RT8458A [RICHTEK]
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| 型号： | RT8458A |
| 厂家： | 
RICHTEK TECHNOLOGY CORPORATION |
| 描述： | 暂无描述 功率因数校正 |
| 文件： | 总13页 (文件大小：256K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
®
RT8458A
High Efficiency PWM Buck LED Driver Controller
General Description
Features
Low Cost and Efficient Buck Converter Solution
Universal Input Voltage Range with Off-Line
Topology
The RT8458Ais a PWM controller with an integrated high
side gate driver. It is used for step down converters by
well controlling the external MOSFET and regulating a
constant output current. The output duty cycle of the
RT8458A can be up to 100% for wider input voltage
application, such as E27 and PAR30 off-line LEDlighting
products.
Programmable Constant LED Current
Dimmable LED Current by ACTL
Output LED String Open Protection
Output LED String Short Protection
Output LED String Over Current Protection
Built-in Thermal Protection
The RT8458A also features a 47kHz fixed frequency
oscillator, an internal −220mV precision reference, and a
PWM comparator with latching logic. The accurate output
LEDcurrent is achieved by an averaging current feedback
loop and the LEDcurrent dimming can be easily controlled
via theACTL pin. The RT8458Aalso has multiple features
to protect the controller from fault conditions, including
Under Voltage Lockout (UVLO), Over Current Protection
(OCP) and Over Voltage Protection (OVP). Additionally,
to ensure the system reliability, the RT8458A is built with
the thermal protection function.
TSOT-23-6 Package
RoHS Compliant and Halogen Free
Applications
E27, PAR30, Offline LED Lights
Marking Information
07= : Product Code
07=DNN
DNN : Date Code
The RT8458A is housed in a TSOT-23-6 package. Thus,
the components in the whole LED driver system can be
made very compact.
Simplified Application Circuit
V
IN
C
IN
R
R
VCC1
VCC2
D2
RT8458A
Analog
Dimming
VCC
ACTL
C
VCC
VC
GATE
Q1
R
VC
C
GND
VC2
SENSE
C
VC1
L1
R
S
LED+
LED-
C
OUT
D1
Copyright 2014 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8458A-09 August 2014
www.richtek.com
1
RT8458A
Ordering Information
Pin Configurations
RT8458A
(TOP VIEW)
Package Type
J6 : TSOT-23-6
SENSE
VC ACTL
6
5
2
4
3
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
VCC GND GATE
TSOT-23-6
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.
Functional Pin Description
Pin No.
Pin Name
Pin Function
Supply Voltage Input of the Chip. For good bypass, a ceramic capacitor near the
VCC pin is required.
1
VCC
2
3
GND
Ground of the Chip.
GATE
Gate Driver Output for External MOSFET Switch.
Analog Dimming Control Input. The effective dimming range is between 0.1V to
1.2V. If VACTL is greater than 1.2V, the ACTL dimming signal high is internally
clamped around 1.3V. If dimming is not used, a pull up resistor or a voltage holding
capacitor between ACTL and GND pins should be used.
4
ACTL
5
6
VC
PWM Loop Compensation Node.
LED Current Sense Input. The Typical sensing threshold is 220mV between the
SENSE and GND pin.
SENSE
Copyright 2014 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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2
DS8458A-09 August 2014
RT8458A
Function Block Diagram
+
VREF
12V
Chip Enable
+
-
17V/8V
47kHz
OSC
S
R
R
OVP
GATE
GND
VCC
+
200k
35V
-
CCOMP
Control
Circuit
VC
-
+
SENSE
ACTL
OTP
-220mV
Dimming
OP1
Operation
The RT8458A is a Buck PWM current mode controller
with an integrated high side gate driver. The start up voltage
of RT8458A is around 17V. Once VCC is above 17V,
RT8458A will maintain operation until VCC drops below
8V.
in each OSC cycle. The GATE turns low until the current
comparator (CCOMP) resets the gate driver. The GATE
will be set high again by OSC and the next switching
cycle repeats.
The adjustment of the regulated sense current threshold
(dimming) can be achieved by varying ACTL pin voltage.
The typical range ofACTL voltage adjustment is between
0.1V and 1.2V.
The RT8458A's main control loop consists of a 47kHz
fixed frequency oscillator, an internal −220mV precision
current sense threshold OPAMP (OP1), and a PWM
comparator (CCOMP) with latching logic. In normal
operation, the GATE turns high when the gate driver is
set by the oscillator (OSC). The lower the average of the
sensed current is below the loop-regulated −220mV
threshold, the higher the VC pin voltage (OP1 output) will
go high. Higher the VC voltage means longer the GATE
turn-on period. The GATE of RT8458A can turn on more
than 100% duty. It is not always that the GATE turns low
The RT8458A is equipped with protection from several fault
conditions, including input voltage Under Voltage Lockout
(UVLO), Over Current Protection (OCP) and VIN/VOUT
Over Voltage Protection (OVP). Additionally, to ensure
the system reliability, the RT8458A is built with internal
thermal protection function.
Copyright 2014 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8458A-09 August 2014
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3
RT8458A
Absolute Maximum Ratings (Note 1)
Supply Input Voltage, VCC---------------------------------------------------------------------------------------------- −0.3V to 40V
GATE Voltage (Note 8) ------------------------------------------------------------------------------------------------- −0.3V to 17V
ACTL Voltage (Note 6) ------------------------------------------------------------------------------------------------- −0.3V to 8V
VC Voltage ------------------------------------------------------------------------------------------------------------------ −0.3V to 6V
SENSE Voltage ------------------------------------------------------------------------------------------------------------ −1V to 0.3V
PowerDissipation, PD @ TA = 25°C
TSOT-23-6 ------------------------------------------------------------------------------------------------------------------- 0.392W
Package Thermal Resistance (Note 2)
TSOT-23-6, θJA ------------------------------------------------------------------------------------------------------------- 255°C/W
TSOT-23-6, θJC ------------------------------------------------------------------------------------------------------------- 135°C/W
Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°C
Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model)---------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 4)
Supply Input Voltage, VCC---------------------------------------------------------------------------------------------- 17V to 31V
Junction Temperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C
Electrical Characteristics
(VCC = 24VDC, TA = 25°C, unless otherwise specified)
Parameter
Symbol
VST
Test Conditions
Min
Typ
Max
Unit
Input Start-Up Voltage
--
17
19
V
Minimum Operation Voltage
After Start-Up
VIN(MIN)
--
8
9
V
Maximum ICC to cause VCC stop
hiccup at low end of VCC hysteresis
level
Maximum Startup Current in
VCC Hiccup Operation
IST(MAX)
--
250
300
A
Input Supply Current
Input Shutdown Current
Oscillator
ICC
IQC
After Start-Up, VCC = 24V
Before Start-Up, VCC = 5V
--
--
2
1
5
5
mA
A
Switching Frequency
fSW
38
--
47
--
56
kHz
%
Maximum Duty in Transient
Operation
DMAX(TR)
VC = 3V
100
Maximum Duty in Steady
State Operation
DMAX
--
97
--
%
Blanking Time
tBLANK
(Note 7)
(Note 7)
--
--
300
600
--
--
ns
ns
Minimum Off Time
tOff(MIN)
Copyright 2014 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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DS8458A-09 August 2014
RT8458A
Parameter
Current Sense Amplifier
Current Sense Voltage
Sense Input Current
VC Sourcing Current
VC Sinking Current
Symbol
Test Conditions
Min
Typ
Max
Unit
VSENSE
ISENSE
(Note 5)
(Note 7)
213 220 227
mV
A
A
A
V
--
--
--
11
20
--
--
--
IVC_Source VSENSE = 150mV (Note 7)
IVC_Sink
VSENSE = 250mV (Note 7)
180
VC Threshold for PWM Switch Off VVC
1.15 1.25 1.35
GATE Driver Output
GATE Pin Maximum Voltage
VGATE
VGATE_H
No Load at GATE Pin
--
10.5 12.1
-- 12.5
0.01 0.75
12.6
16
14
V
V
I
GATE = 50mA
IGATE = 100A
GATE = 50mA
GATE Voltage High
--
I
1.2
--
GATE Voltage Low
VGATE_L
V
IGATE = 100A
--
--
--
--
--
0.5
60
GATE Drive Rise Time
1nF Load at GATE
1nF Load at GATE
1nF Load at GATE
1nF Load at GATE
150
100
0.5
0.8
ns
ns
A
GATE Driver Fall Time
30
GATE Drive Source Peak Current
GATE Driver Sink Peak Current
LED Dimming
0.25
0.5
A
Analog Dimming ACTL Pin Input
Current
IACTL
VACTL = 1.2V
--
--
--
1
5
A
V
LED Current On Threshold at
ACTL
VACTL_On
VACTL_Off
1.2
0.1
1.3
0.2
LED Current Off Threshold at
ACTL
V
OVP
Over Voltage Protection
Thermal Protection
Thermal Shutdown Temperature
VOVP
VCC Pin
32
--
35
38
--
V
TSD
150
C
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. 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.
Note 5. The RT8458A achieves precise LED average current with a current feedback loop to sense the average LED current, in
the deep discontinuous mode operation especially when a small inductor is used small current offset might occur
due to current waveform distortion of the nature of the discontinuous operation. This offset current is consistent over
production.
Note 6. If a 1MΩ resistor is connected between the control input and ACTL pin, the control input voltage can be up to 36V.
Note 7. Guaranteed by design, not subjected to production test.
Note 8. The GATE voltage is internally clamped and varies with operating conditions.
Copyright 2014 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8458A-09 August 2014
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5
RT8458A
Typical Application Circuit
V
MAIN
V
IN
C
IN
R
1M
VCC1
10µF/
400V
R
511k
VCC2
D2
FR107
R
B
10
R
1M
ACTL
RT8458A
VCC ACTL
4
3
1
C
VCC
4.7µF
R
22R
G
5
2
GATE
VC
Q1
ZD1 short
Optional
Optional
Optional
R
VC
C
GND
10k
VC2
6
SENSE
C
1nF
VC1
L1
3.3nF
R
S
0.63
680µH
LED+
ZD2 39V
Optional
LED-
C
D1
ES1J
OUT
220µF/50V
V
V
: 85V to 264V
IN_AC
: 30V
OUT
I
: 350mA
OUT
Copyright 2014 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
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6
DS8458A-09 August 2014
RT8458A
Typical Operating Characteristics
Efficiency vs. Input Voltage
Efficiency vs. Number of LED
100
100
85VAC
10LED
9LED
8LED
7LED
110VAC
150VAC
180VAC
220VAC
264VAC
95
95
90
90
85
85
80
80
6LED
5LED
4LED
3LED
75
75
VIN_AC = 85V to 264V,
IOUT = 350mA, LED3 to LED10 pcs
VIN_AC = 85V to 264V,
IOUT = 350mA, LED3 to LED10 pcs
70
70
85 105 125 145 165 185 205 225 245 265
Input Voltage (V)
3
4
5
6
7
8
9
10
Number of LED (pcs)
LED Current vs. Output Voltage
LED Current vs. Input Voltage
400
350
300
250
200
150
100
50
400
380
360
340
320
300
IOUT = 350mA (L = 0.68mH)
IOUT = 250mA (L = 1.5mH)
IOUT = 100mA (L = 3.3mH)
VIN_AC = 110V, IOUT = 350mA, LED3 to LED10 pcs
VIN_AC = 85V to 264V, LED10 pcs
0
85 105 125 145 165 185 205 225 245 265
Input Voltage (V)
0
4
8
12
16
20
24
28
32
36
Output Voltage (V)
SENSE Threshold vs. Input Voltage
SENSE Threshold vs. Temperature
220
218
216
214
212
210
208
206
204
202
200
230
225
220
215
210
205
200
IOUT = 350mA (L = 0.68mH)
IOUT = 250mA (L = 1.5mH)
IOUT = 100mA (L = 3.3mH)
VIN_AC = 85V to 264V, LED10 pcs
85 105 125 145 165 185 205 225 245 265
Input Voltage (V)
-50
-25
0
25
50
75
100
125
Temperature (°C)
Copyright 2014 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8458A-09 August 2014
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7
RT8458A
Switching Frequency vs. VCC
Switching Frequency vs. Temperature
55
51
47
43
39
35
55
51
47
43
39
35
0
4
8
12
16
20
24
28
32
36
-50
-25
0
25
50
75
100
125
VCC (V)
Temperature (°C)
SENSE Threshold vs. ACTL Voltage
Input and Output Current
250
200
150
100
50
VIN
(400V/Div)
IIN
(1A/Div)
VOUT
(50V/Div)
IOUT
VIN_AC = 264V, IOUT = 350mA,
LED 10 pcs, L = 0.68mH
(500mA/Div)
0
0
0.5
1
1.5
2
2.5
3
Time (25ms/Div)
ACTL Voltage (V)
Power On
Power Off
VIN
VIN
(400V/Div)
(400V/Div)
VOUT
VOUT
(20V/Div)
(20V/Div)
IOUT
(500mA/Div)
IOUT
(500mA/Div)
VIN = 264VAC,
IOUT = 350mA, LED 10 pcs, L = 0.68mH
VIN = 264VAC,
IOUT = 350mA, LED 10 pcs, L = 0.68mH
Time (25ms/Div)
Time (25ms/Div)
Copyright 2014 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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DS8458A-09 August 2014
RT8458A
Application Information
Start-up Resistor
The RT8458A is a high efficiency PWM Buck LED driver
controller for high brightness LEDapplication. Its high side
floating gate driver is used to control the Buck converter
via an external MOSFET and regulate the constant output
current.
Start-up resistor should be chosen not to exceed the
maximum start-up current. Otherwise, the RT8458A may
latch low and will never start. Start-up current = 130V/R1
for 110VAC regions, 260V/R1 for 220VAC regions. The
typical start-up current is 250μA.
The RT8458Acan achieve high accuracy LEDoutput current
via the average current feedback loop control. The internal
sense voltage (−220mV typ.) is used to set the average
output current. The oscillator’s frequency is fixed at
47kHz to get better switching performance. Once the
average current is set by the external resistor, RS, the
output LED current can be dimmed by varying the ACTL
voltage.
Input Diode Bridge Rectifier Selection
The current rating of the input bridge rectifier is dependent
on the VOUT /VIN transformation ratio. The voltage rating of
the input bridge rectifier, VBR, on the other hand, is only
dependent on the input voltage. Thus, the VBR rating is
calculated as below :
VBR = 1.2( 2 VAC(MAX)
)
Under Voltage Lockout (UVLO)
where VAC,Max is the maximum input voltage (RMS) and
the parameter 1.2 is used for safety margin.
The RT8458A includes a UVLO feature with 9V hysteresis.
TheGATE terminal turns on when VIN rises over 17V (typ.).
TheGATE terminal turns off when VIN falls below 8V (typ.)
For this example :
VBR = 1.2( 2 VAC(MAX)) = (1.2 2 110) = 187V
Setting Average Output Current
If the input source is universal, VBR will reach 448V. In
this case, a 600V, 0.5A bridge rectifier can be chosen.
The output current that flows through the LED string is
set by an external resistor, RS, which is connected between
theGNDand SENSE pins. WithACTL pin voltage greater
Input Capacitor Selection
than 1.2V, the relationship between output current, IOUT
,
The input capacitor supplies the peak current to the
inductor and flattens the current ripple on the input. The
low ESR condition is required to avoid increasing power
loss. The ceramic capacitor is recommended due to its
excellent high frequency characteristic and low ESR. For
maximum stability over the entire operating temperature
range, capacitors with better dielectric are suggested. The
minimum capacitor is given by :
and RS is shown below :
0.22
IOUT
=
(A)
RS
Analog Dimming Control
TheACTL terminal is driven by an external voltage, VACTL
,
to adjust the output current to an average value set by RS.
The voltage range for VACTL to adjust the output current is
from 0.1V to 1.2V. For VACTL between 0.1V to 1.2V, the
output current value will be determined by the following
formula :
V
I
OUT(MAX) OUT(MAX)
C
IN
2
2
( 2 V
) V
f
AC
AC(MIN)
DC(MIN)
where fAC is the AC input source frequency and η is the
efficiency of the whole system.
VACTL 0.1
IOUTavg = (0.22V/RS )
1.1
Notice that VDC(MIN) is the minimum voltage at bridge
rectifier, output and VDC(MIN) should be larger than 2 x
Component Selection
For component selection, an example is shown below for
a typical RT8458Aapplication, where VIN = 110 to 90VAC/
60Hz, LED output voltage = 30V, and output current =
200mA. The user can follow this procedure to design
applications with wider AC voltage input and DC output
voltage as well.
VOUT(MAX)
.
For a 90 to 264VAC universal input range, the VDC(MIN) is
90V, therefore the LEDstring voltage VOUT(MAX) should be
less than 45V.
Copyright 2014 Richtek Technology Corporation. All rights reserved.
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9
RT8458A
For this particular example :
current and the diode reverse voltage rating should be
greater than 1.2 times the maximum input voltage,
assuming a 20% output current ripple.
300.2
CIN
= 13.7μF
2
2
( 2 90) 90 0.960
The peak voltage stress of diode is :
In addition, the voltage rating of the input filter capacitor,
VCIN, should be large enough to handle the input
voltage.
VD = 1.2( 2 VAC(MAX)) = 1.2( 2 110) = 187V
The current rating of diode is :
VCIN (1.2 2 VAC(MAX)) = (1.2 2 110) = 187V
ID = 1.2IOUT,PK = 1.21.20.2 = 0.288A
If the input source is universal (VIN = 90V to 264V), VD will
reach 448V. A 600V, 2A ultra-fast diode can be used in
this example.
Thus, a 22μF / 250V electrolytic capacitor can be chosen
in this case.Due to its large ESR, the electrolytic capacitor
is not suggested for high current ripple applications.
MOSFET Selection
Inductor Selection
The peak current through this MOSFET will be over the
maximum output current. This component current rating
should be greater than 1.2 times the maximum load
current and the reverse voltage rating of the MOSFET
should be greater than 1.2 times the maximum input
voltage, assuming a 20% output current ripple.
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current, ΔIL, increases with higher VIN
and decreases with higher inductance, as shown in
equation below :
V
VOUT
V
OUT
IL
1
f x L
The peak voltage rating of the MOSFET is :
IN
To optimize the ripple current, the RT8458Aoperates the
Buck converter in BCM (Boundary-Condition Mode). The
largest ripple current will occur at the highest VIN. To
guarantee that the ripple current stays below the specified
value, the inductor value should be chosen according to
the following equation :
VQ = 1.2( 2 VAC(MAX)) = 1.2( 2 110) = 187V
The current rating of MOSFET is :
IQ = 1.2IOUT,PK = 1.21.20.2 = 0.288A
If the input source is universal (VIN = 90V to 264V), VQ
will reach 448V. A 600V, 2A N-MOSFET can be chosen
for this example.
VOUT TS (1D)
L =
2IOUT
3020.83μs(10.333)
Output Capacitor Selection
=
= 1.04mH
20.2
The selection of COUT is determined by the required ESR
to minimize output voltage ripple. Moreover, the amount
of bulk capacitance is also a key for COUT selection to
ensure that the control loop is stable. Loop stability can
be checked by viewing the load transient response. The
output voltage ripple, ΔVOUT, is determined by :
where D is the duty cycle and TS is the switching period.
Forward Diode Selection
When the power switch turns off, the path for the current
is through the diode connected between the switch output
and ground. This forward biased diode must have minimum
voltage drop and recovery time. The reverse voltage rating
of the diode should be greater than the maximum input
voltage and the current rating should be greater than the
maximum load current.
1
VOUT IL ESR
8fOSCCOUT
where fOSC is the switching frequency and ΔIL is the
inductor ripple current. The output voltage ripple will be
the highest at the maximum input voltage since ΔIL
increases with input voltage. Multiple capacitors placed in
parallel may be needed to meet the ESR and RMS current
handling requirement. Dry tantalum, special polymer,
In reality, the peak current through the diode is more than
the maximum output current. This component current
rating should be greater than 1.2 times the maximum load
Copyright 2014 Richtek Technology Corporation. All rights reserved.
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10
DS8458A-09 August 2014
RT8458A
aluminum electrolytic and ceramic capacitors are all
common selections and available in surface mount
packages. Tantalum capacitors have the highest
capacitance density, but it is important to only use ones
that pass the surge test for use in switching power
supplies. Special polymer capacitors offer very low ESR
value, but with the trade-off of lower capacitance density.
Aluminum electrolytic capacitors have significantly higher
ESR, but still can be used in cost-sensitive applications
for ripple current rating and long term reliability
considerations.
TSOT-23-6 package, the thermal resistance, θJA, is 255°C/
W on a standard JEDEC 51-3 single-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) / (255°C/W) = 0.392W for
TSOT-23-6 package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curve in Figure 1 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
0.45
Thermal Protection
Single-Layer PCB
0.40
A thermal protection feature is included to protect the
RT8458Afrom excessive heat damage. When the junction
temperature exceeds a threshold of 150°C, the thermal
protection will turn off the GATE terminal.
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Soldering Process of Pb-free Package Plating
To meet the current RoHS requirements, pure tin is
selected to provide forward and backward compatibility
with both the current industry standard SnPb-based
soldering processes and higher temperature Pb-free
processes. In the whole Pb-free soldering processes pure
tin is required with a maximum 260°C (<10s) for proper
soldering on board, referring to J-STD-020 for more
information.
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum PowerDissipation
Layout Considerations
Thermal Considerations
For best performance of the RT8458A, the following layout
guidelines should be strictly followed.
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 :
The hold up capacitor, CVCC, must be placed as close
as possible to the VCC pin.
The output capacitor, COUT, must be placed as close as
possible to the LED terminal.
The powerGNDshould be connected to a strong ground
plane.
PD(MAX) = (TJ(MAX) − TA) / θJA
RS should be connected between the GND pin and
where TJ(MAX) is the maximum junction temperature, TAis
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
SENSE pin.
Keep the main current traces as short and wide as
possible.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
Place L1, Q1, RS, and D1 as close to each other as
possible.
Copyright 2014 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8458A-09 August 2014
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RT8458A
Place the compensation
components as close as
possible to the IC.
V
MAIN
R
R
VCC1
VCC2
Power GND
C
VC1
R
VC
R
ACTL
C
VC2
C
ACTL
SENSE VC ACTL
6
5
2
4
3
VCC
D2
R
B
R
G
Q1
D1
VCC GND GATE
L1
R
C
S
VCC
LED+
SENSE
Analog GND
C
OUT
LED-
Power GND
Place the capacitor
as close as
Narrow trace to avoid
the switching noise.
Place the output capacitor
C as close as possible
OUT
C
VCC
possible to the VCC pin.
to LED terminal.
Figure 2. PCB Layout Guide
Copyright 2014 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
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12
DS8458A-09 August 2014
RT8458A
Outline Dimension
H
D
L
C
A
B
b
A1
e
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
1.000
0.100
1.803
0.559
3.000
3.099
1.041
0.254
0.610
Min
Max
A
A1
B
0.700
0.000
1.397
0.300
2.591
2.692
0.838
0.080
0.300
0.028
0.000
0.055
0.012
0.102
0.106
0.033
0.003
0.012
0.039
0.004
0.071
0.022
0.118
0.122
0.041
0.010
0.024
b
C
D
e
H
L
TSOT-23-6 Surface Mount 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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13
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