LTC3424_15 Datasheet, PDF (5/12 Pages) Linear Technology – Low Output Voltage, 3MHz Micropower Synchronous Boost Converters

TYPICAL PERFOR A CE CHARACTERISTICS
LTC3423/LTC3424
Shutdown Threshold
1.10
1.05
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
–55
–15
25
65
TEMPERATURE (°C)
105 125
3423/24 G13
Burst Mode Operation Current
44
42
40
38
36
34
32
30
–55
–15
25
65
TEMPERATURE (°C)
105 125
3423/24 G14
PI FU CTIO S
R_t (Pin 1): Timing Resistor to Program the Oscillator
Frequency.
f_OSC
=
3 •10¹⁰
R_t
Hz
MODE/SYNC (Pin 2): Burst Mode Select and Oscillator
Synchronization.
MODE/SYNC = High. Enable Burst Mode operation. The
inductor peak inductor current will be 400mA and
return to zero current on each cycle. During Burst Mode
operation the operation is variable frequency, providing
a significant efficiency improvement at light loads. It is
recommended the Burst Mode operation only be en-
tered once the part has started up.
MODE/SYNC = Low. Disable Burst Mode operation and
maintain low noise, constant frequency operation.
MODE/SYNC = External CLK. Synchronization of the
internal oscillator and Burst Mode operation disable. A
clock pulse width of 100ns to 2µs is required to
synchronize.
V_IN (Pin 3): Voltage Sense for Internal Circuitry.
SW (Pin 4): Switch Pin. Connect inductor and optional
Schottky diode here. Minimize trace length to keep EMI
down.
GND (Pin 5): Signal and Power Ground for the IC.
V_DD (Pin 6): Power Source for the IC. Typically derived
from a higher voltage power converter. Requires an input
of 2.7V to 5.5V. A 2.2µF ceramic bypass capacitor is
recommended as close to the pins as possible.
V_OUT (Pin 7): Output of the Synchronous Rectifier.
FB (Pin 8): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 1.5V to
5.5V. The feedback reference voltage is typically 1.25V.
V_C (Pin 9): Error Amp Output. A frequency compensation
network is connected to this pin to compensate the loop.
See the section “Compensating the Feedback Loop” for
guidelines.
SHDN (Pin 10): Shutdown. Grounding this pin shuts down
the IC. Tie to >1V to enable (V_DD or digital gate output).
During shutdown the output voltage will hold up to V_IN
minus a diode drop due to the body diode of the PMOS
synchronous switch. If the application requires a com-
plete disconnect during shutdown then refer to section
“Output Disconnect”.
34234f
5