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PDF GS2576 Data sheet ( Hoja de datos )
| Número de pieza | GS2576 | |
| Descripción | 52kHz 3A Step-Down Voltage Regulator | |
| Fabricantes | Globaltech | |
| Logotipo |  |
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52kHz 3A Step-Down Voltage Regulator
Product Description
Features
The GS2576 series of regulators are monolithic
integrated circuits that provide all the active functions
for a step-down switching regulator, capable of driving
3A load with excellent line and load regulation. This
device is available in fixed output voltages of 3.3V, 5V
and an adjustable output version.
Requiring a minimum number of external
components, these regulators are simple to use and
include internal frequency compensation and a
fixed-frequency oscillator.
The GS2576 series offers a high-efficiency
replacement for popular three-terminal linear
regulators. It substantially reduces the size of the heat
sink, and in some cases no heat sink is required.
A standard series of inductors optimized for use with
the GS2576. This feature greatly simplifies the design
of switch-mode power supplies.
Other features include a guaranteed ±4% tolerance
on output voltage within specified input voltages and
output load conditions, and ±10% on the oscillator
frequency. External shutdown is included, featuring
50µA (typical) standby current. The output switch
includes cycle-by-cycle current limiting, as well as
thermal shutdown for full protection under fault
conditions..
3.3V, 5V and adjustable output versions
Adjustable version output voltage range, 1.23V
to 37V
± 4% max over line and load conditions
Guaranteed 3A output current
40V wide input voltage range
Requires only 4 external components
52 kHz fixed frequency oscillator
TTL shutdown capability, low power standby
mode
High efficiency
Uses readily available standard inductors
Thermal shutdown and current limit protection
Applications
Simple high-efficiency step-down regulator
On-card switching regulators
Positive to negative converter
Efficient pre-regulator for linear regulators
Block Diagram
Unregulated
DC Input
+VIN
1
Internal
Regulator
ON / OFF
ON / OFF
5
CIN
FEEDBACK
4
R2
Fixd Gain
Error Amplifier
R1
1k
Comparator
1.23V
Band-Gap
Reference
52 kHz
Oscillator
Reset
Driver
3A
Switch
Thermal
Shutdown
Current
Limit
OUTPUT
2
Regulator
Output
VOUT
L1
GND
3
COUT
L
O
A
D
D1
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1
Free Datasheet http://www.datasheet4u.com/
1 page  
Globaltech Semiconductor
Typical Applications
As in any switching regulator, the layout of the printed board (PCB) is very important. Rapidly switching currents
associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces
can generate voltage transients, which can generate electromagnetic interferences (EMI) and affect the desired
operation. As indicated in the Figure 1, to minimize inductance and ground loops, the length of the leads indicated
by heavy lines should be kept as short as possible.
For best results, single-point grounding (as indicated) or ground plane construction should be used.
On the other hand, the PCB area connected to the Pin 2 (emitter of the internal switch) of the GS2576 should be
kept to a minimum in order to minimize coupling to sensitive circuitry.
Another sensitive part of the circuit is the feedback. It is important to keep the sensitive feedback wiring short. To
assure this, physically locate the programming resistors near to the regulator, when using the Adjustable version of
the GS2576 regulator.
Fixed Output Voltage Versions (Figure 1a)
FEEDBACK
4
+VIN
1
GS2576 -
FIXED OUTPUT
OUTPUT
2
CIN
100μ F
3
GND
5
ON / OFF
L1
100μ H
D1
MBR360
VOUT
COUT
1000μ F
Adjustable Output Voltage Version (Figure 1b)
+VIN
1
GS2576
ADJUSTABLE
FEEDBACK
4
OUTPUT
2
CIN
100μ F
3
GND
5
ON / OFF
D1
MBR360
L1
100μ H
COUT
1000μ F
VOUT
R2
R1
CIN— 100µF, 75V Aluminum Electrolytic
COUT— 1000µF, 25V, Aluminum Electrolytic
D1— Schottky, MBR360
L1— 100 µH
R1-2.0k, 0.1%
R2-6.12k, 0.1%
VOUT=VREF (1+R2 /R1), R2 = R1 (VOUT / VREF - 1), where VREF = 1.23V, R1 between 1k and 5k
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Free Datasheet http://www.datasheet4u.com/
5 Page 
Globaltech Semiconductor
Application Information (Continue)
Inductor Ripple Current
When the switcher is operating in the continuous mode, the inductor current waveform ranges from a
triangular to a sawtooth type of waveform (depending on the input voltage). For a given input voltage
and output voltage, the peak-to-peak amplitude of this inductor current waveform remains constant. As
the load current rises or falls, the entire sawtooth current waveform also rises or falls. The average DC
value of this waveform is equal to the DC load current (in the buck regulator configuration).
If the load current drops to a low enough level, the bottom of the sawtooth current waveform will reach
zero, and the switcher will change to a discontinuous mode of operation. This is a perfectly acceptable
mode of operation. Any buck switching regulator (no matter how large the inductor value is) will be
forced to run discontinuous if the load current is light enough.
Output Capacitor
An output capacitor is required to filter the output voltage and is needed for loop stability. The capacitor
should be located near the GS2576 using short pc board traces. Standard aluminum electrolytics are
usually adequate, but low ESR types are recommended for low output ripple voltage and good stability.
The ESR of a capacitor depends on many factors, some which are: the value, the voltage rating,
physical size and the type of construction. In general, low value or low voltage (less than 12V)
electrolytic capacitors usually have higher ESR numbers.
The amount of output ripple voltage is primarily a function of the ESR (Equivalent Series Resistance) of
the output capacitor and the amplitude of the inductor ripple current (△IIND). See the section on inductor
ripple current in Application Hints.
The lower capacitor values (220 µF–1000 µF) will allow typically 50 mV to 150 mV of output ripple
voltage, while larger-value capacitors will reduce the ripple to approximately 20 mV to 50 mV.
Output Ripple Voltage = (△IIND) (ESR of COUT)
To further reduce the output ripple voltage, several standard electrolytic capacitors may be paralleled,
or a higher-grade capacitor may be used. Such capacitors are often called “high-frequency,”
“low-inductance,” or “low-ESR.” These will reduce the output ripple to 10 mV or 20 mV. However, when
operating in the continuous mode, reducing the ESR below 0.03W can cause instability in the regulator.
Tantalum capacitors can have a very low ESR, and should be carefully evaluated if it is the only output
capacitor. Because of their good low temperature characteristics, a tantalum can be used in parallel with
aluminum electrolytic, with the tantalum making up 10% or 20% of the total capacitance. The capacitor’s
ripple current rating at 52 kHz should be at least 50% higher than the peak-to-peak inductor ripple
current.
Catch Diode
Buck regulators require a diode to provide a return path for the inductor current when the switch is off.
This diode should be located close to the GS2576 using short leads and short printed circuit traces.
Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best
efficiency, especially in low output voltage switching regulators (less than 5V). Fast-Recovery,
High-Efficiency, or Ultra-Fast Recovery diodes are also suitable, but some types with an abrupt turn-off
characteristic may cause instability and EMI problems. A fast-recovery diode with soft recovery
characteristics is a better choice. Standard 60 Hz diodes (e.g., 1N4001 or 1N5400, etc.) are also not
suitable.
Output Voltage Ripple and Transients
The output voltage of a switching power supply will contain a sawtooth ripple voltage at the switcher
frequency, typically about 1% of the output voltage, and may also contain short voltage spikes at the
peaks of the sawtooth waveform.
The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of
the output capacitor. (See the inductor selection in the application hints.) The voltage spikes are
present because of the fast switching action of the output switch, and the parasitic inductance of the
output filter capacitor. To minimize these voltage spikes, special low inductance capacitors can be used,
and their lead lengths must be kept short. Wiring inductance, stray capacitance, as well as the scope
probe used to evaluate these transients, all contribute to the amplitude of these spikes.
An additional small LC filter (20 µH & 100 µF) can be added to the output (as shown in Figure 7) to
further reduce the amount of output ripple and transients. A 10 x reduction in output ripple voltage and
transients is possible with this filter.
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11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet GS2576.PDF ] | |
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