Datasheet

LT3844
7
3844fb
FUNCTIONAL DIAGRAM
PIN FUNCTIONS
BOOST (Pin 16): The BOOST pin is the supply for the
bootstrapped gate drive and is externally connected to a
low ESR ceramic boost capacitor referenced to SW pin.
The recommended value of the BOOST capacitor, C
BOOST
,
is 50 times greater than the total input capacitance of the
topside MOSFET. In most applications 0.1μF is adequate.
The maximum voltage that this pin sees is V
IN
+ V
CC
,
ground referred.
Exposed Pad (Pin 17): SGND. The exposed leadframe is
internally connected to the SGND pin. Solder the exposed
pad to the PCB ground for electrical contact and optimal
thermal performance.
–
+
–
+
–
+
–
+
V
IN
UVLO
(<4V)
BST
UVLO
8V
REGULATOR
FEEDBACK
REFERENCE
–
+
–
+
1.231V
3.8V
REGULATOR
INTERNAL
SUPPLY RAIL
1
9
6
V
IN
V
CC
UVLO
(<6V)
SHDN
DRIVE
CONTROL
NOL
SWITCH
LOGIC
DRIVE
CONTROL
BURST_EN
V
C
C
SS
SENSE
–
V
FB
0.5V
2μA
50μA
Burst Mode
OPERATION
R
SQ
OSCILLATOR
SLOPE COMP
GENERATOR
BOOST
TG
SW
V
CC
PGND
SYNC
f
SET
R
SET
SENSE
+
SGND
BOOSTED SWITCH
DRIVER
CURRENT
SENSE
COMPARATOR
12
7
8
13
14
10
11
5
3
100mV
4
2
16
15
V
REF
+ 200mV
SOFT-START
BURST DISABLE
DRIVER
FAULT CONDITION:
V
IN
UVLO
V
CC
UVLO
V
SHDN
UVLO
C
SS
CLAMPED TO
V
FB
+ V
BE
V
REF
~1V
–
+
g
m
ERROR
AMP
–
+
M1
D2
D3
D1
L1
(OPTIONAL)
R
SENSE
3844 FD
C
C2
C
C1
R1
RA
RB
V
IN
C
IN
R2
C
BOOST
V
OUT
C
OUT
C
VCC
R
C