Electronic Components Datasheet Search |
|
NCV8856 Datasheet(PDF) 9 Page - ON Semiconductor |
|
NCV8856 Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 19 page NCV8856 www.onsemi.com 9 DETAILED OPERATING DESCRIPTION General The NCV8856 is a synchronous buck controller with internal 1.5 A gate drivers designed to drive NMOS FETs. The internal gate drivers simplify design, improve performance and efficiency and minimize board area. The controller uses an 800 mV, 2.0% reference, allowing for a wide range of precise output voltage programmability. The NCV8856 also provides a programmable fixed frequency range of 170 kHz to 500 kHz, allowing more design flexibility in compromising efficiency versus components’ size and cost. This frequency is conveniently set with an external resistor to ground. An external clock signal can also be used to synchronize the NCV8856 to a higher operating frequency during operation. To protect against possible damage of external power−stage components, excessive inrush of current during start−up is prevented by an internal soft−start, and inductor current is limited via average current limiting (ACL) and cycle−by−cycle overcurrent protection (OCP). Thermal shutdown (TSD) is also implemented to protect the device from overheating. Average Current Mode Control The NCV8856 employs an average current mode control (ACMC) architecture to regulate the output voltage. ACMC uses two loops, as seen in Figure 19. Through the current error amplifier (CEA), the inner current loop monitors the inductor current with the unity gain current sense amplifier (CSA). The current loop responds to input voltage changes, affecting the line transient response. Using the voltage error amplifier (VEA), the outer voltage loop monitors the output voltage, responding to output load changes, affecting the load transient response. Feedback resistors in the voltage loop select the output voltage. L CSA VEA CEA C PWM and Gate Drivers Inner Current Loop Outer Voltage Loop Gain=1 Figure 19. ACMC Loops VSW RS RL VOUT VREF Unlike voltage mode control (VMC) of buck regulators, which almost always require the extra components of a Type−III compensation network for adequate transient response, ACMC buck regulators use Type−II compensation. This greatly simplifies the compensator design and optimization process, while offering much faster transient response than a Type−I compensation network. Additionally, the two−loop system separates the effects of output components between the two loops, further simplifying the compensation process. Type−II compensation places a zero and two poles in each of the error loops to offset the effects of the inherent open−loop response. This compensation requires a resistor and two capacitors in the feedback loop for each of the error amplifiers, shown as complex impedances in Figure 19. An input resistor from the CSA to the CEA sets the gain of the CEA. The voltage loop also has a pair of feedback resistors from VOUT to set the output voltage and gain of the VEA. Enable The enable input (EN) is a TTL−compatible input used to activate the internal LDO. The NCV8856 is disabled when the EN pin is pulled below the enable input logic low threshold voltage, causing a normal shutdown to occur, putting the part into a low quiescent current sleep mode. Once the device has been disabled it must remain disabled for the minimum disable time (20 ms) or abnormal startup behavior may be observed after enable is asserted. When the EN pin is pulled above the enable input logic high threshold voltage, the part is enabled, the LDO output is brought up and then the internal soft−start begins. |
Similar Part No. - NCV8856 |
|
Similar Description - NCV8856 |
|
|
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 |