UNISONIC TECHNOLOGIES CO., LTD
USL3633
Preliminary
LINEAR INTEGRATED CIRCUIT
NON-ISOLATED BUCK
OFFLINE LED DRIVER
DESCRIPTION
The UTC
USL3633
is a high performance, high precision and
low cost constant current LED driver for non-isolated buck
application. The device operates in critical conduction mode and
is suitable for 85V~265V universal input offline LED lighting. It
operates in critical conduction mode, the output current does not
change with the inductance and LED output voltage.
The UTC
USL3633
integrates a 600V power MOSFET. It can
achieve excellent constant current performance with very few
external components, so the system cost and size are minimized.
The UTC
USL3633
offers rich protection functions to improve
the system reliability, including LED open circuit protection, LED
short circuit protection, V
CC
under voltage protection, CS resistor
short circuit protection and thermal regulation function.
SOP-8
FEATURES
* Critical conduction mode operation
* Internal 600V Power MOSFET
* Ultra low operating current
* No auxiliary winding
* ±5% LED output current accuracy
* LED short protection
* LED open protection
* V
CC
under voltage protection
* Current sensing resistor short protection
* Thermal regulation function
ORDERING INFORMATION
Ordering Number
USL3633G-S08-R
Package
SOP-8
Packing
Tape Reel
USL3633G-S08-R
(1)Packing Type
(2)Package Type
(3)Green Package
(1) R: Tape Reel
(2) S08: SOP-8
(3) G: Halogen Free and Lead Free
MARKING
www.unisonic.com.tw
Copyright © 2015 Unisonic Technologies Co., Ltd
1 of 6
QW-R103-097.b
USL3633
PIN CONFIGURATION
Preliminary
LINEAR INTEGRATED CIRCUIT
PIN DESCRIPTION
PIN NAME
GND
R
OVP
NC
V
CC
DRAIN
CS
DESCRIPTION
Ground
Over voltage protection setting pn. Connect a resistor to GND
No connection. Should be connected to GND(Pin1)
Power supply pin
Internal HV Power MOSFET Drain.
Current sense pin. Connect a sense resistor between this pin and GND pin.
PIN NO.
1
2
3
4
5, 6
7, 8
BLOCK DIAGRAM
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QW-R103-097.b
USL3633
Preliminary
LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATING
PARAMETER
SYMBOL
RATINGS
UNIT
V
CC
Pin Maximum Sink Current
I
CC_MAX
5
mA
Internal HV MOSFET Drain Voltage
D
RAIN
-0.3~600
V
Current Sense Pin Input Voltage
CS
-0.3~6
V
Over-Voltage Setting Pin Voltage
R
OVP
-0.3~6
V
Power Dissipation
P
D
0.45
W
Junction Temperature
T
J
-40~+150
°C
Storage Temperature
T
STG
-55~+150
°C
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
RECOMMENDED OPERATION CONDITIONS
SYMBOL
I
LED1
I
LED2
V
LED min
RATINGS
280
350
>15
UNIT
mA
mA
V
PARAMETER
Output LED Current @ V
OUT
=72V
(Input Voltage 176V~265V)
Output LED Current @ V
OUT
=36V
(Input Voltage 176V~265V)
Minimum LED Loading Voltage
THERMAL RESISTANCES CHARACTERISTICS
SYMBOL
θ
JA
RATING
145
UNIT
°C/W
PARAMETER
Junction to Ambient
ELECTRICAL CHARACTERISTICS
(Notes 1, 2) (Unless otherwise specified, V
CC
=14V and T
A
=25°C)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN TYP MAX UNIT
Supply Voltage Section
V
CC
Clamp Voltage
V
CC_CLAMP
1mA
16.8
V
V
CC
Turn On Threshold
V
CC_ON
V
CC
Rising
13.8
V
V
CC
Turn Off Threshold
V
CC_UVLO
V
CC
Falling
9
V
V
CC
Startup Current
I
ST
V
CC
= V
CC-ON
- 1V
160 250
µA
V
CC
Operating Current
I
OP
F
OP
=70KHz
200 300
µA
Current Sense Section
Threshold Voltage for Peak Current Limit
V
CS_peak
390 400 410
mV
Threshold Voltage for Peak Current Limit When
V
CS_SHORT
Output Short
200
mV
Output Short
Leading Edge Blanking Time for Current Sense
T
LEB
350
ns
Switch Off Delay Time
T
DELAY
200
ns
Internal Time Control Section
Minimum OFF Time
T
OFF_MIN
4.5
µs
Maximum OFF Time
T
OFF_MAX
240
µs
Maximum On Time
T
ON_MAX
35
µs
R
OVP
Pin Voltage
V
ROVP
0.5
V
MOSFET Section
Static Drain-source On-resistance
R
DS_ON
V
GS
=15V/I
DS
=0.4A
5
Ω
Drain-Source Breakdown Voltage
BV
DSS
V
GS
=0V/I
DS
=250µA
600
V
Power MOSFET Drain Leakage Current
I
DSS
V
GS
=0V/V
DS
=600V
1
µA
Thermal Regulation Section
Thermal Regulation Temperature
T
REG
150
°C
Notes: 1. Production testing of the chip is performed at 25°C.
2. The maximum and minimum parameters specified are guaranteed by test, the typical value are guaranteed
by design, characterization and statistical analysis.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
3 of 6
QW-R103-097.b
USL3633
Preliminary
LINEAR INTEGRATED CIRCUIT
APPLICATION INFORMATION
The UTC
USL3633
is a high performance non-isolated Buck converter specially designed for LED lighting. The
device integrates a 600V power MOSFET. With very few external components, the converter achieves excellent
constant current control. And it does not need auxiliary winding for powering the IC or voltage sensing, thus the
system size and cost is greatly reduced.
Start Up
When system powered up, the V
CC
pin capacitor is charged up by the start up resistor. When the V
CC
pin voltage
reaches the start up threshold, the internal circuits start operating. The UTC
USL3633
integrates a 17V zener
diode to clamp the V
CC
voltage.
Constant Current Control
Cycle by Cycle current sense is adjusted in UTC
USL3633,
the CS pin is connected to the current sense
comparator, and the voltage on CS pin is compared with the internal 400mV reference voltage. The MOSFET will be
switched off when the voltage on CS pin reaches the Peak Current threshold. The CS comparator includes a 350ns
leading edge blanking time. After the MOSFET switched off, the OFF time controller would open the MOSFET again
at time up. At that moment, CS pin voltage is 0mV usually.
The Delta inductor current is given by:
I
PK
=
400
(mA
）
R
CS
Where, R
CS
is the current sense resistor value.
The current in LED can be calculated by the equation:
I
LED
=
Where, I
PK
is the Peak current of the inductor.
Inductor Selection
The UTC
USL3633
works under inductor current critical conduction mode. When the power MOFET is switched
on, the current in the inductor rises up from zero, the on time of the MOSFET can be calculated by the equation:
I
PK
200
=
(mA
）
2
R
CS
t
on
½
L
I
PK
V
IN
-
V
LED
Where,
L is the inductance value
V
IN
is the DC bus voltage after the rectifier bridge
V
LED
is the voltage on the LED
After the power MOSFET is switched off, the current in the inductor decreases. When the inductor current
reaches zero, the power MOSFET is turned on again by IC internal logic. The off time of the MOSFET is given by:
t
off
½
The inductance can be calculated by the equation:
L
I
PK
V
LED
L
½
V
LED
(
V
IN
-
V
LED
)
freq
I
PK
V
IN
The freq is the system switching frequency, which is proportional to the input voltage. So the minimum switching
frequency is set at lowest input voltage, and the maximum switching frequency is set at highest input voltage.
The minimum and maximum off time of UTC
USL3633
is set at 4.5µs and 240µs, respectively. Referring to the
equation of t
OFF
calculation, if the inductance is too small, the t
OFF
may be smaller than the minimum off time, system
will operate in discontinuous conduction mode and the output current will be smaller than the designed value. If the
inductance is too large, the t
OFF
may be larger than the maximum off time, the outputt current will not be constant
follow design value. So it is important to choose a proper inductance, we recommend user to regulate the inductance
value for 70KHz application.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
4 of 6
QW-R103-097.b
USL3633
Preliminary
LINEAR INTEGRATED CIRCUIT
APPLICATION INFORMATION(Cont.)
Over Voltage Protection
The over voltage protection can be programmed by the R
OVP
pin resistor. The R
OVP
pin voltage is 0.5V.
When the LED is open circuit, the output voltage increases gradually, and the demagnetization time gets shorter.
The demagnetization time at OVP---- Tovp can be calculated by the open circuit protection voltage:
T
OVP
≈
L
I
PK
V
OVP
Where，
Vovp is the open circuit protection voltage
And then the Rovp resistor value can be calculated by the equation:
R
OVP
≈ 19
To
p
10
6
(kΩ)
Protection Function
The UTC
USL3633
offers rich protection functions to improve the system reliability, including LED open/short
protection, CS resistor short protection, V
CC
under voltage protection, thermal regulation. When the LED is open
circuit, the system will trigger the over voltage protection and stop switching.
When the LED short circuit is detected, the system works at low frequency (about 5kHz), and the CS pin turn off
threshold is reduced to 200mV. So the system power consumption is very low. At some catastrophic fault condition,
such as CS resistor shorted or inductor saturated, the internal fast fault detection circuit will be triggered, the system
stops switching immediately.
After the system enters into fault condition, the V
CC
voltage will decrease until it reaches the UVLO threshold,
then the system will re-start again. If the fault condition is removed, the system will recover to normal operation.
Thermal Regulation
The UTC
USL3633
integrates thermal regulation function. When the system is over temperature, the output
current is gradually reduced; the output power and thermal dissipation are also reduced. The system temperature is
regulated and the system reliability is improved. The thermal regulation temperature is set to 150°C internally.
PCB Layout
The following rules should be followed in UTC
USL3633
PCB layout:
Bypass Capacitor
The bypass capacitor on V
CC
pin should be as close as possible to the V
CC
Pin and GND pin.
R
OVP
Pin
The R
OVP
resistor should be as close as possible to the R
OVP
Pin.
Ground Path
The power ground path for current sense should be short, and the power ground path should be separated from
small signal ground path before connecting to the negative node of the bulk capacitor.
The Area of Power Loop
The area of main current loop should be as small as possible to reduce EMI radiation, such as the inductor, the
power MOSFET, the output diode and the bus capacitor loop.
NC pin
The NC pin should be connected to GND (pin1).
Drain Pin
To increase the copper area of DRAIN pin for better thermal dissipation. However too large copper area may
compromise EMI performance.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
5 of 6
QW-R103-097.b
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