LSP5502
2A Synchronous Step Down DC/DC Converter
1/12 Rev. 1.8
www.liteon-semi.com
PIN ASSIGNMENT
18
7
6
5
2
3
4
SS
EN
COMP
FB
BS
IN
SW
GND
(TOP View)
SOP-8L
PIN DESCRIPTION
Name No. Description
BS 1
Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver.
Connect a 0.01uF capacitor between BS and SW.
IN 2
Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor
in the Application Information section.
SW 3 Switch Output. Connect this pin to the switching end of the inductor.
GND 4 Ground.
FB 5
Feedback Input. The voltage at this pin is regulated to 0.925V. Connect to the
resistor divider between output and ground to set output voltage.
COMP 6
Compensation Pin. See Stability Compensation in the Application Information
section.
EN 7
Enable Input. When higher than 2.5V, this pin turns the IC on. When lower than
1.3V, this pin turns the IC off. Output voltage is discharged when the IC is off. This
pin should not be left open.
SS 8
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from
SS to GND to set the soft-start period. A 0.1µF capacitor sets the soft-start period
to 15ms. To disable the soft-start feature, leave SS unconnected.
TYPICAL APPLICATION
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
GENERAL DESCRIPTION
The LSP5502 is a monolithic synchronous buc
k
regulator. The device integrates 120m MOSFETS
that provide 2
A
continuous load current over a wide
operating input voltage of 4.5V to 27V. Current mode
control provides fast transient response and
cycle-by-cycle current limit.
An adjustable soft-start prevents inrush current at turn
on. In shutdown mode, the supply current drops
below 1µA.
This device, available in an 8-pin SOP package,
provides a very compact system solution with minimal
reliance on external components.
FEATURES
2A Output Current
Wide 4.5V to 27V Operating Input Range
Integrated 120m Power MOSFET Switches
Output Adjustable from 0.925V to 24V
Up to 96% Efficiency
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 400KHz Frequency
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
8-Pin SOP Package
LSP5502
2A Synchronous Step Down DC/DC Converter
2/12 Rev. 1.8
www.liteon-semi.com
ABSOLUTE MAXIMUM RATINGS
Parameter Value Unit
IN Supply Voltage -0.3 to 30 V
SW Voltage -1 to VIN + 0.3 V
BS Voltage VSW – 0.3 to VSW + 6 V
EN, FB, COMP Voltage -0.3 to 6 V
Continuous SW Current Internally limited A
Junction to Ambient Thermal Resistance (JA)
(Test on Approximately 3 in2 Copper Area 1OZ copper FR4 board)70 °C/W
Junction to Ambient Case Resistance (JC) 20 °C/W
Maximum Power Dissipation 0.76 W
Operating Temperature -20 to 85 °C
Storage Temperature -55 to 150 °C
Lead Temperature (Soldering, 10 sec) 300 °C
(
Note: Exceeding these limits may damage the device. Exposure to absolute maximum rating conditions for long
periods may affect device reliability.)
Recommended Operating Conditions
Symbol Parameter Min Max Unit
VIN Input Voltage 4.5 27 V
TJ Operating Junction Temperature Range -20 125 oC
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA= 25°C unless otherwise specified.)
Parameter Symbol Test Conditions Min. Typ. Max. Unit
Input Operating Voltage VIN V
OUT = 1.0V, ILOAD = 0A to 2A 4.5 27 V
Input Holdup Voltage VOUT = 1.0V, ILOAD = 0A to 2A 4.5 V
Feedback Voltage VFB 4.5V VIN 20V 0.900 0.925 0.950 V
Feedback Overvoltage Threshold 1.1 V
High-Side Switch-On Resistance 120 m
Low-Side Switch-On Resistance 120 m
High-Side Switch Leakage VEN = 0V, VSW = 0V 9 10 µA
Upper Switch Current Limit 3.5 4.0 A
Lower Switch Current Limit 0.9 A
COMP to Current Limit
Transconductance GCOMP 5.2 A/V
Error Amplifier Transconductance GEA ICOMP = ±10µA 800 µA/V
Error Amplifier DC Gain AVEA 480 V/V
Switching Frequency fSW 350 400 470 kHz
Short Circuit Switching Frequency VFB = 0 150 kHz
Maximum Duty Cycle DMAX V
FB = 0.8V 90 %
Minimum On Time 220 nS
EN Shutdown Threshold Voltage VEN Rising 1.1 1.3 1.5 V
EN Shutdown Threshold Voltage
Hysterisis 200 mV
EN Lockout Threshold Voltage 2.2 2.5 2.7 V
EN Lockout Hysterisis 210 mV
LSP5502
2A Synchronous Step Down DC/DC Converter
3/12 Rev. 1.8
www.liteon-semi.com
M1
0.12Ω
M2
0.12Ω
Supply Current in Shutdown VEN = 0 0.3 3.0 µA
IC Supply Current in Operation VEN = 3V, VFB = 1.0V 1.4 1.5 mA
Input UVLO Threshold Rising UVLO VEN Rising 3.80 4.05 4.40 V
Input UVLO Threshold Hysteresis 210 mV
Soft-start Current VSS = 0V 6 µA
Soft-start Period CSS = 0.1µF 15 mS
Thermal Shutdown Temperature Hysteresis = 10°C 160 °C
FUNCTIONAL BLOCK DIAGRAM
6
7
8
5
2
1
3
4
INTERNAL
REGULATORS
FB
SS
COMP
EN
7V
Zener
1.1V
0.3V
0.925V
2.5V
1.5V
OVP
SHUTDOWN
COMPARATOR
ERROR
AMPLIFIER
LOCKOUT
COMPARATOR
EN OK
6uA
OSCILLATOR
150/400KHz
RAMP
CLK
1.2V OVP
IN<4.10V
IN
CURRENT
COMPARATOR
CURRENT
SENSE
AMPLIFIER
5V
IN
BS
SW
GND
S Q
R Q
FUNCTIONAL DESCRIPTION
The LSP5502 is a synchronous rectified, cur-rent-mode, step-down regulator. It regulates in-put voltages from 4.5V
to 23V down to an out-put voltage as low as 0.925V, and supplies up to 2A of load current.
The LSP5502 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 trans-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 LSP5502 FB pin exceeds 20% of the nominal regulation voltage of 0.925V, the over volt-age comparator
is tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side switch off.
LSP5502
2A Synchronous Step Down DC/DC Converter
4/12 Rev. 1.8
www.liteon-semi.com
APPLICATION INFORMATION
Output Voltage Setting
Figure1. Output Voltage Setting
Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors
RFB1 and RFB2 based on the output voltage. Typically, use RFB2 10k and determine RFB1 from the following
equation:
(1)
Table 1-Recommended Resistance Values
VOUT RFB1 RFB2
1.0V 1.0kΩ 12kΩ
1.2V 3.0kΩ 10kΩ
1.8V 9.53kΩ 10kΩ
2.5V 16.9kΩ 10kΩ
3.3V 26.1kΩ 10kΩ
5V 44.2kΩ 10kΩ
12V 121kΩ 10kΩ
Inductor Selection
The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent
on the inductance value: higher inductance reduces the peak-to-peak ripple current. The trade off for high
inductance value is the increase in inductor core size and series resistance, and the reduction in current handling
capability. In general, select an inductance value L based on the ripple current requirement:
RIPPLEOUTMAXSWIN
OUTINOUT
KIfV
)VV(V
L−•
=
(2)
where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum
output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 30% to correspond to the peak-to-peak
ripple current being 30% of the maximum output current.
With this inductor value, the peak inductor current is IOUT • (1 + KRIPPLE / 2). Make sure that this peak inductor current
is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. Typical
inductor values for various output voltages are shown in Table 1.
VOUT 1.0V 1.2V 1.5V 1.8V 2.5V 3.3V 5V
L 4.7uH 4.7uH 6.8µH6.8µH 10µH 10µH 15µH
Table 1. Typical Inductor Values
Input Capacitor
LSP5502
2A Synchronous Step Down DC/DC Converter
5/12 Rev. 1.8
www.liteon-semi.com
The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the
converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during
switching, its ESR also affects efficiency.
The input capacitance needs to be higher than 10µF. The best choice is the ceramic type; however, low ESR
tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the
output current. The input capacitor should be placed close to the IN and G pins of the IC, with the shortest traces
possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1µF ceramic
capacitor is placed right next to the IC.
Output Capacitor
The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is:
ESRRIPPLEOUTMAXRIPPLE RKIV = OUT
LC
SW
fIN
V2
•8
+ (3)
where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW
is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output
capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value can be
used for ceramic capacitors. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR
multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR.
For ceramic output capacitors, typically choose a capacitance of about 22µF. For tantalum or electrolytic capacitors,
choose a capacitor with less than 50m ESR.
Optional Schottky Diode
During the transition between high-side switch and low-side switch, the body diode of the low side power MOSFET
conducts the inductor current. The forward voltage of this body diode is high. An optional Schottky diode may be
paralleled between the SW pin and GND pin to improve overall efficiency. Table 2 lists example Schottky diodes and
their Manufacturers.
Table 2-Diode Selection Guide
Part Number Voltage/Current Rating Vendor
B130 30V,1A Lite-on Semiconductor Corp.
MBRS130 30V,1A International Rectifier
VIN =12V VOUT =5V/2A
LSP5502
IN
EN FB
SW
GND
C1 C2
C5
47pF
L1
C6
10nF
44.2k
R2
10k
R3
6.8k
COMP
R4
100k
BS
R1
C4
2.2nF
2
7
3
5
1
86
SS
0.1µF
C3
4
15µH/2A
22uF/16V
C7
22µF/10V
CERAMIC
x2
0.1uF
(＊)
(＊)
LSP5502
2A Synchronous Step Down DC/DC Converter
6/12 Rev. 1.8
www.liteon-semi.com
Stability Compensation
CCOMP2 is needed only for high ESR output capacitor
Figure 2. Stability Compensation
The feedback loop of the IC is stabilized by the components at the COMP pin, as shown in Figure 2. The DC loop
gain of the system is determined by the following equation:
(4)
The dominant pole P1 is due to CCOMP:
COMPVEA
EA
1P CAπ2
G
f=
(5)
The second pole P2 is the output pole:
OUTOUT
OUT
2P CVπ2
I
f=
(6)
The first zero Z1 is due to RCOMP and CCOMP:
COMPCOMP
1Z CRπ2
1
f=
(7)
And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used):
2COMPCOMP
3P CRπ2
1
f=
(8)
The following steps should be used to compensate the IC:
STEP1. Set the crossover frequency at 1/10 of the switching frequency via RCOMP:
(9)
but limit RCOMP to 10k maximum.
STEP2. Set the zero fZ1 at 1/4 of the crossover frequency. If RCOMP is less than 10k, the equation for CCOMP is:
)F(
R
108.1
C
COMP
5
COMP
−
×
=
(10)
If RCOMP is limited to 10k, then the actual crossover frequency is 10/ (VOUTCOUT). Therefore:
)F(CV102.1C OUTOUT
5
COMP
−
×= (11)
STEP3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the crossover frequency,
an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is:
ESRCOUT
R
)(V012.0,
C
101.1
Min OUT
OUT
6
Ω
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛•
×
≥
−
(12)
LSP5502
2A Synchronous Step Down DC/DC Converter
7/12 Rev. 1.8
www.liteon-semi.com
And the proper value for CCOMP2 is:
COMP
ESRCOUTOUT
2COMP R
RC
C=
(13)
Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such as
100pF may improve stability against PCB layout parasitic effects.
Table 3 shows some calculated results based on the compensation method above.
VOUT COUT RCOMP CCOMP CCOMP2
1.0V 22µF Ceramic 1.5kΩ 10nF 100pF
1.2V 22µF Ceramic 1.7kΩ 10nF 100pF
1.8V 22µF Ceramic 2.2kΩ 6.8nF 100pF
2.5V 22µF Ceramic 3.6kΩ 4.7nF 100pF
3.3V 22µF Ceramic 4.7kΩ 3.3nF 47pF
5V 22µF Ceramic 6.8kΩ 2.2nF 47pF
1.0V 47µF SP Cap 3.0kΩ 6.8nF 470pF
1.2V 47µF SP Cap 3.6kΩ 4.7nF 330pF
1.8V 47µF SP Cap 5.6kΩ 3.3nF 220pF
2.5V 47µF SP Cap 6.8kΩ 2.2nF 200pF
3.3V 47µF SP Cap 10kΩ 2.0nF 150pF
5V 47µF SP Cap 10kΩ 2.2nF 150pF
1.0V 470µF/6.3V/30mΩ 10kΩ 2.2nF 1nF
1.2V 470µF/6.3V/30mΩ 10kΩ 3.3nF 1nF
1.8V 470µF/6.3V/30mΩ 10kΩ 4.7nF 1nF
2.5V 470µF/6.3V/30mΩ 10kΩ 6.8nF 1nF
3.3V 470µF/6.3V/30mΩ 10kΩ 8.2nF 1nF
5V 470µF/10V/30mΩ 10kΩ 10nF 1nF
Table3. Typical Compensation for Different Output Voltages and Output Capacitors
LSP5502
2A Synchronous Step Down DC/DC Converter
8/12 Rev. 1.8
www.liteon-semi.com
VIN =12V VOUT =5V/2A
LSP5502
IN
EN FB
SW
GND
C1 C2
C5
47pF
L1
C6
10nF
44.2k
R2
10k
R3
6.8k
COMP
R4
100k
BS
R1
C4
2.2nF
2
7
3
5
1
86
SS
0.1µF
C3
4
15µH/2A
22uF/16V
C7
22µF/10V
CERAMIC
x2
0.1uF
Figure 3 shows a sample LSP5502 application circuit generating 5V/2A output.
VIN =12V VOUT =1V/2A
LSP5502
IN
EN FB
SW
GND
C1 C2
0.1µF
C5
100pF
L1
C6
10nF
1k
R2
12k
R3
1.5k
COMP
R4
100k
BS
R1
C4
10nF
2
7
3
5
1
86
SS
0.1µF
C3
4
4.7µH/2A
22µF/16V
C7
22µF/6.3V
CERAMIC
x2
Figure 4 shows a sample LSP5502 application circuit generating 1.0V/2A output.
(＊) To improve quality, it is recommended to choose a capacitance of about 1uF for C3.
For system security, it is recommended to place a 0.1uF capacitor from EN Pin to ground.
(＊)
(＊)
(＊)
(＊)
LSP5502
2A Synchronous Step Down DC/DC Converter
9/12 Rev. 1.8
www.liteon-semi.com
TYPICAL CHARACTERISTICS
Start up soft start Vin=12V, Vout=5V Iout=2A Operating status Vin=12V, Vout=5V Iout=2A
ripple of Vout Vin=12V, Vout=5V Iout=3A SCP
LSP5502
2A Synchronous Step Down DC/DC Converter
10/12 Rev. 1.8
www.liteon-semi.com
Efficiency vs Input Voltage（Vout=5.0V)
50
60
70
80
90
100
0 500 1000 1500 2000
Io(mA)
η(%)
VIN=8V
VIN=12V
VIN=18V
VIN
=
23V
Efficiency vs Input Voltage（Vout=5.0V)
50
60
70
80
90
100
0 500 1000 1500 2000
Io(mA)
η(%)
VIN=5V
VIN=8V
VIN=12V
VIN=18V
VIN=23V
12Vin 5.0Vout Efficiency curve 12Vin 1.0Vout Efficiency curve
ORDERING INFORMATION
LSP5502 X X X
P ackage :
S: SOP8 Packin g :
Blank : Tube or Bulk
A : Tape & Reel C : - 20 ~ 85 C
Temperat ure :
MARKING INFORMATION
( Vout=1.0V)
LSP5502
2A Synchronous Step Down DC/DC Converter
11/12 Rev. 1.8
www.liteon-semi.com
PACKAGE INFORMATION
Dimensions In Millimeters Dimensions In Inches
Symbol Min. Nom. Max. Min. Nom. Max.
A 1.35 1.6 1.75 0.053 0.063 0.069
A1 0.1 0.25 0.004 0.01
A2 1.25 1.45 1.55 0.049 0.057 0.061
B 0.31 0.41 0.51 0.012 0.016 0.02
C 0.1 0.2 0.25 0.0039 0.008 0.01
D 4.8 4.9 5 0.192 0.196 0.2
E 3.8 3.9 4 0.148 0.154 0.16
e 1.27 BSC 0.050 BSC
H 5.7 6 6.3 0.224 0.236 0.248
L 0.4 0.71 1.27 0.015 0.028 0.05
0
8 0
8
LSP5502
2A Synchronous Step Down DC/DC Converter
12/12 Rev. 1.8
www.liteon-semi.com
Important Notice and Disclaimer
LSC reserves the right to make changes to this document and its products and specifications a
t
any time without notice. Customers should obtain and confirm the latest product informatio
n
and specifications before final design, purchase or use.
LSC makes no warranty, representation or guarantee regarding the suitability of its products fo
r
any particular purpose, nor does LSC assume any liability for application assistance or custome
r
p
roduct design. LSC does not warrant or accept any liability with products which are purchase
d
or used for any unintended or unauthorized application.
N
o license is granted by implication or otherwise under any intellectual property rights of LSC.
LSC products are not authorized for use as critical components in life support devices or systems withou
t
express written approval of LSC.
