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| 型号： | LM2575-12IN |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 4 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PDIP16 |
| 封装： | MS-001BB, PLASTIC, DIP-16 |
| 文件页数： | 12/12页 |
| 文件大小： | 195K |
| 代理商： | LM2575-12IN |
www.ti.com
Output Voltage Ripple and Transients
Feedback Connection
ON/OFF Input
Grounding
LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
SLVS569D – JANUARY 2005 – REVISED JULY 2005
APPLICATION INFORMATION (continued)
The LM2575 can operate in either continuous or discontinuous mode. With heavy load currents, the inductor
current flows continuously and the regulator operates in continuous mode. Under light load, the inductor fully
discharges and the regulator is forced into the discontinuous mode of operation. For light loads (approximately
200 mA or less), this discontinuous mode of operation is perfectly acceptable and may be desirable solely to
keep the inductor value and size small. Any buck regulator eventually will operate in discontinuous mode when
the load current is light enough.
The type of inductor chosen can have advantages and disadvantages. If high performance/quality is a concern,
then more-expensive toroid core inductors are the best choice, as the magnetic flux is contained completely
within the core, resulting in less EMI and noise in nearby sensitive circuits. Inexpensive bobbin core inductors,
however, generate more EMI as the open core will not confine the flux within the core. Multiple switching
regulators located in proximity to each other are particularly susceptible to mutual coupling of magnetic fluxes
from each other’s open cores. In these situations, closed magnetic structures (such as a toroid, pot core, or
E-core) are more appropriate.
Regardless of the type and value of inductor used, the inductor never should carry more than its rated current.
Doing so may cause the inductor to saturate, in which case the inductance quickly drops, and the inductor looks
like a low-value resistor (from the dc resistance of the windings). As a result, switching current rises dramatically
(until limited by the current-by-current limiting feature of the LM2575) and can result in overheating of the
inductor and the IC itself. Note that different types of inductors have different saturation characteristics.
As with any switching power supply, the output of the LM2575 will have a sawtooth ripple voltage at the switching
frequency. Typically about 1% of the output voltage, this ripple is due mainly to the inductor sawtooth ripple
current and the ESR of the output capacitor (see note on COUT). Furthermore, the output also may contain small
voltage spikes at the peaks of the sawtooth waveform. This is due to the fast switching of the output switch and
the parasitic inductance of COUT. These voltage spikes can be minimized through the use of low-inductance
capacitors.
There are several ways to reduce the output ripple voltage: a larger inductor, a larger COUT, or both. Another
method is to use a small LC filter (20
H and 100 F) at the output. This filter can reduce the output ripple
voltage by a factor of 10 (see Figure 2).
For fixed voltage options, FEEDBACK must be wired to VOUT. For the adjustable version, FEEDBACK must be
connected between the two programming resistors. Again, both of these resistors should be in close proximity to
the regulator, and each should be less than 100 k
to minimize noise pickup.
ON/OFF should be grounded or be a low-level TTL voltage (typically <1.6 V) for normal operation. To shut down
the LM2575 and put it in standby mode, a high-level TTL or CMOS voltage should be supplied to this pin.
ON/OFF should not be left open and safely can be pulled up to VIN with or without a pullup resistor.
The power and ground connections of the LM2575 must be low impedance to help maintain output stability. For
the 5-pin packages, both pin 3 and tab are ground, and either connection can be used as they are both part of
the same lead frame. With the 16-pin and 24-pin packages, all the ground pins (including signal and power
grounds) should be soldered directly to wide PCB copper traces to ensure low-inductance connections and good
thermal dissipation.
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相关代理商/技术参数 |
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| LM2575-12T | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Easy Switcher 1.0 A Step-Down Voltage Regulator(389.50 k) |
| LM2575-12TA5R | 制造商:FCI 制造商全称:First Components International 功能描述:1.0A Step - Down Voltage Switching Regulators 1A output current |
| LM2575-12TA5T | 制造商:FCI 制造商全称:First Components International 功能描述:1.0A Step - Down Voltage Switching Regulators 1A output current |
| LM2575-12TB5BT | 制造商:FCI 制造商全称:First Components International 功能描述:1.0A Step - Down Voltage Switching Regulators 1A output current |
| LM2575-12TB5T | 制造商:FCI 制造商全称:First Components International 功能描述:1.0A Step - Down Voltage Switching Regulators 1A output current |
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