LTC3448_15 Datasheet, PDF (6/20 Pages) Linear Technology – 1.5MHz/2.25MHz, 600mA Synchronous Step-Down Regulator with LDO Mode

LTC3448
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Load Step
V_OUT
100mV/DIV
AC COUPLED
I_LOAD
250mA/DIV
I_L
500mA/DIV
V_IN = 3.6V
10µs/DIV
V_OUT = 1.5V
I_LOAD = 100mA TO 600mA
3448 G18
External Mode Control (Constant
1mA Load)
SWITCHER
SWITCHER
V_OUT
20mV/DIV
LDO
AC COUPLED
MODE PIN
2V/DIV
V_OUT = 1.5V
T_A = 25°C
200µs/DIV
3448 G19
PI FU CTIO S
V_FB (Pin 1): Feedback Pin. This pin receives the feedback
voltage from an external resistive divider across the
output.
V_OUT (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
I_LDO(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 I_LDO(OFF). The minimum required capacitance on this
pin is 2µF.
MODE (Pin 3): Linear Regulator Control. Grounding this
pin turns off the linear regulator. Setting this pin to V_IN
turns on the linear regulator regardless of the load current.
Tying this pin midrange (i.e., to V_OUT) 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 50µs
after the RUN pin is pulled high.
V_IN (Pin 4): Main Supply Pin. This pin must be closely
decoupled to GND with a 2.2µF 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 = V_IN. 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 <1µA supply current. Do not leave RUN floating.
Exposed Pad (Pin 9): Ground. This pin must be soldered
to PCB.
3448f
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