LC5720S Application Note Rev.1.0

LC5720S APPLICATION NOTE
LC5720S
Application Note
Rev.1.0
Rev.1.0
SANKEN ELECTRIC CO., LTD.
http://www.sanken-ele.co.jp
Copy Right: SANKEN ELECTRIC CO., LTD.
Page.1
LC5720S APPLICATION NOTE
Rev.1.0
CONTENTS
General Descriptions ................................................................................................................. 3
1. Absolute Maximum Ratings ............................................................................................ 4
2. Recommended Operation Conditions............................................................................. 4
3. Electrical Characteristics ................................................................................................. 5
4. Functional Block Diagram ............................................................................................... 7
5. Pin Assign & Functions .................................................................................................... 7
6. Typical Application Circuit ............................................................................................. 8
7. Package Information ........................................................................................................ 9
8. Functional Description ................................................................................................... 10
8.1 PWM Current Control.......................................................................................... 10
8.2 LED Dimming ........................................................................................................ 11
8.3 Overcurrent Protection Function (OCP) ............................................................ 11
8.4 Overvoltage Protection Function (OVP) ............................................................. 12
8.5 Selection of application circuit ............................................................................. 12
8.6 Setting of External Inductor ................................................................................. 15
8.7 The Internal Power Dissipation Pd ...................................................................... 17
8.8 Phase Compensation (COMP terminal) .............................................................. 20
8.9 Peripheral Parts Design ........................................................................................ 22
8.10 Peripheral Parts Design ...................................................................................... 22
9. Example Pattern Layout ................................................................................................ 24
10. Design Considerations .................................................................................................. 26
IMPORTANT NOTES ........................................................................................................... 28
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Page.2
LC5720S APPLICATION NOTE
General Descriptions
Rev.1.0
Package
SOP8
The LC5720S product is the power IC for LED
driver which incorporates a power MOSFET and a
controller IC in a package.
This product is a DC/DC converter which features
are; wide input voltage range, 500kHz operating
frequency, and Buck/ Boost/ Buck-Boost converter
can be selected with external circuit configuration.
LED string current can be set with the external
resistor, and LED dimming can be controlled by the
digital input signal. The rich set of protection
features helps to realize low component counts, and
high performance-to-cost power supply.
Characteristics
Features
Input voltage range
Output current
RDS(ON)
 Operation Types: The following converter types
are applicable by the external circuit configuration
・Buck Converter
・Boost Converter
・Buck-Boost Converter
 High Efficienby: η > 90%(TYP)
 Operation Frequency: 500kHz(TYP)
 LED string current setting with an external resistor.
 Current Detection voltage of LED string:
100mV±5%
Thus, low power loss and high accuracy LED
string current can be achieved by setting of an
external resistor.
 PWM Dimming Frequency: available to
20kHz(MAX)
 Package: HSOP8
Heat slag in the back can increase heat dissipation
effect by connecting it to GND pattern
 Protection Functions
・Overcuurent Protection Function (OCP)
------ Pulse-by-pulse basis
・OvervoltageProtection Function (OVP)
------ Auto restart
・Thermal Shutdown Protection Function (TSD)
------ Auto restart
9.5V (MIN)～50V(MAX)
2A(MAX)
215mΩ(TYP)
Applications
 LED lighting fixtures
 LED light bulbs
Product name
Lot Number(3digit)
LC5720S
SK YMW
xxxx
Y=The last digit of the year：(0 to 9)
M= Month：
(1 to 9,O=”10”,N=”11”,D=”12”)
W=Manufacturing week：
(1 to 5)
Control Number(4digit)
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Page.3
LC5720S APPLICATION NOTE
Rev.1.0
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.
 Unless specifically noted, Ta is 25°C
Table.1
Characteristic
Pins
Symbol
Rating
Unit
VIN Pin Voltage
5－3
VIN
−0.3 to 50.0
V
SW Pin Voltage
4―3
VSW
−0.3 to 50.0
V
CSP Pin Voltage
6―3
VCSP
−0.3 to 50.0
V
CSN Pin Voltage
Differential Voltage
bwteen CSP and CSN Pins
COMP Pin Voltage
7―3
VCSN
−0.3 to 50.0
V
6―7
VCSP-CSN
−0.3 to 5.5
V
1―3
VCOMP
−0.3 to 5.5
V
8―3
VDIM
−0.3 to 5.5
V
(2)
―
PD
1.35
W
(3)
―
TJ
125
°C
(2)
―
θj-a
74
℃/W
(1)
―
Top
−40 to 125
°C
―
TSTG
−40 to 150
°C
DIM Pin Voltage
Allowable Power Dissipation
of MOSFET
Junction Temperature
in Operation
Thermal Resistance
(junction-ambient air)
Operating ambient
temperature
Notes
(1)
Storage Temperature
(1)
However, it is limited by Junction temperature.
(2)
When mounted on a 40×40mm Glass-epoxy board (copper area in a 25×25mm).
Non-movement
(3)
Thermal shutdown temperature is approximately 150°C
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
Pins
Symbol
MIN
MAX
Unit
VIN Pin Voltage
5−3
VIN
9.5
50
V
CSP Pin Voltage
6−3
VCSP
4.75
50
V
―
Io
0
2
0
1
―
∆IL
－
0.8
Output current
Peak to Peak Inductor Ripple
current
(4)
A
A
Operating ambient
(4)
-40
+85
Top
―
℃
temperature
(4)
To be used within the allowable package power dissipation characteristics (fig. 1)
(5)
Buck circuit：2A, Boost circuit／Buckboost circuit：1A, ⊿IL ≦0.8A.
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Page.4
Notes
(5)
Buck
(5)
Boost/Buckboost
LC5720S APPLICATION NOTE
Rev.1.0
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.
Electrical Characteristics of Control Part (MIC) Unless specifically noted, Ta is 25°C, VIN=15V
Characteristic
Pins
Symbol
MIN
TYP
MAX
Unit
Operation Start Voltage
5−3
VIN(ON)
7.7
8.5
9.4
V
Operation Stop Voltage
5−3
VIN(OFF)
7.2
8.0
8.9
V
Operation Hysteresis Voltage
5−3
VIN(HYS)
0.1
0.3
0.5
V
Circuit Current in Operation
Circuit Current in
None-Operation
Operation Frequeny
5−3
IIN(ON)
3.0
4.5
7.0
mA
5−3
IIN(OFF)
400
600
1000
μA
4−3
fOSC
420
500
570
kHz
Minimum On-Duty Cycle
4−3
tON(MIN)
50
75
100
ns
VCOMP=0V
Maximum On-Duty Cycle
4−3
DMAX
89
94
98
%
VCOMP=4V
On-Time1
4−3
tON(1)
300
600
800
ns
VCOMP=0.7V
On-Time2
4−3
tON(2)
0.85
1.4
1.8
μs
4−3
tCON
0.14
0.33
0.63
μs
VCOMP=1.2V
VCOMP=0.7V,
ISW=2A
Current Detection Voltage
6−7
VCS
95
100
105
mV
CSP Pin Sink Current
6−3
ICSP
85
130
175
μA
CSN Pin Sink Current
7−3
ICSN
40
65
95
μA
CSP Pin Minimum Voltage
6−3
VCSP(MIN)
4.75
―
―
V
COMP Pin Source Current
1−3
ICOMP(SRC
−95
−60
−38
μA
VCS=20mV,
VCOMP=2V
COMP Pin Sink Current
1−3
ICOMP(SNK)
38
60
95
μA
VCS=180mV,
VCOMP=2V
―
gM
―
750
―
μs
VCS=50 to 150mV
6−7
VCS(OVP)
200
240
280
mV
4−3
ISW(LIM)
2.5
3.5
4.7
A
4−3
RSW(L)
―
200
―
mΩ
DIM Pin Voltage for LED On
8−3
VDIM(ON)
1.2
1.4
1.7
V
DIM Pin Voltage for LED Off
8−3
VDIM(OFF)
0.75
1
1.2
V
8−3
VDIM(HYS)
0.3
0.5
0.7
V
FDIM
32
―
20000
Hz
TJ(TSD)
150
160
―
°C
TJ(TSDHYS)
―
20
―
°C
On-Time for Current Contol
(6)
Error Amplifier Conductance
Overvoltage Protection
(OVP) Threshold Voltage
SW Pin Current Limit
SW Pin On-Resistance
(6)
DIM Pin Hysteresis Voltage
(6)
DIM Pin Dimming Frequency
8−3
Thermal Shutdown Activating (6)
―
Temperature
Thermal Shutdown Hysteresis (6)
―
Temperature
(6)
Verified by design/characterization
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Page.5
Notes
VIN=6.5V
ISW=1A
LC5720S APPLICATION NOTE
Allowable package power dissipation
When mounted on a 40×40mm Glass-epoxy board (copper area in a 25×25mm).
fig.1
Package power dissipation of LC5720S
(Thermal Derating Curve)
Note1 : The power dissipation in fig.1 is calculated at the junction temperature 125 ℃.
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Page.6
Rev.1.0
LC5720S APPLICATION NOTE
Rev.1.0
4. Functional Block Diagram
fig.2 Block diagram
5. Pin Assign & Functions
Table.4
COMP
VDD
NC
CSN
GND
CSP
SW
Pin No.
Symbol
1
COMP
2
NC
3
GND
4
SW
5
VIN
6
CSP
7
CSN
8
DIM
Functions
DIM
EN/DIM
VIN
fig.3 Pin Assign
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External phase compensation terminal.
No-Connection
Ground terminal.
Switching Output. Switching node that drives the external
inductor.
Supply Input.
Input capacitor CIN is connected between VIN and GND.
Current Sense Input Positive. Reference potential for the
current sense input.
Current Sense Input Negative. Connect current sense
resistor to sense output current.
PWM Dimming Signal Input.
Page.7
LC5720S APPLICATION NOTE
Rev.1.0
6. Typical Application Circuit
Examples for LED lighting power supply
Input
voltage
5
CIN
VIN
CSP
6
RCS
LC5720S
LC5700S
CSN
COUT
7
ROVP
8
LED
DS
DIM
DZOVP
1
COMP
CS
CP
SW
GND
3
Output
voltage
4
L
RS

fig.4-1 Buck converter
Input voltage  Output voltage
Input
voltage
L
5
CIN
VIN

DS
6
CSP
RCS
LC5720S
LC5700S
COUT
7
CSN
ROVP
8
1
DIM
COMP
CS
CP
GND
3
LED
4
SW
DZOVP
Output
voltage
RS

fig.4-2 Boost converter
Input voltage  Output voltage
Input
voltage
L

DS
CCSP
5
CIN
VIN
CSP
6
RCS
LC5720S
LC5700S
CSN
COUT
7
ROVP
8
LED
DIM
DZOVP
1
COMP
CS
CP
GND
3
SW
4
Output
voltage
RS

fig.4-3 Buck-Boost Converter
Input voltage  Output voltage  Input voltage
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Page.8

LC5720S APPLICATION NOTE
Rev.1.0
7. Package Information
HSOP8
8
7
6
5
1
2
3
4
Detail drawing of the A mark
NOTES:
1) All dimensions are in Millimeter
2) Pb-free. Device composition compliant with the RoHS directive
fig.5 Package outline
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Page.9
LC5720S APPLICATION NOTE
Rev.1.0
8. 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).
8.1 PWM Current Control
The current control circuit is shown in fig.6.
CS
RS
1
Osillator
COMP
+
CSP 6
RCS
－
ROVP
－
Q
S
+
－
External components
CSN 7
VCS
LED
COUT
Output
voltage
R
SW 4
+
+
Σ
－
fig.6 Current control circuit
For enhanced response speed and stability, current mode control (peak current mode control) is used for constant
current control of the output current.
The operating frequency, fOSC, is fixed to 500kHz.
LED string current is detected by the current detection resistor, RCS.
The voltage of RCS is detected by both CSP and CSN pins. This IC compares this voltage with the Current Detection
Voltage, VCS, and makes a target value for current control.
The constant current is controlled so that the detection voltage of peak current of internal power MOSFET is close to
the target value, and thus the LED string current is constant.
The constant current of LED string, IOUT, is calculated by the following with RCS as the current detection resistor and
ROVP as the resistor for overvoltage protection in the case that LED string is open.
IOUT 
where;
VCS  ICSN  (RCS  ROVP)
RCS
･･･(1)
ICSN : the CSN Pin Sink Current, 9.5μA.
VCS : the Current Detection Voltage, 100mV.
Also, IOUT can be expressed by the following, if ICSN×(RCS+ROVP) is negligibly small against VCS.
IOUT 
VCS
RCS
･･･(2)
ROVP value should be chosen so that IOUT is within the acceptable accuracy range referring to the calculation in “8.4
Overvoltage Protection Function (OVP)”.
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Page.10
LC5720S APPLICATION NOTE
Rev.1.0
8.2 LED Dimming
LED dimming is controlled by the duty cycle of PWM digital signal which is input to DIM pin.
The constant current output turns ON/OFF by the following signal input voltage to DIM pin which is within the
absolute maximum rating; −0.3V to 5.5V.
・When DIM Pin Voltage for LED On, VDIM(ON)= 1.4V or more is input, IOUT flows.
・When DIM Pin Voltage for LED Off, VDIM(OFF)= 1V or less is input, IOUT stops.
The constant current value is controlled with the current detection resistor, R CS, and the current detection voltage, VSC.
When DIM pin voltage is less than VDIM(ON), COMP pin voltage is held with the fixed voltage, and when DIM pin
voltage is more than VDIM(ON), COMP pin voltage is increased from this hold voltage.
This makes the constant current startup speed fast at DIM dimming.
The Dimming-ratio depends on the duty ratio of the PWM-digital-dimming signal pulse (fig.7).
PWM Dimming with 1kHz, Duty 50%
PWM Dimming with 1kHz, Duty 25%
CH2: Dimming signal (2V/div)
CH3: LED current
(0.2A/div)
CH1: SW pin voltage (10V/div)
PWM Dimming with 1kHz, Duty 75%
fig.7
PWM Dimming with Duty 100%
Actual waveform in Dimming operation
8.3 Overcurrent Protection Function (OCP)
The IC incorporates Overcurrent Protection Function (OCP) limited the current flowing to SW terminal (fig.8).
When the current to SW terminal reaches ISW(LIM)= 3.5A, the internal power MOSFET turns off on pulse-by-pulse
basis.This protection is activated in case of the constant current detection failure or the output end shorted.
SW 4
PWM
LOGIC
+
OCP
－
GND 3
fig.8
Overcurrent protecton circuit
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Page.11
LC5720S APPLICATION NOTE
Rev.1.0
8.4 Overvoltage Protection Function (OVP)
If LED string is open and the constant current loop is cut, the output voltage increases more than the controlled
voltage. As shown in fig.9, the OVP Function with the circuit connected ROVP and a zener diode, DZOVP, is done OVP
protection. After LED string is open, when DZOVP is conducted, the output voltage is limited to the sum voltage of the
zener voltage of DZOVP and the Overvoltage Protection (OVP) Threshold Voltage, VCS=240mV.
CSP
6
RCS
ICSN
CSN
CSP
COUT
7
CSN
6
RCS
ICSN
7
ROVP
COUT
ROVP
IDZ
IOUT
DZOVP
DZOVP
LED
Normal operation
fig.9
LED string is open
Overvoltage protection circuit
The allowable current of DZOVP, IDZ, can be expressed by the following with PDZ as the allowable dissipation and VDZ
as the zener voltage of DZOVP.
IDZ 
PDZ
VDZ
･･･(3)
The ROVP value, by which the loss of DZOVP is less than the allowable dissipation, is chosen by the following with
ICSN as the CSN Pin Sink Current and RCS as the constant current detection resistor.
ROVP 
VCS ( OVP)
 RCS
IDZ  ICSN
･･･(4)
Also, when ICSN is negligibly small against IDZ, the approximate equation of Equation (4) becomes as follows.
ROVP 
VCS ( OVP)
 RCS
IDZ
･･･(5)
ROVP value should be chosen so that the loss of DZOVP is less than the allowable dissipation in OVP protection, and
IOUT is within the acceptable accuracy range.
DZOVP value, VDZ, should be chosen to be higher than the maximum output voltage of LED string to avoid DZ OVP
conduction during the normal operation.
8.5 Selection of application circuit
Select application circuit properly in the relations with the LED strings voltage and the input voltage VIN in the Table
6.
Table.6
Relations between the input voltage and the LED string voltage .
VIN＞(n × VFLED)＋Vcs
VIN＜(n × VFLED)＋Vcs
VIN(Low)＜(n × VFLED)＋Vcs＜VIN(High)
Circuit type
Buck
Boost
Buckboost
The number of LED which can be serial connection in LC5710S becomes as follows in the Table 7 in each circuit
type. But, there are the following 1) - 4) as a factor which a movement condition is restricted to.
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Page.12
LC5720S APPLICATION NOTE
Rev.1.0
1) Settlement of the input voltage under VIN (ON) ･･･The setup that VIN is under 9.5V is impossible by the start
condition of the IC.
2) VIN(MAX) or Vsw(MAX) ･･･As an example, the condition that VIN or Vsw voltage reaches 40V by
80%-derating against 50V which is the absolute maximum ratings.
3) A limitation (0.05<Duty<0.89) by the minimum or maximum ON-duty.
4) The input and output condition that "Inductor peak current ILp" reaches threshold of "SW current limit ISW
(LIM) =2.5A (Min)" .
Table.7
VIN(or Vsw)＜40V(50V×0.8), 0.05＜Duty＜0.89 are common condition.
Range of the VIN(V)
Number of
Vout or
Buck-type
Boost-type
Buckboost-type
LED (pcs)
(Serial
connection)
LED strings
voltage(V)
1
2
3
4
5
6
7
8
9
10
11
3.6
7.1
10.6
14.1
17.6
21.1
24.6
28.1
31.6
35.1
38.6
ILED=2.0A，⊿IL=0.8A
ILED=1.0A，⊿IL=0.4A
ILED=1.0A，⊿IL=0.4A
MIN(V)
9.50
9.50
11.91
15.84
19.78
23.71
27.64
31.57
35.51
39.44
MIN(V)
MAX(V)
9.50
9.50
9.50
10.30
11.80
13.40
15.20
16.80
18.40
10.07
13.40
16.72
20.05
23.37
26.70
30.02
33.35
36.67
MIN(V)
9.5
9.5
9.5
10.9
13.6
16.3
MAX(V)
40.00
40.00
40.00
40.00
40.00
40.00
40.00
40.00
40.00
40.00
MAX(V)
36.4
32.9
29.4
25.9
22.4
18.9
For non ･･･In case of following condition, VIN under VIN (ON), VIN or Vsw reaches 40V, and ILp reaches ISW(LIM),
it is the setup which doesn't become utility. When a table 7 is graphed, they are shown in the fig10 – the fig12.
Number of LEDs serial connection n(pcs)
Buck-type Number of LEDs serial connection vs．Range of VIN
×10
×9
×8
×7
×6
×5
×4
×3
×2
×1
0
5
10
15
20
25
30
Input voltage VIN(V)
fig.10
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Page.13
35
40
45
LC5720S APPLICATION NOTE
Rev.1.0
Number of LEDs serial connection n(pcs)
Boost-type Number of LEDs serial connection vs．Range of VIN
×11
×10
×9
×8
×7
×6
×5
×4
×3
×2
×1
0
5
10
15
20
25
30
Input voltage VIN(V)
35
40
45
fig.11
Number of LEDs serial connection n(pcs)
Buckboost-type Number of LEDs serial connection vs．Range of
VIN
×6
×5
×4
×3
×2
×1
0
5
10
15
20
25
30
35
40
45
Input voltage VIN(V)
fig.12
The fig12 – the fig14 are based on the calculation. You must reduce ILED,frequency and Vout when surge voltage
is big in the waveform of the SW terminal, and when the heat generation of the IC is high. And, you must use it
within the range of “Thermal Derating Curve” of the fig1.
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Page.14
LC5720S APPLICATION NOTE
Rev.1.0
8.6 Setting of External Inductor
The each operation of Buck, Boost and Buck-Boost converter is explained as follows.
The inductance value is designed so that the operation becomes Continuous Conduction Mode (CCM) which the
inductance current flows continuously, because the load current of LED lighting application is constant.
The duty, D, is set within the following range, based on “3. Electrical Characteristics”.
tON(MIN)×FOSC ＜ D ＜DMAX
･･･(6)
Therefore, Duty-D is within the range of 0.89 from 0.05 ( 0.05＜ D ＜0.89).
The output voltage, VOUT, can be calculated by the following with VOUT as the output voltage, IL as the inductor
current, and ΔIL as the ripple current of inductor current.
Vout= n×VFLED＋VCS
･･･(7)
where; VFLED : Forward voltage drop of a LED(･･･VF=3.5V／1PCS)
n : The number of LED in series
VCS : Current Detection Voltage, VCS= 100mV
Table.8
Equations to calculate Necessary Inductance L
Buck type
Boost type
Buckboost type
VIN
Vout
VIN＋Vout
SW terminal voltage
Vsw
ON-duty “D”
＋
Inductor average
current ILAVE
ILED
Inductor peak current
ILp
＋
Necessary Inductance L
⊿
⊿
＋
⊿
⊿
＋
⊿
⊿
In case of Buck-type, as for the Drain-current which flows into the SW terminal, Drain-current becomes equal to LED
current. But, in case of Boost-type, or in case of Buckboost-type, for example when the Duty-D is 0.5, if it is same
inductor-ripple current, Drain-current is doubled from Buck-type. Be careful to this point.
Inductor-ripple-current is "⊿IL=0.8A(Max)", it is based on a recommendation. And, by the condition of
internal-over-current-protection, because it is required that Inductor-peak-current “ILp” doesn't reach
"ISW (LIM) =2.5A (MIN)". Substantially, the current which can be supplied to LED becomes as follows (you must
satisfy together a temperature limitation referring to the fig.1).
*Buck- type ･･･ 2.0A ，⊿IL=0.8A(Max)
*Boost-type/Buckboost-type ･･･ 1.0A ，⊿IL=0.4A(Max)
A calculation example graph is shown as follows (Refer to the fig13－ the fig15).
And, a VF of white-LED for the lighting is prescribed with 3.5V, and calculated with 5pcs series-connection
(Vout=17.6V).
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Page.15
LC5720S APPLICATION NOTE
Rev.1.0
Buck-type Necessary Inductance L calculation example
LED=5pcs series,VIN=24V
Necessary Inductance L(μH)
100
10
1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Inductor-ripple current ⊿IL(A)
fig.13
Boost-type Necessary Inductance L calculation ezample
LED=5pcs series,VIN=12V
Necessary Inductance L(μH)
100
10
1
0.1
0.15
0.2
0.25
0.3
Inductor-ripple current⊿IL(A)
fig.14
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Page.16
0.35
0.4
LC5720S APPLICATION NOTE
Rev.1.0
Buckboost-type Necessary Inductance L calculation example
LED=5pcs series,VIN=Vout±20%
Necessary Inductance L(μH)
1000
fig13－fig15 Necessary
Inductance L calculation
example
*FOSC = 500kHz
*Number of LED = 5pcs series
The value of graph is calculated
following the equation in the
Table8.
100
10
1
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Inductor-ripple current⊿IL(A)
fig.15
Note:
*Necessary inductance value grows big by the setup whose “⊿IL is small”.
As a tendency of characteristics of the Inductor,
・In case of big Inductance value, allowable current limits decrease.
・The contour of Inductor becomes large with the core size when allowable current is satisfied and Inductance is
kept.
As a circuit application of the LED driver, it has Buck-type, Boost-type and Buckboost-type as same as the DC/DC
converter,
As a setup of ⊿IL, generally, it is said that the cost performance of 20%-30 % of the setups of output current is the
best.
When it says easily,"⊿IL=Iout×α(α=0.2 to 0.3)" is best choice.
8.7 The Internal Power Dissipation Pd
8.7.1 The loss Pcont of the control circuit
The loss Pcont of the control circuit depends on the input voltage and frequency. (fig.16) .
The loss of control circuit Pcont(mW)
LC5720S VIN vs. Pcont characteristics
450
400
350
300
250
200
150
100
50
0
0
5
10
15
20
25
30
35
40
45
50
Input Voltage VIN(V)
fig.16
The loss of the control circuit is prescribed with containing the steady loss by circuit static electric current Iq and
the drive loss which drives internal PowerMOSFET. A fig.16 is the total of the loss of circuit electric current and
the drive loss. Read near value in the fig.16, and substitute it when you calculate a loss.
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Page.17
LC5720S APPLICATION NOTE
Rev.1.0
8.7.2 The switching-speed of internal PowerMOSFET
As for the fig.17, in the calculation of the switching-time of internal PowerMOSFET, this is based on the
assumption with no influence such as Prasitic-Inductance in main-circuit. It is prescribed with "turn-on time tr" and
"turn-off time tf" being the same speeds.
The switching time(Tsw:tr,tf) (nsec)
LC5720S SW terminal voltage vs. Tsw characteristics
80
70
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
40
45
50
SW terminal voltage Vsw(V)
fig.17
However,actually,The internal PowerMOSFET is connected with the main-circuit of the voltage conversion part.
By the condition of pattern wiring, the switching-speed becomes fast, or becomes slow.
･In case of the pattern which Parasitic-Inductance inheres in, probably it becomes fast.
･In case of the pattern which high-impedance inheres in, probably it becomes slow.
Approve it in advance.
There is no problem if actual measurement value is substituted when an actual movement wave form can be
observed with oscilloscope and so on.
8.7.3 The loss of internal PowerMOSFET .
As the loss of internal-PowerMOSFET, there are the loss of "steady-ON" by the ON-resistance "Ron" between the
"source" and "drain", and the switching-loss by the switching-time in the fig.17.
Buck-type, Boost-type and Buckboost-type, the loss of PowerMOSFET of each type are shown the approximation
in the Table9.
Table.9
Loss of “Steady-ON” Pon
Switching loss Psw
Buck type
Ron×(ILED)2×Ton×Fosc
2×{VIN×(ILED／2)×Tsw×Fosc}
Boost type
Ron×(ILAVE)2×Ton×Fosc
2×{Vout×(ILAVE／2)×Tsw×Fosc}
Buckboost
type
Ron×(ILAVE)2×Ton×Fosc
2×{(VIN＋Vout)×(ILAVE／2)×Tsw×Fosc}
*
･Ton=(1／Fosc)×D･･･D=Duty (Refer to Table7.)
･Tsw is prescribed by the value (sec) of the fig19 with "turn-on time tr" and "turn-off time tf" being the same
speeds. In the same period, switching occurs twice. There is no problem if actual measurement value is
substituted when an actual movement wave form can be observed with oscilloscope and so on.
･Fosc= oscillating frequency (Hz)
･In case of the Buck-type, ILED(A)=ILAVE(A)
･Refer to a Table 7 for ILAVE (A).
･Ron is "ON-resistance(Ω)" of the internal PowerMOSFET, between drain and source.
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Page.18
LC5720S APPLICATION NOTE
Rev.1.0
8.7.4 Power dissipation in the IC, Pd
The internal loss is to follow a equation (8).
Pd=Pcont＋Pon＋Psw
･･･(8)
(Calculation example in the Buck-type)
Conditions:Fosc=500kHz､VIN=24V､LED strings voltage=17.6V(5LEDs)､ILED=2A､Ron=0.215Ω.
･Pcont=200mW (It was referred from fig.16.)
･Pon=0.215(Ω)×1(A)×1(A)×1.46E-6(sec)×500E+3(Hz) ≒0.157W
･Psw=2×{24(V)×(1(A)／2)×35E-9(sec)×500E+3(Hz)} ≒0.42W
∴Pd=0.2(W)＋0.157(W)＋0.42(W) =0.777W
(Calculation example in the Boost-type)
Conditions:Fosc=500kHz､VIN=12V､LED strings voltage=17.6V(5LEDs)､ILED=1A､Ron=0.215Ω.
･Pcont=100mW (It was referred from fig.16.)
･Pon=0.215(Ω)×1.467(A)×1.467(A)×0.636E-6(sec)×500E+3(Hz) ≒0.147W
･Psw=2×{17.6(V)×(1.467(A)／2)×25E-9(sec)×500E+3(Hz)} ≒0.322W
∴Pd=0.1(W)＋0.147(W)＋0.322(W) =0.567W
(Calculation example in the Buckboost-type)
Conditions:Fosc=500kHz､VIN=17V､LED strings voltage=17.6V(5LEDs)､ILED=0.5A､Ron=0.215Ω.
･Pcont=140mW (It was referred from fig.16.)
･Pon=0.215(Ω)×1.018(A)×1.018(A)×1.016E-6(sec)×500E+3(Hz) ≒0.113W
･Psw=2×{(17(V)＋17.6(V))×(1.018(A)／2)×48E-9(sec)×500E+3(Hz)} ≒0.422W
∴Pd=0.14(W)＋0.113(W)＋0.422(W) =0.675W
Notes:
The thermal resistance θj-a of the package is becomes 74(℃／W). Thermal shutdown( protection
function:TSD) may activate by the condition of Pd.
When ambient temperature is defined as “Ta”, Junction temperature “Tj” is shown with a equation (9).
Tj=(Pd×θj-a)＋Ta
･･･(9)
The "ON-resistance" Ron of internal PowerMOSFET has a positive temperature coefficient.
When Tj is nearing 100(℃) , Ron has the possibility to increase about 1.5 times from condition of Tj=25(℃).
*Be careful.
When temperature of the IC is high, you must have the following item reduced.
･Oscillating frequency
･Value of the ILED
･The number of LED serial connection
Or, you must establish the input voltage condition again, you must put Pd within the area of “Thermal Derating
Curve” in the fig.1.
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Page.19
LC5720S APPLICATION NOTE
Rev.1.0
8.8 PHASE COMPENSATION (COMP terminal)
8.8.1 The calculation of the Phase compensation "fixed-number" .
In the fig.4 of sixth clauses – Typcal application circuit example, as for the Phase-compensation fixed-number of
the COMP terminal connection, "Rs, Cs, Cp", they are calculated in accordance with the equation of the Table10.
Table.10
Rs
Cp
Cs
Requirement decision
(←When a left equation satisfies a
condition.) Cp
RLed
Fz2
Fc of the Buck-type
Fc of the Boost-type
*Co : Capacitance of output capacitor (F), Vout : Output voltage (V), Fc : Crossover frequency (Hz), ESR : The
equivalent serial resistance of the output capacitor (Ω), RLed : The resistance when LED was considered a
resistance load (Ω), ILED : Average current of LED (A), Fz2 : The zero point frequency which is characteristic of
Boost-type (Hz) ・・・ This does the function of the zero in the gain-characteristics, and this does the function of
the pole in the phase-compensation. L : Inductance of the main inductor (H), D : Duty (On-period/period of a
cycle), refer to Table7. *Cp is necessary because ESR is big when a output capacitor COUT is aluminum
electrolytic capacitor.
The setup of crossover-frequency Fc is different in the Buck-type and the Boost-type.Usually, at the case of
Buck-type, Fc is set up in less than 1/10 of Fosc.
But, it has the condition of 'a righthalf plane zero' in case of Boost-type of the Current-Mode.
Therefore you must calculate Fz2 by the equation of Fz2 of the Table9, and you must set up Crossover-frequency
Fc in less than 1/10 of Fz2.
*” K” is the multiplier which is characteristic of the feedback loop of LC5720S.
K=2.497E-4
8.8.2 Rs,Cs, calculation example (COUT: ceramics capacitor)
Table.11 Buck-type ,Fosc=500kHz, ILED=2A, ⊿IL=0.8A
Number
Inductanc
Co total
of LED
Vout(V)
VIN(V)
eL
capacitance(
serial
connection
1
2
3
4
5
6
7
8
9
3.6
7.1
10.6
14.1
17.6
21.1
24.6
28.1
31.6
5
12
15
18
24
28
33
36
40
Co total
ESR
(μ H)
μ F)
(mΩ )
2.7
7.5
8.2
8.2
12
15
18
18
18
1
1
1
1
1
1
1
1
1
10
10
10
10
10
10
10
10
10
Fc(kHz)
Rs(kΩ )
Cs(pF)
50
50
50
50
50
50
50
50
50
4.53
8.93
13.33
17.73
22.13
26.53
30.93
35.34
39.74
2814
1427
956
719
576
480
412
361
321
*The numerical value in the table shows value in calculation.
*Select a part from the near fixed-number , because numerical value doesn't agree completely in the geometric
progression such as E12 series and E24 series.
* Decide a fixed-number after you surely confirm a movement in the experiment.
*The capacity of Cout and ESR are the expressions of 'the total'. When Ceramics capacitor of the little size more
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Page.20
LC5720S APPLICATION NOTE
Rev.1.0
than one are connected in parallel , it is shown that it becomes the numerical value of the table in the total.
*Table12 is the same situations,too.
Table.12 Boost-type, Fosc=500kHz, ILED=1A, ⊿IL=0.4A
Number
Inductanc
Co total
of LED
Vout(V)
VIN(V)
eL
capacitance(
serial
connection
2
3
3
4
4
5
6
6
7
7
7
8
8
9
10
7.1
10.6
10.6
14.1
14.1
17.6
21.1
21.1
24.6
24.6
24.6
28.1
28.1
31.6
35.1
5
5
7
7
9
12
12
15
12
15
18
15
18
18
24
Co total
ESR
(μ H)
μ F)
(mΩ )
7.5
15
12
18
18
20
27
22
33
33
27
36
33
39
39
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
Fc(kHz)
Rs(kΩ )
Cs(pF)
14.952
5.007
12.268
6.149
10.164
13.028
8.05
15.436
5.649
8.827
15.535
7.083
11.127
8.373
13.401
2.67
1.33
3.27
2.18
3.6
5.77
4.27
8.19
3.5
5.46
9.61
5.01
7.86
6.65
11.83
15956
95286
15874
47510
17387
8478
18523
5037
32259
13214
4266
17962
7279
11433
4018
*In theBuckboost-type, Relations between "Duty D" and the movement mode are as the following.
D＞0.5：Boost mode
D＜0.5：Buck mode
Referring to the Table11 - the Table12, adjust compensation value in accordance with the condition of the use,
under the actual movement .
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Page.21
LC5720S APPLICATION NOTE
Rev.1.0
8.9 Peripheral Parts Design
Take care to use properly rated and proper type of components.
The following circuit symbols refer to “6. Typical Application Circuit”.
 Inductor L
This is a choke coil for smoothing LED current.
When the indactance is larger, the output ripple current is smaller, and the current stability is improved.
In actual operation, it should be considered so that the coil is not saturated by the peak of ripple current.
If the coil is saturated, the surge current beyond expectations flows. Thus LED, IC and peripheral circuit will be
damaged.
 Diode DS
This is a free-wheel diode for Buck converter, and this is a boost diode for Boost and Buck-Boost converter.
For diode selection, the withstanding voltage and the recovery time (trr) are important. In case that diode with a
long trr is used, the large surge current flows into power MOSFET when power MOSFET turns on. Thus, it may
cause noise increasing, malfunction and efficiency decreasing.
It is recommended to choose from Schottky barrier diode and Ultra-fast diode according to the withstanding
voltage.
 Current detection resistor RCS
If the current detection resistor with high inductance is used, it may cause malfunctioning because of the high
frequency current flowing through it.
It is recommended to choose a low equivalent series inductance and high surge tolerant type for the current
detection resistor.
 Input capacitor CIN
This is a smoothing capacitor for main power supply. When the capacitance is larger, the ripple voltage is smaller.
It is recommended to choose the capacitance according to the output power because the ripple voltage becomes
bigger when the output power increases even if the same capacitance.
 Output capacitor COUT
By the ipple current specification of LED string, it is recommended to determine whether COUT is needed or not, or
to determine the capacitance value.
If large ripple current can be set, the inductance of L can be smaller, the COUT capacitance can be smaller or the
COUT can be removed. Thus, the power supply will be downsized and reduced the cost.
If the small ripple current is set, the inductance of L is increased or COUT is connected in parallel with LED string.
Thus, the heat generation of LED string, which is caused by ripple current variation, can be reduced.
In addition, if LED string is far from the output edge of power supply, COUT is connected close to LED string in
parallel so that the ripple voltage and ripple current can be reduced.
 Phase compensation network CP, CS, RS
These are the "phase compensation parts" of a control-loop to connect to the COMP terminal. Connect the GND
side of the "phase compensation parts" to GND Pin of the IC at shortest wiring. When it is far from GND of the IC,
noise appears in the COMP terminal by the influence such as parasitic-inductance of the pattern, and the faulty
operation occurs often. Be careful.
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Page.22
LC5720S APPLICATION NOTE
Rev.1.0
8.10 Reference Design Example
(A)Buck-type
Fosc=500kHz
ILED=2A
Inductor ripple current ⊿IL=0.8A
Number of LED=5LEDs(Vout=17.6V)
VIN=24V
Vsw=24V
Cout(ESR)=10mΩ/ceramics capacitor
Cp(C4)：Open
*SJPB-L6 being used as the D1 is
manufactured by "Sanken-electric Co".
(B)Boost-type
Fosc=500kHz
ILED=1A
Inductor ripple current ⊿IL=0.4A
Number of LED=7LEDs(Vout=17.6V)
VIN=12V
Vsw=17.6V
Cout(ESR)=10mΩ/ ceramics capacitor
Cp(C4)：Open
*SJPB-L6 being used as the D1 is
manufactured by "Sanken-electric Co".
(C)Buckboost-type
Fosc=500kHz
ILED=1A
Inductor ripple current ⊿IL=0.4A
Number of LED=5LEDs(Vout=17.6V)
VIN=17V
Vsw=34.6V
Cout(ESR)=10mΩ/ ceramics capacitor
Cp(C4)：Open
*SJPB-L6 being used as the D1 is
manufactured by "Sanken-electric Co".
*The above reference design example is only a guide. Decide the fixed-number on your circuit board after you
confirm a movement in the actual working,experiment adjustment.
fig.18 (a) - (c) Reference design example
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Page.23
LC5720S APPLICATION NOTE
Rev.1.0
9. Example Pattern Layout
For the LC5710S,the LC5711S and the LC5720S, the circuit board pattern of demonstration-board
by our company is shown in the following.
manufactured
9.1 pattern layout
For Buck-type (parts mounting side)
For Buck-type(back side)
For Boost-type/Buckboost-type
(parts mounting side)
For Boost-type/Buckboost-type(back side)
fig.19 Demo-board pattern layout
*Foot print drawing
fig.20 Footprint drawing
for LC5720S
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Page.24
LC5720S APPLICATION NOTE
Rev.1.0
9.2Circuit diagram of Demonstration-Board
9.2.1 For Buck-type
J1
fig.20
*LC5710S/LC5720S : R5 and R6 must be open. Jumper-J1 must be inserted. C7 and R7 are used only with LC5710S.
9.2.2 For Boost-type and Buckboost-type
J2
J1
fig.21
*The setup of Jumper
For Boost-type:
J1= Insert, J2= Open
For Buckboost-type: J1= Open, J2= Insert
* C7 and R7 are used only with LC5710S.
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Page.25
LC5720S APPLICATION NOTE
Rev.1.0
10. Design Considerations
Trace and Component Layout 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.22, 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.
(B)Boost-type
(A)Buck-type
(C)Buckboost-type
fig.22 High frequency current loops（hatched portion）
fig.23 shows practical trace design examples and considerations. In addition, observe the following:
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
The traces of RCS should be connected to CSP pin and CSN pin with dedicated traces respectively, in order to
reduce noises when the current is detected. When the noise between CSP and CSN is high, a filter capacitor
Cf can be added like a "Page8, sixth clauses-application circuit example",too.
(4)Peripheral components
The components for phase compensation such as C P, CS, RS should be connected close to COMP pin and
GND pin.
(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.
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Page.26
LC5720S APPLICATION NOTE
Rev.1.0
(A)Buck-type
Input
voltage
5
VIN
CIN
CSP
LC5720S
LC5700S
RCS
DS
CSN
8
6
ROVP
7
DIM
COUT
LED
DZOVP
1
COMP
CS
CP
GND
3
SW
Output
voltage
4
L
Main circuit
GND of Control circit
RS
(B)Boost-type
Input
voltage
DS
L
5
CIN
VIN
CSP
6
RCS
LC5720S
LC5700S
CSN
ROVP
7
LED COUT
8 DIM
1
COMP
CS
SW
GND
3
4
Output
voltage
DZOVP
Main circuit
GND of Control circit
RS
(C)Buckboost-type
Input
voltage
DS
L
5
VIN
CSP
RCS
LC5720S
LC5700S
CIN
CCSP
6
CSN
ROVP
7
COUT
8 DIM
1
CS
COMP
DZOVP
GND
3
SW
4
Output
voltage
RS
Fig.23 The trace of the pattern
Copy Right: SANKEN ELECTRIC CO., LTD.
LED
Page.27
Main circuit
GND of Control circit
LC5720S APPLICATION NOTE
Rev.1.0
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.
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Page.28