![]() |
Electronic Components Datasheet Search |
|
NCV887740D1R2G Datasheet(PDF) 8 Page - ON Semiconductor |
|
|
NCV887740D1R2G Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 15 page ![]() NCV8877 www.onsemi.com 8 THEORY OF OPERATION + Figure 14. Current Mode Control Schematic Oscillator Slope Compensation Q S R NCV8877 Voltage Error VEA CSA PWM Comparator Gate Drive L ISNS GDRV VOUT WAKEUP ROSC DISB DISABLE RL CO VOUT VIN RSNS ROSC VC RDAMP CDECOUPLING GND DISB The DISB pin provides an IC disable function. When a DC logic-low voltage is applied to this pin, the NCV8877 enters a low quiescent sleep mode, permitting an external signal to either shutdown the IC or disable the wakeup function. Regulation The NCV8877 is a non−synchronous boost controller designed to supply a minimum output voltage during Start−Stop vehicle operation battery voltage sags. The NCV8877 is in low quiescent current sleep mode under normal battery operation (12 V) and is enabled when the supply voltage drops below the descending threshold (7.3 V for the NCV887700). Boost operation is initiated when the supply voltage is below the regulation set point (6.8 V for the NCV887700). Once the supply voltage sag condition ends and begins to increase, the NCV8877 boost operation will cease when the supply voltage increases beyond the regulation set point. The NCV8877 low quiescent current sleep mode resumes once the supply voltage increases beyond the ascending voltage threshold (7.6 V for the NCV887700). The NCV8877 VOUT pin serves the dual purpose: (1) powering the NCV8877 and (2) providing the regulation feedback signal. The feedback network is imbedded within the IC to eliminate the constant current battery drain that would exist with the use of external voltage feedback resistors. There is no soft−start operating mode. The NCV8877 will instantly respond to a voltage sag so as to maintain normal operation of downstream loads. Once the NCV8877 is enabled, the voltage error operational transconductance amplifier supplies current to set VC to 1.1 V to minimize the feedback loop response time when the battery voltage sag goes below the regulation set point. Current Mode Control The NCV8877 incorporates a current mode control scheme, in which the PWM ramp signal is derived from the power switch current. This ramp signal is compared to the output of the error amplifier to control the on−time of the power switch. The oscillator is used as a fixed−frequency clock to ensure a constant operational frequency. The resulting control scheme features several advantages over conventional voltage mode control. First, derived directly from the inductor, the ramp signal responds immediately to line voltage changes. This eliminates the delay caused by the output filter and the error amplifier, which is commonly found in voltage mode controllers. The second benefit comes from inherent pulse−by−pulse current limiting by merely clamping the peak switching current. Finally, since current mode commands an output current rather than voltage, the filter offers only a single pole to the feedback loop. This allows for a simpler compensation. The NCV8877 also includes a slope compensation scheme in which a fixed ramp generated by the oscillator is added to the current ramp. A proper slope rate is provided to improve circuit stability without sacrificing the advantages of current mode control. Current Limit The NCV8877 features two current limit protections, peak current mode and over current latch off. When the current sense amplifier detects a voltage above the peak current limit between ISNS and GND after the current limit leading edge blanking time, the peak current limit causes the power switch to turn off for the remainder of the cycle. Set the current limit with a resistor from ISNS to GND, with R = VCL / Ilimit. |
Similar Part No. - NCV887740D1R2G |
|
Similar Description - NCV887740D1R2G |
|
|
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 |