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PDF L5983 Data sheet ( Hoja de datos )
| Número de pieza | L5983 | |
| Descripción | 1.5A step-down switching regulator | |
| Fabricantes | STMicroelectronics | |
| Logotipo |  |
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L5983
1.5A step-down switching regulator
Features
■ 1.5A DC output current
■ 2.9V to 18V input voltage
■ Output voltage adjustable from 0.6V
■ 250kHz switching frequency, programmable
up to 1MHz
■ Internal soft-start
■ Inhibit
■ Low dropout operation: 100% duty cycle
■ Voltage feed-forward
■ Zero load current operation
■ Over current and thermal protection
■ VQFN3x3-8L package
Applications
■ Consumer:
STB, DVD, DVD recorder, car audio, LCD TV
and monitors
■ Industrial:
Chargers, car battery, PLD, PLA, FPGA
■ Networking: XDSL, modems, DC-DC modules
■ Computer:
Optical storage, hard disk drive, printers,
audio/graphic cards
Figure 1. Application circuit
VFQFPN8 3x3
Description
The L5983 is a step down switching regulator with
2.0A current limited embedded power MOSFET,
so it is able to deliver an output current in excess
of 1.5A DC to the load.
The input voltage can range from 2.9V to 18V,
while the output voltage can be set starting from
0.6V to VIN. Having a minimum input voltage of
2.9V, the device is suitable for also for the 3.3V
bus.
Requiring a minimum set of external components,
the device includes an internal 250kHz switching
frequency oscillator that can be externally
adjusted up to 1MHz.
The QFN package with exposed pad allows
reducing the RthJA down to approximately
60°C/W.
October 2007
Rev 2
1/37
www.st.com
37
1 page  
www.DataSEhleeect4tUri.ccoaml characteristics
3 Electrical characteristics
TJ=25°C, VCC=12V, unless otherwise specified.
L5983
5/37
5 Page 
www.DataSFhuenetc4Uti.oconmal description
L5983
4.2 Soft-start
The soft-start is essential to assure correct and safe start up of the step-down converter. It
avoids inrush current surge and makes the output voltage increases monothonically.
The soft -start is performed by a staircase ramp on the non-inverting input (VREF) of the
Error Amplifier. So the output voltage slew rate is:
Equation 1
SROUT
=
SRVREF
⋅
⎛
⎝
1
+
RR-----12--⎠⎞
where SRVREF is the slew rate of the non-inverting input and R1, R2 is the resistor divider to
regulate the output voltage (see Figure 7). The soft-start stair case consists of 64 steps of
9.5mV each one, from 0V to 0.6V. The time base of one step is of 32 clock cycles. So the
soft start time and then the output voltage slew rate depend on the switching frequency.
Figure 7. Soft start scheme.
Soft start time results:
Equation 2
SSTIME
=
3----2-----⋅---6---4--
Fsw
For example with a switching frequency of 250kHz the SSTIME is 8ms.
11/37
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet L5983.PDF ] | |
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