LC5220 Series Off-Line LED Driver IC Application Note

Application Information
LC5220 Series Off-Line LED Driver IC
General Description
The LC5220 series is the power IC for non-isolated LED
driver applications with commercial power supply. It
provides constant output current control for driving LEDs.
The buck or buck-boost topology is selectable by peripheral
circuit structure.
The product incorporates a power MOSFET and a controller
IC in a single industry-standard package. It includes various
functions, and this design allows the achievement of highly
cost-effective LED lighting power supply systems by reducing external component count and minimizing PCB area.
SOP8
(LC5220S series)
DIP8
(LC5220D series)
Figure 1. The LC5220D series package is a fully molded DIP8
with pin 7 removed for greater isolation, and the LC5220S series
package is an SOP8.
Features and Benefits
• Buck and buck-boost topology; selectable by peripheral
circuit structure
• Built-in fixed reference voltage limiting constant current
control; high precision regulator improves current
precision and simplifies setting of current level
• Sleep function, with latch mode; input high, 3 V or more,
on REF pin turns off IC output to LEDs
• Enable function; input low on REF pin toggles IC output
to LEDs
• High input voltage; up to 250 V or 450 V, depending
on product
• Built-in constant current control; PWM method, output
current adjustable by the voltage input on the REF pin
• External adjustable PWM dimming control
• Protection features:
▫ Open protection (OPP) with latched shutdown; protects
IC when a free-wheeling diode is open
▫ Undervoltage lockout (UVLO)
▫ Overcurrent protection (OCP) with latched shutdown;
variable OCP threshold linked to REF pin voltage
▫ Thermal shutdown (TSD) with auto restart
LC5220-AN, Rev. 1.3
Applications
• LED lighting fixtures
• LED light bulbs
The product lineups for the LC5220 series provide the following
options:
Input Voltage
Output
Current
(A)
Part
Number
Absolute
Maximum
(V)
LC5222D
250
25 to 200
0.5
LC5223D
250
25 to 200
1.0
LC5225D
450
25 to 400
0.5
LC5226D
450
25 to 400
1.0
LC5222S
250
25 to 200
0.5
LC5225S
450
25 to 400
0.5
Recommended
Operating Range*
(V)
Package
DIP8
SOP8
*Minimum input voltage of recommended range depends on LED
output voltage and converter topology.
SANKEN ELECTRIC CO., LTD.
Table of Contents
General Specifications
Functional Block Diagram
Pin-out Diagrams and Descriptions
Package Diagram
Electrical Characteristics
Typical Application Circuit
3
3
4
6
9
Functional Description
Internal Circuit Descriptions
Regulator
Band Gap Reference
Reference Control
Current Detect
PWM Control
OCP (Overcurrent Protection) Blanking
OPP (Open Protection) Logic
UVLO (Undervoltage Lock Out)
TSD (Thermal Shutdown)
Output Control Logic
Gate Driver
Internal Power MOSFET
PMW Current Control
PWM On-Time Period
Turning-Off Period
PWM Off-Time Period
Turning-On Period
Internal PWM Control Circuit
REF Pin Input Operation
Internal PWM Reference Voltage, VCCR
OCP Reference Voltage, VOCR
ENABLE Signal
SLEEP Signal
Buck-Boost Operation
Buck-Boost Circuit Features
Buck-Boost Circuit Operation
PWM On-Time Period
Turning-Off Period
PWM Off-Time Period
Overcurrent Protection Function (OCP)
Current Value Setting for Dimming Control
Using Internal PWM Dimming
Using External PWM Dimming
Using Internal and External PWM Dimming
10
10
10
10
10
10
10
10
10
11
11
11
11
11
11
11
11
12
12
13
13
13
13
14
14
14
14
14
14
15
15
16
16
16
17
Application Information
Typical Application Components
External Component Selection
LC5220-AN, Rev. 1.3
18
18
SANKEN ELECTRIC CO., LTD.
2
Functional Block Diagram
VBB
6(7)
LC5220
Control Part
1
TSD
Band Gap
Reference
PWM 2
PWM _IN
CC
REF 3
Reference
Control
CC_REF
Current
Detect
OCP_REF
SEN_IN
OC
UVLO
PWM
Control
OCP
Blanking
REG
Regulator
UVLO
TSD
PWM
OCP
OPP
SLEEP
ENABLE
Output
Control
Logic
5(5,6) OUT
OPP
Logic
Gate Driver
4
8
GND
SEN
Pin numbers in parentheses refer to the SOP8 package
Pin List Table
Name
Pin-out Diagrams
REG 1
8 GND
PWM 2
REF 3
6 VBB
SEN 4
5 OUT
DIP8
(LC5220D series)
REG 1
8 GND
PWM 2
7 VBB
Number
Function
DIP8
SOP8
REG
1
1
Internal regulator supply, provides current to internal and external circuits;
connect a 0.1 μF bypass capacitor between this pin and GND.
PWM
2
2
Input for PWM control: to use internal PWM, connect a capacitor for setting offtime; to use external PWM, connect to PWM signal source.
REF
3
3
Reference voltage input: sets peak output current of OUT pin (internal power
MOSFET) for internal PWM control, enables toggling output of OUT pin
(Enable function), and enables latched shutdown of output (Sleep function)
SEN
4
4
Output current detection: detects peak output current for internal PWM control,
and detects overcurrent for OCP; connect to current detection resistor.
OUT
5
5, 6
6
7
Supply voltage, provides power to internal circuits through internal regulator.
Drain of internal power MOSFET.
REF 3
6 OUT
VBB
SEN 4
5 OUT
GND
8
8
Ground pin.
―
7
―
LC5220D DIP8 pin removed to increase creepage distance between high
voltage pin and low voltage pin. Note: Apply user’s criteria for creepage
distance when using LC5220S SOP8.
SOP8
(LC5220S series)
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
3
Package Diagram
DIP8 package
9.4 ±0.3
5
1
4
6.5 ±0.2
8
1.0 +0.3
-0.05
+0.3
1.52
-0.05
3.3 ±0.2
7.5 ±0.5
4.2 ±0.3
3.4 ±0.1
(7.6 TYP)
0.2 5 + 0.
- 0.01
5
０～１５° ０～１５°
2.54 TYP
0.89 TYP
0.5 ±0.1
Unit: mm
8
LC522x
SK YMD D
XXXX
1
Part Number
Lot Number
Y is the last digit of the year (0 to 9)
M is the month (1 to 9, O, N, or D)
D is a period of days:
1 – 1st to 10th
2 – 11th to 20th
3 – 21st to 31st
Sanken Control Number
Pb-free. Device composition compliant
with the RoHS directive.
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
4
Package Diagram
SOP8 package
1
0.695 TYP
6.2 ±0.3
5
4.4 ±0.2
8
4
0 ~ 10°
0.4±0.2
0.05 ±0.05
1.27±0.05
+0.1
0.15 –0.05
1.5 ±0.1
5.2 ±0.3
0.10
0.12 M
0.4±0.1
Unit: mm
LC522x
SK YMD
XXXX
Part Number
Lot Number
Y is the last digit of the year (0 to 9)
M is the month (1 to 9, O, N, or D)
D is a period of days (1 to 3):
1 – 1st to 10th
2 – 11th to 20th
3 – 21st to 31st
Sanken Control Number
Pb-free. Device composition compliant
with the RoHS directive.
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
5
Electrical Characteristics
• For additional details, refer to the datasheet of each product.
• The polarity value for current specifies a sink as "+ ," and a
source as “−,” referencing the IC.
• When pin numbers of the SOP8 differ from those of the DIP8,
they are indicated in parentheses for the SOP8.
Absolute Maximum Ratings Unless specifically noted, TA is 25°C
Characteristic
Symbol
Main Power Supply Voltage
Output Breakdown Voltage
Pins
LC5222
LC5223
VBB
6–8
(7 – 8)
LC5225
LC5226
VO(BR)
Output Current1
Notes
LC5222
LC5223
5–4
(5,6 – 4)
LC5225
LC5226
LC5222
LC5225
IO
Pulse width ≥ 1 μs
LC5223
LC5226
5–4
(5,6 – 4)
Rating
Unit
250
V
450
V
250
V
450
V
0.5
A
1.0
A
PWM Pin Voltage2
VPWM
2–8
−0.3 to VZ
V
REF Pin Voltage2
VREF
3–8
−0.3 to VZ
V
SEN Pin Voltage
VSEN
Allowable Power Dissipation3,4
PD
Pulse width ≥ 1 μs
4–8
−0.3 to 4.0
V
Mounted on Sanken evaluation board for
SOP8
–
0.85
W
Mounted on Sanken evaluation board for
DIP8
–
1.73
W
°C
Operating Temperature Range
TA
–
−40 to 105
Storage Temperature Range
Tstg
–
−40 to 150
°C
Junction Temperature
TJ
–
150
°C
current rating may be limited by duty cycle, ambient temperature, and heat sinking. Under any set of conditions, do not exceed the specified
junction temperature, TJ .
2V here is the breakdown voltage of the Zener diode that is internally connected between the PWM and REF pins and GND; V = 6.3 V (typ).
Z
Z
Maximum input current is 1 mA.
3Allowable Power Dissipation, P , depends on PWB pattern layout.
D
4Refer T versus P curve.
A
D
Allowable Power Dissipation, PD (W)
1Output
2.02
R
Mounted on the Sanken
evaluation board
θJ
1.5
1.5
D
72 IP
°C
/W
A＝
Fff
ffff
1.01
PD =0.85W
Fff
ffff
0.5
0.5
Rθ SOP
JA ＝
147
°
C/W
Fff
Ffff
0
LC5220-AN, Rev. 1.3
PD =1.73W
Fff
ffff
00
25
25
50
75
100
125
50
75
100
125
Ambient Temperature, TA (°C)
SANKEN ELECTRIC CO., LTD.
150
150
6
Recommended Operating Conditions*
Characteristic
Power Supply Voltage
Average Output Current
REF Pin Input Voltage
Case Temperature
Symbol
VBB
IO(AVG)
VREF
TC
Notes
LC5222
LC5223
LC5225
LC5226
Minimum input voltage depends on
LED output voltage and converter
topology.
LC5222
LC5225
LC5223
LC5226
Normal operation
Center of branded side, TJ ≤ 150°C.
Pins
6–8
(7 – 8)
5–4
(5,6 – 4)
Min.
Max.
Unit
25
200
V
25
400
V
–
0.4
A
–
0.8
A
3–8
0.2
2.5
V
–
–
105
°C
*Recommended operating conditions means the operation conditions maintained normal function shown in electrical characteristics.
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
7
Electrical Characteristics Unless specifically noted, TA is 25°C, VBB is 140 V
Characteristic
Power Supply Current
Output MOSFET Breakdown Voltage
Output MOSFET ON Resistance
Body Diode Forward Voltage
Symbol
Test Conditions
IBBs
Output off
IBB
Normal operation
V(BR)DSS
RDS(ON)
VF
Min.
Typ.
Max.
Unit
6–8
(7 – 8)
–
1
1.5
mA
–
2.5
4.0
mA
250
–
–
V
450
–
–
V
LC5222
LC5223
ID = 1 mA
LC5225
LC5226
ID = 1 mA
LC5222
ID = 0.5 A
–
1.2
2.2
Ω
LC5223
ID = 1.0 A
–
0.7
1.3
Ω
LC5225
ID = 0.5 A
–
3.5
6
Ω
LC5226
ID = 1.0 A
–
1.7
3
Ω
LC5222
IF = 0.5 A
–
0.8
1.0
V
LC5223
IF = 1.0 A
–
0.75
1.2
V
LC5225
IF = 0.5 A
LC5226
IF = 1.0 A
UVLO Threshold ( Turn on)
VUVLO(ON)
VBB pin
UVLO Threshold ( Turn off)
VUVLO(OFF)
VBB pin
REG Output Voltage
Pins
5–4
(5,6 – 4)
5–4
(5,6 – 4)
4–5
(4 – 5,6)
–
0.8
0.9
V
–
0.88
1.0
V
6–8
(7 – 8)
–
14
–
V
–
12
–
V
1–8
9.6
10
10.4
V
VREG
IREG = 0 mA
REG Output Current
IREG
VREG = 9 V
1–8
−2
–
–
mA
Enable Output Threshold Voltage
VENB
REF pin
3–8
–
0.15
0.19
V
Sleep Mode Threshold Voltage
VSLP
REF pin
3–8
2.85
3.0
–
V
REF Pin Input Current
IREF
3–8
−10
–
10
μA
Current Control Detection Voltage
VSEN
4–8
0.4 × VREF
– 0.3
0.4 × VREF
0.4 × VREF
+ 0.3
V
0.77
0.8
0.83
V
–
0.4 × VREF
+ 0.7
–
V
VREF = 0.2 to 2.0 V
VREF = 2.0 to 3.0 V
VREF = 0.2 to 2.0 V
4–8
OCP Detection Voltage
VOCP
–
1.5
–
V
SEN Pin Input Current
ISEN
4–8
−10
–
10
μA
PWM Pin Low Voltage
VPWM(L)
2–8
–
2
–
V
PWM Pin High Voltage
VPWM(H)
2–8
–
3
–
V
PWM Pin Output Current
IPWM
2–8
–
−20
–
μA
PWM Blanking Time
tBLK(P)
–
–
0.3
–
μs
OCP Blanking Time
tBLK(O)
VREF = 2.0 to 3.0 V
Operation Frequency
fPWM
Duty cycle = 50%
PWM Off-Time
tOFF
CPWM = 100 pF
–
–
0.2
–
μs
2–8
–
–
200
kHz
–
–
17
–
μs
–
25
–
ns
Output MOSFET Rise Time
tr
IO = 0.4 A
5–4
(5,6 – 4)
Output MOSFET Fall Time
tf
IO = 0.4 A
5–4
(5,6 – 4)
–
50
–
ns
Thermal Shutdown Threshold
TTSD
Temperature of Control Part
–
–
150
–
°C
Thermal Shutdown Hysteresis
TTSD(HYS)
Temperature of Control Part
–
–
55
–
°C
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
8
Typical Application Circuit
VIN
Line
Filter
AC
Input
CIN
REG VBB
R1
R2
C3
VLED
LEDs
LC5220
C1
C2
D1
REF
PWM
OUT
GND
L1
SEN
CPWM
RS
Figure 2. Typical application circuit example for a buck configuration; for component values, see Application Information section
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
9
Functional Description
Internal Circuit Descriptions
This section describes the functions displayed in the Functional
Block diagram.
Regulator
This regulator steps-down from the supply voltage, VBB, to 10 V,
and provides power to internal circuits and external devices. A
ceramic capacitor of 0.1 μF should be connected at the REG pin
to stabilize operation because some pulse currents flow through
the gate capacitor when charging the internal power MOSFET.
Band Gap Reference
This is a high precision voltage source, which generates a reference voltage that is not susceptible to fluctuations of the power
supply voltage and/or temperature, and is used as a reference voltage for internal current control.
Reference Control
This function controls an internal reference voltage and the on/off
switching of the internal power MOSFET in response to the input
voltage at the REF pin.
There are two reference voltages generated by this function. One
is CC_REF for peak current control when using internal PWM
control, and the other is OCP_REF for overcurrent protection
(OCP).
In addition, the SLP (Sleep mode) comparator, with a reference
voltage of 3 V, and the ENB (Enable) comparator with a refer-
CC_REF
OCP_REF
CC
+
CC Comp
Current Detect
This detects the output current of the IC by the voltage of the
detection resistor, RS, connected to SEN pin.
Two comparators compare SEN_IN voltage with internal reference voltages: CC_REF, the reference voltage of the CC comparator for peak current control of internal PWM; and OCP_REF, the
reference voltage of the OCP comparator for overcurrent protection (OCP) (see figure 3).
PWM Control
This is PWM control circuit for the internal power MOSFET,
which includes the constant current control by internal PWM, and
the external PWM by external PWM signal. It has a 20 μA current
source for setting the fixed off-time (see figure 4).
OCP (Overcurrent Protection) Blanking
When an overcurrent fault condition is indicated by the OC signal
from the Current Detect circuit, this function outputs the OCP
signal. In this circuit, the OCP Blanking Time, tBLK(O) , is built-in
to prevent malfunctions caused by surge voltages generated by
turning off the internal power MOSFET.
OPP (Open Protection) Logic
This function detects open conditions on the free-wheeling diode
line and prevents resulting circuit failure. When the free-wheeling
diode line opens during operation of the IC without the OPP
function, the recirculation path for energy stored in the inductor
is cut off. Thus, the internal power MOSFET can be damaged if it
applies this energy. This function is also available for the protection of a buck-boost configuration, when LEDs open.
UVLO (Undervoltage Lock Out)
This continually monitors whether the output voltage from the
Regulator function is normal, and prevents abnormal operation
resulting from low input voltage. When the VBB pin voltage is
OC
+
ence voltage 0.15 V are provided. These are used to generate the
SLEEP signal and ENABLE control signals respectively.
OCP Comp
SEN_IN
Figure 3. Current Detect circuit
5.6V
20μA
PWM_IN
6V
3.0V
2.0V
+
PWM
OT Comp
Q
S
R
S
R
Q
Disc. Pulse
I
O
CC
Blank Pulse
I
O
Figure 4. PWM Control circuit
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
10
lower than the UVLO threshold (turn-off), the IC reverts to the
state before startup. In addition, this function is available during
power-on reset, for releasing latched shutdowns resulting from
operation of protection functions.
TSD (Thermal Shutdown)
This continually monitors the chip temperature of the Control
Part. When the temperature increases to TTSD or higher, the
output of OUT pin turns off to prevent damage from abnormally
high temperature.
After TSD operation, when the temperature decreases to TTSD
minus TTSD(HYS) or lower, or after cycling power to the IC (that is,
the VBB pin voltage falling down to VUVLO(OFF) and then rising
to VUVLO(ON) ), the IC returns to normal operation. Because this
circuit is in the Control Part, there is a delay before temperature
increases in the internal power MOSFET are conducted to the
Control Part. If the temperature of power MOSFET increases
rapidly, the power MOSFET may be damaged before TSD is
activated. Therefore, it is necessary design the application well to
protect against this.
Output Control Logic
This controls the enabling and disabling of the output of the OUT
pin according to signals from PWM control circuit and the various protection circuits. The resulting logic operation is set to nonlatch mode or latch mode by the input signal as shown in table 1.
The output is enabled only when all input signals indicate the output can be turned on safely. To release latch mode, cycling power
to the IC is required.
Gate Driver
Gate driver for internal power MOSFET.
Internal Power MOSFET
An internal power MOSFET for LED driving is incorporated in
the IC series, according to the individual product ratings for current and voltage.
PMW Current Control
• The polarity value for current specifies a sink as "+ ," and a
source as “−,” referencing the IC.
• All of the parameter values used in these descriptions are typical
values, unless they are specified as minimum or maximum.
• The basic current control of internal PWM is shown in the following with a buck configuration circuit.
PWM On-Time Period
At startup, or during normal operation before the output current through the LED string reaches the target current level, the
internal power MOSFET turns on and the output current flows
through the ION path shown in figure 5.
Turning-Off Period
The output current through the LED string is equivalent to the
current through the detection resistor, RS , and thus the LED current is detected at the SEN pin as a voltage. When the SEN pin
voltage, VSEN , is equal to the internal PWM reference voltage,
VCCR , the internal power MOSFET turns off.
PWM Off-Time Period
• When the internal power MOSFET turns off, the current
recirculation diode, D1 , is forward biased by the back electromotive force (BEMF) in the inductor, L1 , and D1 turns on. Then
the energy stored in L1 during PWM on-time flows through the
recirculation path shown as IOFF in figure 5.
ION
VIN
IOFF
Table 1. Control Logic States
Input Signal
Latch Mode
UVLO
Non-latched
TSD
Conditions for Output Disable
(Power MOSFET Off)
When REG pin voltage decreases
Non-latched
When the Control Part overheats
PWM
Non-latched
When PWM control outputs the
off signal
OCP
Latched
When OCP is detected
OPP
Latched
When free-wheeling diode line open
SLEEP
Latched
When REF pin voltage increases to
3 V or higher
ENABLE
Non-latched
When REG pin voltage decreases to
less than 0.15 V
LC5220-AN, Rev. 1.3
D1
C3
LC5220
VLED
LEDs
OUT
MOSFET
L1
GND SEN
VSEN
RS
Figure 5. Output current flow in a buck configuration during
PWM on-time and off-time periods
SANKEN ELECTRIC CO., LTD.
11
Turning-On Period
After the fixed off-time, tOFF , the internal power MOSFET turns
on again, and the PWM on-time period repeats. The cycle is
shown in figure 6.
Internal PWM Control Circuit
The internal PWM control circuit is shown in figure 7, and the
operation timing diagram is shown in figure 8.
When the internal power MOSFET turns on, the load current
increases, and the SEN pin voltage, VSEN, also increases. This
voltage is compared to the internal PWM reference voltage,
VCCR, in the Current Detect comparator, CC Comp, which is
connected to the SEN pin. When VSEN is more than VCCR , CC
Comp inverts, as shown at point A in figure 8. After this signal is
received, the output Q of the RS flip-flop is reset, and a turn-off
signal is transmitted from the AND gate to the gate control logic,
to the Gate Driver, and to the internal power MOSFET. After that,
the internal power MOSFET turns off. At the same time, a MOS
switch for discharging CPWM , connected to the PWM pin, turns
on, and CPWM is discharged.
When VPWM decreases to less than 2 V, the Off-Time comparator,
OT Comp, inverts and the the Q of RS flip-flop is set. Then the
MOS switch for discharging CPWM turns off, and CPWM is again
charged by the 20 μA internal constant current source.
When VPWM increases to more than 3 V, the fixed off-time period
expires and then the internal power MOSFET turns on. After
LED
current
I LED
VCCR
VSEN
ION
IOFF
EN
DS
ION
IOFF
CCComp OUT
I ON
IOFF
I ON
CC
I OFF
Comp
DS
t BLK(P)
LED current
ILED
DS
t BLK(P)
Negative IN
of OT Comp
VCCR
EN
VPWM
OT Comp OUT
VSEN
ON
MOSFET
OFF
MOSFE T
OFF
t OFF
ON
5.6V
20μA
CPWM
ON
A
t OFF
B
LC5220
PWM Control
3.0V
2.0V
PWM _IN
OFF
Figure 8. Constant current control circuit operation
Figure 6. Constant current control operation in a buck
configuration
PWM
ON
+
VPWM
6V
Q
PWM
OT Comp
S
R
S
Q
Disc. Pulse
I
O
R
Output Control
Logic
OUT To Load
Blank Pulse
I
Gate Driver
CC
O
VREF
VCCR
Reference Control
REF
Current Detect
-
0.8
0
0
2
CC_REF
VCCR
CC Comp
SEN_IN
VSEN
SEN
+
RS
V REF
GND
Figure 7. Current control circuit
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
12
that, the operation reverts to the initial state, as shown at point B
of figure 8. The VSEN voltage is detected in the on-time period
except during the PWM blanking time, tBLK(P) , to prevent malfunction.
As shown in figure 9, the CC_REF signal transitions between
variable and constant slope at the REF pin input voltage, VREF ,
of 2 V:
• Case of VREF < 2 V
VCCR = 0.4 × VREF
IPEAK = 0.4 × VREF / RS
REF Pin Input Operation
The REF pin input voltage is used by the Reference Control
function to generate two internal reference voltages and two logic
signals: the reference voltages are VCCR and VOCP , and the logic
signals are OFF(Disable) and Latched Shutdown(Sleep). These
operate as follows.
According to equation 1, VCCR is proportional to VREF . Thus the
peak output current, IPEAK , is proportional to VREF in this range.
Therefore, an external DC voltage on the REF pin can control the
output current.
Internal reference voltage(V)
Internal PWM Reference Voltage, VCCR
The CC_REF signal voltage, VCCR , is used for the internal PWM
Control function. The SEN pin voltage,VSEN , which occurs at the
external current detection resistor, RS , is controlled so that the
peak voltage of VSEN is equal to VCCR .
• Case of VREF > 2 V
VCCR = 0.8 (V)
IPEAK = 0.8 (V) / RS
_OS
F×
=VRE
VCCR
0
0
C C_R EF
0.4
1.0
0.15
2.0
3.0
REF pin input voltage,VR EF (V)
On
(Enable )
O ut
OCP Reference Voltage, VOCR
The OCP_REF signal voltage, VOCR , is used for the OCP function. As shown in figure 9, this voltage is offset from VCCR by
VOCP_OS . When VSEN increases to more than VOCR , the internal
power MOSFET is shut down in latch mode. To release latch
mode, cycling power to the IC (that is, the VBB pin voltage falling down to VUVLO(OFF) and then rising to VUVLO(ON) ) is required.
VOCP_OS is 0.7 V, and is reduced by increasing temperature.
Therefore, this characteristic makes OCP activation quicker at
higher temperatures, at which withstand voltages are lower.
VO C R _O S
VO
0.8
(3)
(4)
In equation 3, VCCR is not set relative to VREF , and is fixed.
Because this voltage is generated from the internal stabilized reference voltage, it is not affected by the precision of VREF in this
range. The external current detection resistor, RS , sets the peak
output current.
O C P _R EF
R
+VOC
CR
C
V
=
CR
(1)
(2)
Lat ch ed
Shutdown
(Sleep)
ENABLE Signal
When the REF pin input voltage, VREF , exceeds the Enable voltage, VENB = 0.15 V , the ENABLE (enable output) signal is output
to the Output Control Logic circuit. Conversely, when VREF is
Off (Disable)
Figure 9. Input−output characteristic of the Reference Control function
VIN
PC1
R5
R4
C3
D1
REG VBB
R1
R3
R2
C2
REF
PWM
CPWM
D2
OUT
GND
LEDs
PC1
LC5220
C1
VLED
L1
SEN
RS
Figure 10. Sleep mode application circuit example implementing external protection (OVP)
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
13
less than VENB , the output is kept off regardless of other signals.
This signal is not latched, and is available to turn-off LEDs by
connecting the REF pin to GND.
VIN (input voltage) > VLED (output voltage)
When the input voltage is low or the total voltage across the
LEDs in series is high, some limitations occur.
SLEEP Signal
When the REF pin input voltage, VREF, exceeds the Sleep voltage, VSLP = 3.0 V, the SLEEP signal is output to the Output Control Logic circuit, and the internal power MOSFET is shut down
in latch mode. To release latch mode, cycling power to the IC
(that is, the VBB pin voltage falling down to VUVLO(OFF) and then
rising to VUVLO(ON) ) is required. This function allows an external
protection circuit, such as overvoltage protection (see figure 10),
to turn-off the internal power MOSFET in response to an load
open, or other fault condition.
In the LC5220 series, it is possible to use a buck-boost converter
by changing the way of connecting the load. The operation range
of buck-boost converter is:
VIN + VLED < VO(max) (maximum output voltage)
However, as compared to the input voltage, the output voltage
fluctuation and the ripple current on the LEDs may be worse than
those with a buck converter configuration. It is necessary to take
that into consideration.
Unless a protection circuit (for example, the circuit in figure 10)
is used, the withstand voltage of C3 could be exceeded in a fault
condition. In a buck configuration without the protection, when
an LED is open, the C3 voltage would be charged to approximately VIN .
Buck-Boost Circuit Operation
In the buck-boost converter configuration, the internal PWM current control operates as follows:
PWM On-Time Period
At startup, or during normal operation before the output current through the LED string reaches the target current level, the
internal power MOSFET turns on and the output current flows
through the I'ON path shown in figure 11. During the on-time,
an inductor, L1, stores energy, and no current flows through the
LED string. If it is not acceptable to intermittently flow the current through the LED string, add a capacitor in parallel to the
LED string.
Again referring to figure 10, when an overvoltage occurs, it is
detected by the network of R5, PC1 (source side), and D2 , and
the REF pin voltage is increased to 3 V or higher by the pullup
R4 and PC1 (detector side). The IC enters latched Sleep mode,
turning-off the internal power MOSFET to prevent excessive output voltage. Latched Sleep mode can be used not only for OVP
for an open LED, but also for other protections with appropriate
application circuits.
Turning-Off Period
The current through an inductor, L1 , is equivalent to the current through the detection resistor, RS , and thus the L1 current is
detected at the SEN pin as a voltage. When the SEN pin voltage,
VSEN , is equal to the internal PWM reference voltage, VCCR , the
internal power MOSFET turns off.
Buck-Boost Operation
Buck-Boost Circuit Features
Figure 5 shows the typical application circuit for buck converter
operation. In order for that circuit to operate, the following condition must be fulfilled:
I'ON
VIN
I'OFF
L1
C3
VLED
LEDs
LC5220
OUT
MOSFET
GND SEN
GND
D1
VSEN
RS
Figure 11. Output current flow in buck-boost configuration
during PWM on-time and off-time periods
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
14
PWM Off-Time Period
When the internal power MOSFET turns off, the current recirculation diode, D1 , is forward biased by the back electromotive
force (BEMF) in the inductor, L1 , and D1 turns on. Then the
energy stored in L1 during PWM on-time flows through the recirculation path shown as I'OFF in figure 11, turning on the LEDs.
PWM On-Time Period
After the fixed off-time, tOFF , the internal power MOSFET turns
on again, and the PWM on-time period repeats. The cycle is
shown in figure 12.
Note: In a buck-boost topology, if the LED load is open, the
recirculation path for energy stored in an inductor is cut off, so
when the internal power MOSFET applies the energy, it would
I'ON
I'OFF
I'ON
fail. The LC5220 series prevents such a failure because it has an
additional function for protection against open loads.
Overcurrent Protection Function (OCP)
Figure 13 shows the OCP circuit, and figure 14 shows the OCP
operation timing diagram. The OCP comparator, OCP Comp, is
connected to SEN pin, and compares the VSEN voltage detected
by RS with the OCP reference voltage, VOCR .
When VSEN is greater than VOCR , OCP Comp inverts, and an
OCP condition is detected. When the OCP signal is received, the
internal power MOSFET is shut down in latch mode by the latch
function of the Output Control Logic circuit. To release latch
mode, cycling power to the IC (that is, the VBB pin voltage falling down to VUVLO(OFF) and then rising to VUVLO(ON) ) is required.
I'OFF
VOCR
VCCR
VSEN
LED current
ILED
VCCR
OCP Comp OUT
VSEN
MOSFET
ON
OFF
OCP Comp
OFF
t'OFF
ON
I
Logic
OC
Gate Driver
Current Detect
VOCR
OCP Comp
0
0
2
OUT To Load
OCP Ouput Control
Blank Pulse
Reference Control
VREF
Latched Off
LC5220
O
REF
DS
Figure 14. Overcurrent protection (OCP) operation
OCP Blanking
PWM
EN
ON
MOSFE T
Figure 12. Constant current control operation in buck-boost
configuration
PWM
Control
DS
tBLK(O)
OCP_REF
SEN_IN
VSEN
SEN
+
RS
VOCR
VREF
GND
Figure 13. Overcurrent protection (OCP) circuit
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
15
The OCP detection is in the on-time period, except for the OCP
Blanking Time, tBLK(O) , to prevent malfunction.
REG
Note: The OCP function is activated only when the SEN pin
voltage, VSEN , reaches VOCR by excessive output current flowing
to RS . Therefore if the output current is restricted to less than its
target value, for example by current limitations of the inductor,
even though the LEDs are shorted, OCP would not be activated.
Current Value Setting for Dimming Control
REF
PWM
R2
IPEAK = VCCR / RS
where VCCR is as described in the REF Pin Input Operation section. The LC5220 series allows external adjustment of the current
flowing through the LED string, using either of the following
methods:
C2
SEN
GND
CPWM
RS
(A) Analog input
The LC5220 series allows constant current control using the
internal PWM control, an external PWM signal, or a combination
of both of them.
Using Internal PWM Dimming
The LC5220 series has a built-in PWM constant current control
circuit, and thus can achieve a constant current drive system for
the LED string using few external components. The peak output
current, IPEAK , for driving the LED string is calculated as follows:
LC5220
R1
REG
LC5220
LPF
R LPF
REF
PWM
PWM
signal
CLPF
GND
SEN
CPWM
RS
(B) Integrated PWM analog input
Figure 15. Dimming application circuit with internal PWM
• Adjust the analog voltage on the REF pin (figure 15A)
• Input the analog voltage integrated PWM signal through a low
pass filter, LPF, to the REF pin (figure 15B)
Using External PWM Dimming
Using an external PWM signal allows applying the LC5220 series
as a high voltage power switch. In this configuration, the output
of the OUT pin turns on and off according to a logic signal input
to the PWM pin. Because this control is not activated by the
internal PWM current control circuit, an external current control
circuit is needed. The frequency of the input PWM signal is recommended to be in the range 20 to 200 kHz.
As shown in figure 16, there is no CPWM on the PWM pin, allowing the PWM signal to be input to the PWM pin through an open
drain device. Do not use the device with CMOS output because
its output is shorted when the internal power MOSFET for discharging CPWM turns on. The range of the REF pin voltage, VREF ,
should be 0.15 to 3 V, and the SEN pin should be connected to
GND.
Note: Both OCP and OPP protection are invalid when using this
configuration.
LC5220-AN, Rev. 1.3
REG
LC5220
R1
Small signal
MOSFET
REF
PWM
R2
PWM
signal
GND
SEN
C2
Truth Table for External PWM
PWM Signal
OUT Pin
Low
On
High
Off
Figure 16. Dimming application circuit with external PWM
SANKEN ELECTRIC CO., LTD.
16
Using Internal and External PWM Dimming
This configuration combines the two configurations described
above: the internal PWM control circuit determines the limitation
of the peak output current flowing through the LED string, and
the external PWM circuit controls the average current. This configuration is effective for a low frequency external PWM range,
200 to 500 Hz. This circuit is shown in figure 17.
The narrower the duty cycle of the external PWM signal is, the
bigger the average LED output current is. At 100% duty cycle,
the LED output current is 0 A. The timing diagram is shown in
figure 18.
REG
LC5220
R1
Small signal
MOSFET
REF
PWM
R2
PWM
signal
C2
GND
SEN
CPWM
Truth Table for Combined Internal and External PWM
PWM Signal
LED Current Control
Low
Internal PWM current control
High
LED current off
Figure 17. Dimming application circuit with combined internal and external PWM
PWM
signal
VPWM
LED current
ILED
IC operation
Internal PWM
Off
Figure 18. Combined internal and external PWM operation
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
17
Application Information
Typical Application Components
The typical application circuit for a buck configuration in figure 2
is an example for a basic peripheral circuit. Table 2 provides an
listing of parts in figure 2, as examples for the sole purpose of
reference for the initial use of the IC. These are typical values,
but do not take into the application usage conditions such as PCB
layout, LED types, or circuit noise. It is necessary to take account
of such factors fully while designing and components should be
validated by operation in the actual application.
External Component Selection
The following recommendations should be observed when selecting components for use with the LC5220 series.
• LEDs The relation between the LED ratings and the output current ratings of the IC should be considered.
In buck configuration, the total forward voltage drop, VLED , of
LEDs in series should be less than the input voltage, VIN , because
the LEDs would be turned off if VLED were more than VIN . Normally, a VLED of 9 to 60 V is assumed.
With a buck-boost topology, the IC is capable of turning on LEDs
on the condition that VLED is more than VIN . Refer to the BuckBoost Circuit Operation section.
• L1 This is an inductor for smoothing output current. When the
value of L1 is higher, the LED ripple current is lower, and thus
the current stability is improved.
Normally, an L1 value of 0.5 to 10 mH is assumed. In actual
operation, it should be rated so that the inductor is not saturated
by the peak of the ripple current. If the inductor becomes saturated by an unexpectedly high surge current flow, the LEDs and
the IC could be damaged.
• D1 This is a free-wheeling diode for recirculation of the output
current. The energy stored during the PWM on-time period is
provided to LEDs through this diode during the off-time period.
The withstand voltage and recovery time, tRR , should be considered. If a diode with a long recovery time, tRR , is selected,
surge current may flow into the OUT pin when the internal
power MOSFET turns on. As a result, it would cause increased
noise, potentially malfunction due to the noise, and decreased
efficiency. Thus, it is recommended to select a diode equivalent
to the diode recommended in table 2, which has a tRR of approximately 30 ns, or a diode with a lower tRR.
• CIN This is an input smoothing capacitor. When the value of CIN
is high, the input and output ripple voltages are small. In addition,
given a certain capacitance level, the greater the output power is,
the greater the ripple voltages are. Thus it is necessary to select
the value according to the output power.
The IC is capable of operation in VIN full-wave rectification with
an input capacitor rated as low as approximately 1000 pF, instead
of an electrolytic capacitor. Therefore the configuration without
electrolytic capacitor enhances the power supply system operation life, and reduces system size and cost.
Note: If the lower peak of the ripple voltage of the VBB pin is
allowed to fall below the UVLO threshold (turn off) or the output
voltage is less than VLED in a buck configuration, the LEDs are
turned off. Thus it is necessary to take account of the value of CIN .
• C1 This is a capacitor for stabilizing the internal regulator. It is
required to provide the charge current for charging the gate of the
internal power MOSFET, and to maintain a stable voltage.
Table 2. Reference Specification of a Buck Configuration Circuit
Input voltage: 100 VAC, LED output voltage: 15 V, LED peak output current: 0.3 A
Symbol
Part Type
Values and Ratings
Description
LED
LED
―
L1
Inductor
1 mH / 1 A
D1
Fast recovery
rectifier diode
RD2A
CIN
Capacitor
Up to 4.7 μF / 450 V
C1
Capacitor
0.1 μF / 25 V
C2
Capacitor
1000 pF (to 0.1 μF) / 25 V
C3
Capacitor
0.1 μF / 250 V
Smoothing capacitor for reducing LED ripple current (Optional)
CPWM
Capacitor
100 pF / 25 V
PWM off-time setting capacitor (internal PMW control)
1/
8
Choke coil for smoothing current
Free-wheeling diode for recirculation
R1
Resistor
R2
Resistor
51 kΩ / 1/8 W
RS
Resistor
1.0 Ω / 1 W
LC5220-AN, Rev. 1.3
620 kΩ /
User-defined
W
Main supply source filtering capacitor; 1 nF or higher can be used
Internal regulator stabilizing capacitor
REF pin voltage stabilizing capacitor
Resistor for setting peak output current on OUT pin
Resistor for setting peak output current on OUT pin
Resistor for output current detection
SANKEN ELECTRIC CO., LTD.
18
Normally, a ceramic capacitor of 0.1 μF is used. A too-low value
of this capacitor causes decreased switching speed, and malfunctions. Conversely, a too-high value causes a longer startup time
because a long charging time for this capacitor delays startup of
the power supply. These factors should be carefully evaluated.
To use the internal reference voltage, the range of the REF pin
voltage, VREF , is set to be 2 to 3 V.
For example, to set VREF to 2.4 V, when an R1 of 510 kΩ and an
R2 of 160 kΩ are chosen:
The capacitor should be placed as close to the IC as possible.
• REF pin capacitor C2 C2 is a capacitor which prevents noise at
the REF pin. Because the OCP detection voltage, VOCP , is dependent on the REF pin voltage, according to the REF pin voltage,
VOCP rises during startup. For this reason, when the capacity of
C2 is large, the VOCP value during startup rises slowly.
When the output capacitor, C3, is connected, if the capacity of
both C2 and C3 is large, OCP may operate during startup. Then,
the REF pin voltage (the voltage which determines VOCP) and
the SEN pin voltage during startup need to be checked, and a C2
capacity at which the OCP does not operate is to be selected.
• Output capacitor C3 (Optional) As a measure against LED cur-
rent ripple on the LEDs, the output capacitor, C3 , is connected in
parallel to the LEDs if needed.
C3 is in an electric discharge state at the time of power activation.
If a power supply is switched on during this state, it is as if the
load is in short circuit state, the inductor current increases during
startup, and the OCP may operate. Then, the REF pin voltage
(the voltage which determines VOCP ) and the SEN pin voltage
during startup need to be checked, and a C3 capacity in which the
OCP does not operate is to be selected.
• R1, R2, and RS These resistors determine the peak output current, IPEAK, flowing to the LEDs. There are two methods for setting the reference current values, internal or external.
To input the reference voltage externally, the range of the REF
pin voltage, VREF , is set to be 0.2 to 2 V.
The peak output current is calculated as follows:
IPEAK = 0.4 × VREF / RS
(5)
VREF = VREG × R2 / (R1 + R2)
(6)
For example, to set IPEAK to 0.3 A, when an R1 of 620 kΩ, an R2
of 51 kΩ, and an RS of 1 Ω are chosen:
IPEAK ≈
0.4 × 10 (V) × 51 (kΩ)
0.3 A
1 (Ω) × (620 (kΩ) + 51 (kΩ)) ≈
The variation of IPEAK results from that of the REG output voltage, R1 , R 2, and RS .
LC5220-AN, Rev. 1.3
10 (V) × 160 (kΩ)
2.4 V
510 (kΩ) + 160 (kΩ) ≈
VREF ≈
The peak output current is calculated as follows:
IPEAK = 0.8 (V) / RS
For example, to set IPEAK to 0.3 A, when an RS of 2.7 Ω
is chosen:
IPEAK ≈ 0.8 (V) / 2.7 (Ω) ≈ 0.3 A
The variation of IPEAK results from that of the internal reference
voltage and RS .
In actual operation, the current value is higher than that calculated by the above equations because there is some propagation
delay in internal circuit. Especially when the input voltage is high
and the inductance value is low, the di/dt slope of the current is
high, and the actual current value is much higher than the calculated current value.
The current flowing to R1 and R2 affects the losses in the internal
regulator directly. Therefore it is recommended to select R1 and
R2, such that 500 kΩ < R1 + R2 , in order to restrict current as
much as possible.
It is recommended that the detection resistor, RS, have an allowable power dissipation that is twice to three times as much as
the loss in RS as margin, because the output current flows to it
when the internal power MOSFET turns on, and the loss may be
comparatively big.
• CPWM This determines the fixed off-time when using internal
PWM control. The recommended value is 100 pF, however the
proper value is changeable according to the load conditions of the
user-selected LEDs. When the CPWM value is small, the off-time
is short, and thus the operation frequency increases.
The following equation shows the relation between CPWM and
off-time:
tOFF (μs) = 0.15 × CPWM (pF) + 2
(7)
When the recommended CPWM value, 100 pF, is used, tOFF is
calculated as follows:
tOFF = 0.15 × 100 (pF) + 2 ≈ 17 μs
SANKEN ELECTRIC CO., LTD.
19
• 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 products or design your products by using Sanken 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.
LC5220-AN, Rev. 1.3
SANKEN ELECTRIC CO., LTD.
20