®
RT8540
1.5A Flash LED Driver with I2C Compatible Interface
General Description
Features
The RT8540 is a high efficiency synchronous Boost
converter capable of delivering up to 1.5A maximum output
current. It is an ideal power solution for up to three LEDs
photoflash applications in all single-cell Lithium-ion/
polymer battery powered products.
Input Voltage Range : 2.5V to 5.5V
Three Flash LED Channel Output
Operational Modes
Torch Mode and Flash Strobe
Voltage Regulation Converter with Down Output
Voltage Mode
Shutdown Mode
Up to 1.5A Regulated Output Current
Up to 85% Efficiency with Small Magnetics at
Current Regulation
2MHz Switching Frequency
Dual Wire Camera Module Interface
Tx-MASK Input to Inhibit Flash operation
Shutdown Current < 1μ
μA
2
I C Setting Torch Mode Current Level
I2C Setting Flash Mode Current Level
I2C Setting Safety Timer
Over-Voltage (Open LED), Over-Current (Short
Circuit), and Over-Temperature Protection
Flash Current Optimization with VBAT
LED Temperature Monitoring
I2C Compatible Interface up to 3.4Mbits/s
GPIO and Power Good Output
Privacy Indicator LED Output
Hardware Reset Input
RoHS Compliant and Halogen Free
The RT8540 maintains output current regulation by
switching the internal high-side and low-side switch
transistors. The transistor switches are pulse width
modulated at a fixed frequency of 2MHz. The high switching
frequency allows the use of a small inductor and output
capacitor, making the RT8540 ideally suited for small
battery powered applications. The RT8540 also includes
STRB0, STRB1, Tx-MASK input to simplify torch and flash
synchronization with the camera module. The default timer
can be used to terminate a flash event after a user
programmed delay or as a safety feature. The device
automatically optimizes the LED flash current budget with
the battery voltage condition as a feature.
The RT8540 not only operates as a regulated current
source, but also as a voltage Boost regulator with the
capability of down output voltage mode. The RT8540
contains over-voltage protection, over-current protection
and a thermal management system to protect the device.
The shutdown feature reduces shutdown current to less
than 1μA. The RT8540 is available in the tiny WL-CSP20B 1.82x2.22 (BSC) package to achieve best solution
for PCB space and total BOM cost saving.
Simplified Application Circuit
L
VBAT
2.5V to 5.5V
VIN
CIN1
NTC
TS
PGND
AGND
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8540-00
December 2013
VOUT
SW
RT8540
COUT
LED1
LED2
LED3
INDLED
LED1 LED2 LED3
Privacy
Indicator
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1
RT8540
Applications
Single/Dual/Triple White LED Flash Supply for Cell
Phones, Smart Phones, Tablet PC, Digital Cameras and
other 3C productions
Video Lighting for Digital Video Applications
General LED Lighting Applications
Pin Configurations
(TOP VIEW)
Ordering Information
RT8540
Package Type
WSC : WL-CSP-20B 1.82x2.22 (BSC)
A1
INDLED
B1
SDA
A2
A3
A4
VOUT
AGND
AGND
B2
B3
B4
SCL NRESET STRB0
C1
C2
SW
SW Tx-MASK
C3
D1
D2
D3
LED2
LED1
LED3
C4
TS
D4
PGND PGND STRB1 GPIO/
PGOOD
E1
E2
E3
E4
VIN
WL-CSP-20B 1.82x2.22 (BSC)
Note :
Richtek products are :
RoHS compliant and compatible with the current require-
Suitable for use in SnPb or Pb-free soldering processes.
ments of IPC/JEDEC J-STD-020.
Marking Information
0P : Product Code
0PW
W : Date Code
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is a registered trademark of Richtek Technology Corporation.
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RT8540
Functional Pin Description
Pin No.
Pin Name
Pin Function
A1
INDLED
Constant Current Source Output. This pin provides a constant current source to
drive low VF LEDs. Connect to LED anode.
A2
VOUT
Output of Boost Converter. Connect a 10F or larger ceramic capacitor from
VOUT to ground as close as possible to IC.
A3, A4
AGND
Analog Ground.
B1
SDA
Serial Interface Address/Data Input. This pin must not be left floating and must
be terminated.
B2
SCL
Serial Interface Clock Input. This pin must not be left floating and must be
terminated.
NRESET
Master Hardware Reset Input.
2
NRESET = LOW : The device is forced to shutdown mode. The I C control I/F
and all internal control registers will be reset.
NRESET = HIGH : The device operates normally.
STRB0
LED1/2/3 Enable Control Input. This pin can be used to enable/disable the high
power LEDs connected to the device.
STRB0 = LOW : LED1, LED2 and LED3 current regulators are turned off.
STRB0 = HIGH : LED2, LED2 and LED3 current regulators are active. The
LED current level (video light or flash current) is defined according to the
STRB1 logic level.
SW
Switch Node of Boost Converter. Connect an inductor between SW and VIN.
C3
Tx-MASK
LED Flash Inhibit Control Input. Pulling this pin high turns the LED from flash to
video light operation, thereby reducing almost instantaneously the peak current
loading from the battery.
C4
TS
NTC Resistor Connection. This pin can be used to monitor the LED
temperature. Connect a 220k NTC resistor from the TS to ground. If this
function is not used, the TS pin should be tied to VIN or left floating.
PGND
Power Ground. Connect PGND to AGND underneath IC. The exposed pad
must be soldered to a large PCB and connected to GND for maximum power
dissipation.
D3
STRB1
LED Current Level Selection Input. Pulling this input high disables the video
light watchdog timer.
STRB1 = LOW : flash mode is enabled.
STRB1 = HIGH : video light mode is enabled.
D4
GPIO/PGOOD
GPIO Input or Power Good Indicator.
E1
LED2
Current Source of LED Channel 2.
E2
LED1
Current Source of LED Channel 1.
E3
LED3
Current Source of LED Channel 3.
E4
VIN
Power Input. Connect Battery to the input power supply voltage. Connect a
4.7F or larger ceramic capacitor from VIN to ground as close as possible to
the IC.
B3
B4
C1, C2
D1, D2
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8540-00
December 2013
is a registered trademark of Richtek Technology Corporation.
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RT8540
Function Block Diagram
VOUT
VIN
UVLO
2MHz
Oscillator
BG
VIN Droop
Comparator
VIN
OVP
Well
Controller
+
EA
-
COMP
+
PWM
Logic
/Driver
SW
AGND
OCP
SDA
STRB0
STRB1
Tx-MASK
NRESET
TS
PGND
ISENSE
SCL
Logic
Controller
LED
Temperature
Monitor
Hot Die
Indicator
LED1
LED2
LED3
Analog
MUX
DACs
Low-Dropout N-MOSFET
Current Source
INDLED Current Source
GPIO/PGOOD
INDLED
GPIO/
PGOOD
Operation
The RT8540 is a high efficiency synchronous Boost
converter capable of delivering up to 1.5A maximum output
current, and it maintains output current regulation by
switching the internal high-side and low-side switch
transistors. The transistor switches are pulse width
modulated at a fixed frequency of 2MHz. The RT8540 also
includes STRB0, STRB1, Tx-MASK input to simplify torch
and flash synchronization with the camera module. The
RT8540 is designed for one, two or three LEDs driving for
torch and flash application, it provides an I2C software
command or dedicated zero latency hardware signals to
trigger the torch and flash operation. The OVP function
prevents the RT8540 from damaging while open-LED or
open-circuit condition is occurred.
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is a registered trademark of Richtek Technology Corporation.
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RT8540
Absolute Maximum Ratings
(Note 1)
Supply Voltage, VIN ------------------------------------------------------------------------------------------------------Boost Output Voltage, VOUT -------------------------------------------------------------------------------------------Switch Node Voltage, SW -----------------------------------------------------------------------------------------------Current Source Voltage, LED1, LED2, LED3, INDLED -----------------------------------------------------------Other Pins, STRB0, STRB1, SCL, SDA, Tx-MASK, TS, GPIO/PGOOD ------------------------------------Power Dissipation, PD @ TA = 25°C
WL-CSP-20B 1.82x2.22 (BSC) ----------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WL-CSP-20B 1.82x2.22 (BSC), θJA -----------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) -----------------------------------------------------------------------------------------------------CDM (Charge Device Model) ---------------------------------------------------------------------------------------------
Recommended Operating Conditions
−0.3V to 6.5V
−0.3V to 6.5V
−0.3V to 6.5V
−0.3V to 6.5V
−0.3V to 6V
2.72W
36.7°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
500V
(Note 4)
Input Voltage, VIN ---------------------------------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3.7V, CIN = 4.7μF, COUT = 10μF, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
2.3
2.4
V
--
590
700
A
--
1
5
A
VIN
--
5.5
--
5.7
--
2
Power Supply
Under-Voltage Lockout
VUVLO
VIN Quiescent Current
IQ
VIN Shutdown Current
ISD
IOUT = 0mA, no switching (Voltage
regulation mode)
Output
Current Regulation Mode
Output Voltage Range
VOUT
Internal Feedback Voltage
Accuracy
VFB
Output Over-Voltage
Protection (OVP)
VOVP
OVP Hysteresis
VOVP_HYS VOUT Falling
Voltage Regulation Mode
3.825
2.5V < VIN < 4.8V, Boost mode, PWM
2
voltage regulation
VOUT Rising, 0000 OV [3:0] 0100
4.5
4.65
4.8
VOUT Rising, 0101 OV [3:0] 1111
5.8
6
6.2
--
150
--
0mA I LED1/3 100mA
10
--
10
100mA ILED1/3 400mA
7.5
--
7.5
10
--
10
V
%
V
mV
Current Source of LED Current
LED1/3 Current Accuracy
ILED1/3
LED1/3 Current Matching
IMAT
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December 2013
%
%
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RT8540
Parameter
Symbol
LED2 Current Accuracy
ILED2
INDLED Current Accuracy
IIND
Test Conditions
Min
Typ
Max
Unit
0mA I LED2 250mA
10
--
10
250mA I LED2 800mA
7.5
--
7.5
1.5V (V IN V INDLED) 2.5V,
2.6mA IIND 15.8mA
20
--
20
%
--
0.05
--
%/C
--
0.05
--
%/C
%
LED1/2/3 Current Temperature
Coefficient
INDLED Current Temperature
Coefficient
LED1/2/3 Sense Voltage
VSEN
LED1/2/3 = Full-Scale Current
--
300
--
mV
LED1/2/3 Input Leakage Current
ILED_LKG
VLED1/2/3 = 5V
--
0.1
4
A
INDLED Input Leakage Current
IIND_LKG
VINDLED = 0V
--
0.1
1
A
LED1 Start-Up Current
IST1
55
--
--
A
LED2 Start-Up Current
IST2
55
--
--
A
LED3 Start-Up Current
IST3
55
--
--
A
1.8
2
2.2
MHz
10
--
--
s
LED Forward Voltage (VOUT
VLED1) < 1V
LED Forward Voltage (VOUT
VLED2) < 1V
LED Forward Voltage (VOUT
VLED3) < 1V
Oscillator and Timer
Operating Frequency
FOSC
Reset Pulse Width
tNRESET
Flash Mode
Power Switch
N-MOSFET RON
NRON
VOUT = 3.6V
--
75
--
m
P-MOSFET RON
PRON
VOUT = 3.6V
--
95
--
m
Leakage into SW
ILKG_SW
VOUT = 0V, SW = 3.6V
--
0.3
4
A
VOUT = 4.95V, ILIM = 0
--
1650
--
mA
VOUT = 4.95V, ILIM = 1
--
2150
--
mA
140
160
--
C
--
20
--
C
Thermistor Bias Current
--
23.8
--
A
LEDWARN bit = 1
39
44.5
50
k
12.5
14.5
16.5
k
VIH
1.2
--
--
VIL
--
--
0.4
-VIN
0.4
--
0.3
--
--
--
--
0.3
--
400
--
Protection Function
Current Limit
IOCP
Thermal Shutdown Threshold
TSD
TSD_HYS
Thermal Shutdown Hysteresis
Temperature Sense Current Source
TS Resistance (Warning
Temperature)
IO_TS
TS Resistance (Hot Temperature)
Logic Control
SCL, SDA,
High-Level
GPIO/PGOOD, STRB0,
STRB1, Tx-MASK,
Low-Level
NRESET Input Voltage
SDA Low-Lev el Output Voltage
GPIO Output Voltage
LEDHOT bit = 1
V
VOL_SDA
High-Level
VOH_GPIO
Low-Level
VOL_GPIO DIR = 1, IOL = 5mA
STRB0, STRB1, NRESET, Tx-MASK
RPD
Pull-Down Resistance
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IOL = 8mA
DIR = 1, GPIOTYPE = 0,
IOH = 8mA
STRB0, STRB1, NRESET,
Tx-MASK < 0.4V
V
V
k
is a registered trademark of Richtek Technology Corporation.
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RT8540
I2C Interface Timing Characteristics (1)
Parameter
Symbol
SCL Clock Frequency
fSCL
Bus Free Time Between a
STOP and START Condition
tBUF
Hold Time (Repeated) START
tHD, tSTA
Condition
LOW Period of the SCL Clock tLOW
HIGH Period of the SCL Clock tHIGH
Setup Time for a Repeated
START Condition
tSU, tSTA
Data Setup Time
tSU, tDAT
Data Hold Time
tHD, tDAT
Test Conditions
Min
Typ
Max
Standard mode
--
--
100
Fast mode
--
--
400
Standard mode
4.7
--
--
Fast mode
1.3
--
--
4
--
--
s
Fast mode
600
--
--
ns
Standard mode
4.7
--
--
Fast mode
1.3
--
--
4
--
--
s
Fast mode
600
--
--
ns
Standard mode
4.7
--
--
s
Fast mode
600
--
--
ns
Standard mode
250
--
--
Fast mode
100
--
--
Standard mode
0
--
3.45
Fast mode
0
--
0.9
--
1000
Standard mode
Standard mode
Standard mode
Rising Time of SCL Signal
tRCL
Fast mode
Rising Time of SCL Signal
After a Repeated START
Condition and After an
Acknowledge BIT
tRCL1
Falling Time of SCL Signal
tFCL
Standard mode
Fast mode
Standard mode
Fast mode
Standard mode
Rising Time of SDA Signal
tRDA
Fast mode
Standard mode
Falling Time of SDA Signal
tFDA
Fast mode
Setup Time for STOP
Condition
tSU, tSTO
Capacitive Load for SDA and
SCL
CB
Standard mode
Fast mode
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
20 +
0.1CB
Unit
kHz
s
s
ns
s
ns
--
300
--
1000
ns
--
300
--
300
ns
--
300
--
1000
ns
--
300
--
300
ns
--
300
4
--
--
s
600
--
--
ns
--
--
400
pF
(1) Specified by design. Not tested in production.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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RT8540
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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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is a registered trademark of Richtek Technology Corporation.
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RT8540
Typical Application Circuit
L
2.2µH
VBAT
2.5V to 5.5V
VOUT
SW
RT8540
CIN1
4.7µF
CIN2
Option
VIN
LED1
LED2
LED3
NTC
2
I C
TS
INDLED
STRB0
GPIO/
PGOOD
STRB1
SCL
Tx-MASK
SDA
NRESET
PGND
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COUT
10µF
LED1 LED2 LED3
Privacy
Indicator
AGND
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RT8540
Typical Operating Characteristics
LED Power Efficiency vs. Input Voltage
100
90
90
80
80
70
70
60
Efficiency (%)
Efficiency (%)
LED Power Efficiency vs. Input Voltage
100
ILED2 = 800mA
ILED2 = 400mA
ILED2 = 200mA
ILED2 = 150mA
ILED2 = 100mA
ILED2 = 75mA
50
40
30
60
ILED1 = ILED3 = 350mA, ILED2 = 600mA
ILED1 = ILED3 = 250mA, ILED2 = 550mA
ILED1 = ILED3 = 100mA, ILED2 = 200mA
ILED1 = ILED3 = 50mA, ILED2 = 100mA
50
40
30
20
20
10
10
0
0
2.5
3
3.5
4
4.5
5
2.8
5.5
3.25
LED2 Current vs. Input Voltage
4.6
5.05
5.5
LED1 + LED3 Current vs. Input Voltage
1000
200
900
LED1 + LED3 Current (mA)
ILED2 = 800mA
800
LED2 Current (mA)
4.15
Input Voltage (V)
Input Voltage (V)
ILED2 = 400mA
ILED2 = 200mA
ILED2 = 150mA
ILED2 = 100mA
ILED2 = 75mA
700
600
500
400
300
200
180
160
140
ILED1 = ILED3 = 150mA
120
100
ILED1 = ILED3 = 100mA
80
60
40
20
100
0
0
2.5
3
3.5
4
4.5
5
2.4
5.5
3.02
LED2 Current vs. LED2 Current Digital Code
180
180
160
160
100
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
80
60
LED1 Current (mA)
200
120
4.88
5.5
140
120
100
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
80
60
40
40
20
20
0
4.26
LED1 Current vs. LED1 Current Digital Code
200
140
3.64
Input Voltage (V)
Input Voltage (V)
LED2 Current (mA)
3.7
0
0
20
40
60
80
100 120 140 160 180 200
LED2 Current Digital Code (mA)
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10
0
20
40
60
80
100 120 140 160 180 200
LED1 Current Digital Code (mA)
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RT8540
LED2 Current vs. LED2 Current Digital Code
900
180
800
160
700
LED2 Current (mA)
LED3 Current (mA)
LED3 Current vs. LED3 Current Digital Code
200
140
120
100
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
80
60
600
500
400
300
40
200
20
100
0
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
0
0
20
40
60
80
100 120 140 160 180 200
0
100
LED3 Current Digital Code (mA)
400
400
350
350
300
250
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
100
50
600
700
800
900
300
250
200
VIN = 2.5V
VIN = 3.6V
VIN = 4.5V
150
100
0
0
50
100
150
200
250
300
350
400
450
0
LED1 Current Digital Code (mA)
50
100
150
200
250
300
350
400
450
LED3 Current Digital Code (mA)
Efficiency vs. Output Current
INDLED Current vs. Headroom Voltage
100
18
90
16
INDLED = 0111
80
14
12
Efficiency (%)
INLED Current (mA)
500
50
0
INDLED = 0110
10
INDLED = 0011
8
INDLED = 0010
6
INDLED = 0001
4
70
60
VIN =
VIN =
VIN =
VIN =
50
40
30
VOUT = 4.95V, ILIM = 1750mA,
Voltage Mode Regulation
10
0
0.35
2.5V
3V
3.6V
4.2V
20
2
0
0.72
1.09
1.46
1.83
Headroom Voltage (V)
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400
LED3 Current vs. LED3 Current Digital Code
450
LED3 Current (mA)
LED1 Current (mA)
LED1 Current vs. LED1 Current Digital Code
150
300
LED2 Current Digital Code (mA)
450
200
200
December 2013
2.2
1
10
100
1000
Output Current (mA)
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RT8540
Output Voltage vs. Output Current
5.00
90
4.95
80
4.90
Output Voltage (V)
Efficiency (%)
Efficiency vs. Output Current
100
70
VIN =
VIN =
VIN =
VIN =
60
50
40
2.5V
3V
3.6V
4.2V
30
20
4.85
VIN =
VIN =
VIN =
VIN =
4.80
4.75
4.70
4.65
4.60
VOUT = 3.825V, ILIM = 1750mA,
Voltage Mode Regulation
10
0
VOUT = 4.95V, ILIM = 1750mA,
Voltage Mode Regulation
4.55
4.50
1
10
100
1000
10000
0
200
400
Output Current (mA)
600
800
1000 1200 1400 1600
Output Current (mA)
Quiescent Current vs. Input Voltage
Shutdown Current vs. Input Voltage
600
5
500
Shutdown Current (µA)1
Quiescent Current (µA)
2.5V
3V
3.6V
4.2V
400
300
200
100
0
4
3
2
1
0
2.4
3.02
3.64
4.26
4.88
5.5
2.4
3.64
4.26
4.88
Input Voltage (V)
Torch Mode Power On
Flash Mode Power On
VIN
(1V/Div)
VOUT
(2V/Div)
VIN
(1V/Div)
VOUT
(2V/Div)
I LED
(200mA/Div)
I LED
(500mA/Div)
VIN = 3.6V, ILED1 = ILED2 = ILED3 = 525mA
Time (250μs/Div)
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3.02
Input Voltage (V)
5.5
VIN = 3.6V, ILED1 = ILED2 = ILED3 = 1600mA
Time (500μs/Div)
is a registered trademark of Richtek Technology Corporation.
DS8540-00
December 2013
RT8540
Voltage Mode Load Transient
Voltage Mode Load Transient
IOUT = 50mA to 500mA
IOUT = 50mA to 500mA
VOUT
(200mV/Div)
VOUT
(200mV/Div)
IOUT
(200mA/Div)
IOUT
(200mA/Div)
VIN = 3.6V, VOUT = 4.95V, ILIM = 1750mA
VIN = 3.6V, VOUT = 3.825V, ILIM = 1750mA
Time (100μs/Div)
Time (100μs/Div)
Torch Mode Ripple & Spike
Flash Mode Ripple & Spike
VIN
(50mV/Div)
VIN
(100mV/Div)
VOUT
(50mV/Div)
VOUT
(100mV/Div)
VLX
(5V/Div)
VLX
(5V/Div)
I LED
(500mA/Div)
I LED
(2A/Div)
ILED1 + ILED2 + ILED3 = 525mA
Time (500ns/Div)
ILED1 + ILED2 + ILED3 = 1600mA
Time (250ns/Div)
Tx-MASK Operation
STRB0
(2V/Div)
Tx-MASK
(2V/Div)
I LED
(500mA/Div)
VIN = 3.6V, ILIM = 1750mA, STRB1= 0,
DCLC13 [2:0] = 010, DCL2 [2:0] = 010,
FC13 [4:0] = 00100, FC2 [5:0] = 001000
Time (500μs/Div)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8540-00
December 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT8540
Application Information
The RT8540 is a Boost converter that provides a current
regulated output to drive high current white LEDs for camera
flash applications. The IC adopts three channels to provide
accurately regulated current flow through three separate
white LEDs.
The RT8540 provides the ability to regulate the input voltage
that is higher than the designed output voltage with its
down-conversion mode. The RT8540 turns off its downconversion mode automatically once the input voltage falls
to approximately 200mV below the output voltage.
Soft-Start
The RT8540 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 inrush current for a typical period of 400μs.
Inductor Selection
The RT8540 adopts fixed frequency PWM control
architecture. For stable operation and the 2MHz high
switching frequency, it is recommended to use a 2.2μH
inductor. Small size and high efficiency are the major
concerns for portable device, so the inductor should have
low core loss at 2MHz and low DCR for better efficiency.
Capacitor Selection
Input and output ceramic capacitors of 10μF are
recommended for RT8540 applications. For better voltage
filtering, ceramic capacitors with low ESR are
recommended. The best performance of the RT8540 can
be achieved by using the capacitor of large capacitance.
X5R and X7R types are suitable because of their wider
voltage and temperature ranges.
Input UVLO
Torch Mode and Flash Mode Operation
The input operating voltage range of the LED driver is from
2.5V to 5.5V. The RT8540 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 2.3V typically with a hysteresis of 200mV.
The RT8540 is designed for one, two or three LEDs driving
for torch and flash application, it provides an I2C software
command or dedicated zero latency hardware signals to
trigger the torch and flash operation.
Over Voltage Protection (Open-LED, Open-Circuit)
In setting RT8540's hardware, the LED1, LED2 and LED3
pins must not be left floating to prevent the IC from overvoltage protection. For driving one or two LEDs with higher
current, the LED1 to LED3 inputs should be connected
together. Figure 1 shows the recommend LED setup for a
single, dual or triple-LED application
The RT8540 provides an internal over-voltage protection
to limit its output voltage. The OVP function prevents the
RT8540 from damaging while open-LED or open-circuit
condition is occurred. The switching will be re-started
again once the open circuit condition is removed, and then
the IC will return to normal operation.
Over-Temperature Protection
The RT8540 provides an over-temperature protection to
prevent the IC from overheating. When the junction
temperature of the RT8540 rises above 160°C, the OTP
function will be triggered and then the LED driver will be
shutdown. The OTP of the RT8540 comes with a
hysteresis of 20°C. Once the temperature is reduced
below the over-temperature protection threshold by 20°C,
the IC will enter normal operation again.
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14
LED Hardware Setup
RT8540
VOUT
COUT
LED1
LED2
LED3
Single LED
is a registered trademark of Richtek Technology Corporation.
DS8540-00
December 2013
RT8540
RT8540
VOUT
MODE_CTRL [1:0] = 01
The STRB0, STRB1 inputs are disabled. No matter what
situation of the STRB0, STRB1 inputs and the
START_FLASH/TIMER (SFT) bit, the IC regulates the
LED current in video light mode (DCLC bits).
COUT
LED1
LED2
LED3
MODE_CTRL [1:0] must be refreshed within less than
13.0 seconds (STRB1 = 0) to prevent the IC from
shutdown due to video light safety timeout. Moreover,
by pulling the STRB1 signal high, the video light
watchdog timer can be disabled.
Dual LED
RT8540
VOUT
COUT
LED1
LED2
LED3
Triple LED
Figure 1. White LED Hardware Setup Options
Triggering Torch and Flash
The RT8540 provides several options for driving the video
light and flash. The IC operates in different modes according
to different settings of the MODE_CTRL [1:0] bits for
maximum system integration flexibility. The video light
and flash can be triggered via hardware signals (STRB0,
STRB1) or software I2C command. For torch lighting, the
RT8540 provides a watchdog timer which must be
refreshed within 13.0 seconds. This function can also be
disabled as following description.
MODE_CTRL [1:0] = 10
The STRB0, STRB1 inputs are enabled. The RT8540
triggers the flash pulse by synchronization signals or
by a software command (START_FLASH/TIMER (SFT)
bit). According to the STRB0, STRB1 input, the LEDs
can be enabled or disabled. Then, the flash safety timer
will be activated and the video light watchdog timer will
be disabled.
Level-Sensitive Flash Trigger (STT = 0)
In this mode, the RT8540 drives the high-power LEDs by
flash-current level and the safety timer (STIM) is activated.
The STIM [2:0] register determines the maximum duration
of the flash pulse.
A rising edge triggers the safety timer and it can be stopped
by a negative logic on the synchronization source (STRB0,
STRB1 = 0) or by a timeout event (TO bit).
STOBE0
TORCH
STOBE0
STOBE1
DURATION < STIM
TIMER
LED CONTROL
LED OFF
TORCH
LED OFF
LED OFF
FLASH
Figure 2. Hardware Synchronized Video Light and Flash Strobe
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RT8540
Rising-Edge Flash Trigger (STT = 1)
of the flash pulse. The RT8540 triggers the flash strobe by
adopting a rising edge on the synchronization source
(STRB0, STRB1 = 0) or a positive transition on the STARTFLASH/TIMER (SFT) bit.
In this mode, the RT8540 drives the high power LEDs by
flash-current level and the safety timer (STIM) is activated.
The STIM [2:0] register determines the maximum duration
TORCH
STOBE0
STOBE0
STOBE1
DURATION < STIM
TIMER
LED CONTROL
LED OFF
TORCH
LED OFF
LED OFF
FLASH
Figure 3. Edge Sensitive Timer (Single Trigger Event)
Down Mode
Voltage Mode
Normally, a Boost converter regulates output voltages
which are higher than the input voltage. For better
conversion when input voltages are higher than output
voltages, a down mode is implemented. In the voltageregulation mode, when the input voltage reaches or
exceeds the output voltage, the converter enters down
mode. In this mode, the behavior of internal P-MOSFET
is changed and increases the power losses in the converter
which should be taken into account for thermal design.
As soon as the input voltage falls to approximately 200mV
below the output voltage, the down mode is automatically
turned off.
In this mode, the RT8540 operates as a constant output
voltage Boost regulator. By setting the mode control bit
MODE_CTRL [1:0] = 11, the IC enters voltage mode
operation. A constant output voltage can be regulated by
the RT8540 according to the OV [3:0] bit settings (between
3.825V and 5.7V in 125mV steps). The LED current sinks
LED1 to LED2 will be turned off in voltage mode.
Internal Register Settings
Mode_Ctrl [1:0]
ENVM bit
11
0
00
1
11
1
The RT8540 provides an integrated software control bit
(ENVM bit) to force the converter to enter voltage mode
operation.
Operating Modes
LEDs are turned off and the converter
operates in voltage regulation mode (VM);
the output voltage is set via register OV [3:0].
Indicator
The RT8540 provides privacy indicator that can be used
to indicate when a person is being photographed or filmed.
The privacy indicator can be activated by adopting INDC
[3:0] bits, ranging from 2.6mA to 15.8mA in 7 programmable
current steps or by using the white LEDs with pulse width
modulation.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8540-00
December 2013
RT8540
RT8540 Register Summary
Address : 0110011x
Address
0x00
Name
Bit7
Bit6
Control10
RESET
FREE
Reset
Value
0
0
0
0
1
0
1
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Control1
0x01
0x04
0x05
0x06
0x07
Bit2
Bit1
Bit0
DCLC2 [2:0]
FC2 [5:0]
0
0
0
1
0
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
MODE_CTRL [1:0]
ENVM
FC13 [4:0]
Reset
Value
0
0
0
0
1
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
HPLF
SELSTIM
(W) TO (R)
STT
SFT
Tx-MASK
0
0
0
0
0
R
R
R/W
R/W
R/W
STIM [2:0]
Reset
Value
1
1
0
Read/Write
R/W
R/W
R/W
Control4
Reset
Value
Read/Write
PG
0
0
0
0
0
0
0
0
R/W
R
R
R/W
R/W
R/W
R/W
R/W
Control5
NA
ENPSM
DIR(W)
STSTRB1
(R)
GPIO
ENLED2
ENLED1
Reset
Value
0
1
1
0
1
0
1
0
Read/Write
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Control6
ENTS
Reset
Value
0
0
0
0
1
0
0
1
Read/Write
R/W
R/W
R
R
W
W
W
W
Control7
ENBATM
ON
Reset
Value
0
1
0
0
0
1
1
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R
R
R
HOTDIE [1:0]
December 2013
ILIM
INC [3:0]
GPIOTYPE ENLED3
LEDHOT LEDWARN LEDHDR
BATDROOP [2:0]
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8540-00
Bit3
DCLC13 [2:0]
MODE_CTRL [1:0]
Control3
0x03
Bit4
Reset
Value
Control2
0x02
Bit5
OV [3:0]
FREE
REVID [2:0]
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RT8540
Address
0x00
Name
Bit7
Bit6
Control10
RESET
FREE
Reset Value
0
0
0
0
1
0
1
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Bit3
Bit2
Bit1
Bit0
RESET
DCLC13 [2:0]
DCLC2 [2:0]
Address
Name
Control1
0x01
Bit5
Bit4
Bit3
Bit2
DCLC13 [2:0]
Bit1
Bit0
DCLC2 [2:0]
Register Reset bit.
0 : Normal operation.
1 : Default values are set to all internal registers.
Video Light Current Control bits (LED1/3).
000 : 0mA
001 : 25mA
010 : 50mA
011 : 75mA
100 : 100mA
101 : 125mA
110 : 150mA
111 : 175mA
Video Light Current Control bits (LED2).
000 : 0mA
001 : 25mA
010 : 50mA
011 : 75mA
100 : 100mA
101 : 125mA
110 : 150mA
111 : 175mA
Bit7
Bit6
Bit5
Bit4
MODE_CTRL [1:0]
FC2 [5:0]
Reset Value
0
0
0
1
0
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
MODE_CTRL [1:0]
FC2 [5:0]
Register Reset bit.
00 : Device in shutdown mode.
01 : Device operations in video light mode.
10 : Device operation in Flash mode.
11 : Device operation as constant voltage source.
To avoid device shutdown by video light safety timeout, MODE_CTRL [1 : 0] bits need to
be refreshed within less than 13.0s.
Writing to REGISTER1 [7 : 6] automatically updates REGISTER2 [7 : 6].
Flash Current Control bits (LED2).
000000 : 0mA
000001 : 25mA
000010 : 50mA
000011 : 75mA
000100 : 100mA
000101 : 125mA
000110 : 150mA
000111 : 175mA
000111 : 175mA
001000 : 200mA
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is a registered trademark of Richtek Technology Corporation.
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RT8540
FC2 [5:0]
Address
Name
Control2
0x02
001001 : 225mA
001010 : 250mA
001011 : 275mA
001100 : 300mA
001101 : 325mA
001110 : 350mA
001111 : 375mA
010000 : 400mA
010001 : 425mA
010010 : 450mA
010011 : 475mA
010100 : 500mA
010101 : 525mA
010110 : 550mA
010111 : 575mA
011000 : 600mA
011001 : 625mA
011010 : 650mA
011011 : 675mA
011100 : 700mA
011101 : 725mA
011110 : 750mA
011111 : 775mA
100000...111111 : 800mA
Bit7
Bit6
MODE_CTRL [1:0]
Bit5
Bit3
ENVM
Bit2
Bit1
Bit0
FC13 [4:0]
Reset Value
0
0
0
0
1
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
MODE_CTRL [1:0]
ENVM
FC13 [4:0]
Register Reset bit.
00 : Device in shutdown mode.
01 : Device operations in video light mode.
10 : Device operation in Flash mode.
11 : Device operation as constant voltage source.
To avoid device shutdown by video light safety timeout, MODE_CTRL [1 : 0] bits need to
be refreshed within less than 13.0s.
Writing to REGISTER2 [6 : 5] automatically updates REGISTER1 [6 : 5] .
Enable Voltage Mode bit.
0 : Normal operation.
1 : Forces the device into a constant voltage source.
In read mode, the ENVM bit is automatically updated to reflect the logic stats of the ENVM
input pin.
Flash Current Control bits (LED1/3).
00000 : 0mA
00001 : 25mA
00010 : 50mA
00011 : 75mA
00100 : 100mA
00101 : 125mA
00110 : 150mA
00111 : 175mA
00111 : 175mA
01000 : 200mA
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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Bit4
December 2013
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RT8540
FC13 [4:0]
Address
Name
01001 : 225mA
01010 : 250mA
01011 : 275mA
01100 : 300mA
01101 : 325mA
01110 : 350mA
01111 : 375mA
10000...11111 : 400mA
Bit7
Control3
0x03
Bit6
Bit5
STIM [2:0]
Bit4
Bit3
Bit2
Bit1
Bit0
HPLF
SELSTIM
(W) TO (R)
STT
SFT
Tx-MASK
Reset Value
1
1
0
0
0
0
0
0
Read/Write
R/W
R/W
R/W
R
R
R/W
R/W
R/W
Safety Timer bits.
STIM [2:0]
HPFL
SELSTIM
STIM [2:0]
RANGE 0
RANGE 1
000
68.2ms
5.3ms
001
102.2ms
10.7ms
010
136.3ms
16.0ms
011
170.4ms
21.3ms
STIM [2:0]
RANGE 0
RANGE 1
100
204.5ms
26.6ms
101
340.8ms
32.0ms
110
579.3ms
37.3ms
111
852ms
71.5ms
High-Power LED Failure Flag.
0 : Proper LED operation.
1 : LED open or OCP.
Safety Timer Selection Range (Write Only).
0 : Safety timer range 0.
1 : Safety timer range 1.
TO
Time-Out Flag (Read Only)
0 : No time-out event occurred.
1 : Time-out event occurred. Time-out flag is reset at re-start of the safety timer.
STT
Safety Timer Trigger bit.
0 : LED safety timer is level sensitive.
1 : LED safety timer is rising edge sensitiv e.
This bit is only valid for MODE_CTRL [1 : 0] =10
SFT
Start/Flash Timer bit.
In write mode, this bit initiates a flash strobe sequence.
0 : No change is the high-power LED current.
1 : High-power LED current ramps to the flash current level.
In read mode, this bit indicates the high-power LED status.
0 : High-power LEDs are idle.
1 : Ongoing high-power LED flash strobe.
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RT8540
Tx-MASK
Flash Blanking Control bit.
In write mode, this bit enables/disables the flash blanking/LED current reduction function.
0 : Flash blanking disabled.
1 : LED current is reduced to video light level when Tx-MASK input is high.
In read mode, this flag indicates whether or not the flash masking input has been activated.
Tx-MASK flag is reset after readout of the flag.
0 : No flash blanking event occurred.
1 : Tx-MASK input triggered.
Address
Name
Bit7
Control4
PG
0x04
Reset Value
0
0
0
Read/Write
R/W
R
R
PG
HOTDIE [1:0]
Bit6
Bit5
HOTDIE [1:0]
Bit4
Bit3
Bit2
0
0
0
0
0
R/W
R/W
R/W
R/W
R/W
ILIM
Bit1
Bit0
INC [3:0]
Power Good bit.
In write mode, this bit selects the functionality of the GPIO/PG output.
0 : PG signal is routed to the GPIO port.
1 : GPIO PORT VALUE bit is routed to the GPIO port.
In read mode, this bit indicates the output voltage conditions.
0 : The converter is not operating within the voltage regulation limits.
1 : The output voltage is within its nominal value.
Instantaneous Die Temperature bits.
00 : TJ < +55C.
01 : +55C < T J < +70C.
10 : TJ > +70C.
11 : Thermal shutdown tripped. Indicator flag reset after readout.
Inductor Valley Current Limit bit.
The ILIM bit can only be set before the device enters operation (i. e. initial shutdown state).
ILIM
Valley Current Limit Setting
ILIM Bit Setting
1650mA
Low
2150mA
High
Indicator Light Control bits.
INDC [3:0]
INDC [3:0]
0000
Privacy indicator turned off
0001
INDLED current = 2.6mA
0010
INDLED current = 5.2mA
0011
INDLED current = 7.9mA
0100
Privacy indicator turned off
0101
INDLED current = 5.2mA
0110
INDLED current = 10.4mA
0111
INDLED current = 15.8mA
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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December 2013
Privacy Indicator INDLED Channel
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21
RT8540
INDC [3:0]
Address
0x05
INDC [3:0]
Privacy Indicator LED1/3 Channel (1)
0000
5% PWM dimming rato
0001
11% PWM dimming rato
0010
17% PWM dimming rato
0011
23% PWM dimming rato
0100
30% PWM dimming rato
0101
36% PWM dimming rato
0110
48% PWM dimming rato
0111
67% PWM dimming rato
Name
Bit7
Bit6
Bit5
Bit4
Control5
NA
ENPSM
DIR(W)
STSTRB1(R)
GPIO
Reset Value
0
1
1
0
1
Read/Write
R
R/W
R/W
R/W
R/W
ENPSM
STSTRB1
DIR
GPIO
GPIOTYPE
Bit2
Bit1
Bit0
ENLED2
ENLED1
0
1
0
R/W
R/W
R/W
GPIOTYPE ENLED3
Enable/Disable Power-Save Mode bit.
0 : Power-save mode disabled.
1 : Power-save mode enabled.
STRB1 Input Status bit (Read Only).
This bit indicates the logic state on the STRB1 state.
GPIS Direction bit.
0 : GPIO configured as input.
1 : GPIO configured as output.
GPIO Port Value.
This bit contains the GPIO port value.
GPIO Port Type.
0 : GPIO is configured as push-pull output.
1 : GPIO is configured as open-drain output.
ENLED3
Enable/Disable High-Current LED3 bit.
0 : LED3 input is disabled.
1 : LED3 input is enabled.
ENLED2
Enable/Disable High-Current LED2 bit.
0 : LED2 input is disabled.
1 : LED2 input is enabled.
ENLED1
Enable/Disable High-Current LED1 bit.
0 : LED1 input is disabled.
1 : LED1 input is enabled.
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Bit3
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RT8540
Address
0x06
Name
Bit7
Control6
ENTS
Reset Value
0
0
0
0
1
0
0
1
Read/Write
R/W
R/W
R
R
W
W
W
W
ENTS
LEDHOT
LEDWARN
LEDHDR
Bit6
Bit5
Bit4
Bit3
Bit2
LEDHOT LEDWARN LEDHDR
Bit1
Bit0
OV [3:0]
Enable/Disable LED Temperature Monitoring.
0 : LED temperature monitoring disabled.
1 : LED temperature monitoring enabled.
LED Excessive Temperature Flag.
This bit can be reset by writing a logic level zero.
0 : TS input voltage > 0.345V.
1 : TS input voltage < 0.345V.
LED Temperature Warning Flag (Read Only).
This flag is reset after readout.
0 : TS input voltage > 1.05V.
1 : TS input voltage < 1.05V.
LED High-Current Regulator Headroom Voltage Monitoring bit.
This bit returns the headroom voltage status of the LED high-current regulators. This value
is being updated at the end of a flash strobe, prior to the LED current ramp-down phase.
0 : Low headroom voltage.
1 : Sufficient headroom voltage.
Output Voltage Selection bits.
In write mode, these bits are used to set the target output voltage (refer to voltage
regulation mode). In applications requiring dynamic voltage control, care should be taken
to set the new target code after voltage mode operation has been enabled (MODE_CTRL
[1:0] = 11 and/or ENVM bit = 1).
OV [3:0]
OV [3:0]
Target Output Voltage
0000
3.825V
0001
3.950V
0010
4.075V
0011
4.200V
0100
4.325V
0101
4.450V
0110
4.575V
0111
4.700V
1000
4.825V
1001
4.950V
1010
5.075V
1011
5.200V
1100
5.325V
1101
5.450V
1110
5.575V
1111
5.700V
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RT8540
Address
0x07
Name
Bit7
Control7
ENBATMON
Reset Value
0
1
0
0
0
1
1
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R
R
R
ENBATMON
BATDROOP [2:0]
REVID [2:0]
Bit6
Bit4
BATDROOP [2:0]
Bit3
Bit2
FREE
Bit1
Bit0
REVID [2:0]
Enable/Disable Battery Voltage Droop Monitoring Bit.
0 : Battery voltage droop monitoring disable.
1 : Battery voltage droop monitoring enable.
Battery Voltage Droop.
000 : 50mV.
001 : 75mV.
010 : 100mV.
011 : 125mV.
100 : 150mV.
101 : 175mV.
110 : 200mV.
111 : 225mV
Silicon Revision ID.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
24
Bit5
is a registered trademark of Richtek Technology Corporation.
DS8540-00
December 2013
RT8540
Thermal Considerations
Layout Consideration
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 :
For the best performance of the RT8540, following PCB
layout guidelines should be strictly followed.
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, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WL-CSP-20B 1.82x2.22 (BSC) package, the thermal
resistance, θJA, is 36.7°C/W on a standard JEDEC 51-7
The AGND and PGND of the IC should be connected to
the ground plane of the PCB.
The output bypass capacitor should be placed as close
to the IC as possible.
The trace lengths from the IC to the inductor, input
capacitor and the output capacitor must be kept as short,
direct and wide as possible.
CIN and COUT of the RT8540 should be placed as close
as possible and connected to PGND of the IC.
It is recommended to add additional PCB exposed pad
area for the flash LEDs for maximized heat-sinking
ability. This is necessary for high current application
and long flash duration application.
four-layer thermal test board. The maximum power
dissipation at TA = 25°C can be calculated by the following
formula :
The trace lengths from the IC to the
inductor, input capacitor and the
output capacitor must be kept as
short, direct and wide as possible.
PD(MAX) = (125°C − 25°C) / (36.7°C/W) = 2.72W for
WL-CSP-20B 1.82x2.22 (BSC) package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 4 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
10µF
A1
INDLED
2.2µH
To VIN (E4)
4.7µH
3.0
Maximum Power Dissipation (W)1
B1
SDA
Battery
2.5
A4
AGND
B2
B3
B4
SCL NRESET STRB0
C1
C2
SW
SW Tx-MASK
TS
D1
D2
D4
LED2
The exposed pad of the
IC should be connected
to the ground plane of
the PCB.
1.5
A3
AGND
C3
D3
C4
PGND PGND STRB1 GPIO/
PGOOD
E1
E2
E3
E4
Four-Layer PCB
2.0
A2
VOUT
LED1
LED3
VIN
GND
1.0
Figure 5. PCB Layout Guide for WL-CSP-20B 1.82x2.22
(BSC)
0.5
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 4. Derating Curve of Maximum Power Dissipation
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8540-00
December 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
25
RT8540
Outline Dimension
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.500
0.600
0.020
0.024
A1
0.200
0.260
0.008
0.010
b
0.290
0.350
0.011
0.014
D
2.170
2.270
0.085
0.089
D1
E
1.600
1.770
0.063
1.870
0.070
0.074
E1
1.200
0.047
e
0.400
0.016
20B WL-CSP 1.82x2.22 Package (BSC)
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.
www.richtek.com
26
DS8540-00
December 2013
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