 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1772BES6 Datasheet(PDF) 6 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1772BES6 Datasheet(HTML) 6 Page - Linear Technology |
|
|
6 / 16 page  LTC1772B 6 1772bfa OPERATION Main Control Loop The LTC1772B is a constant frequency current mode switching regulator. During normal operation, the external P-channel power MOSFET is turned on each cycle when the oscillator sets the RS latch (RS1) and turned off when the current comparator (ICMP) resets the latch. The peak inductor current at which ICMP resets the RS latch is controlled by the voltage on the ITH/RUN pin, which is the output of the error amplifier EAMP. An external resistive divider connected between VOUT and ground allows the EAMP to receive an output feedback voltage VFB. 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 low. Releasing ITH/RUNallowsaninternal0.5μAcurrent source to charge up the external compensation network. When the ITH/RUN pin reaches 0.35V, the main control loop is enabled with the ITH/RUN voltage then pulled up to its zero current level of approximately 0.85V. As the external compensation network continues to charge up, the corresponding output current trip level follows, allow- ing normal operation. Comparator OVP guards against transient overshoots > 7.5% by turning off the external P-channel power MOSFET and keeping it off until the fault is removed. Low Load Current Operation Under very light load current conditions, the ITH/RUN pin voltage will be very close to the zero current level of 0.85V. As the load current decreases further, an internal offset at the current comparator input will assure that the current comparator remains tripped (even at zero load current) and the regulator will start to skip cycles, as it must, in order to maintain regulation. This behavior allows the regulator to maintain constant frequency down to very light loads, resulting in less low frequency noise generation over a wide load current range. Figure 2 illustrates this result for the circuit of Figure 1 using both an LTC1772 in Burst Mode operation and an LTC1772B (non-Burst Mode operation). At an output cur- rent of 100mA, the Burst Mode operation part exhibits an output ripple of approximately 60mVP-P, whereas the non-Burst Mode operation part has an output ripple of only 20mVP-P. At lower output current levels, the improvement is even greater. This comes at a tradeoff of lower efficiency for the non-Burst Mode operation part (see Figure 1). Also notice the constant frequency operation of the LTC1772B, even at 5% of maximum output current. 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 Figure 2. Output Ripple Waveforms for the Circuit of Figure 1. VOUT Ripple for Figure 1 Circuit Using LTC1772 Burst Mode Operation. VOUT Ripple for Figure 1 Circuit Using LTC1772B Non-Burst Mode Operation. VIN = 3.6V VOUT = 2.5V IOUT = 100mA 5μs/DIV 20mVAC/DIV 1772 F02a VIN = 3.6V VOUT = 2.5V IOUT = 100mA 5μs/DIV 20mVAC/DIV 1772 F02b (Refer to Functional Diagram) |
Similar Part No. - LTC1772BES6 |
|
Similar Description - LTC1772BES6 |
|
|
|
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
