5
LTC3423/LTC3424
34234f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Burst Mode Operation Current
R
t
(Pin 1): Timing Resistor to Program the Oscillator
Frequency.
f
R
Hz
OSC
t
=
310
10
•
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.
UU
U
PI FU CTIO S
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”.
Shutdown Threshold
TEMPERATURE (°C)
–55
VOLTAGE (V)
0.80
65
125
3423/24 G13
0.70
0.60
–15 25 105
0.90
1.00
1.10
0.75
0.65
0.85
0.95
1.05
TEMPERATURE (°C)
–55
CURRENT (µA)
36
38
65
125
3423/24 G14
34
32
30
–15 25 105
40
42
44
