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LTC3526L-2 Datasheet(PDF) 9 Page - Linear Technology |
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LTC3526L-2 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  LTC3526L-2/LTC3526LB-2 3526lb2fa Zero Current Comparator The zero current comparator monitors the inductor cur- rent to the output and shuts off the synchronous rectifier when this current reduces to approximately 30mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. Synchronous Rectifier To control inrush current and to prevent the inductor current from running away when VOUT is close to VIN, the P-channel MOSFET synchronous rectifier is only enabled when VOUT > (VIN + 0.24V). Anti-Ringing Control The anti-ring circuit connects a resistor across the in- ductor to prevent high frequency ringing on the SW pin during discontinuous current mode operation. Although the ringing of the resonant circuit formed by L and CSW (capacitance on SW pin) is low energy, it can cause EMI radiation. Output Disconnect The LTC3526L-2/LTC3526LB-2 are designed to allow true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows for VOUT to go to zero volts during shutdown, drawing no cur- rent from the input source. It also allows for inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, there must not be an external Schottky diode connected between SW and VOUT. The output disconnect feature also allows VOUT to be pulled high, without any reverse current into a battery connected to VIN. Thermal Shutdown If the die temperature exceeds 160°C, the LTC3526L-2/ LTC3526LB-2 will go into thermal shutdown. All switches will be off and the soft-start capacitor will be discharged. The device will be enabled again when the die temperature drops by about 15°C. Burst Mode OPERATION The LTC3526L-2 will enter Burst Mode operation at light load current and return to fixed frequency PWM mode when the load increases. Refer to the Typical Performance Characteristics to see the output load Burst Mode thresh- old current vs VIN. The load current at which Burst Mode operation is entered can be changed by adjusting the inductor value. Raising the inductor value will lower the load current at which Burst Mode operation is entered. In Burst Mode operation, the LTC3526L-2 still switches at a fixed frequency of 2MHz, using the same error amplifier and loop compensation for peak current mode control. This control method eliminates any output transient when switching between modes. In Burst Mode opera- tion, energy is delivered to the output until it reaches the nominal regulation value, then the LTC3526L-2 transi- tions to sleep mode where the outputs are off and the LTC3526L-2consumesonly9µAofquiescentcurrentfrom VOUT. When the output voltage droops slightly, switching resumes. This maximizes efficiency at very light loads by minimizing switching and quiescent losses. Burst Mode output voltage ripple, which is typically 1% peak-to-peak, can be reduced by using more output capacitance (10µF or greater), or with a small capacitor (10pF to 50pF) con- nected between VOUT and FB. As the load current increases, the LTC3526L-2 will au- tomatically leave Burst Mode operation. Note that larger output capacitor values may cause this transition to oc- cur at lighter loads. Once the LTC3526L-2 has left Burst Mode operation and returned to normal operation, it will remain there until the output load is reduced below the burst threshold current. Burst Mode operation is inhibited during start-up and soft- start and until VOUT is at least 0.24V greater than VIN. The LTC3526LB-2 features continuous PWM operation at 2MHz. At very light loads, the LTC3526LB-2 will exhibit pulse-skipping operation. (Refer to Block Diagram) operaTion |
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Similar Description - LTC3526L-2 |
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