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LTC1149-3.3 Datasheet(PDF) 5 Page - Linear Technology |
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LTC1149-3.3 Datasheet(HTML) 5 Page - Linear Technology |
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5 / 20 page  5 LTC1149 LTC1149-3.3/LTC1149-5 PI FU CTIO S PGATE (Pin 1): Level-Shifted Gate Drive Signal for Top P-Channel MOSFET. The voltage swing at Pin 1 is from VIN to VIN – VCC. VIN (Pin 2): Main Supply Input Pin. VCC (Pin 3): Output Pin of Low Dropout 10V Regulator. Pin 3 is not protected against DC short circuits. PDRIVE (Pin 4): High Current Gate Drive for Top P-Channel MOSFET. The voltage swing at Pin 4 is from VCC to ground. VCC (Pin 5): Regulated 10V Input for Driver and Control Supplies. Must be closely decoupled to power ground. CT (Pin 6): External capacitor CT from Pin 6 to ground sets the operating frequency. (The frequency is also dependent on the ratio VOUT/VIN.) ITH (Pin 7): Gain Amplifier Decoupling Point. The current comparator threshold increases with the Pin 7 voltage. SENSE– (Pin 8): Connects to internal resistive divider which sets the output voltage in LTC1149-3.3 and LTC1149-5 versions. Pin 8 is also the (–) input for the current comparator. SENSE+ (Pin 9): The (+) Input for the Current Comparator. A built-in offset between Pins 8 and 9 in conjunction with RSENSE sets the current trip threshold. SHDN1/VFB (Pin 10): In fixed output voltage versions, Pin 10 serves as a shutdown pin for the control circuitry only (VCC is not affected). Taking Pin 10 of the LTC1149-3.3 or LTC1149-5 high holds both MOSFETs off. Must be at ground potential for normal operation. For the LTC1149 adjustable version, Pin 10 serves as the feedback pin from an external resistive divider used to set the output voltage. SGND (Pin 11): Small-Signal Ground. Must be routed separately from other grounds to the (–) terminal of COUT. PGND (Pin 12): Driver Power Ground. Connects to source of N-channel MOSFET and the (–) terminal of CIN. NGATE (Pin 13): High Current Drive for Bottom N-channel MOSFET. The voltage swing at Pin 13 is from ground to VCC. RGND (Pin 14): Low Dropout Regulator Ground. Con- nects to power ground. SHDN2 (Pin 15): Master Shutdown Pin. Taking Pin 15 high shuts down VCC and all control circuitry; requires a logic signal with tr, tf < 1µs. CAP (Pin 16): Charge Compensation Pin. A capacitor from Pin 16 to VCC provides the charge required by the P-drive level-shift capacitor during supply transitions. The Pin 16 capacitor must be larger than the Pin 4 capacitor. OPERATIO (Refer to Functional Diagram) The LTC1149 series uses a current mode, constant off- time architecture to synchronously switch an external pair of complementary power MOSFETs. Operating frequency is set by an external capacitor at the timing capacitor, Pin 6. The output voltage is sensed either by an internal voltage divider connected to SENSE–, Pin 8 (LTC1149-3.3 and LTC1149-5) or an external divider returned to VFB Pin 10 (LTC1149). 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 LTC1149 series automatically switches between two modes of operation, burst and continuous. The voltage comparator is the primary control element for Burst Mode operation, while the gain block controls the output voltage in continu- ous mode. A low dropout 10V regulator provides the operating volt- age VCC for the MOSFET drivers and control circuitry. The driver outputs at Pins 4 and 13 are referenced to ground, which fulfills the N-channel MOSFET gate drive require- ment. The P-channel gate drive at Pin 1 must be refer- enced to the main supply input VIN, which is accomplished by level-shifting the Pin 4 signal via an internal 500k resistor and external capacitor. During the switch “ON” cycle in continuous mode, current comparator C monitors the voltage between Pins 8 and 9 connected across an external shunt in series with the inductor. When the voltage across the shunt reaches its threshold value, the PGATE output is switched to VIN, turning off the P-channel MOSFET. The timing capacitor connected to Pin 6 is now allowed to discharge at a rate determined by the off-time controller. The discharge |
Similar Part No. - LTC1149-3.3_15 |
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Similar Description - LTC1149-3.3_15 |
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