UNISONIC TECHNOLOGIES CO., LTD
UD38501
38V 5A SYNCHRONOUS BUCK
CONVERTER
DESCRIPTION
CMOS IC
The UTC
UD38501
is a monolithic synchronous buck regulator.
The device integrates internal high side and external low side
power MOSFETs, and provides 5A of continuous load current over
a wide input voltage of 8V to 38V. 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 80mΩ high side Power MOSFET Switches
* Output Adjustable from V
FB
(1V) to 20V
* Up to 95% 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
UD38501G-SH2-R
Package
HSOP-8
Packing
Tape Reel
UD38501G-SH2-R
(1)Packing Type
(2)Package Type
(3)Green Package
(1) R: Tape Reel
(2) SH2: HSOP-8
(3) G: Halogen Free and Lead Free
MARKING
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Copyright © 2015 Unisonic Technologies Co., Ltd
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UD38501
PIN CONFIGURATION
BS 1
IN 2
GND
SW 3
LG 4
6
5
COMP
FB
8
7
VDD
EN
CMOS IC
PIN DESCRIPTION
PIN NAME
BS
IN
SW
LG
PAD
FB
COMP
EN
VDD
DESCRIPTION
Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with 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.
Gate drive for external low side N-MOSFET..
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.
Enable control. Pull high to turn on. Do not float.
Internal regulator pin
PIN NO.
1
2
3
4
5
6
7
8
BLOCK DIAGRAM
IN
CURRENT
SENSE
AMPLIFIER
VDD
Internal
Regulator
Input UVLO
7.0V
VDD
BS
EN
2.5V
1.1V
M1
PWM Control
&
Protect Logic
SW
FB
COMP
1V
Softstart
LG
GND
Thermal
Protection
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QW-R115-009.A
UD38501
ABSOLUTE MAXIMUM RATING
(T
A
=25°C, unless otherwise specified)
PARAMETER
SYMBOL
V
IN
V
SW
V
BS
CMOS IC
RATINGS
UNIT
Supply Voltage
-0.3 ~ +42
V
Switch Node Voltage
-0.3 ~ V
IN
+0.3
V
Boost Voltage
V
SW
-0.3 ~ V
SW
+ 6
V
All Other Pins Voltage
-0.3 ~ +6
V
Lead Temperature
T
L
260
°C
Junction Temperature
T
J
150
°C
Storage Temperature
T
STG
-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
SYMBOL
V
IN
V
OUT
T
A
RATINGS
8 ~ 38
V
FB
~ 20
-40 ~ +85
UNIT
V
V
°C
PARAMETER
Input Supply Voltage
Output Voltage
Ambient Temperature
THERMAL CHARACTERISTICS
PARAMETER
SYMBOL
RATINGS
UNIT
Junction To Ambient
θ
JA
15
°C/W
Junction to Case
θ
JC
40
°C/W
2
Note:
θ
JA
is measured with the PCB copper area of approximately 1 in (Multi-layer). That need connect to exposed
pad.
ELECTRICAL CHARACTERISTICS
(V
IN
=12V, T
A
=25°C, unless otherwise specified)
SYMBOL
V
IN
I
SD
I
CCQ
V
FB
O
VP_FB
R
DS(ON)
TEST CONDITIONS
V
EN
= 0V
V
EN
=5.0V, V
FB
=1.05V
8V≤V
IN
≤38V
MIN
8
TYP
0.7
0.7
1.00
1.1X
80
6.0
40
40
5
160
60
90
220
2.5
210
7.0
800
V
IN
Rising
40
5
3
150
30
MAX
38
1.3
1.5
1.02
UNIT
V
mA
mA
V
V
FB
mΩ
μA
A
ns
ns
V
KHz
KHz
%
ns
V
mV
V
mV
V
V
ms
°C
°C
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PARAMETER
Input Voltage Range
Shutdown Supply Current
Quiescent Current
Feedback Voltage
Feedback Overvoltage Threshold
High-Side Switch On Resistance (Note)
High-Side Switch Leakage Current
Upper Switch Current Limit
LG Rise Time
LG Fall Time
LG Driver Bias Supply Voltage
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
Minimum On Time (Note)
EN Lockout Threshold Voltage
EN Lockout Hysterisis
Input Under Voltage Lockout Threshold
Input Under Voltage Lockout Threshold
Hysteresis
Input Over Voltage Lockout Threshold
Input Over Voltage Lockout Threshold
Hysteresis
Soft-Start Period
Thermal Shutdown
Thermal Shutdown Hysterisis
Note: Guaranteed by design.
www.unisonic.com.tw
0.98
T
LXR
T
LXF
F
OSC1
F
OSC2
D
MAX
T
ON(min)
E
NH(LOCK)
UVLO
UVLO-Hys
OVLO
OVLO-Hys
T
SD
T
SH
V
EN
=0V, V
SW
=0V
Minimum Duty Cycle
C
LX
=1000pF
C
LX
=1000pF
10
5.1
V
FB
=<0.5V
V
IN
Rising
6.5
7.5
UNISONIC TECHNOLOGIES CO., LTD
UD38501
FUNCTION DESCRIPTIONS
CMOS IC
The UTC
UD38501
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 V
FB
, and supplies up to 5A of load current.
The UTC
UD38501
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
voltage at the COMP pin is compared to the switch current measured internally to control the output voltage.
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
UD38501
FB pin exceeds 10% of the nominal regulation voltage of V
FB
, the over voltage
comparator is tripped and the COMP pin is discharged to GND, forcing the high-side switch off.
APPLICATION INFORMATION
COMPONENT SELECTION
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:
V
OUT
½
V
FB
R1
R2
R2
For example, V
FB
=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.
V
IN
Inductor
<28V
47uH
<35V
33uH
The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI
requirements.
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QW-R115-009.A
UD38501
TYPICAL APPLICATION CIRCUIT
CMOS IC
Input
C17
220µF
50V
C7
10µF
20V
R4
100kΩ
EN
V
DD
C4
C3
0.1µF
3.3nF
R5
C6
0Ω C5
0.1µF
100nF
IN
BS
UTC
UD38501
L1
33µH
Output
5V 5A
PDA(GND)
SW
LG
Q1
NMOS
R1
40kΩ
R2
10kΩ
COMP
R3
15kΩ
FB
C2
470µF
10V
C8
22µF
10V
V
OUT
=V
FB
× (1+R1/R2), V
FB
= 1.00V, R2 suggest 10k~30kΩ
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R115-009.A
微控制器 MCU
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