UM1661
High Efficiency Low Noise PFM Step-Up DC/DC Converter
UM1661
SOT23-6
General Description
The UM1661 PFM step-up DC/DC Converter drives white LEDs with a constant current to
provide backlight in cell phones, PDAs, and other hand-held devices. It features allowing series
connection of the white LEDs so that the LED currents are identical for uniform brightness. An
enable input can be pulsed repeatedly to adjust LEDs brightness. The fast 500kHz to 2MHz
operation frequency allows for smaller capacitor and inductor. Fault condition protection uses
cycle-by-cycle current limiting to sense maximum inductor current and over-voltage protection.
The 0.2V low reference voltage minimizes the power loss across the current sense resistor.
The converter can operate from 2V to 6V, and capable of delivering maximum 200mA output
current at 4-LEDs application with 3V input voltage. Quiescent current drawn from power source
is as low as 120uA. All of these features make UM1661 be suitable for the portable devices,
which are supplied by a single battery.
Applications
Compact Back Light Module
Power Source for LED
Constant Current Source
Features
Up to 24V Output Voltage
Wide Operation Range: 2V to 6V
Maximum 2MHz Operating Frequency
PWM Dimming Control
Shutdown Current <1μA
Current Limit Cycle-by-Cycle
Low Current Sense Threshold: 200mV
24V Over Output Voltage Protection
Compact SOT23-6 Package
Pin Configurations
Top View
WW: Week Code
UM1661
SOT23-6
Ordering Information
Part Number
UM1661
Packaging Type
SOT23-6
Marking Code
LE9
Shipping Qty
3000pcs/7Inch
Tape & Reel
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UM1661
Pin Description
Pin Number
1
2
3
4
5
6
Symbol
LX
GND
FB
CE
OVP
VIN
Switching Pin
Ground Pin
Pin for Feedback Voltage
Chip Enable Pin (Active with “H”)
Over Voltage Protection
Power Supply Pin
Function
Absolute Maximum Ratings
Symbol
V
IN
V
CE
I
LX
V
LX
P
D
T
A
T
J
T
STG
T
L
Parameter
Supply Voltage on VIN
Voltages on Pin CE
LX Pin Output Current
LX Pin Voltage
Continuous Power Dissipation
Operating Ambient Temperature
Operating Junction Temperature
Storage Temperature Range
Maximum Lead Temperature for Soldering 10
seconds
Value
-0.3 to +8.0
-0.3 to V
IN
+0.3
1.6
24
250
-40 to +85
+125
-40 to +150
+260
Unit
V
V
A
V
mW
°
C
°
C
°
C
°
C
Electrical Characteristics
(V
IN
= 3.0V, V
CE
= 3.0V, T
A
= 25° unless otherwise noted)
C,
Symbol
Parameter
Test Conditions
V
IN
Input Voltage Range
V
FB
Feedback Voltage
I
FB
FB Pin Bias Current
V
FB
= 0.3V
I
Q
Quiescent Current
V
CE
= 0V
F
OSC
_
Maximum Switching
V
FB
=0V
Frequency
MAX
I
Limit
Switching Current Limit
V
CESAT
Switching V
CESAT
I
LX
=300mA
I
LX
Switching pin Leak Current
V
LX
=5V
V
CEH
CE Voltage High
CE=0V to 3V
V
CEL
CE Voltage Low
CE=3V to 0V
I
CE
CE pin Bias Current
V
OVP
Over Voltage Protection
Min
2.0
0.190
10
Typ
0.200
45
93
0.4
2
1.6
260
0.11
Max
6.0
0.210
100
120
1.0
Unit
V
V
nA
μA
MHz
A
mV
μA
V
V
μA
V
1.5
0.4
18
24
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UM1661
Function Block Diagram
OVP
VIN
LX
Start-up
Logic
OSC
Driver
FB
-
+
200mV
Error
Amp
-
PFM
Control
Logic
CE
Chip
Enable
Current
Limit
GND
Typical Application Circuit
L1
VIN
10μH
D1
SS14
LED1
LED17
LED1
+
+
Cin
4.7μF
Cout
4.7μF
LED1
LED19
VIN
LX
OVP
LED1
LED20
ON
UM1661
CE
GND
FB
OFF
R1
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+
LED18
R5
UM1661
Typical Operating Characteristics
(V
IN
= 3.0V, V
CE
= 3.0V, T
A
= 25° unless otherwise noted)
C,
Efficiency vs. Output Current
VIN=2.5V
100
90
80
70
100
90
80
70
Efficiency vs. Output Current
VIN=3.0V
Efficiency(%)
60
50
40
30
20
10
0
0
20
40
60
80
100
120
Efficiency(%)
60
50
40
30
20
10
0
0
20
40
60
80
100
120
Output Current(mA)
Output Current(mA)
100
90
80
70
Efficiency vs. Output Current
80
CE Pin Bias Current vs. CE Voltage
70
VIN=VCE
VIN=6.0V
CE Pin Bias Current(uA)
60
50
40
30
20
10
0
0
1
2
3
4
5
6
Efficiency(%)
60
50
40
30
20
10
0
0
20
40
60
80
100
120
Output Current(mA)
CE Pin Voltage(V)
50
45
40
CE Pin Current vs. Temperature
VIN=VCE
VCE=6.0V
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Quiescent Current vs. Supply Voltage
VCE=0V
35
30
25
20
15
10
5
0
30
40
50
60
70
o
VCE=3.0V
VCE=2.5V
80
90
100
Quiescent Current(uA)
CE Pin Current(uA)
0
1
2
3
4
5
6
Temperature( C)
Supply Voltage(V)
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UM1661
Typical Operating Characteristics (Continued)
(V
IN
= 3.0V, V
CE
= 3.0V, T
A
= 25° unless otherwise noted)
C,
Quiescent Current vs. Supply Voltage
VCE=VIN,VFB=0.3V
100
90
80
60
50
40
30
20
10
0
0.22
0.20
FB Pin Voltage vs. Supply Voltage
Quiescent Current(uA)
FB Pin Voltage(V)
0
1
2
3
4
5
6
70
0.18
0.16
0.14
0.12
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Supply Voltage(V)
Supply Voltage(V)
0.22
FB Pin Voltage vs. Temperature
VIN=VCE=3.0V
4.0
3.5
Switch Frequency vs. Supply Voltage
4LED*100mA
Switch Frequency(MHZ)
0.20
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
FB Pin Voltage(V)
0.18
0.16
0.14
0.12
20
30
40
50
60
70
o
80
90
100
Temperature( C)
Supply Voltage(V)
2.00
1.75
Switch Frequency vs. Temperature
4LED*100mA
Maximum Output Current vs. Output Voltage
600
Maximum Output Current (mA)
Switch Frequency(MHZ)
500
VIN=6V
400
300
200
100
0
1.50
1.25
1.00
0.75
0.50
0.25
0.00
20
30
40
50
60
70
o
VIN=3V
VIN=2.5V
0
5
10
15
20
25
30
80
90
100
Temperature( C)
Output Voltage (V)
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