LSP5502 Datasheet PDF - Lite-On

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LSP5502
Lite-On

Part Number LSP5502
Description 2A Synchronous Step Down DC/DC Converter
Page 11 Pages


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LSP5502
2A Synchronous Step Down DC/DC Converter
FEATURES
2A Output Current
Wide 4.5V to 27V Operating Input Range
Integrated 120mPower 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
GENERAL DESCRIPTION
The LSP5502 is a monolithic synchronous buck
regulator. The device integrates 120mMOSFETS
that provide 2A 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.
TYPICAL APPLICATION
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
PIN ASSIGNMENT
SOP-8L
(TOP View)
BS 1
8 SS
IN 2
7 EN
SW 3
6 COMP
GND 4
5 FB
PIN DESCRIPTION
Name
BS
No.
1
IN
SW
GND
FB
2
3
4
5
COMP
6
EN 7
SS 8
Description
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.
Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor
in the Application Information section.
Switch Output. Connect this pin to the switching end of the inductor.
Ground.
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.
Compensation Pin. See Stability Compensation in the Application Information
section.
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.
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.
1/11 Rev. 1.7
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LSP5502
2A Synchronous Step Down DC/DC Converter
ABSOLUTE MAXIMUM RATINGS
Parameter
Value
Unit
IN Supply Voltage
-0.3 to 30
V
SW Voltage
BS Voltage
EN, FB, COMP Voltage
-1 to VIN + 0.3
VSW – 0.3 to VSW + 6
-0.3 to 6
V
V
V
Continuous SW Current
Internally limited
A
(Test on AJpupnrcotixoinmtaoteAlym3biienn2tCTohpeprmeraAl rReeas1isOtaZnccoepp(eθrJAF)R4 board)
70
°C/W
Junction to Ambient Case Resistance (θJC)
Maximum Power Dissipation
20
0.76
°C/W
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
VIN
TJ
Parameter
Input Voltage
Operating Junction Temperature Range
Min Max Unit
4.5 27
-20 125
V
oC
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA= 25°C unless otherwise specified.)
Parameter
Symbol
Test Conditions
Input Operating Voltage
VIN VOUT = 1.0V, ILOAD = 0A to 2A
Input Holdup Voltage
Feedback Voltage
Feedback Overvoltage Threshold
VOUT = 1.0V, ILOAD = 0A to 2A
VFB 4.5V VIN 20V
High-Side Switch-On Resistance
Low-Side Switch-On Resistance
High-Side Switch Leakage
VEN = 0V, VSW = 0V
Upper Switch Current Limit
Lower Switch Current Limit
COMP to Current Limit
Transconductance
GCOMP
Error Amplifier Transconductance
Error Amplifier DC Gain
Switching Frequency
Short Circuit Switching Frequency
Maximum Duty Cycle
Minimum On Time
GEA
AVEA
fSW
DMAX
ICOMP = ±10µA
VFB = 0
VFB = 0.8V
EN Shutdown Threshold Voltage
VEN Rising
EN Shutdown Threshold Voltage
Hysterisis
EN Lockout Threshold Voltage
EN Lockout Hysterisis
2/11
Min.
4.5
0.900
350
1.1
2.2
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Typ.
4.5
0.925
1.1
120
120
9
3.5
0.9
5.2
800
480
400
150
90
220
1.3
200
2.5
210
Max.
27
0.950
10
4.0
Unit
V
V
V
V
m
m
µA
A
A
A/V
µA/V
V/V
470 kHz
kHz
%
nS
1.5 V
mV
2.7 V
mV
Rev. 1.7
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LSP5502
2A Synchronous Step Down DC/DC Converter
Supply Current in Shutdown
IC Supply Current in Operation
Input UVLO Threshold Rising
Input UVLO Threshold Hysteresis
Soft-start Current
Soft-start Period
Thermal Shutdown Temperature
UVLO
VEN = 0
VEN = 3V, VFB = 1.0V
VEN Rising
VSS = 0V
CSS = 0.1µF
Hysteresis = 10°C
0.3 3.0
1.4 1.5
3.80 4.05 4.40
210
6
15
160
µA
mA
V
mV
µA
mS
°C
FUNCTIONAL BLOCK DIAGRAM
FB 5
1.1V
0.3V
SS 8
0.925V
COMP 6
EN 7
7V
Zener
2.5V
1.5V
OVP
RAMP
OSCILLATOR
150/400KHz CLK
ERROR
AMPLIFIER
6uA
CURRENT
SENSE
AMPLIFIER
SQ
RQ
CURRENT
COMPARATOR
2 IN
5V
1 BS
M1
0.12
3 SW
M2
0.12
EN OK
LOCKOUT
COMPARATOR
SHUTDOWN
COMPARATOR
1.2V
OVP
4 GND
IN<4.10V
IN
INTERNAL
REGULATORS
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.
3/11
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Rev. 1.7
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LSP5502
2A Synchronous Step Down DC/DC Converter
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 10kand determine RFB1 from the following
equation:
(1)
Table 1-Recommended Resistance Values
VOUT
1.0V
1.2V
1.8V
2.5V
3.3V
5V
12V
RFB1
1.0k
3.0k
9.53k
16.9k
26.1k
44.2k
121k
RFB2
12k
10k
10k
10k
10k
10k
10k
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:
L
=
VOUT
VIN fSW
(VIN VOUT )
IOUTMAX K RIPPLE
(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 6.8µH 6.8µH 10µH 10µH 15µH
Table 1. Typical Inductor Values
Input Capacitor
4/11
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Rev. 1.7
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