LTC3824

6

3824fc

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

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

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

2.5V

1.8V

100k

Burst Mode

DISABLE

R

0.025V

0.8V

2.5V

6μ

SS

SHUTDOWN

1.5V

GND

1.1V

SYNC/

MODE

+

+

+

–

+

+

+

–

+

SS

+

C2

0.1μF

CAP

Q1

M1

8V

B1

0.5V

FB

RF2

RF1

GATE

Y5

L

Y6

Y3

2.5V

Y2

GM

R2

R3

SLOPE

COMP

R1

2k

C1

470pF

0.1μF

D6

D7

D4

D1

E1

M2

0.3μA

Y1

OR1

SENSE

0.1V

50pF

PWM

REFERENCE