应用笔记 959

Dual 600mA Buck Vonverter for Logic Supply and Core Supply at 1V or Less


摘要 : This application note shows how to reconfigure the MAX1970 2.5V buck converter for logic and core supplies less than 1V. Schematic is shown. Data for load, line, and cross regulation are given.

The MAX1970 was developed as a dual 600mA buck converter for input voltages as low as 2.6V and output voltages down to 1.2V. However, many current generation CPUs require core supplies of 1V or less. The MAX1970 can be reconfigured with an alternate output feedback sensing circuit to meet this requirement with no sacrifice in regulation. Internally the non-inverting input of the MAX1970's error amplifier is connected to 1.20V reference, which yields a feed back threshold of 1.20V. The circuit of Figure 1 uses the 2.5V logic supply (VOUT2) to bias the feedback divider resistor network, R2 and R3, enabling the other output voltage, VOUT1, to be set as:
VOUT1 = 1.20V (VOUT2 1.20V) (R2/R3)
As seen from the equation above, VOUT2 must be greater than 1.20V for VOUT1 to be less than 1.20V. In Figure 1, R2 equals to 2K, hence VOUT1 = 1.0V. VOUT2 is internally program to 2.5V via FBSEL2 (refer to the MAX1970 data sheet). Table 1 below shows the measured results of the line, load and cross regulation of Figure 1.

Figure 1. Typical application circuit for 3.3V ±10% input.
Figure 1.

Table 1. Measured Results of Line, Load, and Cross Regulation
   VIN
   IOUT1
   VOUT1
   IOUT2
   VOUT2
   3.0V
   10mA
   1.001V
   10mA
   2.507V
   3.0V    10mA    1.001V    600mA    2.505V
   3.0V
   600mA
   0.998V
   600mA
   2.505V
   3.0V    600mA    0.998V    10mA    2.507V
   3.3V
   10mA
   1.001V
   10mA
   2.507V
   3.3V    10mA    1.001V    600mA    2.505V
   3.3V
   600mA
   0.998V
   600mA
   2.505V
   3.3V    600mA    0.998V    10mA    2.507V
   3.6V
   10mA
   1.001V
   10mA
   2.507V
   3.6V    10mA    1.001V    600mA    2.505V
   3.6V
   600mA
   1.000V
   600mA
   2.505V
   3.6V    600mA    1.000V    10mA    2.507V

As seen from Table 1, the worst-case voltage variation for VOUT1, the 1.0V output, is less than 0.3% for all combination of input voltages from 3.0V to 3.6V, and output currents from 10mA to 600mA.

下一步
EE-Mail 订阅EE-Mail,接收关于您感兴趣的新文档的自动通知。
Download 下载,PDF格式
© , Maxim Integrated Products, Inc.
The content on this webpage is protected by copyright laws of the United States and of foreign countries. For requests to copy this content, contact us.
APP 959:
应用笔记 959,AN959, AN 959, APP959, Appnote959, Appnote 959