 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1433C Datasheet(PDF) 7 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1433C Datasheet(HTML) 7 Page - Linear Technology |
|
|
7 / 20 page  7 LTC1433/LTC1434 OPERATION (Refer to Functional Diagram) Having only the small MOSFET on with low load current reduces switching and gate charge losses, hence boosting efficiency. For the device to go into low current mode, two conditions must be satisfied: the peak current of the inductor should not exceed 260mA and the voltage at the ITH pin should not exceed 0.6V. When either one of the conditions is exceeded, the big MOSFET will be turned on at the next clock cycle. Dropout Operation When the input supply voltage decreases toward the output voltage, the rate of change of inductor current during the on cycle decreases. This reduction means that the P-channel MOSFETs will remain on for more than one oscillator cycle since the ICOMP is not tripped. Further reduction in input supply voltage will eventually cause the 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 MOSFETs. Typically under dropout, both the power MOSFETs are on since the voltage on the ITH pin is greater than 0.6V. Frequency Synchronization A phase-locked loop (PLL) is available on the LTC1434 to allow the oscillator to be synchronized to an external source connected to the PLLIN pin. The output of the phase detector at the PLL LPF pin is also the control input of the oscillator, which operates over a 0V to 2.4V range corresponding to – 30% to + 30% in the oscillator’s center frequency. When locked, the PLL aligns the turn-on of the MOSFETs to the rising edge of the synchronizing signal. When the PLLIN is left open, PLL LPF goes low, forcing the oscillator to minimum frequency. Power-On Reset The POR pin is an open-drain output which pulls low when the regulator is out of regulation. When the output voltage rises to within 5% of regulation, a timer is started which releases POR after 216 (65536) oscillator cycles. In shut- down the POR output is pulled low. Short-Circuit Protection When the output is shorted to ground, the frequency of the oscillator will be reduced to about 1/4.5 of its designed rate. This low frequency allows the inductor current to discharge, thereby preventing runaway. The oscillator’s frequency will gradually increase to its designed rate when the output voltage increases above 0.65V. APPLICATIONS INFORMATION The basic LTC1434 application circuit is shown in Figure 1. External component selection is driven by the load requirement and begins with the selection of COSC and L. Next, the Schottky diode D1 is selected followed by CIN and COUT. COSC Selection for Operating Frequency The LTC1433/LTC1434 use a constant frequency archi- tecture with the frequency determined by an external oscillator capacitor COSC. During the on-time, COSC is charged by a fixed current plus an additional current which is proportional to the output voltage of the phase detector (VPLL LPF on LTC1434). When the voltage on the COSC capacitor reaches 1.19V, it is reset to ground. The process then repeats. The value of COSC is calculated from the desired operating frequency. Assume the phase-locked loop has no external oscillator input, i.e. VPLL LPF = 0V. CpF Frequency kHz OSC ()= () 137 10 11 4 . – A graph for selecting COSC vs Frequency is given in Figure 2. For the LTC1433, the expression above is also appli- cable since its oscillator is internally set up to run at a condition equal to VPLL LPF = 0V. Therefore when using the graph for determining the capacitance value for the oscil- lator frequency, the VPLL LPF = 0V curve should be used for LTC1433. |
Similar Part No. - LTC1433C |
|
Similar Description - LTC1433C |
|
|
|
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
