7
LT1612
sn1612 1612fs
OPERATIO
U
Figure 3. Output Voltage Ripple is 20mV
P-P
for
the Circuit of Figure 1
Burst Mode Operation Defeat
To maintain high efficiency at light loads, the LT1612 will
automatically shift into Burst Mode operation (MODE = 0V
or floating). In this mode of operation the oscillator and
switch drive circuitry is alternately turned on and off,
reducing quiescent current to 160µA. This reduces power
consumption but also adds low frequency voltage ripple to
the output. Figure 3 shows switching waveforms for a 5V
to 3.3V converter running in Burst Mode operation. Output
voltage ripple is approximately 20mV
P-P
. If the MODE pin
is pulled high, Burst Mode operation will be inhibited and
the oscillator runs continuously with no low frequency
ripple at the output. See Figures 4 and 5.
Figure 4. Transient Response for the Circuit of Figure 1
with the MODE Pin Tied to Ground or Floating
Figure 5. With the MODE Pin Tied High, Low
Frequency Output Voltage Ripple Is No Longer Present
1612 F03
V
OUT
20mV/DIV
AC COUPLED
IL
200mA/DIV
5µs/DIV
1612 F04
V
OUT
200mV/DIV
AC COUPLED
I
LOAD
10mA TO 310mA
0.1ms/DIV
I
L
200mA/DIV
1612 F05
V
OUT
200mV/DIV
AC COUPLED
I
LOAD
10mA TO 300mA
0.1ms/DIV
I
L
200mA/DIV
