Datasheet

LTC3422
10
3422fa
OPERATIO
U
BURST must be able to sink up to 4mA. Burst Mode
operation is inhibited during soft-start.
If V
IN
is greater than V
OUT
– 300mV, the part will exit Burst
Mode operation and the synchronous rectifier will be
disabled.
Note that if the load current applied during forced Burst
Mode operation (BURST is grounded) exceeds the current
that can be supplied, the output voltage will start to droop
and the LTC3422 will automatically come out of Burst
Mode operation and enter fixed frequency mode, raising
V
OUT
. Once regulation is achieved, the LTC3422 will then
enter Burst Mode operation once again (since the user is
still
commanding this by grounding BURST ) and the cycle
will repeat, resulting in about 4% output ripple. The
maximum average current that can be supplied in Burst
Mode operation is given by:
I
V
V
nmA
OUT MAX
IN
OUT
()
•
=
275
i
Output Disconnect and Inrush Current Limiting
The LTC3422 is designed to allow true output disconnect
by eliminating body diode conduction of the internal
P-channel MOSFET rectifier. This allows V
OUT
to go to zero
volts during shutdown without drawing any current from
2mA
880mV TO
1.16V
SSDONE
0 = PWM MODE
1 = Burst Mode
OPERATION
BURST
COMP
ERROR AMP/
SLEEP COMP
UVLO
COMP
V
CC
BURST
SLEEP
C
C1
C
B
R
Z
R
B
V
C
I
OUT
10,000
V
REF
– 4%
V
REF
±1%
–
+
–
+
–
+
COMP CLAMP
500mV TO 1V
7
BURST
3422 AI01
3
FB
6
Simplified Diagram of Automatic Burst Mode Control Circuit