LT3840

11

3840fa

For more information www.linear.com/LT3840

operaTion

peak inductor current. A resistor and capacitor on ICOMP

compensate the current control loop. Figure 2 includes

the block diagram of the average current control loop

and transfer functions showing the relationship between

Auxiliary Bias Supply

The LT3840 wide input voltage range is made possible

with the auxiliary bias supply switching regulator. Other

switching regulator controllers typically use a linear volt-

This approach is limited by power dissipation at high

input voltage and dropout at low voltage. The LT3840

bias regulator efficiently generates a 7.5V bias voltage,

capable of adequately driving large multiple MOSFETs, at

input voltages as low as 2.5V and as high as 60V.

The auxiliary bias supply is a monolithic buck-boost, peak

current mode topology. The switching frequency is fixed

andsynchronizedwiththeLT3840synchronousbuckcon-

troller. The switching regulator is internally compensated

Figure 2. Average Output Current Limit Functional Block Diagram and Transfer Curves

SW

–

+

1V

– –

+

GM

20x

ICOMP

MAXIMUM

AVERAGE

CURRENT

CONTROL

ICTRL

IMON

TRANSFER FUNCTION

MAX. AVG. SENSE VOLTAGE

vs ICTRL

300

200

100

0

30

40

50

600

800

20

400 500

700

900 1000

10

0

TRANSFER FUNCTION

IMON vs AVG.

SENSE VOLTAGE

1000

900

800

700

600

500

400

300

200

100

0

40

50

0

10

20

30

3840 F02

–

+