Datasheet LTC3526L, LTC3526LB (Analog Devices) - 9

LTC3526L/LTC3526LB operAtion
(Refer to Block Diagram)
when this current reduces to approximately 30mA. This
Burst Mode OPERATION
prevents the inductor current from reversing in polarity, The LTC3526L will enter Burst Mode operation at light load improving efficiency at light loads. current and return to fixed frequency PWM mode when the
Synchronous Rectifier
load increases. Refer to the Typical Performance Character- istics to see the output load Burst Mode threshold current To control inrush current and to prevent the inductor vs VIN. The load current at which Burst Mode operation is current from running away when VOUT is close to VIN, the entered can be changed by adjusting the inductor value. P-channel MOSFET synchronous rectifier is only enabled Raising the inductor value will lower the load current at when VOUT > (VIN + 0.24V). which Burst Mode operation is entered.
Anti-Ringing Control
In Burst Mode operation, the LTC3526L still switches at a fixed frequency of 1MHz, using the same error amplifier The anti-ring circuit connects a resistor across the in- and loop compensation for peak current mode control. ductor to prevent high frequency ringing on the SW pin This control method eliminates any output transient during discontinuous current mode operation. Although when switching between modes. In Burst Mode opera- the ringing of the resonant circuit formed by L and CSW tion, energy is delivered to the output until it reaches the (capacitance on SW pin) is low energy, it can cause EMI nominal regulation value, then the LTC3526L transitions radiation. to sleep mode where the outputs are off and the LTC3526L consumes only 9µA of quiescent current from V
Output Disconnect
OUT. When the output voltage droops slightly, switching resumes. The LTC3526L/LTC3526LB are designed to al ow true output This maximizes efficiency at very light loads by minimizing disconnect by eliminating body diode conduction of the switching and quiescent losses. Burst Mode output voltage internal P-channel MOSFET rectifier. This allows for VOUT ripple, which is typically 1% peak-to-peak, can be reduced to go to zero volts during shutdown, drawing no current by using more output capacitance (10µF or greater), or from the input source. It also allows for inrush current with a small capacitor (10pF to 50pF) connected between limiting at turn-on, minimizing surge currents seen by the VOUT and FB. input supply. Note that to obtain the advantages of output As the load current increases, the LTC3526L will auto- disconnect, there must not be an external Schottky diode matically leave Burst Mode operation. Note that larger connected between SW and VOUT. The output disconnect output capacitor values may cause this transition to feature also allows VOUT to be pulled high, without any occur at lighter loads. Once the LTC3526L has left Burst reverse current into a battery connected to VIN. Mode operation and returned to normal operation, it will
Thermal Shutdown
remain there until the output load is reduced below the burst threshold current. If the die temperature exceeds 160°C, the LTC3526L/LT- C3526LB will go into thermal shutdown. All switches will Burst Mode operation is inhibited during start-up and soft- be off and the soft-start capacitor will be discharged. The start and until VOUT is at least 0.24V greater than VIN. device will be enabled again when the die temperature The LTC3526LB features continuous PWM operation at drops by about 15°C. 1MHz. At very light loads, the LTC3526LB will exhibit pulse-skip operation. 3526lfc Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts