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PDF LSP3170 Data sheet ( Hoja de datos )
| Número de pieza | LSP3170 | |
| Descripción | 2A Step Down DC/DC Converter | |
| Fabricantes | Lite-On | |
| Logotipo |  |
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Liteon Semiconductor Corporation
LSP3170
2A Step Down DC/DC Converter
FEATURES
2A Output Current
Up to 95% Efficiency
4.6V to 24V Input Range
40µA Shutdown Supply Current
400kHz Switching Frequency
Adjustable Output Voltage
Cycle-by-Cycle Current Limit Protection
Thermal Shutdown Protection
Frequency Foldback at Short Circuit
Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
SOP8L Package
GENERAL DESCRIPTION
The LSP3170 is a current-mode step-down DC/DC
converter that generates up to 2A of output current at
400kHz switching frequency.
Consuming only 40µA in shutdown mode, the
LSP3170 is highly efficient with peak operating
efficiency at 95%. Protection features include
cycle-by-cycle current limit, thermal shutdown, and
frequency foldback at short circuit.
The LSP3170 is available in a SOP8L package and
requires very few external devices for operation.
TYPICAL APPLICATION
TFT LCD Monitors
Portable DVDs
Car-Powered or Battery-Powered Equipments
Set-Top Boxes
Telecom Power Supplies
DSL and Cable Modems and Routers
Termination Supplies
PIN ASSIGNMENT
(Top View)
PIN DESCRIPTION
Name
BS
No.
1
IN 2
SW 3
G4
FB 5
COMP
6
EN 7
N/C 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 1.222V. 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
2.0V, this pin turns the IC off. Output voltage is discharged when the IC is off.
When left unconnected, EN is pulled high internally.
Not Connected.
1/10 Rev1.5
1 page  
Liteon Semiconductor Corporation
LSP3170
2A Step Down DC/DC Converter
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.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode
must have a current rating higher than the maximum output current and a reverse voltage rating higher than the
maximum input voltage.
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:
fP1
=
G EA
2 πAVEA C C OM P
(5)
The second pole P2 is the output pole:
fP2
=
IOUT
2πVOUT COUT
(6)
The first zero Z1 is due to RCOMP and CCOMP:
fZ1
=
1
2πRCOMP CCOMP
(7)
And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used):
fP3
1
= 2πRCOMP CCOMP2
(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 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:
CCOMP
= 1.8 × 10 −5
RCOMP
(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,
5/10 Rev1.5
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet LSP3170.PDF ] | |
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