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參數(shù)資料
| 型號： | SP6640 |
| 元件分類： | DC/DC變換器 |
| 英文描述： | 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) |
| 中文描述： | 可調(diào)，高效率，低智商，降壓型DC - DC轉(zhuǎn)換器電壓（3.3V或可調(diào)電壓，高效，低智商，步降型DC - DC變換器） |
| 文件頁數(shù)： | 10/13頁 |
| 文件大?。?/td> | 82K |
| 代理商： | SP6640 |
10
Rev. 2/23/01
SP6639/40/53 5/ 3.3/ 3V Adj, High Efficiency, Low I
Q
Step-Down DC-DC Converter Copyright 2001Sipex Corporation
P
External Diode
In most SP6639/40/53 circuits, the current in the
external diode (D1, Figure 3) changes abruptly
from zero to its peak value each time LX switches
off. To avoid excessive losses, the diode must
have a fast turn-on time. For low-power circuits
with peak currents less than 100mA, signal di-
odes such as the 1N4148 perform well. The
1N5817 diode works well for high power circuits
or for maximum efficiency at low power. 1N5817
equivalent diodes are also available in surface
mount packages (Table 1). Although the 1N4001
and other general-purpose rectifiers are rated for
high currents, they are unacceptable because
their slow turn-off times result in excessive losses.
Minimum Load
Under no-load conditions, because leakage from
the PMOS power switch (see the LX Leakage
Current vs. Temperature graph in the Typical
Operating Characteristics) and from the internal
resistor from V+ to V
OUT
, leakage current may
be supplied to the output capacitor, even when
the switch is off. This will usually not be a
problem for a 5V output at room temperature,
since the diode’s reverse leakage current and the
feedback resistor’s current typically drain the
excess. However, if the diode leakage is very
low (which can occur at low temperatures and/or
small output voltages), charge may build up on
the output capacitor, making it rise above its set
point. If this happens, add a small load resistor
capacitor (typically 1MW) to the output to pull
a few extra microamps of current from the out-
put capacitor.
Layout
Several of the external components in a SP6639/
40/53 circuit experience peak currents up to
600mA. Whenever one of these components
connects to ground, there is a potential for
ground bounce. Ground bounce occurs when
high currents flow through the parasitic resis-
tance of PC board traces. What one component
interprets as ground can differ from the IC’s
ground by several millivolts. This may increase
the SP6639/40/53’s output ripple, since the er-
ror comparator (which is referenced to ground)
will generate extra switching pulses when they
are not needed. It is essential that the input filter
capacitor’s ground lead, the SP6639/40/53’s
GND pin, the diode’s anode, and the output
filter capacitor’s ground lead are as close to-
gether as possible.
Inverter Configuration
Figure 5 shows the SP6639/40/53 in a floating
ground configuration. By tying what would
normally be the output to the supply-voltage
ground, the IC’s GND pin is forced to regulated
–5V (SP6639), 3.3V (SP6640), or –3V (SP6653).
Avoid exceeding the maximum differential volt-
age of 7.5V from V+ to V
OUT
. Other negative
voltages can be generated by placing a voltage
divider across C
OUT
and connecting the tap point
to VFB in the same manner as the normal step-
down configuration.
Two AA Batteries to 5V, 3.3V or 3V
For battery-powered applications, where the sig-
nal ground does not have to correspond to the
power-supply ground, the circuit in Figure 5
generates 5V (SP6639), 3.3V (SP6640), or 3V
(SP6653) from a pair of AA batteries. Connect
the V
IN
ground point to your system’s input, and
connect the output to your system’s ground in-
put. This configuration, since the IC’s internal
power FET has V
IN
+ V
OUT
of gate drive.
Figure 5. Inverting Configuration
C
IN
100
μ
F
V
OUT
VFB
6
8
4
5
1
7
SP6639
GND
SHDN
V
+
1N5817
L = 100
μ
F
+
+
-
C
OUT
100
μ
F
-5V
V
IN
L
X
+
-
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| 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) |
| SP6641BEK-3.3 | Low Noise Evaluation Board |
| SP6641AEK-3.3 | Circular Connector; No. of Contacts:3; Series:MS27466; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:9; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:9-98 RoHS Compliant: No |
| SP6641AEK-5.0 | Low Noise Evaluation Board |
| SP6641AKEB-3.3 | Circular Connector; No. of Contacts:4; Series:MS27484; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:12; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:12-4 RoHS Compliant: No |
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| SP6641AEK-3.3 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Noise Evaluation Board |
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