 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1700 Datasheet(PDF) 9 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1700 Datasheet(HTML) 9 Page - Linear Technology |
|
|
9 / 36 page  LTC1871 9 1871fe OPERATION Figure 2. Using the SENSE Pin On the LTC1871 reset pulse to the main RS latch. Because this RS latch is reset-dominant, the power MOSFET is actively held off for the duration of an output overvoltage condition. The LTC1871 can be used either by sensing the voltage drop across the power MOSFET or by connecting the SENSE pin to a conventional shunt resistor in the source of the power MOSFET, as shown in Figure 2. Sensing the voltage across the power MOSFET maximizes converter efficiency and minimizes the component count, but limits the output voltage to the maximum rating for this pin (36V). By connecting the SENSE pin to a resistor in the source of the power MOSFET, the user is able to program output voltages significantly greater than 36V. Programming the Operating Mode For applications where maximizing the efficiency at very light loads (e.g., <100μA) is a high priority, the current in the output divider could be decreased to a few micro- amps and Burst Mode operation should be applied (i.e., the MODE/SYNC pin should be connected to ground). In applications where fixed frequency operation is more critical than low current efficiency, or where the lowest output ripple is desired, pulse-skip mode operation should be used and the MODE/SYNC pin should be connected to the INTVCC pin. This allows discontinuous conduction mode (DCM) operation down to near the limit defined by the chip’s minimum on-time (about 175ns). Below this output current level, the converter will begin to skip cycles in order to maintain output regulation. Figures 3 and 4 show the light load switching waveforms for Burst Mode and pulse-skip mode operation for the converter in Figure 1. Burst Mode Operation Burst Mode operation is selected by leaving the MODE/ SYNC pin unconnected or by connecting it to ground. In normal operation, the range on the ITHpincorrespondingto no load to full load is 0.30V to 1.2V. In Burst Mode opera- tion, if the error amplifier EA drives the ITH voltage below 0.525V, the buffered ITH input to the current comparator C1 will be clamped at 0.525V (which corresponds to 25% of maximum load current). The inductor current peak is then held at approximately 30mV divided by the power COUT VSW VSW 2a. SENSE Pin Connection for Maximum Efficiency (VSW < 36V) VOUT VIN GND L D + COUT RS 1871 F02 2b. SENSE Pin Connection for Precise Control of Peak Current or for VSW > 36V VOUT VIN GND L D + GATE GND VIN SENSE GATE GND VIN SENSE The nominal operating frequency of the LTC1871 is pro- grammed using a resistor from the FREQ pin to ground and can be controlled over a 50kHz to 1000kHz range. In addition, the internal oscillator can be synchronized to an external clock applied to the MODE/SYNC pin and can be locked to a frequency between 100% and 130% of its nominal value. When the MODE/SYNC pin is left open, it is pulled low by an internal 50k resistor and Burst Mode operation is enabled. If this pin is taken above 2V or an external clock is applied, Burst Mode operation is disabled and the IC operates in continuous mode. With no load (or an extremely light load), the controller will skip pulses in order to maintain regulation and prevent excessive output ripple. The RUN pin controls whether the IC is enabled or is in a low current shutdown state. A micropower 1.248V reference and comparator C2 allow the user to program the supply voltage at which the IC turns on and off (comparator C2 has 100mV of hysteresis for noise immunity). With the RUN pin below 1.248V, the chip is off and the input supply current is typically only 10μA. An overvoltage comparator OV senses when the FB pin exceeds the reference voltage by 6.5% and provides a |
Similar Part No. - LTC1700 |
|
Similar Description - LTC1700 |
|
|
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
