Electronic Components Datasheet Search |
|
RT8525D Datasheet(PDF) 8 Page - Richtek Technology Corporation |
|
|
RT8525D Datasheet(HTML) 8 Page - Richtek Technology Corporation |
8 / 12 page 8 RT8525D www.richtek.com DS8525D-00 June 2012 © Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Applications Information The RT8525D is a wide input operating voltage range step up controller. High voltage output and large output current are feasible by using an external N-MOSFET. The protection functions include output over voltage, output under voltage, over temperature and current limiting protection. Boost Output Voltage Setting The regulated output voltage is set by an external resistor divider according to the following equation : ⎛⎞ ×⎜⎟ ⎝⎠ FB1 OUT FB FB FB2 R V = V 1+ , where V = 1.25V (typ.) R The recommended value of RFB2 should be at least 1k Ω for saving sacrificing. Moreover, placing the resistor divider as close as possible to the chip can reduce noise sensitivity. Boost Switching Frequency The RT8525D boost driver switching frequency is able to be adjusted by a resistor RSW ranging from 18k Ω to 220k Ω. The following figure illustrates the corresponding switching frequency within the resistor range. Figure 1. Boost Switching Frequency Switching Frequency vs. RSW 0 100 200 300 400 500 600 0 50 100 150 200 250 RSW (k ) Ω Boost Loop Compensation The voltage feedback loop can be compensated by an external compensation network consisted of RC, CC1 and CC2. Choose RC to set high frequency gain for fast transient response. Select CC1 and CC2 to set the zero and pole to maintain loop stability. A typical compensation for the RT8525D is choosing 3k Ω for RC and 27nF for CC1. Soft-Start The soft-start of the RT8525D can be achieved by connecting a capacitor from the SS pin to GND. The built- in soft-start circuit reduces the start-up current spike and output voltage overshoot. The external capacitor charged by an internal 4 μA constant charging current determines the soft-start time. The SS pin limits the rising rate of the COMP pin voltage and thereby limits the peak switch current. The soft-start interval is set by the soft-start capacitor according to the following equation : ≅× × 5 SS SS tC 5 10 A typical value for the soft-start capacitor is 0.33 μF. The soft-start capacitor is discharged when EN voltage falls below its threshold after shutdown delay or UVLO occurs. Slope Compensation and Current Limiting A slope compensation is applied to avoid sub-harmonic oscillation in current-mode control. The slope compensation voltage is generated by the internal ramp current flow through a slope compensation resistor RSLP. The inductor current is sensed by the sensing resistor RS. Both of them are added and presented on the ISW pin. The internal ramp current is rising linearly form zero at the beginning of each switching cycle to 50 μA in maximum on-time of each cycle. The slope compensation resistor RSLP can be calculated by the following equation : where RS is current sensing resistor, L is inductor value, and fSW is boost switching frequency. The current flow through inductor during charging period is detected by a sensing resistor RS. Besides, the slope compensation voltage also attributes magnitude to ISW. As the voltage at the ISW pin is over 0.4V, the DRV will be pulled low and turn off the external N-MOSFET. So that the inductor will be forced to leave charging stage and enter discharging stage to prevent over current. The current limiting can be calculated by the following equation: () −× ×× × OUT IN S SLP SW VV R R > 2L 50μ f |
Similar Part No. - RT8525D |
|
Similar Description - RT8525D |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |