UM1361S
Hysteretic Buck High Brightness LED Driver with Internal Switch
UM1361S SOT23-5
General Description
The UM1361S 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 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 UM1361S comes in small SOT23-5 package. It is ideal for industrial and general lighting
applications.
Applications
Features
Hysteretic Control with High Side Current
Sensing
Integrated 40V 0.5Ω NDMOS
> 90% Efficiency
Wide Input Voltage Range: 6V to 40V
±5% LED Current Accuracy
Adjustable Constant LED Current
Analog or PWM Control Signal for PWM
Dimming
Over Temperature, Open Circuit LED
Protection
Up to 1MHz Switching Frequency
Pb-Free SOT23-5 Package
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,
C
onstant Current
Source
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UM1361S
Pin Configurations
Top View
5
4
LX
1
5
VIN
EQXYW
GND
2
VSET
3
4
ISENSE
1
2
3
X: Internal Code; Y: Year Code; W: Week Code
UM1361S
SOT23-5
Ordering Information
Part Number
UM1361S
Packaging Type
SOT23-5
Marking Code
EQX
Shipping Qty
3000pcs/7Inch
Tape & Reel
Pin Description
Pin
Number
1
2
Symbol
LX
GND
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 I
OUT
nom
Drive with PWM signal from open-collector or open-drain transistor, to
adjust output current. Adjustment range 1% to 100% of I
OUT
nom for f＜
500Hz and 2% to 100% of I
OUT
nom for f>20kHz.
Connect resistor R
S
from this pin to VIN to define nominal average
output current I
OUT
nom = 0.1/R
S
Input voltage (6V to 40V). Decouple to ground with 10μF or higher X7R
ceramic capacitor close to device.
Function
3
VSET
4
5
ISENSE
VIN
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UM1361S
Absolute Maximum Ratings
Over operating free-air temperature (unless otherwise noted) (Note 1)
Symbol
V
IN
V
LX,
V
ISENSE
V
SET
θ
jA
θ
jC
T
J
T
STG
T
L
Parameter
Input Voltage Range
Voltages on LX, ISENSE
V
SET
Pin Voltage
Thermal Resistance (Junction to Ambient)
Thermal Resistance (Junction to Case)
Maximum Junction Temperature
Storage Temperature Range
Maximum Lead Temperature for Soldering 5
seconds
Value
-0.3 to +45
-0.3 to +45
-0.3 to +6
250
130
+170
-65 to +170
+300
Unit
V
V
V
°
C/W
°
C/W
°
C
°
C
°
C
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
V
IN
T
A
T
J
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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UM1361S
Electrical Characteristics
(V
IN
= 16V, T
A
= 25° unless otherwise noted)
C,
Symbol
Parameter
Test Conditions
Min
Typ
V
IN
Input Voltage Range
6
R
S
=0.3Ω
333
I
LED
Output Current
R
S
=0.1Ω
1
Quiescent Current
VSET pin floating,
I
Q
0.6
without switching
V
IN
= 16V
I
SD
Shutdown Current
VSET pin grounded
37
Mean current sense
Measured on ISENSE
V
SENSE
95
100
threshold voltage
pin with respect to VIN
Sense threshold
V
SENSE_HYS
±
13
hysteresis
ISENSE pin input
I
SENSE
V
SENSE
=V
IN
-0.1
16
current
V
SET
range on VSET
V
en
For DC dimming
0.3
pin
DC voltage on VSET
V
enon
V
en
rising
0.25
pin to enable
DC voltage on VSET
V
enoff
V
en
falling
0.2
pin to disable
LX switch on
R
LX
I
LX
=100mA
0.5
resistance
LX switch leakage
I
LX(leak)
current
V
IN
= 16V, V
OUT
=9.6V
(3LEDs), L=47μH,
F
LX
Operating frequency
233
△I=0.25A
(I
LED
=1A)
Recommended
F
LXmax
maximum switch
frequency
Recommended
Ton_rec
minimum switch ON
For 4% accuracy
500
time
Max duty cycle
98
Recommended duty
D
LX
25
cycle range
T
PD
Internal comparator
45
(Note 2)
propagation delay
Over temperature
T
OTP
155
protection
Temperature
T
OTP_Hys
30
protection hystersis
I
XLmax
Current Limit
Peak inductor current
1.5
Note 2: Parameters are not tested at production, but guaranteed by design.
Max
40
Unit
V
mA
A
mA
50
105
μA
mV
%
μA
2.5
V
V
V
Ω
5
μA
kHz
1.0
MHz
ns
%
75
%
ns
°
C
°
C
A
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UM1361S
Function Block Diagram
VIN
D1
LED
Rs
LX
VIN
ISENSE
L1
GM
C1
Regulator
BG
VSET
Ref
R2
Low Voltage
Detector
OTP
VSET
EN
Logic
&
Driver
Internal
Enable
GND
Ilimit
R1
Typical Application Circuit
D1
Rs
0.3Ω
VIN(6V-40V)
VIN
ISENSE
Ci
10μF
Floating
UM1361S
VSET
LX
L1
100μH
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http://www.union-ic.com Rev.05 Nov.2014
5/13
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