 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3772BEDDB Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3772BEDDB Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 20 page  8 LTC3772B 3772bfa OPERATIO (Refer to the Functional Diagram) Main Control Loop (Normal Operation) The LTC3772B is a constant frequency current mode step- down switching regulator controller. During normal op- eration, the external P-channel MOSFET is turned on each cycle when the oscillator sets the RS latch and turned off when the current comparator resets the latch. The peak inductor current at which the current comparator trips is controlled by the voltage on the ITH/RUN pin, which is the output of the error amplifier. The negative input to the error amplifier is the output feedback voltage VFB, which is generated by an external resistor divider connected be- tween VOUT and ground. When the load current increases, it causes a slight decrease in VFB relative to the 0.8V reference, which in turn causes the ITH/RUN voltage to increase until the average inductor current matches the new load current. The main control loop is shut down by pulling the ITH/RUN pin to ground. Releasing the ITH/RUN pin allows an internal 1 µA current source to charge up the external compensation network. When the ITH/RUN pin voltage reaches approximately 0.6V, the main control loop is enabled and the ITH/RUN voltage is pulled up by a clamp to its zero current level of approximately one diode voltage drop (0.7V). As the external compensation net- work continues to charge up, the corresponding peak inductor current level follows, allowing normal operation. The maximum peak inductor current attainable is set by a clamp on the ITH/RUN pin at 1.2V above the zero current level (approximately 1.9V). Dropout Operation When the input supply voltage decreases towards the output voltage, the rate of change of inductor current during the on cycle decreases. This reduction means that at some input-output differential, the external P-channel MOSFET will remain on for more than one oscillator cycle (start dropping off-cycles) since the inductor current has not ramped up to the threshold set by the error amplifier. Further reduction in input supply voltage will eventually cause the external P-channel MOSFET to be turned on 100%; i.e., DC. The output voltage will then be determined by the input voltage minus the voltage drop across the sense resistor, the MOSFET and the inductor. Undervoltage Lockout Protection To prevent operation of the external P-channel MOSFET with insufficient gate drive, an undervoltage lockout cir- cuit is incorporated into the LTC3772B. When the input supply voltage drops below approximately 2V, the P-channel MOSFET and all internal circuitry other than the undervoltage block itself are turned off. Input supply current in undervoltage is approximately 1 µA. Short-Circuit Protection If the output is shorted to ground, the frequency of the oscillator is folded back from 550kHz to approximately 200kHz while maintaining the same minimum on time. This lower frequency allows the inductor current to safely discharge, thereby preventing current runaway. After the short is removed, the oscillator frequency will gradually increase back to 550kHz as VFB rises through 0.3V on its way back to 0.8V. Overvoltage Protection If VFB exceeds its regulation point of 0.8V by more than 10% for any reason, such as an output short-circuit to a higher voltage, the overvoltage comparator will hold the external P-channel MOSFET off. This comparator has a typical hysteresis of 40mV. Peak Current Sense Voltage Selection and Slope Compensation (IPRG Pins) When a controller is operating below 20% duty cycle, the maximum sense voltage allowed across the external P-channel MOSFET is 138mV, 70mV or 208mV for the three respective states of the IPRG pin. |
Similar Part No. - LTC3772BEDDB |
|
Similar Description - LTC3772BEDDB |
|
|
|
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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
