LTC3421_15 Datasheet, PDF (10/16 Pages) Linear Technology – 3A, 3MHz Micropower Synchronous Boost Converter with Output Disconnect

LTC3421
U
OPERATIO
Simplified Diagram of Automatic Burst Mode Control Circuit
V_CC
–
V_REF
–4%
+
UV
SSDONE
1mA I_OUT/3000
FB 1
–
V_REF
+
±1%
ERROR AMP/
SLEEP COMP
–
0.9V/
+
1.1V
9 BURST
R_B
C_B
TO
MODULATOR
SLEEP
SSDONE
24 V_C
R_COMP
C_COMP
CLAMP
0.5V TO 1V
MODE
1 = Burst Mode
OPERATION
0 = PWM MODE
3421 TA03
The circuit connected to BURST should be able to sink or
source up to 2mA. Note that Burst Mode operaton is
inhibited during start-up and soft-start.
Note that if V_IN is above V_OUT – 0.3V, the part will exit Burst
Mode operation and the synchronous rectifier will be
disabled.
Note that if the load applied during forced Burst Mode
operation exceeds the current that can be supplied, the
output voltage will start to droop and the part will auto-
matically come out of Burst Mode operation and enter fixed
frequency mode, raising V_OUT. The maximum current that
can be supplied in Burst Mode operation is given by:
10
( ) ^IO(MAX)
=
2 • ¹⁺
0.55
V_OUT
– V_IN
in amps
V_IN
OUTPUT DISCONNECT AND INRUSH LIMITING
The LTC3421 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
the input source. It also allows for inrush current limiting
at turn-on, minimizing surge currents seen by the input
supply. Note that to obtain the advantages of output
3421f