 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1147-3.3 Datasheet(PDF) 6 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1147-3.3 Datasheet(HTML) 6 Page - Linear Technology |
|
|
6 / 16 page  6 LTC1147-3.3 LTC1147-5/LTC1147L sn1147 1147fds (Pin 3) to increase the current comparator threshold, thus tracking the load current. The sequence of events for Burst Mode operation is very similar to continuous operation with the cycle interrupted by the voltage comparator. When the output voltage is at or above the desired regulated value, the P-channel MOS- FET is held off by comparator V and the timing capacitor continues to discharge below VTH1. When the timing capacitor discharges past VTH2, voltage comparator S trips, causing the internal sleep line to go low. The circuit now enters sleep mode with the power MOS- FET turned off. In sleep mode, a majority of the circuitry is turned off, dropping the quiescent current from 1.6mA to 160 µA. The load current is now being supplied from the output capacitor. When the output voltage has dropped by the amount of hysteresis in comparator V, the P-channel MOSFET is again turned on and this process repeats. To avoid the operation of the current loop interfering with Burst Mode operation, a built-in offset VOS is incorporated in the gain stage. This prevents the current comparator threshold from increasing until the output voltage has dropped below a minimum threshold. Using constant off-time architecture, the operating fre- quency is a function of the input voltage. To minimize the frequency variation as dropout is approached, the off-time controller increases the discharge current as VIN drops below VOUT + 1.5V. In dropout the P-channel MOSFET is turned on continuously (100% duty cycle), providing low dropout operation with VOUT ≈ VIN. The LTC1147 series uses a current mode, constant off- time architecture to switch an external P-channel power MOSFET. Operating frequency is set by an external capaci- tor at CT (Pin 2). The output voltage is sensed by an internal voltage divider connected to SENSE– (Pin 4). A voltage comparator V, and a gain block G, compare the divided output voltage with a reference voltage of 1.25V. To optimize efficiency, the LTC1147 series automatically switchs between two modes of operation, burst and continuous. The voltage compara- tor is the primary control element when the device is in Burst Mode operation, while the gain block controls the output voltage in continuous mode. During the switch “on” cycle in continuous mode, current comparator C monitors the voltage between Pins 4 and 5 connected across an external shunt in series with the inductor. When the voltage across the shunt reaches its threshold value, the PDRIVE output is switched to VIN, turning off the P-channel MOSFET. The timing capacitor connected to Pin 2 is now allowed to discharge at a rate determined by the off-time controller. The discharge cur- rent is made proportional to the output voltage (measured by Pin 4) to model the inductor current, which decays at a rate which is also proportional to the output voltage. When the voltage on the timing capacitor has discharged past VTH1, comparator T trips, setting the flip-flop. This causes the PDRIVE output to go low turning the P-channel MOSFET back on. The cycle then repeats. As the load current increases, the output voltage de- creases slightly. This causes the output of the gain stage LTC1147L Adjustable Applications When an output voltage other than 3.3V or 5V is required, the LTC1147L adjustable version is used with an external resistive divider from VOUT to VFB (Pin 6) (see Figure 7). The regulated voltage is determined by: VOUT = 1.25 R2 R1 ) ) 1+ To prevent stray pickup a 100pF capacitor is suggested across R1 located close to the LTC1147L. For Figure 1 applications with VOUT below 2V, or when RSENSE is moved to ground, the current sense comparator inputs operate near ground. When the current comparator is operated at less than 2V common mode, the off-time increases approximately 40%, requiring the use of a smaller timing capacitor CT. APPLICATIO S I FOR ATIO OPERATIO (Refer to Functional Diagram) |
Similar Part No. - LTC1147-3.3_15 |
|
Similar Description - LTC1147-3.3_15 |
|
|
|
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
