数据搜索系统,热门电子元器件搜索 |
|
FAN5026MTC 数据表(PDF) 10 Page - Fairchild Semiconductor |
|
FAN5026MTC 数据表(HTML) 10 Page - Fairchild Semiconductor |
10 / 17 page 10 www.fairchildsemi.com FAN5026 Rev. 1.0.5 Figure 9. Optimal 90° Phasing for DDR2 Initialization and Soft Start Assuming EN is high, FAN5026 is initialized when VCC exceeds the rising UVLO threshold. Should VCC drop below the UVLO threshold, an internal Power-On Reset function disables the chip. The voltage at the positive input of the error amplifier is limited by the voltage at the SS pin which is charged with a 5 µA current source. Once CSS has charged to VREF (0.9V) the output voltage will be in regulation. The time it takes SS to reach 0.9V is: where T0.9 is in seconds if CSS is in µF. When SS reaches 1.5V, the Power Good outputs are enabled and hysteretic mode is allowed. The converter is forced into PWM mode during soft start. Current Processing Section The following discussion refers to Figure 10. The current through RSENSE resistor (ISNS) is sampled shortly after Q2 is turned on. That current is held, and summed with the output of the error amplifier. This effec- tively creates a current mode control loop. The resistor connected to ISNSx pin (RSENSE) sets the gain in the current feedback loop. For stable operation, the voltage induced by the current feedback at the PWM comparator input should be set to 30% of the ramp amplitude at maximum load current and line voltage. The following expression estimates the recommended value of RSENSE as a function of the maximum load current (ILOAD(MAX)) and the value of the MOSFET’s RDS(ON): RSENSE must, however, be kept higher than: Figure 10. Current Limit / Summing Circuits VDDQ VTT CLK (1) T 0.9 0.9 C SS × 5 ------------------------- = (2a) R SENSE I LOAD MAX () RDS ON () 4.1K • • 30% 0.125 V IN MAX () • • ----------------------------------------------------------------------------- 100 – = (2b) R SENSE MIN () I LOAD MAX () RDS ON () • 150 µA ----------------------------------------------------------- 100 – = LDRV PGND ISNS in + in – 2.5V ILIM det. R SENSE SS 1.5M C SS VSEN V to I Reference and Soft Start 17pF I1B = ISNS 9 I2 = 4 * ILIM 3 ILIM 0.9V R ILIM ILIM mirror S/H TO PWM COMP 4.14K 300K I1A = ISNS 0.17pF |
类似零件编号 - FAN5026MTC |
|
类似说明 - FAN5026MTC |
|
|
链接网址 |
隐私政策 |
ALLDATASHEETCN.COM |
ALLDATASHEET是否为您带来帮助? [ DONATE ] |
关于 Alldatasheet | 广告服务 | 联系我们 | 隐私政策 | 链接交换 | 制造商名单 All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |