APW7060 Ver la hoja de datos (PDF) - Anpec Electronics
Número de pieza
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Fabricante
APW7060 Datasheet PDF : 16 Pages
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APW7060
Application Information
Soft Start
Soft start can be initiated in several ways. One way is
when the input bias supply to the 5VCC and 12VCC
is above 4.2V and 10.2V respectively. The other way
is when the part comes out of shutdown. In both ways,
the soft start cycle will last for 2ms. During this period,
the reference to the error amplifier of the PWM con-
troller and linear controller will gradually slew up to its
final value of 0.8V. This effectively will force both out-
put voltages to track this reference ramp rate. Hence
both outputs will reach regulation at the same time.
Figure 3 illustrates this graphically.
Maximum Output Voltage of Linear Controller
The maximum drive voltage at DRIVE2 is determined
by the applied voltage at 12VCC pin. Since this pin
drives an external N-channel pass MOSFET, there-
fore the maximum output voltage of the linear regula-
tor is dependent upon the required gate-to-source volt-
age to sustain the load current.
VOUT2MAX = 12VCC - VGSpass
Component Selection Guidelines
Soft-start at Powering ON
+12V
+5V
VOUT2
VOUT1
Ch1 : +5V, 1V/Div, DC
Ch2 : +12V, 2V/Div, DC
Ch3 : VOUT1, 1V/Div, DC
Ch4 : VOUT2, 1V/Div, DC
Time : 1mS/Div
BW = 20MHz
.ECKH/Figure 3.
Linear Regulator Transient Response Optimiza-
tion
The linear regulator is stable over all load current.
However, the transient response can be further en-
hanced by connecting a RC network between the FB2
and DRIVE2 pin. Depending on the output capacitance
and load current of the application, the value of this
RC network is then varied. A good starting point for
the resistor value is 6.8kΩ and 470pF for the capacitor.
PWM Regulator Output Capacitor
The selection of C is determined by the required
OUT
effective series resistance (ESR) and voltage rating
rather than the actual capacitance requirement. There-
fore select high performance low ESR capacitors that
are intended for switching regulator applications. In
some applications, multiple capacitors have to be
paralled to achieve the desired ESR value. If tantalum
capacitors are used, make sure they are surge tested
by the manufactures. If in doubt, consult the capaci-
tors manufacturer.
Input Capacitor Selection
The input capacitor is chosen based on the voltage
rating and the RMS current rating. For reliable
operation, select the capacitor voltage rating to be at
least 1.3 times higher than the maximum input voltage.
The maximum RMS current rating requirement is ap-
proximately IOUT/2 , where IOUT is the load current.
During power up, the input capacitors have to handle
large amount of surge current. If tantalum capacitors
are used, make sure they are surge tested by the
manufactures. If in doubt, consult the capacitors
manufacturer.
For high frequency decoupling, a ceramic capacitor
between 0.1uF to 1uF can be connected between
5VCC and ground pin.
Copyright ANPEC Electronics Corp.
10
Rev. A.3 - Oct., 2003
www.anpec.com.tw
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