Datasheet

LTC3824
7
3824fg
block DiagraM
applicaTions inForMaTion
Operation
The LTC3824 is a constant frequency current mode buck
controller with programmable switching frequency up to
600kHz.
Referring to the Block Diagram, the LTC3824’s basic
functions include a transconductance amplifier gm to
regulate the output voltage and control the current mode
PWM current loop, the necessary logic to control the
PWM switching cycles, a high speed gate driver to drive
an external high power P-channel MOSFET and a voltage
regulator to bias the gate driver circuit.
In normal operation each switching cycle starts with switch
turn-on and the inductor current is sampled through the
current sense resistor. This current is amplified and then
compared to the error amplifier output V
C
to turn the
switch off. Voltage loop regulates the output voltage to the
programmed level through the output resistor divider and
the error amplifier. Amplifier E1 regulates the gate drive
low to approximately 8V below V
CC
for V
CC
higher than
9V, and C
CAP
stabilizes the voltage. Note that when V
CC
is
lower than 9V, gate drive high will be within 0.5V of V
CC
and gate drive low within 1V of ground.
Important features include shutdown, current limit, soft-
start, synchronization and low quiescent current.
+
–
3824 BD
+
50KHz FOLDBACK
SYNC DISABLE
Burst Mode
OPERATION
CONTROL
OSC
S
Q
2V
2.5V1.8V
100k
Burst Mode
DISABLE
R
0.025V
V
REF
0.8V
2.5V
5µA
V
C
SS
SHUTDOWN
1.5V
GND
1.1V
SYNC/
MODE
R
SET
R
FREQ
+
–
+
–
+
–
+
–
+
+
–
+
+
–
+
–
+
+
+
–
+
SS
+
C2
C
CAP
0.1µF
CAP
Q1
M1
8V
B1
0.5V
FB
RF2
RF1
R
S
GATE
Y5
L
C
OUT
V
OUT
V
IN
Y6
Y2
GM
R1
2k
C1
470pF
C
SS
0.1µF
D6
SLOPE
COMP
D7
D4
D1
E1
V
CC
M2
0.3µA
Y1
OR1
SENSE
0.1V
50pF
PWM
V
REF
REFERENCE
+
–
1
6
+
+