LM2727 datasheet(16/22 Pages) NSC

Part #	LM2727

Description	N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages

PDF	22 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

Logo

16 / 22 page

Example Circuits (Continued)

The circuits in Figure 6 are intended for ADSL applications,

where the high switching frequency keeps noise out of the

data transmission range. In this design, the 1.8 and 3.3V

outputs come up simultaneously by using the same softstart

capacitor. Because two current sources now charge the

same capacitor, the capacitance must be doubled to achieve

the same softstart time. (Here, 40nF is used to achieve a

5ms softstart time.) A common softstart capacitor means

that, should one circuit enter current limit, the other circuit

will also enter current limit. In addition, if both circuits are

built with the LM2727, a UVP or OVP fault on one circuit will

cause both circuits to latch off. The additional compensation

components Rc2 and Cc3 are needed for the low ESR, all

ceramic output capacitors, and the wide (3x) range of Vin.

20049407

FIGURE 6. 1.8V and 3.3V, 1A, 1.4MHz, Simultaneous

LM2727 Datasheet(PDF) 16 Page - National Semiconductor (TI)