LTC3427_15 Datasheet, PDF (5/12 Pages) Linear Technology – 500mA, 1.25MHz Synchronous Step-Up DC/DC Converter in 2mm 2mm DFN Package

LTC3427
PI FU CTIO S
SW (Pin 1): Switch Pin for the Inductor Connection.
Minimize trace length between SW and the inductor. For
discontinuous inductor current, an internal 200Ω imped-
ance is connected from SW to V_IN to eliminate high
frequency ringing, reducing EMI radiation.
GND (Pin 2): Signal and Power Ground. Provide a short,
direct PCB path between GND and the (–) side of the input
and output capacitor(s).
V_IN (Pin 3): Input Supply Voltage. Connect V_IN to the input
supply and decouple with a 2.2µF or larger ceramic
capacitor as close to V_IN as possible.
SHDN (Pin 4): Shutdown Input. Less than 350mV on
SHDN shuts down the LTC3427. Placing 1V or more on
SHDN enables the LTC3427.
FB (Pin 5): Feedback Input to the Error Amplifier. Connect
resistor divider tap to this pin. Referring to the Block
Diagram, V_OUT can be adjusted from 1.8V to 5.25V by:
V_OUT
=
1.24V
•
⎛
⎝⎜
1+
R1⎞
R2 ⎠⎟
V_OUT (Pin 6): Output Voltage Sense Input and Drain of the
Internal Synchronous Rectifier MOSFET. Driver bias is
derived from V_OUT. PCB trace length from V_OUT to the
output filter capacitor(s) should be as short and wide as
possible.
Exposed Pad (Pin 7): Ground for the LTC3427. This pin
must be soldered to the PCB ground plane for electrical
connection and rated thermal performance.
BLOCK DIAGRA
V_IN
1.8V TO 5V
+
C_IN
2.2µF
4
SHDN
3
V_IN
L1
4.7µH
SHUTDOWN
AND
V_BIAS
V_IN
SHDN
ANTIRING
PWM
LOGIC
AND
DRIVERS
1
SW
OPTIONAL
BULK CONTROL
SIGNALS
V_OUT
6
CURRENT
SENSE
IZERO
COMP
V_OUT
1.8V TO 5.25V
PWM
COMP
+
Σ
I_LIM
+
REF
SLOPE COMPENSATION
REFERENCE
THERMAL
SHUTDOWN
1.24V
1V
GAIN ERROR
AMPLIFIER
R1
FB
5
R2
1.24V
START-UP
SOFT-START
EXPOSED PAD
7
OSCILLATOR
GND
2
3427 BD
C_OUT
4.7µF
3427fa
5