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PDF L5985 Data sheet ( Hoja de datos )

Número de pieza L5985
Descripción 2A step-down switching regulator
Fabricantes STMicroelectronics 
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L5985
2A step-down switching regulator
Features
2A 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 and 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 L5985 is a step down switching regulator with
2.5A current limited embedded power MOSFET,
so it is able to deliver up to 2A DC current to the
load depending on the application condition.
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 buses staring from
for 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
1/36
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L5985 pdf
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3 Electrical characteristics
Electrical characteristics
TJ=25°C, VCC=12V, unless otherwise specified.
Table 3. Electrical characteristics
Symbol
Parameter
Test condition
VCC
VCCON
VCCOFF
Operating input voltage
range
Turn on VCC threshold
Turn off VCC threshold
(1)
(1)
(1)
RDSON Mosfet on resistance
(1)
ILIM Maximum limiting current
Oscillator
FSW Switching frequency
(1)
VFSW
D
FADJ
FSW pin voltage
Duty Cycle
Adjustable switching
frequency
RFSW=33k
Dynamic characteristics
VFB Feedback voltage
DC characteristics
2.9V<VCC<18V
IQ
IQST-BY
Quiescent current
Total stand-by quiescent
current
Duty Cycle=0,
VFB=0.8V
Inhibit
INH threshold voltage
INH current
Device ON level
Device OFF level
INH=0
Soft start
TSS Soft start duration
FSW=Floating
FSW=1MHz,
RFSW=33k
Values
Min Typ Max
Unit
2.9 18
2.9 V
2.4
x 150 x
m
150 300
2.5 2.9 3.3
A
225 250 275
x 250 x
1.262
0 100
1000
KHz
V
%
KHz
0.593 0.6 0.607 V
2.4 mA
20 30 µA
0.6
V
1.9
7.5 10 µA
7.4 8.2 9.1
ms
2
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L5985 arduino
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Functional description
4.3 Error amplifier and compensation
The Error Amplifier (E/A) provides the error signal to be compared with the sawtooth to
perform the Pulse Width Modulation. Its non-inverting input is internally connected to a 0.6V
voltage reference, while its inverting input (FB) and output (COMP) are externally available
for feedback and frequency compensation. In this device the Error amplifier is a Voltage
Mode Operational Amplifier so with high DC gain and low output impedance.
The uncompensated Error Amplifier characteristics are the following:
Table 4. Uncompensated Error Amplifier characteristics
Low frequency Gain
100dB
GBWP
4.5MHz
Slew Rate
7V/µs
Output voltage swing
0 to 3.3V
Maximum source/sink current
25mA/40mA
In continuos conduction mode (CCM), the transfer function of the power section has two
poles due to the LC filter and one zero due to the ESR of the output capacitor. Different
kinds of compensation networks can be used depending on the ESR value of the output
capacitor. In case the zero introduced by the output capacitor helps to compensate the
double pole of the LC filter a type II compensation network can be used. Otherwise, a type
III compensation network has to be used (see Chapter 5.4 for details about the
compensation network selection).
Anyway the methodology to compensate the loop is to introduce zeros to obtain a safe
phase margin.
11/36

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