April 2012 : LT Journal of Analog Innovation | 37
design ideas
Designing with the LTM8047 and LTM8048 is easy. Figure 1 shows a complete LTM8047-bad isolated power supply , requiring only the addition of capaci-tors for input , output , and biasing , and a resistor to t the output voltage. The LTM8048 requires only one more com-ponent: a resistor to t the voltage of the LDO output , as shown in Figure 2.A s is the ca with most flyback convert-ers , the output voltage can be above or below the input , accommodating a wide range of operating conditions. And , as is nature of flyback converters , the amount of current that the LTM8047 and LTM8048 can deliver depends on the input voltage. Figure 3 shows the load capability of a typical LTM8047 at 2.5V , 3.3V and 5V outputs. The LTM8048 features the same load capability. The linear post regulator integrated into the LTM8048 is a high perfor-mance 300m A device , boasting a low dropout of less than 450m V at room temp , full load. A s shown in Figure 4, the output noi and ripple of the post
µModule Converters Take the Hassle Out of Designing Isolated Power Supplies
David Ng
Sometimes a system needs a little bit of isolated power, but designing an isolated power supply is rarely easy. The nature of isolated supplies makes them complicated and touchy, resulting in late nights and long weekends spent on design and debug. The LTM8047 and LTM8048 µModule converters take the hassle out of designing isolated power supplies, placing a flyback regulator in a compact 9mm × 11.25mm × 4.92mm BGA RoHS compliant package. The controller, power switching and rectification elements, as well as transformer and isolated feedback circuitry are all integrated. Both parts
operate from 3.1V to 32V inputs and produce over 1W of isolated power. The LTM8048 is identical to the LTM8047, but adds an integrated 300mA linear post regulator.
V V OUT 5V 280mA (15V IN )Figure 1. The LTM8047 only requires four additional components to implement an isolated 5V power supply that accepts an 3.1V–29V input.
杜心五
LTspice IV
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V V OUT25V
Figure 2. The LTM8048 is the LTM8047 with the addition of an LDO post regulator.
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V IN (V)
M A X I M U M V O U T 1 L O A D (m A )
500
450400200300100
250350150Figure 3. Maximum load capability of the LTM8047 and LTM8048 depends on the input voltage.Figure 4. The output noi of the LTM8048 post regulator is less than 1mV .
1µs/DIV
V OUT 500µV/DIV (AC-COUPLED)内外交困
日照旅游攻略38 | April 2012 :
LT Journal of Analog Innovation
减肥食谱表格21天
regulator is less than 1m V . The measurements were taken using a 150MH z HP-461A differential amplifier.The LTM8047 and LTM8048 both integrate a trans-former that is rated for 725VDC isolation. Every isolated µModule converter is factory tested for 100% reliabil-ity , with 725V applied in one direction for one cond , followed by the rever voltage for one cond.
For flexibility , there is no circuitry connected between the primary and condary , so if a safety capacitor or other ele-ments are required for a system , they can be added. This flex-ibility allows various configurations of the output. A s shown in Figure 5, for example , two LTM8047s can be combined to deliver individually regulated positive and negative outputs.
unit2CONCLUSION
The LTM8047 and LTM8048 are two flyback µModule con-verters that can be ud to produce more than 1W of isolated power from a small , easy-to-u , 9mm × 11.25mm × 4.92mm BGA package. The LTM8048 is nearly identical to the LTM8047, but with an integrated high performance post regulator. n
The LTM8047 and LTM8048 are two flyback µModule converters that can be ud to produce more than 1W of isolated power from a small, easy-to-u, 9mm × 11.25mm × 4.92mm BGA package.
IN )
作者用英语怎么说V IN )
Figure 5. U two LTM8047 converters to produce ±5V from a 3.5V–31V input.
平衡表CONCLUSION
The LTC3226 enables amless super-capacitor-bad power backup solu-tions by integrating the functions of a charge pump , an LDO and an ideal diode controller in a compact low pro-file 3mm × 3mm 16-pin QFN package. Its low 50µA quiescent current and small footprint make it particularly suitable for battery powered applications , as well as 3.3V systems that require protec-tion from short power interruptions. n
One of the limitations of supercapacitors is low cell voltage , typically 2.7V , requir-ing a ries connection of two cells for 5V applications. Since supercapacitors have more lf-discharge due to leak-age than most batteries , they require cell balancing to prevent overcharging of one of the ries capacitors. The LTC3226 charge pump is equipped with an active balancer circuit , thus eliminating the need for external balancing resistors. However , since this balancer has limited source and sink capability , the charge pump is equipped with voltage clamp circuitry which constantly monitors cell
voltages during the charging process and prevents the cells from overcharging. A fast comparator detects when the input voltage falls unacceptably low and enables the LDO which powers the load from the supercapacitors. This power-fail threshold is programmed by an external resistor divider via the PFI pin. The output of the PFI compara-tor drives an open-drain output on the PFO pin to indicat
e the status of the input source. An external resistor divider to the LDO_FB pin ts the LDO output voltage.
LTC 3226, from page 38
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