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LTC1265-3.3 Datasheet(PDF) 5 Page - Linear Technology |
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LTC1265-3.3 Datasheet(HTML) 5 Page - Linear Technology |
5 / 16 page 5 LTC1265/LTC1265-3.3/LTC1265-5 (Pin 9 connection shown for LTC1265-3.3 and LTC1265-5; change create LTC1265) The LTC1265 uses a constant off-time architecture to switch its internal P-channel power MOSFET. The off time is set by an external timing capacitor at CT (Pin 5). The operating frequency is then determined by the off time and the difference between VIN and VOUT. The output voltage is set by an internal resistive divider (LTC1265-3.3 and LTC1265-5) connected to SENSE– (Pin 7) or an external divider returned to VFB (Pin 9 for LTC1265). 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 LTC1265 automatically switches between continuous and Burst Mode operation. The volt- age comparator is the primary control element when the device is in Burst Mode operation, while the gain block controls the output voltage in continuous mode. When the load is heavy, the LTC1265 is in continuous operation. During the switch ON time, current comparator C monitors the voltage between Pins 7 and 8 connected across an external shunt in series with the inductor. When the voltage across the shunt reaches the comparator’s threshold value, its output signal will change state, setting the flip flop and turning the internal P-channel MOSFET off. The timing capacitor connected to Pin 5 is now allowed to discharge at a rate determined by the off-time controller. When the voltage on the timing capacitor has discharged past VTH1, comparator T trips, sets the flip flop and causes the switch to turn on. Also, the timing capacitor is re- charged. The inductor current will again ramp up until the current comparator C trips. The cycle then repeats. When the load current increases, the output voltage de- creases slightly. This causes the output of the gain stage (Pin 6) to increase the current comparator threshold, thus tracking the load current. When the load is relatively light, the LTC1265 automati- cally goes into Burst Mode operation. The current loop is interrupted when the output voltage exceeds the desired regulated value. The hysteretic voltage comparator V trips when VOUT is above the desired output voltage, shutting off the switch and causing the capacitor to discharge. This (Refer to Functional Diagram) PWR VIN SENSE+ SENSE– 5pF 100k LBIN SGND ITH VIN SENSE– VFB VTH1 VTH2 SLEEP PGND SW 13k VOS VFB ADJUSTABLE VERSION 25mV TO 150mV OFF-TIME CONTROL SHDN LB0UT CT V C R S Q – + T S A3 REFERENCE G 1265 FD 5 2 3 6 11 4 10 9 7 8 14 12 1, 13 FU CTIO AL DIAGRA OPERATIO |
Similar Part No. - LTC1265-3.3 |
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Similar Description - LTC1265-3.3 |
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