參數(shù)資料
型號(hào)： SP6639
元件分類： DC/DC變換器
英文描述： Adjustable, High Efficiency, Low I Q , Step-Down DC-DC Converter(5V或可調(diào)電壓，高效，低I Q，步降DC-DC變換器)
中文描述： 可調(diào)，高效率，低智商，降壓型DC - DC轉(zhuǎn)換器（5V的或可調(diào)電壓，高效，低智商，步降型DC - DC變換器）
文件頁(yè)數(shù)： 7/13頁(yè)
文件大小： 82K
代理商： SP6639
7
Rev. 2/23/01 SP6639/40/53 5/ 3.3/ 3V, Adj High Efficiency, Low I
Q
Step-Down DC-DC Converter Copyright 2001 Sipex Corporation
P
Figure 1. Simplified Step-Down Converter
GETTING STARTED
Designing power supplies with the SP6639/40/
53 is easy. The few required external compo-
nents are readily available. The most general
applications use the following components:
1) Capacitors: For the input and output filter
capacitors, try using electrolytics in the 100
μ
F
range, or use low-ESF capacitors to minimize
output ripple. Capacitor values are not critical.
2) Diode: Use the popular 1N5817 equivalent
Schottky diode.
3) Inductor: For the highest output current,
choose a 100
μ
H inductor with an incremental
saturation current rating of at least 600mA. To
obtain the highest efficiencies and smallest size,
refer to the Inductor Selection section.
DETAILED DESCRIPTION
Figure 1 shows a simplified, step-down DC-DC
converter. When the switch is closed, a voltage
equal to (V+ - VOUT) is applied to the inductor.
The current through the inductor ramps up, stor-
ing energy in the inductor's magnetic field. The
same current also flows into the output filter
capacitor and load. When the switch opens, the
current continues to flow through the inductor in
the same direction, but must also flow through
the diode. The inductor alone supplies current to
the load when the switch is open. The current
decays to zero as the energy stored in the inductor's
magnetic field is transferred to the output filter
capacitor and the load.
Figure 2 shows what happens to the ideal circuit
of Figure 1 if the switch turns on with a 66% duty
cycle and V+ =3/2 V
The inductor current
rises more slowly than it falls because the mag-
nitude of the voltage applied during t
is less
than that applied during t
Varying the duty
cycle and switching frequency keeps the peak
current constant as input voltage varies. The
SP6639/40/53 control the switch ( t
and t
OFF
)
according to the following equations:
These three equations ensure constant peak cur-
rents for a given inductor value, across all output
voltages (ignoring the voltage drop across the
diode (D1) and the resistive losses in the switch
and inductor.) The variable duty cycle also
ensures that the current through the inductor
discharges to zero at the end of each pulse.
Figure 3 shows the SP6639/40/53 block dia-
gram and a typical connection in which 7V is
converted to 5V (SP6639), 3.3V (SP6640), or
3.0V (SP6653). The sequence of events in this
application is as follows:
Equation (1) t
ON
= 50
μ
sV/ (V+ - V
OUT
)
Equation (2) t
OFF
= 50
μ
sV/ V
OUT
Equation (3)I
PEAK
= 50
μ
sV/L
Figure 2. Simplified Step-Down Converter Operation
C
OUT
V
+
I
L
+
+
V
OUT
V
L
L
I
L
AT 200mA/DIV
V
L
AT 5V/DIV
0A
0V
SWITCH ON
SWITCH ON
SWITCH OFF
SWITCH OFF
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PDF描述
SP6640 Adjustable, High Efficiency, Low I Q , Step-Down DC-DC Converter(3.3V或可調(diào)電壓，高效，低I Q，步降DC-DC變換器)
SP6653 Adjustable, High Efficiency, Low I Q , Step-Down DC-DC Converter(3V或可調(diào)電壓，高效，低I Q，步降DC-DC變換器)
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