LTC3526L datasheet(9/16 Pages) LINER

9 / 16 page

LTC3526/LTC3526B

3526bfd

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-ringing control connects a resistor across the

inductor 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 LTC3526/LTC3526B 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 current

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 the SW pin and VOUT. The output dis-

connect feature also allows VOUTtobepulledhigh,without

any reverse current into a battery connected to VIN.

Thermal Shutdown

If the die temperature exceeds 160°C, the LTC3526/

LTC3526B 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 LTC3526 will automatically enter Burst Mode opera-

tion at light load 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 LTC3526 still switches at a

fixed frequency of 1MHz, 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 LTC3526 transitions to

sleep mode where the outputs are off and the LTC3526

consumes only 9µA of quiescent current from VOUT. When

the output voltage droops slightly, switching resumes.

Thismaximizesefficiencyatverylightloadsbyminimizing

switchingandquiescentlosses.BurstModeoutputvoltage

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) connected between

VOUT and FB.

As the load current increases, the LTC3526 will automati-

cally leave Burst Mode operation. Note that larger output

capacitorvaluesmaycausethistransitiontooccuratlighter

loads.OncetheLTC3526hasleftBurstModeoperationand

returned to normal operation, it will remain there until the

output load is reduced below the burst threshold.

Burst Mode operation is inhibited during start-up and soft-

start and until VOUT is at least 0.24V greater than VIN.

The LTC3526B features continuous PWM operation at

1MHz. At very light loads, the LTC3526B will exhibit

pulse-skip operation.

(Refer to Block Diagram)

operaTion

LTC3526L Datasheet(PDF) 9 Page - Linear Technology

LTC3526L Datasheet(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL