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LTC3448

3448f

TYPICAL PERFOR A CE CHARACTERISTICS

(From Figure 1a Except for the Resistive Divider Resistor Values)

Load Step

External Mode Control (Constant

1mA Load)

PI FU CTIO S

VFB (Pin 1): Feedback Pin. This pin receives the feedback

voltage from an external resistive divider across the

output.

VOUT (Pin 2): Output Pin. This pin connects to an external

resistor divider and the linear regulator output. Connect

externally to the inductor and the output capacitor. The

internal linear regulator will supply current up to the

ILDO(OFF) current. Load currents above that are supplied by

the buck regulator. Internal circuitry automatically enables

the buck switching regulator at load currents higher than

the ILDO(OFF). The minimum required capacitance on this

pin is 2

µF.

MODE (Pin 3): Linear Regulator Control. Grounding this

pin turns off the linear regulator. Setting this pin to VIN

turns on the linear regulator regardless of the load current.

Tying this pin midrange (i.e., to VOUT) will place the linear

regulator in auto mode, where turn on/off is a function of

the load current. In applications where MODE is externally

driven high or low, this pin should be held low for 50

µs

after the RUN pin is pulled high.

VIN (Pin 4): Main Supply Pin. This pin must be closely

decoupled to GND with a 2.2

µF or greater ceramic

capacitor.

SW (Pin 5): Switch Node Connection to Inductor. This pin

connects to the drains of the internal main and synchro-

nous power MOSFET switches.

FREQ (Pin 6): Frequency Select. Switching frequency is

set to 1.5MHz when FREQ = 0V and to 2.25MHz when

FREQ = VIN. Do not float this pin.

SYNC (Pin 7): External Synchronization Pin. The oscilla-

tion frequency can be synchronized to an external oscilla-

tor applied to this pin. For external frequencies above

2.2MHz, pull FREQ high.

RUN (Pin 8): Run Control Input. Forcing this pin above

1.5V enables the part. Forcing this pin below 0.3V shuts

down the device. In shutdown, all functions are disabled

drawing <1

µA supply current. Do not leave RUN floating.

Exposed Pad (Pin 9): Ground. This pin must be soldered

to PCB.

VOUT

100mV/DIV

AC COUPLED

500mA/DIV

ILOAD

250mA/DIV

VIN = 3.6V

VOUT = 1.5V

ILOAD = 100mA TO 600mA

µs/DIV

3448 G18

VOUT

20mV/DIV

AC COUPLED

MODE PIN

2V/DIV

VOUT = 1.5V

TA = 25°C

200

µs/DIV

3448 G19

SWITCHER

LDO

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