Datasheet

UNISONIC TECHNOLOGIES CO., LTD
UU28121
CMOS IC
1.2MHz, HIGH VOLTAGE,
BOOST CONVERTER

DESCRIPTION
The UTC UU28121 is a current mode step up converter
intended for small, low power applications.
The converter input voltage ranging from 2.5V to 5.5V. The
Output voltage can be set up to 28V. The frequency is 1.2MHz
allows the use of small external inductors and capacitors and
provides fast transient response. Internal soft start results in small
inrush current and extends battery life. Internal power MOSFET
with very low RDS (ON) provides high efficiency. The UTC
UU28121 automatically transits from PWM to PFM during light load
condition further increasing efficiency. The converter also provides
protection functions such as under-voltage lockout, current limit
and thermal shutdown.

FEATURES
* 2.5V~5.5V operating input voltage range
* 1.2MHz Fixed Switching Frequency
* Adjustable output voltage range up to 28V
* Internal 1.2A switching current limit
* Internal Soft-start Function
* Current limit and Thermal shutdown protection
* Under voltage Lockout

ORDERING INFORMATION
Ordering Number
UU28121G-AF5-R

Package
SOT-25
Packing
Tape Reel
MARKING
www.unisonic.com.tw
Copyright © 2016 Unisonic Technologies Co., Ltd
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UU28121

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PIN CONFIGURATION
VCC
EN
5
4
1
2
3
SW
GND
FB
PIN DESCRIPTION
PIN NO.
1
2
3
4
5

CMOS IC
PIN NAME
SW
GND
FB
EN
VCC
DESCRIPTION
Switching Pin.
Ground Pin.
Feedback Pin.
Chip Enable & Dimming pin. Active high. Internal pull low.
VCC Input Pin.
BLOCK DIAGRAM
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
CMOS IC
ABSOLUTE MAXIMUM RATING (TA=25°C, unless otherwise specified)
PARAMETER
SYMBOL
RATINGS
UNIT
VCC Pin Voltage
VIN
-0.3 ~ 6.5
V
SW Pin Voltage
VSW
-0.3 ~ 30
V
EN, FB Pins Voltage
-0.3 ~ VIN+0.3
V
Operating Junction Temperature
TOPR
-40 ~ +125
°C
Storage Temperature Range
TSTG
-65 ~ +150
°C
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.

RECOMMENDED OPERATING CONDITIONS
PARAMETER
Input Supply Voltage
Ambient Temperature

SYMBOL
VIN
TA
RATINGS
2.5 ~ 5.5
-40 ~ +125
UNIT
V
°C
THERMAL CHARACTERISTICS
PARAMETER
SYMBOL
RATINGS
UNIT
Junction To Ambient
θJA
270
°C/W
Junction to Case
θJC
110
°C/W
Note: θJA is measured with the PCB copper are (need connect to GND of the UTC UU28121) of approximately 1 in2
(Multi-layer).

ELECTRICAL CHARACTERISTICS
(VIN=5V, VEN=5V, IOUT=20mA, TA=25°C, unless otherwise specified)
PARAMETER
SYMBOL
TEST CONDITIONS
Input Voltage Range
VIN
Input UVLO
UVLO Rising
UVLO Hysteresis
Step-Up Voltage Adjust Range
VOUT
Quiescent Current
ICCQ
IOUT=0mA, VFB=1.5V
Shutdown Current
ISD
VEN=0V
FB Pin Voltage
VFB
FB Pin Current
IFB
VFB=1.3V
Line Regulation
VIN=2.5~5.5V, IOUT=20mA
Load Regulation
VIN=5V, IOUT=1mA~400mA
Switching Frequency
FOSC
Maximum Duty
DMAX
N-Channel MOSFET Current Limit
ILIM
Duty=50%
VCC=3V, ISW=1A
MOSFET On-resistance
RDS(on)
VCC=5V, ISW=1A
SW Leakage Current
ISWL
VSW=28V, VFB=1.5V
EN High-level Input Voltage
VIH
EN Low-level Input Voltage
VIL
EN Hysteresis
Hys
Thermal Shutdown
TDS
Thermal Shutdown Hysteresis
TSH
UNISONIC TECHNOLOGIES CO., LTD
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MIN
2.5
TYP
2.25
0.2
3
MAX
5.5
2.45
28
150
250
1
4
1.213 1.238 1.263
±100
0.2
0.2
900
1200 1500
87
90
1.6
600
500
1
1.4
0.4
200
150
35
UNIT
V
V
V
V
μA
μA
V
nA
%
%
KHz
%
A
mΩ
μA
V
V
mV
°C
°C
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CMOS IC
FUNCTION DESCRIPTION
Setting the Output Voltage
Application circuit item shows the basic application circuit with UTC UU28121 adjustable output version. The
external resistor sets the output voltage according to the following equation:
VOUT=1.238V×(1+
R2
)
R1
Table 1. Resistor Selection for Common Output Voltages
VOUT(V)
12
16
24
27
R1(kΩ)
54
39
39
36
R2(kΩ)
470
470
720
750
For most applications, R2 is a suggested a value by 300K~850KΩ. Place the resistor-divider as close to the IC as
possible to reduce the noise sensitivity.
Under Voltage Lockout (UVLO)
To avoid mis-operation of the device at low input voltages an under voltage lockout is included that disables the
device, if the input voltage falls below (2.25V~200mV).
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input
capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency
switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used.
Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small
temperature coefficients. A 4.7µF ceramic capacitor for most applications is sufficient. For a lower output power
requirement application, this value can be decreased.
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The
output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R
dielectrics are recommended due to their low ESR and high ripple current. A 2.2uF ceramic capacitors works for
most of the applications. Higher capacitor values can be used to improve the load transient response.
UNISONIC TECHNOLOGIES CO., LTD
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UU28121

CMOS IC
TYPICAL APPLICATION CIRCUIT
1. VOUT < 18V
R3
100K
C1
2.2uF
D1
SB240
L1
4.7uH
VIN=5V
R1
470K
U1
5
4
1
VCC
SW
EN
FB 3
GND
2
C3
0.1uF
VOUT=12V
R2
54K
C2
2.2uF
VOUT=1.238V×(1+ R1 )
R2
R1 Suggest 300K~850K
2. VOUT ≥ 18V
R3
100K
C1
2.2uF
D1
SB240
L1
2.2~4.7uH
VIN=5V
U1
5
4
1
VCC
SW
EN
FB 3
C3
0.1uF
GND
2
VOUT=24V
R1
720K
R2
39K
C3
22pF
C2
2.2uF
VOUT=1.238V×(1+ R1 )
R2
R1 Suggest 300K~850K
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CMOS IC
TYPICAL CHARACTERISTICS
UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or
other parameters) listed in products specifications of any and all UTC products described or contained
herein. UTC products are not designed for use in life support appliances, devices or systems where
malfunction of these products can be reasonably expected to result in personal injury. Reproduction in
whole or in part is prohibited without the prior written consent of the copyright owner. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
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www.unisonic.com.tw
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