LITEON LSP5502SAC

Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
„ FEATURES
z 2A Output Current
z Wide 4.5V to 30V Operating Input Range
z Integrated 100mΩ Power MOSFET Switches
z Output Adjustable from 0.925V to 28V
z Up to 96% Efficiency
z Programmable Soft-Start
z Stable with Low ESR Ceramic Output Capacitors
z Fixed 400KHz Frequency
z Cycle-by-Cycle Over Current Protection
z Input Under Voltage Lockout
z 8-Pin SOP Package
„ GENERAL DESCRIPTION
The LSP5502 is a monolithic synchronous buck
regulator. The device integrates 100mΩ MOSFETS
that provide 2A continuous load cur-rent over a wide
operating input voltage of 4.5V to 30V. Current mode
control provides fast transient response and
cycle-by-cycle cur-rent limit.
An adjustable soft-start prevents inrush current at turn
on. In shutdown mode, the supply cur-rent 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
z
z
z
z
z
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
„ PIN ASSIGNMENT
(Top View)
„ PIN DESCRIPTION
Name
No.
BS
1
IN
2
SW
G
3
4
FB
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 0.1uF 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.
When left unconnected, EN is pulled high internally.
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
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
„
ABSOLUTE MAXIMUM RATINGS
Parameter
Value
Unit
IN Supply Voltage
-0.3 to 32
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 7
V
Continuous SW Current
Internally limited
A
Junction to Ambient Thermal Resistance (θJA)
70
°C/W
(Test on Approximately 3 in2 Copper Area 1OZ copper FR4 board)
Junction to Ambient Case Resistance (θJC)
20
°C/W
Maximum Power Dissipation
0.76
W
Operating Junction Temperature
-40 to 150
°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.)
„
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA= 25°C unless otherwise specified.)
Parameter
Symbol
Input Operating Voltage
Input Holdup Voltage
Feedback Voltage
Feedback Overvoltage Threshold
High-Side Switch-On Resistance
Low-Side Switch-On Resistance
High-Side Switch Leakage
Upper Switch Current Limit
Lower Switch Current Limit
COMP to Current Limit
Transconductance
Error Amplifier Transconductance
Error Amplifier DC Gain
Switching Frequency
Short Circuit Switching Frequency
Maximum Duty Cycle
Minimum On Time
EN Shutdown Threshold Voltage
EN Shutdown Threshold Voltage
Hys-terisis
EN Lockout Threshold Voltage
EN Lockout Hysterisis
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
Test Conditions
Min.
VIN
VOUT = 1.0V, ILOAD = 0A to 2A
4.5
VFB
VOUT = 1.0V, ILOAD = 0A to 2A
4.5V ≤ VIN ≤ 20V
0.900
VEN = 0V, VSW = 0V
GCOMP
GEA
AVEA
fSW
DMAX
∆ICOMP = ±10µA
350
VFB = 0
VFB = 0.8V
VEN Rising
1.1
Typ.
4.5
0.925
1.1
100
100
9
3.5
0.9
Max.
Unit
30
V
0.950
10
4.0
5.2
A/V
800
480
400
150
90
220
1.3
µA/V
V/V
kHz
kHz
%
nS
V
470
1.5
200
2.2
UVLO
VEN = 0
VEN = 3V, VFB = 1.0V
VEN Rising
VSS = 0V
CSS = 0.1µF
Hysteresis = 10°C
2/11
3.80
V
V
V
mΩ
mΩ
µA
A
A
2.5
210
0.3
1.4
4.05
210
12
10
160
mV
2.7
3.0
1.5
4.40
V
mV
µA
mA
V
mV
µA
mS
°C
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
„
FUNCTIONAL BLOCK DIAGRAM
„
FUNCTIONAL DESCRIPTION
The LSP5502 is a synchronous rectified, cur-rent-mode, step-down regulator. It regulates in-put voltages from 4.5V
to 30V 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 voltage comparator is
tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side switch off.
3/11
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified 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 ≈ 10kΩ and determine RFB1 from the following
equation:
(1)
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:
VOUT • ( VIN − VOUT )
L=
VIN f SW I OUTMAX 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
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:
4/11
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
VRIPPLE = I OUTMAX K RIPPLE R ESR
+
VIN
28 • f SW 2 LC OUT
(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 50mΩ 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.
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:
G EA
f P1 =
2 πAVEA C COMP
(5)
The second pole P2 is the output pole:
I OUT
fP 2 =
2πVOUT C OUT
(6)
The first zero Z1 is due to RCOMP and CCOMP:
1
fZ1 =
2πR COMP C COMP
(7)
And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used):
1
fP 3 =
2πR COMP C COMP 2
(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:
5/11
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
(9)
but limit RCOMP to 10kΩ maximum.
STEP2. Set the zero fZ1 at 1/4 of the crossover frequency. If RCOMP is less than 10kΩ, the equation for CCOMP is:
C COMP =
1 . 8 × 10 −5
R COMP
(F )
(10)
If RCOMP is limited to 10kΩ, then the actual crossover frequency is 10/ (VOUTCOUT). Therefore:
CCOMP = 1.2 × 10 −5 VOUT COUT
(F )
(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:
R ESRCOUT
⎛ 1 . 1 × 10 −6
≥ Min ⎜⎜
,0. 012 • VOUT
⎝ COUT
⎞
⎟
⎟
⎠
(Ω)
(12)
And the proper value for CCOMP2 is:
C COMP 2 =
C OUT R ESRCOUT
R COMP
(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
1.0V
1.2V
1.8V
2.5V
3.3V
5V
1.0V
1.2V
1.8V
2.5V
3.3V
5V
1.0V
1.2V
1.8V
2.5V
3.3V
5V
COUT
22µF Ceramic
22µF Ceramic
22µF Ceramic
22µF Ceramic
22µF Ceramic
22µF Ceramic
47µF SP Cap
47µF SP Cap
47µF SP Cap
47µF SP Cap
47µF SP Cap
47µF SP Cap
470µF/6.3V/30mΩ
470µF/6.3V/30mΩ
470µF/6.3V/30mΩ
470µF/6.3V/30mΩ
470µF/6.3V/30mΩ
470µF/10V/30mΩ
RCOMP
1.5kΩ
1.7kΩ
2.2kΩ
3.6kΩ
4.7kΩ
6.8kΩ
3.0kΩ
3.6kΩ
5.6kΩ
6.8kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
CCOMP
10nF
10nF
6.8nF
4.7nF
3.3nF
2.2nF
6.8nF
4.7nF
3.3nF
2.2nF
2.0nF
2.2nF
2.2nF
3.3nF
4.7nF
6.8nF
8.2nF
10nF
CCOMP2
100pF
100pF
100pF
100pF
47pF
47pF
470pF
330pF
220pF
200pF
150pF
150pF
1nF
1nF
1nF
1nF
1nF
1nF
Table3. Typical Compensation for Different Output Voltages and Output Capacitors
6/11
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
Figure 3 shows a sample LSP5502 application circuit generating 5V/2A output.
Figure3. LSP5502 5V/2A Output Application
Figure 4 shows a sample LSP5502 application circuit generating 1.0V/2A output.
Figure4. LSP5502 1.0V/2A Output Application
7/11
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
„ 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
12Vin 5.0Vout Efficiency curve
Efficiency vs Input Voltage（Vout=5.0V)
12Vin 1.0Vout Efficiency curve
VIN=8V
VIN=12V
VIN=18V
VIN=23V
Efficiency vs Input Voltage（Vout=1.0V)
VIN=8V
VIN=12V
VIN=18V
VIN=23V
100
90
90
80
80
η(%)
100
η(%)
VIN=5V
70
70
60
60
0
500
1000
1500
Io(mA)
50
Io(mA)
50
0
2000
8/11
500
1000
1500
2000
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
„
ORDERING INFORMATION
„
MARKING INFORMATION
9/11
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
θ
H
E
PACKAGE INFORMATION
D
C
B
A1
e
A
7ο(4х)
A2
„
Symbol
A
A1
A2
B
C
D
E
e
H
L
θ
Dimensions In Millimeters
Nom.
Max.
1.60
1.75
0.25
1.45
1.55
0.41
0.51
0.20
0.25
4.90
5.00
3.90
4.00
1.27TYP.
5.80
5.99
6.30
0.38
0.71
1.27
0ο
8ο
Min.
1.35
0.10
1.35
0.33
0.19
4.80
3.80
10/11
Dimensions In Inches
Min.
Nom.
0.053
0.063
0..004
0.053
0.057
0.013
0.016
0.0075
0.008
0.192
0.196
0.148
0.154
0.050TYP.
0.228
0.236
0.015
0.028
0ο
Max.
0.069
0.010
0.061
0.020
0.010
0.200
0.160
0.248
0.050
8ο
Rev1.1
Liteon Semiconductor Corporation
LSP5502
2A Synchronous Rectified Step Down DC/DC Converter
„
UPDATE HISTORY
Date
20090601
20090609
Version
V1.0
V1.1
Descriptions
Preliminary release version;
Revise the Vin from 23V to 30V;
11/11
Rev1.1