Datasheet

UNISONIC TECHNOLOGIES CO., LTD
UD38252
CMOS IC
38V SYNCHRONOUS BUCK
CONVERTER WITH CC/CV

DESCRIPTION
UTC UD38252 is a wide input voltage, high efficiency Active CC
step-down DC/DC converter that operates in either CV (Constant
Output Voltage) mode or CC (Constant Output Current) mode.
UTC UD38252 provides up to 2.5A output current at 160kHz
switching frequency. Current mode control provides fast transient
response and cycle-by-cycle current limit.
An internal soft-start prevents inrush current at turn-on, provides
a very compact solution with minimal external components.

HSOP-8
FEATURES
* Wide 8V to 38V Operating Input Range
* Integrated 140mΩ Power MOSFET Switches
* Output Adjustable from VFB(1.00V±2%) to 5.5V
* Up to 92% Efficiency
* Internal Soft-Start.
* Stable with Low ESR Ceramic Output Capacitors
* Fixed 160KHz Frequency
* Cycle-by-Cycle Over Current Protection
* Input Under/Over Voltage Lockout

ORDERING INFORMATION
Ordering Number
UD38252G-SH2-R
Package
HSOP-8
Packing
Tape Reel
UD38252G-SH2-R

(1)Packing Type
(1) R: Tape Reel
(2)Package Type
(2) SH2: HSOP-8
(3)Green Package
(3) G: Halogen Free and Lead Free
MARKING
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Copyright © 2015 Unisonic Technologies Co., Ltd
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QW-R115-008.A
UD38252

CMOS IC
PIN CONFIGURATION
BS 1
8 SEN2
IN 2
7 SEN1
GND
SW 3
6 COMP
5
GND 4

PIN DESCRIPTION
PIN NO.
PIN NAME
1
BS
2
IN
3
SW
4
GND
PAD
5
FB
6
COMP
7
8
SEN1
SEN2

FB
DESCRIPTION
Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with 24ohm +
0.1uF ceramic cap.
Power Input pin. Bypass IN to GND with a suitably large capacitor to eliminate noise on
the input to the IC.
Power Switching Output. SW is the switching node that supplies power to the output.
Connect the output LC filter from SW to the output load.
Ground.
Ground (Connect to GND).
Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a
resistive voltage divider from the output voltage.
Compensation Node. COMP is used to compensate the regulation control loop.
Connect a series RC network from COMP to GND to compensate the regulation control
loop.
The Current Sense Input (-) pin.
The Current Sense Input (+) pin = VOUT.
BLOCK DIAGRAM
IN
Internal
Power
CURRENT
SENSE
AMPLIFIER
Input UVLO
7.0V
VDD
BS
SEN+
M1
SEN1.1V
FB
PWM Control
&
Protect Logic
SW
1V
M2
COMP
Softstart
Thermal
Protection
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GND
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UD38252

CMOS IC
ABSOLUTE MAXIMUM RATING (TA=25°C, unless otherwise specified)
PARAMETER
SYMBOL
RATINGS
UNIT
Supply Voltage
VIN
-0.3 ~ +42
V
Switch Node Voltage
VSW
-0.3 ~ VIN+0.3
V
Boost Voltage
VBS
VSW-0.3 ~ VSW+ 6
V
All Other Pins Voltage
-0.3 ~ +6
V
Lead Temperature
TL
260
°C
Junction Temperature
TJ
150
°C
Storage Temperature
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
Output Voltage
Ambient Temperature

SYMBOL
VIN
VOUT
TA
RATINGS
8 ~ 38
VFB ~ 6
-40 ~ +85
UNIT
V
V
°C
THERMAL CHARACTERISTICS
PARAMETER
SYMBOL
RATINGS
Junction To Ambient
θJA
40
Junction to Case
θJC
15
Note: θJA is measured with the PCB copper area of approximately 1 in2(Multi-layer). That need connect to
pad.

UNIT
°C/W
°C/W
exposed
ELECTRICAL CHARACTERISTICS (VIN=12V, TA=25°C, unless otherwise specified)
PARAMETER
Input Voltage Range
Quiescent Current
Feedback Voltage
Feedback Overvoltage Threshold
High-Side Switch On Resistance (Note)
Low-Side Switch On Resistance (Note)
High-Side Switch Leakage Current
Upper Switch Current Limit
Lower Switch Current Limit
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
Minimum On Time (Note1)
Sense Voltage
VIN OVP Turn-Off Voltage
VIN OVP Hysteresis
Input Under Voltage Lockout Threshold
Input Under Voltage Lockout Threshold
Hysteresis
Soft-Start Period
Thermal Shutdown
Thermal Shutdown Hysterisis
Note: Guaranteed by design.
SYMBOL
TEST CONDITIONS
VIN
ICCQ
VFB=1.05V
VFB
8V≤VIN≤38V
OVP(FB)
RDS(ON)1
RDS(ON)2
VFB=1.05V, VSW=0V
Minimum Duty Cycle
From Drain to Source
FOSC1
FOSC2
VFB=<0.5V
DMAX
TON(min)
△VSEN (VSEN2)-(VSEN1)
Input voltage rising
Input voltage falling
UVLO
VIN Rising
0.98
TYP
1
1.00
1.1X
150
140
MAX
38
1.5
1.02
10
2.9
114
6.5
3.5
0.9
160
60
90
220
120
40
5
7.0
126
7.5
UNIT
V
mA
V
VFB
mΩ
mΩ
μA
A
A
KHz
KHz
%
ns
mV
V
V
V
UVLO-Hys
800
mV
TSD
TSH
3
150
30
ms
°C
°C
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
MIN
8
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UD38252

CMOS IC
FUNCTION DESCRIPTIONS
The UTC UD38252 is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages
from 8V to 38V down to an output voltage as low as VFB, and supplies up to 2.5A of load current.
The UTC UD38252 uses current-mode control to regulate the output voltage. The output voltage is measured at
FB through a resistive voltage divider and amplified through the internal Tran conductance error amplifier.
The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output
voltage. Since the high side MOSFET requires a gate voltage greater than the input voltage, a boost capacitor
connected between SW and BS is needed to drive the high side gate. The boost capacitor is charged from the
internal 5V rail when SW is low.
When the UTC UD38252 FB pin exceeds 10% of the nominal regulation voltage of VFB, the over voltage
comparator is tripped and the COMP pin is discharged to GND, forcing the high-side switch off.

APPLICATION INFORMATION
Setting the Output Voltage
The output voltage is set using a resistive voltage divider from the output voltage to FB pin. The voltage divider
divides the output voltage down to the feedback voltage by the ratio.
Thus the output voltage is:
VOUT  VFB 
R1  R2
R2
For example, VFB =1.00V for a 5.0V output voltage, R2 is 10kΩ, and R1 is 40kΩ.
Inductor Selection
The inductor is required to supply constant current to the output load while being driven by the switched input
voltage. A larger value inductor will result in less ripple current that will result in lower output ripple voltage. However,
the larger value inductor will have a larger physical size, higher series resistance, and/or lower saturation current. A
good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be
approximately 30% of the maximum switch current limit.
VIN
<28V
<35V
Inductor
33uH
22uH
The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI
requirements.
CC Measurement (L=33uH)
RSEN
100mΩ
IOUT
900mA
50mΩ
2000mA
UNISONIC TECHNOLOGIES CO., LTD
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40mΩ
2500mA
37mΩ
2700mA
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UD38252
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CMOS IC
TYPICAL APPLICATION CIRCUIT
L1 33μH
Input 8~38V
C7
100μF
50V
C1
2.2μF
40V
D1
SK34
C5
100μF
IN
SW
BS
UTC
COMP UD38252
C3
3.3nF
PAD
VOUT
5V 2.4A
37mΩ
R5
24Ω
C6
0.1μF
RSEN
R1 C2
40kΩ 10μF
10V
C8
470μF
10V
SEN1
SEN2
GND
R2
10kΩ
FB
R3
15kΩ
VOUT=VFB × (1+R1/R2), VFB = 1.00V, R2 suggest 1K~30KΩ
ISEN = 2.7A (ISEN≒VSEN(0.1V) / RSEN(37mΩ))
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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UD38252

CMOS IC
TYPICAL CHARACTERISTICS
Quiescent Current vs. Input Voltage
Quiescent Current, ICCQ (mA)
Quiescent Current, ICCQ (mA)
Efficiency, EFF (%)
Efficiency Test (VOUT=5V)
100
90
80
70
60
50
40
30
20
10
0
12VIN
24VIN
0
2.0
1.2
1.0
0.8
0.6
0.4
0.2
0
0
10
20
30
Input Voltage, VIN (A)
40
Power On
VIN=12V, VOUT=5V, IOUT=0A
Frequency vs. Input Voltage
175
173
171
169
167
165
163
161
159
157
155
0.5
1.0
1.5
Output Current, IOUT (A)
2.0
1.8
1.6
1.4
VIN
SW
VOUT
IOUT
0
10
20
30
Input Voltage, VIN (A)
40
Power On
VIN=12V, VOUT=5V, ILOAD=2A
Power On
VIN=24V, VOUT=5V, ILOAD=2A
VIN
VIN
SW
SW
VOUT
IOUT
VOUT
IOUT
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QW-R115-008.A
UD38252

CMOS IC
TYPICAL CHARACTERISTICS (Cont.)
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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