UM1351
Hysteretic Buck High Brightness LED Driver with Internal Switch
UM1351Y SOT89-5
UM1351S SOT23-5
General Description
The UM1351 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 UM1351 can drive up to 8 series connected LEDs. The device operates from an input
supply between 6V and 35V and employs hysteretic control with a high side current sense resistor
to set the constant output current up to 700mA. 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 24 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 UM1351 comes in small SOT89-5 and SOT23-5 packages. It is ideal for industrial and
general lighting applications.
Applications
Features
Hysteretic Control with High Side Current
Sensing
Integrated 35V 0.5Ω NDMOS
Up to 98% Efficiency
Wide Input Voltage Range: 6V to 35V
±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 SOT89-5 and SOT23-5 Packages
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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UM1351
Pin Configurations
Top View
5
4
LX 1
5 VIN
GND 2
UM1351Y
XX
1
2
3
GND
VSET 3
4 ISENSE
XX: Week Code
UM1351Y
SOT89-5
5
VSET
1
5
ISENSE
4
5FA
GND
2
1
LX
3
4
VIN
2
M: Month Code
UM1351S
SOT23-5
Ordering Information
Part Number
UM1351Y
UM1351S
Packaging Type
SOT89-5
SOT23-5
Marking Code
UM1351Y
5FA
Shipping Qty
1000pcs/7Inch
Tape & Reel
3000pcs/7Inch
Tape & Reel
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M
3
UM1351
Pin Description
Pin Number
UM1351Y UM1351S
1
2
3
2
Symbol
LX
GND
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 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＜
100kHz.
Connect a capacitor from this pin to ground to
increase soft-start time.
(Default soft-start time=10μs. Additional soft-start
time is approximately 700μs/nF.)
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 35V). Decouple to ground with 10μF
or higher X7R ceramic capacitor close to device.
3
1
VSET
4
5
5
4
ISENSE
VIN
Absolute Maximum Ratings
Over operating free-air temperature (unless otherwise noted) (Note 1)
Symbol
V
IN
V
LX
,
V
ISENSE
V
SET
θ
JA
T
J
T
STG
T
L
Parameter
Input Voltage Range
Voltages on LX, ISENSE
VSET Pin Voltage
Thermal Resistance (Junction to SOT89-5
Ambient)
SOT23-5
Maximum Junction Temperature
Storage Temperature Range
Maximum Lead Temperature for Soldering 5
seconds
Value
-0.3 to +35
-0.3 to +35
-0.3 to +6
100
230
+150
-55 to +150
+300
Unit
V
V
V
°
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
35
85
150
Unit
V
°
C
°
C
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UM1351
Electrical Characteristics
(V
IN
= 16V, T
A
= 25° unless otherwise noted)
C,
Symbol
Parameter
Test Conditions
Min
V
IN
Input voltage range
6
R
S
=0.33Ω
I
LED
Output current
R
S
=0.15Ω
Quiescent current
VSET pin floating,
I
Q
without switching
V
IN
= 16V
I
SD
Shutdown current
VSET=GND, V
IN
=16V
Mean current sense
Measured on ISENSE pin
V
SENSE
95
threshold voltage
with respect to VIN
Sense threshold
V
SENSE_HYS
hysteresis
ISENSE pin input
I
SENSE
V
SENSE
=V
IN
-0.1
current
V
SET
range on VSET
V
EN
For DC dimming
0.3
pin
DC voltage on VSET
V
ENON
V
EN
rising
pin to enable
DC voltage on VSET
V
ENOFF
V
EN
falling
pin to disable
LX switch on
R
LX
I
LX
=700mA
resistance
LX switch leakage
I
LX(leak)
current
T
SS
Soft start time
V
IN
=16V, C
EN
=1nF
V
IN
= 16V, L=47μH,
F
LX
Operating frequency
V
OUT
=9.6V(3 LEDs),
ILED=700mA
Recommended
F
LXmax
maximum switch
frequency
Recommended
T
on_rec
minimum
For 4% accuracy
(Note 2)
switch ON time
Max duty cycle
Recommended duty
D
LX
25
cycle range
T
PD
Internal comparator
(Note 2)
propagation delay
Over temperature
T
OTP
protection
Temperature
T
OTP_HYS
protection hysteresis
I
XLmax
Current limit
0.75
Note 2: Parameters are not tested at production, but guaranteed by design.
Typ
303
666
430
30
100
±
15
20
Max
35
Unit
V
mA
μA
60
105
μA
mV
%
μA
2.5
0.25
0.2
0.5
5
700
350
V
V
V
Ω
μA
μs
kHz
1.0
MHz
500
100
75
45
150
40
1.0
ns
%
%
ns
°
C
°
C
A
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UM1351
Function Block Diagram
VIN
D1
LED
Rs
VIN
ISENSE
LX
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
0.33Ω
VIN(6V-35V)
VIN
ISENSE
Ci
10μF
Floating
UM1351
VSET
LX
L1
100μH
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