UM1360
Hysteretic Buck High Brightness LED Driver with Internal Switch
UM1360Y SOT89-5
General Description
The UM1360 is a PWM step-down converter with internal power switch, designed for driving
single or multiple series connected LEDs efficiently from a voltage source higher than the LED
voltage. The UM1360 can drive up to 10 series connected LEDs. The device operates from an
input supply between 6V and 40V and employs hysteretic control with a high side current sense
resistor to set the constant output current up to 1A. The device is well suited for applications
requiring a wide input range. The high side current sensing and an integrated current sensing
circuitry minimize the number of external components while delivering an accurate average
output current. Depending upon supply voltage and external components, this device can provide
up to 30 watts of output power.
Output current can be adjusted below the set value, by applying an external control signal to the
VSET pin. The VSET pin will accept either a DC voltage or a PWM waveform. Dedicated pulse
width modulation (PWM) input enables pulsed LED dimming over a wide range of brightness
levels. A hysteretic control method ensures excellent input supply rejection and fast response
during load transients and PWM dimming.
Applying a voltage of 0.2V or lower to the VSET pin turns the output off and switches the device
into a low current standby state. The UM1360 employs spread spectrum technique to greatly
reduce its interference to other part of the system.
The UM1360 comes in small SOT89-5 package. It is ideal for industrial and general lighting
applications.
Applications
Features
Low Voltage Halogen Replacement
LEDs
Low Voltage Industrial Lighting
LED Back-Side Lighting
Illuminated Signs
DC/DC or AC/DC LED Driver
Application
General Purpose, Constant Current
Source
Hysteretic Control with High Side Current
Sensing
Integrated 40V 0.5Ω NDMOS
Up to 98% Efficiency
Wide Input Voltage Range: 6V to 40V
50V Transient Capability
± 5% LED Current Accuracy
Adjustable Constant LED Current
Single Pin On/Off and Brightness Control
Using DC Voltage or PWM
Spread Spectrum Driver
Over Temperature, Open Circuit LED
Protection
Up to 1MHz Switching Frequency
Pb-Free SOT89-5 Package
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UM1360
Pin Configurations
Top View
4
5
LX 1
5 VIN
GND 2
GND
VSET 3
4 ISENSE
UM1360Y
XX
1
2
3
XX: Week Code
UM1360Y
SOT89-5
Ordering Information
Part Number
Packaging Type
Marking Code
Shipping Qty
UM1360Y
SOT89-5
UM1360Y
1000pcs/7Inch
Tape & Reel
Pin Description
Pin
Number
Symbol
1
LX
2
GND
3
VSET
4
ISENSE
5
VIN
Function
Drain of NDMOS switch.
Ground (0V).
Multi-function On/Off and brightness control pin:
Leave floating for normal operation.
Drive to voltage below 0.2V to turn off output current.
Drive with DC voltage (0.3V<VSET<2.5V) to adjust output current
from 12% to 100% of IOUTnom.
Drive with PWM signal to adjust output current. Adjustment range
1% to 100% of IOUTnom for f≤1kHz.
Connect resistor RS from this pin to VIN to define nominal average
output current IOUTnom=0.1/RS.
Input voltage (6V to 40V). Decouple to ground with 10μF or higher
X7R ceramic capacitor close to device.
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UM1360
Absolute Maximum Ratings
Over operating free-air temperature (unless otherwise noted) (Note 1)
Symbol
VIN
VLX,
VISENSE
VSET
Parameter
Value
Unit
Input Voltage Range
-0.3 to +40
V
Voltages on LX, ISENSE
-0.3 to +40
V
VSET Pin Voltage
-0.3 to +6
V
θJA
Thermal Resistance (Junction to Ambient)
100
°C/W
TJ
Maximum Junction Temperature
+150
°C
-55 to +150
°C
+300
°C
TSTG
TL
Storage Temperature Range
Maximum Lead Temperature for Soldering 5
Seconds
Note 1: These are stress ratings only and functional operation is not implied. Exposure to absolute
maximum ratings for prolonged time periods may affect device reliability. All voltage
values are with respect to network ground terminal.
Recommended Operating Conditions
Symbol
VIN
TA
TJ
Parameter
Input Voltage Range
Operating Ambient Temperature
Operating Junction Temperature
Min
6.0
-40
-40
Typ
Max
40
85
150
Unit
V
°C
°C
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UM1360
Electrical Characteristics
(VIN=16V, TA=25°C, unless otherwise noted)
Symbol
VIN
Parameter
Input Voltage Range
ILED
Output Current
IQ
ISD
VSENSE
VSENSE_HYS
ISENSE
VEN
VENON
VENOFF
RLX
ILX(leak)
FLX
Quiescent Current
without Switching
Shutdown Current
Mean Current Sense
Threshold Voltage
Sense Threshold
Hysteresis
ISENSE Pin Input
Current
VSET Range on VSET
Pin
DC Voltage on VSET
Pin to Enable
DC Voltage on VSET
Pin to Disable
LX Switch on
Resistance
LX Switch Leakage
Current
Operating Frequency
Test Conditions
RS=0.33Ω
RS=0.1Ω
VSET Pin Floating,
VIN=16V
VSET=GND, VIN=16V
Measured on ISENSE Pin
with Respect to VIN
Min
6
95
VSENSE=VIN-0.1
For DC Dimming
Max
40
Unit
V
303
1000
mA
430
μA
35
70
μA
100
105
mV
±15
%
20
μA
0.3
2.5
V
VEN Rising
0.25
V
VEN Falling
0.2
V
ILX=1000mA
0.5
Ω
5
VIN=16V, L1=47μH,
VOUT=9.6V (3 LEDs),
RS=0.1Ω
Recommended
Maximum Switch
Frequency
Recommended
Ton_rec
Minimum
For 4% Accuracy
(Note 2)
Switch ON Time
Max Duty Cycle
Recommended Duty
DLX
25
Cycle Range
TPD
Internal Comparator
(Note 2)
Propagation Delay
Over Temperature
TOTP
Protection
Temperature Protection
TOTP_HYS
Hysteresis
ILXmax
Peak Switch Current
1.5
Continuous Switch
ILXmean
Current
Note 2: Parameters are not tested at production, but guaranteed by design.
FLXmax
Typ
μA
230
kHz
1.0
MHz
500
ns
100
%
75
%
500
ns
150
°C
40
°C
A
1.0
A
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UM1360
Function Block Diagram
D1
VIN
LED
L1
Rs
VIN
LX
ISENSE
GM
Low Voltage
Detector
Regulator
C1
OTP
BG
VSET
Logic
&
Driver
Ref
VSET
EN
R2
Internal
Enable
R1
Ilimit
GND
Typical Application Circuit
D1
Rs 0.33Ω
VIN (6V-40V)
VIN
ISENSE
L1
UM1360
C1
100μH
10μF
Floating
VSET
LX
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UM1360
Typical Operating Characteristics
Efficiency
vs. Vvs.Vin
Rs=0.15Ω)
IN (L1=47µH,
Efficiency
(Rs=0.15Ω,L=47uH)
Efficiency
vs. V
Rs=0.33Ω)
IN (L1=100µH,
Efficiency
vs.Vin
(Rs=0.33Ω,L=100uH)
90
Ef f iciency (%)
90
Ef f iciency (%)
100
100
80
70
1LED
2LED
1LED
2LED
4LED
60
5LED
80
70
3LED
1LED
3LED
6LED
4LED
5LED
6LED
7LED
7LED
8LED
8LED
9LED
9LED
2LED
3LED
5LED 3LED 6LED
1LED
2LED
4LED
5LED
7LED
8LED
4LED
60
7LED
10LED
10LED
6LED
8LED 9LED 9LED
10LED
10LED
50
50
0
5
10
15
20
25
30
35
40
0
5
10
15
VIN (V)
Efficiency
vs. VIN(Rs=0.1Ω,L=33uH)
(L1=33µH, Rs=0.1Ω)
Efficiency vs.Vin
20
VIN (V)
25
30
35
40
Output Output
Current
vs.
VIN(Rs=0.33Ω,L=100uH)
(L1=100µH, Rs=0.33Ω)
Current
vs.Vin
350
100
340
330
90
Output Current (%)
Ef f iciency (%)
320
80
70
1LED
2LED
1LED
2LED
4LED
60
5LED
3LED
310
300
290
280
1LED
3LED
6LED
4LED
5LED
6LED
7LED
7LED
8LED
8LED
9LED9LED
5LED
6LED
8LED
9LED
9LED
7LED
8LED
3LED
6LED
10LED
10LED
250
50
0
5
10
15
20
VIN (V)
25
30
35
0
40
5
10
15
20
25
30
35
40
VIN (V)
Quiescent
vs.Input
Input
Voltage
QuiescentCurrent
Current VS.
Voltage
Shutdown
Current
vs.Input
Input
Voltage
Shutdown
Current VS.
Voltage
530
60
50
Shutdown Current (μA)
500
Quiescent Current (μA)
4LED
5LED
7LED
260
3LED
2LED
4LED
270
10LED
10LED
2LED
1LED
470
440
40
30
20
410
10
380
0
0
5
10
15
20
25
Input Voltage (V)
30
35
40
0
5
10
15
20
25
Input Voltage (V)
30
35
40
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UM1360
Typical Operating Characteristics (Continued)
LED Current vs. VSET
LED Current vs VSET
(VIN=16V,
3 LEDs, L1=33µH, Rs=0.1Ω)
(Vin=16V,3LEDs,33uH,Rs=0.1Ω)
LED Current vs. VSET Duty Cycle
LED Current vs VSET Duty Cycle
(VIN=16V,
3 LEDs, L1=33µH, Rs=0.1Ω)
(Vin=16V,3LEDs,33uH,Rs=0.1Ω)
1000
1000
900
900
800
800
700
700
ILED (mA)
1100
ILED (mA)
1100
600
600
500
500
400
400
300
300
200
200
100
PWM=1kHz
100
0
0
0
10
20
30
40
50
60
Duty Cycle (%)
70
80
90
0
100
1
1.5
VSET (V)
2
2.5
3
Output
Current
Temperature
Output
Current vs.
vs. Temperature
(L1=33µH,
Rs=0.1Ω)
(L= 33μH, Rs=0.1Ω)
Feedback
Feedback Voltage
Voltage vsvs.
Vin VIN
160
960
140
940
120
920
Output Current (mA)
Sense Threshold Voltage (mV)
0.5
100
80
60
900
880
860
40
840
20
820
0
VIN=16V, 3 LEDs
800
0
5
10
15
20
25
30
Input Voltage (V)
35
40
45
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
140
Output
Current
vs.Temperature
Temperature
Output
CurrentChange
Change vs.
(L= 47μH, Rs=0.33Ω)
(L1=47µH,
Rs=0.33Ω)
Deviation from Nominal Set Value (%)
50
40
30
20
10
0
-10
-20
-30
VV
=16V,
3 3LEDs
=16V,
LEDs
ININ
-40
-50
-40
-20
0
20
40
60
80
100
120
140
Temperature (°C)
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UM1360
Typical Operating Characteristics (Continued)
Steady State Waveforms
(VIN=16V, 3 LEDs, L1=100μH, Rs=0.33Ω)
Start Up Waveforms
5V/div
LX
VSET
2V/div
ILED
100mA/div
2μs/div
ILED
10μs/div
500mA/div
100% Duty Cycle Mode
(VIN=10V, 3 LEDs, L1=100μH, Rs=0.33Ω)
Dimming Waveforms
(PWM=50%, VIN=16V, 3 LEDs, L1=100μH, Rs=0.33Ω)
5V/div
PWM
2V/div
LX
200mA/div
ILED
ILED
1ms/div
100mA/div
1ms/div
Hopping Switching Frequency Waveform
Spectrum of the UM1360
(VIN=16V, 3 LEDs, L1=100µH, IOUT=1A)
Fixed Switching Frequency
Waveform Spectrum of Competitor
(VIN=16V, 3 LEDs, L1=100µH, IOUT=1A)
20dB/div
20dB/div
0dB
0dB
500kHz/div
0Hz
500kHz/div
0Hz
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UM1360
Applications Information
Setting Nominal Average Output Current with External Resistor RS
The nominal average output current in the LED(s) is determined by the value of the external
current sense resistor (RS) connected between VIN and ISENSE and is given by:
IOUTnom=0.1/RS [for RS≥0.1Ω]
The table below gives values of nominal average output current for several preferred values of
current setting resistor (Rs) in the typical application circuit as shown on page 5.
Rs (Ω)
0.1
0.13
0.15
0.3
Nominal Average Output Current (mA)
1000
760
667
333
The above values assume that the VSET pin is floating or applied with a voltage higher than
2.5V (must be less than 5V). Note that Rs=0.1Ω is the minimum allowed value of sense
resistor under these conditions to maintain switch current below the specified maximum value.
It is possible to use different values of Rs if the VSET pin is driven from an external voltage.
(See next section).
Output Current Adjustment by External DC Control Voltage
The VSET pin can be driven by an external DC voltage (VEN), as shown, to adjust the output
current to a value below the nominal average value defined by Rs.
D1
Rs 0.13Ω
LED
3W
VIN (6V-40V)
VIN
ISENSE
L1
UM1360
C1
68μH
10μF
VSET
LX
The average output current is given by:
IOUT=(0.1*VEN)/(2.5*Rs) [for 0.3V<VEN<2.5V]
Note that 100% brightness setting corresponds to:
(2.5V≤VEN≤5V)
Output Current Adjustment by PWM Control
A Pulse Width Modulated (PWM) signal with duty cycle PWM can be applied to the VSET
pin, as shown below, to adjust the output current to a value below the nominal average value
set by resistor Rs:
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UM1360
IOUT=(0.1*D)/RS (0≤D≤100%, 2.5V<Vpulse<5V)
IOUT=(Vpulse*0.1*D)/(2.5*RS) (0≤D≤100%, 0.5V<Vpulse<2.5V)
D1
Rs 0.13Ω
LED
3W
VIN (6V-40V)
VIN
C1
ISENSE
L1
UM1360
68μH
10μF
VSET
LX
PWM dimming provides reduced brightness by modulating the LED’s forward current
between 0% and 100%. The LED brightness is controlled by adjusting the relative ratios of
the on time to the off time. A 25% brightness level is achieved by turning the LED on at full
current for 25% of one cycle. To ensure this switching process between on and off state is
invisible by human eyes, the switching frequency must be greater than 100Hz. When above
100Hz, the human eyes average the on and off times, seeing only an effective brightness that
is proportional to the LED’s on-time duty cycle. The advantage of PWM dimming is that the
forward current is always constant, therefore the LED color does not vary with brightness as it
does with analog dimming. Pulsing the current provides precise brightness control while
preserving the color purity.
Capacitor Selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor
appears in series with the supply source impedance and lowers overall efficiency. This
capacitor has to supply the relatively high peak current to the coil and smooth the current
ripple on the input supply. A minimum value of 4.7μF is acceptable if the input source is close
to the device, but higher values will improve performance at lower input voltages, especially
when the source impedance is high. The input capacitor should be placed as close as possible
to the IC.
For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better
dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in
this application and should NOT be used.
Inductor Selection
Recommended inductor values for the UM1360 are in the range 27μH to 220μH. Higher
values of inductance are recommended at higher supply voltages in order to minimize errors
due to switching delays, which result in increased ripple and lower efficiency. Higher values
of inductance also result in a smaller change in output current over the supply voltage range.
The inductor should be mounted as close to the device as possible with low resistance
connections to the LX and VIN pins. The chosen coil should have a saturation current higher
than the peak output current and a continuous current rating above the required mean output
current. Suitable coils for the UM1360 are listed in the table below:
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UM1360
Load Current
IOUT>1A
0.8A<IOUT≤1A
0.4A<IOUT≤0.8A
IOUT≤0.4A
Order
Code
744066330
7447714470
7447714680
7447714101
Inductor
27-47μH
33-82μH
47-100μH
68-220μH
L(μH)
Size
33
47
68
100
1038
1050
1050
1050
DCR
(mΩ)
92
82.5
110
165
Saturation
Current (mA)
1800
2.5
2200
1800
Saturation Current
1.3-1.5 Times of Load Current
Manufacturer
Würth Elektronik
www.we-online.com
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off'
times within the specified limits over the supply voltage and load current range. The following
equations can be used as a guide.
LX Switch 'On' time
TON=(L1*ΔI)/(VIN-VLED-I LED*(RS+RL+RLX))
LX Switch 'Off' time
TOFF=(L1*ΔI)/(VLED+VD+ILED*(RS+RL))
Where:
L1 is the coil inductance (H).
RL is the coil resistance (Ω).
RS is the current sense resistance (Ω).
ILED is the required LED current (A).
ΔI is the coil peak-peak ripple current (A) {internally set to 0.3×ILED}.
VIN is the supply voltage (V).
VLED is the total LED forward voltage (V).
RLX is the switch resistance (Ω) {=0.5Ω nominal}.
VD is the diode forward voltage at the required load current (V).
Diode Selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance
Schottky diode with low reverse leakage at the maximum operating voltage and temperature.
They also provide better efficiency than silicon diodes, due to a combination of lower forward
voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a
continuous current rating higher than the maximum output load current. It is very important to
consider the reverse leakage of the diode when operating above 85°C. Excess leakage will
increase the power dissipation in the device and if close to the load may create a thermal
runaway condition.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will
increase the peak voltage on the LX output. If a silicon diode is used, care should be taken to
ensure that the total voltage appearing on the LX pin including supply ripple, does not exceed
the specified maximum value.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching losses and stable operation. Minimize
ground noise by connecting high current ground returns, the input bypass capacitor ground lead,
and the output filter ground lead to a single point. Place Rs as close as possible to the ISENSE and
VIN. For better noise immunity, a Kelvin connection is strongly recommended between ISENSE
and Rs.
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UM1360
Package Information
UM1360Y SOT89-5
0.
20
0
Outline Drawing
DIMENSIONS
c
L
R
D1
E
Symbol
L
Pin #1 ID
b
b1
e
Top View
End View
A
8°(4X)
MILLIMETERS
A
Typ
1.50
Max
1.60
Min
0.055
Typ
0.059
Max
0.063
b
0.32
-
0.54
0.013
-
0.021
b1
0.38
-
0.62
0.015
-
0.024
c
0.35
-
0.44
0.014
-
0.017
D
4.40
4.50
4.60
0.173
0.177
0.181
D1
1.40
-
1.83
0.055
-
0.072
E
2.30
2.50
2.60
0.091
0.098
0.102
1.20
0.026
e
D
L
Side View
INCHES
Min
1.40
1.50TYP
0.65
-
0.059TYP
-
0.047
Land Pattern
4.50
1.60
1.60
4.55
5.35
3.10
1.80
0.75
0.60
1.50
NOTES:
1. Compound dimension: 4.50×2.50;
2. Unit: mm;
3. General tolerance ±0.05mm unless otherwise
specified;
4. The layout is just for reference.
Tape and Reel Orientation
UM1360Y
XX
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UM1360
GREEN COMPLIANCE
Union Semiconductor is committed to environmental excellence in all aspects of its
operations including meeting or exceeding regulatory requirements with respect to the use
of hazardous substances. Numerous successful programs have been implemented to
reduce the use of hazardous substances and/or emissions.
All Union components are compliant with the RoHS directive, which helps to support
customers in their compliance with environmental directives. For more green compliance
information, please visit:
http://www.union-ic.com/index.aspx?cat_code=RoHSDeclaration
IMPORTANT NOTICE
The information in this document has been carefully reviewed and is believed to be
accurate. Nonetheless, this document is subject to change without notice. Union assumes
no responsibility for any inaccuracies that may be contained in this document, and makes
no commitment to update or to keep current the contained information, or to notify a
person or organization of any update. Union reserves the right to make changes, at any
time, in order to improve reliability, function or design and to attempt to supply the best
product possible.
Union Semiconductor, Inc
Add: Unit 606, No.570 Shengxia Road, Shanghai 201210
Tel: 021-51093966
Fax: 021-51026018
Website: www.union-ic.com
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