LTC3546EUFDPBF datasheet(13/28 Pages) LINER

13 / 28 page

LTC3546

3546fb

OPERATION

The output capacitor and the inductor supply the power

to the load until ITH exceeds 0.31V, turning on the switch

and the main control loop which starts another cycle.

The Burst Mode peak inductor current can be set externally

via the BMC pin. When this pin is set somewhere between

0V to 0.6V, the voltage on this pin controls the Burst Mode

clamp level. When the BMC pin is pulled to VIN, an internal

Burst Mode clamp level is used.

For lower output voltage ripple at low currents, pulse-

skipping mode can be used. In this mode, the LTC3546

continues to switch at constant frequency down to very low

currents, where it will eventually begin skipping pulses.

Finally, in forced continuous mode, the inductor current

is constantly cycled which creates a ﬁxed output voltage

ripple at all output current levels. This feature is desirable in

telecommunications since the noise is a constant frequency

and is thus easy to ﬁlter out. Another advantage of this mode

is that the regulator is capable of both sourcing current into

a load and sinking some current from the output. In forced

continuous operation, an overvoltage comparator monitors

the VFB pin and decreases the current limit whenever an

overvoltage condition is detected (VFB > 0.63V).

The SYNC/MODE pin selects what mode the LTC3546 is in.

The SYNC/MODE pin sets the mode for both regulators.

Dropout Operation

When the input supply voltage decreases toward the

output voltage, the duty cycle increases to 100% which

is the dropout condition. In the dropout condition, the

PMOS switch is turned on continuously with the output

voltage being equal to the input voltage minus the volt-

age drops across the internal P-channel MOSFETs and

inductors.

Low Supply Operation

The LTC3546 incorporates an undervoltage lockout circuit

which shuts down the part when the input voltage drops

below about 2.14V to prevent unstable operation.

LTC3546EUFDPBF Datasheet(PDF) 13 Page - Linear Technology