A
Inductor Selection
capacitor. As shown in Figure 1, ΔVOUT1 can be evaluated
based on the ideal energy equalization. According to the
definition of Q, the Q value can be calculated as the
following equation :
The inductance depends on the maximum input current.
As a general rule, the inductor ripple current range is 20%
to 40% of the maximum input current. If 40% is selected
as an example, the inductor ripple current can be
calculated according to the following equations :
1
2
1
1
Q
x
I
IN IL IOUT IIN IL IOUT
2
2
V
V
x I
1
IN
OUT
OUT(MAX)
x
x
COUT x VOUT1
I
=
IN(MAX)
VOUT
fOSC
x V
IN
= 0.4 x I
IN(MAX)
I
RIPPLE
where fOSC is the switching frequency, and ΔIL is the
inductor ripple current. Bring COUT to the left side to
estimate the value of ΔVOUT1 according to the following
equation :
where η is the efficiency of the converter, IIN(MAX) is the
maximum input current, and IRIPPLE is the inductor ripple
current. The input peak current can then be obtained by
adding the maximum input current with half of the inductor
ripple current as shown in the following equation :
D x IOUT
VOUT1
x COUT x fOSC
where D is the duty cycle and η is the Boost converter
efficiency. Finally, taking ESR into account, the overall
output ripple voltage can be determined by the following
I
1.2 x I
IN(MAX)
PEAK
Note that the saturated current of the inductor must be
greater than IPEAK. The inductance can eventually be
determined according to the following equation :
equation :
D x IOUT
VOUT I x ESR
IN
x (V )2x(VOUT V )
x COUT x fOSC
IN
IN
L
0.4 x (VOUT )2xIOUT(MAX) x fOSC
The output capacitor, COUT, should be selected accordingly.
where fosc is the switching frequency. For better system
performance, a shielded inductor is preferred to avoid EMI
problems.
ΔI
L
Input Current
Inductor Current
Diode Selection
Schottky diodes are chosen for their low forward voltage
drop and fast switching speed. When selecting a Schottky
diode, important parameters such as power dissipation,
reverse voltage rating, and pulsating peak current should
all be taken into consideration.Asuitable Schottky diode's
reverse voltage rating must be greater than the maximum
output voltage and its average current rating must exceed
the average output current. Last of all, the chosen diode
should have a sufficiently low leakage current level, since
it will increase with temperature.
Output Current
Time
(1-D)T
S
Output Ripple
Voltage (ac)
Time
ΔV
OUT1
Figure 1. The Output Ripple Voltage without the
Contribution of ESR
Output Capacitor Selection
Input Capacitor Selection
The output ripple voltage is an important index for
estimating chip performance. This portion consists of two
parts. One is the product of the inductor current with the
ESR of the output capacitor, while the other part is formed
by the charging and discharging process of the output
Low ESR ceramic capacitors are recommended for input
capacitor applications. Low ESR will effectively reduce
the input voltage ripple caused by switching operation. A
10μF capacitor is sufficient for most applications.
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RT8509A
Nevertheless, this value can be decreased for lower output
current requirement. Another consideration is the voltage
rating of the input capacitor which must be greater than
the maximum input voltage.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Four-Layer PCB
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 :
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve of Maximum PowerDissipation
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TAis
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Layout Considerations
For high frequency switching power supplies, the PCB
layout is important to get good regulation, high efficiency
and stability. The following descriptions are the guidelines
for better PCB layout.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-12L 5x5 packages, the thermal resistance, θJA, is
29.5°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 :
For good regulation, place the power components as
close as possible. The traces should be wide and short
enough especially for the high current output loop.
The feedback voltage divider resistors must be near the
feedback pin. The divider center trace must be shorter
and the trace must be kept away from any switching
nodes.
PD(MAX) = (125°C − 25°C) / (29.5°C/W) = 3.38W for
WDFN-12L 5x5 package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curve in Figure 2 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
The compensation circuit should be kept away from the
power loops and be shielded with a ground trace to
prevent any noise coupling.
Minimize the size of the LX node and keep it wide and
shorter. Keep the LX node away from the FB.
The exposed pad of the chip should be connected to a
strong ground plane for maximum thermal consideration.
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DS8509A-00 November 2013
RT8509A
The compensation circuit should be kept away from the power loops and
should be shielded with a ground trace to prevent any noise coupling.
Locate the C2 as close to
the VIN pin as possible.
GND
V
IN
Place the power components
as close as possible. The
traces should be wide and
short especially for the high-
current loop.
C1
C2
R3
GND
R4
COMP
FB
1
2
3
4
5
12 SS
11 VIN
10 VOUT
EN
R1
13
GND
GND
GND
9
8
7
GND
LX
D1
R2
V
OUT
V
OUT
GND
6
LX
C
OUT
L1
The feedback voltage-divider
resistors must near the feedback
pin. The divider center trace
must be shorter and avoid the
trace near any switching nodes.
GND
C
IN
V
IN
More GND via and layout area for
better thermal performance.
V
IN
The switching trace should be wide and
short especially for the high-current loop.
Figure 3. PCB Layout Guide
Copyright 2013 Richtek Technology Corporation. All rights reserved.
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RT8509A
Outline Dimension
2
1
2
1
DETAILA
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.
0.700
0.000
0.175
0.200
4.900
4.250
4.900
3.650
Max.
0.800
0.050
0.250
0.300
5.100
4.350
5.100
3.750
Min.
0.028
0.000
0.007
0.008
0.193
0.167
0.193
0.144
Max.
0.031
0.002
0.010
0.012
0.201
0.171
0.201
0.148
A
A1
A3
b
D
D2
E
E2
e
0.800
0.031
L
0.350
0.450
0.014
0.018
W-Type 12L DFN 5x5 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st 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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