LC5901S DATA SHEET Rev.1.5

LC5901S DATA SHEET
LC5901S
DATA SHEET
Rev.1.5
Rev.1.5
SANKEN ELECTRIC CO., LTD.
http://www.sanken-ele.co.jp
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.1
LC5901S DATA SHEET
Rev.1.5
CONTENTS
General Description---------------------------------------------------------------------------- 3
Absolute maximum ratings ------------------------------------------------------------------ 4
Recommended Operation Conditions------------------------------------------------------ 4
Electrical Characteristics --------------------------------------------------------------------- 5
Functional Block Diagram ------------------------------------------------------------------- 6
Pin Assignmennt & Functions --------------------------------------------------------------- 6
Basic Circuit Connection --------------------------------------------------------------------- 7
Package Information -------------------------------------------------------------------------- 8
Functional Description ------------------------------------------------------------------------ 9
Design flow chart ------------------------------------------------------------------------------25
Packing specifications ------------------------------------------------------------------------26
Typical characteristics -----------------------------------------------------------------------27
IMPORTANT NOTES -----------------------------------------------------------------------29
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.2
LC5901S DATA SHEET
Rev.1.5
General Description
Package
SOP8
The LC5901S is a Buck type Single output LED driver
IC. This product realizes a high efficiency / high
precision LED drive with few add-on parts. It has the
protection function which became satisfactory, and
complies with the wide LED composition, and copes
with analog dimming and PWM dimming.
The LC5901S is an open loop average-mode current
control LED driver IC operating in a constant off-time
mode(Pulse Ratio Control: PRC). The IC features ±2%
current accuracy, tight line and load regulation of the
LED current without any need for loop compensation
or high-side current sensing and slope compensation.
The LC5901S is available in an 8-pin SOP package that
is compact and thin.
Primary specification
Features
Range of Input Voltage: 7V (MIN)～18V(MAX)
The OFF-time (TOFF ) is adjustable from 1.0 to
9.0μsec.
Converter Block
 Operation：Average Current Mode PRC Control
 Adjustable OFF-time:1.0 to 9.0usec
 External Phase Compensation is unnecessary
LED Controller Block
 PWM dimming
 Analogue dimming
 ±2% LED Current Accuracy
Protection Functions
 LED short Protection Pulse by Pulse
 Current Sense short Protection Auto Restart
 VIN UVLO
Auto Restart
 Thermal shutdown(TSD)
Auto Restart
 Package : SOP8
Application
 LED Back-light
 LED Lighting
 LED Light bulb
About Laser Marking
Product’s name
LC5901S
SK YMW
XXXX
Copy Right: SANKEN ELECTRIC CO., LTD.
Lot Number
Y= The last digit of the year (0～9)
M= Manufacturing Month (1～9，O=”10”，N=”11”，D=”12”)
W= Manufacturing Week (1～5)
Campany Control Number(4 digit)
Page.3
LC5901S DATA SHEET
Rev.1.5
1.Absolute maximum ratings
 Certain details refer to the specification sheet of this product.
 The polarity value for current specifies a sink as “+” and a source as “−”, referencing the IC.
 Ta=25°C,unless otherwise noted.
Table.1
Characteristic
Terminal
Symbol
Ratings
Units
VCC terminal voltage
2−3
VCC
−0.3～+18.0
V
CS terminal voltage
1−3
VCS
−0.3～+18.0
V
OUT terminal voltage
4−3
VOUT
−0.3～+18.0
V
RT terminal voltage
5−3
VRT
−0.3～+3.6
V
PWM terminal voltage
6−3
VPWM
−0.3～+3.6
V
UVLO terminal voltage
7−3
VUVLO
−0.3～+3.6
V
REF terminal voltage
8−3
VREF
−0.3～+3.6
V
RT terminal sink current
5-3
IRT
±500
μA
8-3
IREF
±500
μA
―
PD
1.2
W
―
θj- Pin
65
°C /W
―
θj-a
95
°C /W
(3)
―
Tj
150
°C
(1)
―
Top
−40～＋125
°C
―
Tstg
−40～＋150
°C
REF terminal sink current
(1)
Allowable power dissipation
Thermal resistance(junction－
lead (#3pin))
Thermal resistance(junction －
ambient temperature)
Junction temperature
Operating ambient temperature
(2)
(2)
Storage temperature
Remarks
(1)
However, it is limited by Junction temperature.
When mounted on a 40×40mm Glass-epoxy board (copper area in a 25×25mm).
(3)
Thermal shutdown temperature is approximately 150°C
(2)
2. Recommended Operation Conditions
 Recommended Operation Conditions are the required operating conditions to maintain the normal circuit
functions described in the electrical characteristics. In actual operation, it should be within these conditions.
 The polarity value for current specifies a sink as “+” and a source as “−” referencing the IC.
 Unless specifically noted, Ta is 25°C
Table.2
Characteristic
Symbol
VCC terminal voltage
Operating ambient temperature
(4)
(4)
Ratings
MIN
MAX
Units
VIN
8
17
V
TOP
40
85
°C
To be used within the allowable package power dissipation characteristics (TBD)
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.4
Conditions
LC5901S DATA SHEET
Rev.1.5
3. Electrical Characteristics
 Certain details refer to the specification sheet of this product.
 The polarity value for current specifies a sink as “+” and a source as “−”, referencing the IC.
3.1 Electrical Characteristics of Control Part (MIC) Unless specifically noted, Ta=25°C、VIN=12V
Table.3
Items
Terminal
Symbol
Operation Start Voltage
2−3
Operation Stop Voltage
Ratings
Units
Remarks
MIN
TYP
MAX
VCC(ON)
6.5
7.0
7.5
V
2−3
VCC(OFF)
6.0
6.5
7.0
V
Operation Hysteresis Voltage
2−3
VCC(HYS)
－
0.5
－
V
Supply Current
2−3
ICC(ON)
－
1.2
2.0
mA
Supply Current in No Operation
2−3
ICC(OFF)
－
0.35
0.5
mA
VUVLO=0V
OFF Time1
4-3
TOFF1
6.4
8.4
9.8
usec
RRT=80kΩ
OFF Time2
4-3
TOFF2
0.85
1.0
1.2
usec
RRT=10kΩ
Maximum ON Time
4-3
tONMAX
170
220
280
usec
Minimum ON Time
4-3
tONMIN
－
－
1.3
usec
REF voltage1
8-3
VREF1
0.980
1.0
1.020
V
REF voltage2
8-3
VREF2
1.764
1.8
1.836
V
PWM Pin ON Threshold voltage
6-3
VPWM(ON)
1.7
2.0
2.5
V
PWM Pin OFF Threshold voltage
6-3
VPWM(OFF)
0.8
1.1
1.9
V
PWMPin Pull-down Resistance
6-3
RPWM
128
200
280
kΩ
OUT Pin Output Resistance(source)
(5)
4-3
Ron_H
－
17
－
Ω
OUT Pin Output Resistance(sink)
(5)
4-3
Ron_L
－
14
－
Ω
UVLO Pin ON Threshold voltage
7-3
VUVLO(ON)
0.75
1.00
1.3
V
UVLO Pin OFF Threshold voltage
7-3
VUVLO(OFF)
0.65
0.85
1.1
V
UVLO Pin Hysteresis Voltage
7-3
VUVLO(HYS)
0.05
0.15
0.25
V
UVLO Pin Discharge Resistance
7-3
RUVLO
0.5
1.0
1.5
kΩ
UVLO Pin Discharge-Complete
Threshold Voltage
7-3
VUVLO(RST)
180
250
320
mV
1-3
VOCP
2.3
2.5
2.7
V
1-3
tLEB
－
200
－
nsec
OCP Threshold voltage
CS Pin Blanking Time
(5)
Thermal-Shutdown Activation
(5)
－
TSD
－
150
－
Temperature
Thermal Shutdown Hysteresis
(5)
－
TSD(HYS)
－
30
－
Temperature
(5)
Guaranteed by design, not tested.
* The polarity value for current specifies a sink as “+” and a source as “−”, referencing the IC.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.5
°C
°C
RRT=12kΩ
RREF=10kΩ
RRT=10kΩ
RREF=15kΩ
LC5901S DATA SHEET
Rev.1.5
3.2 Functional Block Diagram
fig.1 Function Block Diagram
4. Pin Assignmennt & Functions
Table.4
1
CS
8
REF
VCC
UVLO
GND
PWM
OUT
RT
Pin No.
Symbol
1
CS
Functions
LED Current Sense Input.
2
VCC
Supply Input.
･A Input capacitor is connected between VCC and the GND
terminal to supply current to the IC.
・Supply input voltage range:8V to 17V.
3
GND
Ground terminal.
4
OUT
Gate drive output of external powerMOSFET.
5
RT
This pin is the terminal to set up OFF-time.
A resistor RRT for the adjustment is connected to between the
RT terminal and the GND terminal.
6
PWM
PWM Dimming Signal Input. VPWM (OFF) <VPWM<2.5V.
LC5901S continues off-condition when this pin is held in the
one under VPWM (OFF).
7
UVLO
Sensing terminal for Under Voltage Lockout.
Input the divided voltage of PVIN by Resistance voltage
divider circuit.
8
REF
fig.2 Pin Assignment
Copy Right: SANKEN ELECTRIC CO., LTD.
This is the terminal for LED-current control reference setup.
A resistor RREF for the adjustment is connected between REF
terminal and GND terminal.
Page.6
LC5901S DATA SHEET
Rev.1.5
5. Basic Circuit Connection
5.1 LC5901S Basic circuit connection
LC5901S
The above shows the basic connection of LC5901S. Refer to a fig21 for the circuit diagram of the demonstration
board.
fig.3 LC5901S Basic circuit connection
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.7
LC5901S DATA SHEET
Rev.1.5
6. Package Information
SOP8 Package
Top view
8
1
7
2
6
5
3
4
side view1
side view2
NOTES:
1) All dimensions are in Millimeter
2) Drawing is not to scale.
fig.4 SOP8 Package outline Drawing
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.8
LC5901S DATA SHEET
Rev.1.5
7. Functional Description
All of the parameter values used in these descriptions are typical values of the electrical characteristics, unless they
are specified as minimum or maximum.
With regard to current direction, “+” indicates sink current (toward the IC) and “–” indicates source current (from
the IC).
7.1 PRC(Pulse Ratio Control) method
The control of this IC is adopting "PRC method". The "PRC method" of this product, under the condition of fixed
"OFF-Period" by external setup resistor RRT , and by controlling "ON-Period", the LED current will be controlled
constant current value. It is possible that a system is constructed at a low costs ,because the phase compensation is
unnecessary by adopting PRC method. It is possible to set up "OFF-Period" in the optional time by the value of the
resistor RRT that is connected to the RT terminal.The "ON-Period" is controlled so that "The average LED
current-signal which guessed based on the Switching-current-signal detected in the CS terminal" may become
equal to the value of the REF terminal voltage signal set up separately by the external setup resistor R REF.
7.2 The setup of “OFF-Period “
A setup of "OFF-Period" of LC5901S is set up by the value of the external resistor RRT that was connected to
between the RT terminal (5 pin) and GND terminal (3 pin). The "OFF-Period tOFF" is able to calculate with an
equation (1). The correlation of "OFF-Period" to the resistance value of RRT is shown as the fig 5.
Ω
fig.5 the relations of RRT vs. tOFF .
And, the setup of the resistance value of RRT is an important element to decide LED current ILED.
7.2.1 Setup of switching frequency
By the number of series connection of the LED string, the output voltage VLED is expressed with the LED
individual VF×N(number) + CS terminal voltage (V).
Duty D=VLED／VIN
･･･(2)
TON=TOFF×D／(1－D)
･･･(3)
T=TON＋TOFF ･･･(4)
FOSC=1／T ･･･(5)
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.9
LC5901S DATA SHEET
Rev.1.5
RRT is made 100kΩ. In accordance with the equation(1), T OFF=10μS. The LED individual VF is made
3.5V(Max), then 14 LED's are made a series connection.
D=49V／110V=0.445
TON=10μsec×0.445／(1－0.445)=8μsec
T=10μsec＋8μsec=18μsec →FOSC=1／18μsec=55.55kHz
When it makes the graph of this, a fig 6 - a fig 8 are shown.
fig.6 RRT=100kΩ,VIN=110VDC condition, Number of LED vs. Ton & Frequency
fig.7 RRT=82kΩ,VIN=110VDC condition, Number of LED vs. Ton & Frequency
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.10
LC5901S DATA SHEET
Rev.1.5
fig.8 RRT=47kΩ，VIN=110VDC condition, Number of LED vs. Ton & Frequency
Like this, switching-frequency rises relatively when a "OFF-Period" is set up short. Moreover, when there are
many LED's and VLED is high, it is the character that frequency is decreased because T ON spreads out.
7.3 The Setup of reference voltage(VREF)
The reference voltage is set up by the value of the setup resistor RREF that it was connected to between the REF
terminal (pin 8) and GND terminal (pin 3) , and the setup resistor R RT that it was connected to between the RT
terminal (pin 5) and GND terminal (pin 3) . The reference voltage VREF is able to calculate with an equation (6).
The correlation of the reference voltage VREF to the resistance value of RREF is shown as the fig 9. The setup upper
limit voltage of the reference voltage is 2.5V.
Ω
Ω
fig.9 the relations of RREF vs. VREF .
Fig 9 is the relations of the reference voltage VREF set up by two resistance of RRT and RREF. By the resistance
detector RCS of fig 3, the IC detects the "average LED current" that is flowing to the LED string and the "average
LED current" is converted as the voltage signals. It is prediction controlled so that the value of the detected voltage
signal may become equal to the reference voltage VREF.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.11
LC5901S DATA SHEET
Rev.1.5
7.4 LED Current Setup
By the output current resistance detector RCS,the LED current control detects the LED current ILED when Q1 turns
on. It is prediction controlled so that the average value of the detected LED current signal may become equal to the
reference voltage VREF voltage set up in advance. The setup of LED current( ILED) is able to calculate with an
equation (7). If you want to change LED current value, it can be changed to the optional current value by adjusting
the value of the reference voltage setup resistor RREF that is connected to the REF terminal.
(The LED current can be changed by the adjustment of RREF under the condition that the resistance value of RCS is
fixed.)
Ω
When this is graphed, a fig 10 is shown.
fig.10 VIN=110VDC, RREF vs. ILED
@ RCS=2.2Ω, VREF≦2.5V
And, in the above relations, when RREF adjusting, it becomes high dissolution that RRT is big, and switching
frequency is slow. Though the calculation example of the fig 10 is fixed with RCS=2.2Ω, when this is made 1Ω, the
LED current is 2.2 times. Be sure to take a heat-generation of the external powerMOSFET into consideration,
adjust ILED by RRT and RREF with the actual working confirmation.
7.5 The function of dimming
7.5.1 PWM dimming
In the PWM terminal, the PWM-dimming-signal which satisfies "ON-threshold voltage VPWM (on) =2V" and
"OFF-threshold voltage VPWM (off) =1.0V" is inputted. (The peak voltage of the drive pulse : 2.5V - 3.3V is
recommended.)
The pull-down resistance 200kΩ (typ) is connected between the PWM terminal and the GND terminal.
fig.11 The recommendation of the Dimming pulse
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.12
LC5901S DATA SHEET
Rev.1.5
7.5.2 Analog dimming
In case of analog dimming , input more than DC 2.5V to the PWM terminal , and make adjustment by your
changing RREF connected to the REF terminal.
fig.12 the means of the analog dimming .
A fig 12 (A) is a variable method which variable-resistor is used as RREF. A fig 12 (B) is maximum dimming by
RREF0,and turns on Q1 and Q2 one after another, and composition resistance value is lowered by parallel connection
of RREF1 and RREF2 , and it is the variable method which sets ILED at three steps. Like the fig 10, LED current ILED
can be decreased by making RREF small.
7.6 Gate Drive for External PowerMOSFET
The peripheral circuit of the OUT terminal is shown in the fig 13. The OUT terminal is the terminal for the gate
drive of the external powerMOSFET.
・Select the PowerMOSFET which a gate-threshold voltage VGS (th) can satisfy the condition of the "VGS (th)＜VOUT"
in all the use temperature ranges.
・By connecting the resistors and diode between the OUT terminal and PowerMOSFET's gate, EMI noise can be
controlled. Because turn-on speed and turn-off speed can be reduced.
・To prevent faulty operation by very fast dv/dt in Drain of the PowerMOSFET,connect the discharge resistance of
10kΩ-100kΩ between the gate of the PowerMOSFET and the ground.
SBD
fig.13Gate drive circuit of external PowerMOSFET
As a setup example, in the fig 13, the resistance of "Turn-ON Speed-Adjust" is about 100Ω,and the resistance of
"Turn-OFF Speed-Adjust" is about 10Ω. And, connect in series the resistor of "Turn-off Speed-Adjust" to
schottky-barrier diode(SBD). It is necessary for SBD's withstands-voltage to be the same as PowerMOSFET's
VGSS(Max).
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.13
LC5901S DATA SHEET
Rev.1.5
And, the gate drive voltage is not fixed. It is a system that "the OUT-terminal voltage" and "the VCC-terminal
voltage" are almost equally. When therefore VCC is 17V, the gate drive voltage is about 17V, too. Select the
PowerMOSFET which VGSS(MAx) is ±20V or ±30V . And, in the internal driver output of LC5901S, as for the
circuit resistance on the chip…
･Source resistance ：17Ω(Typ)
･Sink resistance ：14Ω(Typ)
This resistance can't be changed. Therefore,like the fig 13,as for the outside adjustment of the switching-speed,
insert resistor between the OUT terminal of LC5901S and the gate of the external PowerMOSFET.
7.7 Under Volatege Lock Out(UVLO)
LED power supply voltage decline protection.
A voltage divider circuit divides a main power supply voltage P_VIN for LED. The divided voltage (UVLO
signal) is inputted to UVLO terminal. The LC5901S starts a movement when "the UVLO ON-threshold-voltage
VUVLO (ON) ≧1.0V" is inputted. and, it stops a movement when "the UVLO OFF-threshold-voltage VUVLO(OFF)≦
0.985V" is inputted, even the condition that a "High signal" is inputted to the PWM terminal.
And, when OCP protection and tONMAX protection activate, in the UVLO terminal, internal reset switch turns on,
and discharges electricity in less than 250mV.
By the charge-time-constant of the voltage-dividing-resistor(RUVLO1 & RUVLO2) and CUVLO, the movement of
LC5901S stops at the period until the UVLO terminal is charged to the voltage which exceeds "the UVLO
ON-threshold voltage VUVLO (ON)".
fig 14 . the input of the UVLO terminal .
Aside from P_VIN UVLO, there is VCCUVLO which detects VCC inside the IC. The internal VCCUVLO and the
UVLO of UVLO-terminal are "AND" condition. The IC's movement doesn't start when either isn't released.
Be careful of the selection of the resistance value because the detection resistor of UVLO becomes a loss when the
P_VIN voltage is high. When RUVLO2 in the fig 14 is fixed on 100kΩ, a fig 15 becomes the graph of the UVLO
release voltage when the resistance value of RUVLO1 of the voltage dividing resistor was made to change.
And, the capacitor CUVLO which is between UVLO terminal and GND is used for the time constant in the SKIP
movement.
And,in the protection which UVLO function was used for,there is protection of "Maximum ON time=220μsec".
For example,when the condition that the LED load is opened, ON-period expands to Maximum-ON-time because
the CS terminal volatge doesn't reach the reference voltage in control that is the target.
At this moment,the UVLO-terminal voltage is forced discharged, and it becomes protection that is shifted to the
SKIP mode (HICCUP mode).
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.14
LC5901S DATA SHEET
Rev.1.5
fig.15 Setup example of the UVLO release voltage
In the fig 15,
･All typical value･･･VUVLO(ON)=1.00V，RUVLO2=Typ value，RUVLO1=Typ value.
･tolerance(High)･･･VUVLO(ON)=1.05V，RUVLO2=－1%，RUVLO1=＋1%
･tolerance(Low)･･･VUVLO(ON)=0.95V，RUVLO2=＋1%，RUVLO1=－1%
*For convenience of explanation, the allowable tolerance of the resistance is F (± 1%).
In the regular parts (The allowable tolerance J : ± 5%), as the value of the setup resistance grows big, tolerance
width is widened more.
*But, VCC of LC5901S is supplied from other system except for the main circuit P_VIN voltage, and it is the
condition of "VIN (on) ≧7V".
*The start voltage VUVLO (off) of UVLO is 0.985V.
7.8 Over Current Protection(OCP)
Due to the saturation of inductance, the short circuit, and so on, when the both-ends voltage of the output current
detection resistor RCS reaches the condition of the over current protection threshold voltage “VOCP≧2.5V”,then the
PowerMOSFET drive signal VOUT shifts to a “Continuous Low level”, and a UVLO discharge switch activates.
The CS terminal voltage reaches 2.5V (typ). (OCP condition occurrence) .
↓①
By the internal discharge impedance 1kΩ,it discharges CUVLO which is the capacitance of the time constant
between UVLO and GND.The movement is suspended if a UVLO terminal voltage reaches 0.985V (typ).
↓②
After the movement stops, and CUVLO discharge is continued, if the UVLO terminal voltage reaches to threshold
voltage VUVLO (RST) = 250mV,then CUVLO discharge stops.
↓③
The CUVLO of the time constant is charged again via the voltage dividing resistor for UVLO setup.
The movement starts if the UVLO terminal voltage reaches 1V (typ).
↓
When over-load condition isn't canceled, by repeating ① - ③, the SKIP movement (HICCUP) is continued.
The time interval of SKIP can be adjusted by the capacitance of CUVLO and impedance of the voltage dividing
resistor. The main circuit P_VIN is connected to an upside of voltage dividing resistor (R UVLO1). When the voltage of
the main circuit P_VIN changes frequently, the time interval of SKIP doesn't sometimes become stable.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.15
LC5901S DATA SHEET
Rev.1.5
Though the Lead-Edge-Blanking (LEB) is built in inside of the CS terminal, when there is superimposition of the
large surge-noise on voltage signals of the both-ends of RCS, as the fig 16, use a RC filter together.
fig.16 A RC filter setup example for the CS terminal .
As the fixed number of RC-filter,when the time constant of C･R is big, control delay grows big and a movement
sometimes becomes unstable. Be sure to adjust confirmation by the actual working when you add a RC-filter to
cope with the surge-noise.
As for the interval of the SKIP movement (HICCUP), it is based on the character of "discharge and charge" of
CUVLO. When over-load condition isn't canceled in the situation which went into the SKIP movement, though a
SKIP movement goes on, the interval of the skip depends on a charge by the internal discharge resistance 1kΩ
inside of the UVLO terminal,and the composition resistance of "RUVLO1 and RUVLO2".
The terminal voltage of CUVLO at the time "t" by discharging =1V×e-(t／CUVLO×1kΩ)
･･･(8)
*At the VUVLO=1V,though the movement starts after the UVLO release,the moment it started, in case of
occurrence of over-current,then the CUVLO is discharged,and it is shifted to the SKIP movement. Therefore, the
UVLO terminal voltage is discharged from the condition of 1V, and the discharge is continued until
“VUVLO (RST) = 250m V”.
After the discharge is finished,by the composition resistance of RUVLO1 and RUVLO2, the CUVLO is charged
again to VUVLO=1V, this is repeated.
The composition resistance of RUVLO1 and RUVLO2 : RSUM=(RUVLO1×RUVLO2)／(RUVLO1＋RUVLO2)
The divided voltage by voltage dividing resistor "RUVLO1 and RUVLO2": VUVLODIV=VIN×RUVLO2／RUVLO1＋RUVLO2
The terminal voltage of CUVLO at the time "t" by charging =VUVLODIV×(1－e-(t／CUVLO×RSUM) )
･･･(9)
Fig 17 is discharge and charge curve calculation example in setup of CUVLO=0.011μF, in the condition of
VIN=110V, RUVLO1=3.6MΩ, RUVLO2=100kΩ.
The interval of SKIP (TINTSKIP) : (discharge time of 1V→0.25V) + (charging time of 0.25V→1V).
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.16
LC5901S DATA SHEET
Rev.1.5
Discharge time
Charge time
(A) Discharge time curve
(B)Charge time curve
fig.17 discharge and charge curve calculation example
* Adjust CUVLO, and decide a SKIP interval with confirming the heat-generation of each part during the SKIP
movement.
7.9 Maximum ON Time Protection
By the factor such as the short circuit of the output current detection resistor R CS and the decline of the LED drive
power supply voltage, the Maximum ON-period limitation is set up for the PowerMOSFET drive signal, as a
protection when the PowerMOSFET drive signal VOUT continues "High condition".When the ON-period reaches
maximum ON-period tONMAX=220μsec (Typ), the PowerMOSFET drive signal VOUT is shifted to the "Low level"
immediately, and a UVLO discharge switch activates. In this case as well, it becomes same control that SKIP on
the OCP condition. A fig 18 is a waveform that is Maximum-ON-Time-Protection by LED string opening.
LED string is opened
Ch1:VLED:50V/div
Ch2:VUVLO:1V/div
← zero of Ch1&Ch2
Ch3:VCS:1V/div
← zero of Ch3
Ch4:Id:0.5A/div
← zero of Ch4
Time div:400μsec
fig.18 the waveform example of the “Maximum-ON-Time-Protection”.
7.10 Thermal Shutdown(TSD)
When temperature of the IC becomes beyond "Thermal-shutdown activation temperature TJ (TSD) typ. = 150℃
",then the movement is stopped immediately, and the condition of the movement-stop is maintained. It is resumed
to the normal operation automatically when temperature of the IC becomes below "T J (TSD) -TJ (TSD) HYS".
TJ (TSD) HYS is set up in about 30℃.
*Precaution
It is a purpose that as for the "Thermal-shutdown", interrupts an IC from the "Thermal-runaway" against the
"Heat-Generation" due to increase in a loss by the momentary short circuit and so on. In the condition that
continuous-short-circuit and continuous-heat-generation, the movement that is including reliability isn't assured.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.17
LC5901S DATA SHEET
Rev.1.5
8. Precautions for Design
8.1 Peripheral parts
Use each part what conforms to the use condition.
・Input-smoothing-capacitor(Aluminum electrolytic capacitor)
Set up a design margin about the Ripple-current and the withstand-voltage and the life-period properly.
Use the aluminum electrolytic capacitor which has high-allowable-ripple-current value and low-impedance
character for the “Switching-power-supply”.
・Inductor
Set up a design margin properly against rise in temperature by copper loss and the iron loss.
Set up a design margin properly against the magnetic saturation.
・Current detection resistor
As the current detection resistor,use the part which is small-parasitic-inductance and satisfies an allowable power
loss, because high frequency switching current flows.
8.2 Inductor Design
In the LC5901S,with a calculation example of a stage of design,the setup of inductance which becomes the
continuous current mode is recommended. Be careful of this because it is the condition to comply with the
control method of this IC.
Because the LC5901S works as buck converter, as a LED drive power supply, it must supply the voltage beyond
VF of LED which becomes a load. Though it is the PRC method of "fixed T OFF", the TOFF-period is set up by the
resistance value of the setup resistor RRT. A TON-period is controlled automatically, it copes with a voltage V LED to
supply to the LED string. When the voltage (VF×n) of the LED string changes,the frequency changes because TON
changes. VF of LED to use for the calculation must substitute the worst condition value. As the "ON-Duty" of
Buck-converter, there are following relations when VLED is supposed to be high enough, and VF of Flywheel diode
DS is omitted…
･1cycle of Switching T=TON＋TOFF ･･･(10)
･Duty=TON／T=VLED／VIN ･･･(11)
･TON=D×T ･･･(12)
･T=TOFF／(1―D) ･･･(13)
･Switching frequency FOSC=1／T ･･･(14)
Here, about the setup of lowered frequency... When a TOFF-period was set up long, be careful that the
switching-frequency doesn't move into audible frequency range. For example, when it was set up with
TOFF=10μsec, in case of Duty=0.5, 1cycle becomes T=20μsec, therefore the switching-frequency becomes
FOSC=50kHz. In case of Duty=0.8,1cycle becomes T=50μsec, the switching-frequency becomes FOSC=20kHz.
Because the person who can hear the sound of 20kHz by excellent sense of hearing exists,too. In the worst case,
it is recommended that the switching-frequency is set up beyond 30kHz.
Set up the inductance value so that inductor current may become the continuous conduction mode (Continuous
Conduction Mode : CCM). As much as possible, the inductance value is to establish big value so that the
ripple-current may decrease. Then the LED current ILED,and the inductor current become equal mostly. An average
of output current ILED is prescribed with ILED (AVE) . The ripple current is prescribed with ⊿IL. The condition of the
CCM movement becomes the following equation.
ILED(AVE) - ⊿IL / 2 > 0 ･･･(15)
An increment of inductor-current during the ON-State (TON-period) of the PowerMOSFET：⊿ION, The decrement
of inductor-current during the OFF-State (TOFF-period) of the PowerMOSFET：⊿IOFF.
The relations with a ripple-current ⊿IL become “⊿ION=⊿IOFF=⊿IL”.
Because VF is small enough to VLED, and it supposes to ignore VF, As for the ⊿IOFF…
⊿IOFF=VLED×TOFF / L ･･･(16)
It is shown.
It is supposed here as follows.→Number of serial connection of LED:14pcs ,each VF:3.5V, As for necessary VLED...
VLED=3.5V×=14pcs=49V,and ILED=0.35A,Input voltage VIN=110V.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.18
LC5901S DATA SHEET
Rev.1.5
A recommendation of the inductor current condition is the continuous conduction mode...
CCM condition ：ILED(AVE)－(⊿IL／2)＞0 ･･･(15／Review)
ILED(AVE)=0.35A , in accordance with the equation (15) by the condition of the CCM.
⊿IL＜0.7A
With this, the ripple current of COUT which is parallel connection with a LED string is big.
So, because "⊿IL/Io=0.2～0.3" is recommendation of general Buck-type DC/DC converter, the ratio of ⊿IL is
prescribed with 30% of ILED, (⊿IL=0.105A).
From the calculation example of the fig 6, when the frequency is supposed "FOSC=55.55kHz" in case of
"RRT=100kΩ", necessary inductance value is calculated as follows...
L≧{(VIN－VLED)×VLED}／(⊿IL×VIN×FOSC) ･･･(17)
In accordance with the equation (17)...
L≧{(110V－49V)×49V}／(0.105A×110V×55.55kHz)≒4.7[mH]
It is calculated like this.
In case of part selection,the inductor must satisfy DC-superimpotion characteristic based on inductance value
found by the calculation, and it is asked not to cause magnetic saturation with I LED of the use. And, it is necessary
that a heat-generation by DCR of the wire-windings is less than manufacturer guarantee value.
8.3 Flywheel Diode
To revive energy during the OFF-preiod of external PowerMOSFET in a switching-cycle,the Flywheel diode
(Flywheel Diode DS of the figure 3) is necessary. Be sure to use the Fast Recovery Diodes / the Ultra Fast
Recovery Diodes which has short reverse-recovery-time (Trr). Don't use the Rectifier Diode which the
reverse-recovery-time is long. (for example, for rectification of commercial-power-supply.)
Because the big short circuit current flows in recovery-period then diode is giving off heat itself and the
normality movement of the main circuit is obstructed, in the worst case,it is sometimes damaged. And, by the use
condition, if the reverse-direction-withstand-voltage can be permitted, the Schottky Barrier Diodes is possible to
use. As for current of the Flywheel Diode, the peak current of "I LED+ (⊿ IL/2)" flows in the T OFF-period, and it
is repeated in the switching-frequency.
8.4 The Input Smoothing Capacitor(Aluminum electrolytic capacitor)
When the power source supplied to main circuit has an impedance = 0 which is an ideal case, the input current to
main circuit is supplied 100% by the power supply and ripple current scarcely flows across the smoothing
capacitor, but in specifying the ripple current of the capacitor, the worst condition is considered on the assumption
that there exists no ideal power supply.It is assumed that the current is supplied 100% by the worst smoothing
capacitor. An input smoothing electrolytic capacitor repeats discharge and charge. A calculation is done with the
following process.
IIN(AVE)=ILED×D
･･･(18)
※D：Duty (=VLED／VIN or TON／TON+TOFF)､ ILED: LED average current
As for the inductor ripple current ⊿IL…
⊿IL={(VIN－VLED)×TON}／L
ILp’={ILED+(⊿IL／2)}－IIN(AVE)
ILb’={ILED－(⊿IL／2)}－IIN(AVE)
･･･(19)
･･･(20)
･･･(21)
1)Discharge Current
fig.19 Ripple current model
･･･(22)
in the input smoothing
electrolytic capacitor
2)Charge Current
･･･(23)
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.19
LC5901S DATA SHEET
Rev.1.5
3)Total ripple current of Input Smoothing Electrolytic Capacitor (ICIN)
･･･(24)
(Calculation example)
*Conditions:VIN=110VDC､VLED=49V(3.5V×14pcs)､ILED=0.35A､Duty=0.445､RRT=100kΩ(TOFF=10μsec)､
TON=8μsec､in case of⊿IL=0.105A, When it is calculated by using the equation (18) – (24)…
･IIN(AVE)=0.35A×0.445=0.156A
･ILp’={0.35A＋(0.105A／2)}－0.156A=0.246A
･ILb’={0.35A－(0.105A／2)}－0.156A=0.141A
●Discharge current
･ICIN RIPPLE(DIS)=SQRT{8μsec×(0.246A2＋0.246A×0.141A＋0.141A2)／3×18μsec}=0.131A
●Charge current
･ICIN RIPPLE(CHG)=SQRT{(1-0.445)×0.156A2}=0.116A
●Total ripple current
ICIN RIPPLE=SQRT{0.131A2＋0.116A2}=0.175A(RMS)
When the derating against allowable ripple current of the electrolytic capacitor is set at 90%, and you must select
the part, it is necessary that can flow current more than "ICIN RIPPLE/0.9=0.194A" .
8.5 Current Detection Resistor
As for the current detection resistor can't use a inductive resistor such as a wire-winding type. Unexpected faulty
operation sometimes occurs by the surge-voltage in a parasitic inductance element and so on. Use non-inductive
resistor such as Metal Plate Resistor /Metal Film Resistor/Carbon Film Resistor. Mount so that lead may become
as short as possible in case of Axial lead-type/Radial lead-type .
*Calculation of loss
Conditions:RCS=2.2Ω, RRT=100kΩ, RREF=64.16kΩ, VREF=0.77V(ILED=0.35A)
As for the average loss of the detection resistor RCS, when the current of RCS is prescribed with IRCS…
IRCS=ILED×D
PRCS=IRCS2×RCS
･･･(25)
･･･(26)
IRCS=0.35A×0.445=0.156A
PRCS=0.156A2×2.2Ω=53.5mW
In case of normal operation,when it thought about only this,1/4W or 1/8W seems to be all right as a power-rating
of the 2.2Ω resistor.
But, for some reason, for example, when they became "V CS=2.5V, IRCS=1.136A" continuance under
abnormal condition. To prevent "RCS of 2.2Ω" from being damaged on this worst condition...
For example, PRCS’=1.136A2×2.2Ω=2.839W. ←This electric power is consumed in RCS.
When the derating-factor is supposed 50%, the current detection resistor to stand 5.678W is necessary.
And, it shall not be applied when there is protection cooperation with the fuse and so on separately.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.20
LC5901S DATA SHEET
Rev.1.5
8.6 External PoweMOSFET
Selecting condition :
1)Maximum input voltage of between Drain and Source (VDSS)
The voltage of “VIN-VF (Flywheel Diode)” is inputted between Drain of the PowerMOSFET and Source in
the TOFF-period. But, when it considers that the surge-voltage is superimposed on the Vds at the time of
turn-OFF. When it is selected in consideration of the safety, as for the Good selection of Vdss, it may be an
approximate goal of more than 2 times of V IN.
2) Maximum input voltage of between Gate and Source (VGSS)
The gate drive voltage of LC5901S is not fixed, and changes in proportion to the VCC voltage. Pay
attention to this point. When it seems that the VCC voltage fluctuates to an upper limit 17V of the
recommendation range, select the VGSS specification of 20V-30V. Fundamentally,when stabilized 12V is being
inputted to the VCC terminal, the peak value in the pulse wave form of V OUT is about 12V.
3)Others…
In the PowerMOSFET,there is the tendency that the kind of the big internal chip in the big package has
low-on-resistance. But, there is the relationship of trade-off. Because, for example the Ciss (capacitance of
junction) and so on increases, and big drive current is necessary. When the drive ability of LC5901S is taken into
consideration, it seems that the PowerMOSFET of TO-220 classes or smaller size is good selection as a
combination.
8.7 The Output Smoothing Capacitor
Decide a COUT excuse and capacity in accordance with ripple current specifications of the LED string. When
the ripple current can be set up greatly, the inductance value of inductor can be set up small, and C OUT capacity
can be decreased or deleted. By this setup,the decrease of the scale of the circuit and the cost can be done. When
you make the ripple current small, enlarge the inductance value of innductor, and or connect C OUT to the LED
string by parallel-connection. When the ripple current is set up small, the heat-generation of LED by a fluctuation
of the ripple current can be decreased. And, when a LED string is in the far position from the OUTPUT, the
COUT should be connected near the LED string by parallel-connection, and reduce the ripple current.
The ripple current effective value of output capacitor is calculated from the equation (27).
Irms 
⊿IL
-----(27)
2 3
In case of “⊿IL = 0.5A”,
Irms 
0.5
2 3
Therefore a capacitor with the allowable ripple current of 0.14A or higher is
needed. The output ripple voltage of regulator Vrip is determined by the
product of choke current ripple portion ΔIL (= COUT) discharge and charge
current) and output capacitor COUT equivalent series resistance ESR.
≒ 0.14 A
Vrip  ⊿IL  Cout ESR -----(28)
It is necessary to select a capacitor with low equivalent series resistance ESR in order to lower the output ripple
voltage. As for general electrolytic capacitors of same product series, the ESR shall be lower for products of
higher capacitance with same breakdown voltage, or of higher breakdown voltage with same capacitance.
When ⊿IL = 0.5A, Vrip = 40mV,
Cout ESR  40  0.5  80m
A capacitor with ESR of 80mΩ or lower should be selected. Since the ESR varies with temperature and
increases at low temperature, it is required to check the ESR at the actual operating temperatures. It is
recommended to contact capacitor manufacturers for the ESR value since it is peculiar to every capacitor series.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.21
LC5901S DATA SHEET
Rev.1.5
8.8 PCB Layout & Recommended Land Pattern
8.8.1 Example pattern trace
The pattern traces of the demonstration board of LC5901S is shown in the following.
* Demonstration board (For Evaluation board :t=1.6mm,Single sided PCB,Thickness of Cupper foil=35μm)
fig.20(A) Top Layer(Silk printing)
fig.20(B). Bottom Layer(Back side)
* The above circuit board has the possibility that it is amended for the improvement.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.22
LC5901S DATA SHEET
Rev.1.5
NOTES: For SOP8 package
1) Dimension is in millimeters, dimension in bracket is in inches.
2) Drawing is not to scale.
fig.21 Recommended land pattern(Foot printing)
8.8.2 The circuit diagram of the Demo-board
P_VIN:DC110V, VCC=13V, L01=2.2mH, C1=1nF, C2=C3=22nF, C4=Open, C5=0.22μF, C6=220pF,
C7=Open, C8=0.33μF/250V, C9=22μF/25V, C10=10μF/250V, D01=SF28G, D02=1N414WS, IC04=none,
Q1=KF9N25D, R1=Open, R2=none, R3=none, R4=none, R5=6.8kΩ, R6=R7=R8=1MΩ, R9=100kΩ,
R10=200kΩ, R11=100Ω, R12=10Ω, R13=10kΩ, R14=1kΩ, R15=1Ω/2W, R16=2Ω/2W, R17=Open,
* An optional part is contained because it is the circuit board which evaluates an experiment, too.
fig.22 The circuit diagram of the Demo-board
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.23
LC5901S DATA SHEET
Rev.1.5
8.8.3 Attention in circuit board design .
PCB circuit trace design and component layout affect IC functioning during operation. Unless they are proper,
malfunction, significant noise, and large power dissipation may occur.
Circuit loop traces flowing high frequency current, as shown in fig.23, should be designed as wide and short as
possible to reduce trace impedance.
In addition, earth ground traces affect radiation noise, and thusshould be designed as wide and short as possible.
Switching mode power supplies consist of current traces with high frequency and high voltage, and thus trace design
and component layout should be done in compliance with all safety guidelines.
Furthermore, because an integrated power MOSFET is being used as the switching device, take account of the
positive thermal coefficient of RDS(ON) for thermal design.
fig.23 High frequency current loops（hatched portion）
IC peripheral circuit
(1) Main Circuit Traces
Main circuit traces carry the switching current; therefore, widen and shorten them as much as possible.
The loop formed with CIN, VIN pin, and GND pin should be small in order to reduce the inductances of the
traces against high frequency current.
(2) Traces around GND pin
Main circuit GND and Control circuit GND should be connected to the vicinity of GND pin with dedicated
traces respectively, in order to avoid interference of the switching current with the control circuit.
(3) Traces around the current detection resistor, RCS
To decrease noise in the current detection, wire the neighborhood of RCS for the pattern of RCS connected
with the CS terminal and the CS terminal by the special pattern.
(4) Peripheral components
Connect the TOFF setup resistor RRT and the reference voltage setup resistor RREF near the GND terminal in the
same way, too. Be careful that the GND-pattern where the main-circuit-current flows, and a signal
GND-pattern don't become the common-impedance.
(5) When COUT is used, it should be connected close to LED string.
* As for the GND pattern, be careful that routes for the Main-circuit(switching current flows), and the routes
for the small-signal don’t become common impedance.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.24
LC5901S DATA SHEET
Rev.1.5
9. Design flow chart
Inductor setup
VLED：(VF×n)
VIN
ILED
Setup condition
PowerMOSFET
Flywheel-diode setup
Caluculation of Duty
COUT setup
RRT
TOFF setup
CIN setup
TON
Calculation of FOSC
External UVLOsetup
RUVLO1
RUVLO2
SKIP internal setup
CUVLO
This flow chart is for design rationale
(on paper) that a fixed number is only set up.
RREF→VREF
RCS→VCS
RREF vs. ILED setup
The noise(EMI) countermeasure in the actual
working and the thermal countermeasure aren't
contained.
As for these, adjust it by the actual working
experiment separately.
⊿IL setup
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.25
LC5901S DATA SHEET
Rev.1.5
10. Packing specifications
10.1 Taping & Reel outline
φ1.55
Pocket
5.55
5.5
0.3
12.0
Round
Sprocket
Holes
φ2.05
6.7
2.47
8.0
4.0
EIAJ No.TE1208
2.0
fig. 24 Taping outline
Notes:
1) All dimensions in millimeters
2) Surface resistance：under 109Ω
3) Drawing is not to scale
Notes:
1) All dimensions in
millimeters
2) Drawing is not to
scale.
φ13
±0.2
EIAJ No.RRM-12DC
13.5 ±0.5
17.5 ±1.0
fig. 25 Reel outline
Copy Right: SANKEN ELECTRIC CO., LTD.
φ330±2
±0.8
φ80±1
φ21
Page.26
Quantity
4000pcs／reel
LC5901S DATA SHEET
Rev.1.5
11.Typical characteristics
Conditions：VCC=12V,RRT=10kΩ，RREF=5kΩ，Ta=25℃
8.1 VCC vs. ICC(ON)
8.2 VCC vs. ICC(OFF)
fig.26
fig.27
8.3 VPWM vs. VOUT
8.4 VUVLO vs. VREF
fig.28
fig.29
8.5 VUVLO vs. IUVLO
8.6 VCS vs. IUVLO (VCS=2.5V→OCP/HICCUP)
fig.30
Copy Right: SANKEN ELECTRIC CO., LTD.
fig.31
Page.27
LC5901S DATA SHEET
Rev.1.5
8.8 Ta vs.Ton(Min)
←Activate
Recovery→
8.7 Ta vs. VOUT (Thermal Shut-down Activation)
fig.32
fig.33
8.9 Ta vs. Ton(Max)
8.10 Ta vs. T OFF (RRT=10kΩ)
fig.34
fig.35
8.11 Ta vs. TOFF(RRT=80kΩ)
8.12 Ta vs.VREF(RREF=5kΩ)
fig.36
fig.37
8.13 Ta vs. PWM Pin Pull-down Resistance
fig.38
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.28
LC5901S DATA SHEET
Rev.1.5
IMPORTANT NOTES
 The contents in this document are subject to changes, for improvement and other purposes, without notice.
Make sure that this is the latest revision of the document before use.
 Application and operation examples described in this document are quoted for the sole purpose of
reference for the use of the products herein and Sanken can assume no responsibility for any infringement
of industrial property rights, intellectual property rights or any other rights of Sanken or any third party
which may result from its use.
 Although Sanken undertakes to enhance the quality and reliability of its products, the occurrence of
failure and defect of semiconductor products at a certain rate is inevitable. Users of Sanken products are
requested to take, at their own risk, preventative measures including safety design of the equipment or
systems against any possible injury, death, fires or damages to the society due to device failure or
malfunction.
 Sanken products listed in this document are designed and intended for the use as components in general
purpose electronic equipment or apparatus (home appliances, office equipment, telecommunication
equipment, measuring equipment, etc.).
When considering the use of Sanken products in the applications where higher reliability is required
(transportation equipment and its control systems, traffic signal control systems or equipment, fire/crime
alarm systems, various safety devices, etc.), and whenever long life expectancy is required even in general
purpose electronic equipment or apparatus, please contact your nearest Sanken sales representative to
discuss, prior to the use of the products herein.
The use of Sanken products without the written consent of Sanken in the applications where extremely
high reliability is required (aerospace equipment, nuclear power control systems, life support systems,
etc.) is strictly prohibited.
 In the case that you use Sanken semiconductor products or design your products by using Sanken
semiconductor products, the reliability largely depends on the degree of derating to be made to the rated
values. Derating may be interpreted as a case that an operation range is set by derating the load from each
rated value or surge voltage or noise is considered for derating in order to assure or improve the reliability.
In general, derating factors include electric stresses such as electric voltage, electric current, electric
power etc., environmental stresses such as ambient temperature, humidity etc. and thermal stress caused
due to self-heating of semiconductor products. For these stresses, instantaneous values, maximum values
and minimum values must be taken into consideration.
In addition, it should be noted that since power devices or IC’s including power devices have large
self-heating value, the degree of derating of junction temperature affects the reliability significantly.
 When using the products specified herein by either (i) combining other products or materials therewith or
(ii) physically, chemically or otherwise processing or treating the products, please duly consider all
possible risks that may result from all such uses in advance and proceed therewith at your own
responsibility.
 Anti radioactive ray design is not considered for the products listed herein.
 Sanken assumes no responsibility for any troubles, such as dropping products caused during transportation out of Sanken’s distribution network.
 The contents in this document must not be transcribed or copied without Sanken’s written consent.
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.29