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PDF LSP3172 Data sheet ( Hoja de datos )
| Número de pieza | LSP3172 | |
| Descripción | Wide Input 2.5A Step Down DC/DC Converter | |
| Fabricantes | JBS | |
| Logotipo |  |
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JOINT BAYSE MICONDUCTOR CO.,LTDLSP317
:LGH,QSXW$6WHS'RZQ'&'&&RQYHUWHU
FEATURES
z 2.5A Output Current
z Up to 90% Efficiency
z 7V to 30V Input Range
z 40µA Shutdown Supply Current
z 400kHz Switching Frequency
z Adjustable Output Voltage
z Cycle-by-Cycle Current Limit Protection
z Thermal Shutdown Protection
z Frequency Foldback at Short Circuit
z Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
z SOP8L Package
TYPICAL APPLICATION
z TFT LCD Monitors
z Portable DVDs
z Car-Powered or Battery-Powered Equipments
z Set-Top Boxes
z Telecom Power Supplies
z DSL and Cable Modems and Routers
z Termination Supplies
GENERAL DESCRIPTION
The LSP3172 is a current-mode step-down DC/DC
converter that generates up to 2.5A of output current
at 400kHz switching frequency.
Consuming only 40µA in shutdown mode, the
LSP3172 is highly efficient with peak operating
efficiency at 90%. Protection features include
cycle-by-cycle current limit, thermal shutdown, and
frequency foldback at short circuit.
The LSP3172 is available in a SOP8L package and
requires very few external devices for operation.
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.
1/9
1 page  
JOINT BAY SEMICONDUCTOR CO.,LTDLSP317
:LGH,QSXW$6WHS'RZQ'&'&&RQYHUWHU
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:
1
fZ1 = 2πRCOMPCCOMP (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 3.4kΩ maximum.
STEP2. Set the zero fZ1 at 1/4 of the crossover frequency. If RCOMP is less than 3.4kΩ, the equation for CCOMP
is:
CCOMP
= 1.8 × 10 −5
RCOMP
(F )
(10)
If RCOMP is limited to 3.4kΩ, then the actual crossover frequency is 3.4 / (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:
5/9
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet LSP3172.PDF ] | |
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