UM1660
Low Power DC/DC Boost Converter
UM1660S SOT23-5
UM1660DA DFN6 2.0×
2.0
General Description
The UM1660 is a PFM controlled step-up DC-DC converter with a switching frequency up to
1MHz. The device is ideal to generate output voltage for small to medium LCD bias supplies and
white LED backlight supplies from a single cell Li-Ion battery. The part can also be used to
generate standard 3.3V/5V to 12V power conversions.
With a high switching frequency of 1MHz, a low profile and small board area solution can be
achieved using a chip coil and an ultra small ceramic output capacitor. The UM1660 has an
internal 400mA switch current limit, offering lower output voltage ripple. The low quiescent
current (typically 36µ together with an optimized control scheme, allows device operation at
A)
very high efficiencies over the entire load current range.
Applications
Features
2.0V to 6.0V Input Voltage Range
Adjustable Output Voltage up to 28V
400mA Internal Switch Current
Up to 1MHz Switching Frequency
36µ Typical No Load Quiescent Current
A
1µ Maximum Shutdown Current
A
Internal Soft-Start
Available in Tiny SOT23-5 and DFN6
2.0× Packages
2.0
LCD Bias Supply
White LED Supply for LCD Backlights
Digital Still Camera
PDAs, Organizers and Handheld PCs
Cellular Phones
Standard 3.3V/5V to 12V Conversion
Pin Configurations
(Top View)
Top View
5
4
SW
1
5
VIN
PHO
1
2
GND
2
M
3
FB
3
4
EN
M: Month Code
UM1660S
SOT23-5
(Top View)
VIN
GND
EN
1
2
3
6
5
4
SW
NC
FB
Marking Pin1
AAG
M: Month Code
UM1660DA
DFN6 2.0×
2.0
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M
UM1660
Ordering Information
Part Number
UM1660S
UM1660DA
Packaging Type
SOT23-5
DFN6 2.0×
2.0
Marking Code
PHO
AAG
Shipping Qty
3000pcs/7Inch
Tape & Reel
3000pcs/7Inch
Tape & Reel
Pin Description
Pin Number
UM1660S
1
2
3
UM1660DA
6
2
4
Symbol
Function
Connect the inductor and the Schottky diode to this pin.
This is the switch pin and is connected to the drain of the
internal power MOSFET.
Ground
This is the feedback pin of the device. Connect this pin to
the external voltage divider to program the desired output
voltage.
This is the enable pin of the device. Pulling this pin to
ground forces the device into shutdown mode reducing the
supply current to less than 1µ This pin should not be left
A.
floating and needs to be terminated.
Supply voltage pin
Not connected
SW
GND
FB
4
5
-
3
1
5
EN
VIN
NC
Absolute Maximum Ratings
Over operating free-air temperature (unless otherwise noted) (Note 1)
Symbol
Parameter
Value
V
IN
V
FB,
V
EN
V
SW
P
D
T
J
T
STG
Supply Voltage on VIN (Note 2)
Voltages on FB, EN (Note 2)
Switch Voltage on SW (Note 2)
Continuous Power Dissipation SOT23-5
at T
A
= 25°
C
DFN6 2.0×
2.0
Operating Junction Temperature
-0.3 to +7.0
-0.3 to V
IN
+0.3
30
0.35
0.7
-40 to +150
Unit
V
V
V
W
°
C
Storage Temperature Range
-65 to +150
°
C
Maximum Lead Temperature for Soldering 10
T
L
+260
°
C
seconds
Note 1: Stresses beyond those listed under absolute maximum ratings may cause permanent
damage to the device. These are stress ratings only, and functional operation of the
device at these or any other conditions beyond those indicated under recommended
operating conditions is not implied. Exposure to absolute-maximum-rated conditions for
extended periods may affect device reliability.
Note 2: All voltage values are with respect to network ground terminal.
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UM1660
Recommended Operating Conditions
Symbol
Parameter
V
IN
Input Voltage Range
V
OUT
Output Voltage Range
L
Inductor (Note 3)
f
Switching Frequency (Note 3)
C
IN
Input Capacitor (Note 3)
C
OUT
Output Capacitor (Note 3)
T
A
Operating Ambient Temperature
T
J
Operating Junction Temperature
Note 3: Refer to application section for further information.
Min
2.0
2.2
Typ
Max
6.0
28
1
4.7
1
-40
-40
85
125
Unit
V
V
μH
MHz
μF
μF
°
C
°
C
10
Function Block Diagram
SW
VIN
Under Voltage
Lockout
Bias Supply
400ns Min
Off Time
Error Comparator
FB
-
+
V
REF
=1.233V
R
RS Latch
Logic
Gate
Driver
S
Power MOSFET
N-Channel
Current Limit
EN
6μs Max
On Time
Soft Start
+
R
SENSE
-
GND
Figure 1. UM1660 function block diagram
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UM1660
Electrical Characteristics
(V
IN
= 2.4 V, EN = VIN, C
IN
=4.7μF, C
OUT
=1μF, L=10μH, T
A
= -40° to 85° typical values are
C
C,
at T
A
= 25° unless otherwise noted)
C,
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
SUPPLY CURRENT
V
IN
Input Voltage Range
2.0
6.0
V
I
OUT
=0mA,
Operating Quiescent
I
Q
not switching
36
70
μA
Current
V
FB
= 1.3V
I
SD
Shutdown Current
EN=GND
0.1
1
μA
Under-voltage Lockout
V
UVLO
1.5
1.8
V
Threshold
ENABLE
EN High Level Input
V
IH
1.3
V
Voltage
EN Low Level Input
V
IL
0.4
V
Voltage
EN Input Leakage
I
L
EN=GND or VIN
0.1
1
μA
Current
POWER SWITCH AND CURRENT LIMIT
Maximum Switch
V
SW
28
V
Voltage
t
ON
Maximum On Time
4
6
7.5
μs
t
OFF
Minimum Off Time
250
400
550
ns
MOSFET On
R
DS(ON)
V
IN
= 2.4V, I
SW
=50mA
750
1200
mΩ
Resistance
MOSFET Leakage
V
SW
=28V
1
10
μA
Current
MOSFET Current
I
LIM
350
400
450
mA
Limit
OUTPUT
Adjustable Output
V
OUT
V
IN
28
V
Voltage Range
Internal Voltage
V
REF
1.233
V
Reference
Feedback Input Bias
I
FB
V
FB
= 1.3V
1
μA
Current
Feedback Trip Point
V
FB
2.0V ≤ V
IN
≤ 6.0V
1.196 1.233 1.270
V
Voltage
2.0V ≤ V
IN
≤ 6.0V ;
Line Regulation
V
OUT
=18V;
0.05
%/V
(Note 4)
I
LOAD
=10mA
V
IN
= 2.4V;
Load Regulation
V
OUT
=18V;
0.15
%/mA
(Note 4)
0mA﹤I
OUT
﹤25mA;
Note 4: The line and load regulation depend on the external component selection.
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UM1660
Operation
The UM1660 features a constant off-time control scheme. Operation can be best understood by
referring to the function block diagram. The converter monitors the output voltage, and as soon as
the feedback voltage falls below the reference voltage of typically 1.233V, the internal switch
turns on and the current ramps up. The switch turns off as soon as the inductor current reaches the
internally set peak current of typically 400mA. The second criteria that turns off the switch is the
maximum on-time of 6µ (typical). This is just to limit the maximum on-time of the converter to
s
cover for extreme conditions. As the switch is turned off the external Schottky diode is forward
biased delivering the current to the output. The switch remains off for a minimum of 400ns
(typical), or until the feedback voltage drops below the reference voltage again. Using this PFM
peak current control scheme the converter operates in discontinuous conduction mode (DCM)
where the switching frequency depends on the output current, which results in very high
efficiency over the entire load current range.
Peak Current Control
The internal switch turns on until the inductor current reaches the typical dc current limit (I
LIM
) of
400mA. There is approximately a 100ns delay from the time the current limit is reached and when
the internal logic actually turns off the switch. During this 100ns delay, the peak inductor current
will increase. This increase demands a larger saturation current rating for the inductor. This
saturation current can be approximated by the following equation:
I
peak
(
typ
)
½
I
LIM
Vin
100
ns
L
The higher the input voltage and the lower the inductor value, the greater the peak current.
Soft-Start
All inductive step-up converters exhibit high inrush current during start-up if no special
precaution is made. This can cause voltage drops at the input rail during start up and may result in
an unwanted or early system shut down. The UM1660 limits this inrush current by increasing the
current limit in two steps from I
LIM
/4 for 256 cycles to I
LIM
/2 for the next 256 cycles, and then full
current limit.
Enable
Pulling the enable pin (EN) to ground shuts down the device reducing the shutdown current to
1µ (typical). Since there is a conductive path from the input to the output through the inductor
A
and Schottky diode, the output voltage is equal to the input voltage during shutdown. The enable
pin needs to be terminated and should not be left floating. Using a small external transistor
disconnects the input from the output during shutdown as shown in the figure below.
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