lm2742mtcx National Semiconductor Corporation, lm2742mtcx Datasheet - Page 16

• Manufacturer Part Number: lm2742mtcx
• Description: N-channel Fet Synchronous Buck Regulator Controller For Low Output Voltages
• Manufacturer: National Semiconductor Corporation

www.national.com
The circuits in Figure 7 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 out-
puts 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
FIGURE 7. 1.8V and 3.3V, 1A, 1.4MHz, Simultaneous
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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. The additional compensation components
Rc2 and Cc3 are needed for the low ESR, all ceramic output
capacitors, and the wide (3x) range of Vin.
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