EL7516 데이터 시트보기 (PDF) - International Rectifier
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EL7516 Datasheet PDF : 11 Pages
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EL7516
For noise sensitive application, a 0.1µF placed in parallel
with the larger output capacitor is recommended to reduce
the switching noise coupled from the LX switching node.
Schottky Diode
In selecting the Schottky diode, the reverse break down
voltage, forward current and forward voltage drop must be
considered for optimum converter performance. The diode
must be rated to handle 1.5A, the current limit of the
EL7516. The breakdown voltage must exceed the maximum
output voltage. Low forward voltage drop, low leakage
current, and fast reverse recovery will help the converter to
achieve the maximum efficiency.
Input Capacitor
The value of the input capacitor depends the input and
output voltages, the maximum output current, the inductor
value and the noise allowed to put back on the input line. For
most applications, a minimum 10µF is required. For
applications that run close to the maximum output current
limit, input capacitor in the range of 22µF to 47µF is
recommended.
The EL7516 is powered from the VIN. To. High frequency
0.1µF by-pass cap is recommended to be close to the VIN
pin to reduce supply line noise and ensure stable operation.
Loop Compensation
The EL7516 incorporates an transconductance amplifier in
its feedback path to allow the user some adjustment on the
transient response and better regulation. The EL7516 uses
current mode control architecture which has a fast current
sense loop and a slow voltage feedback loop. The fast
current feedback loop does not require any compensation.
The slow voltage loop must be compensated for stable
operation. The compensation network is a series RC
network from COMP pin to ground. The resistor sets the high
frequency integrator gain for fast transient response and the
capacitor sets the integrator zero to ensure loop stability. For
most applications, the compensation resistor in the range of
2K to 7.5K and the compensation capacitor in the range of
3nF to 10nF.
Soft-Start
The soft-start is provided by an internal 6µA current source
charges the external CSS, the peak MOSFET current is
limited by the voltage on the capacitor. This in turn controls
the rising rate of the output voltage. The regulator goes
through the start-up sequence as well after the SHDN pin is
pulled to HI.
Frequency Selection
The EL7516 switching frequency can be user selected to
operate at either at constant 620kHz or 1.25MHz.
Connecting FSEL pin to ground sets the PWM switching
frequency to 620kHz. When connect FSEL high or VDD,
switching frequency is set to 1.25MHz.
Shut-Down Control
When shut-down in is pulled low, the EL7516 is shut-down
reducing the supply current to <3µA.
Maximum Output Current
The MOSFET current limit is nominally 1.5A and guaranteed
1.3A. This restricts the maximum output current IOMAX
based on the following formula:
IL = IL-AVG + (1 ⁄ 2 × ∆IL)
where:
IL = MOSFET current limit
IL-AVG = average inductor current
∆IL = inductor ripple current
∆IL = -V----I--NL-----××-----([--V(---V-O---O---+--+---V--V--D---D--I-O-I--O--D--D--E--E--)--)--×--–---F-V---S-I--N-----]
VDIODE = Schottky diode forward voltage, typically, 0.6V
FS = switching frequency, 600KHz or 1.2MHz
IL-AVG
=
I--O-----U----T--
1–D
D = MOSFET turn-on ratio:
D
=
1
–
------------------V----I--N--------------------
VOUT + VDIODE
The following table gives typical maximum Iout values for
1.2MHz switching frequency and 22µH inductor:
VIN (V)
2.5
2.5
2.5
3.3
3.3
3.3
5
5
TABLE 1.
VOUT (V)
5
9
12
5
9
12
9
12
IOMAX (mA)
570
325
250
750
435
330
650
490
Thermal Performance
The EL7516 uses a fused-lead package, which has a
reduced θJA of 100°C/W on a four-layer board and 115°C/W
on a two-layer board. Maximizing copper around the ground
pins will improve the thermal performance.
This device also has internal thermal shut-down set at
around 130°C to protect the component.
10
FN7333.3
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